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  • Computed Tomography Perfusion (CTP) to Predict Response to Recanalization in Ischemic Stroke Project (CRISP) Recruiting

    The overall goal of the CTP to predict Response to recanalization in Ischemic Stroke Project (CRISP) is to develop a practical tool to identify acute stroke patients who are likely to benefit from endovascular therapy. The project has two main parts. During the first part, the investigators propose to develop a fully automated system (RAPID) for processing of CT Perfusion (CTP) images that will generate brain maps of the ischemic core and penumbra. There will be no patient enrollment in part one of this project. During the second part, the investigators aim to demonstrate that physicians in the emergency setting, with the aid of a fully automated CTP analysis program (RAPID), can accurately predict response to recanalization in stroke patients undergoing revascularization. To achieve this aim the investigators will conduct a prospective cohort study of 240 consecutive stroke patients who will undergo a CTP scan prior to endovascular therapy. The study will be conducted at four sites (Stanford University, St Luke's Hospital, University of Pittsburgh Medical Center, and Emory University/Grady Hospital). Patients will have an early follow-up MRI scan within 12+/-6 hours to assess reperfusion and a late follow-up MRI scan at day 5 to determine the final infarct.

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Teaching

2013-14 Courses


Publications

Journal Articles


  • High-resolution cerebral blood volume imaging in humans using the blood pool contrast agent ferumoxytol MAGNETIC RESONANCE IN MEDICINE Christen, T., Ni, W., Qiu, D., Schmiedeskamp, H., Bammer, R., Moseley, M., Zaharchuk, G. 2013; 70 (3): 705-710

    View details for DOI 10.1002/mrm.24500

    View details for Web of Science ID 000323543600012

  • Acute Stroke Imaging Research Roadmap II STROKE Wintermark, M., Albers, G. W., Broderick, J. P., Demchuk, A. M., Fiebach, J. B., Fiehler, J., Grotta, J. C., Houser, G., Jovin, T. G., Lees, K. R., Lev, M. H., Liebeskind, D. S., Luby, M., Muir, K. W., Parsons, M. W., von Kummer, R., Wardlaw, J. M., Wu, O., Yoo, A. J., Alexandrov, A. V., Alger, J. R., Aviv, R. I., Bammer, R., Baron, J., Calamante, F., Campbell, B. C., Carpenter, T. C., Christensen, S., Copen, W. A., Derdeyn, C. P., Haley, C., Khatri, P., Kudo, K., Lansberg, M. G., Latour, L. L., Lee, T., Leigh, R., Lin, W., Lyden, P., Mair, G., Menon, B. K., Michel, P., Mikulik, R., Nogueira, R. G., Ostergaard, L., Pedraza, S., Riedel, C. H., Rowley, H. A., Sanelli, P. C., Sasaki, M., Saver, J. L., Schaefer, P. W., Schellinger, P. D., Tsivgoulis, G., Wechsler, L. R., White, P. M., Zaharchuk, G., Zaidat, O. O., Davis, S. M., Donnan, G. A., Furlan, A. J., Hacke, W., Kang, D., Kidwell, C., Thijs, V. N., Thomalla, G., Warach, S. J. 2013; 44 (9): 2628-2639

    View details for DOI 10.1161/STROKEAHA.113.002015

    View details for Web of Science ID 000329982500063

    View details for PubMedID 23860298

  • Prospective motion correction using inductively coupled wireless RF coils MAGNETIC RESONANCE IN MEDICINE Ooi, M. B., Aksoy, M., Maclaren, J., Watkins, R. D., Bammer, R. 2013; 70 (3): 639-647

    View details for DOI 10.1002/mrm.24845

    View details for Web of Science ID 000323543600005

  • Advanced imaging improves prediction of hemorrhage after stroke thrombolysis ANNALS OF NEUROLOGY Campbell, B. C., Christensen, S., Parsons, M. W., Churilov, L., Desmond, P. M., Barber, P. A., Butcher, K. S., Levi, C. R., De Silva, D. A., Lansberg, M. G., Mlynash, M., Olivot, J., Straka, M., Bammer, R., Albers, G. W., Donnan, G. A., Davis, S. M. 2013; 73 (4): 510-519

    View details for DOI 10.1002/ana.23837

    View details for Web of Science ID 000319523800012

  • The Effects of Alteplase 3 to 6 Hours After Stroke in the EPITHET-DEFUSE Combined Dataset Post Hoc Case-Control Study STROKE Ogata, T., Christensen, S., Nagakane, Y., Ma, H., Campbell, B. C., Churilov, L., Lansberg, M. G., Straka, M., De Silva, D. A., Mlynash, M., Bammer, R., Olivot, J., Desmond, P. M., Albers, G. W., Davis, S. M., Donnan, G. A. 2013; 44 (1): 87-93

    Abstract

    Two phase 2 studies of alteplase in acute ischemic stroke 3 to 6 hours after onset, Echoplanar Imaging Thrombolytic Evaluation Trial (EPITHET; a randomized, controlled, double-blinded trial), and Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution Study (DEFUSE; open-label, treatment only) using MR imaging-based outcomes have been conducted. We have pooled individual patient data from these to assess the response to alteplase. The primary hypothesis was that alteplase would significantly attenuate infarct growth compared with placebo in mismatch-selected patients using coregistration techniques.The EPITHET-DEFUSE study datasets were pooled while retaining the original inclusion and exclusion criteria. Significant hypoperfusion was defined as a Tmax delay >6 seconds), and coregistration techniques were used to define MR diffusion-weighted imaging/perfusion-weighted imaging mismatch. Neuroimaging, parameters including reperfusion, recanalization, symptomatic intracerebral hemorrhage, and clinical outcomes were assessed. Alteplase and placebo groups were compared for the primary outcome of infarct growth as well for secondary outcome measures.From 165 patients with adequate MR scans in the EPITHET-DEFUSE pooled data, 121 patients (73.3%) were found to have mismatch. For the primary outcome analysis, 60 patients received alteplase and 41 placebo. Mismatch patients receiving alteplase had significantly attenuated infarct growth compared with placebo (P=0.025). The reperfusion rate was also increased (62.7% vs 31.7%; P=0.003). Mortality and clinical outcomes were not different between groups.The data provide further evidence that alteplase significantly attenuates infarct growth and increases reperfusion compared with placebo in the 3- to 6- hour time window in patients selected based on MR penumbral imaging.

    View details for DOI 10.1161/STROKEAHA.112.668301

    View details for Web of Science ID 000312883800016

    View details for PubMedID 23250996

  • Prospective motion correction using inductively coupled wireless RF coils. Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine Ooi, M. B., Aksoy, M., Maclaren, J., Watkins, R. D., Bammer, R. 2013

    Abstract

    A novel prospective motion correction technique for brain MRI is presented that uses miniature wireless radio-frequency coils, or "wireless markers," for position tracking.Each marker is free of traditional cable connections to the scanner. Instead, its signal is wirelessly linked to the MR receiver via inductive coupling with the head coil. Real-time tracking of rigid head motion is performed using a pair of glasses integrated with three wireless markers. A tracking pulse-sequence, combined with knowledge of the markers' unique geometrical arrangement, is used to measure their positions. Tracking data from the glasses is then used to prospectively update the orientation and position of the image-volume so that it follows the motion of the head.Wireless-marker position measurements were comparable to measurements using traditional wired radio-frequency tracking coils, with the standard deviation of the difference < 0.01 mm over the range of positions measured inside the head coil. Wireless-marker safety was verified with B1 maps and temperature measurements. Prospective motion correction was demonstrated in a 2D spin-echo scan while the subject performed a series of deliberate head rotations.Prospective motion correction using wireless markers enables high quality images to be acquired even during bulk motions. Wireless markers are small, avoid radio-frequency safety risks from electrical cables, are not hampered by mechanical connections to the scanner, and require minimal setup times. These advantages may help to facilitate adoption in the clinic. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

    View details for PubMedID 23813444

  • Clinical Assessment of Standard and Generalized Autocalibrating Partially Parallel Acquisition Diffusion Imaging: Effects of Reduction Factor and Spatial Resolution AMERICAN JOURNAL OF NEURORADIOLOGY Andre, J. B., Zaharchuk, G., Fischbein, N. J., Augustin, M., Skare, S., Straka, M., Rosenberg, J., Lansberg, M. G., Kemp, S., Wijman, C. A., Albers, G. W., Schwartz, N. E., Bammer, R. 2012; 33 (7): 1337-1342

    Abstract

    PI improves routine EPI-based DWI by enabling higher spatial resolution and reducing geometric distortion, though it remains unclear which of these is most important. We evaluated the relative contribution of these factors and assessed their ability to increase lesion conspicuity and diagnostic confidence by using a GRAPPA technique.Four separate DWI scans were obtained at 1.5T in 48 patients with independent variation of in-plane spatial resolution (1.88 mm(2) versus 1.25 mm(2)) and/or reduction factor (R = 1 versus R = 3). A neuroradiologist with access to clinical history and additional imaging sequences provided a reference standard diagnosis for each case. Three blinded neuroradiologists assessed scans for abnormalities and also evaluated multiple imaging-quality metrics by using a 5-point ordinal scale. Logistic regression was used to determine the impact of each factor on subjective image quality and confidence.Reference standard diagnoses in the patient cohort were acute ischemic stroke (n = 30), ischemic stroke with hemorrhagic conversion (n = 4), intraparenchymal hemorrhage (n = 9), or no acute lesion (n = 5). While readers preferred both a higher reduction factor and a higher spatial resolution, the largest effect was due to an increased reduction factor (odds ratio, 47 ± 16). Small lesions were more confidently discriminated from artifacts on R = 3 images. The diagnosis changed in 5 of 48 scans, always toward the reference standard reading and exclusively for posterior fossa lesions.PI improves DWI primarily by reducing geometric distortion rather than by increasing spatial resolution. This outcome leads to a more accurate and confident diagnosis of small lesions.

    View details for DOI 10.3174/ajnr.A2980

    View details for Web of Science ID 000307628200025

    View details for PubMedID 22403781

  • Model for the correction of motion-induced phase errors in multishot diffusion-weighted-MRI of the head: Are cardiac-motion-induced phase errors reproducible from beat-to-beat? MAGNETIC RESONANCE IN MEDICINE O'Halloran, R. L., Holdsworth, S., Aksoy, M., Bammer, R. 2012; 68 (2): 430-440

    Abstract

    In diffusion-weighted imaging, multishot acquisitions are problematic due to intershot inconsistencies of the phase caused by motion during the diffusion-encoding gradients. A model for the motion-induced phase errors in diffusion-weighted-MRI of the brain is presented, in which rigid-body and nonrigid-body motion are separated. In the model, it is assumed that nonrigid-body motion is due to cardiac pulsation, and that the motion patterns are repeatable from beat-to-beat. To test the validity of this assumption, the repeatability of nonrigid-body motion-induced phase errors is quantified in three healthy volunteers. Nonrigid-body motion-induced phase was found to significantly correlate (P < 0.05) with pulse-oximeter waveforms in ~83% of the pixels tested across all slices and subjects.

    View details for DOI 10.1002/mrm.23245

    View details for Web of Science ID 000306318900014

    View details for PubMedID 22213138

  • Combined spin- and gradient-echo perfusion-weighted imaging MAGNETIC RESONANCE IN MEDICINE Schmiedeskamp, H., Straka, M., Newbould, R. D., Zaharchuk, G., Andre, J. B., Olivot, J., Moseley, M. E., Albers, G. W., Bammer, R. 2012; 68 (1): 30-40

    Abstract

    In this study, a spin- and gradient-echo echo-planar imaging (SAGE EPI) MRI pulse sequence is presented that allows simultaneous measurements of gradient-echo and spin-echo dynamic susceptibility-contrast perfusion-weighted imaging data. Following signal excitation, five readout trains were acquired using spin- and gradient-echo echo-planar imaging, all of them with echo times of less than 100 ms. Contrast agent concentrations in brain tissue were determined based on absolute R2* and R(2) estimates rather than relative changes in the signals of individual echo trains, producing T(1)-independent dynamic susceptibility-contrast perfusion-weighted imaging data. Moreover, this acquisition technique enabled vessel size imaging through the simultaneous quantification of R2* and R(2), without an increase in acquisition time. In this work, the concepts of SAGE EPI pulse sequence and results in stroke and tumor imaging are presented. Overall, SAGE EPI combined the advantages of higher sensitivity to contrast agent passage of gradient-echo perfusion-weighted imaging with better microvascular selectivity of spin-echo perfusion-weighted imaging.

    View details for DOI 10.1002/mrm.23195

    View details for Web of Science ID 000305119100004

    View details for PubMedID 22114040

  • Hybrid prospective and retrospective head motion correction to mitigate cross-calibration errors MAGNETIC RESONANCE IN MEDICINE Aksoy, M., Forman, C., Straka, M., Cukur, T., Hornegger, J., Bammer, R. 2012; 67 (5): 1237-1251

    Abstract

    Utilization of external motion tracking devices is an emerging technology in head motion correction for MRI. However, cross-calibration between the reference frames of the external tracking device and the MRI scanner can be tedious and remains a challenge in practical applications. In this study, we present two hybrid methods, both of which combine prospective, optical-based motion correction with retrospective entropy-based autofocusing to remove residual motion artifacts. Our results revealed that in the presence of cross-calibration errors between the optical tracking device and the MR scanner, application of retrospective correction on prospectively corrected data significantly improves image quality. As a result of this hybrid prospective and retrospective motion correction approach, the requirement for a high-quality calibration scan can be significantly relaxed, even to the extent that it is possible to perform external prospective motion tracking without any prior cross-calibration step if a crude approximation of cross-calibration matrix exists. Moreover, the motion tracking system, which is used to reduce the dimensionality of the autofocusing problem, benefits the retrospective approach at the same time.

    View details for DOI 10.1002/mrm.23101

    View details for Web of Science ID 000302619400005

    View details for PubMedID 21826729

  • Optical motion tracking to improve image quality in MRI of the brain IMAGE RECONSTRUCTION FROM INCOMPLETE DATA VII Maclaren, J., Aksoy, M., Ooi, M., Bammer, R. 2012; 8500

    View details for DOI 10.1117/12.953612

    View details for Web of Science ID 000312165100002

  • The infarct core is well represented by the acute diffusion lesion: sustained reversal is infrequent JOURNAL OF CEREBRAL BLOOD FLOW AND METABOLISM Campbell, B. C., Purushotham, A., Christensen, S., Desmond, P. M., Nagakane, Y., Parsons, M. W., Lansberg, M. G., Mlynash, M., Straka, M., De Silva, D. A., Olivot, J., Bammer, R., Albers, G. W., Donnan, G. A., Davis, S. M. 2012; 32 (1): 50-56

    Abstract

    Diffusion-weighted imaging (DWI) is commonly used to assess irreversibly infarcted tissue but its accuracy is challenged by reports of diffusion lesion reversal (DLR). We investigated the frequency and implications for mismatch classification of DLR using imaging from the EPITHET (Echoplanar Imaging Thrombolytic Evaluation Trial) and DEFUSE (Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution) studies. In 119 patients (83 treated with IV tissue plasminogen activator), follow-up images were coregistered to acute diffusion images and the lesions manually outlined to their maximal visual extent in diffusion space. Diffusion lesion reversal was defined as voxels of acute diffusion lesion that corresponded to normal brain at follow-up (i.e., final infarct, leukoaraiosis, and cerebrospinal fluid (CSF) voxels were excluded from consideration). The appearance of DLR was visually checked for artifacts, the volume calculated, and the impact of adjusting baseline diffusion lesion volume for DLR volume on perfusion-diffusion mismatch analyzed. Median DLR volume reduced from 4.4 to 1.5?mL after excluding CSF/leukoaraiosis. Visual inspection verified 8/119 (6.7%) with true DLR, median volume 2.33?mL. Subtracting DLR from acute diffusion volume altered perfusion-diffusion mismatch (T(max)>6 seconds, ratio>1.2) in 3/119 (2.5%) patients. Diffusion lesion reversal between baseline and 3 to 6?hours DWI was also uncommon (7/65, 11%) and often transient. Clinically relevant DLR is uncommon and rarely alters perfusion-diffusion mismatch. The acute diffusion lesion is generally a reliable signature of the infarct core.

    View details for DOI 10.1038/jcbfm.2011.102

    View details for Web of Science ID 000299010000008

    View details for PubMedID 21772309

  • Cerebral CT Perfusion Using an Interventional C-Arm Imaging System: Cerebral Blood Flow Measurements AMERICAN JOURNAL OF NEURORADIOLOGY Ganguly, A., Fieselmann, A., Marks, M., Rosenberg, J., Boese, J., Deuerling-Zheng, Y., Straka, M., Zaharchuk, G., Bammer, R., Fahrig, R. 2011; 32 (8): 1525-1531

    Abstract

    CTP imaging in the interventional suite could reduce delays to the start of image-guided interventions and help determine the treatment progress and end point. However, C-arms rotate slower than clinical CT scanners, making CTP challenging. We developed a cerebral CTP protocol for C-arm CBCT and evaluated it in an animal study.Five anesthetized swine were imaged by using C-arm CBCT and conventional CT. The C-arm rotates in 4.3 seconds plus a 1.25-second turnaround, compared with 0.5 seconds for clinical CT. Each C-arm scan had 6 continuous bidirectional sweeps. Multiple scans each with a different delay to the start of an aortic arch iodinated contrast injection and a novel image reconstruction algorithm were used to increase temporal resolution. Three different scan sets (consisting of 6, 3, or 2 scans) and 3 injection protocols (3-mL/s 100%, 3-mL/s 67%, and 6-mL/s 50% contrast concentration) were studied. CBF maps for each scan set and injection were generated. The concordance and Pearson correlation coefficients (? and r) were calculated to determine the injection providing the best match between the following: the left and right hemispheres, and CT and C-arm CBCT.The highest ? and r values (both 0.92) for the left and right hemispheres were obtained by using the 6-mL 50% iodinated contrast concentration injection. The same injection gave the best match for CT and C-arm CBCT for the 6-scan set (? = 0.77, r = 0.89). Some of the 3-scan and 2-scan protocols provided matches similar to those in CT.This study demonstrated that C-arm CBCT can produce CBF maps that correlate well with those from CTP.

    View details for DOI 10.3174/ajnr.A2518

    View details for Web of Science ID 000295706200027

    View details for PubMedID 21757522

  • Clinical Application of Readout-Segmented-Echo-Planar Imaging for Diffusion-Weighted Imaging in Pediatric Brain AMERICAN JOURNAL OF NEURORADIOLOGY Holdsworth, S. J., Yeom, K., Skare, S., Gentles, A. J., Barnes, P. D., Bammer, R. 2011; 32 (7): 1274-1279

    Abstract

    RS-EPI has been suggested as an alternative approach to EPI for high-resolution DWI with reduced distortions. To determine whether RS-EPI is a useful approach for routine clinical use, we implemented GRAPPA-accelerated RS-EPI DWI at our pediatric hospital and graded the images alongside standard accelerated (ASSET) EPI DWI used routinely for clinical studies.GRAPPA-accelerated RS-EPI DWIs and ASSET EPI DWIs were acquired on 35 pediatric patients using a 3T system in 35 pediatric patients. The images were graded alongside each other by using a 7-point Likert scale as follows: 1, nondiagnostic; 2, poor; 3, acceptable; 4, standard; 5, above average; 6, good; and 7, outstanding.The following were the average scores for EPI and RS-EPI, respectively: resolution, 3.5/5.2; distortion level, 2.9/6.0; SNR, 3.4/4.1; lesion conspicuity, 3.3/5.9; and diagnostic confidence, 3.2/6.0. Overall, the RS-EPI had significantly improved diagnostic confidence and more reliably defined the extent and structure of several lesions. Although ASSET EPI scans had better SNR per scanning time, the higher spatial resolution as well as reduced blurring and distortions on RS-EPI scans helped to better reveal important anatomic details at the cortical-subcortical levels, brain stem, temporal and inferior frontal lobes, skull base, sinonasal cavity, cranial nerves, and orbits.This work shows the importance of both resolution and decreased distortions in the clinics, which can be accomplished by a combination of parallel imaging and alternative k-space trajectories such as RS-EPI.

    View details for DOI 10.3174/ajnr.A2481

    View details for Web of Science ID 000294275100023

    View details for PubMedID 21596809

  • Real-Time Optical Motion Correction for Diffusion Tensor Imaging MAGNETIC RESONANCE IN MEDICINE Aksoy, M., Forman, C., Straka, M., Skare, S., Holdsworth, S., Hornegger, J., Bammer, R. 2011; 66 (2): 366-378

    Abstract

    Head motion is a fundamental problem in brain MRI. The problem is further compounded in diffusion tensor imaging because of long acquisition times, and the sensitivity of the tensor computation to even small misregistration. To combat motion artifacts in diffusion tensor imaging, a novel real-time prospective motion correction method was introduced using an in-bore monovision system. The system consists of a camera mounted on the head coil and a self-encoded checkerboard marker that is attached to the patient's forehead. Our experiments showed that optical prospective motion correction is more effective at removing motion artifacts compared to image-based retrospective motion correction. Statistical analysis revealed a significant improvement in similarity between diffusion data acquired at different time points when prospective correction was used compared to retrospective correction (P<0.001).

    View details for DOI 10.1002/mrm.22787

    View details for Web of Science ID 000293256800008

    View details for PubMedID 21432898

  • RAPID Automated Patient Selection for Reperfusion Therapy A Pooled Analysis of the Echoplanar Imaging Thrombolytic Evaluation Trial (EPITHET) and the Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution (DEFUSE) Study STROKE Lansberg, M. G., Lee, J., Christensen, S., Straka, M., De Silva, D. A., Mlynash, M., Campbell, B. C., Bammer, R., Olivot, J., Desmond, P., Davis, S. M., Donnan, G. A., Albers, G. W. 2011; 42 (6): 1608-1614

    Abstract

    The aim of this study was to determine if automated MRI analysis software (RAPID) can be used to identify patients with stroke in whom reperfusion is associated with an increased chance of good outcome.Baseline diffusion- and perfusion-weighted MRI scans from the Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution study (DEFUSE; n=74) and the Echoplanar Imaging Thrombolytic Evaluation Trial (EPITHET; n=100) were reprocessed with RAPID. Based on RAPID-generated diffusion-weighted imaging and perfusion-weighted imaging lesion volumes, patients were categorized according to 3 prespecified MRI profiles that were hypothesized to predict benefit (Target Mismatch), harm (Malignant), and no effect (No Mismatch) from reperfusion. Favorable clinical response was defined as a National Institutes of Health Stroke Scale score of 0 to 1 or a ? 8-point improvement on the National Institutes of Health Stroke Scale score at Day 90.In Target Mismatch patients, reperfusion was strongly associated with a favorable clinical response (OR, 5.6; 95% CI, 2.1 to 15.3) and attenuation of infarct growth (10 ± 23 mL with reperfusion versus 40 ± 44 mL without reperfusion; P<0.001). In Malignant profile patients, reperfusion was not associated with a favorable clinical response (OR, 0.74; 95% CI, 0.1 to 5.8) or attenuation of infarct growth (85 ± 74 mL with reperfusion versus 95 ± 79 mL without reperfusion; P=0.7). Reperfusion was also not associated with a favorable clinical response (OR, 1.05; 95% CI, 0.1 to 9.4) or attenuation of lesion growth (10 ± 15 mL with reperfusion versus 17 ± 30 mL without reperfusion; P=0.9) in No Mismatch patients.MRI profiles that are associated with a differential response to reperfusion can be identified with RAPID. This supports the use of automated image analysis software such as RAPID for patient selection in acute stroke trials.

    View details for DOI 10.1161/STROKEAHA.110.609008

    View details for Web of Science ID 000291032700038

    View details for PubMedID 21493916

  • Refining the Definition of the Malignant Profile Insights From the DEFUSE-EPITHET Pooled Data Set STROKE Mlynash, M., Lansberg, M. G., De Silva, D. A., Lee, J., Christensen, S., Straka, M., Campbell, B. C., Bammer, R., Olivot, J., Desmond, P., Donnan, G. A., Davis, S. M., Albers, G. W. 2011; 42 (5): 1270-1275

    Abstract

    To refine the definition of the malignant magnetic resonance imaging profile in acute stroke patients using baseline diffusion-weighted magnetic resonance imaging (DWI) and perfusion-weighted magnetic resonance imaging (PWI) findings from the pooled DEFUSE/EPITHET database.Patients presenting with acute stroke within 3 to 6 hours from symptom onset were treated with tissue plasminogen activator or placebo. Baseline and follow-up DWI and PWI images from both studies were reprocessed using the same software program. A receiver operating characteristic curve analysis was used to identify Tmax and DWI volumes that optimally predicted poor outcomes (modified Rankin Scale 5-6) at 90 days in patients who achieved reperfusion.Sixty-five patients achieved reperfusion and 46 did not reperfuse. Receiver operating characteristic analysis identified a PWI (Tmax>8 s) volume of >85 mL as the optimal definition of the malignant profile. Eighty-nine percent of malignant profile patients had poor outcome with reperfusion versus 39% of patients without reperfusion (P=0.02). Parenchymal hematomas occurred more frequently in malignant profile patients who experienced reperfusion versus no reperfusion (67% versus 11%, P<0.01). DWI analysis identified a volume of 80 mL as the best DWI threshold, but this definition was less sensitive than were PWI-based definitions.Stroke patients likely to suffer parenchymal hemorrhages and poor outcomes following reperfusion can be identified from baseline magnetic resonance imaging findings. The current analysis demonstrates that a PWI threshold (Tmax>8 s) of approximately 100 mL is appropriate for identifying these patients. Exclusion of malignant profile patients from reperfusion therapies may substantially improve the efficacy and safety of reperfusion therapies. Clinical Trial Registration Information- URL: http://www.clinicaltrials.gov. Unique identifier: NCT00238537.

    View details for DOI 10.1161/STROKEAHA.110.601609

    View details for Web of Science ID 000289835900023

    View details for PubMedID 21474799

  • Mild traumatic brain injury: is diffusion imaging ready for primetime in forensic medicine? Topics in magnetic resonance imaging Grossman, E. J., Inglese, M., Bammer, R. 2010; 21 (6): 379-386

    Abstract

    Mild traumatic brain injury (MTBI) is difficult to accurately assess with conventional imaging because such approaches usually fail to detect any evidence of brain damage. Recent studies of MTBI patients using diffusion-weighted imaging and diffusion tensor imaging suggest that these techniques have the potential to help grade tissue damage severity, track its development, and provide prognostic markers for clinical outcome. Although these results are promising and indicate that the forensic diagnosis of MTBI might eventually benefit from the use of diffusion-weighted imaging and diffusion tensor imaging, healthy skepticism and caution should be exercised with regard to interpreting their meaning because there is no consensus about which methods of data analysis to use and very few investigations have been conducted, of which most have been small in sample size and examined patients at only one time point after injury.

    View details for DOI 10.1097/RMR.0b013e31823e65b8

    View details for PubMedID 22158131

  • An introduction to model-independent diffusion magnetic resonance imaging. Topics in magnetic resonance imaging Van, A. T., Granziera, C., Bammer, R. 2010; 21 (6): 339-354

    Abstract

    q-Space-based techniques such as diffusion spectrum imaging, q-ball imaging, and their variations have been used extensively in research for their desired capability to delineate complex neuronal architectures such as multiple fiber crossings in each of the image voxels. The purpose of this article was to provide an introduction to the q-space formalism and the principles of basic q-space techniques together with the discussion on the advantages as well as challenges in translating these techniques into the clinical environment. A review of the currently used q-space-based protocols in clinical research is also provided.

    View details for DOI 10.1097/RMR.0b013e31823e6303

    View details for PubMedID 22158128

  • Three-dimensional T-1, T-2 and proton density mapping with inversion recovery balanced SSFP MAGNETIC RESONANCE IMAGING Newbould, R. D., Skare, S. T., Alley, M. T., Gold, G. E., Bammer, R. 2010; 28 (9): 1374-1382

    Abstract

    By combining a balanced steady-state free precession (bSSFP) readout with an initial inversion pulse, all three contrast parameters, T(1), T(2) and proton density (M(0)), may be rapidly calculated from the signal progression in time. However, here it is shown that this technique is quite sensitive to variation in the applied transmit RF (B(1)) field, leading to pronounced errors in calculated values. Two-dimensional (2D) acquisitions are taxed to accurately quantify the relaxation, as the short RF pulses required by SSFP's rapid TR contain a broad spectrum of excitation angles. A 3D excitation using a large diameter excitation coil was able to correctly quantify the parameters. While the extreme B(1) sensitivity was previously problematic and has precluded use of IR-bSSFP for relaxometry, in this work these obstacles were significantly reduced, allowing the rapid quantification of T(1), T(2) and M(0). The results may further be used to simulate image contrast from common sequences, such as a T(1)-weighted or fluid-attenuated inversion recovery (FLAIR) examination.

    View details for DOI 10.1016/j.mri.2010.06.004

    View details for Web of Science ID 000283906800015

    View details for PubMedID 20692784

  • Real-Time Diffusion-Perfusion Mismatch Analysis in Acute Stroke JOURNAL OF MAGNETIC RESONANCE IMAGING Straka, M., Albers, G. W., Bammer, R. 2010; 32 (5): 1024-1037

    Abstract

    Diffusion-perfusion mismatch can be used to identify acute stroke patients that could benefit from reperfusion therapies. Early assessment of the mismatch facilitates necessary diagnosis and treatment decisions in acute stroke. We developed the RApid processing of PerfusIon and Diffusion (RAPID) for unsupervised, fully automated processing of perfusion and diffusion data for the purpose of expedited routine clinical assessment. The RAPID system computes quantitative perfusion maps (cerebral blood volume, CBV; cerebral blood flow, CBF; mean transit time, MTT; and the time until the residue function reaches its peak, T(max)) using deconvolution of tissue and arterial signals. Diffusion-weighted imaging/perfusion-weighted imaging (DWI/PWI) mismatch is automatically determined using infarct core segmentation of ADC maps and perfusion deficits segmented from T(max) maps. The performance of RAPID was evaluated on 63 acute stroke cases, in which diffusion and perfusion lesion volumes were outlined by both a human reader and the RAPID system. The correlation of outlined lesion volumes obtained from both methods was r(2) = 0.99 for DWI and r(2) = 0.96 for PWI. For mismatch identification, RAPID showed 100% sensitivity and 91% specificity. The mismatch information is made available on the hospital's PACS within 5-7 min. Results indicate that the automated system is sufficiently accurate and fast enough to be used for routine care as well as in clinical trials.

    View details for DOI 10.1002/jmri.22338

    View details for Web of Science ID 000284190200002

    View details for PubMedID 21031505

  • Effects of motion and b-matrix correction for high resolution DTI with short-axis PROPELLER-EPI NMR IN BIOMEDICINE Aksoy, M., Skare, S., Holdsworth, S., Bammer, R. 2010; 23 (7): 794-802

    Abstract

    Short-axis PROPELLER-EPI (SAP-EPI) has been proven to be very effective in providing high-resolution diffusion-weighted and diffusion tensor data. The self-navigation capabilities of SAP-EPI allow one to correct for motion, phase errors, and geometric distortion. However, in the presence of patient motion, the change in the effective diffusion- encoding direction (i.e. the b-matrix) between successive PROPELLER 'blades' can decrease the accuracy of the estimated diffusion tensors, which might result in erroneous reconstruction of white matter tracts in the brain. In this study, we investigate the effects of alterations in the b-matrix as a result of patient motion on the example of SAP-EPI DTI and eliminate these effects by incorporating our novel single-step non-linear diffusion tensor estimation scheme into the SAP-EPI post-processing procedure. Our simulations and in-vivo studies showed that, in the presence of patient motion, correcting the b-matrix is necessary in order to get more accurate diffusion tensor and white matter pathway reconstructions.

    View details for DOI 10.1002/nbm.1490

    View details for Web of Science ID 000283014300011

    View details for PubMedID 20222149

  • Combined Arterial Spin Label and Dynamic Susceptibility Contrast Measurement of Cerebral Blood Flow MAGNETIC RESONANCE IN MEDICINE Zaharchuk, G., Straka, M., Marks, M. P., Albers, G. W., Moseley, M. E., Bammer, R. 2010; 63 (6): 1548-1556

    Abstract

    Dynamic susceptibility contrast (DSC) and arterial spin labeling (ASL) are both used to measure cerebral blood flow (CBF), but neither technique is ideal. Absolute DSC-CBF quantitation is challenging due to many uncertainties, including partial- volume errors and nonlinear contrast relaxivity. ASL can measure quantitative CBF in regions with rapidly arriving flow, but CBF is underestimated in regions with delayed arrival. To address both problems, we have derived a patient-specific correction factor, the ratio of ASL- and DSC-CBF, calculated only in short-arrival-time regions (as determined by the DSC-based normalized bolus arrival time [Tmax]). We have compared the combined CBF method to gold-standard xenon CT in 20 patients with cerebrovascular disease, using a range of Tmax threshold levels. Combined ASL and DSC CBF demonstrated quantitative accuracy as good as the ASL technique but with improved correlation in voxels with long Tmax. The ratio of MRI-based CBF to xenon CT CBF (coefficient of variation) was 90 +/- 30% (33%) for combined ASL and DSC CBF, 43 +/- 21% (47%) for DSC, and 91 +/- 31% (34%) for ASL (Tmax threshold 3 sec). These findings suggest that combining ASL and DSC perfusion measurements improves quantitative CBF measurements in patients with cerebrovascular disease.

    View details for DOI 10.1002/mrm.22329

    View details for Web of Science ID 000278164400015

    View details for PubMedID 20512858

  • Self-encoded Marker for Optical Prospective Head Motion Correction in MRI MEDICAL IMAGE COMPUTING AND COMPUTER-ASSISTED INTERVENTION - MICCAI 2010, PT I Forman, C., Aksoy, M., Hornegger, J., Bammer, R. 2010; 6361: 259-266
  • Self-encoded marker for optical prospective head motion correction in MRI. Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention Forman, C., Aksoy, M., Hornegger, J., Bammer, R. 2010; 13: 259-266

    Abstract

    The tracking and compensation of patient motion during a magnetic resonance imaging (MRI) acqusition is an unsolved problem. For brain MRI, a promising approach recently suggested is to track the patient using an in-bore camera and a checkerboard marker attached to the patient's forehead. However, the possible tracking range of the head pose is limited by the locally attached marker that must be entirely visible inside the camera's narrow field of view (FOV). To overcome this shortcoming, we developed a novel self-encoded marker where each feature on the pattern is augmented with a 2-D barcode. Hence, the marker can be tracked even if it is not completely visible in the camera image. Furthermore, it offers considerable advantages over the checkerboard marker in terms of processing speed, since it makes the correspondence search of feature points and marker-model coordinates, which are required for the pose estimation, redundant. The motion correction with the novel self-encoded marker recovered a rotation of 18 degrees around the principal axis of the cylindrical phantom in-between two scans. After rigid registration of the resulting volumes, we measured a maximal error of 0.39 mm and 0.15 degrees in translation and rotation, respectively. In in-vivo experiments, the motion compensated images in scans with large motion during data acquisition indicate a correlation of 0.982 compared to a corresponding motion-free reference.

    View details for PubMedID 20879239

  • Robust GRAPPA-Accelerated Diffusion-Weighted Readout-Segmented (RS)-EPI MAGNETIC RESONANCE IN MEDICINE Holdsworth, S. J., Skare, S., Newbould, R. D., Bammer, R. 2009; 62 (6): 1629-1640

    Abstract

    Readout segmentation (RS-EPI) has been suggested as a promising variant to echo-planar imaging (EPI) for high-resolution imaging, particularly when combined with parallel imaging. This work details some of the technical aspects of diffusion-weighted (DW)-RS-EPI, outlining a set of reconstruction methods and imaging parameters that can both minimize the scan time and afford high-resolution diffusion imaging with reduced distortions. These methods include an efficient generalized autocalibrating partially parallel acquisition (GRAPPA) calibration for DW-RS-EPI data without scan time penalty, together with a variant for the phase correction of partial Fourier RS-EPI data. In addition, the role of pulsatile and rigid-body brain motion in DW-RS-EPI was assessed. Corrupt DW-RS-EPI data arising from pulsatile nonlinear brain motion had a prevalence of approximately 7% and were robustly identified via k-space entropy metrics. For DW-RS-EPI data corrupted by rigid-body motion, we showed that no blind overlap was required. The robustness of RS-EPI toward phase errors and motion, together with its minimized distortions compared with EPI, enables the acquisition of exquisite 3 T DW images with matrix sizes close to 512(2).

    View details for DOI 10.1002/mrm.22122

    View details for Web of Science ID 000272067600029

    View details for PubMedID 19859974

  • Performance of PROPELLER relative to standard FSE T2-weighted imaging in pediatric brain MRI PEDIATRIC RADIOLOGY Vertinsky, A. T., Rubesova, E., Krasnokutsky, M. V., Bammer, S., Rosenberg, J., White, A., Barnes, P. D., Bammer, R. 2009; 39 (10): 1038-1047

    Abstract

    T2-weighted fast spin-echo imaging (T2-W FSE) is frequently degraded by motion in pediatric patients. MR imaging with periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) employs alternate sampling of k-space to achieve motion reduction.To compare T2-W PROPELLER FSE (T2-W PROP) with conventional T2-W FSE for: (1) image quality; (2) presence of artefacts; and (3) ability to detect lesions.Ninety-five pediatric patients undergoing brain MRI (1.5 T) were evaluated with T2-W FSE and T2-W PROP. Three independent radiologists rated T2-W FSE and T2-W PROP, assessing image quality, presence of artefacts, and diagnostic confidence. Chi-square analysis and Wilcoxon signed rank test were used to assess the radiologists' responses.Compared with T2-W FSE, T2-W PROP demonstrated better image quality and reduced motion artefacts, with the greatest benefit in children younger than 6 months. Although detection rates were comparable for the two sequences, blood products were more conspicuous on T2-W FSE. Diagnostic confidence was higher using T2-W PROP in children younger than 6 months. Average inter-rater agreement was 87%.T2-W PROP showed reduced motion artefacts and improved diagnostic confidence in children younger than 6 months. Thus, use of T2-W PROP rather than T2-W FSE should be considered in routine imaging of this age group, with caution required in identifying blood products.

    View details for DOI 10.1007/s00247-009-1292-8

    View details for Web of Science ID 000269861000003

    View details for PubMedID 19669747

  • Arterial Spin-Label Imaging in Patients with Normal Bolus Perfusion-weighted MR Imaging Findings: Pilot Identification of the Borderzone Sign RADIOLOGY Zaharchuk, G., Bammer, R., Straka, M., Shankaranarayan, A., Alsop, D. C., Fischbein, N. J., Atlas, S. W., Moseley, M. E. 2009; 252 (3): 797-807

    Abstract

    To determine whether perfusion abnormalities are depicted on arterial spin-labeling (ASL) images obtained in patients with normal bolus perfusion-weighted (PW) magnetic resonance (MR) imaging findings.Institutional review board approval and written informed patient consent were obtained. This study was HIPAA compliant. Consecutive patients suspected or known to have cerebrovascular disease underwent 1.5-T brain MR imaging, including MR angiography, gradient-echo PW imaging, and pseudocontinuous ASL imaging, between October 2007 and January 2008. Patients with normal bolus PW imaging findings were retrospectively identified, and two neuroradiologists subsequently evaluated the ASL images for focal abnormalities. The severity of the borderzone sign-that is, bilateral ASL signal dropout with surrounding cortical areas of hyperintensity in the middle cerebral artery borderzone regions-was classified by using a four-point scale. For each group, the ASL-measured mean mixed cortical cerebral blood flow (CBF) at the level of the centrum semiovale was evaluated by using the Jonckheere-Terpstra test.One hundred thirty-nine patients met the study inclusion criteria, and 41 (30%) of them had normal bolus PW imaging findings. Twenty-three (56%) of these 41 patients also had normal ASL imaging findings. The remaining 18 (44%) patients had the ASL borderzone sign; these patients were older (mean age, 71 years +/- 11 [standard deviation] vs 57 years +/- 16; P < .005) and had lower mean CBF (30 mL/100 g/min +/- 12 vs 46 mL/100 g/min +/- 12, P < .003) compared with the patients who had normal ASL imaging findings. Five patients had additional focal ASL findings that were related to either slow blood flow in a vascular structure or postsurgical perfusion defects and were not visible on the PW images.Approximately half of the patients with normal bolus PW imaging findings had abnormal ASL findings-most commonly the borderzone sign. Results of this pilot study suggest that ASL imaging in patients who have this sign and are suspected of having cerebrovascular disease yields additional and complementary hemodynamic information.

    View details for DOI 10.1148/radiol.2523082018

    View details for Web of Science ID 000270809500022

    View details for PubMedID 19703858

  • Optimal definition for PWI/DWI mismatch in acute ischemic stroke patients JOURNAL OF CEREBRAL BLOOD FLOW AND METABOLISM Kakuda, W., Lansberg, M. G., Thijs, V. N., Kemp, S. M., Bammer, R., Wechsler, L. R., Moseley, M. E., Parks, M. P., Albers, G. W. 2008; 28 (5): 887-891

    Abstract

    Although the perfusion-weighted imaging/diffusion-weighted imaging (PWI/DWI) mismatch model has been proposed to identify acute stroke patients who benefit from reperfusion therapy, the optimal definition of a mismatch is uncertain. We evaluated the odds ratio for a favorable clinical response in mismatch patients with reperfusion compared with no reperfusion for various mismatch ratio thresholds in patients enrolled in the diffusion and perfusion imaging evaluation for understanding stroke evolution (DEFUSE) study. A mismatch ratio of 2.6 provided the highest sensitivity (90%) and specificity (83%) for identifying patients in whom reperfusion was associated with a favorable response. Defining mismatch with a larger PWI/DWI ratio may provide greater power for detecting beneficial effects of reperfusion.

    View details for DOI 10.1038/sj.jcbfm.9600604

    View details for Web of Science ID 000255261300003

    View details for PubMedID 18183031

  • Single-step Nonlinear diffusion tensor estimation in the presence of microscopic and macroscopic motion MAGNETIC RESONANCE IN MEDICINE Aksoy, M., Liu, C., Moseley, M. E., Bammer, R. 2008; 59 (5): 1138-1150

    Abstract

    Patient motion can cause serious artifacts in diffusion tensor imaging (DTI), diminishing the reliability of the estimated diffusion tensor information. Studies in this field have so far been limited mainly to the correction of miniscule physiological motion. In order to correct for gross patient motion it is not sufficient to correct for misregistration between successive shots; the change in the diffusion-encoding direction must also be accounted for. This becomes particularly important for multishot sequences, whereby-in the presence of motion-each shot is encoded with a different diffusion weighting. In this study a general mathematical framework to correct for gross patient motion present in a multishot and multicoil DTI scan is presented. A signal model is presented that includes the effect of rotational and translational motion in the patient frame of reference. This model was used to create a nonlinear least-squares formulation, from which the diffusion tensors were obtained using a nonlinear conjugate gradient algorithm. Applications to both phantom simulations and in vivo studies showed that in the case of gross motion the proposed algorithm performs superiorly compared to conventional methods used for tensor estimation.

    View details for DOI 10.1002/mrm.21558

    View details for Web of Science ID 000255230700024

    View details for PubMedID 18429035

  • Identifying systematic errors in quantitative dynamic-susceptibility contrast perfusion imaging by high-resolution multi-echo parallel EPI NMR IN BIOMEDICINE Jochimsen, T. H., Newbould, R. D., Skare, S. T., Clayton, D. B., Albers, G. W., Moseley, M. E., Bammer, R. 2007; 20 (4): 429-438

    Abstract

    Several obstacles usually confound a straightforward perfusion analysis using dynamic-susceptibility contrast-based magnetic resonance imaging (DSC-MRI). In this work, it became possible to eliminate some of these sources of error by combining a multiple gradient-echo technique with parallel imaging (PI): first, the large dynamic range of tracer concentrations could be covered satisfactorily with multiple echo times (TE) which would otherwise result in overestimation of image magnitude in the presence of noise. Second, any bias from T(1) relaxation could be avoided by fitting to the signal magnitude of multiple TEs. Finally, with PI, a good tradeoff can be achieved between number of echoes, brain coverage, temporal resolution and spatial resolution. The latter reduces partial voluming, which could distort calculation of the arterial input function. Having ruled out these sources of error, a 4-fold overestimation of cerebral blood volume and flow remained, which was most likely due to the completely different relaxation mechanisms that are effective in arterial voxels compared with tissue. Hence, the uniform tissue-independent linear dependency of relaxation rate upon tracer concentration, which is usually assumed, must be questioned. Therefore, DSC-MRI requires knowledge of the exact dependency of transverse relaxation rate upon tracer concentration in order to calculate truly quantitative perfusion maps.

    View details for DOI 10.1002/nbm.1107

    View details for Web of Science ID 000246767000004

    View details for PubMedID 17044140

  • Clinical multishot DW-EPI through parallel imaging with considerations of susceptibility, motion, and noise MAGNETIC RESONANCE IN MEDICINE Skare, S., Newbould, R. D., Clayton, D. B., Albers, G. W., Nagle, S., Bammer, R. 2007; 57 (5): 881-890

    Abstract

    Geometric distortions and poor image resolution are well known shortcomings of single-shot echo-planar imaging (ss-EPI). Yet, due to the motion immunity of ss-EPI, it remains the most common sequence for diffusion-weighted imaging (DWI). Moreover, both navigated DW interleaved EPI (iEPI) and parallel imaging (PI) methods, such as sensitivity encoding (SENSE) and generalized autocalibrating parallel acquisitions (GRAPPA), can improve the image quality in EPI. In this work, DW-EPI accelerated by PI is proposed as a self-calibrated and unnavigated form of interleaved acquisition. The PI calibration is performed on the b = 0 s/mm2 data and applied to each shot in the rest of the DW data set, followed by magnitude averaging. Central in this study is the comparison of GRAPPA and SENSE in the presence of off-resonances and motion. The results show that GRAPPA is more robust than SENSE against both off-resonance and motion-related artifacts. The SNR efficiency was also investigated, and it is shown that the SNR/scan time ratio is equally high for one- to three-shot high-resolution diffusion scans due to the shortened EPI readout train length. The image quality improvements without SNR efficiency loss, together with motion tolerance, make the GRAPPA-driven DW-EPI sequence clinically attractive.

    View details for DOI 10.1002/mrm.21176

    View details for Web of Science ID 000246052800010

    View details for PubMedID 17457876

  • Cutting-edge imaging of the spine NEUROIMAGING CLINICS OF NORTH AMERICA Vertinsky, A. T., Krasnokutsky, M. V., Augustin, M., Bammer, R. 2007; 17 (1): 117-?

    Abstract

    Damage to the spinal cord may be caused by a wide range of pathologies and generally results in profound functional disability. A reliable diagnostic workup of the spine is very important because even relatively small lesions in this part of the central nervous system can have a profound clinical impact. MR imaging has become the method of choice for the detection and diagnosis of many spine disorders. Various innovative MR imaging methods have been developed to improve neuroimaging, including better pulse sequences and new MR contrast parameters. These new "cutting-edge" technologies have the potential to impact profoundly the ease and confidence of spinal disease interpretation and offer a more efficient diagnostic workup of patients suffering from spinal disease.

    View details for DOI 10.1016/j.nic.2007.01.003

    View details for Web of Science ID 000247043800010

    View details for PubMedID 17493543

  • Augmented generalized SENSE reconstruction to correct for rigid body motion MAGNETIC RESONANCE IN MEDICINE Bammer, R., Aksoy, M., Liu, C. 2007; 57 (1): 90-102

    Abstract

    The correction of motion artifacts continues to be a significant problem in MRI. In the case of uncooperative patients, such as children, or patients who are unable to remain stationary, the accurate determination and correction of motion artifacts becomes a very important prerequisite for achieving good image quality. The application of conventional motion-correction strategies often produces inconsistencies in k-space data. As a result, significant residual artifacts can persist. In this work a formalism is introduced for parallel imaging in the presence of motion. The proposed method can improve overall image quality because it diminishes k-space inconsistencies by exploiting the complementary image encoding capacity of individual receiver coils. Specifically, an augmented version of an iterative SENSE reconstruction is used as a means of synthesizing the missing data in k-space. Motion is determined from low-resolution navigator images that are coregistered by an automatic registration routine. Navigator data can be derived from self-navigating k-space trajectories or in combination with other navigation schemes that estimate patient motion. This correction method is demonstrated by interleaved spiral images collected from volunteers. Conventional spiral scans and scans corrected with proposed techniques are shown, and the results illustrate the capacity of this new correction approach.

    View details for DOI 10.1002/mrm.21106

    View details for Web of Science ID 000243538900012

    View details for PubMedID 17191225

  • Magnetic resonance imaging profiles predict clinical response to early reperfusion: The diffusion and perfusion imaging evaluation for understanding stroke evolution (DEFUSE) study ANNALS OF NEUROLOGY Albers, G. W., Thijs, V. N., Wechsle, L., Kemp, S., Schlaug, G., Skalabrin, E., Bammer, R., Kakuda, W., Lansberg, M. G., Shuaib, A., Coplin, W., Hamilton, S., Moseley, M., Marks, M. P. 2006; 60 (5): 508-517

    Abstract

    To determine whether prespecified baseline magnetic resonance imaging (MRI) profiles can identify stroke patients who have a robust clinical response after early reperfusion when treated 3 to 6 hours after symptom onset.We conducted a prospective, multicenter study of 74 consecutive stroke patients admitted to academic stroke centers in North America and Europe. An MRI scan was obtained immediately before and 3 to 6 hours after treatment with intravenous tissue plasminogen activator 3 to 6 hours after symptom onset. Baseline MRI profiles were used to categorize patients into subgroups, and clinical responses were compared based on whether early reperfusion was achieved.Early reperfusion was associated with significantly increased odds of achieving a favorable clinical response in patients with a perfusion/diffusion mismatch (odds ratio, 5.4; p = 0.039) and an even more favorable response in patients with the Target Mismatch profile (odds ratio, 8.7; p = 0.011). Patients with the No Mismatch profile did not appear to benefit from early reperfusion. Early reperfusion was associated with fatal intracranial hemorrhage in patients with the Malignant profile.For stroke patients treated 3 to 6 hours after onset, baseline MRI findings can identify subgroups that are likely to benefit from reperfusion therapies and can potentially identify subgroups that are unlikely to benefit or may be harmed.

    View details for DOI 10.1002/ana.20976

    View details for Web of Science ID 000242545100006

    View details for PubMedID 17066483

  • Fast patient workup in acute stroke using parallel imaging. Topics in magnetic resonance imaging Augustin, M., Fazekas, F., Bammer, R. 2004; 15 (3): 207-219

    Abstract

    Treatment of ischemic stroke is a very frustrating topic for neurologists. Presently, the most promising therapy seems to be thrombolysis of the clot. However, this intervention is associated with complication risks, most significantly the risk of post-treatment hemorrhage. This risk of bleeding increases not only with the size of the ischemic brain tissue but also with the time-to-treatment interval. Studies suggest a time window of 3 hours for most effective treatment. Hence, there is demand for a rapid imaging workup, which thus far has been accomplished with computed tomography. Because of the risks associated with thrombolytic therapy, more detailed information is desirable. The distinction between patients with viable ischemically challenged neural tissue and those with complete infarcts is of great importance, and computed tomography is insufficient for this task. This is also true for outlining the etiology of stroke, which may impact treatment. For these tasks, magnetic resonance imaging has been proposed. However, comprehensive imaging protocols take time, which is limited in stroke treatment. Therefore, new imaging techniques are required that provide both in-depth information and short scanning times. Parallel imaging is uniquely suited for this purpose.

    View details for PubMedID 15480002

  • Analysis and generalized correction of the effect of spatial gradient field distortions in diffusion-weighted imaging MAGNETIC RESONANCE IN MEDICINE Bammer, R., Markl, M., Barnett, A., Acar, B., Alley, M. T., Pelc, N. J., Glover, G. H., Moseley, M. E. 2003; 50 (3): 560-569

    Abstract

    Nonuniformities of magnetic field gradients can cause serious artifacts in diffusion imaging. While it is well known that nonlinearities of the imaging gradients lead to image warping, those imperfections can also cause spatially dependent errors in the direction and magnitude of the diffusion encoding. This study shows that the potential errors in diffusion imaging are considerable. Further, we show that retrospective corrections can be applied to reduce these errors. A general mathematical framework was formulated to characterize the contribution of gradient nonuniformities to diffusion experiments. The gradient field was approximated using spherical harmonic expansion, and this approximation was employed (after geometric distortions were eliminated) to predict and correct the errors in diffusion encoding. Before the corrections were made, the experiments clearly revealed marked deviations of the calculated diffusivity for fields of view (FOVs) generally used in diffusion experiments. These deviations were most significant farther away from the magnet's isocenter. For an FOV of 25 cm, the resultant errors in absolute diffusivity ranged from approximately -10% to +20%. Within the same FOV, the diffusion-encoding direction and the orientation of the calculated eigenvectors can be significantly altered if the perturbations by the gradient nonuniformities are not considered. With the proposed correction scheme, most of the errors introduced by gradient nonuniformities can be removed.

    View details for DOI 10.1002/mrm.10545

    View details for Web of Science ID 000185174500015

    View details for PubMedID 12939764

  • In vivo MR tractography using diffusion imaging EUROPEAN JOURNAL OF RADIOLOGY Bammer, R., Acar, B., Moseley, M. E. 2003; 45 (3): 223-234

    Abstract

    Diffusion in structured tissue, such as white matter or muscle, is anisotropic. MR diffusion tensor imaging (DTI) measures anisotropy per pixel and provides the directional information relevant for MR tractography or fiber tracking in vivo. MR tractography is non-invasive, relatively fast, and can be repeated multiple times without destructing important tissue. Moreover, the combination with other MR images is relatively simple. In this paper, the basic principles of tractography are presented. Different tracking methods with varying degrees of complexity are introduced and their potential strengths and weaknesses are discussed. Clinical applications and different strategies for evaluating the fidelity of tracking results are reviewed.

    View details for Web of Science ID 000181482500008

    View details for PubMedID 12595107

  • Diffusion tensor imaging using single-shot SENSE-EPI MAGNETIC RESONANCE IN MEDICINE Bammer, R., Auer, M., Keeling, S. L., Augustin, M., Stables, L. A., Prokesch, R. W., Stollberger, R., Moseley, M. E., Fazekas, F. 2002; 48 (1): 128-136

    Abstract

    SENSitivity Encoding (SENSE) greatly enhances the quality of diffusion-weighted echo-planar imaging (EPI) by reducing blurring and off-resonance artifacts. Such improvement would also be desirable for diffusion tensor imaging (DTI), but measures derived from the diffusion tensor can be extremely sensitive to any kind of image distortion. Whether DTI is feasible in combination with SENSE has not yet been explored, and is the focus of this study. Using a SENSE-reduction factor of 2, DTI scans in eight healthy volunteers were carried out with regular- and high-resolution acquisition matrices. To further improve the stability of the SENSE reconstruction, a new coil-sensitivity estimation technique based on variational calculus and the principles of matrix regularization was applied. With SENSE, maps of the trace of the diffusion tensor and of fractional anisotropy (FA) had improved spatial resolution and less geometric distortion. Overall, the geometric distortions were substantially removed and a significant resolution enhancement was achieved with almost the same scan time as regular EPI. DTI was even possible without the use of quadrature body coil (QBC) reference scans. Geometry-factor-related noise enhancement was only discernible in maps generated with higher-resolution matrices. Error boundaries for residual fluctuations in SENSE reconstructions are discussed. Our results suggest that SENSE can be combined with DTI and may present an important adjunct for future neuroimaging applications of this technique.

    View details for DOI 10.1002/mrm.10184

    View details for Web of Science ID 000176648900016

    View details for PubMedID 12111940

  • Improved image reconstruction from sensitivity-encoded data by wavelet denoising and Tikhonov regularization 2002 IEEE INTERNATIONAL SYMPOSIUM ON BIOMEDICAL IMAGING, PROCEEDINGS Liang, Z. P., Bammer, R., Ji, J., Pelc, N. J., Glover, G. H. 2002: 493-496
  • Improved diffusion-weighted single-shot echo-planar imaging (EPI) in stroke using Sensitivity Encoding (SENSE) MAGNETIC RESONANCE IN MEDICINE Bammer, R., Keeling, S. L., Augustin, M., Pruessmann, K. P., Wolf, R., Stollberger, R., Hartung, H. P., Fazekas, F. 2001; 46 (3): 548-554

    Abstract

    Diffusion-weighted single-shot EPI (sshEPI) is one of the most important tools for the diagnostic assessment of stroke patients, but it suffers from well known artifacts. Therefore, sshEPI was combined with SENSitivity Encoding (SENSE) to further increase EPI's potential for stroke imaging. Eight healthy volunteers and a consecutive series of patients (N = 8) with suspected stroke were examined with diffusion-weighted SENSE-sshEPI using different reduction factors (1.0 < or = R < or = 3.0). Additionally, a high-resolution diffusion-weighted SENSE-sshEPI scan was included. All examinations were diagnostic and of better quality than conventional sshEPI. No ghostings or aliasing artifacts were discernible, and EPI-related image distortions were markedly diminished. Chemical shift artifacts and eddy current-induced image warping were still present, although to a markedly smaller extent. Measured direction-dependent diffusion-coefficients and isotropic diffusion values were comparable to previous findings but showed less fluctuation. We have demonstrated the technical feasibility and clinical applicability of diffusion-weighted SENSE-sshEPI in patients with subacute stroke. Because of the faster k-space traversal, this novel technique is able to reduce typical EPI artifacts and increase spatial resolution while simultaneously remaining insensitive to bulk motion.

    View details for Web of Science ID 000170740300020

    View details for PubMedID 11550248

  • Magnetic resonance diffusion tensor imaging for characterizing diffuse and focal white matter abnormalities in multiple sclerosis MAGNETIC RESONANCE IN MEDICINE Bammer, R., Augustin, M., Strasser-Fuchs, S., Seifert, T., Kapeller, P., Stollberger, R., Ebner, F., Hartung, H. P., Fazekas, F. 2000; 44 (4): 583-591

    Abstract

    High-resolution diffusion tensor imaging (DTI) was performed in 14 patients with clinically definite multiple sclerosis (MS) and the trace of the diffusion tensor () and the fractional anisotropy (FA) were determined in normal appearing white matter (NAWM) and in different types of focal MS lesions. A small but significant increase of the in NAWM compared to control white matter ((840 +/- 85) x 10(-6) mm(2)/sec vs. (812 +/- 59) x 10(-6) mm(2)/sec; P < 0.01) was found. In addition, there was a significant decrease in the FA of normal-appearing regions containing well-defined white matter tracts, such as the genu of the internal capsule. In non-acute lesions, the of T(1)-hypointense areas was significantly higher than that of T(1)-isointense lesions ((1198 +/- 248) x 10(-6) mm(2)/sec vs. (1006 +/- 142) x 10(-6) mm(2)/sec; P < 0. 001), and there was a corresponding inverse relation of FA. Diffusion characteristics of active lesions with different enhancement patterns were also significantly different. DTI with a phase navigated interleaved echo planar imaging technique may be used to detect abnormalities of isotropic and anisotropic diffusion in the NAWM and selected fiber tracts of patients with MS throughout the entire brain, and it demonstrates substantial differences between various types of focal lesions.

    View details for Web of Science ID 000089671300012

    View details for PubMedID 11025514

  • Diffusion-weighted imaging of patients with subacute cerebral ischemia: Comparison with conventional and contrast-enhanced MR imaging AMERICAN JOURNAL OF NEURORADIOLOGY Augustin, M., Bammer, R., Simbrunner, J., Stollberger, R., Hartung, H. P., Fazekas, F. 2000; 21 (9): 1596-1602

    Abstract

    The importance of diffusion-weighted imaging (DWI) for delineating acute ischemic lesions has been investigated extensively; however, few studies have investigated the role of DWI in the subacute stage of stroke. Because these lesions tend to appear bright throughout the first days of ischemia, owing to restricted diffusion, we speculated that DWI could also improve the detection of subacute infarcts as compared with conventional and contrast-enhanced MR imaging.Interleaved echo-planar DWI with phase navigation was performed on a 1.5-T MR unit in a consecutive series of 53 patients (mean age, 66 +/- 14 years) with suspected recent cerebral ischemia. The interval between onset of clinical symptoms and MR imaging ranged from 1 to 14 days (mean, 6 +/- 4 days). Contrast material was given to 28 patients in a dose of 0.1 mmol/kg.DWI clearly delineated recent ischemic damage in 39 patients (74%) as compared with 33 (62%) in whom lesions were identified or suspected on conventional T2-weighted images. DWI provided information not accessible with T2-weighted imaging in 17 patients when evidence of lesion multiplicity or detection of clinically unrelated recent lesions was included for comparison. Subacute ischemic lesions were also seen more frequently on DWI sequences than on contrast-enhanced images (20 versus 13 patients). DWI was more likely to make a diagnostic contribution in the first week of stroke and in patients with small lesions or preexisting ischemic cerebral damage than was conventional MR imaging.Recent ischemic damage is better shown on DWI sequences than on conventional and contrast-enhanced MR images throughout the first days after stroke and may provide further information about the origin of clinical symptoms. Adding DWI to imaging protocols for patients with subacute cerebral ischemia is recommended.

    View details for Web of Science ID 000090110900007

    View details for PubMedID 11039337

  • Diffusion-weighted MR imaging of the spinal cord AMERICAN JOURNAL OF NEURORADIOLOGY Bammer, R., Fazekas, F., Augustin, M., Simbrunner, J., Strasser-Fuchs, S., Seifert, T., Stollberger, R., Hartung, H. P. 2000; 21 (3): 587-591

    Abstract

    Diffusion-weighted MR imaging may increase the sensitivity and specificity of MR imaging for certain pathologic conditions of the spinal cord but is rarely performed because of several technical issues. We therefore tested a novel phase-navigated spin-echo diffusion-weighted interleaved echo-planar imaging sequence in seven healthy volunteers and six patients with intramedullary lesions. We performed diffusion-weighted MR imaging of the spinal cord with high spatial resolution. Different patterns of diffusion abnormalities observed in patient studies support the possible diagnostic impact of diffusion-weighted MR imaging for diseases of the spinal cord.

    View details for Web of Science ID 000085860900027

    View details for PubMedID 10730657

  • High resolution diffusion tensor imaging using interleaved echo-planar imaging MEDICAL IMAGING 2000: PHYSIOLOGY AND FUNCTION FORM MULTIDIMENSIONAL IMAGES Bammer, R., Augustin, M., Seifert, T., Strasser-Fuchs, S., Stollberger, R., Wach, P., Hartung, H. P., Fazekas, F. 2000; 1 (23): 2-11
  • Parallel imaging strategies for high-speed Magnetic Resonance diffusion imaging MEDICAL IMAGING 2000: PHYSIOLOGY AND FUNCTION FORM MULTIDIMENSIONAL IMAGES Bammer, R., Stollberger, R., Augustin, M., Seifert, T., Strasser-Fuchs, S., Wach, P., Hartung, H. P., Fazekas, F. 2000; 1 (23): 12-22
  • Improved T2* Imaging without Increase in Scan Time: SWI Processing of 2D Gradient Echo. AJNR. American journal of neuroradiology Soman, S., Holdsworth, S. J., Barnes, P. D., Rosenberg, J., Andre, J. B., Bammer, R., Yeom, K. W. 2013; 34 (11): 2092-2097

    Abstract

    BACKGROUND AND PURPOSE:2D gradient-echo imaging is sensitive to T2* lesions (hemorrhages, mineralization, and vascular lesions), and susceptibility-weighted imaging is even more sensitive, but at the cost of additional scan time (SWI: 5-10 minutes; 2D gradient-echo: 2 minutes). The long acquisition time of SWI may pose challenges in motion-prone patients. We hypothesized that 2D SWI/phase unwrapped images processed from 2D gradient-echo imaging could improve T2* lesion detection.MATERIALS AND METHODS:2D gradient-echo brain images of 50 consecutive pediatric patients (mean age, 8 years) acquired at 3T were retrospectively processed to generate 2D SWI/phase unwrapped images. The 2D gradient-echo and 2D SWI/phase unwrapped images were compared for various imaging parameters and were scored in a blinded fashion.RESULTS:Of 50 patients, 2D gradient-echo imaging detected T2* lesions in 29 patients and had normal findings in 21 patients. 2D SWI was more sensitive than standard 2D gradient-echo imaging in detecting T2* lesions (P < .0001). 2D SWI/phase unwrapped imaging also improved delineation of normal venous structures and nonpathologic calcifications and helped distinguish calcifications from hemorrhage. A few pitfalls of 2D SWI/phase unwrapped imaging were noted, including worsened motion and dental artifacts and challenges in detecting T2* lesions adjacent to calvaria or robust deoxygenated veins.CONCLUSIONS:2D SWI and associated phase unwrapped images processed from standard 2D gradient-echo images were more sensitive in detecting T2* lesions and delineating normal venous structures and nonpathologic mineralization, and they also helped distinguish calcification at no additional scan time. SWI processing of 2D gradient-echo images may be a useful adjunct in cases in which longer scan times of 3D SWI are difficult to implement.

    View details for DOI 10.3174/ajnr.A3595

    View details for PubMedID 23744690

  • Comparison of the response to endovascular reperfusion in relation to site of arterial occlusion. Neurology Lemmens, R., Mlynash, M., Straka, M., Kemp, S., Bammer, R., Marks, M. P., Albers, G. W., Lansberg, M. G. 2013; 81 (7): 614-618

    Abstract

    We explored the relationship between the site of vascular occlusion and the response to endovascular treatment in patients with acute ischemic stroke and also considered the impact of mismatch profile.DEFUSE-2 was a prospective cohort study of patients treated with endovascular therapy. Patients with internal carotid artery (ICA) and middle cerebral artery (MCA) involvement were included in this substudy. Mismatch and reperfusion status was assessed on MRI. Favorable clinical response was defined as an improvement of at least 8 points on the NIH Stroke Scale.Reperfusion rates were comparable in both groups (61% for ICA and 59% for MCA). In the setting of reperfusion, percentages of favorable clinical response were similar between patients with stroke due to ICA (65%) and MCA (63%) occlusions. When reperfusion was not achieved, favorable outcomes were less frequent with obstructions of the ICA (9%) than the MCA (52%). Among target mismatch patients, the adjusted odds ratio for favorable clinical response associated with reperfusion was 39.7 (95% confidence interval 1.4-1,132.8) for ICA occlusions vs 5.1 (95% confidence interval 1.4-19.3) for MCA occlusions.Endovascular reperfusion is associated with favorable clinical response regardless of the location of the arterial occlusion. This association is strongest for target mismatch patients with ICA occlusions. Target mismatch patients with either ICA or MCA occlusions appear to be good candidates for endovascular reperfusion therapy.

    View details for DOI 10.1212/WNL.0b013e3182a08f07

    View details for PubMedID 23851962

  • Impact of diffusion-weighted imaging lesion volume on the success of endovascular reperfusion therapy. Stroke; a journal of cerebral circulation Olivot, J., Mosimann, P. J., Labreuche, J., Inoue, M., Meseguer, E., Desilles, J., Rouchaud, A., Klein, I. F., Straka, M., Bammer, R., Mlynash, M., Amarenco, P., Albers, G. W., Mazighi, M. 2013; 44 (8): 2205-2211

    Abstract

    BACKGROUND AND PURPOSE: Diffusion-weighted imaging (DWI) lesion volume is associated with poor outcome after thrombolysis, and it is unclear whether endovascular therapies are beneficial for large DWI lesion. Our aim was to assess the impact of pretreatment DWI lesion volume on outcomes after endovascular therapy, with a special emphasis on patients with complete recanalization. METHODS: We analyzed data collected between April 2007 and November 2011 in a prospective clinical registry. All acute ischemic stroke patients with complete occlusion of internal carotid artery or middle cerebral artery treated by endovascular therapy were included. DWI lesion volumes were measured by the RAPID software. Favorable outcome was defined by modified Rankin Scale of 0 to 2 at 90 days. RESULTS: A total of 139 acute ischemic stroke patients were included. Median DWI lesion volume was 14 cc (interquartile range, 5-43) after a median onset time to imaging of 110 minutes (interquartile range, 77-178). Higher volume was associated with less favorable outcome (adjusted odds ratio, 0.55; 95% confidence interval, 0.31-0.96). A complete recanalization was achieved in 65 (47%) patients after a median onset time of 238 minutes (interquartile range, 206-285). After adjustment for volume, complete recanalization was associated with more favorable outcome (adjusted odds ratio, 6.32; 95% confidence interval, 2.90-13.78). After stratification of volume by tertiles, complete recanalization was similarly associated with favorable outcome in the upper 2 tertiles (P<0.005). CONCLUSIONS: Our results emphasize the importance of initial DWI volume and recanalization on clinical outcome after endovascular treatment. Large DWI lesions may still benefit from recanalization in selected patients.

    View details for DOI 10.1161/STROKEAHA.113.000911

    View details for PubMedID 23760215

  • 3D isotropic high-resolution diffusion-weighted MRI of the whole brain with a motion-corrected steady-state free precession sequence MAGNETIC RESONANCE IN MEDICINE O'Halloran, R. L., Aksoy, M., Van, A. T., Bammer, R. 2013; 70 (2): 466-478

    Abstract

    The main obstacle to high-resolution (<1.5 mm isotropic) 3D diffusion-weighted MRI is the differential motion-induced phase error from shot-to-shot. In this work, the phase error is addressed with a hybrid 3D navigator approach that corrects motion-induced phase in two ways. In the first, rigid-body motion is corrected for every shot. In the second, repeatable nonrigid-body pulsation is corrected for each portion of the cardiac cycle. These phase error corrections were implemented with a 3D diffusion-weighted steady- state free precession pulse sequence and were shown to mitigate signal dropouts caused by shot-to-shot phase inconsistencies compared to a standard gridding reconstruction in healthy volunteers. The proposed approach resulted in diffusion contrast more similar to the contrast observed in the reference echo-planer imaging scans than reconstruction of the same data without correction. Fractional anisotropy and Color fractional anisotropy maps generated with phase-corrected data were also shown to be more similar to echo-planer imaging reference scans than those generated without phase correction. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.24489

    View details for Web of Science ID 000322128300019

    View details for PubMedID 23042686

  • Clinical outcomes strongly associated with the degree of reperfusion achieved in target mismatch patients: pooled data from the diffusion and perfusion imaging evaluation for understanding stroke evolution studies. Stroke; a journal of cerebral circulation Inoue, M., Mlynash, M., Straka, M., Kemp, S., Jovin, T. G., Tipirneni, A., Hamilton, S. A., Marks, M. P., Bammer, R., Lansberg, M. G., Albers, G. W. 2013; 44 (7): 1885-1890

    Abstract

    BACKGROUND AND PURPOSE: To investigate relationships between the degree of early reperfusion achieved on perfusion-weighted imaging and clinical outcomes in the Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution studies. We hypothesized that there would be a strong correlation between the degree of reperfusion achieved and clinical outcomes in target mismatch (TMM) patients. METHODS: The degree of reperfusion was calculated on the basis of the difference in perfusion-weighted imaging volumes (time to maximum of tissue residue function [Tmax]>6 s) between the baseline MRI and the early post-treatment follow-up scan. Patients were grouped into quartiles, on the basis of degree of reperfusion achieved, and the association between the degree of reperfusion and clinical outcomes in TMM and no TMM patients was assessed. Favorable clinical response was determined at day 30 on the basis of the National Institutes of Health Stroke Scale and good functional outcome was defined as a modified Rankin Scale score ?2 at day 90. RESULTS: This study included 121 patients; 98 of these had TMM. The median degree of reperfusion achieved was not different in TMM patients (60%) versus No TMM patients (64%; P=0.604). The degree of reperfusion was strongly correlated with both favorable clinical response (P<0.001) and good functional outcome (P=0.001) in TMM patients; no correlation was present in no TMM. The frequency of achieving favorable clinical response or good functional outcome was significantly higher in TMM patients in the highest reperfusion quartile versus the lower 3 quartiles (88% versus 41% as odds ratio, 10.3; 95% confidence interval, 2.8-37.5; and 75% versus 34% as odds ratio, 5.9; 95% confidence interval, 2.1-16.7, respectively). A receiver operating characteristic curve analysis identified 90% as the optimal reperfusion threshold for predicting good functional outcomes. CONCLUSIONS: The degree of reperfusion documented on perfusion-weighted imaging after reperfusion therapies corresponds closely with clinical outcomes in TMM patients. Reperfusion of ?90% of the perfusion lesion is an appropriate goal for reperfusion therapies to aspire to.

    View details for DOI 10.1161/STROKEAHA.111.000371

    View details for PubMedID 23704106

  • Prospective optical motion correction for 3D time-of-flight angiography. Magnetic resonance in medicine Kopeinigg, D., Aksoy, M., Forman, C., Straka, M., Seaman, D., Rosenberg, J., Fleischmann, D., Hornegger, J., Bammer, R. 2013; 69 (6): 1623-1633

    Abstract

    Magnetic resonance angiograms are often nondiagnostic due to patient motion. In clinical practice, the available time to repeat motion-corrupted scans is very limited-especially in patients who suffer from acute cerebrovascular conditions. Here, the feasibility of an optical motion correction system to prospectively correct patient motion for 3D time-of-flight magnetic resonance angiography was investigated. Experiments were performed on five subjects with and without parallel imaging (SENSE R = 2) on a 1.5 T unit. Two human readers assessed the data and were in good agreement (kappa: 0.77). The results from this study indicate that the optical motion correction system greatly reduces motion artifacts when motion was present and did not impair the image quality in the absence of motion. Statistical analysis showed no significant difference between the (vendor-provided) SENSE and the nonaccelerated acquisitions. In conclusion, the optical motion correction system tested in this study has the potential to greatly improve 3D time-of-flight angiograms regardless of whether it is used with or without SENSE. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.24423

    View details for PubMedID 22887025

  • Simultaneous perfusion and permeability measurements using combined spin- and gradient-echo MRI. Journal of cerebral blood flow and metabolism Schmiedeskamp, H., Andre, J. B., Straka, M., Christen, T., Nagpal, S., Recht, L., Thomas, R. P., Zaharchuk, G., Bammer, R. 2013; 33 (5): 732-743

    Abstract

    The purpose of this study was to estimate magnetic resonance imaging-based brain perfusion parameters from combined multiecho spin-echo and gradient-echo acquisitions, to correct them for T1-, T2-, and -related contrast agent (CA) extravasation effects, and to simultaneously determine vascular permeability. Perfusion data were acquired using a combined multiecho spin- and gradient-echo (SAGE) echo-planar imaging sequence, which was corrected for CA extravasation effects using pharmacokinetic modeling. The presented method was validated in simulations and brain tumor patients, and compared with uncorrected single-echo and multiecho data. In the presence of CA extravasation, uncorrected single-echo data resulted in underestimated CA concentrations, leading to underestimated single-echo cerebral blood volume (CBV) and mean transit time (MTT). In contrast, uncorrected multiecho data resulted in overestimations of CA concentrations, CBV, and MTT. The correction of CA extravasation effects resulted in CBV and MTT estimates that were more consistent with the underlying tissue characteristics. Spin-echo perfusion data showed reduced large-vessel blooming effects, facilitating better distinction between increased CBV due to active tumor progression and elevated CBV due to the presence of cortical vessels in tumor proximity. Furthermore, extracted permeability parameters were in good agreement with elevated T1-weighted postcontrast signal values.

    View details for DOI 10.1038/jcbfm.2013.10

    View details for PubMedID 23462570

  • Comparison of Readout-Segmented Echo-Planar Imaging (EPI) and Single-Shot EPI in Clinical Application of Diffusion-Weighted Imaging of the Pediatric Brain. AJR. American journal of roentgenology Yeom, K. W., Holdsworth, S. J., Van, A. T., Iv, M., Skare, S., Lober, R. M., Bammer, R. 2013; 200 (5): W437-43

    Abstract

    OBJECTIVE. Readout-segmented echo-planar imaging (EPI) has been suggested as an alternative to single-shot EPI for diffusion-weighted imaging (DWI) with reduced distortion. However, clinical comparisons of readout-segmented EPI and EPI DWI are limited by unmatched imaging parameters and reconstruction procedures. Our goal was to compare the clinical utility of generalized autocalibrating partial parallel acquisition (GRAPPA)-accelerated readout-segmented EPI DWI with GRAPPA-accelerated EPI DWI for visualization of the pediatric brain in regions prone to distortion, such as the orbit, skull base, and posterior fossa. SUBJECTS AND METHODS. Thirty consecutive patients (mean age, 7.8 years) presenting with orbital, skull base, and posterior fossa neuropathologic abnormalities were scanned at 3 T. Images were obtained using GRAPPA-accelerated readout-segmented EPI and GRAPPA-accelerated EPI with an identical scanning time, acceleration factor, target resolution, and image postprocessing procedure. The two datasets were independently reviewed by two blinded neuroradiologists. Imaging studies were evaluated for resolution, signal-to-noise ratio (SNR), contrast, distortion, lesion conspicuity, and diagnostic confidence and graded using a 7-point Likert scale (1, nondiagnostic; 7, outstanding). RESULTS. There was good reader agreement in the scores (? = 0.66; 95% CI, 0.54-0.78). The mean scores for EPI and readout-segmented EPI, respectively, were as follows: resolution, 5.0 and 6.0; SNR, 5.5 and 3.0; contrast, 3.7 and 3.2; distortion, 4.8 and 6.0; lesion conspicuity, 4.6 and 5.1; and diagnostic confidence, 4.7 and 5.4. Readout-segmented EPI was superior in resolution, distortion reduction, lesion conspicuity, and diagnostic confidence, whereas EPI scored better in SNR and contrast. Readout-segmented EPI was considered the better sequence overall in 85% of the cases. CONCLUSION. This study shows the benefits of improved resolution and reduced distortion of readout-segmented EPI in evaluating the orbit, skull base, and posterior fossa, sites of common neuropathologic abnormalities in children.

    View details for DOI 10.2214/AJR.12.9854

    View details for PubMedID 23617511

  • Image domain propeller fast spin echo MAGNETIC RESONANCE IMAGING Skare, S., Holdsworth, S. J., Lilja, A., Bammer, R. 2013; 31 (3): 385-395

    Abstract

    A new pulse sequence for high-resolution T2-weighted (T2-w) imaging is proposed - image domain propeller fast spin echo (iProp-FSE). Similar to the T2-w PROPELLER sequence, iProp-FSE acquires data in a segmented fashion, as blades that are acquired in multiple TRs. However, the iProp-FSE blades are formed in the image domain instead of in the k-space domain. Each iProp-FSE blade resembles a single-shot fast spin echo (SSFSE) sequence with a very narrow phase-encoding field of view (FOV), after which N rotated blade replicas yield the final full circular FOV. Our method of combining the image domain blade data to a full FOV image is detailed, and optimal choices of phase-encoding FOVs and receiver bandwidths were evaluated on phantom and volunteers. The results suggest that a phase FOV of 15-20%, a receiver bandwidth of ±32-63 kHz and a subsequent readout time of about 300 ms provide a good tradeoff between signal-to-noise ratio (SNR) efficiency and T2 blurring. Comparisons between iProp-FSE, Cartesian FSE and PROPELLER were made on single-slice axial brain data, showing similar T2-w tissue contrast and SNR with great anatomical conspicuity at similar scan times - without colored noise or streaks from motion. A new slice interleaving order is also proposed to improve the multislice capabilities of iProp-FSE.

    View details for DOI 10.1016/j.mri.2012.08.010

    View details for Web of Science ID 000316827400008

    View details for PubMedID 23200683

  • Combined prospective and retrospective correction to reduce motion-induced image misalignment and geometric distortions in EPI MAGNETIC RESONANCE IN MEDICINE Ooi, M. B., Muraskin, J., Zou, X., Thomas, W. J., Krueger, S., Aksoy, M., Bammer, R., Brown, T. R. 2013; 69 (3): 803-811

    Abstract

    Despite rigid-body realignment to compensate for head motion during an echo-planar imaging time-series scan, nonrigid image deformations remain due to changes in the effective shim within the brain as the head moves through the B(0) field. The current work presents a combined prospective/retrospective solution to reduce both rigid and nonrigid components of this motion-related image misalignment. Prospective rigid-body correction, where the scan-plane orientation is dynamically updated to track with the subject's head, is performed using an active marker setup. Retrospective distortion correction is then applied to unwarp the remaining nonrigid image deformations caused by motion-induced field changes. Distortion correction relative to a reference time-frame does not require any additional field mapping scans or models, but rather uses the phase information from the echo-planar imaging time-series itself. This combined method is applied to compensate echo-planar imaging scans of volunteers performing in-plane and through-plane head motions, resulting in increased image stability beyond what either prospective or retrospective rigid-body correction alone can achieve. The combined method is also assessed in a blood oxygen level dependent functional MRI task, resulting in improved Z-score statistics.

    View details for DOI 10.1002/mrm.24285

    View details for Web of Science ID 000315331300021

    View details for PubMedID 22499027

  • Early Diffusion-Weighted Imaging and Perfusion-Weighted Imaging Lesion Volumes Forecast Final Infarct Size in DEFUSE 2 STROKE Wheeler, H. M., Mlynash, M., Inoue, M., Tipirneni, A., Liggins, J., Zaharchuk, G., Straka, M., Kemp, S., Bammer, R., Lansberg, M. G., Albers, G. W. 2013; 44 (3): 681-685

    Abstract

    It is hypothesized that early diffusion-weighted imaging (DWI) lesions accurately estimate the size of the irreversibly injured core and thresholded perfusion-weighted imaging (PWI) lesions (time to maximum of tissue residue function [Tmax] >6 seconds) approximate the volume of critically hypoperfused tissue. With incomplete reperfusion, the union of baseline DWI and posttreatment PWI is hypothesized to predict infarct volume.This is a substudy of Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution Study 2 (DEFUSE 2); all patients with technically adequate MRI scans at 3 time points were included. Baseline DWI and early follow-up PWI lesion volumes were determined by the RAPID software program. Final infarct volumes were assessed with 5-day fluid-attenuated inversion recovery and were corrected for edema. Reperfusion was defined on the basis of the reduction in PWI lesion volume between baseline and early follow-up MRI. DWI and PWI volumes were correlated with final infarct volumes.Seventy-three patients were eligible. Twenty-six patients with >90% reperfusion show a high correlation between early DWI volume and final infarct volume (r=0.95; P<0.001). Nine patients with <10% reperfusion have a high correlation between baseline PWI (Tmax >6 seconds) volume and final infarct volume (r=0.86; P=0.002). Using all 73 patients, the union of baseline DWI and early follow-up PWI is highly correlated with final infarct volume (r=0.94; P<0.001). The median absolute difference between observed and predicted final volumes is 15 mL (interquartile range, 5.5-30.2).Baseline DWI and early follow-up PWI (Tmax >6 seconds) volumes provide a reasonable approximation of final infarct volume after endovascular therapy.

    View details for DOI 10.1161/STROKEAHA.111.000135

    View details for Web of Science ID 000315447400024

    View details for PubMedID 23390119

  • Magnetic resonance imaging profile of blood-brain barrier injury in patients with acute intracerebral hemorrhage. Journal of the American Heart Association Aksoy, D., Bammer, R., Mlynash, M., Venkatasubramanian, C., Eyngorn, I., Snider, R. W., Gupta, S. N., Narayana, R., Fischbein, N., Wijman, C. A. 2013; 2 (3)

    Abstract

    Spontaneous intracerebral hemorrhage (ICH) is associated with blood-brain barrier (BBB) injury, which is a poorly understood factor in ICH pathogenesis, potentially contributing to edema formation and perihematomal tissue injury. We aimed to assess and quantify BBB permeability following human spontaneous ICH using dynamic contrast-enhanced magnetic resonance imaging (DCE MRI). We also investigated whether hematoma size or location affected the amount of BBB leakage.Twenty-five prospectively enrolled patients from the Diagnostic Accuracy of MRI in Spontaneous intracerebral Hemorrhage (DASH) study were examined using DCE MRI at 1 week after symptom onset. Contrast agent dynamics in the brain tissue and general tracer kinetic modeling were used to estimate the forward leakage rate (K(trans)) in regions of interest (ROI) in and surrounding the hematoma and in contralateral mirror-image locations (control ROI). In all patients BBB permeability was significantly increased in the brain tissue immediately adjacent to the hematoma, that is, the hematoma rim, compared to the contralateral mirror ROI (P<0.0001). Large hematomas (>30 mL) had higher K(trans) values than small hematomas (P<0.005). K(trans) values of lobar hemorrhages were significantly higher than the K(trans) values of deep hemorrhages (P<0.005), independent of hematoma volume. Higher K(trans) values were associated with larger edema volumes.BBB leakage in the brain tissue immediately bordering the hematoma can be measured and quantified by DCE MRI in human ICH. BBB leakage at 1 week is greater in larger hematomas as well as in hematomas in lobar locations and is associated with larger edema volumes.

    View details for DOI 10.1161/JAHA.113.000161

    View details for PubMedID 23709564

  • Apparent diffusion coefficient threshold for delineation of ischemic core. International journal of stroke : official journal of the International Stroke Society Purushotham, A., Campbell, B. C., Straka, M., Mlynash, M., Olivot, J. M., Bammer, R., Kemp, S. M., Albers, G. W., Lansberg, M. G. 2013

    Abstract

    MRI-based selection of patients for acute stroke interventions requires rapid accurate estimation of the infarct core on diffusion-weighted MRI. Typically used manual methods to delineate restricted diffusion lesions are subjective and time consuming. These limitations would be overcome by a fully automated method that can rapidly and objectively delineate the ischemic core. An automated method would require predefined criteria to identify the ischemic core.The aim of this study is to determine apparent diffusion coefficient-based criteria that can be implemented in a fully automated software solution for identification of the ischemic core.Imaging data from patients enrolled in the Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution (DEFUSE) study who had early revascularization following intravenous thrombolysis were included. The patients' baseline restricted diffusion and 30-day T2 -weighted fluid-attenuated inversion recovery lesions were manually delineated after coregistration. Parts of the restricted diffusion lesion that corresponded with 30-day infarct were considered ischemic core, whereas parts that corresponded with normal brain parenchyma at 30 days were considered noncore. The optimal apparent diffusion coefficient threshold to discriminate core from noncore voxels was determined by voxel-based receiver operating characteristics analysis using the Youden index.51?045 diffusion positive voxels from 14 patients who met eligibility criteria were analyzed. The mean DWI lesion volume was 24 (±?23) ml. Of this, 18 (±?22) ml was ischemic core and 3 (±?5) ml was noncore. The remainder corresponded to preexisting gliosis, cerebrospinal fluid, or was lost to postinfarct atrophy. The apparent diffusion coefficient of core was lower than that of noncore voxels (P?

    View details for PubMedID 23802548

  • In vivo investigation of restricted diffusion in the human brain with optimized oscillating diffusion gradient encoding. Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine Van, A. T., Holdsworth, S. J., Bammer, R. 2013

    Abstract

    PURPOSE: Previous studies in phantoms and animals using animal MR systems have shown promising results in using oscillating gradient spin echo (OGSE) diffusion acquisition to depict microstructure information. The OGSE approach has also been shown to be a sensitive biomarker of tumor treatment response and white matter-related diseases. Translating these studies to a human MR scanner faces multiple challenges due to the much weaker gradient system. The goals of this study are to optimize the OGSE acquisition for a human MR system and investigate its applicability in the in vivo human brain. METHODS: An analytical analysis of the OGSE modulation spectrum was provided. Based on this analysis and thorough simulation experiments, the OGSE acquisition was optimized in terms of diffusion waveform shape, waveform timing, and sequence timing-to achieve higher diffusion sensitivity and better sampling of the diffusion spectrum. RESULTS: The trapezoid-cosine waveform was found to be the optimal OGSE waveform. At the three employed peak encoding frequencies of 18 Hz, 44 Hz, and 63 Hz, the waveform polarity for the least blurry sampling of the diffusion spectrum was 90+/180-, 90+/180+, and 90+/180+, respectively. For the highest diffusion-to-noise ratio at 63 Hz, the b-value was 200 s/mm(2) and the echo time was 116 ms. Using the optimized sequence, a frequency dependence of the measured apparent diffusion coefficients was observed in white matter-dominant regions such as the corpus callosum. CONCLUSION: The obtained results demonstrate, for the first time, the potential of using an OGSE acquisition for investigating microstructure information on a human MR system. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

    View details for PubMedID 23447055

  • Diffusion weighted vertical gradient and spin echo MAGNETIC RESONANCE IN MEDICINE Engstrom, M., Bammer, R., Skare, S. 2012; 68 (6): 1755-1763

    Abstract

    In this work, diffusion weighting and parallel imaging is combined with a vertical gradient and spin echo data readout. This sequence was implemented and evaluated on healthy volunteers using a 1.5 and a 3 T whole-body MR system. As the vertical gradient and spin echo trajectory enables a higher k-space velocity in the phase-encoding direction than single-shot echo planar imaging, the geometrical distortions are reduced. When combined with parallel imaging such as generalized autocalibrating partially parallel acquisition, the geometric distortions are reduced even further, while also keeping the minimum echo time reasonably low. However, this combination of a diffusion preparation and multiple refocusing pulses during the vertical gradient and spin echo readout, generally violates the Carr-Purcell-Meiboom-Gill condition, which leads to interferences between echo pathways. To suppress the stimulated echo pathway, refocusing pulses with a sharper slice profiles and an odd/even crusher variation scheme were implemented and evaluated. Being a single-shot acquisition technique, the reconstructed images are robust to rigid-body head motion and spatially varying brain motion, both of which are common sources of artifacts in diffusion MRI.

    View details for DOI 10.1002/mrm.24506

    View details for Web of Science ID 000311398600009

    View details for PubMedID 23008151

  • Functional Brain Basis of Hypnotizability ARCHIVES OF GENERAL PSYCHIATRY Hoeft, F., Gabrieli, J. D., Whitfield-Gabrieli, S., Haas, B. W., Bammer, R., Menon, V., Spiegel, D. 2012; 69 (10): 1064-1072

    Abstract

    Focused hypnotic concentration is a model for brain control over sensation and behavior. Pain and anxiety can be effectively alleviated by hypnotic suggestion, which modulates activity in brain regions associated with focused attention, but the specific neural network underlying this phenomenon is not known.To investigate the brain basis of hypnotizability.Cross-sectional, in vivo neuroimaging study performed from November 2005 through July 2006.Academic medical center at Stanford University School of Medicine.Twelve adults with high and 12 adults with low hypnotizability.Functional magnetic resonance imaging to measure functional connectivity networks at rest, including default-mode, salience, and executive-control networks; structural T1 magnetic resonance imaging to measure regional gray and white matter volumes; and diffusion tensor imaging to measure white matter microstructural integrity.High compared with low hypnotizable individuals had greater functional connectivity between the left dorsolateral prefrontal cortex, an executive-control region of the brain, and the salience network composed of the dorsal anterior cingulate cortex, anterior insula, amygdala, and ventral striatum, involved in detecting, integrating, and filtering relevant somatic, autonomic, and emotional information using independent component analysis. Seed-based analysis confirmed elevated functional coupling between the dorsal anterior cingulate cortex and the dorsolateral prefrontal cortex in high compared with low hypnotizable individuals. These functional differences were not due to any variation in brain structure in these regions, including regional gray and white matter volumes and white matter microstructure.Our results provide novel evidence that altered functional connectivity in the dorsolateral prefrontal cortex and dorsal anterior cingulate cortex may underlie hypnotizability. Future studies focusing on how these functional networks change and interact during hypnosis are warranted.

    View details for Web of Science ID 000309412800009

    View details for PubMedID 23026956

  • MRI profile and response to endovascular reperfusion after stroke (DEFUSE 2): a prospective cohort study LANCET NEUROLOGY Lansberg, M. G., Straka, M., Kemp, S., Mlynash, M., Wechsler, L. R., Jovin, T. G., Wilder, M. J., Lutsep, H. L., Czartoski, T. J., Bernstein, R. A., Chang, C. W., Warach, S., Fazekas, F., Inoue, M., Tipirneni, A., Hamilton, S. A., Zaharchuk, G., Marks, M. P., Bammer, R., Albers, G. W. 2012; 11 (10): 860-867

    Abstract

    Whether endovascular stroke treatment improves clinical outcomes is unclear because of the paucity of data from randomised placebo-controlled trials. We aimed to establish whether MRI can be used to identify patients who are most likely to benefit from endovascular reperfusion.In this prospective cohort study we consecutively enrolled patients scheduled to have endovascular treatment within 12 h of onset of stroke at eight centres in the USA and one in Austria. Aided by an automated image analysis computer program, investigators interpreted a baseline MRI scan taken before treatment to establish whether the patient had an MRI profile (target mismatch) that suggested salvageable tissue was present. Reperfusion was assessed on an early follow-up MRI scan (within 12 h of the revascularisation procedure) and defined as a more than 50% reduction in the volume of the lesion from baseline on perfusion-weighted MRI. The primary outcome was favourable clinical response, defined as an improvement of 8 or more on the National Institutes of Health Stroke Scale between baseline and day 30 or a score of 0-1 at day 30. The secondary clinical endpoint was good functional outcome, defined as a modified Rankin scale score of 2 or less at day 90. Analyses were adjusted for imbalances in baseline predictors of outcome. Investigators assessing outcomes were masked to baseline data.138 patients were enrolled. 110 patients had catheter angiography and of these 104 had an MRI profile and 99 could be assessed for reperfusion. 46 of 78 (59%) patients with target mismatch and 12 of 21 (57%) patients without target mismatch had reperfusion after endovascular treatment. The adjusted odds ratio (OR) for favourable clinical response associated with reperfusion was 8·8 (95% CI 2·7-29·0) in the target mismatch group and 0·2 (0·0-1·6) in the no target mismatch group (p=0·003 for difference between ORs). Reperfusion was associated with increased good functional outcome at 90 days (OR 4·0, 95% CI 1·3-12·2) in the target mismatch group, but not in the no target mismatch group (1·9, 0·2-18·7).Target mismatch patients who had early reperfusion after endovascular stroke treatment had more favourable clinical outcomes. No association between reperfusion and favourable outcomes was present in patients without target mismatch. Our data suggest that a randomised controlled trial of endovascular treatment for patients with the target mismatch profile is warranted.National Institute for Neurological Disorders and Stroke.

    View details for DOI 10.1016/S1474-4422(12)70203-X

    View details for Web of Science ID 000309634300011

    View details for PubMedID 22954705

  • Diffusion tensor imaging (DTI) with retrospective motion correction for large-scale pediatric imaging JOURNAL OF MAGNETIC RESONANCE IMAGING Holdsworth, S. J., Aksoy, M., Newbould, R. D., Yeom, K., Van, A. T., Ooi, M. B., Barnes, P. D., Bammer, R., Skare, S. 2012; 36 (4): 961-971

    Abstract

    To develop and implement a clinical DTI technique suitable for the pediatric setting that retrospectively corrects for large motion without the need for rescanning and/or reacquisition strategies, and to deliver high-quality DTI images (both in the presence and absence of large motion) using procedures that reduce image noise and artifacts.We implemented an in-house built generalized autocalibrating partially parallel acquisitions (GRAPPA)-accelerated diffusion tensor (DT) echo-planar imaging (EPI) sequence at 1.5T and 3T on 1600 patients between 1 month and 18 years old. To reconstruct the data, we developed a fully automated tailored reconstruction software that selects the best GRAPPA and ghost calibration weights; does 3D rigid-body realignment with importance weighting; and employs phase correction and complex averaging to lower Rician noise and reduce phase artifacts. For select cases we investigated the use of an additional volume rejection criterion and b-matrix correction for large motion.The DTI image reconstruction procedures developed here were extremely robust in correcting for motion, failing on only three subjects, while providing the radiologists high-quality data for routine evaluation.This work suggests that, apart from the rare instance of continuous motion throughout the scan, high-quality DTI brain data can be acquired using our proposed integrated sequence and reconstruction that uses a retrospective approach to motion correction. In addition, we demonstrate a substantial improvement in overall image quality by combining phase correction with complex averaging, which reduces the Rician noise that biases noisy data.

    View details for DOI 10.1002/jmri.23710

    View details for Web of Science ID 000308884300022

    View details for PubMedID 22689498

  • Ultra-high resolution diffusion tensor imaging of the microscopic pathways of the medial temporal lobe NEUROIMAGE Zeineh, M. M., Holdsworth, S., Skare, S., Atlas, S. W., Bammer, R. 2012; 62 (3): 2065-2082

    Abstract

    Diseases involving the medial temporal lobes (MTL) such as Alzheimer's disease and mesial temporal sclerosis pose an ongoing diagnostic challenge because of the difficulty in identifying conclusive imaging features, particularly in pre-clinical states. Abnormal neuronal connectivity may be present in the circuitry of the MTL, but current techniques cannot reliably detect those abnormalities. Diffusion tensor imaging (DTI) has shown promise in defining putative abnormalities in connectivity, but DTI studies of the MTL performed to date have shown neither dramatic nor consistent differences across patient populations. Conventional DTI methodology provides an inadequate depiction of the complex microanatomy present in the medial temporal lobe because of a typically employed low isotropic resolution of 2.0-2.5 mm, a low signal-to-noise ratio (SNR), and echo-planar imaging (EPI) geometric distortions that are exacerbated by the inhomogeneous magnetic environment at the skull base. In this study, we pushed the resolving power of DTI to near-mm isotropic voxel size to achieve a detailed depiction of mesial temporal microstructure at 3 T. High image fidelity and SNR at this resolution are achieved through several mechanisms: (1) acquiring multiple repetitions of the minimum field of view required for hippocampal coverage to boost SNR; (2) utilizing a single-refocused diffusion preparation to enhance SNR further; (3) performing a phase correction to reduce Rician noise; (4) minimizing distortion and maintaining left-right distortion symmetry with axial-plane parallel imaging; and (5) retaining anatomical and quantitative accuracy through the use of motion correction coupled with a higher-order eddy-current correction scheme. We combined this high-resolution methodology with a detailed segmentation of the MTL to identify tracks in all subjects that may represent the major pathways of the MTL, including the perforant pathway. Tractography performed on a subset of the data identified similar tracks, although they were lesser in number. This detailed analysis of MTL substructure may have applications to clinical populations.

    View details for DOI 10.1016/j.neuroimage.2012.05.065

    View details for Web of Science ID 000307369000073

    View details for PubMedID 22677150

  • Patients With the Malignant Profile Within 3 Hours of Symptom Onset Have Very Poor Outcomes After Intravenous Tissue-Type Plasminogen Activator Therapy STROKE Inoue, M., Mlynash, M., Straka, M., Lansberg, M. G., Zaharchuk, G., Bammer, R., Albers, G. W. 2012; 43 (9): 2494-2496

    Abstract

    The malignant profile has been associated with poor outcomes after reperfusion in the 3- to 6-hour time window. The aim of this study was to estimate the incidence and prognostic implications of the malignant profile, as identified by CT perfusion, in intravenous tissue-type plasminogen activator-treated patients who were imaged <3 hours from stroke onset.The incidence of the malignant profile, based on the previously published optimal perfusion-weighted imaging definition, was assessed in consecutive patients using a fully automated software program (RApid processing of Perfusion and Diffusion [RAPID]). A receiver operating characteristic curve analysis was done to identify time to maximum and core volume thresholds that optimally identify patients with poor outcome (modified Rankin Scale 5-6).Forty-two patients had an interpretable CT perfusion performed within 3 hours of symptom onset. Mean age was 74±14 years and median (interquartile range) National Institutes of Stroke Scale score was 13 (6-19). Four patients (9.5%) met the prespecified criteria for the malignant profile and all 4 had poor outcome. Receiver operating characteristic analysis determined that the best CT perfusion measure to identify patients with poor outcome was a cerebral blood flow based infarct core >53 mL (100% specificity and 67% sensitivity). This criterion identified 5 patients as malignant (12%). The poor outcome rate in these patients was 100% versus 7.1% in the 37 nonmalignant patients (P<0.001).The incidence of the malignant profile on CT perfusion is approximately 10% in tissue-type plasminogen activator-eligible patients imaged within 3 hours of symptom onset. The clinical outcome of these patients is very poor despite intravenous tissue-type plasminogen activator therapy.

    View details for DOI 10.1161/STROKEAHA.112.653329

    View details for Web of Science ID 000308416300050

    View details for PubMedID 22811464

  • Measuring brain oxygenation in humans using a multiparametric quantitative blood oxygenation level dependent MRI approach MAGNETIC RESONANCE IN MEDICINE Christen, T., Schmiedeskamp, H., Straka, M., Bammer, R., Zaharchuk, G. 2012; 68 (3): 905-911

    Abstract

    Quantitative blood oxygenation level dependent approaches have been designed to obtain quantitative oxygenation information using MRI. A mathematical model is usually fitted to the time signal decay of a gradient-echo and spin-echo measurements to derive hemodynamic parameters such as the blood oxygen saturation or the cerebral blood volume. Although the results in rats and human brain have been encouraging, recent studies have pointed out the need for independent estimation of one or more variables to increase the accuracy of the method. In this study, a multiparametric quantitative blood oxygenation level dependent approach is proposed. A combination of arterial spin labeling and dynamic susceptibility contrast methods were used to obtain quantitative estimates of cerebral blood volume and cerebral blood flow. These results were combined with T?2 and T(2) measurements to derive maps of blood oxygen saturation or cerebral metabolic rate of oxygen. In 12 normal subjects, a mean cerebral blood volume of 4.33 ± 0.7%, cerebral blood flow of 43.8 ± 5.7 mL/min/100 g, blood oxygen saturation of 60 ± 6% and cerebral metabolic rate of oxygen 157 ± 23 ?mol/100 g/min were found, which are in agreement with literature values. The results obtained in this study suggest that this methodology could be applied to study brain hypoxia in the setting of pathology.

    View details for DOI 10.1002/mrm.23283

    View details for Web of Science ID 000308098100029

    View details for PubMedID 22162074

  • CBF measurements using multidelay pseudocontinuous and velocity-selective arterial spin labeling in patients with long arterial transit delays: Comparison with xenon CT CBF JOURNAL OF MAGNETIC RESONANCE IMAGING Qiu, D., Straka, M., Zun, Z., Bammer, R., Moseley, M. E., Zaharchuk, G. 2012; 36 (1): 110-119

    Abstract

    To test the theory that velocity-selective arterial spin labeling (VSASL) is insensitive to transit delay.Cerebral blood flow (CBF) was measured in ten Moyamoya disease patients using xenon computed tomography (xeCT) and magnetic resonance imaging (MRI), which included multiple pseudo-continuous ASL (pcASL) with different postlabel delays, VSASL, and dynamic susceptibility contrast (DSC) imaging. Correlation coefficient, root-mean-square difference, mean CBF error between ASL, and gold-standard xeCT CBF measurements as well the dependence of this error on transit delay (TD) as estimated by DSC time-to-peak of the residue function (Tmax) were determined.For pcASL with different postlabel delay time (PLD), CBF measurement with short PLD (1.5-2 sec) had the strongest correlations with xeCT; VSASL had a lower but still significant correlation with a mean coefficient of 0.55. We noted the theoretically predicted dependence of CBF error on Tmax and on PLD for pcASL; VSASL CBF measurements had the least dependence of the error on TD. We also noted effects suggesting that the location of the label decay (blood vs. tissue) impacted the measurement, which was worse for pcASL than for VSASL.We conclude that VSASL is less sensitive to TD than conventional ASL techniques and holds promise for CBF measurements in cerebrovascular diseases with slow flow.

    View details for DOI 10.1002/jmri.23613

    View details for Web of Science ID 000305185700009

    View details for PubMedID 22359345

  • Automated Perfusion Imaging for the Evaluation of Transient Ischemic Attack STROKE Kleinman, J. T., Zaharchuk, G., Mlynash, M., Ogdie, A. A., Straka, M., Lansberg, M. G., Schwartz, N. E., Kemp, S., Bammer, R., Albers, G. W., Olivot, J. 2012; 43 (6): 1556-1560

    Abstract

    Diffusion-weighted imaging (DWI) is recommended for the evaluation of transient ischemic attack. Perfusion imaging can increase the yield of MRI in transient ischemic attack. We evaluated automated bolus perfusion (the time when the residue function reaches its maximum [TMax] and mean transit time [MTT]) and arterial spin labeling (ASL) sequences for the detection of ischemic lesions in patients with transient ischemic attack.We enrolled consecutive patients evaluated for suspicion of acute transient ischemic attack by multimodal MRI within 36 hours of symptom onset. Two independent raters assessed the presence and location of ischemic lesions blinded to the clinical presentation. The prevalence of ischemic lesions and the interrater agreement were 1,410 assessed.From January 2010 to 2011, 93 patients were enrolled and 90 underwent perfusion imaging (69 bolus perfusion and 76 ASL). Overall, 25 of 93 patients (27%) were DWI-positive and 14 (15%) were perfusion-positive but DWI-negative (ASL n=9; TMax n=9; MTT n=2). MTT revealed an ischemic lesion in fewer patients than TMax (7 versus 20, P=0.004). Raters agreed on 89% of diffusion-weighted imaging cases, 89% of TMax, 87% o10f010 MTT, and 90% of ASL cases. The interrater agreement was good for DWI, TMax, and ASL (?=0.73, 0.72, and 0.74, respectively) and fair for MTT (?=0.43). Diffusion and/or perfusion were positive in 39 of 69 (57%) patients with a discharge diagnosis of possible ischemic event.Our results suggest that in patients referred for suspicion of transient ischemic attack, automated TMax is more sensitive than MTT, and both ASL and TMax increase the yield of MRI for the detection of ischemic lesions.

    View details for DOI 10.1161/STROKEAHA.111.644971

    View details for Web of Science ID 000304523800025

    View details for PubMedID 22474058

  • Infarct Growth with and without Intravenous Thrombolysis in Acute Ischemic Stroke Reply ANNALS OF NEUROLOGY De Silva, D. A., Churilov, L., Olivot, J., Christensen, S., Lansberg, M. G., Mlynash, M., Campbell, B. C., Desmond, P., Straka, M., Bammer, R., Albers, G. W., Davis, S. M., Donnan, G. A. 2012; 71 (3): 433-434

    View details for DOI 10.1002/ana.23525

    View details for Web of Science ID 000301922800021

  • Compensation of slice profile mismatch in combined spin- and gradient-echo echo-planar imaging pulse sequences MAGNETIC RESONANCE IN MEDICINE Schmiedeskamp, H., Straka, M., Bammer, R. 2012; 67 (2): 378-388

    Abstract

    Combined acquisition of gradient-echo and spin-echo signals in MRI time series reveals additional information for perfusion-weighted imaging and functional MRI because of differences in the sensitivity of gradient-echo and spin-echo measurements to the properties of the underlying vascular architecture. The acquisition of multiple echo trains within one time frame facilitates the simultaneous estimation of the transversal relaxation parameters R2 and R2*. However, the simultaneous estimation of these parameters tends to be incorrect in the presence of slice profile mismatches between signal excitation and subsequent refocusing pulses. It is shown here that improvements in pulse design reduced R2 and R2* estimation errors. Further improvements were achieved by augmented parameter estimation through the introduction of an additional parameter ? to correct for discordances in slice profiles to facilitate more quantitative measurements. Moreover, the analysis of time-resolved acquisitions revealed that the temporal stability of R2 estimates could be increased with improved pulse design, counteracting low contrast-to-noise ratios in spin-echo-based perfusion and functional MRI.

    View details for DOI 10.1002/mrm.23012

    View details for Web of Science ID 000299376500012

    View details for PubMedID 21858858

  • Yield of CT perfusion for the evaluation of transient ischaemic attack. International journal of stroke : official journal of the International Stroke Society Kleinman, J. T., Mlynash, M., Zaharchuk, G., Ogdie, A. A., Straka, M., Lansberg, M. G., Schwartz, N. E., Singh, P., Kemp, S., Bammer, R., Albers, G. W., Olivot, J. M. 2012

    Abstract

    BACKGROUND: Magnetic resonance diffusion-weighted imaging and perfusion-weighted imaging are able to identify ischaemic 'footprints' in transient ischaemic attack. Computed tomography perfusion (CTP) may be useful for patient triage and subsequent management. To date, less than 100 cases have been reported, and none have compared computed tomography perfusion to perfusion-weighted imaging (PWI). We sought to define the yield of computed tomography perfusion for the evaluation of transient ischaemic attack. METHODS: Consecutive patients with a discharge diagnosis of possible or definite transient ischaemic event who underwent computed tomography perfusion were included in this study. The presence of an ischaemic lesion was assessed on noncontrast computed tomography, automatically deconvolved CTP(TMax) (Time till the residue function reaches its maximum), and when available on diffusion-weighted imaging and PWI(TMax) maps. RESULTS: Thirty-four patients were included and 17 underwent magnetic resonance imaging. Median delay between onset and computed tomography perfusion was 4·4?h (Interquartile range [IQR]: 1·9-9·6), and between computed tomography perfusion and magnetic resonance imaging was 11?h (Interquartile range: 3·8-22). Noncontrast computed tomography was negative in all cases, while CTP(TMax) identified an ischaemic lesion in 12/34 patients (35%). In the subgroup of patients with multimodal magnetic resonance imaging, an ischaemic lesion was found in six (35%) patients using CTP(TMax) versus nine (53%) on magnetic resonance imaging (five diffusion-weighted imaging, nine perfusion-weighted imaging). The additional yield of CTP(TMax) over computed tomography angiography was significant in the evaluation of transient ischaemic attack (12 vs. 3, McNemar, P?=?0·004). CONCLUSIONS: CTP(TMax) found an ischaemic lesion in one-third of acute transient ischaemic attack patients. Computed tomography perfusion may be an acceptable substitute when magnetic resonance imaging is unavailable or contraindicated, and has additional yield over computed tomography angiography. Further studies evaluating the outcome of patients with computed tomography perfusion lesions in transient ischaemic attack are justified at this time.

    View details for PubMedID 23228203

  • High-resolution cerebral blood volume imaging in humans using the blood pool contrast agent ferumoxytol. Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine Christen, T., Ni, W., Qiu, D., Schmiedeskamp, H., Bammer, R., Moseley, M., Zaharchuk, G. 2012

    Abstract

    Cerebral blood volume maps are usually acquired using dynamic susceptibility contrast imaging which inherently limits the spatial resolution and signal to noise ratio of the images. In this study, we used ferumoxytol (AMAG Pharmaceuticals, Inc., Cambridge, MA), an FDA-approved compound, to obtain high-resolution cerebral blood volume maps with a steady-state approach in seven healthy volunteers. R?2* maps (0.8 × 0.8 × 1 mm(3) ) were acquired before and after injection of ferumoxytol and an intraindividual normalization protocol was used to obtain quantitative values. The results show excellent contrast between white and gray matter as well as fine highly detailed vascular structures. An average blood volume of 4% was found in the brain of all volunteers, consistent with prior literature values. A linear relationship was found between ferumoxytol dose (mg/kg) and ?R?2* (1/s) in gray (R(2) = 0.98) and white matter (R(2) = 0.98). A quadratic relationship was found in the sagittal sinus (R(2) = 0.98). The cerebral blood volume maps compare well with lower resolution dynamic susceptibility contrast-MRI and their use should improve the evaluation of small and heterogeneous lesions and facilitate intrapatient and interpatient comparisons. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

    View details for PubMedID 23001902

  • Arterial Spin Labeling Imaging Findings in Transient Ischemic Attack Patients: Comparison with Diffusion- and Bolus Perfusion-Weighted Imaging CEREBROVASCULAR DISEASES Zaharchuk, G., Olivot, J., Fischbein, N. J., Bammer, R., Straka, M., Kleinman, J. T., Albers, G. W. 2012; 34 (3): 221-228

    Abstract

    Since transient ischemic attacks (TIAs) can predict future stroke, it is important to distinguish true vascular events from non-vascular etiologies. Arterial spin labeling (ASL) is a non-contrast magnetic resonance (MR) method that is sensitive to cerebral perfusion and arterial arrival delays. Due to its high sensitivity to minor perfusion alterations, we hypothesized that ASL abnormalities would be identified frequently in TIA patients, and could therefore help increase clinicians' confidence in the diagnosis.We acquired diffusion-weighted imaging (DWI), intracranial MR angiography (MRA), and ASL in a prospective cohort of TIA patients. A subset of these patients also received bolus contrast perfusion-weighted imaging (PWI). Two neuroradiologists evaluated the images in a blinded fashion to determine the frequency of abnormalities on each imaging sequence. Kappa (?) statistics were used to assess agreement, and the ?(2) test was used to detect differences in the proportions of abnormal studies.76 patients met the inclusion criteria, 48 (63%) of whom received PWI. ASL was abnormal in 62%, a much higher frequency compared with DWI (24%) and intracranial MRA (13%). ASL significantly increased the MR imaging yield above the combined DWI and MRA yield (62 vs. 32%, p < 0.05). Arterial transit artifact in vascular borderzones was the most common ASL abnormality (present in 51%); other abnormalities included focal high or low ASL signal (11%). PWI was abnormal in 31% of patients, and in these, ASL was abnormal in 14 out of 15 cases (93%). In hemispheric TIA patients, both PWI and ASL findings were more common in the symptomatic hemisphere. Agreement between neuroradiologists regarding abnormal studies was good for ASL and PWI [? = 0.69 (95% CI 0.53-0.86) and ? = 0.66 (95% CI 0.43-0.89), respectively].In TIA patients, perfusion-related alterations on ASL were more frequently detected compared with PWI or intracranial MRA and were most frequently associated with the symptomatic hemisphere. Almost all cases with a PWI lesion also had an ASL lesion. These results suggest that ASL may aid in the workup and triage of TIA patients, particularly those who cannot undergo a contrast study.

    View details for DOI 10.1159/000339682

    View details for Web of Science ID 000313654100007

    View details for PubMedID 23006669

  • Greater Effect of Stroke Thrombolysis in the Presence of Arterial Obstruction ANNALS OF NEUROLOGY De Silva, D. A., Churilov, L., Olivot, J., Christensen, S., Lansberg, M. G., Mlynash, M., Campbell, B. C., Desmond, P., Straka, M., Bammer, R., Albers, G. W., Davis, S. M., Donnan, G. A. 2011; 70 (4): 601-605

    Abstract

    Recanalization of arterial obstruction is associated with improved clinical outcomes. There are no controlled data demonstrating whether arterial obstruction status predicts the treatment effect of intravenous (IV) tissue plasminogen activator (tPA). We aimed to determine if the presence of arterial obstruction improves the treatment effect of IV tPA over placebo in attenuating infarct growth.We analyzed 175 ischemic stroke patients treated in the 3-6 hour time window from the Echoplanar Imaging Thrombolytic Evaluation Trial (EPITHET) trial (randomized to IV tPA or placebo) and Diffusion and perfusion imaging Evaluation For Understanding Stroke Evolution (DEFUSE) study (all treated with IV tPA). Infarct growth was calculated as the difference between baseline diffusion-weighted imaging (DWI) and final T2 lesion volumes. Baseline arterial obstruction of large intracranial arteries was graded on magnetic resonance angiography (MRA).Among the 116 patients with adequate baseline MRA and final lesion assessment, 72 had arterial obstruction (48 tPA, 24 placebo) and 44 no arterial obstruction (33 tPA, 11 placebo). Infarct growth was lower in the tPA than placebo group (median difference 26ml, 95% confidence interval [CI], 1-50) in patients with arterial obstruction, but was similar in patients with no arterial obstruction (median difference 5ml, 95%CI, -3 to 9). Infarct growth attenuation with tPA over placebo treatment was greater among patients with arterial obstruction than those without arterial obstruction by a median of 32ml (95%CI, 21-43, p < 0.001).The treatment effect of IV tPA over placebo was greater with baseline arterial obstruction, supporting arterial obstruction status as a consideration in selecting patients more likely to benefit from IV thrombolysis.

    View details for DOI 10.1002/ana.22444

    View details for Web of Science ID 000296396700013

    View details for PubMedID 22028220

  • Fluid-Attenuated Inversion Recovery Hyperintensity in Acute Ischemic Stroke May Not Predict Hemorrhagic Transformation CEREBROVASCULAR DISEASES Campbell, B. C., Costello, C., Christensen, S., Ebinger, M., Parsons, M. W., Desmond, P. M., Barber, P. A., Butcher, K. S., Levi, C. R., De Silva, D. A., Lansberg, M. G., Mlynash, M., Olivot, J., Straka, M., Bammer, R., Albers, G. W., Donnan, G. A., Davis, S. M. 2011; 32 (4): 401-405

    Abstract

    Fluid-attenuated inversion recovery (FLAIR) hyperintensity within an acute cerebral infarct may reflect delayed onset time and increased risk of hemorrhage after thrombolysis. Given the important implications for clinical practice, we examined the prevalence of FLAIR hyperintensity in patients 3-6 h from stroke onset and its relationship to parenchymal hematoma (PH).Baseline DWI and FLAIR imaging with subsequent hemorrhage detection (ECASS criteria) were prospectively obtained in patients 3-6 h after stroke onset from the pooled EPITHET and DEFUSE trials. FLAIR hyperintensity within the region of the acute DWI lesion was rated qualitatively (dichotomized as visually obvious or subtle (i.e. only visible after careful windowing)) and quantitatively (using relative signal intensity (RSI)). The association of FLAIR hyperintensity with hemorrhage was then tested alongside established predictors (very low cerebral blood volume (VLCBV) and diffusion (DWI) lesion volume) in logistic regression analysis.There were 49 patients with pre-treatment FLAIR imaging (38 received tissue plasminogen activator (tPA), 5 developed PH). FLAIR hyperintensity within the region of acute DWI lesion occurred in 48/49 (98%) patients, was obvious in 18/49 (37%) and subtle in 30/49 (61%). Inter-rater agreement was 92% (? = 0.82). The prevalence of obvious FLAIR hyperintensity did not differ between studies obtained in the 3-4.5 h and 4.5-6 h time periods (40% vs. 33%, p = 0.77). PH was poorly predicted by obvious FLAIR hyperintensity (sensitivity 40%, specificity 64%, positive predictive value 11%). In univariate logistic regression, VLCBV (p = 0.02) and DWI lesion volume (p = 0.03) predicted PH but FLAIR lesion volume (p = 0.87) and RSI (p = 0.11) did not. In ordinal logistic regression for hemorrhage grade adjusted for age and baseline stroke severity (NIHSS), increased VLCBV (p = 0.002) and DWI lesion volume (p = 0.003) were associated with hemorrhage but FLAIR lesion volume (p = 0.66) and RSI (p = 0.35) were not.Visible FLAIR hyperintensity is almost universal 3-6 h after stroke onset and did not predict subsequent hemorrhage in this dataset. Our findings question the value of excluding patients with FLAIR hyperintensity from reperfusion therapies. Larger studies are required to clarify what implications FLAIR-positive lesions have for patient selection.

    View details for DOI 10.1159/000331467

    View details for Web of Science ID 000299642300014

    View details for PubMedID 21986096

  • Challenges of High-resolution Diffusion Imaging of the Human Medial Temporal Lobe in Alzheimer Disease. Topics in magnetic resonance imaging Zeineh, M. M., Holdsworth, S., Skare, S., Atlas, S. W., Bammer, R. 2010; 21 (6): 355-365

    Abstract

    The human medial temporal lobe performs an essential role in memory formation and retrieval. Diseases involving the hippocampus such as Alzheimer disease present a unique opportunity for advanced imaging techniques to detect abnormalities at an early stage. In particular, it is possible that diffusion imaging will measure abnormal microarchitecture beyond the realm of macroscopic imaging. However, this task is formidable because of the detailed anatomy of the medial temporal lobe, the difficulties in obtaining high-quality diffusion images of adequate resolution, and the challenges in diffusion data processing. Moreover, it is unclear if any differences will be significant for an individual patient or simply groups of patients. Successful endeavors will need to address each of these challenges in an integrated fashion. The rewards of such analysis may be detection of microscopic disease in vivo, which could represent a landmark accomplishment for the field of neuroradiology.

    View details for DOI 10.1097/RMR.0b013e31823f6413

    View details for PubMedID 22158129

  • Advanced diffusion-weighted magnetic resonance imaging techniques of the human spinal cord. Topics in magnetic resonance imaging Andre, J. B., Bammer, R. 2010; 21 (6): 367-378

    Abstract

    Unlike those of the brain, advances in diffusion-weighted imaging (DWI) of the human spinal cord have been challenged by the more complicated and inhomogeneous anatomy of the spine, the differences in magnetic susceptibility between adjacent air and fluid-filled structures and the surrounding soft tissues, and the inherent limitations of the initially used echo-planar imaging techniques used to image the spine. Interval advances in DWI techniques for imaging the human spinal cord, with the specific aims of improving the diagnostic quality of the images, and the simultaneous reduction in unwanted artifacts have resulted in higher-quality images that are now able to more accurately portray the complicated underlying anatomy and depict pathologic abnormality with improved sensitivity and specificity. Diffusion tensor imaging (DTI) has benefited from the advances in DWI techniques, as DWI images form the foundation for all tractography and DTI. This review provides a synopsis of the many recent advances in DWI of the human spinal cord, as well as some of the more common clinical uses for these techniques, including DTI and tractography.

    View details for DOI 10.1097/RMR.0b013e31823e65a1

    View details for PubMedID 22158130

  • COMT genotype affects prefrontal white matter pathways in children and adolescents NEUROIMAGE Thomason, M. E., Dougherty, R. F., Colich, N. L., Perry, L. M., Rykhlevskaia, E. I., Louro, H. M., Hallmayer, J. F., Waugh, C. E., Bammer, R., Glover, G. H., Gotlib, I. H. 2010; 53 (3): 926-934

    Abstract

    Diffusion tensor imaging is widely used to evaluate the development of white matter. Information about how alterations in major neurotransmitter systems, such as the dopamine (DA) system, influence this development in healthy children, however, is lacking. Catechol-O-metyltransferase (COMT) is the major enzyme responsible for DA degradation in prefrontal brain structures, for which there is a corresponding genetic polymorphism (val158met) that confers either a more or less efficient version of this enzyme. The result of this common genetic variation is that children may have more or less available synaptic DA in prefrontal brain regions. In the present study we examined the relation between diffusion properties of frontal white matter structures and the COMT val158met polymorphism in 40 children ages 9-15. We found that the val allele was associated with significantly elevated fractional anisotropy values and reduced axial and radial diffusivities. These results indicate that the development of white matter in healthy children is related to COMT genotype and that alterations in white matter may be related to the differential availability of prefrontal DA. This investigation paves the way for further studies of how common functional variants in the genome might influence the development of brain white matter.

    View details for DOI 10.1016/j.neuroimage.2010.01.033

    View details for Web of Science ID 000282039300015

    View details for PubMedID 20083203

  • MRI Profile of the Perihematomal Region in Acute Intracerebral Hemorrhage STROKE Olivot, J., Mlynash, M., Kleinman, J. T., Straka, M., Venkatasubramanian, C., Bammer, R., Moseley, M. E., Albers, G. W., Wijman, C. A. 2010; 41 (11): 2681-2683

    Abstract

    The pathophysiology of the presumed perihematomal edema immediately surrounding an acute intracerebral hemorrhage is poorly understood, and its composition may influence clinical outcome. Method-Twenty-three patients from the Diagnostic Accuracy of MRI in Spontaneous intracerebral Hemorrhage (DASH) study were prospectively enrolled and studied with MRI. Perfusion-weighted imaging, diffusion-weighted imaging, and fluid-attenuated inversion recovery sequences were coregistered. TMax (the time when the residue function reaches its maximum) and apparent diffusion coefficient values in the presumed perihematomal edema regions of interest were compared with contralateral mirror and remote ipsilateral hemispheric regions of interest.Compared with mirror and ipsilateral hemispheric regions of interest, TMax (the time when the residue function reaches its maximum) and apparent diffusion coefficient were consistently increased in the presumed perihematomal edema. Two thirds of the patients also exhibited patchy regions of restricted diffusion in the presumed perihematomal edema.The MRI profile of the presumed perihematomal edema in acute intracerebral hemorrhage exhibits delayed perfusion and increased diffusivity mixed with areas of reduced diffusion.

    View details for DOI 10.1161/STROKEAHA.110.590638

    View details for Web of Science ID 000283443500058

    View details for PubMedID 20947849

  • Temporal and Spatial Profile of Brain Diffusion- Weighted MRI After Cardiac Arrest STROKE Mlynash, M., Campbell, D. M., LeProust, E. M., Fischbein, N. J., Bammer, R., Eyngorn, I., Hsia, A. W., Moseley, M., Wijman, C. A. 2010; 41 (8): 1665-1672

    Abstract

    Diffusion-weighted magnetic resonance imaging of the brain is a promising technique to help predict functional outcome in comatose survivors of cardiac arrest. We aimed to evaluate prospectively the temporal-spatial profile of brain apparent diffusion coefficient changes in comatose survivors during the first 8 days after cardiac arrest.Apparent diffusion coefficient values were measured by 2 independent and blinded investigators in predefined brain regions in 18 good- and 15 poor-outcome patients with 38 brain magnetic resonance imaging scans and were compared with those of 14 normal controls. The same brain regions were also assessed qualitatively by 2 other independent and blinded investigators.In poor-outcome patients, cortical structures, in particular the occipital and temporal lobes, and the putamen exhibited the most profound apparent diffusion coefficient reductions, which were noted as early as 1.5 days and reached a nadir between 3 and 5 days after the arrest. Conversely, when compared with normal controls, good-outcome patients exhibited increased diffusivity, in particular in the hippocampus, temporal and occipital lobes, and corona radiata. By qualitative magnetic resonance imaging readings, 1 or more cortical gray matter structures were judged to be moderately to severely abnormal in all poor-outcome patients except for the 3 patients imaged within 24 hours after the arrest.Brain diffusion-weighted imaging changes in comatose, postcardiac arrest survivors in the first week after the arrest are region and time dependent and differ between good- and poor-outcome patients. With increasing use of magnetic resonance imaging in this context, it is important to be aware of these relations.

    View details for DOI 10.1161/STROKEAHA.110.582452

    View details for Web of Science ID 000280330700015

    View details for PubMedID 20595666

  • Breathheld Autocalibrated Phase-Contrast Imaging JOURNAL OF MAGNETIC RESONANCE IMAGING Lew, C., Alley, M. T., Spielman, D. M., Bammer, R., Chan, F. P. 2010; 31 (4): 1004-1014

    Abstract

    To compare generalized autocalibrating partially parallel acquisitions (GRAPPA), modified sensitivity encoding (mSENSE), and SENSE in phase-contrast magnetic resonance imaging (PC-MRI) applications.Aliasing of the torso can occur in PC-MRI applications. If the data are further undersampled for parallel imaging, SENSE can be problematic in correctly unaliasing signals due to coil sensitivity maps that do not match that of the aliased volume. Here, a method for estimating coil sensitivities in flow applications is described. Normal volunteers (n = 5) were scanned on a 1.5 T MRI scanner and underwent PC-MRI scans using GRAPPA, mSENSE, SENSE, and conventional PC-MRI acquisitions. Peak velocity and flow through the aorta and pulmonary artery were evaluated.Bland-Altman statistics for flow in the aorta and pulmonary artery acquired with mSENSE and GRAPPA methods (R = 2 and R = 3 cases) have comparable mean differences to flow acquired with conventional PC-MRI. GRAPPA and mSENSE PC-MRI have more robust measurements than SENSE when there is aliasing artifact caused by insufficient coil sensitivity maps. For peak velocity, there are no considerable differences among the mSENSE, GRAPPA, and SENSE reconstructions and are comparable to conventional PC-MRI.Flow measurements of images reconstructed with autocalibration techniques have comparable agreement with conventional PC-MRI and provide robust measurements in the presence of wraparound.

    View details for DOI 10.1002/jmri.22127

    View details for Web of Science ID 000276328200028

    View details for PubMedID 20373447

  • Improvements in Parallel Imaging Accelerated Functional MRI Using Multiecho Echo-Planar Imaging MAGNETIC RESONANCE IN MEDICINE Schmiedeskamp, H., Newbould, R. D., Pisani, L. J., Skare, S., Glover, G. H., Pruessmann, K. P., Bammer, R. 2010; 63 (4): 959-969

    Abstract

    Multiecho echo-planar imaging (EPI) was implemented for blood-oxygenation-level-dependent functional MRI at 1.5 T and compared to single-echo EPI with and without parallel imaging acceleration. A time-normalized breath-hold task using a block design functional MRI protocol was carried out in combination with up to four echo trains per excitation and parallel imaging acceleration factors R = 1-3. Experiments were conducted in five human subjects, each scanned in three sessions. Across all reduction factors, both signal-to-fluctuation-noise ratio and the total number of activated voxels were significantly lower using a single-echo EPI pulse sequence compared with the multiecho approach. Signal-to-fluctuation-noise ratio and total number of activated voxels were also considerably reduced for nonaccelerated conventional single-echo EPI when compared to three-echo measurements with R = 2. Parallel imaging accelerated multiecho EPI reduced geometric distortions and signal dropout, while it increased blood-oxygenation-level-dependent signal sensitivity all over the brain, particularly in regions with short underlying T*(2). Thus, the presented method showed multiple advantages over conventional single-echo EPI for standard blood-oxygenation-level-dependent functional MRI experiments.

    View details for DOI 10.1002/mrm.22222

    View details for Web of Science ID 000276064300013

    View details for PubMedID 20373397

  • Geography, Structure, and Evolution of Diffusion and Perfusion Lesions in Diffusion and Perfusion Imaging Evaluation For Understanding Stroke Evolution (DEFUSE) STROKE Olivot, J., Mlynash, M., Thijs, V. N., Purushotham, A., Kemp, S., Lansberg, M. G., Wechsler, L., Gold, G. E., Bammer, R., Marks, M. P., Albers, G. W. 2009; 40 (10): 3245-3251

    Abstract

    The classical representation of acute ischemic lesions on MRI is a central diffusion-weighted imaging (DWI) lesion embedded in a perfusion-weighted imaging (PWI) lesion. We investigated spatial relationships between final infarcts and early DWI/PWI lesions before and after intravenous thrombolysis in the Diffusion and perfusion imaging Evaluation For Understanding Stroke Evolution (DEFUSE) study.Baseline and follow-up DWI and PWI lesions and 30-day fluid-attenuated inversion recovery scans of 32 patients were coregistered. Lesion geography was defined by the proportion of the DWI lesion superimposed by a Tmax (time when the residue function reaches its maximum) >4 seconds PWI lesion; Type 1: >50% overlap and Type 2: < or = 50% overlap. Three-dimensional structure was dichotomized into a single lesion (one DWI and one PWI lesion) versus multiple lesions. Lesion reversal was defined by the percentage of the baseline DWI or PWI lesion not superimposed by the early follow-up DWI or PWI lesion. Final infarct prediction was estimated by the proportion of the final infarct superimposed on the union of the DWI and PWI lesions.Single lesion structure with Type 1 geography was present in only 9 patients (28%) at baseline and 4 (12%) on early follow-up. In these patients, PWI and DWI lesions were more likely to correspond with the final infarcts. DWI reversal was greater among patients with Type 2 geography at baseline. Patients with multiple lesions and Type 2 geography at early follow-up were more likely to have early reperfusion.Before thrombolytic therapy in the 3- to 6-hour time window, Type 2 geography is predominant and is associated with DWI reversal. After thrombolysis, both Type 2 geography and multiple lesion structure are associated with reperfusion.

    View details for DOI 10.1161/STROKEAHA.109.558635

    View details for Web of Science ID 000270229800016

    View details for PubMedID 19679845

  • Improving Dynamic Susceptibility Contrast MRI Measurement of Quantitative Cerebral Blood Flow using Corrections for Partial Volume and Nonlinear Contrast Relaxivity: A Xenon Computed Tomographic Comparative Study JOURNAL OF MAGNETIC RESONANCE IMAGING Zaharchuk, G., Bammer, R., Straka, M., Newbould, R. D., Rosenberg, J., Olivot, J., Mlynash, M., Lansberg, M. G., Schwartz, N. E., Marks, M. M., Albers, G. W., Moseley, M. E. 2009; 30 (4): 743-752

    Abstract

    To test whether dynamic susceptibility contrast MRI-based CBF measurements are improved with arterial input function (AIF) partial volume (PV) and nonlinear contrast relaxivity correction, using a gold-standard CBF method, xenon computed tomography (xeCT).Eighteen patients with cerebrovascular disease underwent xeCT and MRI within 36 h. PV was measured as the ratio of the area under the AIF and the venous output function (VOF) concentration curves. A correction was applied to account for the nonlinear relaxivity of bulk blood (BB). Mean CBF was measured with both techniques and regression analyses both within and between patients were performed.Mean xeCT CBF was 43.3 +/- 13.7 mL/100g/min (mean +/- SD). BB correction decreased CBF by a factor of 4.7 +/- 0.4, but did not affect precision. The least-biased CBF measurement was with BB but without PV correction (45.8 +/- 17.2 mL/100 g/min, coefficient of variation [COV] = 32%). Precision improved with PV correction, although absolute CBF was mildly underestimated (34.3 +/- 10.8 mL/100 g/min, COV = 27%). Between patients correlation was moderate even with both corrections (R = 0.53).Corrections for AIF PV and nonlinear BB relaxivity improve bolus MRI-based CBF maps. However, there remain challenges given the moderate between-patient correlation, which limit diagnostic confidence of such measurements in individual patients.

    View details for DOI 10.1002/jmri.21908

    View details for Web of Science ID 000270522900007

    View details for PubMedID 19787719

  • Using Diffusion Tensor Imaging and Fiber Tracking to Characterize Diffuse Perinatal White Matter Injury: A Case Report JOURNAL OF CHILD NEUROLOGY Yeatman, J. D., Ben-Shachar, M., Bammer, R., Feldman, H. M. 2009; 24 (7): 795-800

    Abstract

    Prematurity is associated with white matter injury. Diffusion tensor imaging, a new magnetic resonance imaging technique, identifies white matter fiber tracts and quantifies structural properties. We used diffusion tensor imaging fiber tracking to compare white matter characteristics in a 12-year-old born prematurely and full-term control. We divided fibers passing through the corpus callosum into 7 segments based on cortical projection zones and analyzed them for fractional anisotropy, axial diffusivity, and radial diffusivity. We also compared corticospinal and somatosensory tracts in the participant and control. The participant had decreased fractional anisotropy in every callosal segment, particularly in superior and posterior parietal projections. Fractional anisotropy of the corticospinal and somatosensory tracts was not lower in the participant than control. Fiber tracking allowed precise localization and visualization of white matter injuries of the corpus callosum associated with prematurity. Quantitative measures suggested myelin deficiencies across the corpus callosum, particularly in parietal projections.

    View details for DOI 10.1177/0883073808331080

    View details for Web of Science ID 000267347000002

    View details for PubMedID 19435729

  • Relationships Between Cerebral Perfusion and Reversibility of Acute Diffusion Lesions in DEFUSE Insights from RADAR STROKE Olivot, J., Mlynash, M., Thijs, V. N., Purushotham, A., Kemp, S., Lansberg, M. G., Wechsler, L., Bammer, R., Marks, M. P., Albers, G. W. 2009; 40 (5): 1692-1697

    Abstract

    Acute ischemic lesions with restricted diffusion can resolve after early recanalization. The impact of superimposed perfusion abnormalities on the fate of acute diffusion lesions is unclear.Data were obtained from DEFUSE, a prospective multicenter study of patients treated with IV tPA 3 to 6 hours after stroke onset. Thirty-two patients with baseline diffusion and perfusion lesions and 30 day FLAIR scans were coregistered. The acute diffusion lesion was divided into 3 regions according to the Tmax delay of the superimposed perfusion lesion: normal baseline perfusion; mild-moderately hypoperfused (2 s8 s). The reversal rate was calculated as the percentage of the acute diffusion lesion that did not overlap with the final infarct on 30-day FLAIR. Diffusion reversal rates were compared based on whether a favorable clinical response occurred and whether early recanalization was achieved.On average, 54% of the acute diffusion lesion volume had normal perfusion. Diffusion reversal rates were significantly increased among cases with favorable clinical response and in patients with early recanalization, especially in regions with normal baseline perfusion. The portion of the diffusion lesion with normal perfusion had significantly higher mean apparent diffusion coefficient values and reversal rates.Acute ischemic lesions with restricted diffusion are most likely to recover if reperfusion occurs within 6 hours of symptom onset, and reversibility is associated with early recanalization and favorable clinical outcome. We propose the term RADAR (Reversible Acute Diffusion lesion Already Reperfused) to describe regions of acute restricted diffusion with normal perfusion.

    View details for DOI 10.1161/STROKEAHA.108.538082

    View details for Web of Science ID 000265579800027

    View details for PubMedID 19299632

  • New Methods in Diffusion-Weighted and Diffusion Tensor Imaging MAGNETIC RESONANCE IMAGING CLINICS OF NORTH AMERICA Bammer, R., Holdsworth, S. J., Veldhuis, W. B., Skare, S. T. 2009; 17 (2): 175-?

    Abstract

    Considerable strides have been made by countless individual researchers in diffusion-weighted imaging (DWI) to push DWI from an experimental tool, limited to a few institutions with specialized instrumentation, to a powerful tool used routinely for diagnostic imaging. The field of DWI constantly evolves, and progress has been made on several fronts. These developments are primarily composed of improved robustness against patient and physiologic motion, increased spatial resolution, new biophysical and tissue models, and new clinical applications for DWI. This article aims to provide a succinct overview of some of these new developments and a description of some of the major challenges associated with DWI.

    View details for DOI 10.1016/j.mric.2009.01.011

    View details for Web of Science ID 000266557700002

    View details for PubMedID 19406353

  • Prognostic Value of Brain Diffusion-Weighted Imaging after Cardiac Arrest ANNALS OF NEUROLOGY Wijman, C. A., Mlynash, M., Caulfield, A. F., Hsia, A. W., Eyngorn, I., Bammer, R., Fischbein, N., Albers, G. W., Moseley, M. 2009; 65 (4): 394-402

    Abstract

    Outcome prediction is challenging in comatose postcardiac arrest survivors. We assessed the feasibility and prognostic utility of brain diffusion-weighted magnetic resonance imaging (DWI) during the first week.Consecutive comatose postcardiac arrest patients were prospectively enrolled. AWI data of patients who met predefined specific prognostic criteria were used to determine distinguishing apparent diffusion coefficient (ADC) thresholds. Group 1 criteria were death at 6 months and absent motor response or absent pupillary reflexes or bilateral absent cortical responses at 72 hours or vegetative at 1 month. Group 2 criterion was survival at 6 months with a Glasgow Outcome Scale score of 4 or 5 (group 2A) or 3 (group 2B). The percentage of voxels below different ADC thresholds was calculated at 50 x 10(-6) mm(2)/sec intervals.Overall, 86% of patients underwent DWI. Fifty-one patients with 62 brain DWIs were included. Forty patients met the specific prognostic criteria. The percentage of brain volume with an ADC value less than 650 to 700 x 10(-6)mm(2)/sec best differentiated between Group 1 and Groups 2A and 2B combined (p < 0.001), whereas the 400 to 450 x 10(-6)mm(2)/sec threshold best differentiated between Groups 2A and 2B (p = 0.003). The ideal time window for prognostication using DWI was between 49 and 108 hours after the arrest. When comparing DWI in this time window with the 72-hour neurological examination, DWI improved the sensitivity for predicting poor outcome by 38% while maintaining 100% specificity (p = 0.021).Quantitative DWI in comatose postcardiac arrest survivors holds promise as a prognostic adjunct.

    View details for DOI 10.1002/ana.21632

    View details for Web of Science ID 000265656200008

    View details for PubMedID 19399889

  • Perfusion MRI (Tmax and MTT) correlation with xenon CT cerebral blood flow in stroke patients NEUROLOGY Olivot, J., Mlynash, M., Zaharchuk, G., Straka, M., Bammer, R., Schwartz, N., Lansberg, M. G., Moseley, M. E., Albers, G. W. 2009; 72 (13): 1140-1145

    Abstract

    While stable xenon CT (Xe-CT) cerebral blood flow (CBF) is an accepted standard for quantitative assessment of cerebral hemodynamics, the accuracy of magnetic resonance perfusion-weighted imaging (PWI-MRI) is unclear. The Improved PWI Methodology in Acute Clinical Stroke Study compares PWI findings with Xe-CT CBF values in patients experiencing symptomatic severe cerebral hypoperfusion.We compared mean transit time (MTT) and Tmax PWI-MRI with the corresponding Xe-CT CBF values in 25 coregistered regions of interest (ROIs) of multiple sizes and locations in nine subacute stroke patients. Comparisons were performed with Pearson correlation coefficients (R). We performed receiver operating characteristic (ROC) curve analyses to define the threshold of Tmax and absolute MTT that could best predict a Xe-CT CBF <20 mL/100 g/minute.The subjects' mean (SD) age was 50 (15) years, the median (interquartile range [IQR]) NIH Stroke Scale score was 2 (2-6), and the median (IQR) time between MRI and Xe-CT was 12 (-7-19) hours. The total number of ROIs was 225, and the median (IQR) ROI size was 550 (360-960) pixels. Tmax correlation with Xe-CT CBF (R = 0.63, p < 0.001) was stronger than absolute MTT (R = 0.55, p < 0.001), p = 0.049. ROC curve analysis found that Tmax >4 seconds had 68% sensitivity, 80% specificity, and 77% accuracy and MTT >10 seconds had 68% sensitivity, 77% specificity, and 75% accuracy for predicting ROIs with Xe-CT CBF <20 mL/100 g/minute.Our results suggest that in subacute ischemic stroke patients, Tmax correlates better than absolute mean transit time (MTT) with xenon CT cerebral blood flow (Xe-CT CBF) and that both Tmax >4 seconds and MTT >10 seconds are strongly associated with Xe-CT CBF <20 mL/100 g/minute. CBF = cerebral blood flow; DBP = diastolic blood pressure; DEFUSE = Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution; DWI = diffusion-weighted imaging; EPITHET = Echoplanar Imaging Thrombolytic Evaluation Trial; FOV = field of view; ICA = internal carotid artery; IQR = interquartile range; MCA = middle cerebral artery; MTT = mean transit time; NIHSS = NIH Stroke Scale; PWI = perfusion-weighted imaging; PWI-MRI = magnetic resonance perfusion-weighted imaging; ROC = receiver operating characteristic; ROI = region of interest; SBP = systolic blood pressure; SVD = singular value decomposition; Xe-CT = xenon CT.

    View details for DOI 10.1212/01.wnl.0000345372.49233.e3

    View details for Web of Science ID 000264709000007

    View details for PubMedID 19332690

  • Optimal Tmax Threshold for Predicting Penumbral Tissue in Acute Stroke STROKE Olivot, J., Mlynash, M., Thijs, V. N., Kemp, S., Lansberg, M. G., Wechsler, L., Bammer, R., Marks, M. P., Albers, G. W. 2009; 40 (2): 469-475

    Abstract

    We sought to assess whether the volume of the ischemic penumbra can be estimated more accurately by altering the threshold selected for defining perfusion-weighting imaging (PWI) lesions.DEFUSE is a multicenter study in which consecutive acute stroke patients were treated with intravenous tissue-type plasminogen activator 3 to 6 hours after stroke onset. Magnetic resonance imaging scans were obtained before, 3 to 6 hours after, and 30 days after treatment. Baseline and posttreatment PWI volumes were defined according to increasing Tmax delay thresholds (>2, >4, >6, and >8 seconds). Penumbra salvage was defined as the difference between the baseline PWI lesion and the final infarct volume (30-day fluid-attenuated inversion recovery sequence). We hypothesized that the optimal PWI threshold would provide the strongest correlations between penumbra salvage volumes and various clinical and imaging-based outcomes.Thirty-three patients met the inclusion criteria. The correlation between infarct growth and penumbra salvage volume was significantly better for PWI lesions defined by Tmax >6 seconds versus Tmax >2 seconds, as was the difference in median penumbra salvage volume in patients with a favorable versus an unfavorable clinical response. Among patients who did not experience early reperfusion, the Tmax >4 seconds threshold provided a more accurate prediction of final infarct volume than the >2 seconds threshold.Defining PWI lesions based on a stricter Tmax threshold than the standard >2 seconds delay appears to provide more a reliable estimate of the volume of the ischemic penumbra in stroke patients imaged between 3 and 6 hours after symptom onset. A threshold between 4 and 6 seconds appears optimal for early identification of critically hypoperfused tissue.

    View details for DOI 10.1161/STROKEAHA.108.526954

    View details for Web of Science ID 000262784900021

    View details for PubMedID 19109547

  • Prefrontal Plasticity and Stress Inoculation-Induced Resilience DEVELOPMENTAL NEUROSCIENCE Katz, M., Liu, C., Schaer, M., Parker, K. J., Ottet, M., Epps, A., Buckmaster, C. L., Bammer, R., Moseley, M. E., Schatzberg, A. F., Eliez, S., Lyons, D. M. 2009; 31 (4): 293-299

    Abstract

    Coping with mild early life stress tends to make subsequent coping efforts more effective and therefore more likely to be used as a means of arousal regulation and resilience. Here we show that this developmental learning-like process of stress inoculation increases ventromedial prefrontal cortical volumes in peripubertal monkeys. Larger volumes do not reflect increased cortical thickness but instead represent surface area expansion of ventromedial prefrontal cortex. Expansion of ventromedial prefrontal cortex coincides with increased white matter myelination inferred from diffusion tensor magnetic resonance imaging. These findings suggest that the process of coping with early life stress increases prefrontal myelination and expands a region of cortex that broadly controls arousal regulation and resilience.

    View details for DOI 10.1159/000216540

    View details for Web of Science ID 000267787200006

    View details for PubMedID 19546566

  • An Auto-Calibrated, Angularly Continuous, Two-Dimensional GRAPPA Kernel for Propeller Trajectories MAGNETIC RESONANCE IN MEDICINE Skare, S., Newbould, R. D., Nordell, A., Holdsworth, S. J., Bammer, R. 2008; 60 (6): 1457-1465

    Abstract

    The k-space readout of propeller-type sequences may be accelerated by the use of parallel imaging (PI). For PROPELLER, the main benefits are reduced blurring due to T(2) decay and specific absorption ratio (SAR) reduction, whereas, for EPI-based propeller acquisitions, such as Turbo-PROP and short-axis readout propeller EPI (SAP-EPI), the faster k-space traversal alleviates geometric distortions. In this work, the feasibility of calculating a two-dimensional (2D) GRAPPA kernel on only the undersampled propeller blades themselves is explored, using the matching orthogonal undersampled blade. It is shown that the GRAPPA kernel varies slowly across blades; therefore, an angularly continuous 2D GRAPPA kernel is proposed, in which the angular variation of the weights is parameterized. This new angularly continuous kernel formulation greatly increases the numerical stability of the GRAPPA weight estimation, allowing for generation of fully sampled diagnostic quality images using only the undersampled propeller data.

    View details for DOI 10.1002/mrm.21788

    View details for Web of Science ID 000261225100021

    View details for PubMedID 19025911

  • Patients with Acute Stroke Treated with Intravenous tPA 3-6 Hours after Stroke Onset: Correlations between MR Angiography Findings and Perfusion- and Diffusion-weighted Imaging in the DEFUSE Study RADIOLOGY Marks, M. P., Olivot, J., Kemp, S., Lansberg, M. G., Bammer, R., Wechsler, L. R., Albers, G. W., Thijs, V. 2008; 249 (2): 614-623

    Abstract

    To study magnetic resonance (MR) angiography findings in patients with acute stroke treated with intravenous tissue plasminogen activator (tPA) in relationship to perfusion- and diffusion-weighted imaging changes and clinical outcome.Patients treated with intravenous tPA 3-6 hours after stroke onset (with informed consent) were evaluated in a HIPAA-compliant multicenter prospective study approved by all institutional review boards. MR imaging and MR angiography studies were performed before and 3-6 hours after treatment. MR angiography studies that were technically adequate at both time points were evaluated for occlusion, decreased flow, any early recanalization, and degree of recanalization. These results were compared with favorable clinical response (an improvement in National Institutes of Health Stroke Scale score of >or=8 points at 30 days or a modified Rankin scale score of 0 or 1 at 30 days) in patients with and those without mismatch between perfusion- and diffusion-weighted imaging at baseline.Seventy-four patients were enrolled in the initial investigation; pre- and posttreatment MR angiography studies were both technically adequate in 62 patients. MR angiography demonstrated occlusion or decreased flow in 46 patients. Patients with isolated middle cerebral artery (MCA) occlusion and early recanalization at MR angiography had higher rates of favorable clinical response than those with tandem internal carotid artery-MCA occlusion and early recanalization (P = .05). Any early recanalization was not associated with favorable clinical response, but degree of recanalization did correlate with favorable clinical response (P = .048). Favorable clinical response was more frequently seen in patients with mismatch between perfusion- and diffusion-weighted imaging findings at baseline who experienced early recanalization than in those who did not have early recanalization (odds ratio = 6.2; 95% confidence interval: 1.3, 30.2; P = .021). No relationship between early recanalization and favorable clinical response was seen in patients without mismatch.Early recanalization seen at MR angiography before and after treatment coupled with diffusion- and perfusion-weighted imaging data may predict clinical outcome in patients with stroke treated with tPA 3-6 hours after symptom onset.

    View details for DOI 10.1148/radiol.2492071751

    View details for Web of Science ID 000260215400027

    View details for PubMedID 18936316

  • Magnetic Resonance Imaging Techniques: fMRI, DWI, and PWI SEMINARS IN NEUROLOGY Holdsworth, S. J., Bammer, R. 2008; 28 (4): 395-406

    Abstract

    Magnetic resonance imaging (MRI) is a noninvasive technique which can acquire important quantitative and anatomical information from an individual in any plane or volume at comparatively high resolution. Over the past several years, developments in scanner hardware and software have enabled the acquisition of fast MRI imaging, proving extremely useful in various clinical and research applications such as in brain mapping or functional MRI (fMRI), perfusion-weighted imaging (PWI), and diffusion-weighted imaging (DWI). These techniques have revolutionized the use of MRI in the clinics, providing great insight into physiologic mechanisms and pathologic conditions. Since these relatively new areas of MRI have relied on fast scanning techniques, they have only recently been widely introduced to clinical sites. As such, this review article is devoted to the technological aspects of these techniques, as well as their roles and limitations in neuroimaging applications.

    View details for DOI 10.1055/s-0028-1083697

    View details for Web of Science ID 000260171100002

    View details for PubMedID 18843569

  • The MRA-DWI mismatch identifies patients with stroke who are likely to benefit from reperfusion STROKE Lansberg, M. G., Thijs, V. N., Bammer, R., Olivot, J., Marks, M. P., Wechsler, L. R., Kemp, S., Albers, G. W. 2008; 39 (9): 2491-2496

    Abstract

    The aim of this exploratory analysis was to evaluate if a combination of MR angiography (MRA) and diffusion-weighted imaging (DWI) selection criteria can be used to identify patients with acute stroke who are likely to benefit from early reperfusion.Data from DEFUSE, a study of 74 patients with stroke who received intravenous tissue plasminogen activator in the 3- to 6-hour time window and underwent MRIs before and approximately 4 hours after treatment were analyzed. The MRA-DWI mismatch model was defined as (1) a DWI lesion volume less than 25 mL in patients with a proximal vessel occlusion; or (2) a DWI lesion volume less than 15 mL in patients with proximal vessel stenosis or an abnormal finding of a distal vessel. Favorable clinical response was defined as an improvement on the National Institutes of Health Stroke Scale score of at least 8 points between baseline and 30 days or a National Institutes of Health Stroke Scale score

    View details for DOI 10.1161/STROKEAHA.107.508572

    View details for Web of Science ID 000258727000015

    View details for PubMedID 18635861

  • Cognitive processing speed and the structure of white matter pathways: Convergent evidence from normal variation and lesion studies NEUROIMAGE Turken, A. U., Whitfield-Gabrieli, S., Bammer, R., Baldo, J. V., Dronkers, N. F., Gabrieli, J. D. 2008; 42 (2): 1032-1044

    Abstract

    We investigated the relation between cognitive processing speed and structural properties of white matter pathways via convergent imaging studies in healthy and brain-injured groups. Voxel-based morphometry (VBM) was applied to diffusion tensor imaging data from thirty-nine young healthy subjects in order to investigate the relation between processing speed, as assessed with the Digit-Symbol subtest from WAIS-III, and fractional anisotropy, an index of microstructural organization of white matter. Digit-Symbol performance was positively correlated with fractional anisotropy of white matter in the parietal and temporal lobes bilaterally and in the left middle frontal gyrus. Fiber tractography indicated that these regions are consistent with the trajectories of the superior and inferior longitudinal fasciculi. In a second investigation, we assessed the effect of white matter damage on processing speed using voxel-based lesion-symptom mapping (VLSM) analysis of data from seventy-two patients with left-hemisphere strokes. Lesions in left parietal white matter, together with cortical lesions in supramarginal and angular gyri were associated with impaired performance. These findings suggest that cognitive processing speed, as assessed by the Digit-Symbol test, is closely related to the structural integrity of white matter tracts associated with parietal and temporal cortices and left middle frontal gyrus. Further, fiber tractography applied to VBM results and the patient findings suggest that the superior longitudinal fasciculus, a major tract subserving fronto-parietal integration, makes a prominent contribution to processing speed.

    View details for DOI 10.1016/j.neuroimage.2008.03.057

    View details for Web of Science ID 000258695200056

    View details for PubMedID 18602840

  • Relationships between infarct growth, clinical outcome, and early recanalization in Diffusion and perfusion imaging For Understanding Stroke Evolution (DEFUSE) STROKE Olivot, J., Mlynash, M., Thijs, V. N., Kemp, S., Lansberg, M. G., Wechsler, L., Schlaug, G., Bammer, R., Marks, M. P., Albers, G. W. 2008; 39 (8): 2257-2263

    Abstract

    The purpose of this study was to determine the relationships between ischemic lesion growth, recanalization, and clinical response in stroke patients with and without a perfusion/diffusion mismatch.DEFUSE is an open label multicenter study in which 74 consecutive acute stroke patients were treated with intravenous tPA 3 to 6 hours after stroke onset. Magnetic resonance imaging (MRI) scans were obtained before, 3 to 6 hours after, and 30 days after treatment. Lesion growth was defined as the difference between the final infarct volume (30 day FLAIR) and the baseline diffusion lesion. Baseline MRI profiles were used to categorize 44 patients into Mismatch versus Absence of Mismatch subgroups. Early recanalization was assessed in 28 patients with an initial vessel lesion on magnetic resonance angiography. Infarct growth was compared based on whether a favorable clinical response (FCR) occurred and whether early recanalization was achieved.In the Mismatch subgroup, FCR was associated with less infarct growth P=0.03 and early recanalization was predictive of both FCR (odds ratio: 22, P=0.047) and reduced infarct growth P=0.024. There was no significant relationship between recanalization, infarct growth, and clinical outcome in the Absence of Mismatch subgroup. A threshold of <7 cc of growth had the highest sensitivity and specificity for predicting a FCR in Mismatch patients (odds ratio: 65, P=0.015, sensitivity 82%, specificity 75%).In contrast to Absence of Mismatch patients, significant associations between recanalization, reduced infarct growth, and favorable clinical response were documented in patients with a perfusion/diffusion mismatch who were treated with tPA within 3 to 6 hours after stroke onset. These findings support the Mismatch hypothesis but require validation in a larger study.

    View details for DOI 10.1161/STROKEAHA.107.511535

    View details for Web of Science ID 000257993400011

    View details for PubMedID 18566302

  • Fast parallel spiral chemical shift imaging at 3T using iterative SENSE reconstruction MAGNETIC RESONANCE IN MEDICINE Mayer, D., Kim, D., Spielman, D. M., Bammer, R. 2008; 59 (4): 891-897

    Abstract

    Spiral chemical shift imaging (CSI) is a fast CSI technique that simultaneously encodes 1D spectral and 2D spatial information. Therefore, it potentially allows one to perform a 2D-CSI experiment in a single shot. However, for most applications, limitations on maximum gradient strength and slew rate make multiple excitations necessary in order to achieve a desired spectral bandwidth. In this work we reduce the number of spatial interleaves and, hence, the minimum total measurement time of spiral CSI by using an iterative sensitivity encoding reconstruction algorithm which utilizes complementary spatial encoding afforded by the spatially inhomogeneous sensitivity profiles of individual receiver coils. The performance of the new method was evaluated in phantom and in vivo experiments. Parallel spiral CSI produced maps of brain metabolites similar to those obtained using conventional gridding reconstruction of the fully sampled data with only a small decrease in time-normalized signal-to-noise ratio and a small increase in noise for higher acceleration factors.

    View details for DOI 10.1002/mrm.21572

    View details for Web of Science ID 000254645500027

    View details for PubMedID 18383298

  • Readout-segmented EPI for rapid high resolution diffusion imaging at 3T EUROPEAN JOURNAL OF RADIOLOGY Holdsworth, S. J., Skare, S., Newbould, R. D., Guzmann, R., Blevins, N. H., Bammer, R. 2008; 65 (1): 36-46

    Abstract

    Readout mosaic segmentation has been suggested as an alternative approach to EPI for high resolution diffusion-weighted imaging (DWI). In the readout-segmented EPI (RS-EPI) scheme, segments of k-space are acquired along the readout direction. This reduces geometric distortions due to the decrease in readout time. In this work, further distortion reduction is achieved by combining RS-EPI with parallel imaging (PI). The performance of the PI-accelerated RS-EPI scheme is assessed in volunteers and patients at 3T with respect to both standard EPI and PI-accelerated EPI. Peripherally cardiac gated and non-gated RS-EPI images are acquired to assess whether motion due to brain pulsation significantly degrades the image quality. Due to the low off-resonance of PI-driven RS-EPI, we also investigate if the eddy currents induced by the diffusion gradients are low enough to use the Stejskal-Tanner diffusion preparation instead of the twice-refocused eddy-current compensated diffusion preparation to reduce TE. It is shown that non-gated phase corrected DWI performs equally as well as gated acquisitions. PI-driven DW RS-EPI images with substantially less distortion compared with single-shot EPI are shown in patients-allowing the delineation of structures in the lower parts of the brain. A twice-refocused diffusion preparation was found necessary to avoid blurring in the DWI data. This paper shows that the RS-EPI scheme may be an important alternative sampling strategy to EPI to achieve high resolution T2-weighted and diffusion-weighted images.

    View details for DOI 10.1016/j.ejrad.2007.09.016

    View details for Web of Science ID 000253086400005

    View details for PubMedID 17980534

  • Parallel imaging reconstruction for arbitrary trajectories using k-space sparse matrices (kSPA) MAGNETIC RESONANCE IN MEDICINE Liu, C., Bammer, R., Moseley, M. E. 2007; 58 (6): 1171-1181

    Abstract

    Although the concept of receiving MR signal using multiple coils simultaneously has been known for over two decades, the technique has only recently become clinically available as a result of the development of several effective parallel imaging reconstruction algorithms. Despite the success of these algorithms, it remains a challenge in many applications to rapidly and reliably reconstruct an image from partially-acquired general non-Cartesian k-space data. Such applications include, for example, three-dimensional (3D) imaging, functional MRI (fMRI), perfusion-weighted imaging, and diffusion tensor imaging (DTI), in which a large number of images have to be reconstructed. In this work, a systematic k-space-based reconstruction algorithm based on k-space sparse matrices (kSPA) is introduced. This algorithm formulates the image reconstruction problem as a system of sparse linear equations in k-space. The inversion of this system of equations is achieved by computing a sparse approximate inverse matrix. The algorithm is demonstrated using both simulated and in vivo data, and the resulting image quality is comparable to that of the iterative sensitivity encoding (SENSE) algorithm. The kSPA algorithm is noniterative and the computed sparse approximate inverse can be applied repetitively to reconstruct all subsequent images. This algorithm, therefore, is particularly suitable for the aforementioned applications.

    View details for DOI 10.1002/mrm.21334

    View details for Web of Science ID 000251346800012

    View details for PubMedID 17969012

  • SENSE phase-constrained magnitude reconstruction with iterative phase refinement MAGNETIC RESONANCE IN MEDICINE Lew, C., Pineda, A. R., Clayton, D., Spielman, D., Chan, F., Bammer, R. 2007; 58 (5): 910-921

    Abstract

    Conventional sensitivity encoding (SENSE) reconstruction is based on equations in the complex domain. However, for many MRI applications only the magnitude is relevant. If there exists an estimate of the underlying phase information, a magnitude-only phase-constrained reconstruction can help to improve the conditioning of the SENSE reconstruction problem. Consequently, this reduces g-factor-related noise enhancement. In previous attempts at phase-constrained SENSE reconstruction, image quality was hampered by strong aliasing artifacts resulting from inadequate phase estimates and high sensitivity to phase errors. If a full-resolution phase image is used, a significant reduction in aliasing errors and better noise properties compared to SENSE can be obtained. An iterative scheme that improves the phase estimate to better approximate the phase is presented. The mathematical framework of the new approach is provided together with comparisons of conventional SENSE, phase-constrained SENSE, and the new phase-refinement method. Both theory and experimental verification demonstrate significantly better noise performance at high reduction factors, i.e., close to the theoretical limit. For applications that need only magnitude data, an iterative phase-constrained SENSE reconstruction can provide substantial SNR improvement over SENSE reconstruction and less artifacts than phase-constrained SENSE.

    View details for DOI 10.1002/mrm.21284

    View details for Web of Science ID 000250560000008

    View details for PubMedID 17969127

  • Revision of the theory of tracer transport and the convolution model of dynamic contrast enhanced magnetic resonance imaging JOURNAL OF MATHEMATICAL BIOLOGY Keeling, S. L., Bammer, R., Stollberger, R. 2007; 55 (3): 389-411

    Abstract

    Counterexamples are used to motivate the revision of the established theory of tracer transport. Then dynamic contrast enhanced magnetic resonance imaging in particular is conceptualized in terms of a fully distributed convection-diffusion model from which a widely used convolution model is derived using, alternatively, compartmental discretizations or semigroup theory. On this basis, applications and limitations of the convolution model are identified. For instance, it is proved that perfusion and tissue exchange states cannot be identified on the basis of a single convolution equation alone. Yet under certain assumptions, particularly that flux is purely convective at the boundary of a tissue region, physiological parameters such as mean transit time, effective volume fraction, and volumetric flow rate per unit tissue volume can be deduced from the kernel.

    View details for DOI 10.1007/s00285-007-0089-3

    View details for Web of Science ID 000248907200005

    View details for PubMedID 17429633

  • Risk factors of symptomatic intracerebral hemorrhage after tPA therapy for acute stroke STROKE Lansberg, M. G., Thijs, V. N., Bammer, R., Kemp, S., Wijman, C. A., Marks, M. P., Albers, G. W. 2007; 38 (8): 2275-2278

    Abstract

    Studies evaluating predictors of tPA-associated symptomatic intracerebral hemorrhage (SICH) have typically focused on clinical and CT-based variables. MRI-based variables have generally not been included in predictive models, and little is known about the influence of reperfusion on SICH risk.Seventy-four patients were prospectively enrolled in an open-label study of intravenous tPA administered between 3 and 6 hours after symptom onset. An MRI was obtained before and 3 to 6 hours after tPA administration. The association between several clinical and MRI-based variables and tPA-associated SICH was determined using multivariate logistic regression analysis. SICH was defined as a > or = 2 point change in National Institutes of Health Stroke Scale Score (NIHSSS) associated with any degree of hemorrhage on CT or MRI. Reperfusion was defined as a decrease in PWI lesion volume of at least 30% between baseline and the early follow-up MRI.SICH occurred in 7 of 74 (9.5%) patients. In univariate analysis, NIHSSS, DWI lesion volume, PWI lesion volume, and reperfusion status were associated with an increased risk of SICH (P<0.05). In multivariate analysis, DWI lesion volume was the single independent baseline predictor of SICH (odds ratio 1.42; 95% CI 1.13 to 1.78 per 10 mL increase in DWI lesion volume). When early reperfusion status was included in the predictive model, the interaction between DWI lesion volume and reperfusion status was the only independent predictor of SICH (odds ratio 1.77; 95% CI 1.25 to 2.50 per 10 mL increase in DWI lesion volume).Patients with large baseline DWI lesion volumes who achieve early reperfusion appear to be at greatest risk of SICH after tPA therapy.

    View details for DOI 10.1161/STROKEAHA.106.480475

    View details for Web of Science ID 000248455100016

    View details for PubMedID 17569874

  • Perfusion mapping with multiecho multishot parallel imaging EPI MAGNETIC RESONANCE IN MEDICINE Newbould, R. D., Skare, S. T., Jochimsen, T. H., Alley, M. T., Moseley, M. E., Albers, G. W., Bammer, R. 2007; 58 (1): 70-81

    Abstract

    Echo-planar imaging (EPI) is the standard technique for dynamic susceptibility-contrast (DSC) perfusion MRI. However, EPI suffers from well-known geometric distortions, which can be reduced by increasing the k-space phase velocity. Moreover, the long echo times (TEs) used in DSC lead to signal saturation of the arterial input signal, and hence to severe quantitation errors in the hemodynamic information. Here, through the use of interleaved shot acquisition and parallel imaging (PI), rapid volumetric EPI is performed using pseudo-single-shot (ss)EPI with the effective T(*)(2) blur and susceptibility distortions of a multishot EPI sequence. The reduced readout lengths permit multiple echoes to be acquired with temporal resolution and spatial coverage similar to those obtained with a single-echo method. Multiecho readouts allow for unbiased R(*)(2) mapping to avoid incorrect estimation of tracer concentration due to signal saturation or T(1) shortening effects. Multiecho perfusion measurement also mitigates the signal-to-noise ratio (SNR) reduction that results from utilizing PI. Results from both volunteers and clinical stroke patients are presented. This acquisition scheme can aid most rapid time-series acquisitions. The use of this method for DSC addresses the problem of signal saturation and T(1) contamination while it improves image quality, and is a logical step toward better quantitative MR PWI.

    View details for DOI 10.1002/mrm.21255

    View details for Web of Science ID 000248488400009

    View details for PubMedID 17659630

  • Evaluation of the clinical-diffusion and perfusion-diffusion mismatch models in DEFUSE STROKE Lansberg, M. G., Thijs, V. N., Hamilton, S., Schlaug, G., Bammer, R., Kemp, S., Albers, G. W. 2007; 38 (6): 1826-1830

    Abstract

    The perfusion-diffusion mismatch (PDM) model has been proposed as a tool to select acute stroke patients who are most likely to benefit from reperfusion therapy. The clinical-diffusion mismatch (CDM) model is an alternative method that is technically less challenging because it does not require perfusion-weighted imaging. This study is an evaluation of these 2 models in the DEFUSE dataset.DEFUSE is an open-label multicenter study in which acute stroke patients were treated with intravenous tPA between 3 and 6 hours after symptoms onset and an MRI was obtained before and 3 to 6 hours after treatment. Presence of PDM and CDM was determined for each patient.Based on conventional predefined mismatch criteria, PDM was present in 54% of the DEFUSE population and CDM in 62%. There was no agreement beyond chance between the 2 mismatch models (kappa 0.07). The presence of PDM was associated with an increased chance of favorable clinical response after reperfusion (OR, 5.4; P=0.039). Reperfusion was not associated with a significant increase in the rate of favorable clinical response in patients with CDM (OR, 2.2; P=0.34). Using optimized mismatch criteria, determined retrospectively based on DEFUSE data, the OR for favorable clinical response was 70 (P=0.001) for PDM and 5.1 (P=0.066) for CDM.The PDM model appears to be more accurate than the CDM model for selecting patients who are likely to benefit from reperfusion therapy in the 3- to 6-hour time window.

    View details for DOI 10.1161/STROKEA.HA.106.480145

    View details for Web of Science ID 000246827100026

    View details for PubMedID 17495217

  • Peak velocity and flow quantification validation for sensitivity-encoded phase-contrast MR imaging ACADEMIC RADIOLOGY Lew, C. D., Alley, M. T., Bammer, R., Spielman, D. M., Chan, F. P. 2007; 14 (3): 258-269

    Abstract

    Phase-contrast (PC) magnetic resonance imaging (MRI) technique has important clinical applications in blood flow quantification and pressure gradient estimation by velocity measurement. Parallel imaging using sensitivity encoding (SENSE) may substantially reduce scan time. We demonstrate the utility of PC-MRI measurements accelerated by SENSE under clinical conditions.Accuracy and repeatability of a SENSE-PC implementation was evaluated by comparison with a commercial PC sequence with five normal volunteers. Twenty-six patients were then scanned with SENSE-PC at reduction factors (R = 1, 2, and 3). Blood flow and peak velocity were measured in the aorta and pulmonary trunk in 16 patients and peak velocity was measured at the coarctation of 10 patients. Quantitative flow, shunt ratio, and peak velocity measurements obtained with different reduction factors were compared using correlation, linear regression, and Bland-Altman statistics. All studies were approved by an Institutional Review Board, and informed consent was acquired from all subjects.The correlation coefficients for all comparisons were >0.962 and with high statistical significance (P < .01). Linear regression slopes ranged between 0.96 and 1.11 for flow and 0.88 to 1.05 for peak velocity. For flow, the Bland-Altman statistics yielded a total mean difference ranging from -0.02 to 0.05) L/minute with 2 standard of deviation limits ranging from -0.52 to 0.75 L/minute. For peak velocity, the total mean difference ranged from -0.10 to -0.004) milliseconds with 2-SD limits ranging from -0.062 to 0.46 milliseconds. R = 3 to R = 1 comparisons had greater 2-SD limits than R = 2 to R = 1 comparisons.SENSE PC-MRI measurements for flow and pressure gradient estimation were comparable to conventional PC-MRI.

    View details for DOI 10.1016/j.acra.2006.11.008

    View details for Web of Science ID 000246861100003

    View details for PubMedID 17307658

  • Restricted field of view magnetic resonance imaging of a dynamic time series MAGNETIC RESONANCE IN MEDICINE Pisani, L., Bammer, R., Glover, G. 2007; 57 (2): 297-307

    Abstract

    A restricted field of view (rFOV) approach for imaging a dynamic time series of volumes of limited spatial extent within a larger subject is described. The shorter readout with rFOV-MRI can be exploited to either limit image artifacts or increase spatial resolution. To accomplish rFOV imaging of a multislice volume for a dynamic series, an outer volume suppression (OVS) preparation that saturates signal external to a cylinder through the subject is followed by slice-selective excitation and a spiral readout. The pass- and stopband efficiencies of the OVS in an agar gel phantom were 97% (+/-1.5%) and 3% (+/-1%), respectively. Profiles of the temporal signal-to-noise ratio (SNR) were measured in a phantom and an adult brain. The rFOV sequence reduced distortions from off-resonance signal and T2*-induced blurring compared to a conventional sequence. Sequence utility is demonstrated for high-resolution rFOV functional MRI (fMRI) in the visual cortex. The rFOV sequence may prove to be useful for other multislice dynamic and high-resolution imaging applications.

    View details for DOI 10.1002/mrm.21115

    View details for Web of Science ID 000243946300009

    View details for PubMedID 17260360

  • Balanced SSFP imaging of the musculoskeletal system JOURNAL OF MAGNETIC RESONANCE IMAGING Gold, G. E., Hargreaves, B. A., Reeder, S. B., Block, W. F., Kijowski, R., Vasanawala, S. S., Kornaat, P. R., Bammer, R., Newbould, R., Bangerter, N. K., Beaulieu, C. F. 2007; 25 (2): 270-278

    Abstract

    Magnetic resonance imaging (MRI), with its unique ability to image and characterize soft tissue noninvasively, has emerged as one of the most accurate imaging methods available to diagnose bone and joint pathology. Currently, most evaluation of musculoskeletal pathology is done with two-dimensional acquisition techniques such as fast spin echo (FSE) imaging. The development of three-dimensional fast imaging methods based on balanced steady-state free precession (SSFP) shows great promise to improve MRI of the musculoskeletal system. These methods may allow acquisition of fluid sensitive isotropic data that can be reformatted into arbitrary planes for improved detection and visualization of pathology. Sensitivity to fluid and fat suppression are important issues in these techniques to improve delineation of cartilage contours, for detection of marrow edema and derangement of other joint structures.

    View details for DOI 10.1002/jmri.20819

    View details for Web of Science ID 000244133000006

    View details for PubMedID 17260387

  • Time-resolved 3D quantitative flow MRI of the major intracranial vessels: Initial experience and comparative evaluation at 1.5T and 3.0T in combination with parallel imaging MAGNETIC RESONANCE IN MEDICINE Bammer, R., Hope, T. A., Aksoy, M., Alley, M. T. 2007; 57 (1): 127-140

    Abstract

    Exact knowledge of blood flow characteristics in the major cerebral vessels is of great relevance for diagnosing cerebrovascular abnormalities. This involves the assessment of hemodynamically critical areas as well as the derivation of biomechanical parameters such as wall shear stress and pressure gradients. A time-resolved, 3D phase-contrast (PC) MRI method using parallel imaging was implemented to measure blood flow in three dimensions at multiple instances over the cardiac cycle. The 4D velocity data obtained from 14 healthy volunteers were used to investigate dynamic blood flow with the use of multiplanar reformatting, 3D streamlines, and 4D particle tracing. In addition, the effects of magnetic field strength, parallel imaging, and temporal resolution on the data were investigated in a comparative evaluation at 1.5T and 3T using three different parallel imaging reduction factors and three different temporal resolutions in eight of the 14 subjects. Studies were consistently performed faster at 3T than at 1.5T because of better parallel imaging performance. A high temporal resolution (65 ms) was required to follow dynamic processes in the intracranial vessels. The 4D flow measurements provided a high degree of vascular conspicuity. Time-resolved streamline analysis provided features that have not been reported previously for the intracranial vasculature.

    View details for DOI 10.1002/mrm.21109

    View details for Web of Science ID 000243538900015

    View details for PubMedID 17195166

  • Propeller EPI in the other direction MAGNETIC RESONANCE IN MEDICINE Skare, S., Newbould, R. D., Clayton, D. B., Bammer, R. 2006; 55 (6): 1298-1307

    Abstract

    A new propeller EPI pulse sequence with reduced sensitivity to field inhomogeneities is proposed. Image artifacts such as blurring due to Nyquist ghosting and susceptibility gradients are investigated and compared with those obtained in previous propeller EPI studies. The proposed propeller EPI sequence uses a readout that is played out along the short axis of the propeller blade, orthogonal to the readout used in previous propeller methods. In contrast to long-axis readout propeller EPI, this causes the echo spacing between two consecutive phase-encoding (PE) lines to decrease, which in turn increases the k-space velocity in this direction and hence the pseudo-bandwidth. Long- and short-axis propeller EPI, and standard single-shot EPI sequences were compared on phantoms and a healthy volunteer. Diffusion-weighted imaging (DWI) was also performed on the volunteer. Short-axis propeller EPI produced considerably fewer image artifacts compared to the other two sequences. Further, the oblique blades for the long-axis propeller EPI were also prone to one order of magnitude higher residual ghosting than the proposed short-axis propeller EPI.

    View details for DOI 10.1002/mrm.20890

    View details for Web of Science ID 000238051000010

    View details for PubMedID 16676335

  • Efficient simulation of magnetic resonance imaging with Bloch-Torrey equations using intra-voxel magnetization gradients JOURNAL OF MAGNETIC RESONANCE Jochimsen, T. H., Schafer, A., Bammer, R., Moseley, M. E. 2006; 180 (1): 29-38

    Abstract

    The process of image formation in magnetic resonance imaging (MRI) can be simulated by means of an iterative solution of Bloch-Torrey equations. This is a useful accessory to analyze the influence of sample properties, sequence parameters and hardware specifications on the MRI signal. In this paper, a computer algorithm is presented which is based on calculating partial derivatives of the magnetization vector. This technique allows more efficient simulation than summation of isochromats (the latter being commonly employed for this purpose) and, as a result, the effect of diffusion on the MRI signal can be calculated iteratively. A detailed description of the algorithm is given, and its feasibility for different applications is studied. It is shown that the algorithm is most applicable to simulating the effect of field perturbations, i.e. intra-voxel dephasing, but is also useful for other typical imaging experiments and the simulation of diffusion weighting.

    View details for DOI 10.1016/j.jmr.2006.01.001

    View details for Web of Science ID 000236978400003

    View details for PubMedID 16434221

  • Comparison of minimally invasive and conventional open posterolateral lumbar fusion using magnetic resonance imaging and retraction pressure studies JOURNAL OF SPINAL DISORDERS & TECHNIQUES Stevens, K. J., Spenciner, D. B., Griffiths, K. L., Kim, K. D., Zivienenberg-Lee, M., Alamin, T., Bammer, R. 2006; 19 (2): 77-86

    Abstract

    To determine whether minimally invasive lumbar spinal fusion results in less paraspinal muscle damage than conventional open posterior fusion.The maximum intramuscular pressure (IMP) generated by a minimally invasive and standard open retractor was compared in cadavers using an ultra-miniature pressure transducer. In a second clinical study, eight patients with either minimally invasive or open posterolateral lumbar spinal fusion underwent magnetic resonance imaging (MRI) scanning approximately 6 months post surgery. MRI was used to estimate edema and atrophy within multifidus, with T2 mapping and diffusion-weighted imaging allowing quantification of differences between the two surgical techniques.IMP measured with the minimally invasive retractor was 1.4 versus 4.7 kPa with the open retractor (P < 0.001). The minimally invasive retractor produced a transient maximal IMP only on initial expansion. Maximum IMP was constant throughout open retractor deployment. Striking visual differences in muscle edema were seen between open and minimally invasive groups on MRI. The mean T2 relaxation time at the level of fusion was 47 milliseconds in the minimally invasive and 90 milliseconds in the open group (P = 0.013). The mean apparent diffusion coefficient was 1357 x 10(-6) mm/s and 1626 x 10(-6) mm(2)/s (P = 0.0184), respectively.The peak IMP generated by the minimally invasive retractor was significantly less than with the open retractor. Postoperatively, less muscle edema was demonstrated after the minimally invasive lumbar spinal fusion, with lower mean T2 and apparent diffusion coefficient measurements supporting the hypothesis that less damage occurs using a minimally invasive approach.

    View details for Web of Science ID 000237437600001

    View details for PubMedID 16760779

  • Simultaneous phase correction and SENSE reconstruction for navigated multi-shot DWI with non-cartesian k-space sampling MAGNETIC RESONANCE IN MEDICINE Liu, C. L., Moseley, M. E., Bammer, R. 2005; 54 (6): 1412-1422

    Abstract

    Phase-navigated multi-shot acquisition and parallel imaging are two techniques that have been applied to diffusion-weighted imaging (DWI) to diminish distortions and to enhance spatial resolution. Specifically, sensitivity encoding (SENSE) has been combined with single-shot echo planar imaging (EPI). Thus far, it has been difficult to apply parallel imaging methods, like SENSE, to multi-shot DWI because motion-induced phase error varies from shot to shot and interferes with sensitivity encoding. Although direct phase subtraction methods have been introduced to correct this phase error, they generally are not suitable for SENSE reconstruction, and they cannot remove all the motion artifacts even if the phase error is fully known. Here, an effective algorithm is proposed to correct the motion-induced phase error using an iterative reconstruction. In this proposed conjugate-gradient (CG) algorithm, the phase error is treated as an image encoding function. Given the complex perturbation terms, diffusion-weighted images can be reconstructed using an augmented sensitivity map. The mathematical formulation and image reconstruction procedures of this algorithm are similar to the SENSE reconstruction. By defining a dynamic composite sensitivity, the CG phase correction method can be conveniently incorporated with SENSE reconstruction for the application of multi-shot SENSE DWI. Effective phase correction and multi-shot SENSE DWI (R = 1 to 3) are demonstrated on both simulated and in vivo data acquired with PROPELLER and SNAILS.

    View details for DOI 10.1002/mrm.20706

    View details for Web of Science ID 000233655200012

    View details for PubMedID 16276497

  • White matter development during childhood and adolescence: A cross-sectional diffusion tensor imaging study CEREBRAL CORTEX Barnea-Goraly, N., Menon, V., Eckert, M., Tamm, L., Bammer, R., Karchemskiy, A., Dant, C. C., Reiss, A. L. 2005; 15 (12): 1848-1854

    Abstract

    Maturation of brain white matter pathways is an important factor in cognitive, behavioral, emotional and motor development during childhood and adolescence. In this study, we investigate white matter maturation as reflected by changes in anisotropy and white matter density with age. Thirty-four children and adolescents aged 6-19 years received diffusion-weighted magnetic resonance imaging scans. Among these, 30 children and adolescents also received high-resolution T1-weighed anatomical scans. A linear regression model was used to correlate fractional anisotropy (FA) values with age on a voxel-by-voxel basis. Within the regions that showed significant FA changes with age, a post hoc analysis was performed to investigate white matter density changes. With increasing age, FA values increased in prefrontal regions, in the internal capsule as well as in basal ganglia and thalamic pathways, the ventral visual pathways, and the corpus callosum. The posterior limb of the internal capsule, intrathalamic connections, and the corpus callosum showed the most significant overlaps between white matter density and FA changes with age. This study demonstrates that during childhood and adolescence, white matter anisotropy changes in brain regions that are important for attention, motor skills, cognitive ability, and memory. This typical developmental trajectory may be altered in individuals with disorders of development, cognition and behavior.

    View details for DOI 10.1093/cercor/bhi062

    View details for Web of Science ID 000233217300002

    View details for PubMedID 15758200

  • Arithmetic ability and parietal alterations: A diffusion tensor imaging study in Velocardiofacial syndrome COGNITIVE BRAIN RESEARCH Barnea-Goraly, N., Eliez, S., Menon, V., Bammer, R., Reiss, A. L. 2005; 25 (3): 735-740

    Abstract

    Velocardiofacial syndrome (VCFS) is a congenital anomaly that causes somatic as well as cognitive and psychiatric impairments. Previous studies have found specific deficits in arithmetic abilities in subjects with VCFS. In this study, we investigated whether abnormalities in white matter pathways are correlated with reduced arithmetic ability. Nineteen individuals with VCFS aged 7-19 years received diffusion-weighted magnetic resonance imaging (MRI) scans. A linear regression model was used to correlate fractional anisotropy (FA) values with scores of the arithmetic subscale on the WISC/WAIS on a voxel-by-voxel basis, after covarying for any IQ- and age-related effects. There was a statistically significant positive correlation between the arithmetic score on the WISC/WAIS and FA values in white matter tracts adjacent to the left supramarginal and angular gyri, as well as along the left intraparietal sulcus. Inferior parietal lobe white matter structural aberrations may contribute to reduced arithmetic ability in VCFS.

    View details for DOI 10.1016/j.cogbrainres.2005.09.013

    View details for Web of Science ID 000234236500014

    View details for PubMedID 16260124

  • Clinical importance of microbleeds in patients receiving IV thrombolysis NEUROLOGY Kakuda, W., Thijs, V. N., Lansberg, M. G., Bammer, R., Wechsler, L., Kemp, S., Moseley, M. E., Marks, M. P., Albers, G. W. 2005; 65 (8): 1175-1178

    Abstract

    Cerebral microbleeds (MBs) detected on gradient echo (GRE) imaging may be a risk factor for hemorrhagic complications in patients with stroke treated with IV tissue plasminogen activator (tPA).The authors prospectively evaluated patients with acute ischemic stroke treated with IV tPA between 3 and 6 hours of symptom onset. MRI scans, including GRE imaging, were performed prior to tPA treatment, 3 to 6 hours after treatment and at day 30. The authors compared the frequency of hemorrhagic complications after thrombolysis in patients with and without MBs on their baseline GRE imaging.Seventy consecutive patients (mean age, 71 +/- 29 years; 31 men, 39 women) were included. MBs were identified in 11 patients (15.7%) on baseline GRE imaging. There was no significant difference in the frequency of either symptomatic or asymptomatic hemorrhagic complications after thrombolysis between patients with and without MBs at baseline. None of the 11 patients with MBs (0%) at baseline had a symptomatic intracerebral hemorrhage compared with 7 of 59 patients who did not have baseline MBs (11.9%). In addition, no patients with baseline MBs had asymptomatic hemorrhagic transformation observed at the site of any pre-treatment MB.The presence of cerebral microbleeds on gradient echo imaging does not appear to substantially increase the risk of either symptomatic or asymptomatic brain hemorrhage following IV tissue plasminogen activator administered between 3 and 6 hours after stroke onset.

    View details for Web of Science ID 000232813600008

    View details for PubMedID 16247042

  • Limitations of apparent diffusion coefficient-based models in characterizing non-Gaussian diffusion MAGNETIC RESONANCE IN MEDICINE Liu, C. L., Bammer, R., Moseley, M. E. 2005; 54 (2): 419-428

    Abstract

    Diffusion in complex heterogeneous structures, for example, the neural fiber system, is non-gaussian. Recently, several methods have been introduced to address the issue of non-gaussian diffusion in multifiber systems. Some are based on apparent diffusion coefficient (ADC) analysis; and some are based on q-space analysis. Here, using a simple mathematic derivation, ADC-based models are shown to be mathematically self-inconsistent in the presence of non-gaussian diffusion. Monte Carlo simulation on restricted diffusion is applied to demonstrate the poor data fitting that can result from ADC-based models. Specific comparisons are performed between two generalized diffusion tensor imaging methods: one of them is based on ADC analysis, and the other is shown to be consistent with q-space formalism. The issue of imaging asymmetric microstructures is also investigated. Signal phase and spin exchange are necessary to resolve multiple orientations of an asymmetric structure.

    View details for DOI 10.1002/mrm.20579

    View details for Web of Science ID 000230765700020

    View details for PubMedID 16032684

  • Children's reading performance is correlated with white matter structure measured by diffusion tensor imaging CORTEX Deutsch, G. K., Dougherty, R. F., Bammer, R., Siok, W. T., Gabrieli, J. D., Wandell, B. 2005; 41 (3): 354-363

    Abstract

    We investigated the white matter structure in children (n = 14) with a wide range of reading performance levels using diffusion tensor imaging (DTI), a form of magnetic resonance imaging. White matter structure in a left temporo-parietal region that had been previously described as covarying with reading skill in adult readers also differs between children who are normal and poor readers. Specifically, the white matter structure measured using fractional anisotropy (FA) and coherence index (CI) significantly correlated with behavioral measurements of reading, spelling, and rapid naming performance. In general, lower anisotropy and lower coherence were associated with lower performance scores. Although the magnitude of the differences in children are smaller than those in adults, the results support the hypothesis that the structure of left temporoparietal neural pathways is a significant component of the neural system needed to develop fluent reading.

    View details for Web of Science ID 000228941100008

    View details for PubMedID 15871600

  • Automated method for generating the arterial input function on perfusion-weighted MR imaging: Validation in patients with stroke AMERICAN JOURNAL OF NEURORADIOLOGY Mlynash, M., Eyngorn, I., Bammer, R., Moseley, M., Tong, D. C. 2005; 26 (6): 1479-1486

    Abstract

    The choice of arterial input function (AIF) can have a profound effect on the blood flow maps generated on perfusion-weighted MR imaging (PWI). Automation of this process could substantially reduce operator dependency, increase consistency, and accelerate PWI analysis. We created an automated AIF identification program (auto-AIF) and validated its performance against conventional manual methods.We compared the auto-AIF against manually derived AIFs from multisection PWIs of 22 patients with stroke. Time to peak, curve width, curve height, and voxel location determined with both techniques were compared. The time to maximum of the tissue residue function (Tmax) and cerebral blood flow (CBF) were computed on a per-pixel basis for each AIF. Spatial patterns of 528 map pairs were compared by computing Pearson correlation coefficients between maps generated with each method.All auto-AIF-derived PWI map parameters, including bolus peak, width, and height, were consistently superior to manually derived ones. Reproducibility of the auto-AIF-based Tmax maps was excellent (r = 1.0). Paired Tmax maps and CBF maps from both techniques were well correlated (r = 0.82). Time to identify the AIF was significantly shorter with the auto-AIF method than with the manual technique (mean difference, 72 seconds; 95% confidence interval: 54, 89 seconds).An automated program that identifies the AIF is feasible and can create reliably reproducible and accurate Tmax and CBF maps. Automation of this process could reduce PWI analysis time and increase consistency and may allow for more effective use of PWI in the evaluation of acute stroke.

    View details for Web of Science ID 000229815800037

    View details for PubMedID 15956519

  • Functional organization of human occipital-callosal fiber tracts PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Dougherty, R. F., Ben-Shachar, M., Bammer, R., Brewer, A. A., Wandell, B. A. 2005; 102 (20): 7350-7355

    Abstract

    Diffusion tensor imaging (DTI) and fiber tracking (FT) were used to measure the occipital lobe fiber tracts connecting the two hemispheres in individual human subjects. These tracts are important for normal vision. Also, damage to portions of these tracts is associated with alexia. To assess the reliability of the DTI-FT measurements, occipital-callosal projections were estimated from each subject's left and right hemispheres independently. The left and right estimates converged onto the same positions within the splenium. We further characterized the properties of the estimated occipital-callosal fiber tracts by combining them with functional MRI. We used functional MRI to identify visual field maps in cortex and labeled fibers by the cortical functional response at the fiber endpoint. This labeling reveals a regular organization of the fibers within the splenium. The dorsal visual maps (dorsal V3, V3A, V3B, V7) send projections through a large band in the middle of the splenium, whereas ventral visual maps (ventral V3, V4) send projections through the inferior-anterior corner of the splenium. The agreement between the independent left/right estimates, further supported by previous descriptions of homologous tracts in macaque, validates the DTI-FT methods. However, a principal limitation of these methods is low sensitivity: a large number of fiber tracts that connect homotopic regions of ventral and lateral visual cortex were undetected. We conclude that most of the estimated tracts are real and can be localized with a precision of 1-2 mm, but many tracts are missed because of data and algorithm limitations.

    View details for DOI 10.1073/pnas.0500003102

    View details for Web of Science ID 000229292200053

    View details for PubMedID 15883384

  • Foundations of advanced magnetic resonance imaging. NeuroRx : the journal of the American Society for Experimental NeuroTherapeutics Bammer, R., Skare, S., Newbould, R., Liu, C., Thijs, V., Ropele, S., Clayton, D. B., Krueger, G., Moseley, M. E., Glover, G. H. 2005; 2 (2): 167-196

    Abstract

    During the past decade, major breakthroughs in magnetic resonance imaging (MRI) quality were made by means of quantum leaps in scanner hardware and pulse sequences. Some advanced MRI techniques have truly revolutionized the detection of disease states and MRI can now-within a few minutes-acquire important quantitative information noninvasively from an individual in any plane or volume at comparatively high resolution. This article provides an overview of the most common advanced MRI methods including diffusion MRI, perfusion MRI, functional MRI, and the strengths and weaknesses of MRI at high magnetic field strengths.

    View details for PubMedID 15897944

  • A physical model for DT-MRI based connectivity map computation MEDICAL IMAGE COMPUTING AND COMPUTER-ASSISTED INTERVENTION - MICCAI 2005, PT 1 Yoruk, E., Acar, B., Bammer, R. 2005; 3749: 213-220
  • Occipital-callosal pathways in children - Validation and atlas development WHITE MATTER IN COGNITIVE NEUROSCIENCE: ADVANCES IN DIFFUSION TENSOR IMAGING AND ITS APPLICATIONS Dougherty, R. F., Ben-Shachar, M., Deutsch, G., Potanina, P., Bammer, R., Wandell, B. A. 2005; 1064: 98-?

    Abstract

    Diffusion tensor imaging and fiber tracking were used to measure fiber bundles connecting the two occipital lobes in 53 children of 7-12 years of age. Independent fiber bundle estimates originating from the two hemispheres converge onto the lower half of the splenium. This observation validates the basic methodology and suggests that most occipital-callosal fibers connect the two occipital lobes. Within the splenium, fiber bundles are organized in a regular pattern with respect to their cortical projection zones. Visual cortex dorsal to calcarine projects through a large band that fills much of the inferior half of the splenium, while cortex ventral to calcarine sends projections through a band at the anterior inferior edge of the splenium. Pathways projecting to the occipital pole and lateral-occipital regions overlap the dorsal and ventral groups slightly anterior to the center of the splenium. To visualize these pathways in a typical brain, we combined the data into an atlas. The estimated occipital-callosal fiber paths from the atlas form the walls of the occipital horn of the lateral ventricle, with dorsal paths forming the medial wall and the ventral paths bifurcating into a medial tract to form the inferior-medial wall and a superior tract that joins the lateral-occipital paths to form the superior wall of the ventricle. The properties of these fiber bundles match those of the hypothetical pathways described in the neurological literature on alexia.

    View details for DOI 10.1196/annals.1340.017

    View details for Web of Science ID 000235430200008

    View details for PubMedID 16394151

  • A physical model for DT-MRI based connectivity map computation. Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention Yörük, E., Acar, B., Bammer, R. 2005; 8: 213-220

    Abstract

    In this study we address the problem of extracting a robust connectivity metric for brain white matter. We defined the connectivity problem as an energy minimization task, by associating the DT-field to a physical system composed of nodes and springs, with their constants defined as a function of local structure. Using a variational approach we formulated a fast and stable map evolution, which utilizes an anisotropic kernel smoothing scheme equivalent to a diffusion PDE. The proposed method provides connectivity maps that correlate with normal anatomy on real patient data.

    View details for PubMedID 16685848

  • Self-navigated interleaved spiral (SNAILS): Application to high-resolution diffusion tensor imaging MAGNETIC RESONANCE IN MEDICINE Liu, C. L., Bammer, R., Kim, D. H., Moseley, M. E. 2004; 52 (6): 1388-1396

    Abstract

    A fat-saturated twice-refocused spin echo sequence was implemented on a GE Signa 1.5-T whole-body system for diffusion-weighted imaging. Data were acquired using an analytically designed interleaved variable-density (VD) spiral readout trajectory. This flexible design algorithm allowed real-time prescription on the scanner. Each interleaf of the VD spiral oversampled the center of k-space. The oversampling provided an inherent motion compensation capability. The resultant diffusion-weighted images showed good quality without any retrospective motion correction. An iterated motion correction algorithm was developed to further reduce the signal cancellation artifact caused by motion-induced phase error. In this algorithm, a low-resolution phase map was estimated using the oversampled data in the center of k-space in order to correct for phase error in image space. In vivo diffusion tensor imaging (DTI) studies were performed on the brains of healthy volunteers. High-quality isotropic diffusion-weighted images, trace maps, and FA maps from axial, sagittal, and coronal slices were obtained using a VD spiral readout trajectory with matrix size 256 x 256. To our knowledge, this was also the first time in vivo 512 x 512 DTI results were reported.

    View details for DOI 10.1002/mrm.20289

    View details for Web of Science ID 000225486200022

    View details for PubMedID 15562493

  • A variational approach to magnetic resonance coil sensitivity estimation APPLIED MATHEMATICS AND COMPUTATION Keeling, S. L., Bammer, R. 2004; 158 (2): 359-388
  • Current concepts and advances in clinical parallel magnetic resonance imaging. Topics in magnetic resonance imaging Bammer, R., Schoenberg, S. O. 2004; 15 (3): 129-158

    Abstract

    Parallel imaging (PI) is one of the most promising recent advances in MRI technology and has, similar to the introduction of multidetector helical scanning in CT, revolutionized MR imaging. The speed of all conventional MRI methods has been limited by either gradient strength or their switching times. The basic idea in PI is to use some of the spatial information contained in the individual elements of a radiofrequency (RF) receiver coil array to increase imaging speed. These PI techniques are removing some of the previous limitations in speed of MRI scanners and set the basis for accelerated image formation. Initially, PI was motivated by the wish to accelerate image acquisition without reducing the spatial resolution of the image. However, depending on the application, it turned out that PI harbors several other advantages. Among those is the possibility for higher spatial resolution, shorter breath-holds or multiple averaging to diminish motion artifacts, reduced image blurring and geometric distortions, better temporal resolution, and means for navigator correction. This overview focuses on technical aspects, clinical applications, and ongoing research in different areas of the human body. The critical review demonstrates PI's great versatility as well as the current trends to use this unique technique in the majority of clinical scan protocols.

    View details for PubMedID 15479997

  • Parallel imaging of the abdomen. Topics in magnetic resonance imaging Margolis, D. J., Bammer, R., Chow, L. C. 2004; 15 (3): 197-206

    Abstract

    Parallel imaging holds great potential for improving the quality of diagnostic abdominal MRI. The increased imaging speed afforded by parallel imaging can be translated into the obvious benefits of reduced scan time with set resolution and coverage, improved spatial resolution with set imaging time and coverage, increased anatomic coverage for a set imaging time and resolution, or some combination of the above. Additionally, the reduction in scan time can also allow some sequences that normally require multiple breath-holds to be performed with only one, or simply make breath-hold imaging possible for more patients. The decreased echo-train length allows for truer T2-weighting, less magnetic susceptibility artifact, and less blurring with echo-train imaging. Dynamic contrast-enhanced sequences can be acquired with improved temporal or spatial resolution. All of these potential advantages come with the trade-off of decreased signal-to-noise ratio, but for many patients, the benefits far outweigh the drawbacks and can vastly improve the diagnostic quality of abdominal MRI.

    View details for PubMedID 15480001

  • A comparative evaluation of CH3-DTPA-Gd (NMS60) for contrast-enhanced magnetic resonance angiography MAGNETIC RESONANCE IMAGING Bammer, R., de Crespigny, A. J., Howard, D., Seri, S., Hashiguchi, Y., Nakatani, A., Moseley, M. E. 2004; 22 (5): 619-624

    Abstract

    In a canine model the signal dynamics of a new oligomer-based MR contrast agent (NMS60, 2158 Da) were compared to Gd-DTPA to investigate the agents' potential for magnetic resonance angiography (MRA). Twelve male mongrel dogs were imaged sequentially under anesthesia with two different MRA sequences (Tlw 3DSPGR). Initial enhancement was measured every 9 s for eight points in time. Thereafter, spatial highly resolved MRAs were obtained at 5, 10, 15, 20, 30, 45, and 60 min post-injection of two different dosages. Over the first 20 s following bolus administration the average arterial enhancement of 0.1 mmol(Gd)kg NMS60 was 44% greater than Gd-DTPA. Twenty minutes post-injection the relative signal intensity of NMS60 was as high as the peak signal intensity with Gd-DTPA at the same dosage level (0.1 mmol(Gd)/kg). In the animals that received NMS60 injections the vascular conspicuity was overly superior to those who received Gd-DTPA. No significant toxicity effects were noted for either dosage level. The intermediate weight contrast agent NMS60 offers greater vascular enhancement and retention time than Gd-DTPA. For a given set of optimized imaging parameters this offers improved spatial details, less arterial/venous overlap, and better vascular contrast.

    View details for DOI 10.1016/j.mri.2004.01.044

    View details for Web of Science ID 000221688400003

    View details for PubMedID 15172054

  • Characterizing non-Gaussian diffusion by using generalized diffusion tensors MAGNETIC RESONANCE IN MEDICINE Liu, C. L., Bammer, R., Acar, B., Moseley, M. E. 2004; 51 (5): 924-937

    Abstract

    Diffusion tensor imaging (DTI) is known to have a limited capability of resolving multiple fiber orientations within one voxel. This is mainly because the probability density function (PDF) for random spin displacement is non-Gaussian in the confining environment of biological tissues and, thus, the modeling of self-diffusion by a second-order tensor breaks down. The statistical property of a non-Gaussian diffusion process is characterized via the higher-order tensor (HOT) coefficients by reconstructing the PDF of the random spin displacement. Those HOT coefficients can be determined by combining a series of complex diffusion-weighted measurements. The signal equation for an MR diffusion experiment was investigated theoretically by generalizing Fick's law to a higher-order partial differential equation (PDE) obtained via Kramers-Moyal expansion. A relationship has been derived between the HOT coefficients of the PDE and the higher-order cumulants of the random spin displacement. Monte-Carlo simulations of diffusion in a restricted environment with different geometrical shapes were performed, and the strengths and weaknesses of both HOT and established diffusion analysis techniques were investigated. The generalized diffusion tensor formalism is capable of accurately resolving the underlying spin displacement for complex geometrical structures, of which neither conventional DTI nor diffusion-weighted imaging at high angular resolution (HARD) is capable. The HOT method helps illuminate some of the restrictions that are characteristic of these other methods. Furthermore, a direct relationship between HOT and q-space is also established.

    View details for DOI 10.1002/mrm.20071

    View details for Web of Science ID 000221239000008

    View details for PubMedID 15122674

  • Influence of arterial input function on hypoperfusion volumes measured with perfusion-weighted imaging STROKE Thijs, V. N., Somford, D. M., Bammer, R., Robberecht, W., Moseley, M. E., Albers, G. W. 2004; 35 (1): 94-98

    Abstract

    The arterial input function (AIF) is critical in determining hemodynamic parameters quantitatively with bolus-tracking MRI. We studied the effect of varying the location of measurement of AIF on the volume of hypoperfusion. We compared the volumes of hypoperfusion obtained with different AIFs with the final ischemic lesion volume.We included 13 patients with acute cerebral ischemia in the anterior circulation who underwent diffusion- (DWI) and perfusion (PWI)-weighted imaging within 8 hours after symptom onset and exhibited DWI lesion expansion between baseline and follow-up. AIF was measured at 4 locations: near both middle cerebral arteries (MCAs), in MCA branches adjacent to the largest DWI abnormality, and at the same level on the opposite hemisphere. Hypoperfusion lesion volumes were compared with the DWI volume at follow-up.Large variations in PWI lesion size were found with different AIF locations. The largest PWI lesions were found when AIF was measured at the contralateral MCA. Smaller PWI lesions were found when AIF was measured in the other locations. There was no significant difference between PWI lesion area at baseline and follow-up DWI lesion when AIF was measured at the contralateral MCA. The other PWI lesions significantly underestimated follow-up DWI lesion size.AIF is an important determinant of the size of hypoperfusion lesions measured with PWI. PWI lesion volumes determined with AIF from the contralateral MCA are associated with follow-up lesion volume.

    View details for DOI 10.1161/01.STR.0000106136.15163.73

    View details for Web of Science ID 000187630500020

    View details for PubMedID 14671249

  • Diffusion imaging of the human spinal cord and the vertebral column. Topics in magnetic resonance imaging Bammer, R., Fazekas, F. 2003; 14 (6): 461-476

    Abstract

    During the last decade, diffusion-weighted imaging (DWI) has matured from an experimental tool to a clinically useful modality that has not only significantly impacted the diagnosis of (acute) cerebral stroke but has also shown utility in other abnormalities of the brain. Although DWI should be equally sensitive to changes in the spine, it has been used far less frequently in this region of the body. This is mainly because of the inhomogeneous magnetic environment, the small size of the spinal cord, and increased motion in and around the spine. However, once these limitations are overcome, a whole range of applications can be envisioned. Already now, DWI promises to be able to differentiate between benign and malignant vertebral compression fractures. As in the brain, the immediate reduction of diffusivity following ischemic damage in the spinal cord may provide an early identification of patients with infarction. The study of diffusion anisotropy may open new avenues for the detection and better understanding of damage to the long fiber tracts with important clinical implications for disorders like multiple sclerosis and amyotrophic lateral sclerosis. It may also be possible to address, in a more refined manner, mechanisms of damage such as occur with spondylotic myelopathy. To lay the basis for future research in these areas, we will discuss the most appropriate DWI methods for the spine. Following an overview of the basic principles of DWI and associated pitfalls, the most commonly used imaging methods are addressed. Finally, experimental and clinical applications in the spinal cord and the vertebral column and their clinical relevance thus far are reviewed.

    View details for PubMedID 14872166

  • Generalized reconstruction of phase contrast MRI: Analysis and correction of the effect of gradient field distortions MAGNETIC RESONANCE IN MEDICINE Markl, M., Bammer, R., Alley, M. T., Elkins, C. J., Draney, M. T., Barnett, A., Moseley, M. E., Glover, G. H., Pelc, N. J. 2003; 50 (4): 791-801

    Abstract

    To characterize gradient field nonuniformity and its effect on velocity encoding in phase contrast (PC) MRI, a generalized model that describes this phenomenon and enables the accurate reconstruction of velocities is presented. In addition to considerable geometric distortions, inhomogeneous gradient fields can introduce deviations from the nominal gradient strength and orientation, and therefore spatially-dependent first gradient moments. Resulting errors in the measured phase shifts used for velocity encoding can therefore cause significant deviations in velocity quantification. The true magnitude and direction of the underlying velocities can be recovered from the phase difference images by a generalized PC velocity reconstruction, which requires the acquisition of full three-directional velocity information. The generalized reconstruction of velocities is applied using a matrix formalism that includes relative gradient field deviations derived from a theoretical model of local gradient field nonuniformity. In addition, an approximate solution for the correction of one-directional velocity encoding is given. Depending on the spatial location of the velocity measurements, errors in velocity magnitude can be as high as 60%, while errors in the velocity encoding direction can be up to 45 degrees. Results of phantom measurements demonstrate that effects of gradient field nonuniformity on PC-MRI can be corrected with the proposed method.

    View details for DOI 10.1002/mrm.10582

    View details for Web of Science ID 000185698000019

    View details for PubMedID 14523966

  • Single breath-hold diffusion-weighted imaging of the abdomen JOURNAL OF MAGNETIC RESONANCE IMAGING Chow, L. C., Bammer, R., Moseley, M. E., Sommer, F. G. 2003; 18 (3): 377-382

    Abstract

    To generate high quality diffusion-weighted images (DWI) and corresponding isotropic ADC maps of the abdomen with full organ (kidneys) coverage in a single breath-hold.DWI was performed in 12 healthy subjects with an asymmetric, spin-echo, single-shot EPI readout on a system with high performance gradients (40 mT/minute). The isotropic diffusion coefficient was measured from maps and SNR was determined for both diffusion-weighted and reference images in the liver, spleen, pancreas, and kidneys. In six patients, single-axis diffusion encoding along three orthogonal axes (12 NEX) was employed to assess anisotropic diffusion in kidneys.This technique yielded images of quality and resolution which compares favorably to that of prior work. SNR ranged from 27.0 in liver to 44.1 in kidneys for the diffusion-weighted images, and from 19.6 in liver to 39.0 in kidneys in reference images. ADCs obtained in the renal medulla, renal cortex, liver, spleen, and pancreas were (2091 +/- 55) x 10(-6), (2580 +/- 53) x 10(-6), (1697 +/- 52) x 10(-6), (1047 +/- 82) x 10(-6), and (2605 +/- 168) x 10(-6) mm(2)/second, respectively (mean +/- SE). Apparent diffusion coefficient (ADC) in the renal medulla and cortex were significantly different by paired t-test (P = 4.22 x 10(-10)). Renal medulla and cortex yielded anisotropy indices (AI) of 0.129 and 0.067, respectively.1) Single-shot SE EPI DWI in the abdomen with this technique provides high quality images and maps with full organ coverage in a single breath-hold; 2) ADCs obtained in the renal medulla and cortex are significantly different; and 3) diffusion within the renal medulla is moderately anisotropic.

    View details for DOI 10.1002/jmri.10353

    View details for Web of Science ID 000185016700017

    View details for PubMedID 12938137

  • Basic principles of diffusion-weighted imaging EUROPEAN JOURNAL OF RADIOLOGY Bammer, R. 2003; 45 (3): 169-184

    Abstract

    In diffusion-weighted MRI (DWI), image contrast is determined by the random microscopic motion of water protons. During the last years, DWI has become an important modality in the diagnostic work-up of acute ischemia in the CNS. There are also a few promising reports about the application of DWI to other regions in the human body, such as the vertebral column or the abdomen. This manuscript provides an introduction into the basics of DWI and Diffusion Tensor imaging. The potential of various MR sequences in concert with diffusion preparation are discussed with respect to acquisition speed, spatial resolution, and sensitivity to bulk physiologic motion. More advanced diffusion measurement techniques, such as high angular resolution diffusion imaging, are also addressed.

    View details for Web of Science ID 000181482500002

    View details for PubMedID 12595101

  • Line scan diffusion imaging of the spine AMERICAN JOURNAL OF NEURORADIOLOGY Bammer, R., Herneth, A. M., Maier, S. E., Butts, K., Prokesch, R. W., Do, H. M., Atlas, S. W., Moseley, M. E. 2003; 24 (1): 5-12

    Abstract

    Recent findings suggest that diffusion-weighted imaging might be an important adjunct to the diagnostic workup of disease processes in the spine, but physiological motion and the challenging magnetic environment make it difficult to perform reliable quantitative diffusion measurements. Multi-section line scan diffusion imaging of the spine was implemented and evaluated to provide quantitative diffusion measurements of vertebral bodies and intervertebral disks.Line scan diffusion imaging of 12 healthy study participants and three patients with benign vertebral compression fractures was performed to assess the potential of line scan diffusion imaging of the spinal column. In a subgroup of six participants, multiple b-value (5-3005 s/mm(2)) images were obtained to test for multi-exponential signal decay.All images were diagnostic and of high quality. Mean diffusion values were (230 +/- 83) x 10(-6) mm(2)/s in the vertebral bodies, (1645 +/- 213) x 10(-6) mm(2)/s in the nuclei pulposi, (837 +/- 318) x 10(-6) mm(2)/s in the annuli fibrosi and ranged from 1019 x 10(-6) mm(2)/s to 1972 x 10(-6) mm(2)/s in benign compression fractures. The mean relative intra-participant variation of mean diffusivity among different vertebral segments (T10-L5) was 2.97%, whereas the relative difference in mean diffusivity among participants was 7.41% (P <.0001). The estimated measurement precision was <2%. A bi-exponential diffusion attenuation was found only in vertebral bodies.Line scan diffusion imaging is a robust and reliable method for imaging the spinal column. It does not suffer as strongly from susceptibility artifacts as does echo-planar imaging and is less susceptible to patient motion than are other multi-shot techniques. The different contributions from the water and fat fractions need to be considered in diffusion-weighted imaging of the vertebral bodies.

    View details for Web of Science ID 000180962400004

    View details for PubMedID 12533319

  • Diffusion-tensor imaging of cognitive performance BRAIN AND COGNITION Moseley, M., Bammer, R., Illes, J. 2002; 50 (3): 396-413

    Abstract

    MR methods have for some years been used to assess cognitive performance. Recently, studies have shown that diffusion-tensor imaging (DTI), which provides noninvasive maps of microscopic structural information of oriented tissue in vivo, is finding utility in studies of cognition in the normal and abnormal aging population. These studies suggest that water proton nonrandom, anisotropic diffusion measured by DTI is highly sensitive to otherwise subtle disease processes not easily seen with conventional MRI tissue contrast mechanisms and raises new issues of the role of MR in assessing cognitive potential.

    View details for Web of Science ID 000180058100006

    View details for PubMedID 12480486

  • Local staging of pancreatic carcinoma with multi-detector row CT: Use of curved planar reformations initial experience RADIOLOGY Prokesch, R. W., Chow, L. C., Beaulieu, C. F., Nino-Murcia, M., Mindelzun, R. E., Barnmer, R., Huang, J., Jeffrey, R. B. 2002; 225 (3): 759-765

    Abstract

    To evaluate the utility of curved planar reformations compared with standard transverse images in the assessment of pancreatic tumors.Forty-three patients suspected of having pancreatic tumors underwent contrast material-enhanced biphasic multi-detector row computed tomography (CT). Curved planar reformations were generated along the pancreatic duct, common bile duct, and major mesenteric vessels. Three blinded independent readers assessed the curved planar reformations and transverse images separately for the presence of tumor, resectability, and vascular involvement. The results were compared with those of a consensus panel who evaluated the curved planar reformations and transverse images together along with clinical data and surgical findings.Of 43 patients, 20 had pancreatic malignancies as judged by the consensus panel and proven at biopsy and/or clinical follow-up. For tumor detection, transverse images and curved planar reformations had an average sensitivity of 95.0% and 98.4% (P >.05), respectively, and an average specificity of 90.9% and 91.3% (P >.05), respectively. For tumor resectability, transverse images and curved planar reformations had an average sensitivity of 85.7% and 71.4% (P >.05), respectively, and an average specificity of 85.2% and 84.3% (P >.05), respectively. Average interpretation time was 6.4 minutes with transverse images and 4.1 minutes with curved planar reformations.Curved planar reformations are equivalent to transverse images in the detection of pancreatic tumors and determination of surgical resectability.

    View details for DOI 10.1148/radiol.2253010886

    View details for Web of Science ID 000179420800020

    View details for PubMedID 12461258

  • Isoattenuating pancreatic adenocarcinoma at multi-detector row CT: Secondary signs RADIOLOGY Prokesch, R. W., Chow, L. C., Beaulieu, C. F., Bammer, R., Jeffrey, R. B. 2002; 224 (3): 764-768

    Abstract

    To assess the frequency of isoattenuating pancreatic adenocarcinoma with multi-detector row computed tomography (CT) and determine whether there are specific secondary signs that aid in detection.Fifty-three patients with pancreatic adenocarcinoma underwent contrast material-enhanced biphasic multi-detector row CT with curved planar reformation. Tumors were initially deemed isoattenuating or hypoattenuating to normal pancreatic parenchyma on the basis of visual inspection, and the degree of attenuation was confirmed by calculating the mean attenuation differences between normal pancreatic parenchyma and tumor (tumor-pancreas contrast) during the pancreatic phase. Indirect signs of pancreatic tumor were tabulated in patients with an isoattenuating tumor.Of the 53 patients, six (11%) had isoattenuating tumors with a mean tumor-pancreas contrast of 9.25 HU +/- 11.3 during the pancreatic phase and 4.15 HU +/- 8.5 during the portal venous phase. The secondary signs of pancreatic tumor in these six patients included an interrupted pancreatic duct (n = 5), dilated biliary and pancreatic ducts (n = 1), atrophic distal pancreatic parenchyma (n = 3), and mass effect and/or convex contour abnormality (n = 3). The mean tumor-pancreas contrast for the remaining 47 patients was 74.76 HU +/- 35.61 during the pancreatic phase.With no visible tumor-pancreas contrast for isoattenuating tumors, indirect signs such as mass effect, atrophic distal parenchyma, and an interrupted duct sign are important indicators for the presence of tumor.

    View details for DOI 10.1148/radiol.2243011284

    View details for Web of Science ID 000177621700021

    View details for PubMedID 12202711

  • Diffusion-weighted imaging of the spinal cord: Interleaved echo-planar imaging is superior to fast spin-echo JOURNAL OF MAGNETIC RESONANCE IMAGING Bammer, R., Augustin, M., Prokesch, R. W., Stollberger, R., Fazekas, F. 2002; 15 (4): 364-373

    Abstract

    To compare and evaluate two novel diffusion-weighted sequences, based either on fast spin-echo (FSE) or interleaved echo-planar imaging (EPI) methods, as potential tools for investing spinal cord abnormalities.Following recent improvements, both interleaved EPI (IEPI) and FSE techniques could be alternative approaches for rapid diffusion-weighted imaging (DWI). Therefore, a navigated diffusion-weighted multishot FSE sequence and a fat-suppressed navigated diffusion-weighted IEPI sequence with local shimming capabilities were tested. Both methods were compared in a consecutive series of five healthy volunteers and five patients with suspected intramedullary lesions. The sequences were graded qualitatively as either superior, inferior, or equal in quality, and also quantitatively by measuring the amount of ghosting artifacts in the background. Quantitative measurements of the diffusion coefficients within the spine were included.The overall image quality of IEPI was superior to FSE. Two out of five FSE scans were rated with poor image quality, whereas all IEPI scans were of sufficient quality. The ghosting levels ranged from approximately 3.3% to 6.2% for IEPI and from approximately 7.5% to 18.9% for FSE. Diffusion coefficients measured in healthy volunteers were similar for both IEPI and FSE, but showed higher fluctuations with the FSE technique.Despite potential advantages of FSE, the IEPI technique is preferable for DWI applications in the spinal cord.

    View details for DOI 10.1002/jmri.10075

    View details for Web of Science ID 000174759700002

    View details for PubMedID 11948825

  • CT angiography of the subclavian artery: Utility of curved planar reformations JOURNAL OF COMPUTER ASSISTED TOMOGRAPHY Prokesch, R. W., Coulam, C. H., Chow, L. C., Bammer, R., Rubin, G. D. 2002; 26 (2): 199-201

    Abstract

    Despite advances in the diagnosis and treatment of peripheral vascular occlusive disease, an ever-aging population continues to provide scores of new cases requiring medical care. While traditional angiography has been the mainstay of diagnosis for many years, newer, less invasive techniques such as CT angiography with three-dimensional reformation are rapidly establishing themselves as first-line diagnostic modalities. We present a case of severe left subclavian artery stenosis that demonstrates the utility of curved planar reformation in providing a concise visual summary of the pertinent anatomy and abnormalities.

    View details for Web of Science ID 000174453500008

    View details for PubMedID 11884774

  • Diffusion imaging in multiple sclerosis NEUROIMAGING CLINICS OF NORTH AMERICA Bammer, R., Fazekas, F. 2002; 12 (1): 71-?

    View details for Web of Science ID 000174929600006

    View details for PubMedID 11998254

  • T-1 maps from shifted spin echoes and stimulated echoes MAGNETIC RESONANCE IN MEDICINE Ropele, S., Bammer, R., Stollberger, R., Fazekas, F. 2001; 46 (6): 1242-1245

    Abstract

    A new pulse sequence for fast multislice T1 mapping is presented. This method is based on calculating T1 from spin echo (SE) and stimulated echo (STE) images obtained with different degrees of T1 weighting, and uses the interleaved acquisition scheme of the fast phase acquisition of composite echoes (FastPACE) technique. In contrast to the FastPACE technique, the two echoes are sampled separately. Experimental comparisons confirm that the new sequence layout overcomes most of the FastPACE restrictions, such as its motion sensitivity and the need for a fully complex data set. Moreover, this method offers a higher precision for long T1 values and a further reduction of acquisition time.

    View details for Web of Science ID 000172432900027

    View details for PubMedID 11746593

  • Novel imaging technologies in the assessment of cerebral ageing and vascular dementia ADVANCES IN DEMENTIA RESEARCH Fazekas, F., Ropele, S., Bammer, R., Kapeller, P., Stollberger, R., Schmidt, R. 2000: 45-52
  • Novel imaging technologies in the assessment of cerebral ageing and vascular dementia JOURNAL OF NEURAL TRANSMISSION-SUPPLEMENT Fazekas, F., Ropele, S., Bammer, R., Kapeller, P., Stollberger, R., Schmidt, R. 2000: 45-52

    Abstract

    Introduction of magnetic resonance imaging (MRI) has opened new possibilities for detecting age-related brain tissue changes. The majority of these abnormalities consists of hyperintense foci in the deep and subcortical white matter probably related to microvascular disturbances and of signal hyperintensities around the lateral ventricles. It has also been suggested that these abnormalities may contribute to the development of cognitive impairment. The correlation between age-related signal abnormalities on conventional MRI and neuropsychologic dysfunction is limited, however, and a threshold beyond which such a relation may come into existence has not yet been defined. Poor tissue characterisation by conventional MRI may be one explanation. Therefore, new pulse sequences are expected not only to provide a higher lesion contrast such as the fluid attenuated inversion recovery (FLAIR) technique but also to offer new insights concerning the composition of incidental brain lesions. In this context both magnetisation transfer imaging (MTI) and diffusion weighted imaging (DWI) may serve to gain information about the integrity of cell membranes and organelles and the preservation of axons and fibre tracts. We will review the technical background of these recently developed MR sequences and their first applications to age-associated brain abnormalities.

    View details for Web of Science ID 000088322100008

    View details for PubMedID 10961417

  • Forearm composition contributes to differences in reactive hyperaemia between healthy men and women EUROPEAN JOURNAL OF CLINICAL INVESTIGATION Wascher, T. C., Bammer, R., Stollberger, R., Bahadori, B., Wallner, S., Toplak, H. 1998; 28 (3): 243-248

    Abstract

    Post-ischaemic reactive hyperaemia in the forearm has been suggested as a marker of resistance vessel function. The contribution of forearm composition to the kinetics of reactive hyperaemia is largely unknown. The body composition of men and women differs in that women have a higher body fat content and less lean body mass.In the present study, we investigated whether the kinetics of reactive hyperaemia in the forearm in 14 healthy subjects (seven men and seven women) show gender-specific differences and whether forearm composition contributes to such differences.Peak reactive hyperaemic flow as well as 1-min-flow debt repayment (measured by venous occlusion plethysmography) were significantly higher in male than in female study participants. This difference was explained to > 60% by gender-specific differences in forearm relative muscle mass (as determined by magnetic resonance imaging). The half-life of the reactive hyperaemic response, on the other hand, was not different between men and women and did not show an association with forearm muscle.Our results demonstrate that forearm composition must be considered if peak reactive hyperaemic or flow debt repayment is used as a target, and that dynamic measurements of the reactive hyperaemic process are more suitable to describe the function of resistance arteries than single-point observations.

    View details for Web of Science ID 000072852500012

    View details for PubMedID 9568471

  • Assessing the differences of reactive hyperemic flow due to the contribution of forearm composition using automated tissue segmentation from MR scans and venous occlusion strain gauge plethysmography PHYSIOLOGY AND FUNCTION FROM MULTIDIMENSIONAL IMAGES - MEDICAL IMAGING 1998 Bammer, R., Wascher, T., Pedevilla, M., Wach, P., Ebner, F., Stollberger, R. 1998; 3337: 119-130
  • Assessment of dynamic Magnetic Resonance images using an independent workstation for determination, visualization and quantitative analysis of pharmacokinetic and physiological parameters PHYSIOLOGY AND FUNCTION FROM MULTIDIMENSIONAL IMAGES - MEDICAL IMAGING 1998 Bammer, R., Pedevilla, M., Ropele, S., Wach, P., Ebner, F., Stollberger, R. 1998; 3337: 366-376
  • Improving the diagnostic reliability of dynamic MR-mammography - ROI vs. pixel-by-pixel evaluation CAR '97 - COMPUTER ASSISTED RADIOLOGY AND SURGERY Pedevilla, M., Stollberger, R., Bammer, R., Schmidt, F., Wach, P., Ebner, F. 1997; 1134: 117-122
  • MRSpy: An independent workstation for determination, visualization and quantitative analysis of pharmacokinetic and physiological parameters using dynamic MR data sets CAR '97 - COMPUTER ASSISTED RADIOLOGY AND SURGERY Bammer, R., Stollberger, R., Pedevilla, M., Ropele, S., Ebner, F., Wach, P. 1997; 1134: 111-116
  • Automated tissue classification of extremities using knowledge-based segmentation of MR images CAR '97 - COMPUTER ASSISTED RADIOLOGY AND SURGERY Bammer, R., Stollberger, R., Pedevilla, M., Ropele, S., Ebner, F., Wach, P. 1997; 1134: 252-258

Conference Proceedings


  • Higher rCBV Values In The PWI/DWI Mismatch Area Predict Favorable Clinical Outcome In Acute Ischemic Stroke Lee, J., Lansberg, M. G., Mlynash, M., Straka, M., Bammer, R., Olivot, J., Kemp, S., Albers, G. W. LIPPINCOTT WILLIAMS & WILKINS. 2011: E112-E112
  • Worse Stroke Outcome In Atrial Fibrillation Links To More Severe Hypoperfusion Tu, H. T., Campbell, B. C., Christensen, S., De Silva, D. A., Parsons, M. W., Churilov, L., Olivot, J., Lansberg, M. G., Mlynash, M., Straka, M., Bammer, R., Albers, G. W., Desmond, P. M., Donnan, G. A., Davis, S. M. LIPPINCOTT WILLIAMS & WILKINS. 2011: E119-E119
  • The Combination Of Reperfusion And Recanalization Predicts Favorable Outcome Better Than Reperfusion Or Recanalization Alone In Target Mismatch Patients Lee, J., Lansberg, M. G., Mlynash, M., De Silva, D. A., Christensen, S., Straka, M., Campbell, B. C., Bammer, R., Olivot, J., Desmond, P., Donnan, G. A., Davis, S. M., Albers, G. W. LIPPINCOTT WILLIAMS & WILKINS. 2011: E66-E67
  • Does Presence of Arterial Obstruction Influence the Treatment Effect of Intravenous tPA Over Placebo in the 3-6 Hour Time Window? De Silva, D. A., Churilov, L., Olivot, J. M., Christensen, S., Lansberg, M. G., Mlynash, M., Straka, M., Campbell, B. C., Bammer, R., Albers, G. W., Davis, S. M., Donnan, G. A. LIPPINCOTT WILLIAMS & WILKINS. 2010: E207-E208
  • Diagnostic Accuracy of MRI in Spontaneous Intra-cerebral Hemorrhage (DASH): Initial Results Wijman, C. A., Snider, R. W., Venkatasubramanian, C., Caulfield, A. F., Buckwalter, M., Eyngorn, I., Fischbein, N., Gean, A., Schwartz, N., Lansberg, M., Mlynash, M., Kemp, S., Thai, D., Narayana, R. K., Marks, M., Bammer, R., Moseley, M., Albers, G. W. LIPPINCOTT WILLIAMS & WILKINS. 2010: E210-E211
  • MRI Profile of Blood-Brain Barrier Injury and Perihematomal Edema Following Acute Spontaneous Intracerebral Hemorrhage Aksoy, D., Bammer, R., Venkatasubramanian, C., Narayana, R., Eyngorn, I., Snider, R. W., Fischbein, N. J., Gupta, S. N., Mlynash, M., Wijman, C. A. LIPPINCOTT WILLIAMS & WILKINS. 2010: E312-E312
  • SENSE Diffusion-weighted Imaging Improves Diagnostic Sensitivity in Acute Ischemic Stroke Schwartz, N. E., Newbould, R. D., Skare, S., Zaharchuk, G., Mlynash, M., Olivot, J., Lansberg, M. G., Eyngorn, I., Thai, D., Albers, G. W., Bammer, R. LIPPINCOTT WILLIAMS & WILKINS. 2009: E115-E115
  • Who is most likely to benefit from tPA? The perfusion-diffusion and clinical-diffusion mismatch models disagree Lansberg, M. G., Thijs, V. N., Bammer, R., Wechsler, L. R., O'Donnell, M. J., Olshen, R. A., Wijman, C. A., Kemp, S. M., Albers, G. W. LIPPINCOTT WILLIAMS & WILKINS. 2005: 437-437

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