Bio

Academic Appointments


Honors & Awards


  • Fellow, American Institute for Medical and Biological Engineering (2009)
  • Fellow, International Society for Magnetic Resonance in Medicine (2008)
  • Fellow, Canadian College of Physicists in Medicine (1989)

Professional Education


  • PDF, Univ. of Calif. at San Francisco, Radiology (1986)
  • PhD, University of Toronto, Medical Biophysics (1982)
  • MSc, Stanford University, Electrical Engineering (1977)
  • BASc, University of Toronto, Engineering Science (1976)

Research & Scholarship

Current Research and Scholarly Interests


I am interested in the technology and applications of Magnetic Resonance Imaging (MRI).

I have ongoing research projects involving the basic technology of MRI (e.g. insertable gradient coils and RF components), biophysical measurements using MR (e.g., combined T1 and T2 mapping using efficient imaging sequences), basic science applications of MR (e.g., in-vivo detection rare cell populations using MRI and the use of MR to longitudinally monitor tumor growth deep within tissue starting from a single cell), and clinical applications, especially in cardiovascular disease.

I am presently interested in developing and using in-vivo ultra-high field (e.g. 7 Tesla) Magnetic Resonance techniques to study important human diseases. The increased sensitivity and enhanced contrast mechanisms at these high magnetic field strengths should provide insight to unsolved problems, especially in neuroscience and cancer.

Teaching

2013-14 Courses


Publications

Journal Articles


  • Efficient bloch-siegert B1 (+) mapping using spiral and echo-planar readouts. Magnetic resonance in medicine Saranathan, M., Khalighi, M. M., Glover, G. H., Pandit, P., Rutt, B. K. 2013; 70 (6): 1669-1673

    Abstract

    The Bloch-Siegert (B-S) B(1) (+) mapping technique is a fast, phase-based method that is highly SAR limited especially at 7T, necessitating the use of long repetition times. Spiral and echo-planar readouts were incorporated in a gradient-echo based B-S sequence to reduce specific absoprtion rate (SAR) and improve its scan efficiency. A novel, numerically optimized 4 ms B-S off-resonant pulse at + 1960 Hz was used to increase sensitivity and further reduce SAR compared with the conventional 6 ms Fermi B-S pulse. Using echo-planar and spiral readouts, scan time reductions of 8-16 were achieved. By reducing the B-S pulse width by a factor of 1.5, SAR was reduced by a factor of 1.5 and overall sensitivity was increased by a factor of 1.33 due to the nearly halved resonance offset of the new B-S pulse. This was validated on phantoms and volunteers at 7 T. Magn Reson Med, 2013. 2013 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.24599

    View details for PubMedID 23401024

  • Atherosclerosis Imaging and the Canadian Atherosclerosis Imaging Network CANADIAN JOURNAL OF CARDIOLOGY Tardif, J., Spence, J. D., Heinonen, T. M., Moody, A., Pressacco, J., Frayne, R., L'Allier, P., Chow, B. J., Friedrich, M., Black, S. E., Fenster, A., Rutt, B., Beanlands, R. 2013; 29 (3): 297-303

    Abstract

    Atherosclerosis exacts a large toll on society in the form of cardiovascular morbidity, mortality, and resource use and is exacerbated by the epidemics of obesity and diabetes. Consequently, there is a critical need for more-effective methods of diagnosis, treatment, and prevention of the complications of atherosclerosis. Careful and well-conducted large population studies are needed in order to truly understand the natural history of the disease, its imaging biomarkers, and their links to patient outcomes. The Canadian Atherosclerosis Imaging Network (CAIN) is a unique research network funded by the Canadian Institutes of Health Research and the Canada Foundation for Innovation and designed to address these needs and to enable large population-based imaging studies. The central objective of CAIN is to move innovations in imaging toward their broad application in clinical research and clinical practice for the improved evaluation of cardiac and neurologic vascular disease. CAIN is established as an international resource for studying the natural history, progression, and regression of atherosclerosis, as well as novel therapeutic interventions aimed at atherosclerosis. The network represents Canada's leading atherosclerosis imaging experts, embodying both basic imaging science and clinical imaging research. The network is improving methods of detection and treatment of atherosclerosis and, through a better understanding of the underlying disease itself, improving strategies for disease prevention. The benefits are expected to appear in the next 2 to 3 years. CAIN will drive innovation in imaging technology within the field of cardiology and neurology and improve health outcomes in Canada and worldwide.

    View details for DOI 10.1016/j.cjca.2012.09.017

    View details for Web of Science ID 000317576000006

    View details for PubMedID 23245557

  • Flip angle mapping with the accelerated 3D look-locker sequence. Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine Wade, T., McKenzie, C. A., Rutt, B. K. 2013

    Abstract

    PURPOSE: A new approach to mapping the flip angle quickly and efficiently in 3D based on the Look-Locker technique is presented. METHODS: We modified the accelerated 3D Look-Locker T1 measurement technique to allow rapid measurement of flip angle. By removing the inversion pulses and interleaving two radio frequency pulses with different amplitude, it is possible to fit directly for the true flip angle using a reduced number of parameters. This technique, non-inverted Double Angle Look-Locker, allows quick and efficient mapping of the flip angle in 3D. RESULTS: non-inverted Double Angle Look-Locker is validated in vitro against the actual flip angle imaging technique for a range of flip angles and T1 values. Flip angle maps produced with non-inverted Double Angle Look-Locker can be acquired in approximately 1 min, and are accurate to within 10% of the actual flip angle imaging measurement. It is shown to accurately measure the excited slab profile of several different pulses. An application to correcting in vivo DESPOT T1 data is presented. CONCLUSION: The presented technique is a rapid method for mapping flip angles across a 3D volume, capable of producing a flip angle map in approximately 1 min. Magn Reson Med, 2013. 2013 Wiley Periodicals, Inc.

    View details for PubMedID 23463449

  • Does iron inhibit calcification during atherosclerosis? FREE RADICAL BIOLOGY AND MEDICINE Rajendran, R., Ren Minqin, M. Q., Ronald, J. A., Rutt, B. K., Halliwell, B., Watt, F. 2012; 53 (9): 1675-1679

    Abstract

    Oxidative stress has been implicated in the etiology of atherosclerosis and even held responsible for plaque calcification. Transition metals such as iron aggravate oxidative stress. To understand the relation between calcium and iron in atherosclerotic lesions, a sensitive technique is required that is quantitatively accurate and avoids isolation of plaques or staining/fixing tissue, because these processes introduce contaminants and redistribute elements within the tissue. In this study, the three ion-beam techniques of scanning transmission ion microscopy, Rutherford backscattering spectrometry, and particle-induced X-ray emission have been combined in conjunction with a high-energy (MeV) proton microprobe to map the spatial distribution of the elements and quantify them simultaneously in atherosclerotic rabbit arteries. The results show that iron and calcium within the atherosclerotic lesions exhibit a highly significant spatial inverse correlation. It may be that iron accelerates the progression of atherosclerotic lesion development, but suppresses calcification. Alternatively, calcification could be a defense mechanism against atherosclerotic progression by excluding iron.

    View details for DOI 10.1016/j.freeradbiomed.2012.07.014

    View details for Web of Science ID 000310660400005

    View details for PubMedID 22940067

  • Small-tip-angle spokes pulse design using interleaved greedy and local optimization methods MAGNETIC RESONANCE IN MEDICINE Grissom, W. A., Khalighi, M., Sacolick, L. I., Rutt, B. K., Vogel, M. W. 2012; 68 (5): 1553-1562

    Abstract

    Current spokes pulse design methods can be grouped into methods based either on sparse approximation or on iterative local (gradient descent-based) optimization of the transverse-plane spatial frequency locations visited by the spokes. These two classes of methods have complementary strengths and weaknesses: sparse approximation-based methods perform an efficient search over a large swath of candidate spatial frequency locations but most are incompatible with off-resonance compensation, multifrequency designs, and target phase relaxation, while local methods can accommodate off-resonance and target phase relaxation but are sensitive to initialization and suboptimal local cost function minima. This article introduces a method that interleaves local iterations, which optimize the radiofrequency pulses, target phase patterns, and spatial frequency locations, with a greedy method to choose new locations. Simulations and experiments at 3 and 7 T show that the method consistently produces single- and multifrequency spokes pulses with lower flip angle inhomogeneity compared to current methods.

    View details for DOI 10.1002/mrm.24165

    View details for Web of Science ID 000310062300022

    View details for PubMedID 22392822

  • Hippocampal CA1 apical neuropil atrophy and memory performance in Alzheimer's disease NEUROIMAGE Kerchner, G. A., Deutsch, G. K., Zeineh, M., Dougherty, R. F., Saranathan, M., Rutt, B. K. 2012; 63 (1): 194-202

    Abstract

    Memory loss is often the first and most prominent symptom of Alzheimer's disease (AD), coinciding with the spread of neurofibrillary pathology from the entorhinal cortex (ERC) to the hippocampus. The apical dendrites of hippocampal CA1 pyramidal neurons, in the stratum radiatum/stratum lacunosum-moleculare (SRLM), are among the earliest targets of this pathology, and atrophy of the CA1-SRLM is apparent in postmortem tissue from patients with mild AD. We previously demonstrated that CA1-SRLM thinning is also apparent in vivo, using ultra-high field 7-Tesla (7T) MRI to obtain high-resolution hippocampal microstructural imaging. Here, we hypothesized that CA1-SRLM thickness would correlate with episodic memory performance among patients with mild AD. We scanned nine patients, using an oblique coronal T2-weighted sequence through the hippocampal body with an in-plane resolution of 220 ?m, allowing direct visual identification of subfields - dentate gyrus (DG)/CA3, CA2, CA1, and ERC - and hippocampal strata - SRLM and stratum pyramidale (SP). We present a novel semi-automated method of measuring stratal width that correlated well with manual measurements. We performed multi-domain neuropsychological evaluations that included three tests of episodic memory, yielding composite scores for immediate recall, delayed recall, and delayed recognition memory. Strong correlations occurred between delayed recall performance and the widths of CA1-SRLM (r(2)=0.69; p=0.005), CA1-SP (r(2)=0.5; p=0.034), and ERC (r(2)=0.62; p=0.012). The correlation between CA1-SRLM width and delayed recall lateralized to the left hemisphere. DG/CA3 size did not correlate significantly with any aspect of memory performance. These findings highlight a role for 7T hippocampal microstructural imaging in revealing focal structural pathology that correlates with the central cognitive feature of AD.

    View details for DOI 10.1016/j.neuroimage.2012.06.048

    View details for Web of Science ID 000308770300020

    View details for PubMedID 22766164

  • RF pulse optimization for Bloch-Siegert B-1(+) mapping MAGNETIC RESONANCE IN MEDICINE Khalighi, M. M., Rutt, B. K., Kerr, A. B. 2012; 68 (3): 857-862

    Abstract

    The Bloch-Siegert (B-S) method of B??? mapping has been shown to be fast and accurate, yet has high SAR and moderately long TE. These limitations can lengthen scan times and incur signal loss due to B(0) inhomogeneity, particularly at high field. The B-S method relies on applying a band-limited off-resonant B-S radiofrequency pulse to induce a B???-dependent frequency-shift for resonant spins. A method for optimizing the B-S radiofrequency pulse is presented here, which maximizes B-S B??? measurement sensitivity for a given SAR and T(2) . A 4-ms optimized pulse is shown to have 35% less SAR compared with the conventional 6-ms Fermi pulse while still improving B??? map angle-to-noise ratio by 22%. The optimized pulse performance is validated both in phantom and in vivo brain imaging at 7 T.

    View details for DOI 10.1002/mrm.23271

    View details for Web of Science ID 000308098100022

    View details for PubMedID 22144397

  • Deficient MWF mapping in multiple sclerosis using 3D whole-brain multi-component relaxation MRI NEUROIMAGE Kitzler, H. H., Su, J., Zeineh, M., Harper-Little, C., Leung, A., Krernenchutzky, M., Deoni, S. C., Rutt, B. K. 2012; 59 (3): 2670-2677

    Abstract

    Recent multiple sclerosis (MS) MRI research has highlighted the need to move beyond the lesion-centric view and to develop and validate new MR imaging strategies that quantify the invisible burden of disease in the brain and establish much more sensitive and specific surrogate markers of clinical disability. One of the most promising of such measures is myelin-selective MRI that allows the acquisition of myelin water fraction (MWF) maps, a parameter that is correlated to brain white matter (WM) myelination. The aim of our study was to apply the newest myelin-selective MRI method, multi-component Driven Equilibrium Single Pulse Observation of T1 and T2 (mcDESPOT) in a controlled clinical MS pilot trial. This study was designed to assess the capabilities of this new method to explain differences in disease course and degree of disability in subjects spanning a broad spectrum of MS disease severity. The whole-brain isotropically-resolved 3D acquisition capability of mcDESPOT allowed for the first time the registration of 3D MWF maps to standard space, and consequently a formalized voxel-based analysis of the data. This approach combined with image segmentation further allowed the derivation of new measures of MWF deficiency: total deficient MWF volume (DV) in WM, in WM lesions, in diffusely abnormal white matter and in normal appearing white matter (NAWM). Deficient MWF volume fraction (DVF) was derived from each of these by dividing by the corresponding region volume. Our results confirm that lesion burden does not correlate well with clinical disease activity measured with the extended disability status scale (EDSS) in MS patients. In contrast, our measurements of DVF in NAWM correlated significantly with the EDSS score (R2=0.37; p<0.001). The same quantity discriminated clinically isolated syndrome patients from a normal control population (p<0.001) and discriminated relapsing-remitting from secondary-progressive patients (p<0.05); hence this new technique may sense early disease-related myelin loss and transitions to progressive disease. Multivariate analysis revealed that global atrophy, mean whole-brain myelin water fraction and white matter atrophy were the three most important image-derived parameters for predicting clinical disability (EDSS). Overall, our results demonstrate that mcDESPOT-defined measurements in NAWM show great promise as imaging markers of global clinical disease activity in MS. Further investigation will determine if this measure can serve as a risk factor for the conversion into definite MS and for the secondary transition into irreversible disease progression.

    View details for DOI 10.1016/j.neuroimage.2011.08.052

    View details for Web of Science ID 000299494000066

    View details for PubMedID 21920444

  • Adiabatic RF pulse design for Bloch-Siegert B?1+ mapping. Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine Khalighi, M. M., Rutt, B. K., Kerr, A. B. 2012

    Abstract

    The Bloch-Siegert (B-S) B?1+ mapping method has been shown to be fast and accurate, yet it suffers from high Specific Absorption Rate (SAR) and moderately long echo time. An adiabatic RF pulse design is introduced here for optimizing the off-resonant B-S RF pulse to achieve more B-S B?1+ measurement sensitivity for a given pulse width. The extra sensitivity can be used for higher angle-to-noise ratio B?1+ maps or traded off for faster scans. Using numerical simulations and phantom experiments, it is shown that a numerically optimized 2-ms adiabatic B-S pulse is 2.5 times more efficient than a conventional 6-ms Fermi-shaped B-S pulse. The adiabatic B-S pulse performance is validated in a phantom, and in vivo brain B?1+ mapping at 3T and 7T are shown. Magn Reson Med, 2012. 2012 Wiley Periodicals, Inc.

    View details for PubMedID 23041985

  • Comparing the MRI Appearance of the Lymph Nodes and Spleen in Wild-Type and Immuno-Deficient Mouse Strains PLOS ONE Economopoulos, V., Noad, J. C., Krishnamoorthy, S., Rutt, B. K., Foster, P. J. 2011; 6 (11)

    Abstract

    The goal of this study was to investigate the normal MRI appearance of lymphoid organs in immuno-competent and immuno-deficient mice commonly used in research. Four mice from each of four different mouse strains (nude, NOG, C57BL/6, CB-17 SCID (SCID)) were imaged weekly for one month. Images were acquired with a 3D balanced steady state free precession (bSSFP) sequence. The volume of the lymph nodes and spleens were measured from MR images. In images of nude and SCID mice, lymph nodes sometimes contained a hyperintense region visible on MRI images. Volumes of the nodes were highly variable in nude mice. Nodes in SCID mice were smaller than in nude or C57Bl/6 mice (p<0.0001). Lymph node volumes changed slightly over time in all strains. The spleens of C57Bl/6 and nude mice were similar in size and appearance. Spleens of SCID and NOG mice were significantly smaller (p<0.0001) and abnormal in appearance. The MRI appearance of the normal lymph nodes and spleen varies considerably in the various mouse strains examined in this study. This is important to recognize in order to avoid the misinterpretation of MRI findings as abnormal when these strains are used in MRI imaging studies.

    View details for DOI 10.1371/journal.pone.0027508

    View details for Web of Science ID 000297350800056

    View details for PubMedID 22096586

  • Extended Graphical Model for Analysis of Dynamic Contrast-Enhanced MRI MAGNETIC RESONANCE IN MEDICINE Chen, H., Li, F., Zhao, X., Yuan, C., Rutt, B., Kerwin, W. S. 2011; 66 (3): 868-878

    Abstract

    Kinetic analysis with mathematical models has become increasingly important to quantify physiological parameters in computed tomography (CT), positron emission tomography (PET), and dynamic contrast-enhanced MRI (DCE-MRI). The modified Kety/Tofts model and the graphical (Patlak) model have been widely applied to DCE-MRI results in disease processes such as cancer, inflammation, and ischemia. In this article, an intermediate model between the modified Kety/Tofts and Patlak models is derived from a mathematical expansion of the modified Kety/Tofts model. Simulations and an in vivo experiment involving DCE-MRI of carotid atherosclerosis were used to compare the new extended graphical model with the modified Kety/Tofts model and the Patlak model. In our simulated circumstances and the carotid artery application, we found that the extended graphical model exhibited lower noise sensitivity and provided more accurate estimates of the volume transfer constant (K(trans)) and fractional plasma volume (v(p)) than the modified Kety/Tofts model for DCE-MRI acquisitions of total duration less than 100-300 s, depending on kinetic parameters. In comparison with the Patlak model, we found that the extended graphical model exhibited 74.4-99.8% less bias in estimates of K(trans). Thus, the extended graphical model may allow kinetic modeling of DCE-MRI results with shortened data acquisition periods, without sacrificing accuracy in estimates of K(trans) and v(p).

    View details for DOI 10.1002/mrm.22819

    View details for Web of Science ID 000293988000028

    View details for PubMedID 21394770

  • The Use of Cellular Magnetic Resonance Imaging to Track the Fate of Iron-Labeled Multipotent Stromal Cells after Direct Transplantation in a Mouse Model of Spinal Cord Injury MOLECULAR IMAGING AND BIOLOGY Gonzalez-Lara, L. E., Xu, X., Hofstetrova, K., Pniak, A., Chen, Y., McFadden, C. D., Martinez-Santiesteban, F. M., Rutt, B. K., Brown, A., Foster, P. J. 2011; 13 (4): 702-711

    Abstract

    The objective of this study was to track the fate of iron-labeled, multipotent stromal cells (MSC) after their direct transplantation into mice with spinal cord injuries using magnetic resonance imaging (MRI).Mice with spinal cord injuries received a direct transplant of (1) live MSC labeled with micron-sized iron oxide particles (MPIO); (2) dead, MPIO-labeled MSC; (3) unlabeled MSC; or (4) free MPIO and were imaged at 3 T for 6 weeks after transplantation.Live, iron-labeled MSC appeared as a well-defined region of signal loss in the mouse spinal cord at the site of transplant. However, the MR appearance of dead, iron-labeled MSC and free iron particles was similar and persisted for the 6 weeks of the study.Iron-labeled stem cells can be detected and monitored in vivo after direct transplantation into the injured spinal cord of mice. However, the fate of the iron label is not clear. Our investigation indicates that caution should be taken when interpreting MR images after direct transplantation of iron-labeled cells.

    View details for DOI 10.1007/s11307-010-0393-y

    View details for Web of Science ID 000292310000011

    View details for PubMedID 20686855

  • In Vivo Single Scan Detection of Both Iron-Labeled Cells and Breast Cancer Metastases in the Mouse Brain Using Balanced Steady-State Free Precession Imaging at 1.5 T JOURNAL OF MAGNETIC RESONANCE IMAGING Ribot, E. J., Martinez-Santiesteban, F. M., Simedrea, C., Steeg, P. S., Chambers, A. F., Rutt, B. K., Foster, P. J. 2011; 34 (1): 231-238

    Abstract

    To simultaneously detect iron-labeled cancer cells and brain tumors in vivo in one scan, the balanced steady-state free precession (b-SSFP) imaging sequence was optimized at 1.5 T on mice developing brain metastases subsequent to the injection of micron-sized iron oxide particle-labeled human breast cancer cells.b-SSFP sequence parameters (repetition time, flip angle, and receiver bandwidth) were varied and the signal-to-noise ratio, contrast between the brain and tumors, and the number of detected iron-labeled cells were evaluated.Optimal b-SSFP images were acquired with a 26 msec repetition time, 35 flip angle, and bandwidth of 21 kHz. b-SSFP images were compared with T(2) -weighted 2D fast spin echo (FSE) and 3D spoiled gradient recalled echo (SPGR) images. The mean tumor-brain contrast-to-noise ratio and the ability to detect iron-labeled cells were the highest in the b-SSFP images.A single b-SSFP scan can be used to visualize both iron-labeled cells and brain metastases.

    View details for DOI 10.1002/jmri.22593

    View details for Web of Science ID 000292421800029

    View details for PubMedID 21698713

  • Dynamic and High-Resolution Metabolic Imaging of Hyperpolarized [1-C-13]-Pyruvate in the Rat Brain Using a High-Performance Gradient Insert MAGNETIC RESONANCE IN MEDICINE Mayer, D., Yen, Y., Takahashi, A., Josan, S., Tropp, J., Rutt, B. K., Hurd, R. E., Spielman, D. M., Pfefferbaum, A. 2011; 65 (5): 1228-1233

    Abstract

    Fast chemical shift imaging (CSI) techniques are advantageous in metabolic imaging of hyperpolarized compounds due to the limited duration of the signal amplification. At the same time, reducing the acquisition time in hyperpolarized imaging does not necessarily lead to the conventional penalty in signal-to-noise ratio that occurs in imaging at thermal equilibrium polarization levels. Here a high-performance gradient insert was used in combination with undersampled spiral CSI to increase either the imaging speed or the spatial resolution of hyperpolarized (13)C metabolic imaging on a clinical 3T MR scanner. Both a single-shot sequence with a total acquisition time of 125 ms and a three-shot sequence with a nominal in-plane resolution of 1.5 mm were implemented. The k-space trajectories were measured and then used during image reconstruction. The technique was applied to metabolic imaging of the rat brain in vivo after the injection of hyperpolarized [1-(13)C]-pyruvate. Dynamic imaging afforded the measurement of region-of-interest-specific time courses of pyruvate and its metabolic products, while imaging at high spatial resolution was used to better characterize the spatial distribution of the metabolite signals.

    View details for DOI 10.1002/mrm.22707

    View details for Web of Science ID 000289760800003

    View details for PubMedID 21500253

  • Controlled Self-Assembling of Gadolinium Nanoparticles as Smart Molecular Magnetic Resonance Imaging Contrast Agents ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Liang, G., Ronald, J., Chen, Y., Ye, D., Pandit, P., Ma, M. L., Rutt, B., Rao, J. 2011; 50 (28): 6283-6286

    View details for DOI 10.1002/anie.201007018

    View details for Web of Science ID 000292642600012

    View details for PubMedID 21618367

  • Biodistribution of Neural Stem Cells After Intravascular Therapy for Hypoxic-Ischemia STROKE Pendharkar, A. V., Chua, J. Y., Andres, R. H., Wang, N., Gaeta, X., Wang, H., De, A., Choi, R., Chen, S., Rutt, B. K., Gambhir, S. S., Guzman, R. 2010; 41 (9): 2064-2070

    Abstract

    Intravascular transplantation of neural stem cells represents a minimally invasive therapeutic approach for the treatment of central nervous system diseases. The cellular biodistribution after intravascular injection needs to be analyzed to determine the ideal delivery modality. We studied the biodistribution and efficiency of targeted central nervous system delivery comparing intravenous and intra-arterial (IA) administration of neural stem cells after brain ischemia.Mouse neural stem cells were transduced with a firefly luciferase reporter gene for bioluminescence imaging (BLI). Hypoxic-ischemia was induced in adult mice and reporter neural stem cells were transplanted IA or intravenous at 24 hours after brain ischemia. In vivo BLI was used to track transplanted cells up to 2 weeks after transplantation and ex vivo BLI was used to determine single organ biodistribution.Immediately after transplantation, BLI signal from the brain was 12 times higher in IA versus intravenous injected animals (P<0.0001). After IA injection, 69% of the total luciferase activity arose from the brain early after transplantation and 93% at 1 week. After intravenous injection, 94% of the BLI signal was detected in the lungs (P=0.004) followed by an overall 94% signal loss at 1 week, indicating lack of cell survival outside the brain. Ex vivo single organ analysis showed a significantly higher BLI signal in the brain than in the lungs, liver, and kidneys at 1 week (P<0.0001) and 2 weeks in IA (P=0.007).IA transplantation results in superior delivery and sustained presence of neural stem cells in the ischemic brain in comparison to intravenous infusion.

    View details for DOI 10.1161/STROKEAHA.109.575993

    View details for Web of Science ID 000281503000037

    View details for PubMedID 20616329

  • Imaging Iron-Loaded Mouse Glioma Tumors With bSSFP at 3 T MAGNETIC RESONANCE IN MEDICINE Bernas, L. M., Foster, P. J., Rutt, B. K. 2010; 64 (1): 23-31

    Abstract

    The poor prognosis for patients with high-grade glioma is partly due to the invasion of tumor cells into surrounding brain tissue. The goal of the present work was to develop a mouse model of glioma that included the potential to track cell invasion using MRI by labeling GL261 cells with iron oxide contrast agents prior to intracranial injection. Two types of agents were compared with several labeling schemes to balance between labeling with sufficient iron to curb the dilution effect of cell division while avoiding overwhelming signal loss that could prevent adequate visualization of tumor boundaries. The balanced steady-state free precession (bSSFP) pulse sequence was evaluated for its suitability for imaging glioma tumors and compared to T(2)-weighted two-dimensional fast spin echo (FSE) and T(1)-weighted spoiled gradient recalled echo (SPGR) at 3 T in terms of signal-to-noise ratio and contrast-to-noise ratio efficiencies. Ultimately, a three-dimensional bSSFP protocol consisting of a set of two images with complementary contrasts was developed, allowing excellent tumor visualization with minimal iron contrast when using pulse repetition time = 6 ms and alpha = 40 degrees, and extremely high sensitivity to iron when using pulse repetition time = 22 ms and alpha = 20 degrees. Quantitative histologic analysis validated that the strong signal loss seen in balanced steady state free precession pulse sequence images of iron-loaded tumors correlated well with the presence of iron.

    View details for DOI 10.1002/mrm.22210

    View details for Web of Science ID 000279301500004

    View details for PubMedID 20572128

  • Early Identification of Aortic Valve Sclerosis Using Iron Oxide Enhanced MRI JOURNAL OF MAGNETIC RESONANCE IMAGING Hamilton, A. M., Rogers, K. A., Belisle, A. J., Ronald, J. A., Rutt, B. K., Weissleder, R., Boughner, D. R. 2010; 31 (1): 110-116

    Abstract

    To test the ability of MION-47 enhanced MRI to identify tissue macrophage infiltration in a rabbit model of aortic valve sclerosis (AVS).The aortic valves of control and cholesterol-fed New Zealand White rabbits were imaged in vivo pre- and 48 h post-intravenous administration of MION-47 using a 1.5 Tesla (T) MR clinical scanner and a CINE fSPGR sequence. MION-47 aortic valve cusps were imaged ex vivo on a 3.0T whole-body MR system with a custom gradient insert coil and a three-dimensional (3D) FIESTA sequence and compared with aortic valve cusps from control and cholesterol-fed contrast-free rabbits. Histopathological analysis was performed to determine the site of iron oxide uptake.MION-47 enhanced the visibility of both control and cholesterol-fed rabbit valves in in vivo images. Ex vivo image analysis confirmed the presence of significant signal voids in contrast-administered aortic valves. Signal voids were not observed in contrast-free valve cusps. In MION-47 administered rabbits, histopathological analysis revealed iron staining not only in fibrosal macrophages of cholesterol-fed valves but also in myofibroblasts from control and cholesterol-fed valves.Although iron oxide labeling of macrophage infiltration in AVS has the potential to detect the disease process early, a macrophage-specific iron compound rather than passive targeting may be required.

    View details for DOI 10.1002/jmri.22008

    View details for Web of Science ID 000273336100014

    View details for PubMedID 20027578

  • Three-Dimensional Imaging and Quantification of Both Solitary Cells and Metastases in Whole Mouse Liver by Magnetic Resonance Imaging CANCER RESEARCH Townson, J. L., Ramadan, S. S., Simedrea, C., Rutt, B. K., MacDonald, I. C., Foster, P. J., Chambers, A. F. 2009; 69 (21): 8326-8331

    Abstract

    The metastatic cell population, ranging from solitary cells to actively growing metastases, is heterogeneous and unlikely to respond uniformly to treatment. However, quantification of the entire experimental metastatic cell population in whole organs is complicated by requirements of an imaging modality with the large field of view and high spatial resolution necessary to detect both single cells and metastases in the same organ. Thus, it is difficult to assess differential responses of these distinct metastatic populations to therapy. Here, we develop a magnetic resonance imaging (MRI) technique capable of quantifying the full population of metastatic cells in a secondary organ. B16F1 mouse melanoma cells were labeled with micron-sized iron oxide particles (MPIO) and injected into mouse liver via the mesenteric vein. Livers were removed immediately or at day 9 or 11, following doxorubicin or vehicle control treatment, and imaged using a 3T clinical magnetic resonance scanner and custom-built gradient coil. Both metastases (>200 microm) and MPIO-labeled single cells were detected and quantified from MR images as areas of hyperintensity or hypointensity (signal voids), respectively. We found that 1mg/kg doxorubicin treatment inhibited metastasis growth (n = 11 per group; P = 0.02, t test) but did not decrease the solitary metastatic cell population in the same livers (P > 0.05). Thus, the technique presented here is capable of quickly quantifying the majority of the metastatic cell population, including both growing metastases and solitary cells, in whole liver by MRI and can identify differential responses of growing metastases and solitary cells to therapy.

    View details for DOI 10.1158/0008-5472.CAN-09-1496

    View details for Web of Science ID 000271403000015

    View details for PubMedID 19843857

  • Atherosclerotic Plaque Progression in Carotid Arteries: Monitoring with High-Spatial-Resolution MR Imaging-Multicenter Trial RADIOLOGY Boussel, L., Arora, S., Rapp, J., Rutt, B., Huston, J., Parker, D., Yuan, C., Bassiouny, H., Saloner, D. 2009; 252 (3): 789-796

    Abstract

    To estimate the annualized rate of progression of vessel-wall volume in the carotid arteries in 160 patients by using magnetic resonance (MR) imaging and to establish the fraction of studies that have acceptable image quality. Materials and Methods: The study procedures and consent forms were reviewed and approved by each site's institutional review board. All U.S. study sites conducted all phases of this study in compliance with HIPAA requirements. Written consent was obtained from each participant. One hundred sixty patients with greater than 50% narrowing of the diameter of the carotid artery were recruited at six centers for prospective imaging of the carotid arteries at baseline and 1 year later by using high-spatial-resolution, 1.5-T MR imaging. Studies with unacceptable image quality were excluded. Quantitative changes in atheroma volume were measured on unenhanced T1-weighted images. A multiple linear regression analysis was used to correlate progression with several clinical factors, including statin therapy.All 160 patients completed both baseline and follow-up studies. Of these studies, 67.5% were deemed to have image quality that was acceptable for quantitative analysis. The causes of rejection were motion (46%), deep location of the carotid artery (22%), low bifurcation of the carotid artery (13%), and "other" (19%). The mean annual change in vessel-wall volume was 2.31% +/- 10.88 (standard deviation) (P = .014). At 1-year follow-up, vessel-wall volumes in patients not receiving statin therapy had increased faster compared with those in patients receiving statin therapy: 7.87% +/- 13.58% vs 1.14% +/- 9.9%, respectively (P = .029).Evaluation of results of a multicenter study indicates that quantitative evaluation of the progression of volume of extracranial carotid vessel walls is feasible with 1.5-T MR imaging despite limitations due to patient motion or habitus. In patients who had preexisting carotid disease, the rate of increase in vessel-wall volume was slower in patients receiving statin therapy.

    View details for DOI 10.1148/radiol.2523081798

    View details for Web of Science ID 000270809500021

    View details for PubMedID 19508991

  • Enzyme-Sensitive Magnetic Resonance Imaging Targeting Myeloperoxidase Identifies Active Inflammation in Experimental Rabbit Atherosclerotic Plaques CIRCULATION Ronald, J. A., Chen, J. W., Chen, Y., Hamilton, A. M., Rodriguez, E., Reynolds, F., Hegele, R. A., Rogers, K. A., Querol, M., Bogdanov, A., Weissleder, R., Rutt, B. K. 2009; 120 (7): 592-U92

    Abstract

    Inflammation undermines the stability of atherosclerotic plaques, rendering them susceptible to acute rupture, the cataclysmic event that underlies clinical expression of this disease. Myeloperoxidase is a central inflammatory enzyme secreted by activated macrophages and is involved in multiple stages of plaque destabilization and patient outcome. We report here that a unique functional in vivo magnetic resonance agent can visualize myeloperoxidase activity in atherosclerotic plaques in a rabbit model.We performed magnetic resonance imaging of the thoracic aorta of New Zealand White rabbits fed a cholesterol (n=14) or normal (n=4) diet up to 2 hours after injection of the myeloperoxidase sensor bis-5HT-DTPA(Gd) [MPO(Gd)], the conventional agent DTPA(Gd), or an MPO(Gd) analog, bis-tyr-DTPA(Gd), as controls. Delayed MPO(Gd) images (2 hours after injection) showed focal areas of increased contrast (>2-fold) in diseased wall but not in normal wall (P=0.84) compared with both DTPA(Gd) (n=11; P<0.001) and bis-tyr-DTPA(Gd) (n=3; P<0.05). Biochemical assays confirmed that diseased wall possessed 3-fold elevated myeloperoxidase activity compared with normal wall (P<0.01). Areas detected by MPO(Gd) imaging colocalized and correlated with myeloperoxidase-rich areas infiltrated by macrophages on histopathological evaluations (r=0.91, P<0.0001). Although macrophages were the main source of myeloperoxidase, not all macrophages secreted myeloperoxidase, which suggests that distinct subpopulations contribute differently to atherogenesis and supports our functional approach.The present study represents a unique approach in the detection of inflammation in atherosclerotic plaques by examining macrophage function and the activity of an effector enzyme to noninvasively provide both anatomic and functional information in vivo.

    View details for DOI 10.1161/CIRCULATIONAHA.108.813998

    View details for Web of Science ID 000269051900008

    View details for PubMedID 19652086

  • Nuclear Microscopy: A Novel Technique for Quantitative Imaging of Gadolinium Distribution within Tissue Sections MICROSCOPY AND MICROANALYSIS Rajendran, R., Ronald, J. A., Ye, T., Ren Minqin, M. Q., Chen, J. W., Weissleder, R., Rutt, B. K., Halliwell, B., Watt, F. 2009; 15 (4): 338-344

    Abstract

    All clinically-approved and many novel gadolinium (Gd)-based contrast agents used to enhance signal intensity in magnetic resonance imaging (MRI) are optically silent. To verify MRI results, a "gold standard" that can map and quantify Gd down to the parts per million (ppm) levels is required. Nuclear microscopy is a relatively new technique that has this capability and is composed of a combination of three ion beam techniques: scanning transmission ion microscopy, Rutherford backscattering spectrometry, and particle induced X-ray emission used in conjunction with a high energy proton microprobe. In this proof-of-concept study, we show that in diseased aortic vessel walls obtained at 2 and 4 h after intravenous injection of the myeloperoxidase-sensitive MRI agent, bis-5-hydroxytryptamide-diethylenetriamine-pentaacetate gadolinium, there was a time-dependant Gd clearance (2 h = 18.86 ppm, 4 h = 8.65 ppm). As expected, the control animal, injected with the clinically-approved conventional agent diethylenetriamine-pentaacetate gadolinium and sacrificed 1 week after injection, revealed no significant residual Gd in the tissue. Similar to known in vivo Gd pharmacokinetics, we found that Gd concentration dropped by a factor of 2 in vessel wall tissue in 1.64 h. Further high-resolution studies revealed that Gd was relatively uniformly distributed, consistent with random agent diffusion. We conclude that nuclear microscopy is potentially very useful for validation studies involving Gd-based magnetic resonance contrast agents.

    View details for DOI 10.1017/S1431927609090813

    View details for Web of Science ID 000268422000008

    View details for PubMedID 19575834

  • Predicting abdominal adipose tissue among women with familial partial lipodystrophy METABOLISM-CLINICAL AND EXPERIMENTAL Joy, T., Kennedy, B. A., Al-Attar, S., Rutt, B. K., Hegele, R. A. 2009; 58 (6): 828-834

    Abstract

    The objective of the study was to determine correlations between magnetic resonance imaging (MRI) measures of truncal adiposity (trunk fat percentage [TrF %(MRI)], visceral adipose tissue [VAT], and subcutaneous abdominal adipose tissue [SAT]), simple clinical measures (body mass index [BMI], waist circumference [WC], and waist-to-hip ratio [WHR]), and bioelectrical impedance analysis (BIA)-derived measures (total fat percentage [TF %] and TrF %(BIA)) in female patients with familial partial lipodystrophy (FPLD). Our secondary aim was to generate and cross-validate predictive equations for VAT and SAT using these simple clinical and BIA-derived variables. Measures of truncal adiposity were measured using 1.5-T MRI (VAT, SAT, and TrF %(MRI)) and Tanita (Tokyo, Japan) 8-electrode body composition analyzer BC-418 (TrF %(BIA)) in 13 female FPLD patients. Pearson correlation coefficients were determined among the various adiposity parameters (BMI, WC, WHR, SAT, VAT, TrF %(MRI), TrF %(BIA), and TF %). Equations to estimate VAT and SAT were determined among 6 of the 13 FPLD subjects using multilinear regression analysis, and the best equations were then cross-validated in the remaining 7 subjects. Variables entered into the model included age, BMI, WC, WHR, TrF %(BIA), and TF %. The TrF %(MRI) showed moderate correlation (r = 0.647, P = .02) with the TrF %(BIA), but the discrepancy between the 2 variables increased with increasing truncal adiposity. The strongest correlate for TrF %(MRI) was BMI (r = 0.886, P < .0001). Visceral adipose tissue was poorly associated with simple clinical measures of BMI, WC, and WHR, but was inversely correlated with TF %, TrF %(BIA), and SAT. The TF % was the strongest correlate for both SAT and VAT. Thus, the best regression equation for VAT included age, BMI, WC, and TF % (R(2) = 1.0), whereas that for SAT only included TF % (R(2) = 0.75). The corresponding standard error of the estimate for the predictive equations was approximately 0.03 % and 18.5 % of the mean value of VAT and SAT, respectively. In the cross-validation study, differences between predicted and observed values of SAT were larger than those of VAT. We conclude that, among female FPLD patients, (1) no simple clinical anthropometric measure correlates well with VAT, whereas BMI correlates well with SAT; (2) BIA measure of TF % most strongly correlated with both VAT and SAT; and (3) based on the cross-validation study, VAT but not SAT could be more reliably estimated using the regression equations derived.

    View details for DOI 10.1016/j.metabol.2009.03.001

    View details for Web of Science ID 000266430100013

    View details for PubMedID 19375764

  • Clinical field-strength MRI of amyloid plaques induced by low-level cholesterol feeding in rabbits BRAIN Ronald, J. A., Chen, Y., Bernas, L., Kitzler, H. H., Rogers, K. A., Hegele, R. A., Rutt, B. K. 2009; 132: 1346-1354

    Abstract

    Two significant barriers have limited the development of effective treatment of Alzheimer's disease. First, for many cases the aetiology is unknown and likely multi-factorial. Among these factors, hypercholesterolemia is a known risk predictor and has been linked to the formation of beta-amyloid plaques, a pathological hallmark this disease. Second, standardized diagnostic tools are unable to definitively diagnose this disease prior to death; hence new diagnostic tools are urgently needed. Magnetic resonance imaging (MRI) using high field-strength scanners has shown promise for direct visualization of beta-amyloid plaques, allowing in vivo longitudinal tracking of disease progression in mouse models. Here, we present a new rabbit model for studying the relationship between cholesterol and Alzheimer's disease development and new tools for direct visualization of beta-amyloid plaques using clinical field-strength MRI. New Zealand white rabbits were fed either a low-level (0.125-0.25% w/w) cholesterol diet (n = 5) or normal chow (n = 4) for 27 months. High-resolution (66 x 66 x 100 microm(3); scan time = 96 min) ex vivo MRI of brains was performed using a 3-Tesla (T) MR scanner interfaced with customized gradient and radiofrequency coils. Beta-amyloid-42 immunostaining and Prussian blue iron staining were performed on brain sections and MR and histological images were manually registered. MRI revealed distinct signal voids throughout the brains of cholesterol-fed rabbits, whereas minimal voids were seen in control rabbit brains. These voids corresponded directly to small clusters of extracellular beta-amyloid-positive plaques, which were consistently identified as iron-loaded (the presumed source of MR contrast). Plaques were typically located in the hippocampus, parahippocampal gyrus, striatum, hypothalamus and thalamus. Quantitative analysis of the number of histologically positive beta-amyloid plaques (P < 0.0001) and MR-positive signal voids (P < 0.05) found in cholesterol-fed and control rabbit brains corroborated our qualitative observations. In conclusion, long-term, low-level cholesterol feeding was sufficient to promote the formation of extracellular beta-amyloid plaque formation in rabbits, supporting the integral role of cholesterol in the aetiology of Alzheimer's disease. We also present the first evidence that MRI is capable of detecting iron-associated beta-amyloid plaques in a rabbit model of Alzheimer's disease and have advanced the sensitivity of MRI for plaque detection to a new level, allowing clinical field-strength scanners to be employed. We believe extension of these technologies to an in vivo setting in rabbits is feasible and that our results support future work exploring the role of MRI as a leading imaging tool for this debilitating and life-threatening disease.

    View details for DOI 10.1093/brain/awp031

    View details for Web of Science ID 000265950900022

    View details for PubMedID 19293239

  • Comparison of Gadofluorine-M and Gd-DTPA for Noninvasive Staging of Atherosclerotic Plaque Stability Using MRI CIRCULATION-CARDIOVASCULAR IMAGING Ronald, J. A., Chen, Y., Belisle, A. J., Hamilton, A. M., Rogers, K. A., Hegele, R. A., Misselwitz, B., Rutt, B. K. 2009; 2 (3): 226-234

    Abstract

    Inflammation and neovascularization play critical roles in the stability of atherosclerotic plaques. Whole-body quantitative assessment of these plaque features may improve patient risk-stratification for life-threatening thromboembolic events and direct appropriate intervention. In this report, we determined the utility of the MR contrast agent gadofluorine-M (GdF) for staging plaque stability and compared this to the conventional agent Gd-DTPA.Five control and 7 atherosclerotic rabbits were sequentially imaged after administration of Gd-DTPA (0.2 mmol/kg) and GdF (0.1 mmol/kg) using a T(1)-weighted pulse sequence on a 3-T MRI scanner. Diseased aortic wall could be distinguished from normal wall based on wall-to-muscle contrast-to-noise values after GdF administration. RAM-11 (macrophages) and CD-31 (endothelial cells) immunostaining of MR-matched histological sections revealed that GdF accumulation was related to the degree of inflammation at the surface of plaques and the extent of core neovascularization. Importantly, an MR measure of GdF accumulation at both 1 and 24 hours after injection but not Gd-DTPA at peak enhancement was shown to correlate with a quantitative histological morphology index related to these 2 plaque features.GdF-enhanced MRI of atherosclerotic plaques allows noninvasive quantitative information about plaque composition to be acquired at multiple time points after injection (within 1 and up to 24 hours after injection). This dramatically widens the imaging window for assessing plaque stability that is currently attainable with clinically approved MR agents, therefore opening the possibility of whole-body (including coronary) detection of unstable plaques in the future and potentially improved mitigation of cataclysmic cardiovascular events.

    View details for DOI 10.1161/CIRCIMAGING.108.826826

    View details for Web of Science ID 000266417400012

    View details for PubMedID 19808597

  • The In Vivo Diagnosis of Early-Stage Aortic Valve Sclerosis Using Magnetic Resonance Imaging in a Rabbit Model JOURNAL OF MAGNETIC RESONANCE IMAGING Hamilton, A. M., Rogers, K. A., Drangova, M., Khan, Z., Ronald, J. A., Rutt, B. K., MacLean, K. A., Lacefield, J. C., Boughner, D. R. 2009; 29 (4): 825-831

    Abstract

    To use magnetic resonance imaging (MRI) to identify and monitor early aortic valve sclerosis (AVS) induced by cholesterol feeding in rabbits. AVS is a highly prevalent disease process, affecting more than 25% of the population over age 65. A major obstacle to early stage medical management of AVS has been the lack of an objective noninvasive technique to identify its presence and monitor its progress.Retrospectively gated CINE fast spoiled gradient echo (fSPGR) images of aortic valve cusps were collected at 3-month intervals starting at 6 months using a 1.5 T MR scanner interfaced with a customized surface radiofrequency coil. At 16 months a subset of animals was sacrificed and excised cusps were examined with both high frequency ultrasound (US) and histopathological techniques to validate the MRI method.MR and US analysis identified significant thickening of diseased AV cusps when compared to control (P < 0.05). Histopathological analysis confirmed the presence of human-like AVS in diseased rabbit valves.Early AVS, exemplified by increased valve thickness, can be identified in vivo using high-resolution MRI.

    View details for DOI 10.1002/jmri.21729

    View details for Web of Science ID 000264650000011

    View details for PubMedID 19306405

  • Delta Relaxation Enhanced MR: Improving Activation-Specificity of Molecular Probes through R-1 Dispersion Imaging MAGNETIC RESONANCE IN MEDICINE Alford, J. K., Rutt, B. K., Scholl, T. J., Handler, W. B., Chronik, B. A. 2009; 61 (4): 796-802

    Abstract

    MR molecular imaging enables high-resolution, in vivo study of molecular processes frequently utilizing gadolinium-based probes that specifically bind to a particular biological molecule or tissue. While some MR probes are inactive when unbound and produce enhancement only after binding, the majority are less specific and cause enhancement in either state. Accumulation processes are then required to increase probe concentration in regions of the target molecule/tissue. Herein, a method is described for creating specificity for traditionally nonspecific probes. This method utilizes MR field-cycling methods to produce MRI contrast related to the dependence of R(1) upon magnetic field. It is shown that the partial derivative of R(1) with respect to magnetic field strength, R(1)', can be used as an unambiguous measure of probe binding. T(1)-weighted images and R(1)' images were produced for samples of albumin and buffer both enhanced with the albumin-binding agent Vasovist. For T(1) images, samples with low concentrations of Vasovist in an albumin solution could not be differentiated from samples with higher concentrations of Vasovist in buffer. Conversely, the R(1)' images showed high specificity to albumin. Albumin samples with a 10-microM concentration of Vasovist were enhanced over buffer samples containing up to 16 times more Vasovist.

    View details for DOI 10.1002/mrm.21933

    View details for Web of Science ID 000264499000006

    View details for PubMedID 19189292

  • Scan-rescan and intra-observer variability of magnetic resonance imaging of carotid atherosclerosis at 1.5 T and 3.0 T PHYSICS IN MEDICINE AND BIOLOGY Vidal, A., Bureau, Y., Wade, T., Spence, J. D., Rutt, B. K., Fenster, A., Parraga, G. 2008; 53 (23): 6821-6835

    Abstract

    Carotid atherosclerosis measurements for eight subjects at baseline and 14 +/- 2 days later were examined using 1.5 T and 3.0 T magnetic resonance imaging (MRI). A single observer blinded to field strength, subject and timepoint manually segmented carotid artery wall and lumen boundaries in randomized images in five measurement trials. Mean increases in the signal-to-noise ratios (SNR) for T1-weighted images acquired at 3.0 T compared to 1.5 T were 90% (scan) and 80% (rescan). Despite significantly improved SNR and contrast-to-noise ratios (CNR) for images acquired at 3.0 T, vessel wall volume (VWV) intra-observer variability was not significantly different using coefficients of variation (COV), and intraclass correlation coefficients (ICC). VWV interscan variability and consistency at both field strengths were not statistically different (1.5 T/3.0 T COV = 5.7%/7.8%, R(2) = 0.96 for 1.5 T and R(2) = 0.87 for 3.0 T). A two-way analysis of variance showed a VWV dependence on field strength but not scan timepoint. In addition, a paired t-test showed significant differences in VWV measured at 3.0 T as compared to 1.5 T. These results suggest that although images acquired at 1.5 T have lower SNR and CNR VWV, measurement variability was not significantly different from 3.0 T VWV and that VWV is field-strength dependent which may be an important consideration for longitudinal studies.

    View details for DOI 10.1088/0031-9155/53/23/011

    View details for Web of Science ID 000260859000011

    View details for PubMedID 19001690

  • Gleaning Multicomponent T-1 and T-2 Information From Steady-State Imaging Data MAGNETIC RESONANCE IN MEDICINE Deoni, S. C., Rutt, B. K., Arun, T., Pierpaoli, C., Jones, D. K. 2008; 60 (6): 1372-1387

    Abstract

    The driven-equilibrium single-pulse observation of T(1) (DESPOT1) and T(2) (DESPOT2) are rapid, accurate, and precise methods for voxelwise determination of the longitudinal and transverse relaxation times. A limitation of the methods, however, is the inherent assumption of single-component relaxation. In a variety of biological tissues, in particular human white matter (WM) and gray matter (GM), the relaxation has been shown to be more completely characterized by a summation of two or more relaxation components, or species, each believed to be associated with unique microanatomical domains or water pools. Unfortunately, characterization of these components on a voxelwise, whole-brain basis has traditionally been hindered by impractical acquisition times. In this work we extend the conventional DESPOT1 and DESPOT2 approaches to include multicomponent relaxation analysis. Following numerical analysis of the new technique, renamed multicomponent driven equilibrium single pulse observation of T(1)/T(2) (mcDESPOT), whole-brain multicomponent T(1) and T(2) quantification is demonstrated in vivo with clinically realistic times of between 16 and 30 min. Results obtained from four healthy individuals and two primary progressive multiple sclerosis (MS) patients demonstrate the future potential of the approach for identifying and assessing tissue changes associated with several neurodegenerative conditions, in particular those associated with WM.

    View details for DOI 10.1002/mrm.21704

    View details for Web of Science ID 000261225100014

    View details for PubMedID 19025904

  • Enhanced Cell Uptake of Superparamagnetic Iron Oxide Nanoparticles Functionalized with Dendritic Guanidines BIOCONJUGATE CHEMISTRY Martin, A. L., Bernas, L. M., Rutt, B. K., Foster, P. J., Gillies, E. R. 2008; 19 (12): 2375-2384

    Abstract

    Magnetic resonance imaging (MRI) is a powerful tool for the diagnosis of disease and the study of biological processes such as cancer metastasis and inflammation. Superparamagnetic iron oxide (SPIO) nanoparticles have been shown to be effective contrast agents for labeling cells to provide high sensitivity in MRI, but this sensitivity depends on the ability to label cells with sufficient quantities of SPIO, which can be challenging for nonphagocytic cells such as cancer cells. To address this issue, a novel cell-penetrating polyester dendron with peripheral guanidines was developed and conjugated to the surface of SPIO. The functionalized nanoparticles were characterized by transmission electron microscopy, infrared spectroscopy, and dynamic light scattering, and it was found that the surface functionalization reaction proceeded to completion and did not have any adverse effects on the SPIO. In GL261 mouse glioma cells, the dendritic guanidine exhibited remarkably similar cell-penetrating capabilities to the HIV-Tat(47-57) peptide for the transport of fluorescein, and when conjugated to SPIO, it provided significantly enhanced uptake in comparison with nanoparticles having no dendron or dendrons with hydroxyl or amine peripheries. This uptake led to substantial decreases in the transverse relaxation time (T(2)) of labeled cells relative to control cells. While the nanoparticles functionalized with dendritic guanidines exhibited somewhat greater toxicity than those functionalized with dendrons having hydroxyl or amine peripheries, they were still relatively nontoxic at the low concentrations required for labeling.

    View details for DOI 10.1021/bc800209u

    View details for Web of Science ID 000261767800012

    View details for PubMedID 19053308

  • Three-frequency RF coil designed for optimized imaging of hyperpolarized, C-13-labeled compounds MAGNETIC RESONANCE IN MEDICINE Hancu, I., Wood, S. J., Piel, J., Whitt, D. B., Fish, K. M., Rutt, B. K., Tropp, J., Dixon, W. T. 2008; 60 (4): 928-933

    Abstract

    Imaging exams involving hyperpolarized, (13)C-labeled compounds require novel RF coils for efficient signal utilization. While (13)C coils are required for mapping the spatial distribution of the hyperpolarized compounds, imaging/pulsing at different frequencies is also needed for scan setup steps prior to the image acquisition. Imaging/pulsing at the (1)H frequency is typically used for anatomical localization and shimming. Flip angle (FA) calibration, which is difficult or impossible to achieve at the (13)C frequency, can be accurately performed at the (23)Na frequency using the natural abundance signal that exists in any living tissue. We demonstrate here a single RF resonant structure that is capable of operating linearly at the (1)H and (23)Na frequencies for scan setup steps, and in quadrature at the (13)C frequency for imaging. Images at the three resonant frequencies of this coil are presented from an exam involving hyperpolarized (13)C compounds in vivo.

    View details for DOI 10.1002/mrm.21698

    View details for Web of Science ID 000259651200020

    View details for PubMedID 18816813

  • Comparison of B-mode ultrasound, 3-dimensional ultrasound, and magnetic resonance imaging measurements of carotid atherosclerosis JOURNAL OF ULTRASOUND IN MEDICINE Egger, M., Krasinski, A., Rutt, B. K., Fenster, A., Parraga, G. 2008; 27 (9): 1321-1334

    Abstract

    We compared the intraobserver and interscan variability of carotid atherosclerosis measured using B-mode ultrasound for quantifying intima media thickness (IMT), 3-dimensional ultrasound (3DUS) for quantifying vessel wall volume (VWV) and total plaque volume (TPV), and magnetic resonance imaging (MRI) for measuring VWV. We also evaluated the associations of these measurements and sample sizes required to detect specific changes in patients with moderate atherosclerosis.Ten patients were evaluated with B-mode ultrasound, MRI, and 3DUS twice within 14 +/- 2 days. Measurements of IMT, MRI VWV, 3DUS VWV, and 3DUS TPV were performed by single observers using manual (VWV and TPV) and semiautomated (IMT) segmentation.Intraobserver coefficients of variation were 3.4% (IMT), 4.7% (3DUS VWV), 6.5% (MRI VWV), and 23.9% (3DUS TPV). Interscan coefficients of variation were 8.1% (MRI VWV), 8.9% (IMT), 13.5% (3DUS VWV), and 46.6% (3DUS TPV). Scan-rescan linear regressions were significant for 3DUS TPV (R(2) = 0.57), 3DUS VWV (R(2) = 0.59), and IMT (R(2) = 0.75) and significantly different (P < .05) for MRI VWV (R(2) = 0.87).B-mode ultrasound-derived IMT provided the highest intraobserver and interscan reproducibility. Three-dimensional measurements of VWV derived from 3DUS and MRI provided both high sensitivity and high intraobserver and interscan reliability.

    View details for Web of Science ID 000258853200008

    View details for PubMedID 18716142

  • Ex-vivo cellular MRI with b-SSFP: quantitative benefits of 3 T over 1.5 T MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE Ramadan, S. S., Heyn, C., MacKenzie, L. T., Chambers, A. F., Rutt, B. K., Foster, P. J. 2008; 21 (4): 251-259

    Abstract

    The use of MRI with iron-based magnetic nanoparticles for imaging cells is a rapidly growing field of research. We have recently reported that single iron-labeled cells could be detected, as signal voids, in vivo in mouse brains using a balanced steady-state free precession imaging sequence (b-SSFP) and a customized microimaging system at 1.5 T.In the current study we assess the benefits, and challenges, of using a higher magnetic field strength for imaging iron-labeled cells with b-SSFP, using ex vivo mouse brain specimens imaged with near identical systems at 1.5 and 3.0 T.The substantial banding artifact that appears in 3 T b-SSFP images was readily minimized with RF phase cycling, allowing for banding-free b-SSFP images to be compared between the two field strengths. This study revealed that with an optimal 3 T b-SSFP imaging protocol, more than twice as many signal voids were detected as with 1.5 T.There are several factors that contributed to this important result. First, a greater-than-linear SNR gain was achieved in mouse brain images at 3 T. Second, a reduction in the bandwidth, and the associated increase in repetition time and SNR, produced a dramatic increase in the contrast generated by iron-labeled cells.

    View details for DOI 10.1007/s10334-008-0118-2

    View details for Web of Science ID 000258192300002

    View details for PubMedID 18581153

  • Investigating exchange and multicomponent relaxation in fully-balanced steady-state free precession imagaing JOURNAL OF MAGNETIC RESONANCE IMAGING Deoni, S. C., Rutt, B. K., Jones, D. K. 2008; 27 (6): 1421-1429

    Abstract

    To investigate the effect of chemical exchange and multicomponent relaxation on the rapid T(2) mapping method, DESPOT2 (driven equilibrium single pulse observation of T(2)) and the steady-state free precession (SSFP) sequence upon which it is based. Although capable of rapid T(2) determination, an assumption implicit of the method is single-component relaxation. In many biological tissues (such as white and gray matter), it is well established that the T(2) decay curve is more accurately described by the summation of more than one relaxation species.The effects of exchange were first incorporated into the general SSFP magnetization expressions and its effect on the measured SSFP signal investigated using Bloch-McConnell simulations. Corresponding imaging experiments were performed to support the presented theory.Simulations show the measured multicomponent SSFP signal may be expressed as a linear summation of signal from each species under usual imaging conditions where the repetition time is much less than T(2). Imaging experiments performed using dairy cream demonstrate strong agreement with the presented theory. Finally, using a dairy cream model, we demonstrate quantification of multicomponent relaxation from multiangle SSFP data for the first time, showing good agreement with reference spin-echo values.SSFP and DESPOT2 may provide a new method for investigating multicomponent systems, such as human brain, and disease processes, such as multiple sclerosis.

    View details for DOI 10.1002/jmri.21079

    View details for Web of Science ID 000256327700031

    View details for PubMedID 18504765

  • MRI of early- and late-stage arterial remodeling in a low-level cholesterol-fed rabbit model of atherosclerosis JOURNAL OF MAGNETIC RESONANCE IMAGING Ronald, J. A., Walcarius, R., Robinson, J. F., Hegele, R. A., Rutt, B. K., Rogers, K. A. 2007; 26 (4): 1010-1019

    Abstract

    To monitor early- and late-stage arterial remodeling following low-level cholesterol (CH) feeding in rabbits using a standardized MRI protocol.New Zealand White rabbits were fed a CH diet (0.25% w/w) (n = 15) or normal chow (n = 6) and imaged either at 0, 2, 6, 8, and 11 months ("early-stage") or 12, 14, 16, 18, and 20 months ("late-stage"). T2-weighted fast-spin-echo images ( approximately 200 microm in-plane resolution) of aortic lesions were collected using either a 1.5 or 3.0T MR scanner interfaced with a customized surface RF coil. Luminal (LA), outer vessel wall boundary (OVBA), and vessel wall areas (VWA) were assessed.Among CH-fed animals in the early-stage group, increased VWA associated with decreased OVBA and a more pronounced decrease in LA was first detectable at 8 months. These changes became more evident between 8 and 11 months. In the late-stage group, lesions continued to grow in response to CH-feeding, as VWA significantly increased at regular 2-month intervals. Beyond 16 months, signal intensity differences (reflecting increased lesion complexity) within the vessel wall were noted.This often-overlooked rabbit model combined with customized MR technology holds tremendous promise for studying the natural progression, regression, and remodeling of atherosclerotic lesions.

    View details for DOI 10.1002/jmri.21113

    View details for Web of Science ID 000249898800025

    View details for PubMedID 17896368

  • Obstructive sleep apnea in 2 women with familial partial lipodystrophy due to a heterozygous LMNA R(4)8(2)Q mutation CANADIAN MEDICAL ASSOCIATION JOURNAL Hegele, R. A., Al-Attar, S. A., Rutt, B. K. 2007; 177 (7): 743-745

    View details for DOI 10.1503/cmaj.070135

    View details for Web of Science ID 000249474900015

    View details for PubMedID 17893350

  • Thematic review series: Adipocyte Biology. Lipodystrophies: windows on adipose biology and metabolism. Journal of lipid research Hegele, R. A., Joy, T. R., Al-Attar, S. A., Rutt, B. K. 2007; 48 (7): 1433-1444

    Abstract

    The lipodystrophies are characterized by loss of adipose tissue in some anatomical sites, frequently with fat accumulation in nonatrophic depots and ectopic sites such as liver and muscle. Molecularly characterized forms include Dunnigan-type familial partial lipodystrophy (FPLD), partial lipodystrophy with mandibuloacral dysplasia (MAD), Berardinelli-Seip congenital generalized lipodystrophy (CGL), and some cases with Barraquer-Simons acquired partial lipodystrophy (APL). The associated mutant gene products include 1) nuclear lamin A in FPLD type 2 and MAD type A; 2) nuclear lamin B2 in APL; 3) nuclear hormone receptor peroxisome proliferator-activated receptor gamma in FPLD type 3; 4) lipid biosynthetic enzyme 1-acylglycerol-3-phosphate O-acyltransferase 2 in CGL type 1; 5) integral endoplasmic reticulum membrane protein seipin in CGL type 2; and 6) metalloproteinase ZMPSTE24 in MAD type B. An unresolved question is whether metabolic disturbances are secondary to adipose repartitioning or result from a direct effect of the mutant gene product. Careful analysis of clinical, biochemical, and imaging phenotypes, using an approach called "phenomics," reveals differences between genetically stratified subtypes that can be used to guide basic experiments and to improve our understanding of common clinical entities, such as metabolic syndrome or the partial lipodystrophy syndrome associated with human immunodeficiency virus infection.

    View details for PubMedID 17374881

  • Carotid plaque classification: Defining the certainty with which plaque components can be differentiated MAGNETIC RESONANCE IN MEDICINE Ronen, R. R., Clarke, S. E., Hammond, R. R., Rutt, B. K. 2007; 57 (5): 874-880

    Abstract

    Multicontrast-weighted MRI has the potential to become a powerful tool for assessment of atherosclerotic plaque. However, similarities in MR properties across plaque components limit the certainty with which these components can be differentiated. An understanding of MRI's underlying limitations in distinguishing atherosclerotic plaque components, and optimization of key parameters (including the set of components investigated and contrast weightings used) are required. In this study we analyzed endarterectomy specimens using multicontrast MRI and compared the results with matching histological findings to determine the probability of error, an unbiased measure of the underlying error caused by similarity in the spectral characteristics of components. The total error was >40% when five distinct components were investigated, but this was halved when components with similar functions and intensities were grouped together. When three contrast weightings were used to view plaque, diffusion-weighted imaging (DWI) proved valuable for separating hemorrhage from necrotic core, and "hemorrhage + necrotic" from "loose connective tissue + fibrous tissue." A two-way interaction between contrast weightings and components demonstrated that the value of a contrast can be exploited or marginalized depending on the choice of contrast weightings used.

    View details for DOI 10.1002/mrm.21214

    View details for Web of Science ID 000246052800009

    View details for PubMedID 17457865

  • In vivo riber tracking in the rat brain on a clinical 3T MRI system using a high strength insert gradient coil NEUROIMAGE Mayer, D., Zahr, N. M., Adalsteinsson, E., Rutt, B., Sullivan, E. V., Pfefferbaum, A. 2007; 35 (3): 1077-1085

    Abstract

    In vivo neuroimaging methods permit longitudinal quantitative examination of the dynamic course of neurodegenerative conditions in humans and animal models and enable assessment of therapeutic efforts in mitigating disease effects on brain systems. The study of conditions affecting white matter, such as multiple sclerosis, demyelinating conditions, and drug and alcohol dependence, can be accomplished with diffusion tensor imaging (DTI), a technique uniquely capable of probing the microstructural integrity of white matter fibers in the living brain. We used a 3T clinical MR scanner equipped with an insert gradient coil that yields an order of magnitude increase in performance over the whole-body hardware to acquire in vivo DTI images of rat brain. The resolution allowed for fiber tracking evaluation of fractional anisotropy (FA) and apparent diffusion coefficients in the genu and splenium of the corpus callosum. A comparison of short (46 min) and long (92 min) acquisition time DTI protocols indicated low but adequate signal-to-noise ratio (SNR=6.2) of the shorter protocol to conduct quantitative fiber tracking enhanced by multiple acquisitions. As observed in human studies, FA in the rat splenium was higher than in the genu. Advantages of this technology include the use of similar user interface, pulse sequences, and field strength for preclinical animal and clinical human research, enhancing translational capabilities. An additional benefit of scanning at lower field strength, such as 3 T, is the reduction of artifacts due to main field inhomogeneity relative to higher field animal systems.

    View details for DOI 10.1016/j.neuroimage.2007.01.006

    View details for Web of Science ID 000245956100009

    View details for PubMedID 17331742

  • Investigating the effect of exchange and multicomponent T-1 relaxation on the short repetition time spoiled steady-state signal and the DESPOT1 T-1 guantification method JOURNAL OF MAGNETIC RESONANCE IMAGING Deoni, S. C., Rutt, B. K., Jones, D. K. 2007; 25 (3): 570-578

    Abstract

    To examine the spoiled steady-state (spoiled gradient-recalled echo sequence [SPGR]) signal arising from two-compartment systems and the role of experimental parameters, in particular TR for resolving signal from each compartment.Using Bloch-McConnell simulations, we examined the SPGR signal from two-component systems in which T(1) is much greater than the mean residence time (tau(m)) of proton spins in each component. Specifically, we examined the role of TR on the ability to resolve each components signal, as well as the influence of experimental parameters on derived DESPOT1 T(1) values.Results revealed that when TR < or = 0.01 tau(m), the measured SPGR signal may be modeled as a summation of signal from each species using a no-exchange approximation. Additionally, under this short TR condition, the driven equilibrium single pulse observation of T(1) (DESPOT1) mapping approach provides T(1) values preferentially biased toward the short or long T(1) species, depending on the choice of flip angles.The ability to model the SPGR signal using a no-exchange approximation may permit the quantification multicomponent T(1) relaxation in vivo. Additionally, the ability to preferentially weight the DESPOT1 T(1) value toward the short or long T(1) may provide a useful window into these components.

    View details for DOI 10.1002/jmri.20836

    View details for Web of Science ID 000244698800016

    View details for PubMedID 17326090

  • Magnetic resonance imaging of in vitro glioma cell invasion JOURNAL OF NEUROSURGERY Bernas, L. M., Foster, P. J., Rutt, B. K. 2007; 106 (2): 306-313

    Abstract

    An understanding of single glioma cell invasion has been limited by the static picture provided by histological studies. The ability to nondestructively assess cell invasion dynamically in a full 3D volume would improve the quality and quantity of information available from both in vivo and in vitro experiments. The purpose of this study was to observe glioma cell invasion in a 3D in vitro model using a microimaging protocol at 1.5 tesla and to assess the uptake of micron-sized particles of iron oxide (MPIO) and the consequent effects on cell function.Rat C6 glioma cells were labeled with MPIO to a sufficient extent to allow single cell detection in vitro without significant effects on cell proliferation or plating efficiency. When placed on agar-coated plates, the cells formed stable multicellular tumor spheroids (MCTSs), which were embedded in collagen type I gel and serially visualized using magnetic resonance (MR) imaging and phase-contrast microscopy over 8 days. The MCTSs initially appeared as large susceptibility artifacts on MR images, but within 2 days, as cells moved away from the main MCTS, small discrete areas of signal loss, possibly due to single cells, could be observed and tracked.Glioma cell invasion can be nondestructively observed using MR imaging. The sensitivity of MR imaging, along with its ability to represent full 3D volumes noninvasively over time, makes it ideal for longitudinal in vivo cell tracking studies.

    View details for Web of Science ID 000244519700020

    View details for PubMedID 17410716

  • Quantitative and qualitative differences in subcutaneous adipose tissue stores across lipodystrophy types shown by magnetic resonance imaging. BMC medical imaging Al-Attar, S. A., Pollex, R. L., Robinson, J. F., Miskie, B. A., Walcarius, R., Little, C. H., Rutt, B. K., Hegele, R. A. 2007; 7: 3-?

    Abstract

    Lipodystrophies are characterized by redistributed subcutaneous fat stores. We previously quantified subcutaneous fat by magnetic resonance imaging (MRI) in the legs of two patients with familial partial lipodystrophy subtypes 2 and 3 (FPLD2 and FPLD3, respectively). We now extend the MRI analysis across the whole body of patients with different forms of lipodystrophy.We studied five subcutaneous fat stores (supraclavicular, abdominal, gluteal, thigh and calf) and the abdominal visceral fat stores in 10, 2, 1, 1 and 2 female subjects with, respectively, FPLD2, FPLD3, HIV-related partial lipodystrophy (HIVPL), acquired partial lipodystrophy (APL), congenital generalized lipodystrophy (CGL) and in six normal control subjects.Compared with normal controls, FPLD2 subjects had significantly increased supraclavicular fat, with decreased abdominal, gluteal, thigh and calf subcutaneous fat. FPLD3 subjects had increased supraclavicular and abdominal subcutaneous fat, with less severe reductions in gluteal, thigh and calf fat compared to FPLD2 subjects. The repartitioning of fat in the HIVPL subject closely resembled that of FPLD3 subjects. APL and CGL subjects had reduced upper body, gluteal and thigh subcutaneous fat; the APL subject had increased, while CGL subjects had decreased subcutaneous calf fat. Visceral fat was markedly increased in FPLD2 and APL subjects.Semi-automated MRI-based adipose tissue quantification indicates differences between various lipodystrophy types in these studied clinical cases and is a potentially useful tool for extended quantitative phenomic analysis of genetic metabolic disorders. Further studies with a larger sample size are essential for confirming these preliminary findings.

    View details for PubMedID 17352814

  • Segmentation of thalamic nuclei using a modified k-means clustering algorithm and high-resolution quantitative magnetic resonance imaging at 1.5 T NEUROIMAGE Deoni, S. C., Rutt, B. K., Parrent, A. G., Peters, T. M. 2007; 34 (1): 117-126

    Abstract

    Patient outcome in minimally invasive stereotactic neurosurgical procedures depends on the ability to accurately locate the desired functional region within the deep brain while avoiding the surrounding anatomy. Due to the lack of sufficient contrast within this region in pre-operatively acquired MR images, electrophysiological exploration and histological atlases are currently required to define the surgical target within the thalamus in the treatment of many motor-control disorders. In this paper we introduce a method for segmenting the individual thalamic nuclei based on high-resolution quantitative magnetic resonance images, providing improved target visualization. The method was tested using whole-brain T1 and T2 data acquired from four healthy individuals. Accuracy of the segmentation results was assessed by comparing the center-of-mass coordinates of the segmented nuclei, with coordinates obtained from a classic histological atlas registered to these images. Strong agreement was found, with an average Euclidean distance difference of less than 4.5 mm averaged across all nuclei and all individuals. Reproducibility of the method, determined by calculating the percent similarity of segmentation results derived from data acquired from repeated scan sessions, was greater than 85%. These results illustrate the ability to accurately and reliably segment the primary nuclei of the thalamus and suggest that the method may have utility in the study of individual nuclear regions in disease state as well as for planning deep-brain surgical procedures.

    View details for DOI 10.1016/j.neuroimage.2006.09.016

    View details for Web of Science ID 000242735300012

    View details for PubMedID 17070073

  • Imaging islets labeled with magnetic nanoparticles at 1.5 Tesla DIABETES Tai, J. H., Foster, P., Rosales, A., Feng, B., Hasilo, C., Martinez, V., Ramadan, S., Snir, J., Melling, C. W., Dhanvantari, S., Rutt, B., White, D. J. 2006; 55 (11): 2931-2938

    Abstract

    We have developed a magnetic resonance imaging (MRI) technique for imaging Feridex (superparamagnetic iron oxide [SPIO])-labeled islets of Langerhans using a standard clinical 1.5-Tesla (T) scanner and employing steady-state acquisition imaging sequence (3DFIESTA). Both porcine and rat islets were labeled with SPIO by a transfection technique using a combination of poly-l-lysine and electroporation. Electron microscopy demonstrated presence of SPIO particles within the individual islet cells, including beta-cells and particles trapped between cell membranes. Our labeling method produced a transfection rate of 860 pg to 3.4 ng iron per islet, dependent on the size of the islet. The labeling procedure did not disrupt either the function or viability of the islets. In vitro 3DFIESTA magnetic resonance images of single-labeled islets corresponded with their optical images. In vivo T2*-weighted scan using 1.5 T detected as few as 200 SPIO-labeled islets transplanted under rat kidney capsule, which correlated with immunohistochemistry of the transplant for insulin and iron. Ex vivo 3DFIESTA images of kidneys containing 200, 800 or 2,000 SPIO-labeled islet isografts showed good correlation between signal loss and increasing numbers of islets. These data provide evidence that islets can be labeled with SPIO and imaged using clinically available 1.5- T MRI.

    View details for DOI 10.2337/db06-0393

    View details for Web of Science ID 000241966500001

    View details for PubMedID 17065328

  • Synthetic T-1-weighted brain image generation with incorporated coil intensity correction using DESPOT1 MAGNETIC RESONANCE IMAGING Deoni, S. C., Rutt, B. K., Peters, T. M. 2006; 24 (9): 1241-1248

    Abstract

    The increased use of phased-array and surface coils in magnetic resonance imaging, the push toward increased field strength and the need for standardized imaging across multiple sites during clinical trials have resulted in the need for methods that can ensure consistency of intensity both within the image and across multiple subjects/sites. Here, we describe a means of addressing these concerns through an extension of the rapid T(1) mapping technique - driven equilibrium single-pulse observation of T(1). The effectiveness of the proposed approach was evaluated using human brain T(1) maps acquired at 1.5 T with a multichannel phased-array coil. Corrected "synthetic" T(1)-weighted images were reconstructed by substituting the T(1) values back into the governing signal intensity equation while assuming a constant value for the equilibrium magnetization. To demonstrate signal normalization across a longitudinal study, we calculated synthetic T(1)-weighted images from data acquired from the same healthy subject at four different time points. Signal intensity profiles between the acquired and synthetic images were compared to determine the improvements with our proposed approach. Following correction, the images demonstrate obvious qualitative improvement with increased signal uniformity across the image. Near-perfect signal normalization was also observed across the longitudinal study, allowing direct comparison between the images. In addition, we observe an increase in contrast-to-noise ratio (compared with regular T(1)-weighted images) for synthetic images created, assuming uniform proton density throughout the volume. The proposed approach permits rapid correction for signal intensity inhomogeneity without significantly lengthening exam time or reducing image signal-to-noise ratio. This technique also provides a robust method for signal normalization, which is useful in multicenter longitudinal MR studies of disease progression, and allows the user to reconstruct T(1)-weighted images with arbitrary T(1) weighting.

    View details for DOI 10.1016/j.mri.2006.03.015

    View details for Web of Science ID 000242138300012

    View details for PubMedID 17071345

  • In vivo MRI of cancer cell fate at the single-cell level in a mouse model of breast cancer metastasis to the brain MAGNETIC RESONANCE IN MEDICINE Heyn, C., Ronald, J. A., Ramadan, S. S., Snir, J. A., Barry, A. M., MacKenzie, L. T., Mikulis, D. J., Palmieri, D., Bronder, J. L., Steeg, P. S., Yoneda, T., MacDonald, I. C., Chambers, A. F., Rutt, B. K., Foster, P. J. 2006; 56 (5): 1001-1010

    Abstract

    Metastasis (the spread of cancer from a primary tumor to secondary organs) is responsible for most cancer deaths. The ability to follow the fate of a population of tumor cells over time in an experimental animal would provide a powerful new way to monitor the metastatic process. Here we describe a magnetic resonance imaging (MRI) technique that permits the tracking of breast cancer cells in a mouse model of brain metastasis at the single-cell level. Cancer cells that were injected into the left ventricle of the mouse heart and then delivered to the brain were detectable on MR images. This allowed the visualization of the initial delivery and distribution of cells, as well as the growth of tumors from a subset of these cells within the whole intact brain volume. The ability to follow the metastatic process from the single-cell stage through metastatic growth, and to quantify and monitor the presence of solitary undivided cells will facilitate progress in understanding the mechanisms of brain metastasis and tumor dormancy, and the development of therapeutics to treat this disease.

    View details for DOI 10.1002/mrm.21029

    View details for Web of Science ID 000241761900009

    View details for PubMedID 17029229

  • Resolution and SNR effects on carotid plaque classification MAGNETIC RESONANCE IN MEDICINE Ronen, R. R., Clarke, S. E., Hammond, R. R., Rutt, B. K. 2006; 56 (2): 290-295

    Abstract

    Multicontrast-weighted MRI, which is increasingly being used in combination with automatic classification algorithms, has the potential to become a powerful tool for assessing plaque composition. The current literature, however, does not address the relationship between imaging conditions and segmentation viability well. In this study 13 carotid endarterectomy samples were imaged with a 156-microm in-plane resolution and high signal-to-noise ratio (SNR) using proton density (PD), T1, T2, and diffusion weightings. The maximum likelihood (ML) algorithm was used to classify plaque components, with sets of three contrast weighting intensities used as features. The resolution and SNR of the images were then degraded. Classification accuracy was found to be independent of in-plane resolution between 156 microm and 1250 microm, but dependent on SNR. Accuracy decreased less than 10% for degradation in SNR down to 25% of original values, and decreased sharply thereafter. The robustness of automatic classifiers makes them applicable to a wide range of imaging conditions, including standard in vivo carotid imaging scenarios.

    View details for DOI 10.1002/mrm.20956

    View details for Web of Science ID 000239465500008

    View details for PubMedID 16773656

  • Cellular MRI contrast via coexpression of transferrin receptor and ferritin MAGNETIC RESONANCE IN MEDICINE Deans, A. E., Wadghiri, Y. Z., Bernas, L. M., Yu, X., Rutt, B. K., Turnbull, D. H. 2006; 56 (1): 51-59

    Abstract

    Recently there has been growing interest in the development and use of iron-based contrast agents for cellular imaging with MRI. In this study we investigated coexpression of the transferrin receptor and ferritin genes to induce cellular contrast in a biological system. Expression of transgenic human transferrin receptor and human ferritin H-subunit was induced in a stably transfected mouse neural stem cell line. When grown in iron-rich medium, the transgenic cells accumulated significantly more iron than control cells, with a trend toward an increase in reactive oxygen species, but no detrimental effects on cell viability. This cellular iron significantly increased the transverse relaxivities, R2 and R2*, at 1.5 T and 7 T. By comparing measurements in the same cell samples at 1.5 T and 7 T, we confirmed the expected increase in relaxivity with increasing field strength. Finally, supplemented transgenic cells transplanted into mouse brain demonstrated increased contrast with surrounding neural tissue on T2*-weighted MR brain images compared to controls. These results indicate that dual expression of proteins at different critical points in the iron metabolism pathway may improve cellular contrast without compromising cell viability.

    View details for DOI 10.1002/mrm.20914

    View details for Web of Science ID 000238823600007

    View details for PubMedID 16724301

  • In vivo magnetic resonance imaging of single cells in mouse brain with optical validation MAGNETIC RESONANCE IN MEDICINE Heyn, C., Ronald, J. A., Mackenzie, L. T., MacDonald, I. C., Chambers, A. F., Rutt, B. K., Foster, P. J. 2006; 55 (1): 23-29

    Abstract

    In the current work we demonstrate, for the first time, that single cells can be detected in mouse brain in vivo using magnetic resonance imaging (MRI). Cells were labeled with superparamagnetic iron oxide nanoparticles and injected into the circulation of mice. Individual cells trapped within the microcirculation of the brain could be visualized with high-resolution MRI using optimized MR hardware and the fast imaging employing steady state acquisition (FIESTA) pulse sequence on a 1.5 T clinical MRI scanner. Single cells appear as discrete signal voids on MR images. Direct optical validation was provided by coregistering signal voids on MRI with single cells visualized using high-resolution confocal microscopy. This work demonstrates the sensitivity of MRI for detecting single cells in small animals for a wide range of application from stem cell to cancer cell tracking.

    View details for DOI 10.1002/mrm.20747

    View details for Web of Science ID 000234342800004

    View details for PubMedID 16342157

  • Validation of automatically classified magnetic resonance images for carotid plaque compositional analysis STROKE Clarke, S. E., Beletsky, V., Hammond, R. R., Hegele, R. A., Rutt, B. K. 2006; 37 (1): 93-97

    Abstract

    MRI may be used for noninvasive assessment of atherosclerotic lesions; however, MRI evaluation of plaque composition requires validation against an accepted reference standard, such as the American Heart Association (AHA) lesion grade, defined by histopathological examination.Forty-eight carotid endarterectomy specimen cross-sections had AHA lesion grade determined histopathologically and were concurrently imaged using combinations of 8 MRI contrast weightings in vitro. A maximum likelihood classification algorithm generated MRI "maps" of plaque components, and an AHA lesion grade was assigned correspondingly. Additional analyses compared classification accuracy obtained with a commonly used set of magnetic resonance contrast weightings [proton density (PDw), T1 (T1w), and partial T2 (T2w)] to accuracy obtained with the combination of PDw, T1w, and diffusion-weighted (Dw) contrast.For the 8-contrast combination, the sensitivities for fibrous tissue, necrotic core, calcification, and hemorrhage detection were 83%, 67%, 86%, and 77%, respectively. The corresponding specificities were 81%, 78%, 99%, and 97%. Good agreement (79%) between magnetic resonance and histopathology for AHA classification was achieved. For the PDw, T1w, and Dw combination, the overall classification accuracy was insignificantly different at 78%, whereas the overall classification accuracy using PDw, T1w, and partial T2w contrast weightings was significantly lower at 67%.This study provides proof-of-principle that the composition of atherosclerotic plaques determined by automated classification of high-resolution ex vivo MRI accurately reflects lesion composition defined by histopathological examination.

    View details for DOI 10.1161/01.STR.0000196985.38701.0c

    View details for Web of Science ID 000234148500023

    View details for PubMedID 16339462

  • Semi-automated segmentation and quantification of adipose tissue in calf and thigh by MRI: a preliminary study in patients with monogenic metabolic syndrome. BMC medical imaging Al-Attar, S. A., Pollex, R. L., Robinson, J. F., Miskie, B. A., Walcarius, R., Rutt, B. K., Hegele, R. A. 2006; 6: 11-?

    Abstract

    With the growing prevalence of obesity and metabolic syndrome, reliable quantitative imaging methods for adipose tissue are required. Monogenic forms of the metabolic syndrome include Dunnigan-variety familial partial lipodystrophy subtypes 2 and 3 (FPLD2 and FPLD3), which are characterized by the loss of subcutaneous fat in the extremities. Through magnetic resonance imaging (MRI) of FPLD patients, we have developed a method of quantifying the core FPLD anthropometric phenotype, namely adipose tissue in the mid-calf and mid-thigh regions.Four female subjects, including an FPLD2 subject (LMNA R482Q), an FPLD3 subject (PPARG F388L), and two control subjects were selected for MRI and analysis. MRI scans of subjects were performed on a 1.5T GE MR Medical system, with 17 transaxial slices comprising a 51 mm section obtained in both the mid-calf and mid-thigh regions. Using ImageJ 1.34 n software, analysis of raw MR images involved the creation of a connectedness map of the subcutaneous adipose tissue contours within the lower limb segment from a user-defined seed point. Quantification of the adipose tissue was then obtained after thresholding the connected map and counting the voxels (volumetric pixels) present within the specified region.MR images revealed significant differences in the amounts of subcutaneous adipose tissue in lower limb segments of FPLD3 and FPLD2 subjects: respectively, mid-calf, 15.5% and 0%, and mid-thigh, 25.0% and 13.3%. In comparison, old and young healthy controls had values, respectively, of mid-calf, 32.5% and 26.2%, and mid-thigh, 52.2% and 36.1%. The FPLD2 patient had significantly reduced subcutaneous adipose tissue compared to FPLD3 patient.Thus, semi-automated quantification of adipose tissue of the lower extremity can detect differences between individuals of various lipodystrophy genotypes and represents a potentially useful tool for extended quantitative phenotypic analysis of other genetic metabolic disorders.

    View details for PubMedID 16945131

  • Variation in the carotid bifurcation geometry of young versus older adults - Implications for geometric risk of atherosclerosis STROKE Thomas, J. B., Antiga, L., Che, S. L., Milner, J. S., Steinman, D. A., Spence, J. D., Rutt, B. K., Steinman, D. A. 2005; 36 (11): 2450-2456

    Abstract

    Retrospective analysis of clinical data has demonstrated major variations in carotid bifurcation geometry, in support of the notion that an individual's vascular anatomy or local hemodynamics may influence the development of atherosclerosis. On the other hand, anecdotal evidence suggests that vessel geometry is more homogenous in youth, which would tend to undermine this geometric risk hypothesis. The purpose of our study was to test whether the latter is indeed the case.Cross-sectional images of the carotid bifurcations of 25 young adults (24+/-4 years) and a control group of 25 older subjects (63+/-10 years) were acquired via MRI. Robust and objective techniques were developed to automatically characterize the 3D geometry of the bifurcation and the relative dimensions of the internal, external, and common carotid arteries (ICA, ECA, and CCA, respectively).Young vessels exhibited significantly less interindividual variation in the following geometric parameters: bifurcation angle (48.5+/-6.3 degrees versus 63.6+/-15.4 degrees); ICA angle (21.6+/-6.7 degrees versus 29.2+/-11.3 degrees); CCA tortuosity (0.010+/-0.003 versus 0.014+/-0.011); ICA tortuosity (0.025+/-0.013 versus 0.086+/-0.105); ECA/CCA diameter ratio (0.81+/-0.06 versus 0.75+/-0.13), ICA/CCA (0.81+/-0.06 versus 0.77+/-0.12) diameter ratio, and bifurcation area ratio (1.32+/-0.15 versus 1.19+/-0.35).The finding of more modest interindividual variations in young adults suggests that, if there is a geometric risk for atherosclerosis, its early detection may prove challenging. Taken together with the major interindividual variations seen in older vessels, it suggests a more complex interrelationship between vascular geometry, local hemodynamics, vascular aging, and atherosclerosis, the elucidation of which now calls for prospective studies.

    View details for DOI 10.1161/01.STR.0000185679.62634.0a

    View details for Web of Science ID 000232832200037

    View details for PubMedID 16224089

  • Visualization of thalamic nuclei on high resolution, multi-averaged T-1 and T-2 maps acquired at 1.5 T HUMAN BRAIN MAPPING Deoni, S. C., Josseau, M. J., Rutt, B. K., Peters, T. M. 2005; 25 (3): 353-359

    Abstract

    The ability to differentiate noninvasively between the primary nuclear divisions of the thalamus has immediate clinical applicability for surgical planning and guidance of functional stereotactic procedures. Comparison of prior qualitative magnetic resonance imaging (MRI) studies carried out at field strengths of 1.5 and 4 Tesla have revealed contrast within the thalamus that varies with field strength, suggesting possible differences in the inherent T1 and T2 relaxation times of the constituent nuclei. We investigate this hypothesis through acquisition of high-resolution, multi-averaged deep-brain T1 and T2 maps of a healthy volunteer. Fourteen nuclei were identified using their center-of-mass coordinates (in Talairach space) and average T1 and T2 values obtained from regions of interest placed within each. Results from this analysis revealed significant differences in T1 and T2 between the nuclei with a T1 range from 700 to 1,400 ms and a T2 range from 89 to 122 ms, allowing visual discrimination between the major nuclei groups. Furthermore, the high-resolution images showed distinct borders of T1 and T2 hypointensity surrounding each nucleus, revealing structure not reported previously. These results confirm our hypothesis and demonstrate the potential high-resolution quantitative imaging for nucleus visualization and surgical planning.

    View details for DOI 10.1002/hbm.20117

    View details for Web of Science ID 000230016800008

    View details for PubMedID 15852386

  • Anthropometric data for magmetic resonance imaging of the carotid bifurcation JOURNAL OF MAGNETIC RESONANCE IMAGING Thomas, J. B., Jong, L., Spence, J. D., Wasserman, B. A., Rutt, B. K., Steinman, D. A. 2005; 21 (6): 845-849

    Abstract

    To provide anthropometric data applicable to the design of protocols for high-resolution magnetic resonance imaging (MRI) of the carotid bifurcation, particularly those aimed at elucidating the role of local factors in carotid atherogenesis.Axial black-blood MR images of the carotid bifurcation were acquired from 25 young, healthy volunteers and 25 older, asymptomatic patients, from which were measured a variety of quantities related to the orientation and placement of the bifurcation within the neck.Descriptive statistics were obtained for the following quantities: separation of the bifurcation apices within (57.8+/-6.7 mm) and between (4.9+/-4.1 mm) axial slices; orientation of the bifurcation within the axial plane (31.7+/-26.9 degrees ), and of the common carotid artery (CCA) relative to the sagittal (7.5+/-7.1 degrees ) and coronal (7.9+/-7.8 degrees ) planes; depth of the bifurcation from the skin surface (29.5+/-7.2 mm); and neck width (125.9+/-14.4 mm).In most cases, both carotid arteries may be captured, without aliasing, within a 12-cm field-of-view axial image; however, the two apices will rarely be captured within the same axial slice. The CCA is significantly oblique to the body axis, but at angles sufficiently acute to permit the use of axial slices. Finally, a significant linear relationship between neck width and carotid depth may be used to inform radio frequency (RF) coil selection prior to scanning a subject, and hence facilitate optimal imaging in light of the wide anatomic variations observed.

    View details for DOI 10.1002/jmri.20317

    View details for Web of Science ID 000229453900025

    View details for PubMedID 15906347

  • Multisite trial of MR flow measurement: Phantom and protocol design JOURNAL OF MAGNETIC RESONANCE IMAGING Summers, P. E., Holdsworth, D. W., Nikolov, H. N., Rutt, B. K., Drangova, M. 2005; 21 (5): 620-631

    Abstract

    To describe a portable, easily assembled phantom with well-defined bore geometry together with a series of tests that will form the basis of a standardized quality assurance protocol in a multicenter trial of flow measurement by the MR phase mapping technique.The phantom consists of silicone polymer layers containing parallel straight and stenosed flow channels in one layer and a U-bend in a second layer, separated by hermetically sealed agarose slabs. The phantom is constructed by casting low melting-point metal in an aluminum mold precisely milled to the desired geometry, and then using the low melting-point metal core as a negative around which the silicone is allowed to set. By melting out the metal, the flow channels are established. The milled aluminum mold is reusable, ensuring faithful reproduction of the flow geometry for all phantoms thus produced. The agarose layers provide additional loading and static background signal for background correction. With the use of the described phantom, one can evaluate flow measurement accuracy and repeatability, as well as the influence of several imaging geometry factors: slice offset, in-plane position, and slice-flow obliquity.The new phantom is compact and portable, and is well suited for reassembly. We were able to demonstrate its facility in a battery of tests of interest in evaluating MR flow measurements.The phantom is a robust standardized test object for use in a multicenter trial. Such a trial, to investigate the performance of MR flow measurement using the phantom and the tests we describe, has been initiated.

    View details for DOI 10.1002/jmri.20311

    View details for Web of Science ID 000228653600016

    View details for PubMedID 15834913

  • Detection threshold of single SPIO-Labeled cells with FIESTA MAGNETIC RESONANCE IN MEDICINE Heyn, C., Bowen, C. V., Rutt, B. K., Foster, P. J. 2005; 53 (2): 312-320

    Abstract

    MRI of superparamagnetic iron oxide (SPIO)-labeled cells has become a valuable tool for studying the in vivo trafficking of transplanted cells. Cellular detection with MRI is generally considered to be orders of magnitude less sensitive than other techniques, such as positron emission tomography (PET), single photon emission-computed tomography (SPECT), or optical fluorescence microscopy. However, an analytic description of the detection threshold for single SPIO-labeled cells and the parameters that govern detection has not been adequately provided. In the present work, the detection threshold for single SPIO-labeled cells and the effect of resolution and SNR were studied for a balanced steady-state free precession (SSFP) sequence (3D-FIESTA). Based on the results from both theoretical and experimental analyses, an expression that predicts the minimum detectable mass of SPIO (m(c)) required to detect a single cell against a uniform signal background was derived: m(c) = 5v/(K(fsl) x SNR), where v is the voxel volume, SNR is the image signal-to-noise ratio, and K(fsl) is an empirical constant measured to be 6.2 +/- 0.5 x 10(-5) microl/pgFe. Using this expression, it was shown that the sensitivity of MRI is not very different from that of PET, requiring femtomole quantities of SPIO iron for detection under typical micro-imaging conditions (100 microm isotropic resolution, SNR = 60). The results of this work will aid in the design of cellular imaging experiments by defining the lower limit of SPIO labeling required for single cell detection at any given resolution and SNR.

    View details for DOI 10.1002/mrm.20356

    View details for Web of Science ID 000226651100009

    View details for PubMedID 15678551

  • High-resolution T-1 and T-2 mapping of the brain in a clinically acceptable time with DESPOT1 and DESPOT2 MAGNETIC RESONANCE IN MEDICINE Deoni, S. C., Peters, T. M., Rutt, B. K. 2005; 53 (1): 237-241

    Abstract

    Variations in the intrinsic T(1) and T(2) relaxation times have been implicated in numerous neurologic conditions. Unfortunately, the low resolution and long imaging time associated with conventional methods have prevented T(1) and T(2) mapping from becoming part of routine clinical evaluation. In this study, the clinical applicability of the DESPOT1 and DESPOT2 imaging methods for high-resolution, whole-brain, T(1) and T(2) mapping was investigated. In vivo, 1-mm(3) isotropic whole-brain T(1) and T(2) maps of six healthy volunteers were acquired at 1.5 T with an imaging time of <17 min each. Isotropic maps (0.34 mm(3)) of one volunteer were also acquired (time <21 min). Average signal-to-noise within the 1-mm(3) T(1) and T(2) maps was approximately 20 and approximately 14, respectively, with average repeatability standard deviations of 46.7 ms and 6.7 ms. These results demonstrate the clinical feasibility of the methods in the study of neurologic disease.

    View details for DOI 10.1002/mrm.20314

    View details for Web of Science ID 000226380700033

    View details for PubMedID 15690526

  • Characterization of vibration and acoustic noise in a gradient-coil insert MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE Yao, G. Z., Mechefske, C. K., Rutt, B. K. 2004; 17 (1): 12-27

    Abstract

    High-speed switching of current in gradient coils within high magnetic field strength magnetic resonance imaging (MRI) scanners results in high acoustic sound pressure levels (SPL) in and around these machines. To characterize the vibration properties as well as the acoustic noise properties of the gradient coil, a finite-element (FE) model was developed using the dimensional design specifications of an available gradient-coil insert and the concentration of the copper windings in the coil. This FE model was then validated using experimentally collected vibration data. A computational acoustic noise model was then developed based on the validated FE model. The validation of the finite-element analysis results was done using experimental modal testing of the same gradient coil in a free-free state (no boundary constraints). Based on the validated FE model, boundary conditions (supports) were added to the model to simulate the operating condition when the gradient-coil insert is in place in an MRI machine. Vibration analysis results from the FE model were again validated through experimental vibration testing with the gradient-coil insert installed in the MRI scanner and excited using swept sinusoidal time waveforms. The simulation results from the computational acoustic noise model were also validated through experimental noise measurement from the gradient-coil insert in the MRI scanner using swept sinusoidal time waveform inputs. Comparisons show that the FE model predicts the vibration properties and the computational acoustic noise model predicts the noise characteristic properties extremely accurately.

    View details for DOI 10.1007/s10334-004-0041-0

    View details for Web of Science ID 000224946400003

    View details for PubMedID 15221661

  • Rapid T-2 estimation with phase-cycled variable nutation steady-state free precession MAGNETIC RESONANCE IN MEDICINE Deoni, S. C., Ward, H. A., Peters, T. M., Rutt, B. K. 2004; 52 (2): 435-439

    Abstract

    Variable nutation SSFP (DESPOT2) permits rapid, high-resolution determination of the transverse (T2) relaxation constant. A limitation of DESPOT2, however, is the presence of T2 voids due to off-resonance banding artifacts associated with SSFP images. These artifacts typically occur in images acquired with long repetition times (TR) in the presence of B0 inhomogeneities, or near areas of magnetic susceptibility difference, such that the transverse magnetization experiences a net phase shift during the TR interval. This places constraints on the maximum spatial resolution that can be achieved without artifact. Here, a novel implementation of DESPOT2 is presented incorporating RF phase-cycling which acts to shift the spatial location of the bands, allowing reconstruction of a single, reduced artifact-image. The method is demonstrated in vivo with the acquisition of a 0.34 mm3 isotropic resolution T2 map of the brain with high precision and accuracy and significantly reduced artifact.

    View details for DOI 10.1002/mrm.20159

    View details for Web of Science ID 000223121400028

    View details for PubMedID 15282830

  • Atherosclerotic plaque characterization by MR imaging. Current drug targets. Cardiovascular & haematological disorders Rutt, B. K., Clarke, S. E., Fayad, Z. A. 2004; 4 (2): 147-159

    Abstract

    The MR imaging of carotid artery and aortic plaque has undergone significant improvement in the last decade. Early studies utilizing ex vivo specimens and spin echo or fast spin echo imaging, led to the conclusion that T2-weighting was the best single contrast to characterize carotid plaque morphology. On these images, the fibrous plaque appears bright and the lipid core is dark; thrombus can have variable intensity. There can be an overlap in T2w signal intensities among the various plaque components, which can be partially offset by the use of qualitative or multi-spectral analysis of multiple contrast images. With improvements in coil design, sequence design, main field and gradient capabilities, accurate in vivo differentiation and measurement of these various plaque components should be possible in a few years. Carotid and aortic plaque burden can be accurately measured in vivo today; ongoing longitudinal studies should lead to a better understanding of the relationship between plaque burden and the risk of thromboembolic complications, as well as the effect of diet and drug therapy in hyperlipidemic patients. With these developments in place or soon to be available, MR imaging of the diseased carotid artery and aortic wall may prove to be even more important than MR angiography or other current clinical tests.

    View details for PubMedID 15180487

  • Quantitative diffusion imaging with steady-state free precession MAGNETIC RESONANCE IN MEDICINE Deoni, S. C., Peters, T. M., Rutt, B. K. 2004; 51 (2): 428-433

    Abstract

    The addition of a single, unbalanced diffusion gradient to the steady-state free precession (SSFP) imaging sequence sensitizes the resulting signal to free diffusion. Unfortunately, the confounding influence of both longitudinal (T1) and transverse (T2) relaxation on the diffusion-weighted SSFP (dwSSFP) signal has made it difficult to quantitatively determine the apparent diffusion coefficient (ADC). Here, a multistep method in which the T1, T2, and spin density (Mo) constants are first determined using a rapid mapping technique described previously is presented. Quantitative ADC can then be determined through a novel inversion of the appropriate signal model. The accuracy and precision of our proposed method (which we term DESPOD) was determined by comparing resulting ADC values from phantoms to those calculated from traditional diffusion-weighted echo planar imaging (dwEPI) images. Error within the DESPOD-derived ADC maps was found to be less than 3%, with good precision over a biologically relevant range of ADC values.

    View details for DOI 10.1002/mrm.10708

    View details for Web of Science ID 000188718600030

    View details for PubMedID 14755673

  • Determination of optimal angles for variable nutation proton magnetic spin-lattice, T-1, and spin-spin, T-2, relaxation times measurement MAGNETIC RESONANCE IN MEDICINE Deoni, S. C., Peters, T. M., Rutt, B. K. 2004; 51 (1): 194-199

    Abstract

    T1 and T2 can be rapidly determined with a combination of multiangle spoiled gradient recalled echo (SPGR) and steady-state free precession (SSFP) imaging. Previously, we demonstrated a simple method for determining the set of SPGR and SSFP angles that provided greater T1 and T2 precision than a set of uniformly spaced angles. In this article a more rigorous approach for determining angles is described. Weighted least-squares is also introduced for T1 and T2 estimation and a novel weighting function described. This new approach, suited for imaging applications where large T1 and T2 ranges are anticipated, provides high and uniform precision over a wide range of T1 and T2 values.

    View details for Web of Science ID 000188041500025

    View details for PubMedID 14705061

  • Quantitative assessment of carotid plaque composition using multicontrast MRI and registered histology MAGNETIC RESONANCE IN MEDICINE Clarke, S. E., Hammond, R. R., Mitchell, J. R., Rutt, B. K. 2003; 50 (6): 1199-1208

    Abstract

    MRI is emerging as a promising modality for monitoring carotid atherosclerosis. Multiple MR contrast weightings are required for identification of plaque constituents. In this study, eight MR contrast weightings with proven potential for plaque characterization were used to image carotid endarterectomy specimens. A classification technique was developed to create a tissue-specific map by incorporating information from all MR contrast weightings. The classifier was validated by comparison with micro-CT (calcification only) and with matched histological slices registered to MR images using a nonlinear warping algorithm (other components). A pathologist who was blinded to the classifier results manually segmented digitized histological images. The sensitivity of the classifier, as determined by pixel-by-pixel comparison with the pathologist's segmentation and micro-CT, was 60.4% for fibrous tissue, 83.9% for necrosis, 97.6% for calcification, and 65.2% for loose connective tissue. The corresponding values for specificity were 87.9%, 75.0%, 98.3%, and 94.9%, respectively. In conclusion, multicontrast MRI was successfully used in conjunction with a supervised classification algorithm to identify plaque components in endarterectomy specimens. Furthermore, this methodology will provide a framework for comparing different classification algorithms, and determining which combination of MR contrasts will be most valuable for in vivo plaque imaging.

    View details for DOI 10.1002/mrm.10618

    View details for Web of Science ID 000186991500010

    View details for PubMedID 14648567

  • Peripheral nerve stimulation properties of head and body gradient coils of various sizes MAGNETIC RESONANCE IN MEDICINE Zhang, B. B., Yen, Y. F., Chronik, B. A., McKinnon, G. C., Schaefer, D. J., Rutt, B. K. 2003; 50 (1): 50-58

    Abstract

    Peripheral nerve stimulation (PNS) caused by time-varying magnetic fields has been studied both theoretically and experimentally. A human volunteer study performed on three different body-size gradient coils and one head-size gradient coil is presented in this work. The experimental results were used to generate average PNS threshold parameters for the tested gradient systems. It was found that the average stimulation threshold increases while gradient-region-of-uniformity size decreases. In addition, linear relationships between PNS parameters and diameter of homogeneous gradient spherical volume (DSV) were discovered: SR(min) and DeltaG(min) both vary inverse linearly with DSV. More importantly, the chronaxie value was found to vary inversely linearly with the DSV. This finding indicates that, contrary to the general understanding, the parameter "chronaxie" in the commonly accepted simple stimulation models cannot be considered to be a single-value, nerve-specific constant. A modified linear model for gradient-induced PNS based on these results was developed, which may permit, for the first time, the general prediction of nerve stimulation properties for gradient coils of arbitrary linear region dimension.

    View details for DOI 10.1002/mrm.10508

    View details for Web of Science ID 000183961800008

    View details for PubMedID 12815678

  • Imaging single mammalian cells with a 1.5 T clinical MRI scanner MAGNETIC RESONANCE IN MEDICINE Foster-Gareau, P., Heyn, C., Alejski, A., Rutt, B. K. 2003; 49 (5): 968-971

    Abstract

    In the present work, we demonstrate that the steady-state free precession (SSFP) imaging pulse sequence FIESTA (fast imaging employing steady state acquisition) used in conjunction with a custom-built insertable gradient coil and customized RF coils can be used to detect individual SPIO-labeled cells using a commonly available 1.5 T clinical MRI scanner. This work provides the first evidence that single-cell tracking will be possible using clinical MRI scanners, opening up new possibilities for cell tracking and monitoring of cellular therapeutics in vivo in humans.

    View details for DOI 10.1002/mrm.10417

    View details for Web of Science ID 000182642400024

    View details for PubMedID 12704781

  • Rapid combined T-1 and T-2 mapping using gradient recalled acquisition in the steady state MAGNETIC RESONANCE IN MEDICINE Deoni, S. C., Rutt, B. K., Peters, T. M. 2003; 49 (3): 515-526

    Abstract

    A novel, fully 3D, high-resolution T(1) and T(2) relaxation time mapping method is presented. The method is based on steady-state imaging with T(1) and T(2) information derived from either spoiling or fully refocusing the transverse magnetization following each excitation pulse. T(1) is extracted from a pair of spoiled gradient recalled echo (SPGR) images acquired at optimized flip angles. This T(1) information is combined with two refocused steady-state free precession (SSFP) images to determine T(2). T(1) and T(2) accuracy was evaluated against inversion recovery (IR) and spin-echo (SE) results, respectively. Error within the T(1) and T(2) maps, determined from both phantom and in vivo measurements, is approximately 7% for T(1) between 300 and 2000 ms and 7% for T(2) between 30 and 150 ms. The efficiency of the method, defined as the signal-to-noise ratio (SNR) of the final map per voxel volume per square root scan time, was evaluated against alternative mapping methods. With an efficiency of three times that of multipoint IR and three times that of multiecho SE, our combined approach represents the most efficient of those examined. Acquisition time for a whole brain T(1) map (25 x 25 x 10 cm) is less than 8 min with 1 mm(3) isotropic voxels. An additional 7 min is required for an identically sized T(2) map and postprocessing time is less than 1 min on a 1 GHz PIII PC. The method therefore permits real-time clinical acquisition and display of whole brain T(1) and T(2) maps for the first time.

    View details for DOI 10.1002/mrm.10407

    View details for Web of Science ID 000181297200015

    View details for PubMedID 12594755

  • Reproducibility of image-based computational fluid dynamics models of the human carotid bifurcation ANNALS OF BIOMEDICAL ENGINEERING Thomas, J. B., Milner, J. S., Rutt, B. K., Steinman, D. A. 2003; 31 (2): 132-141

    Abstract

    Recent studies have demonstrated the ability of magnetic resonance imaging (MRI) to provide anatomically realistic boundary conditions for computational fluid dynamics (CFD) simulations of arterial hemodynamics. To date, however, little is known about the overall reproducibility of such image-based CFD techniques. Towards this end we used serial black blood and cine phase contrast MRI to reconstruct CFD models of the carotid bifurcations of three subjects with early atherosclerosis, each imaged three times at weekly intervals. The lumen geometry was found to be precise on average to within 0.15 mm or 5%, while measured flow and heart rates varied by less than 10%. Spatial patterns of a variety of wall shear stress (WSS) indices were largely preserved among the three repeat models. Time-averaged WSS was reproduced best, on average to within 5 dyn/cm2 or 37%, followed by WSS spatial gradients, angle gradients, and oscillatory shear index. The intrasubject flow rate variations were found to contribute little to the overall WSS variability. Instead, reproducibility was determined largely by the precision of the lumen boundary extraction from the individual MR images, itself shown to be a function of the image quality and proximity to the geometrically complex bifurcation region.

    View details for DOI 10.1114/1.1540102

    View details for Web of Science ID 000181202700002

    View details for PubMedID 12627820

  • MRI gradient coil cylinder sound field simulation and measurement JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Mechefske, C. K., Wu, Y. H., Rutt, B. K. 2002; 124 (4): 450-455

    Abstract

    High-field, high-speed Magnetic Resonance Imaging (MRI) generates high sound levels within and nearby the scanner. The mechanism and process that produces the gradient magnetic field (a cylindrical electro-magnet, called the gradient coil cylinder, which produces a spatially and temporally varying magnetic field inside a static background magnetic field) is the primary source of this noise. This noise can cause difficulties in verbal communication in and around the scanner, heightened patient anxiety, temporary hearing loss and possible permanent hearing impairment for health care workers and patients. In order to effectively suppress the sound radiation from the gradient coil cylinder the sound field within and nearby the gradient coil needs to be characterized This characterization may be made using an analytical solution of the sound pressure field, computational simulation, measurement analysis or some combination of these three methods. This paper presents the computational simulation and measurement results of a study of the sound radiation from a head and neck gradient coil cylinder within a 4 Tesla MRI whole body scanner. The measurement results for the sound pressure level distribution along the centerline of the gradient coil cylinder are presented. The sound pressure distributions predicted from Finite Element Analysis of the gradient coil movement during operation and subsequent Boundary Element Analysis of the sound field generated are also presented. A comparison of the measured results and the predicted results shows close agreement. Because of the extremely complex nature of the analytical solution for the gradient coil cylinder, a treatment of the analytical solution and comparison to the computational results for a simple cylinder vibrating in a purely radial direction are also presented and also show close agreement between the two methods thus validating the computational approach used with the more complex gradient coil cylinder.

    View details for DOI 10.1115/1.1488169

    View details for Web of Science ID 000177356200013

    View details for PubMedID 12188211

  • Application of the static dephasing regime theory to superparamagnetic iron-oxide loaded cells MAGNETIC RESONANCE IN MEDICINE Bowen, C. V., Zhang, X. W., Saab, G., Gareau, P. J., Rutt, B. K. 2002; 48 (1): 52-61

    Abstract

    The relaxation rates of iron-oxide nanoparticles compartmentalized within cells were studied and found to satisfy predictions of the static dephasing (SD) regime theory. THP-1 cells in cell culture were loaded using two different iron-oxide nanoparticles (superparamagnetic iron-oxide (SPIO) and ultrasmall SPIO (USPIO)) with four different iron concentrations (0.05, 0.1, 0.2, and 0.3 mg/ml) and for five different incubation times (6, 12, 24, 36, and 48 hr). Cellular iron-oxide uptake was assessed using a newly developed imaging version of MR susceptometry, and was found to be linear with both dose and incubation time. R(2)* sensitivity to iron-oxide loaded cells was found to be 70 times greater than for R(2), and 3100 times greater than for R(1). This differs greatly from uniformly distributed nanoparticles and is consistent with a cellular bulk magnetic susceptibility (BMS) relaxation mechanism. The cellular magnetic moment was large enough that R(2)' relaxivity agreed closely with SD regime theory predictions for all cell samples tested [R(2)'=2 pi/(9 x the square root of 3) x gamma LMD] where the local magnetic dose (LMD) is the sample magnetization due to the presence of iron-oxide particles). Uniform suspensions of SPIO and USPIO produced R(2)' relaxivities that were a factor of 3 and 8 less, respectively, than SD regime theory predictions. These results are consistent with theoretical estimates of the required mass of iron per compartment needed to guarantee SD-regime-dominant relaxivity. For cellular samples, R(2) was shown to be dependent on both the concentration and distribution of iron-oxide particles, while R(2)' was sensitive to iron-oxide concentration alone. This work is an important first step in quantifying cellular iron content and ultimately mapping the density of a targeted cell population.

    View details for DOI 10.1002/mrm.10192

    View details for Web of Science ID 000176648900007

    View details for PubMedID 12111931

  • Improved contrast in multispectral phase images derived from magnetic resonance exams of multiple sclerosis patients MEDICAL PHYSICS Mitchell, J. R., Rutt, B. K. 2002; 29 (5): 727-735

    Abstract

    We describe a method to extract data from multispectral MR exams of patients with Multiple Sclerosis (MS). The technique produces images of "spectral phase" (SP) relative to a reference tissue. SP images allow retrospective suppression of signal in the reference tissue, while maintaining high spatial resolution. Image quality in SP images was determined from MR exams of 5 MS patients selected at random from a clinical trial underway at our institute. Exams consisting of proton density weighted (PDw), T2 weighted (T2w), T1 weighted (T1w), and gadolinium-DTPA enhanced T1w (GAD) images were acquired from each patient. The MR exams were corrected for intensity nonuniformity, then filtered with an algorithm based upon anisotropic diffusion, to reduce noise. Principal component (PC) images and SP images relative to cerebrospinal fluid (SP(CSF)), normal appearing white matter (SP(NAWM)), gray matter (SP(GM)), and temporalis muscle (SP(MUS)) were then calculated. Contrast between tissues and MS lesions in the MR and derived images was then determined by measuring the signal-difference-to-noise ratio (dSNR) between tissues. Our new SP images provided better tissue contrast than the original MR, filtered MR, and PC images. Contrast improved between CSF and NAWM (from 19.5 to 56), CSF and GM (from 15 to 36), GM and NAWM (from 8 to 14), MS lesions and CSF (from 16 to 35), and between MS lesions and NAWM (from 24 to 47). (Maximum contrast in the original MR images compared to maximum contrast in the SP images.) The additional contrast in SP images may aid the quantification and analysis of lesion activity in MR exams of MS patients.

    View details for DOI 10.1118/1.1462637

    View details for Web of Science ID 000175675000011

    View details for PubMedID 12033569

  • Reconstruction of carotid bifurcation hemodynamics and wall thickness using computational fluid dynamics and MRI MAGNETIC RESONANCE IN MEDICINE Steinman, D. A., Thomas, J. B., Ladak, H. M., Milner, J. S., Rutt, B. K., Spence, J. D. 2002; 47 (1): 149-159

    Abstract

    A thorough understanding of the relationship between local hemodynamics and plaque progression has been hindered by an inability to prospectively monitor these factors in vivo in humans. In this study a novel approach for noninvasively reconstructing artery wall thickness and local hemodynamics at the human carotid bifurcation is presented. Three-dimensional (3D) models of the lumen and wall boundaries, from which wall thickness can be measured, were reconstructed from black-blood magnetic resonance imaging (MRI). Along with time-varying inlet/outlet flow rates measured via phase contrast (PC) MRI, the lumen boundary was used as input for computational fluid dynamic (CFD) simulation of the subject-specific flow patterns and wall shear stresses (WSSs). Results from a 59-year-old subject with early, asymptomatic carotid artery disease show good agreement between simulated and measured velocities, and demonstrate a correspondence between wall thickening and low and oscillating shear at the carotid bulb. High shear at the distal internal carotid artery (ICA) was also colocalized with higher WSS; however, a quantitative general relationship between WSS and wall thickness was not found. Similar results were obtained from a 23-year-old normal subject. These findings represent the first direct comparison of hemodynamic variables and wall thickness at the carotid bifurcation of human subjects. The noninvasive nature of this image-based modeling approach makes it ideal for carrying out future prospective studies of hemodynamics and plaque development or progression in otherwise healthy subjects.

    View details for Web of Science ID 000172957500019

    View details for PubMedID 11754454

  • A comparison between human magnetostimulation thresholds in whole-body and head/neck gradient coils MAGNETIC RESONANCE IN MEDICINE Chronik, B. A., Rutt, B. K. 2001; 46 (2): 386-394

    Abstract

    Gradient coil magnetostimulation thresholds were measured in a group of 20 volunteers in both a whole-body gradient coil and a head/neck gradient coil. Both coils were operated using both x and y axes simultaneously (xy oblique mode). The waveform applied was a 64-lobe trapezoidal train with 1-ms flat-tops and varying rise times. Thresholds were based on the subjects' perception of stimulation, and painful sensations were not elicited. Thresholds were expressed in terms of the total gradient excursion required to cause stimulation as a function of the duration of the excursion. Thresholds for each subject were fit to a linear model, and values for the threshold curve slope (SR(min)) and vertical axis intercept (DeltaG(min)) were extracted. For the body coil, the mean values were: SR(min) = 62.2 mT/m/ms, DeltaG(min) = 44.4 mT/m. For the head/neck coil, the mean values were: SR(min) = 87.3 mT/m/ms, DeltaG(min) = 78.9 mT/m. These curve parameters were combined with calculated values for the induced electric field as a function of position within the coil to yield the tissue specific parameters E(r) (electric field rheobase) and tau(c) (chronaxie). For tissue stimulated within the body coil, the mean values were: E(r) = 1.8 V/m, tau(c) = 770 micros. For tissue stimulated within the head/neck coil, the mean values were: E(r) = 1.3 V/m, tau(c) = 1100 micros. Scalar potential contributions were not included in the calculation of induced electric fields. The mean threshold curves were combined with the gradient system performance curves to produce operational limit curves. The operational limit curves for the head/neck coil system were verified to be higher than those of the whole-body coil; however, the head/neck system was also found to be physiologically limited over a greater range of its operation than was the body coil. Subject thresholds between the two coils were not well correlated.

    View details for Web of Science ID 000170114100024

    View details for PubMedID 11477644

  • Effect of black blood MR image quality on vessel wall segmentation MAGNETIC RESONANCE IN MEDICINE Thomas, J. B., Rutt, B. K., Ladak, H. M., Steinman, D. A. 2001; 46 (2): 299-304

    Abstract

    Black blood MRI has become a popular technique for measuring arterial wall area as an indicator of plaque size. Computer-assisted techniques for segmenting vessel boundaries have been developed to increase measurement precision. In this study, the carotid arteries of four normal subjects were imaged at seven different fields of view (FOVs), keeping all other imaging parameters fixed, to determine whether spatial resolution could be increased at the expense of image quality without sacrificing precision. Wall areas were measured via computer-assisted segmentation of the vessel boundaries performed repeatedly by two operators. Analysis of variance (ANOVA) demonstrated that the variability of wall area measurements was below 1.5 mm(2) for in-plane spatial resolutions between 0.22 mm and 0.37 mm. An inverse relationship between operator variability and the signal difference-to-noise ratio (SDNR) demonstrated that semi-automatic segmentation of the wall boundaries was robust for SDNR >3, defining a criterion above which subjective image quality can be degraded without an appreciable loss of information content. Our study also suggested that spatial resolutions higher than 0.3 mm may be required to quantify normal wall areas to within 10% accuracy, but that the reduced SNR associated with the higher resolution may be tolerated by semi-automated wall segmentation without an appreciable loss of precision.

    View details for Web of Science ID 000170114100013

    View details for PubMedID 11477633

  • A semi-automatic technique for measurement of arterial wall from black blood MRI MEDICAL PHYSICS Ladak, H. M., Thomas, J. B., Mitchell, J. R., Rutt, B. K., Steinman, D. A. 2001; 28 (6): 1098-1107

    Abstract

    Black blood magnetic resonance imaging (MRI) has become a popular technique for imaging the artery wall in vivo. Its noninvasiveness and high resolution make it ideal for studying the progression of early atherosclerosis in normal volunteers or asymptomatic patients with mild disease. However, the operator variability inherent in the manual measurement of vessel wall area from MR images hinders the reliable detection of relatively small changes in the artery wall over time. In this paper we present a semi-automatic method for segmenting the inner and outer boundary of the artery wall, and evaluate its operator variability using analysis of variance (ANOVA). In our approach, a discrete dynamic contour is approximately initialized by an operator, deformed to the inner boundary, dilated, and then deformed to the outer boundary. A group of four operators performed repeated measurements on 12 images from normal human subjects using both our semiautomatic technique and a manual approach. Results from the ANOVA indicate that the inter-operator standard error of measurement (SEM) of total wall area decreased from 3.254 mm2 (manual) to 1.293 mm2 (semi-automatic), and the intra-operator SEM decreased from 3.005 mm2 to 0.958 mm2. Operator reliability coefficients increased from less than 69% to more than 91% (inter-operator) and 95% (intra-operator). The minimum detectable change in wall area improved from more than 8.32 mm2 (intra-operator, manual) to less than 3.59 mm2 (inter-operator, semi-automatic), suggesting that it is better to have multiple operators measure wall area with our semi-automatic technique than to have a single operator make repeated measurements manually. Similar improvements in wall thickness and lumen radius measurements were also recorded. Since the semi-automatic technique has effectively ruled out the effect of the operator on these measurements, it may be possible to use such techniques to expand prospective studies of atherogenesis to multiple centers so as to increase access to real patient data without sacrificing reliability.

    View details for Web of Science ID 000169443500024

    View details for PubMedID 11439479

  • Carotid plaque characterization by magnetic resonance imaging: review of the literature. Topics in magnetic resonance imaging DEMARCO, J. K., Rutt, B. K., Clarke, S. E. 2001; 12 (3): 205-217

    Abstract

    Magnetic resonance imaging (MRI) of carotid plaque has undergone significant improvements in the last decade. Early studies utilizing ex vivo specimens and spin-echo or fast spin-echo imaging led to the conclusion that T2 weighting is the best single contrast to characterize carotid plaque morphology. On these images, the fibrous plaque appears bright and the lipid core is dark; thrombus can have variable intensity. There can be an overlap in T2-weighted signal intensities among the various plaque components, which can be partially offset by the use of multispectral analysis of multiple contrast images. With improvements in coil design, sequence design, and main field and gradient capabilities, accurate in vivo differentiation and measurement of these various carotid plaque components should be possible in 3 to 5 years. Ex vivo and in vivo studies have yielded high-resolution measurements of the complex three-dimensional lumen geometry, which are being used to predict hemodynamic forces acting on the lumenal surface. Carotid plaque burden can be accurately measured in vivo today; ongoing longitudinal studies should lead to a better understanding of the relationship between plaque burden and the risk of thromboembolic complications, as well as the effect of diet and drug therapy in hyperlipidemic patients. With these developments in place or soon to be available, MRI of the diseased carotid artery wall may prove to be even more important than magnetic resonance angiography.

    View details for PubMedID 11432578

  • Simple linear formulation for magnetostimulation specific to MRI gradient coils MAGNETIC RESONANCE IN MEDICINE Chronik, B. A., Rutt, B. K. 2001; 45 (5): 916-919

    Abstract

    A simple linear formulation for magnetostimulation thresholds specific to MRI gradient coils is derived based on established hyperbolic electrostimulation strength vs. duration relations. Thresholds are derived in terms of the gradient excursion required to cause stimulation, and it is demonstrated that the threshold curve is a linear function of the gradient switching time. A parameter beta is introduced as being fundamental in the evaluation of gradient coil stimulation. beta is a map of the induced electric field per unit gradient slew rate, and can be calculated directly from the gradient coil wire pattern. Consideration of beta alone is sufficient to compare stimulation thresholds between different gradient coil designs, as well as to evaluate the expected dependency of stimulation threshold on position within the gradient coil. The linear gradient threshold curve is characterized by two parameters: SR(min) and DeltaG(min). SR(min) is the slope of the threshold curve and represents the minimum slew rate required to cause stimulation in the limit of infinite gradient strength. DeltaG(min) is the vertical axis intercept of the curve and represents the minimum gradient excursion required to cause stimulation in the limit of infinite slew rate. Both SR(min) and DeltaG(min) are functions of both beta and the standard tissue parameters E(r) (rheobase) and tau(c) (chronaxie time). The ease with which both the gradient system performance and the stimulation thresholds can be plotted on the same axes is noted and is used to introduce the concept of a piece-wise linear operational limit curve for a gradient system.

    View details for Web of Science ID 000168444000023

    View details for PubMedID 11323819

  • Design and fabrication of a three-axis edge ROU head and neck gradient coil MAGNETIC RESONANCE IN MEDICINE Chronik, B. A., Alejski, A., Rutt, B. K. 2000; 44 (6): 955-963

    Abstract

    The design, fabrication, and testing of a complete three-axis gradient coil capable of imaging the human neck is described. The analytic method of constrained current minimum inductance (CCMI) was used to position the uniform region of the gradient coil adjacent to and extending beyond the physical edge of the coil. The average gradient efficiency of the three balanced axes is 0.37 mT/m/A and the average inductance is 827 microH. With maximum amplifier current of 200A and receive signal sweep width of +/-125 kHz, the average minimum FOV using this gradient set is 7.9 cm. The completed coil has an inner diameter of 32 cm, an outer diameter of 42 cm, and a length (including cabling connections) of 80 cm. The entire coil was built in-house. The structure is actively water cooled. Heating measurements were made to characterize the thermal response of the coil under various operating conditions and it was determined that a continuous current of 100A could be passed through all three axes simultaneously without increasing the internal coil temperature by more than 23 degrees C. Eddy current measurements were made for all axes. With digital compensation, the gradient eddy current components could be adequately compensated. A large B(o) eddy current field is produced by the Gz axis that could be corrected through the use of an auxiliary B(o) compensation coil. Preliminary imaging results are shown in both phantoms and human subjects.

    View details for Web of Science ID 000165551700018

    View details for PubMedID 11108634

  • Gradient-induced acoustic and magnetic field fluctuations in a 4T whole-body MR imager MAGNETIC RESONANCE IN MEDICINE Wu, Y. H., Chronik, B. A., Bowen, C., Mechefske, C. K., Rutt, B. K. 2000; 44 (4): 532-536

    Abstract

    Both the acoustic and magnetic fluctuation frequency response functions for a Siemens AS25 body gradient coil inside a 4 Tesla whole-body MR system were measured and analyzed in this study. In an attempt to correlate the acoustic noise inside the gradient coil with magnetic field oscillations, triangular and trapezoidal gradient impulses of varying amplitudes and widths were used to excite the gradient coil. The acoustic and magnetic responses to these inputs were measured. The results show the existence of discrete resonances in both acoustic and uniform magnetic field fluctuation spectra, while gradient magnetic field fluctuation spectra show no such resonances. In addition, the dominant amplitude peaks in spectra fluctuate similarly with respect to trapezoidal gradient impulse flat-top widths. This implies that these phenomena are correlated, and that the trapezoidal impulse flat-top width may be used as a way to suppress both acoustic noise and uniform magnetic field oscillations.

    View details for Web of Science ID 000089671300006

    View details for PubMedID 11025508

  • MRI measures of middle cerebral artery diameter in conscious humans during simulated orthostasis STROKE Serrador, J. M., Picot, P. A., Rutt, B. K., Shoemaker, J. K., Bondar, R. L. 2000; 31 (7): 1672-1678

    Abstract

    The relationship between middle cerebral artery (MCA) flow velocity (CFV) and cerebral blood flow (CBF) is uncertain because of unknown vessel diameter response to physiological stimuli. The purpose of this study was to directly examine the effect of a simulated orthostatic stress (lower body negative pressure [LBNP]) as well as increased or decreased end-tidal carbon dioxide partial pressure (P(ET)CO(2)) on MCA diameter and CFV.Twelve subjects participated in a CO(2) manipulation protocol and/or an LBNP protocol. In the CO(2) manipulation protocol, subjects breathed room air (normocapnia) or 6% inspired CO(2) (hypercapnia), or they hyperventilated to approximately 25 mm Hg P(ET)CO(2) (hypocapnia). In the LBNP protocol, subjects experienced 10 minutes each of -20 and -40 mm Hg lower body suction. CFV and diameter of the MCA were measured by transcranial Doppler and MRI, respectively, during the experimental protocols.Compared with normocapnia, hypercapnia produced increases in both P(ET)CO(2) (from 36+/-3 to 40+/-4 mm Hg, P<0.05) and CFV (from 63+/-4 to 80+/-6 cm/s, P<0.001) but did not change MCA diameters (from 2.9+/-0.3 to 2.8+/-0.3 mm). Hypocapnia produced decreases in both P(ET)CO(2) (24+/-2 mm Hg, P<0.005) and CFV (43+/-7 cm/s, P<0.001) compared with normocapnia, with no change in MCA diameters (from 2.9+/-0.3 to 2.9+/-0.4 mm). During -40 mm Hg LBNP, P(ET)CO(2) was not changed, but CFV (55+/-4 cm/s) was reduced from baseline (58+/-4 cm/s, P<0.05), with no change in MCA diameter.Under the conditions of this study, changes in MCA diameter were not detected. Therefore, we conclude that relative changes in CFV were representative of changes in CBF during the physiological stimuli of moderate LBNP or changes in P(ET)CO(2).

    View details for Web of Science ID 000088019700033

    View details for PubMedID 10884472

  • Magnetization transfer and multicomponent T2 relaxation measurements with histopathologic correlation in an experimental model of MS JOURNAL OF MAGNETIC RESONANCE IMAGING Gareau, P. J., Rutt, B. K., Karlik, S. J., Mitchell, J. R. 2000; 11 (6): 586-595

    Abstract

    Magnetization transfer and multicomponent T2 imaging techniques were implemented to study guinea pig in vivo. A chronic-progressive model of experimental allergic encephalomyelitis (EAE) was produced, and the inflammatory component of the disease was manipulated using antibodies against integrin. The magnetization transfer ratio (MTR) and T2 relaxation properties were measured in normal-appearing white matter (NAWM) with histological comparisons. Significant reductions in both the mean MTR and the myelin water percentage were measured in NAWM of EAE guinea pig brain. However, the MTR and myelin water percentage appear to measure different aspects of pathology in NAWM in EAE. Reductions in the MTR were prevented or reversed with suppression of inflammation. However, modulation of inflammatory activity was not reflected in the measurement of the myelin water percentage. Since the amount of myelin is not expected to vary with inflammatory-related changes, these observations support our hypothesis that the MTR is sensitive to physiological changes to myelin induced by inflammation, while the short T2 component is a more specific indicator of myelin content in tissue. Pathologic features other than demyelination may be important in the determination of the MTR.

    View details for Web of Science ID 000171294400003

    View details for PubMedID 10862056

  • Design and fabrication of a three-axis multilayer gradient coil for magnetic resonance microscopy of mice. Magma (New York, N.Y.) Chronik, B., Alejski, A., Rutt, B. K. 2000; 10 (2): 131-146

    Abstract

    There is great interest in the non-destructive capabilities of magnetic resonance microscopy for studying murine models of both disease and normal function; however, these studies place extreme demands on the MR hardware, most notably the gradient field system. We designed, using constrained current minimum inductance methods, and fabricated a complete, unshielded three-axis gradient coil set that utilizes interleaved, multilayer axes to achieve maximum gradient strengths of over 2000 mT m(-1) in rise times of less than 50 micros with an inner coil diameter of 5 cm. The coil was wire-wound using a rectangular wire that minimizes the deposited power for a given gradient efficiency. Water cooling was also incorporated into the coil to assist in thermal management. The duty cycle for the most extreme cases of single shot echo planar imaging (EPI) is limited by the thermal response and expressions for maximum rates of image collection are given for burst and continuous modes of operation. The final coil is capable of the collection of single shot EPI images with 6 mm field of view and 94 microm isotropic voxels at imaging rates exceeding 50 s(-1).

    View details for PubMedID 10873203

  • Polyvinyl alcohol-Fricke hydrogel and cryogel: two new gel dosimetry systems with low Fe3+ diffusion PHYSICS IN MEDICINE AND BIOLOGY Chu, K. C., Jordan, K. J., Battista, J. J., Van Dyk, J., Rutt, B. K. 2000; 45 (4): 955-969

    Abstract

    Two new Fricke dosimeter gel systems with low diffusion rates have been developed for 3D radiation dosimetry purposes. Both systems consist of a solution of 20% (by weight) polyvinyl alcohol (PVA) in a 50 mM H2SO4 solution with 0.4 mM ferrous ammonium sulphate and xylenol orange (FX). The difference in the two gels is the way that the gelation process was initiated: either by bringing the temperature to (a) +5 degrees C or (b) -20 degrees C before returning them to room temperature. These gels are termed 'hydrogel' and 'cryogel', respectively. The hydrogel is optically transparent, and can be used with either optical or MRI detection methods for dosimetric imaging. The cryogel is rubbery in texture but opaque, so its internal Fe3+ concentration can only be measured with MRI. The hydrogel's optical attenuation coefficient is linear (r2 = 0.99) with dose from 0 to 20 Gy with a sensitivity of 0.106 cm(-1) Gy(-1) (at 543 nm). In terms of MR relaxation rate, the dose response for both the hydrogel and cryogel was linear (r2 = 0.99) with a sensitivity of 0.020 s(-1) Gy(-1) (at 1.5 T). The Fe3+ diffusion coefficient (at 20 degrees C) was measured to be 0.14 mm2 h(-1), which is significantly lower than similar preparations reported for porcine gelatin or agarose. The PVA-FX gels can be stored for long periods of time before exposure to radiation, since the auto-oxidation rate was 10 times less than that of gelatin-Fricke recipes. The new gels developed in this work are a significant improvement on previous Fricke gel systems.

    View details for Web of Science ID 000086423900011

    View details for PubMedID 10795984

  • Comparison of two blood pool contrast agents for 0.5-T MR angiography: Experimental study in rabbits RADIOLOGY Clarke, S. E., Weinmann, H. J., Dai, E. B., Lucas, A. R., Rutt, B. K. 2000; 214 (3): 787-794

    Abstract

    To evaluate two experimental blood pool agents for potential use in equilibrium phase abdominal magnetic resonance (MR) angiography.MR imaging at 0.5 T was performed in 37 rabbits before and after intravenous injection of a gadolinium-based blood pool contrast agent (SH L 643 A), superparamagnetic iron oxide blood pool agent (SH U 555 C), or gadopentetate dimeglumine. T1-weighted fast spoiled gradient-echo images from the renal arteries to below the iliac bifurcation were obtained. The aorta-to-tissue signal difference-to-noise ratio (SDNR) was measured over time.Both blood pool agents yielded excellent demonstration of the rabbit abdominal aorta. At a dose of 0.1 mmol/kg, both provided a statistically significant increase in aorta-to-tissue SDNR in comparison with that achieved with gadopentetate dimeglumine (200% increase for SH L 643 A, 95% increase for SH U 555 C; P < .05). A 0.1 mmol/kg dose of SH L 643 A provided a 24% increase in SDNR relative to the increase with a 0.37 mmol/kg dose of gadopentetate dimeglumine. Time-dependent enhancement properties of the blood pool agents differed due to differences in elimination method.Both blood pool agents were found to be promising contrast agents for 0.5-T MR angiography; however, their clinical applicability warrants further investigation. The gadolinium-based agent had several advantages over the iron oxide compound, including less T2* dephasing, lack of susceptibility artifacts, and fast renal elimination.

    View details for Web of Science ID 000085478800028

    View details for PubMedID 10715047

  • A transmit-only/receive-only (TORO) RF system for high-field MRI/MRS applications MAGNETIC RESONANCE IN MEDICINE Barberi, E. A., Gati, J. S., Rutt, B. K., Menon, R. S. 2000; 43 (2): 284-289

    Abstract

    The design and operation of a detunable shielded hybrid birdcage RF head coil optimized for human brain imaging at 170 MHz is presented. A high duty-cycle and rapid-switching decoupling scheme that allows uniform RF transmission with the head coil and reception with a surface coil within the volume of the head coil is also demonstrated. In addition, the circumscribing hybrid coil can be biased to operate as a conventional transmit/receive head coil. Our RF design allows the use of higher sensitivity surface coils or phased-array coils at very high magnetic fields where body RF resonators are not currently available or whose use is precluded by specific-absorption ratio restrictions. The design also allows the use of receive-only coils within head gradient inserts, which normally do not allow transmission with an RF body resonator at any field strength.

    View details for Web of Science ID 000084993500016

    View details for PubMedID 10680693

  • Measurement of Gd-DTPA diffusion through PVA hydrogel using a novel magnetic resonance imaging method BIOTECHNOLOGY AND BIOENGINEERING Gordon, M. J., Chu, K. C., Margaritis, A., Martin, A. J., Ethier, C. R., Rutt, B. K. 1999; 65 (4): 459-467

    Abstract

    Polyvinyl alcohol-cryogel (PVA-C) is a hydrogel that is an excellent tissue mimic. In order to characterize mass transfer in this material, as well as to demonstrate in principle the ability to noninvasively measure solute diffusion in tissue, we measured the diffusion coefficient of the magnetic resonance (MR) contrast agent gadolinium diethylene triaminopentaacetic acid (Gd-DTPA) through PVA-C using a clinical MR imager. The method involved filling thick-walled rectangular PVA-C "cups" with known concentrations of Gd-DTPA solutions. Then by using a fast inversion recovery spin echo MR imaging protocol, a signal "null" contour was created in the MR image that corresponded to a second, known concentration of Gd-DTPA. By collecting a series of MR images through the PVA-C wall as a function of time, the displacement of this second known isoconcentration contour could be tracked. Application of Fick's second law of diffusion yielded the diffusion coefficient. Seven separate experiments were performed using various combinations of initial concentrations of Gd-DTPA within the PVA-C cups (3.2, 25.6, or 125 mM) and tracked isoconcentrations contours (0.096, 0.182, or 0.435 mM Gd-DTPA). The experimental results and the predictions of Fick's law were in excellent agreement. The diffusivity of Gd-DTPA through 10% PVA hydrogel was found to be (2.6 +/- 0.04) x 10(-10) m(2)/s (mean +/- s.e.m.). Separate permeability studies showed that the diffusion coefficient of Gd-DTPA through this hydrogel did not change with an applied pressure of up to 7.1 kPa. Accurate measurements could be made within 30 min if suitable Gd-DTPA concentrations were selected. Due to the excellent repeatability and fast data acquisition time, this technique is very promising for future in vivo studies of species transport in tissue.

    View details for Web of Science ID 000083078500010

    View details for PubMedID 10506421

  • In vivo measurements of multi-component T-2 relaxation behaviour in guinea pig brain MAGNETIC RESONANCE IMAGING Gareau, P. J., Rutt, B. K., Bowen, C. V., Karlik, S. J., Mitchell, J. R. 1999; 17 (9): 1319-1325

    Abstract

    Multi-echo Carr-Purcell-Meiboom-Gill (CPMG) imaging sequences were implemented on 1.5 T and 4.0 T imaging systems to test their ability to measure in vivo multi-component T2 relaxation behavior in normal guinea pig brain. The known dependence of accurate T2 measurements on the signal-to-noise ratio (SNR) was explored in vivo by comparing T2 decay data obtained using three methods to increase SNR (improved RF coil design, signal averaging and increased magnetic field strength). Good agreement between T2 values of nickel-doped agarose phantoms was found between imaging and spectroscopic methods. T2 values were determined for gray matter (GM) and white matter (WM) locations from images of guinea pig brain in vivo. T2 measurements of GM were found to be monoexponential at both field strengths. The mean T2 times for GM were 71 ms at 1.5 T, and 53 ms at 4.0T. The highest average SNR was achieved using an improved RF coil at 4.0T. In this case, two peaks were extracted in WM, a "short" T2 peak at approximately 6 ms, and a "medium" T2 peak at approximately 48 ms. T2 values in GM and the major component of WM were significantly decreased at 4.0T compared to 1.5 T. The improved SNR attained with this optimized imaging protocol at 4.0T has allowed for the first time extraction of the myelin-sensitive T2 component of WM in animal brain in vivo.

    View details for Web of Science ID 000083588800010

    View details for PubMedID 10576717

  • A fast 3D Look-Locker method for volumetric T-1 mapping MAGNETIC RESONANCE IMAGING Henderson, E., McKinnon, G., Lee, T. Y., Rutt, B. K. 1999; 17 (8): 1163-1171

    Abstract

    We introduce a fast technique, based on the principles of the 2D Look-Locker T1 measurement scheme, to rapidly acquire the data for accurate maps of T1 in three dimensions. The acquisition time has been shortened considerably by segmenting the acquisition of the k(y) phase encode lines. Using this technique, the data for a 256 x 128 x 32 volumetric T1 measurement can be acquired in 7.6 min. T1 measurements made in phantoms with T1s between 200 and 1200 ms had an accuracy of 4% and a reproducibility of 3.5%. Measurements of T1 made in normal brain using the fast 3D sequence corresponded well with inversion-recovery fast spin-echo measurements.

    View details for Web of Science ID 000082634400008

    View details for PubMedID 10499678

  • Computational blood flow modeling based on in vivo measurements ANNALS OF BIOMEDICAL ENGINEERING Moore, J. A., Rutt, B. K., Karlik, S. J., Yin, K., Ethier, C. R. 1999; 27 (5): 627-640

    Abstract

    Study of the relationship between hemodynamics and atherogenesis requires accurate three-dimensional descriptions of in vivo arterial geometries. Common methods for obtaining such geometries include in vivo medical imaging and postmortem preparations (vessel casts, pressure-fixed vessels). We sought to determine the relative accuracy of these methods. The aorto-iliac (A/I) region of six rabbits was imaged in vivo using contrast-enhanced magnetic resonance imaging (MRI). After sacrifice, the geometry of the A/I region was preserved via vascular casts in four animals, and ex situ pressure fixation (while preserving dimensions) in the remaining two animals. The MR images and postmortem preparations were used to build computer representations of the A/I bifurcations, which were then used as input for computational blood flow analyses. Substantial differences were seen between MRI-based models and postmortem preparations. Bifurcation angles were consistently larger in postmortem specimens, and vessel dimensions were consistently smaller in pressure-fixed specimens. In vivo MRI-based models underpredicted aortic dimensions immediately proximal to the bifurcation, causing appreciable variation in the aorto-iliac parent/child area ratio. This had an important effect on wall shear stress and separation patterns on the "hips" of the bifurcation, with mean wall shear stress differences ranging from 15% to 35%, depending on the model. The above results, as well as consideration of known and probable sources of error, suggests that in vivo MRI best replicates overall vessel geometry (vessel paths and bifurcation angle). However, vascular casting seems to better capture detailed vessel cross-sectional dimensions and shape. It is important to accurately characterize the local aorto-iliac area ratio when studying in vivo bifurcation hemodynamics.

    View details for Web of Science ID 000084518000005

    View details for PubMedID 10548332

  • Characterization of common carotid artery blood-flow waveforms in normal human subjects PHYSIOLOGICAL MEASUREMENT Holdsworth, D. W., Norley, C. J., Frayne, R., Steinman, D. A., Rutt, B. K. 1999; 20 (3): 219-240

    Abstract

    Knowledge of human blood-flow waveforms is required for in vitro investigations and numerical modelling. Parameters of interest include: velocity and flow waveform shapes, inter- and intra-subject variability and frequency content. We characterized the blood-velocity waveforms in the left and right common carotid arteries (CCAs) of 17 normal volunteers (24 to 34 years), analysing 3560 cardiac cycles in total. Instantaneous peak-velocity (Vpeak) measurements were obtained using pulsed-Doppler ultrasound with simultaneous collection of ECG data. An archetypal Vpeak waveform was created using velocity and timing parameters at waveform feature points. We report the following timing (post-R-wave) and peak-velocity parameters: cardiac interbeat interval (T(RR)) = 0.917 s (intra-subject standard deviation = +/- 0.045 s); cycle-averaged peak-velocity (V(CYC)) = 38.8 cm s(-1) (+/-1.5 cm s(-1)); maximum systolic Vpeak = 108.2 cm s(-1) (+/-3.8 cm s(-1)) at 0.152 s (+/-0.008 s); dicrotic notch Vpeak = 19.4 cm s(-1) (+/-2.9 cm s(-1)) at 0.398 s (+/-0.007 s). Frequency components below 12 Hz constituted 95% of the amplitude spectrum. Flow waveforms were computed from Vpeak by analytical solution of Womersley flow conditions (derived mean flow = 6.0 ml s(-1)). We propose that realistic, pseudo-random flow waveform sequences can be generated for experimental studies by varying, from cycle to cycle, only T(RR) and V(CYC) of a single archetypal waveform.

    View details for Web of Science ID 000082242200001

    View details for PubMedID 10475577

  • Scanning time efficient slinky for non-contrast MRA at low field MAGNETIC RESONANCE IMAGING Liu, K. C., Tanttu, J., Castren, A., Rutt, B. K. 1999; 17 (5): 689-698

    Abstract

    To eliminate slab boundary artifact (SBA) for non-contrast multi-slab three-dimensional time-of-flight magnetic resonance angiogram (3D TOF MRA), we have previously developed a novel technique, termed SLINKY (Sliding Interleaved kY) acquisition in which a thin slab continuously "walks" along the z-axis while data are acquired in an interleaved fashion along the kY-axis. It has been demonstrated in our earlier works that SLINKY can suppress the SBA without any assumption of blood flow behavior, such as velocity or direction. At the same time, SLINKY keeps the same SNR as conventional multiple overlapping thin slab acquisition (MOTSA). Yet, this method is sensitive to any phase error along the ky axis. In our earlier application of SLINKY, we used navigator echoes to measure and correct the phase errors along the kY axis. The cost of using navigator echo collection is an increase in the imaging time. We therefore propose an improved SLINKY technique which does not use navigator echo collection for correcting phase errors, reducing the imaging time while keeping the same suppression of slab boundary artifacts. The present study demonstrates that by using a specifically designed RF pulse, the navigator echo collection can be avoided without incurring any extra ghosting or SNR reduction in the reconstructed images.

    View details for Web of Science ID 000080539200006

    View details for PubMedID 10372522

  • Temporal sampling requirements for the tracer kinetics modeling of breast disease MAGNETIC RESONANCE IMAGING Henderson, E., Rutt, B. K., Lee, T. Y. 1998; 16 (9): 1057-1073

    Abstract

    The physiological parameters measured in the tracer kinetics modeling of data from a dynamic contrast-enhanced magnetic resonance (MR) breast exam (blood flow-extraction fraction product [FE], volume of the extracellular extravascular space [Ve], and blood volume [Vb]) may enable non-invasive diagnosis of breast cancer. One of the factors that compromises the accuracy and precision of the parameter estimates, and therefore their diagnostic potential, is the temporal resolution of the MR scans used to measure contrast agent (gadolinium-diethylenetriamine pentaacetic acid [Gd-DTPA]) concentration in an artery (arterial input function [AIF]) and in the tissue (tissue residue function [TRF]). Using computer simulations, we have examined, for several AIF widths, the errors introduced into estimates of tracer kinetic parameters in breast tissue due to insufficient temporal sampling. Temporal sampling errors can be viewed as uncertainties and biases in the parameter estimates introduced by the uncertainty in the relative alignments of the AIF, TRF, and sampling grid. These effects arise from the model's inherent sensitivity to error in either the AIF or TRF, which is dependent on the values of the tracer kinetic parameters and increases with AIF width. Based on the results of the simulations, to ensure that the error in FE and Ve will be under 10% of their true values, we recommend a rapid bolus injection of contrast agent (approximately 10 s), that the AIF be sampled every second, and that the TRF be sampled every 16 s or less. An accurate measurement of Vb requires that the TRF be sampled at least every 4 s. The results of these investigations can be used to set minimum dynamic imaging rates for tracer kinetics modeling of the breast.

    View details for Web of Science ID 000077071700008

    View details for PubMedID 9839990

  • Polar sampling in k-space: Reconstruction effects MAGNETIC RESONANCE IN MEDICINE Lauzon, M. L., Rutt, B. K. 1998; 40 (5): 769-782

    Abstract

    Magnetic resonance images are most commonly computed by taking the inverse Fourier transform of the k-space data. This transformation can potentially create artifacts in the image, depending on the reconstruction algorithm used. For equally spaced radial and azimuthal k-space polar sampling, both gridding and convolution backprojection are applicable. However, these algorithms potentially can yield different resolution, signal-to-noise ratio, and aliasing characteristics in the reconstructed image. Here, these effects are analyzed and their tradeoffs are discussed. It is shown that, provided the modulation transfer function and the signal-to-noise ratio are considered together, these algorithms perform similarly. In contrast, their aliasing behavior is different, since their respective point spread functions (PSF) differ. In gridding, the PSF is composed of the mainlobe and ringlobes that lead to aliasing. Conversely, there are no ringlobes in the convolution backprojection PSF, thus radial aliasing effects are minimized. Also, a hybrid gridding and convolution backprojection reconstruction is presented for radially nonequidistant k-space polar sampling.

    View details for Web of Science ID 000076496700018

    View details for PubMedID 9797162

  • Invasive carcinomas and fibroadenomas of the breast: Comparison of microvessel distributions - Implications for imaging modalities RADIOLOGY Weind, K. L., Maier, C. F., Rutt, B. K., Moussa, M. 1998; 208 (2): 477-483

    Abstract

    To compare spatial patterns of blood vessels between invasive breast carcinomas and fibroadenomas to improve the diagnostic specificity of noninvasive vascular magnetic resonance imaging and color Doppler ultrasound.Nineteen invasive ductal carcinomas and 20 fibroadenomas from 39 patients were stained for factor VIII-related antigen. Vessels smaller than 40 microns were counted in x200 fields defined in peripheral and central areas of the tumor and in normal tissue adjacent to fibroadenomas. Significant differences in vessel density were determined with Student t tests and one-way analyses of variance. Distributions of vessels 40 microns or larger were qualitatively evaluated.There were 9-105 vessels (mean, 31.4 vessels) smaller than 40 microns per x200 peripheral and 4-57 vessels (mean, 20.1 vessels) smaller than 40 microns per x200 central carcinoma field. There was no significant difference in vessel density between the two groups. Peripheral microvessel density was significantly higher (P < .01) than central microvessel density in 15 (79%) of the 19 carcinomas and in three (16%) of 19 fibroadenomas. (A Student t test could not be performed in one case of fibroadenoma; size permitted only one countable field according to the authors' criteria.) The 18 cases with normal tissue had 21-229 vessels (mean, 80.5 vessels) per field; in 16 (89%) of the 18 cases, these vessel counts were significantly higher (P < .01) than those in the fibroadenoma cases. Vessels 40 microns or larger were found mainly in the periphery of carcinomas and were more uniformly distributed in fibroadenomas.Evaluation of the spatial distribution of vessels and the ability to resolve vessel sizes may add valuable information to the imaging-based diagnostic work-up of indeterminate solid breast lesions.

    View details for Web of Science ID 000074891400035

    View details for PubMedID 9680579

  • Hemodynamics of human carotid artery bifurcations: Computational studies with models reconstructed from magnetic resonance imaging of normal subjects JOURNAL OF VASCULAR SURGERY Milner, J. S., Moore, J. A., Rutt, B. K., Steinman, D. A. 1998; 28 (1): 143-156

    Abstract

    The precise role played by hemodynamics, particularly wall shear stress, in the development and progression of vascular disease remains unclear, in large part because of a lack of in vivo studies with humans. Although technical challenges remain for noninvasively imaging wall shear stresses in humans, vascular anatomy can be imaged with sufficiently high resolution to allow reconstruction of three-dimensional models for computational hemodynamic studies. In this paper we present an entirely noninvasive magnetic resonance imaging (MRI) protocol that provides carotid bifurcation geometry and flow rates from which the in vivo hemodynamics can be computed. Maps of average, oscillatory, and gradients of wall shear stress are presented for two normal human subjects, and their data are compared with those computed for an idealized carotid bifurcation model.An MRI protocol was developed to acquire all necessary image data in scan times suitable for patient studies. Three-dimensional models of the carotid bifurcation lumen were reconstructed from serial black blood MR images of two normal volunteers. Common and internal carotid artery flow rate waveforms were determined from MRI phase-contrast velocity imaging in the same subjects and were used to impose fully developed velocity boundary conditions for the computational model. Subject-specific time-resolved velocities and wall shear stresses were then computed with a finite element-based Navier-Stokes equation solver.Models reconstructed from in vivo MRI of two subjects showed obvious differences in branch angle, bulb size and extent, and three-dimensional curvature. Maps of a variety of wall shear stress indices showed obvious qualitative differences in patterns between the in vivo models and between the in vivo models and the idealized model. Secondary, helical flow patterns, induced primarily by the asymmetric and curved in vivo geometries, were found to play a key role in determining the resulting wall shear stress patterns. The use of in vivo flow rate waveforms was found to play a minor but noticeable role in some of the wall shear stress behavior observed.Conventional "averaged" carotid bifurcation models mask interesting hemodynamic features observed in realistic models derived from noninvasive imaging of normal human subjects. Observation of intersubject variations in the in vivo wall shear stress patterns supports the notion that more conclusive evidence regarding the role of hemodynamics in vascular disease may be derived from such individual studies. The techniques presented here, when combined with subject-specific MRI measurements of carotid artery plaque thickness and composition, provide the tools necessary for entirely noninvasive, prospective, in vivo human studies of hemodynamics and the relationship of hemodynamics to vascular disease.

    View details for Web of Science ID 000074830100017

    View details for PubMedID 9685141

  • Sliding interleaved k(Y) (SLINKY) acquisition: A novel 3D MRA technique with suppressed slab boundary artifact JOURNAL OF MAGNETIC RESONANCE IMAGING LIU, K. C., Rutt, B. K. 1998; 8 (4): 903-911

    Abstract

    This work addresses the elimination of the slab boundary artifact (SBA) or venetian blind artifact in three-dimensional multiple overlapped thin slab acquisition (3D MOTSA) for magnetic resonance angiography (MRA). Our method uses a sliding-slab, interleaved kY (SLINKY) data acquisition strategy, equalizing flow-related signal intensity weighting across the entire slab dimension. This technique demodulates signal intensity changes along the slab direction and can essentially eliminate the SBA while retaining the same or better imaging time efficiency than that of conventional MOTSA, providing robustness to complicated flow patterns and thereby resulting in more accurate depiction of vascular morphology. In addition, this technique does not need specialized reconstruction and extra computation. The unique penalty of this technique is the sensitivity to phase inconsistency in the data. Both phantom and in vivo experiments verify the clinical significance of the technique. The new MRA images acquired with this imaging technique show highly reliable mapping of vascular morphology without the SBA and reduction of signal voids in complex/slow flow regions.

    View details for Web of Science ID 000080143600020

    View details for PubMedID 9702893

  • Systematic assessment and evaluation of sliding interleaved k(Y) (SLINKY) acquisition for 3D MRA JOURNAL OF MAGNETIC RESONANCE IMAGING LIU, K. C., Lee, D. H., Rutt, B. K. 1998; 8 (4): 912-923

    Abstract

    In comparison with the conventional three-dimensional multiple overlapped thin slab acquisition (MOTSA) for magnetic resonance angiography (MRA), we have developed a novel sliding interleaved kY (SLINKY) acquisition technique, which can eliminate the slab boundary artifact (SBA) or venetian blind artifact without any a priori knowledge of blood flow. This work addresses the systematic assessment and evaluation of the SLINKY technique and verifies the advantages of SLINKY in the following several aspects: (a) scan time efficiency; (b) signal-to-noise ratio (SNR), and signal-difference-to-noise ratio (SDNR); (c) sensitivity to flow velocity range; (d) sensitivity to flow direction; (e) signal loss in slow/reversal flow regions; and (f) reconstruction efficiency and feasibility. Both phantom and in vivo experiments verify the clinical significance of the technique. The new MRA images acquired with this imaging technique in 31 volunteer/patient examinations show highly reliable mapping of vascular morphology without the SBA and reduction of signal voids in complex/slow flow regions.

    View details for Web of Science ID 000080143600021

    View details for PubMedID 9702894

  • On the nature and reduction of plaque-mimicking flow artifacts in black blood MRI of the carotid bifurcation MAGNETIC RESONANCE IN MEDICINE Steinman, D. A., Rutt, B. K. 1998; 39 (4): 635-641

    Abstract

    Cardiac-gated black blood MRI of the carotid artery bifurcation in normal human subjects shows signal within the lumen suggesting wall thickening or atherosclerotic plaque. This signal was believed to be artifactual, arising from complex flow patterns present at the carotid bifurcation. Computer simulation of the hemodynamics and black blood multislice image acquisition in a model of the carotid bifurcation showed that these artifacts arise from spins recovering their signal within the slow, recirculating flow of the carotid bulb. The computed hemodynamics also suggested that these artifacts could be minimized or eliminated entirely by gating the acquisition of slices in the most artifact-prone region of the carotid bulb within a 250-ms window after peak systole. Application of these predictions to studies of normal volunteers showed that, in most cases, these flow artifacts in black blood MRI can be eliminated simply by altering the phase of the cardiac cycle to which the image acquisition is gated. The observation that the size and placement of the saturation slabs had little effect on these artifacts suggested that, in those cases in which recirculation persists throughout the cardiac cycle, either inversion-recovery or presaturation within the bulb itself would be required to suppress them.

    View details for Web of Science ID 000072700900016

    View details for PubMedID 9543426

  • Practical design of a high-strength breast gradient coil MAGNETIC RESONANCE IN MEDICINE Maier, C. F., Nikolov, H. N., Chu, K. C., Chronik, B. A., Rutt, B. K. 1998; 39 (3): 392-401

    Abstract

    A high-strength three-axis local gradient coil set was constructed for MRI of the breast. Gradient fields with good uniformity (<10% deviation from the desired gradient) over most of the volume required for breast imaging were generated with efficiencies of up to 3.3 mT/m/A. The coils will allow diffusion breast imaging in clinically acceptable examination times. The electrical design, water cooling system, and fabrication techniques are described. Preliminary tests of the coil included images of a grid phantom and diffusion measurements in a short-T2 agarose gel phantom.

    View details for Web of Science ID 000072087900008

    View details for PubMedID 9498595

  • Constrained length minimum inductance gradient coil design MAGNETIC RESONANCE IN MEDICINE Chronik, B. A., Rutt, B. K. 1998; 39 (2): 270-278

    Abstract

    A gradient coil design algorithm capable of controlling the position of the homogeneous region of interest (ROI) with respect to the current-carrying wires is required for many advanced imaging and spectroscopy applications. A modified minimum inductance target field method that allows the placement of a set of constraints on the final current density is presented. This constrained current minimum inductance method is derived in the context of previous target field methods. Complete details are shown and all equations required for implementation of the algorithm are given. The method has been implemented on computer and applied to the design of both a 1:1 aspect ratio (length:diameter) central ROI and a 2:1 aspect ratio edge ROI gradient coil. The 1:1 design demonstrates that a general analytic method can be used to easily obtain very short gradient coil designs for use with specialized magnet systems. The edge gradient design demonstrates that designs that allow imaging of the neck region with a head sized gradient coil can be obtained, as well as other applications requiring edge-of-cylinder regions of uniformity.

    View details for Web of Science ID 000071665800013

    View details for PubMedID 9469710

  • An expandable intravenous RF coil for arterial wall imaging JOURNAL OF MAGNETIC RESONANCE IMAGING Martin, A. J., McLoughlin, R. F., Chu, K. C., Barberi, E. A., Rutt, B. K. 1998; 8 (1): 226-234

    Abstract

    An intravenous (iv) radiofrequency (RF) coil is proposed as a means of obtaining high resolution images of artery wall. The anatomic positioning of peripheral artery/vein pairs was investigated and a phantom mimicking the iliac artery/vein pair was constructed. Imaging results, comparing iv coils with external coils, demonstrated a potential 15- to 20-fold increase in signal-to-noise ratio (SNR) with iv coils. The SNR benefit was measured over a cylindrical volume, adjacent to the coil, and typical of artery position. Prototype expandable iv coils were constructed of Cu-Be loops and introduced via an 8-Fr catheter. The effects of local and remote iv coil tuning were investigated and local tuning was found to provide significant SNR benefits. The in vivo performance of iv RF coils was demonstrated in a porcine animal model. The iv coils were found to be an excellent alternative to intraarterial coils.

    View details for Web of Science ID 000080143000035

    View details for PubMedID 9500285

  • Bi-exponential T-2 decay in dairy cream phantoms MAGNETIC RESONANCE IMAGING Jones, C., MacKay, A., Rutt, B. 1998; 16 (1): 83-85

    Abstract

    MRI phantoms are an important part of any experiment because they provide a reference of known parameters. There are many choices of mono-exponential T2 phantoms, but few choices for bi-exponential T2 phantoms. We have found that dairy cream provides an excellent bi-exponential T2 model with similar relaxation times to those found in white matter. Five cream phantoms of different milk fat percentages (2, 6, 10, 18 and 35 %) were imaged with an optimized Carr-Purcell-Meiboom-Gill sequence. The decay curves for each of the phantoms were fit using Non-Negative Least Squares. We found that the short T2 component fraction relative to the total energy in the distribution correlated linearly (r = 0.9973) with the milk fat percentage. The short T2 time was 38+/-4 ms and the long T2 time was 135+/-4 ms.

    View details for Web of Science ID 000071057200011

    View details for PubMedID 9436951

  • Multistep phase difference phase contrast imaging JMRI-JOURNAL OF MAGNETIC RESONANCE IMAGING Lamothe, M. J., Rutt, B. K. 1997; 7 (5): 838-842

    Abstract

    A new technique for multistep phase-contrast image processing is presented. The N-step method consists of simply forming the linear average of the N-1 adjacent phase-difference signals. It has similar noise reduction properties as other multistep techniques, but the simplicity of the noise variance of the N-step technique allows intuitive insight into phase-difference phase-contrast processing and noise reduction, which can aid in the design of efficient and improved phase-contrast imaging sequences. As well, the computational simplicity of the N-step phase-difference technique compared with any other known multistep technique is advantageous. Like other multistep techniques, it has far more efficient noise reduction properties than simple two-step, multiple average phase-contrast imaging, even when normalized for total scan time. A three-step phase-difference velocity image has 50% less variance than an image acquired with two steps and two scans averaged but is obtained in 25% less scan time. Given its advantages, it should now be the chosen technique for increasing velocity-to-noise and contrast-to-noise ratios in all phase-difference phase-contrast clinical applications.

    View details for Web of Science ID A1997XW88300009

    View details for PubMedID 9307908

  • Experimental determination of the BOLD field strength dependence in vessels and tissue MAGNETIC RESONANCE IN MEDICINE Gati, J. S., Menon, R. S., Ugurbil, K., Rutt, B. K. 1997; 38 (2): 296-302

    Abstract

    High resolution functional MRI (fMRI) experiments were performed in human visual cortex at 0.5, 1.5, and 4 T to determine the blood oxygenation level dependent (BOLD) field strength response within regions of obvious venous vessels and cortical gray matter ("tissue"). T2*-weighted FLASH images were collected in single- and multi-echo mode and used to determine the intrinsic BOLD parameters, namely, signal-to-noise ratio (psi), the apparent transverse relaxation rate (R2*) and the change in R2* (deltaR2*) between the activated and baseline states. The authors find the average percentage signal change (deltaS/S, measured at TE = T2*) to be large in vessels (13.3 +/- 2.3%, 18.4 +/- 4.0%, and 15.1 +/- 1.2%) compared with that in tissue (1.4 +/- 0.7%, 1.9 +/- 0.7%, and 3.3 +/- 0.2%) at 0.5, 1.5, and 4 T, respectively. The signal-to-noise ratio in optimized, fully relaxed proton density weighted gradient echo images was found to increase linearly with respect to the static magnetic field strength (B0). The predicted upper bound on BOLD contrast-to-noise ratio (deltaS/R)max as a function of field strength was calculated and found to behave less than linearly in voxels containing vessels larger than the voxel itself and greater than linearly in voxels containing a mixture of capillaries and veins/venules with a diameter less than that of the voxel.

    View details for Web of Science ID A1997XN62100019

    View details for PubMedID 9256111

  • MR multispectral analysis of multiple sclerosis lesions JOURNAL OF MAGNETIC RESONANCE IMAGING Mitchell, J. R., Jones, C., Karlik, S. J., Kennedy, K., Lee, D. H., Rutt, B., Fenster, A. 1997; 7 (3): 499-511

    Abstract

    Although quantification of the lesion burden from serial MR examinations of patients with multiple sclerosis (MS) is a common technique to assess disease activity in clinical trials, pathologic change may occur within a lesion without a corresponding change in volume. Therefore, measures of lesion volume and composition may improve the sensitivity of detecting disease activity. A new technique has been developed that provides information about the intensity composition of MS lesions in standard spin-echo MR examinations. The new technique is based on the multispectral "feature space" intensity distributions of the lesions and normal tissues. Analysis of MR examinations of materials with known T1 and T2 times showed that feature space position from spin-echo examinations is largely determined from proton density (rho), T2, and the interecho delay. Information about intensity composition was obtained by reducing the multidimensional intensity distribution to one dimension while minimizing the loss of information. This technique was used to analyze eight lesions in standard spin-echo MR examinations of three patients with MS. Lesion distributions were compared between examinations by first calibrating the examinations based on the intensity distributions of cerebrospinal fluid (CSF), an internal reference tissue. Many of the lesion distributions had a distinctive peak at low intensity, corresponding to normal-appearing white matter (WM). Within the lesion distributions, increases in high intensity peaks generally were accompanied by reductions in the WM peak. Serial analysis of the lesion distributions revealed some dramatic fluctuations, even when lesion volume remained constant.

    View details for Web of Science ID A1997XA92300009

    View details for PubMedID 9170034

  • Quantitative diffusion imaging in implanted human breast tumors MAGNETIC RESONANCE IN MEDICINE Maier, C. F., Paran, Y., Bendel, P., Rutt, B. K., Degani, H. 1997; 37 (4): 576-581

    Abstract

    Quantitative diffusion measurements were performed in tumors arising from inoculation of nude mice with two human breast cancer cell lines (MCF7 and T47D) to evaluate the specificity of this technique for characterizing solid tumors. ADC maps were compared to histology and correlated well with gross tumor morphology. Measured ADCs were highly specific for viable and necrotic tumor in the five T47D tumors included in this study (P < 0.02), while only two of the five MCF7 tumors studied developed distinguishable areas of necrosis. No statistically significant difference was observed in ADCs from viable tumor between the different cell lines (P > 0.05).

    View details for Web of Science ID A1997WQ66700014

    View details for PubMedID 9094080

  • Polyvinyl alcohol cryogel: An ideal phantom material for MR studies of arterial flow and elasticity MAGNETIC RESONANCE IN MEDICINE Chu, K. C., Rutt, B. K. 1997; 37 (2): 314-319

    Abstract

    The authors present a unique application of polyvinyl alcohol (PVA) cryogel as an anthropomorphic, elastic, vascular phantom material that can be used in MR imaging. The composition consists of two nontoxic ingredients: water and PVA. The biomechanical and MR properties can be adjusted to be similar to those of excised porcine aortas by varying the number of freeze-thaw cycles to which the PVA solution is exposed. The authors present the T1, T2, shrinkage, and tensile properties of PVA cryogel tubes as a function of freeze-thaw cycles. MR images of a dual elastic aortic phantom undergoing pulsatile motion are shown.

    View details for Web of Science ID A1997WD27200024

    View details for PubMedID 9001158

  • Differences in perceived shape from shading correlate with activity in early visual areas CURRENT BIOLOGY Humphrey, G. K., Goodale, M. A., Bowen, C. V., Gati, J. S., Vilis, T., Rutt, B. K., Menon, R. S. 1997; 7 (2): 144-147

    Abstract

    The perception of shape from shading depends on the orientation of the shading gradient [1] [2] [3] [4]. Displays composed of elements with vertically oriented shading gradients of opposite polarity produce a strong and stable percept of 'concave' and 'convex' elements. If the shading gradients are rotated 90 degrees , the depth percept is reduced and appears much more ambiguous. Results from psychophysical [1] [2] [3] [4] [5] [6], neuropsychological [7] and computational studies [8] [9] suggest that the perception of shape from shading engages specific mechanisms in early cortical visual areas. In a three-dimensional functional magnetic resonance imaging (fMRI) study at 1.5 Tesla using a three-dimensional, interleaved-echoplanar imaging technique and a surface radio frequency (RF) coil placed under the visual cortex, we investigated the activity in these early visual areas associated with viewing shape from shading displays at two different orientations. We found significantly greater activation in area V1 and neighbouring low-level visual areas of cortex when subjects viewed displays that led to weak and unstable depth percepts than when they viewed displays that led to strong and stable depth percepts.

    View details for Web of Science ID A1997WH22600027

    View details for PubMedID 9016702

  • Effects of polar sampling in k-space MAGNETIC RESONANCE IN MEDICINE Lauzon, M. L., Rutt, B. K. 1996; 36 (6): 940-949

    Abstract

    Magnetic resonance imaging allows numerous k-space sampling schemes such as cartesian, polar, spherical, and other non-rectilinear trajectories. Non-rectilinear MR acquisitions permit fast scan times and can suppress motion artifacts. Still, these sampling schemes may adversely affect the image characteristics due to aliasing. Here, the Fourier aliasing effects of uniform polar sampling, i.e., equally spaced radial and azimuthal samples, are explained from the principal point spread function (PSF). The principal PSF is determined by assuming equally spaced concentric ring samples in k-space. The radial effects such as replication, smearing, truncation artifacts, and sampling requirements, are characterized based on the PSF.

    View details for Web of Science ID A1996VU89000016

    View details for PubMedID 8946360

  • Geometric characterization of stenosed human carotid arteries. Academic radiology Smith, R. F., Rutt, B. K., Fox, A. J., Rankin, R. N., Holdsworth, D. W. 1996; 3 (11): 898-911

    Abstract

    The geometry of stenosed carotid bifurcations was analyzed to determine average representations for several stenosis grades.Film angiograms of 62 patients with internal carotid artery stenoses were digitized. Residual lumen boundaries were manually outlined. The outlines were processed with a computer to extract geometric measurements. The measurements were grouped according to stenosis grade and used to create average representations.Accuracy and precision of the outlining technique were +/- 0.020 common carotid diameters (CCD) and +/- 0.025 CCD, respectively. Maximum narrowing of the internal carotid artery occurred at 0.3 CCD +/- 1.5 (mean +/- standard deviation) distal to the flow divider. The region of significant narrowing extended axially 1.2 CCD +/- 1.0. Poststenotic dilatations were observed, with enlargement of 1.3 +/- 0.7 times the normal diameter of the distal internal carotid artery. A tendency toward smaller bifurcation angles with increasing stenosis severity was observed.Three-dimensional geometric models could be created for carotid bifurcations that were disease free (normal) and of arbitrary stenosis grade.

    View details for PubMedID 8959179

  • Improved MR images of arterial specimens by submersion in trichlorotrifluoroethane MAGNETIC RESONANCE IN MEDICINE Chu, K. C., Martin, A. J., Rutt, B. K. 1996; 35 (5): 790-796

    Abstract

    MR images of ex vivo arterial specimens immersed in 1,1,2-trichloro-1,2,2-trifluoroethane (R-113) have improved signal-to-noise ratio and contrast-to-noise ratio. R-113 has no hydrogen atoms, so it yields no proton signal; hence, the contrast between the specimen and its background is maximized. SNR is maximized because (i) R-113 is nonconductive so that coil loading and inductive noise are minimized, and (ii) the volume susceptibility of R-113 closely matches that of water and tissue so that T2* effects are minimized. Short-term submersion of porcine aortas in R-113 was found to have no significant effect on the artery's hydration level, relaxation time, tensile strength, and structure or quantity of elastin, collagen, or smooth muscle cells.

    View details for Web of Science ID A1996UJ17500021

    View details for PubMedID 8722832

  • MR measurement and numerical simulation of steady flow in an end-to-side anastomosis model JOURNAL OF BIOMECHANICS Steinman, D. A., Frayne, R., Zhang, X. D., Rutt, B. K., Ethier, C. R. 1996; 29 (4): 537-542

    Abstract

    Magnetic resonance phase contrast velocity imaging ('MR PC velocimetry') is a powerful tool for measuring blood velocity. While it has been demonstrated that MR PC velocimetry can accurately measure velocity profiles in simple, unidirectional flows, errors can arise when measuring the more complex, multidirectional flows of clinical importance. In this work, we have compared MR PC velocity measurements with numerical simulations of steady flow in a physiologically relevant model of an end-to-side anastomosis, which produces many of the complex flow features expected in vivo. MR PC velocity profiles, measured using both 2D and 3D pulse sequences, showed very good agreement with numerically computed profiles, although at 2D PC data showed slightly larger errors than the 3D PC data in regions of high accelerations and oblique flow, likely due to displacement artifacts. We conclude that, under ideal conditions, MR phase contrast velocimetry can measure complex flow patterns to within 15% accuracy, but that care should be taken when using 2D pulse sequences to measure such complex flows.

    View details for Web of Science ID A1996TZ56600016

    View details for PubMedID 8964783

  • The impact of field strength on image quality in MRI JOURNAL OF MAGNETIC RESONANCE IMAGING Rutt, B. K., Lee, D. H. 1996; 6 (1): 57-62

    Abstract

    As clinical MRI has evolved, there have been numerous arguments for the use of different field strengths. Those favoring high magnetic field (1.5 T and above) include higher signal-to-noise ratio, capability for MR spectroscopy, and other forms of functional MRI, high speed imaging, and high resolution imaging. However, cost remains a significant limitation to the wider dissemination of high field MRI. There are definite cost advantages (capital, operating, siting) to the use of lower field MRI. Much debate has occurred over the past decade regarding the relative diagnostic benefits of high field MRI versus lower field MRI, but few randomized, controlled clinical trials have compared diagnostic accuracy of MRI at various field strengths. In this article, we review the physical principles of the field strength dependence of MRI in relation to image quality. The assessment of the importance of field strength in MR is incomplete without some analysis of diagnostic accuracy versus field strength. Such analysis is difficult to accomplish in an unbiased manner. The use of receiver-operator-characteristic (ROC) analysis is probably the best available method to measure diagnostic accuracy of various imaging methods without bias. An ROC study of diagnostic accuracy of 0.5 T versus 1.5 T MRI, examining several common clinical categories, has recently been conducted at our institution. Results from this study demonstrate diagnostic equivalence between these two field strengths in at least two common clinical disease categories (MS and internal derangement of the knee). These results are discussed and related to results from previous field strength studies.

    View details for Web of Science ID A1996TZ56800010

    View details for PubMedID 8851404

  • NOVEL LOW-DOSAGE HORMONAL REPLACEMENT THERAPY COMPLEMENTS DIETARY-TREATMENT OF MODERATELY HYPERCHOLESTEROLEMIC POSTMENOPAUSAL WOMEN CLINICAL AND INVESTIGATIVE MEDICINE-MEDECINE CLINIQUE ET EXPERIMENTALE Wolfe, B. M., Nisker, J. A., Hutton, L. C., Rutt, B. K. 1995; 18 (5): 362-369

    Abstract

    It is not known whether female hormonal replacement therapy (HRT) influences fasting plasma lipoprotein lipids in diet-treated hypercholesterolemic subjects. Thirteen moderately hypercholesterolemic postmenopausal women were studied during dietary treatment alone with a low fat, low cholesterol diet for the 3 months and during the subsequent 2 y of HRT with dl-norgestrel (0.075 mg daily) and estradiol-17 beta (1 mg, 25 of 28 days) with maintenance of the same diet. Hormonal replacement therapy decreased plasma total cholesterol by 11 +/- 3% (5.7 vs. 6.4 mmol/L, p < 0.005), due to a 17 +/- 3% mean reduction (p < 0.001) in the concentration of plasma low density lipoprotein cholesterol (3.9 vs. 4.7 mmol/L, p < 0.001). The ratio of plasma total cholesterol to high density lipoprotein cholesterol fell significantly by 17 +/- 4% (4.1 vs. 4.9, p < 0.005). Mean fasting plasma concentrations of total triglycerides (1.1 vs. 1.6 mmol/L, p < 0.005) fell by 31 +/- 6%, and very low density lipoprotein triglycerides (0.56 vs. 0.83 mmol/L, p < 0.02) by 33 +/- 9%. Hormonal replacement therapy was well-tolerated, improved mood levels, and increased the mineral content of the vertebral spine significantly, while effectively relieving vasomotor flushing. Hormonal replacement therapy complements the dietary treatment of hypercholesterolemia.

    View details for Web of Science ID A1995RZ62300003

    View details for PubMedID 8529319

  • A NOVEL TRANSVERSE GRADIENT COIL DESIGN FOR HIGH-RESOLUTION MR-IMAGING MAGNETIC RESONANCE IN MEDICINE Maier, C. F., Chu, K. C., Chronik, B. A., Rutt, B. K. 1995; 34 (4): 604-611

    Abstract

    The authors describe a new gradient coil design for high resolution human, animal, specimen, or phantom imaging with high gradient efficiency and a large region of excellent gradient uniformity. Important features of our new design are the simple analytical description of the wire patterns that comprise the design, and ease of construction. Wires are spaced in a sinusoidal distribution around the circumference of the cylinder, and curved in an arcsin shape along the length of the cylinder. This coil produces a magnetic field pointing in a direction transverse to the axis of the coil with a gradient in the direction parallel to the axis of the coil. The same arcsin coil can be used to create a magnetic field pointing in a direction parallel to its axis with a gradient in a direction perpendicular to the coil axis. A prototype coil was constructed; field and inductance calculations were verified. Geometric variations on this coil design were modeled and their performance characteristics compared. This coil design is ideal for rapid implementation of a transverse gradient coil, since no specialized design software is required.

    View details for Web of Science ID A1995RX75100016

    View details for PubMedID 8524029

  • MEASUREMENT OF FLUID-SHEAR RATE BY FOURIER-ENCODED VELOCITY IMAGING MAGNETIC RESONANCE IN MEDICINE Frayne, R., Rutt, B. K. 1995; 34 (3): 378-387

    Abstract

    A new technique for estimating the blood fluid shear rate at the vessel wall is presented. The technique uses Fourier-encoded velocity imaging to determine the velocity distribution within a spatial element (voxel) that straddles the blood-vessel wall interface. By appropriate processing, the velocity distribution (1) can determine the location of the wall-blood interface within the voxel and (2) estimate the velocity profile across the spatial extent of the voxel. From this information, accurate estimates of fluid shear rate may be obtained. Simulations are presented to illustrate this technique and to show the effects of various error sources, including differences in proton densities between blood and wall tissues and flow-related signal changes. Experimental evidence obtained for steady flow in straight tubes is also presented in support of the technique. The mean error in the experimental shear rate estimates found using the proposed technique was -15%. This represents a significant improvement over estimates obtained by extrapolation of the velocity profile over multiple voxels (mean error of -73%).

    View details for Web of Science ID A1995RR68700014

    View details for PubMedID 7500877

  • MR GRADIENT COIL HEAT DISSIPATION MAGNETIC RESONANCE IN MEDICINE Chu, K. C., Rutt, B. K. 1995; 34 (1): 125-132

    Abstract

    The temperature responses of five different gradient coil designs were modeled using simplified engineering equations and measured. The model predicts that the coil temperature approaches a maximum as an inverse exponential, where the maximum temperature is governed by two parameters: a local power density and a cooling term. The power density term is a function of position and is highest where the current paths have minimum widths and are closely packed. The cooling parameter consists of convective, conductive, and radiative components which can be controlled by (1) providing forced cooling, (2) having a coil former with high thermal conductivity and thin walls, and (3) varying the emissivity of the coil surfaces. For a given gradient strength, the average temperature rise is minimized by designing a coil with a small radius and thick copper. The model predicted the local temperature rise, which is also dependent on the current density, to within 5 degrees C of measured values.

    View details for Web of Science ID A1995RF76800018

    View details for PubMedID 7674891

  • ACCURACY OF MR PHASE-CONTRAST VELOCITY-MEASUREMENTS FOR UNSTEADY-FLOW JOURNAL OF MAGNETIC RESONANCE IMAGING Frayne, R., Steinman, D. A., Ethier, C. R., Rutt, B. K. 1995; 5 (4): 428-431

    Abstract

    The accuracy of MR phase contrast (PC) velocity measurements for unsteady flow has been quantitatively assessed. Spatially resolved velocity fields were measured in a long straight tube using a gated PC technique, and the resulting MR PC velocity data were compared with velocities derived from the analytic Womersley solution to the Navier-Stokes equations governing fluid flow. The overall root-mean-square (rms) difference between the measured and analytic velocities was 1.6 cm s-1 for nominally sinusoidal flow waveforms with peak velocities ranging from 51.6 cm s-1 to 59.8 cm s-1. This rms difference corresponded to 7.5% of the mean fluid velocity, which is similar to the cited accuracy of approximately 5% for MR PC velocimetry for steady flows. Linear regression between the PC velocity measurements and the velocities obtained using the analytic expression was highly significant (r2 = 0.997) and yielded a slope of 0.998, close to the expected value of 1. We conclude that the gated MR PC velocity measurements in unsteady flow are accurate.

    View details for Web of Science ID A1995RL65100009

    View details for PubMedID 7549205

  • UNDERSTANDING ACCELERATION INDUCED DISPLACEMENT ARTIFACTS IN PHASE-CONTRAST MR VELOCITY-MEASUREMENTS JMRI-JOURNAL OF MAGNETIC RESONANCE IMAGING Frayne, R., Rutt, B. K. 1995; 5 (2): 207-215

    Abstract

    A theoretical framework for understanding acceleration-induced errors in phase-contrast magnetic resonance velocity measurements has been developed. An important result of this framework is the interpretation of acceleration-induced velocity errors as displacement artifacts due to the delay between velocity and spatial encoding. A rotating-disk phantom was used to confirm the theoretically predicted displacement times (the difference between theory and experiment was 8.2%). Errors were also observed in velocity profiles measured in regions of fluid acceleration downstream from a step stenosis. The magnitude of these errors could be predicted and corrected by using the analytic framework.

    View details for Web of Science ID A1995QM88600013

    View details for PubMedID 7766984

  • FREQUENCY-RESPONSE OF PROSPECTIVELY GATED PHASE-CONTRAST MR VELOCITY-MEASUREMENTS JOURNAL OF MAGNETIC RESONANCE IMAGING Frayne, R., Rutt, B. K. 1995; 5 (1): 65-73

    Abstract

    The authors developed and experimentally verified expressions that describe the frequency response of prospectively gated phase-contrast magnetic resonance velocity measurements. Both interleaved and noninterleaved phase-contrast techniques were evaluated. The primary determinants of the frequency response were (a) the number of interleaved acquisitions (N), (b) the time between acquisitions (delta T), and (c) the degree of balance between the first moments of the velocity-encoding gradients. To quantify the last factor, an imbalance parameter (U) was defined. Depending on the chosen implementation and U, deviations from the ideal frequency responses were predicted and observed. The expressions also revealed an advantage of interleaved acquisitions that use a one-sided gradient configuration: no changes in the frequency response. The effects of concurrently encoding orthogonal velocity components with a Hadamard four-point scheme were examined.

    View details for Web of Science ID A1995QC79000010

    View details for PubMedID 7696811

  • EFFECTS OF PHYSIOLOGICAL WAVE-FORM VARIABILITY IN TRIGGERED MR-IMAGING - THEORETICAL-ANALYSIS JMRI-JOURNAL OF MAGNETIC RESONANCE IMAGING Lauzon, M. L., Holdsworth, D. W., Frayne, R., Rutt, B. K. 1994; 4 (6): 853-867

    Abstract

    One of the assumptions inherent in most forms of triggered magnetic resonance (MR) imaging is that the pulsatile waveform (be it cardiac, respiratory, or some other) is purely periodic. In reality, the periodicity condition is rarely met. Physiologic waveform variability may lead to image artifacts and errors in velocity or volume flow rate estimates. The authors analyze the effects of physiologic waveform variability in triggered MR imaging. They propose that this variability be treated as a modulation of the underlying motion waveform. This report concentrates on amplitude modulation of the velocity waveform, which results in amplitude and phase modulation of the transverse magnetization. Established Fourier and modulation theory and the recently described principles of (k,t)-space were used to derive the appearance of physiologic waveform variability artifacts in triggered MR images and to predict errors in time-averaged and instantaneous velocity estimates that may result from such motion effects, including effects such as ghost overlap. Simulations and experimental results are provided to confirm the theory.

    View details for Web of Science ID A1994PR94400014

    View details for PubMedID 7865947

  • TURBINE FLOW SENSOR FOR VOLUME-FLOW RATE VERIFICATION IN MR MAGNETIC RESONANCE IN MEDICINE Frayne, R., Holdsworth, D. W., Smith, R. F., Kasrai, R., LARSEN, J. P., Rutt, B. K. 1994; 32 (3): 410-417

    Abstract

    A turbine flow sensor for MR flow experiments has been evaluated using reference volume-flow rate measurements obtained using an electromagnetic (EM) flow meter measurements and simultaneous phase contrast (PC) MR acquisitions. After calibration, the device was found to have accuracy (compared with the EM flow meter), linearity, and precision of better than +/- 1%, +/- 3.5%, 3.5%, respectively, in constant flow mode (0 to 30 ml s-1). The frequency response of the flow sensor was flat (within +/- 10%) up to 13.9 Hz. Volume-flow rate measurements on constant and simulated physiologic flow waveforms were in close agreement with both the electromagnetic (EM) flow meter and the gated MR PC estimates.

    View details for Web of Science ID A1994PE25900017

    View details for PubMedID 7984075

  • QUADRUPOLE GRADIENT COIL DESIGN AND OPTIMIZATION - A PRINTED-CIRCUIT BOARD APPROACH MAGNETIC RESONANCE IN MEDICINE Chu, K. C., Rutt, B. K. 1994; 31 (6): 652-659

    Abstract

    Three different dual-axis quadrupole gradient coils for quantitative high resolution MR imaging of small animals, phantoms and specimens were designed and built using printed circuit board technology. Numerical optimization of the conductor positions was used to increase the volume of 0.4% gradient uniformity by up to a factor of four. In one coil, the volume of 5% gradient uniformity occupied 88% and 83% of the overall diameter and length of the coil, respectively. A systematic error of 0.5% in the wire placement was shown to cause a reduction in the volume of 0.4% gradient uniformity by a factor of two, though the region of 5% gradient uniformity was not significantly affected. Heat transfer calculations were used to determine maximum peak and root-mean-squared currents that could safely be applied to the coils.

    View details for Web of Science ID A1994NN57100010

    View details for PubMedID 8057818

  • Poster production by color laser imager. The Journal of biocommunication Rankin, R. N., Downey, D. B., Rutt, B. K., Rankin, R. N. 1994; 21 (3): 22-24

    Abstract

    The scientific poster is an important educational tool at most radiology meetings. The visual impact of the exhibit is important in attracting attention and conveying content to the reader. A new method of designing and producing full-color transilluminated posters in the radiology department using a personal computer and color laser imager is described. The advantages of this approach are author control over the production process and production of a visually interesting exhibit.

    View details for PubMedID 7527802

  • FREQUENCY-RESPONSE OF RETROSPECTIVELY GATED PHASE-CONTRAST MR-IMAGING - EFFECT OF INTERPOLATION JOURNAL OF MAGNETIC RESONANCE IMAGING Frayne, R., Rutt, B. K. 1993; 3 (6): 907-917

    Abstract

    Retrospectively gated phase-contrast (PC) magnetic resonance velocity and volume flow measurements were evaluated in both in vitro and in vivo experiments. The accuracy of these measurements was found to be affected by the interpolation window width required in the reconstruction of retrospectively gated data. Interpolation modified the frequency content of the series of temporal measurements by decreasing the response at higher frequencies. With a series of sinusoidal flow waveforms, the frequency response of one specific implementation of retrospectively gated PC velocity measurements was experimentally determined. The experimental response agreed with the theoretical response predicted from an analysis of the interpolating function (2.2% root-mean-square difference). In vitro experiments with a simulated carotid flow waveform demonstrated errors in the systolic measurements that were a direct result of the modified frequency response. A volunteer study was also undertaken and confirmed the in vitro findings.

    View details for Web of Science ID A1993MG72100016

    View details for PubMedID 8280982

  • GENERALIZED K-SPACE ANALYSIS AND CORRECTION OF MOTION EFFECTS IN MR-IMAGING MAGNETIC RESONANCE IN MEDICINE Lauzon, M. L., Rutt, B. K. 1993; 30 (4): 438-446

    Abstract

    A new approach to understanding and reducing motion artifacts in magnetic resonance imaging (MRI) is introduced. This paper presents a novel technique for correcting generalized motion artifacts arising from translation, rotation, dilation, and compression, or any combination thereof. We also describe a new pulse sequence and a specialized postprocessing technique required to suppress these motion artifacts. The correction algorithm corrects for generalized motion. The theoretical basis of the correction scheme is founded upon the (k,t)-space formalism and the concept of pulse sequence contrast mapping functions. The proposed (k,t) formalism is based on the Fourier projection slice theorem and allows us to determine how motion artifacts arise. The correction technique currently suffers from some spatial resolution and signal-to-noise ratio limitations, and works better for small objects than large objects. These problems will be investigated in subsequent studies.

    View details for Web of Science ID A1993MA37800005

    View details for PubMedID 8255191

  • A GEOMETRICALLY ACCURATE VASCULAR PHANTOM FOR COMPARATIVE-STUDIES OF X-RAY, ULTRASOUND, AND MAGNETIC-RESONANCE VASCULAR IMAGING - CONSTRUCTION AND GEOMETRICAL VERIFICATION MEDICAL PHYSICS Frayne, R., GOWMAN, L. M., Rickey, D. W., Holdsworth, D. W., Picot, P. A., Drangova, M., Chu, K. C., Caldwell, C. B., Fenster, A., Rutt, B. K. 1993; 20 (2): 415-425

    Abstract

    A technique for producing accurate models of vascular segments for use in experiments that assess vessel geometry and flow has been developed and evaluated. The models are compatible with x-ray, ultrasound, and magnetic resonance (MR) imaging systems. In this paper, a model of the human carotid artery bifurcation, is evaluated that has been built using this technique. The phantom consists of a thin-walled polyester-resin replica of the bifurcation through which a blood-mimicking fluid may be circulated. The phantom is surrounded by an agar tissue-mimicking material and a series of fiducial markers. The blood- and tissue-mimicking materials have x-ray, ultrasound, and MR properties similar to blood and tissue; fiducial markers provide a means of aligning images acquired by different modalities. The root-mean-square difference between the inner wall geometry of the constructed model and the desired dimensions was 0.33 mm. Static images were successfully acquired using x-ray, ultrasound, and MR imaging systems, and are free of significant artifacts. Flow images acquired with ultrasound and MR agree qualitatively with each other, and with previously published flow patterns. Volume-flow measurements obtained with ultrasound and MR were within 4.4% of the actual values.

    View details for Web of Science ID A1993KZ77100024

    View details for PubMedID 8497234

  • COMPUTER-CONTROLLED FLOW SIMULATOR FOR MR FLOW STUDIES JMRI-JOURNAL OF MAGNETIC RESONANCE IMAGING Frayne, R., Holdsworth, D. W., GOWMAN, L. M., Rickey, D. W., Drangova, M., Fenster, A., Rutt, B. K. 1992; 2 (5): 605-612

    Abstract

    A novel computer-controlled flow simulator for use in magnetic resonance (MR) flow experiments was evaluated. The accuracy in constant-flow mode was better than 1%. The accuracy in pulsatile-flow mode was found to be dependent on the interconnecting tubing. The short-term and long-term reproducibilities of pulsatile waveforms were less than or equal to 0.4 mL/sec (1 standard deviation). Increased response times due to the lengths of tubing required in MR flow experiments were surmounted by using a modified tubing configuration and precompensated waveforms. Piston reversal was found not to cause major difficulties in MR flow experiments.

    View details for Web of Science ID A1992JP25600019

    View details for PubMedID 1392256

  • INTERACTIVE DISPLAY OF VOLUMETRIC DATA BY FAST FOURIER PROJECTION COMPUTERIZED MEDICAL IMAGING AND GRAPHICS Dunne, S., Napel, S., Rutt, B. 1992; 16 (4): 237-251

    Abstract

    This article describes a new algorithm for reprojection of volumetric data, called Fast Fourier Projection (FFP), which is one to two orders of magnitude faster than conventional methods such as ray casting. The theoretical basis of the new method is developed in a unified mathematical framework encompassing slice imaging and conventional volumetric reprojection methods. Software implementation is discussed in detail. The article closes with an account of experience with a prototype FFP implementation, and applications of the technique in medical visualization.

    View details for Web of Science ID A1992JJ48100001

    View details for PubMedID 1511397

  • VISUALIZING 3-DIMENSIONAL FLOW WITH SIMULATED STREAMLINES AND 3-DIMENSIONAL PHASE-CONTRAST MR IMAGING JMRI-JOURNAL OF MAGNETIC RESONANCE IMAGING Napel, S., Lee, D. H., Frayne, R., Rutt, B. K. 1992; 2 (2): 143-153

    Abstract

    Three-dimensional (3D) velocity maps acquired with 3D phase-contrast magnetic resonance (MR) imaging contain information regarding complex motions that occur during imaging. A technique called simulated streamlines, which facilitates the display and comprehension of these velocity data, is presented. Single or multiple seed points may be identified within blood vessels of interest and tracked through the velocity field. The resulting trajectories are combined with a 3D MR angiogram and displayed with 3D volume visualization software. Mathematical analysis highlights potential applications and pitfalls of the technique, which was implemented both in phantoms and in vivo with excellent results. For example, single streamlines reveal helical flow patterns in aneurysms, and multiple streamlines seeded in the common carotid artery reveal branch filling-time relationships and slow filling of the carotid bulb. The technique is helpful in understanding these complex flow patterns.

    View details for Web of Science ID A1992HK05600003

    View details for PubMedID 1562765

  • A PROTOTYPE HIGH-PURITY GERMANIUM DETECTOR SYSTEM WITH FAST PHOTON-COUNTING CIRCUITRY FOR MEDICAL IMAGING MEDICAL PHYSICS Hasegawa, B. H., Stebler, B., Rutt, B. K., Martinez, A., Gingold, E. L., Barker, C. S., Faulkner, K. G., Cann, C. E., Boyd, D. P. 1991; 18 (5): 900-909

    Abstract

    A data-acquisition system designed for x-ray medical imaging utilizes a segmented high-purity germanium (HPGe) detector array with 2-mm wide and 6-mm thick elements. The detectors are contained within a liquid-nitrogen cryostat designed to minimize heat losses. The 50-ns pulse-shaping time of the preamplifier electronics is selected as the shortest time constant compatible with the 50-ns charge collection time of the detector. This provides the detection system with the fastest count-rate capabilities and immunity from microphonics, with moderate energy resolution performance. A theoretical analysis of the preamplifier electronics shows that its noise performance is limited primarily by its input capacitance, and is independent of detector leakage current up to approximately 100 nA. The system experimentally demonstrates count rates exceeding 1 million counts per second per element with an energy resolution of 7 keV for the 60-keV gamma ray photon from 241Am. The results demonstrate the performance of a data acquisition system utilizing HPGe detector systems which would be suitable for dual-energy imaging as well as systems offering simultaneous x-ray transmission and radionuclide emission imaging.

    View details for Web of Science ID A1991GJ83300005

    View details for PubMedID 1961152

  • FAST FOURIER PROJECTION FOR MR ANGIOGRAPHY MAGNETIC RESONANCE IN MEDICINE Napel, S., Dunne, S., Rutt, B. K. 1991; 19 (2): 393-405

    Abstract

    We have developed a technique called fast Fourier projection which rapidly produces projections through images and is particularly useful for generating MR angiograms. Based on the projection-slice theorem of Fourier transform theory, this method extracts planes from three-dimensional spatial frequency space and computes projections at arbitrary viewing angles by two-dimensional inverse Fourier transformation. Typical computation times are on the order of 1 s per projection. This performance makes possible interactive selection of optimal projection directions for visualizing the desired vasculature in single or stereo-pair angiographic images and drastically reduces the time required to generate sequences of projections for display in movie loops compared to the conventional ray-casting approach. The method is easily implemented on off-line workstations or directly on MRI computer systems.

    View details for Web of Science ID A1991FQ24300029

    View details for PubMedID 1881328

  • MAGNETIC-RESONANCE TECHNIQUES FOR BLOOD-FLOW MEASUREMENT AND VASCULAR IMAGING JOURNAL OF THE CANADIAN ASSOCIATION OF RADIOLOGISTS-JOURNAL DE L ASSOCIATION CANADIENNE DES RADIOLOGISTES Rutt, B. K., Napel, S. 1991; 42 (1): 21-30

    Abstract

    The authors review the history and physical principles behind vascular magnetic resonance imaging (MRI) techniques, developed to measure blood flow noninvasively and to display images of the vasculature. All these techniques have been used to create magnetic resonance angiograms, in which the vasculature is shown in a projection format similar to x-ray angiography. Signal loss limits the effectiveness of "white-blood" magnetic resonance angiography techniques, since slow flow and complex flow often cause a drop in signal and consequently a loss of accuracy in depicting vessel anatomy. "Black-blood" magnetic resonance angiography is described as a method that avoids these problems of signal loss. Selective black-blood magnetic resonance angiography is introduced as a technique for improving the visualization of the vasculature when other signal-void structures are present in the volume of interest.

    View details for Web of Science ID A1991FC78400004

    View details for PubMedID 2001525

  • THE USE OF MAGNETIC-RESONANCE-IMAGING IN EXERTIONAL COMPARTMENT SYNDROMES AMERICAN JOURNAL OF SPORTS MEDICINE Amendola, A., Rorabeck, C. H., VELLETT, D., Vezina, W., Rutt, B., Nott, L. 1990; 18 (1): 29-34

    Abstract

    This prospective, double-blind study was carried out to assess the usefulness of magnetic resonance imaging (MRI) as a noninvasive method in the diagnosis of chronic compartment syndrome (CCS). As well, a new radiopharmaceutical known as methoxy isobutyl isonitrile that has been shown to be taken up by muscle in direct proportion to its blood flow was used to illustrate the possible pathophysiology of this syndrome. Twenty patients with a history of chronic leg pain and possible diagnosis of CCS and five normal volunteers had preexercise and postexercise MRI, nuclear medicine imaging, and static and dynamic slit catheter pressure studies. Nine patients had classic symptoms; only five of these nine had abnormal pressure studies. The other 11 patients had an element of pain at rest and had normal pressure studies. The nuclear blood flow studies were normal in all 25 legs tested in this study. Measurement of intrinsic MRI parameters T1 and T2 in the normal legs as well as in those with an atypical history showed a marked elevation with exercise and a gradual return to baseline postexercise that was similar to the pressure curves. In the five patients with a clinical history and elevated pressures, four had abnormal MRI studies with failure of T1 to return to baseline values. Although these results demonstrate the potential of MRI as a tool for noninvasively monitoring muscle status, clinical history and examination remain important in the diagnosis of CCS. This study indicates that the pathophysiology of exertional compartment syndrome does not appear to be related to ischemia.

    View details for Web of Science ID A1990CL47500005

    View details for PubMedID 2301688

  • PATIENT ANESTHESIA AND MONITORING AT A 1.5-T MRI INSTALLATION MAGNETIC RESONANCE IN MEDICINE Karlik, S. J., HEATHERLEY, T., Pavan, F., Stein, J., Lebron, F., Rutt, B., Carey, L., Wexler, R., Gelb, A. 1988; 7 (2): 210-221

    Abstract

    This paper describes the facilities successfully used to provide patient monitoring and anesthesia support in a 1.5-T imaging installation. The requirements for the MRI site for anesthetic gases, shielded power, and radiofrequency ports are outlined. Specific modifications in anesthesia machines, anesthesia cart, laryngoscope, mercury sphygmomanometer, oximeter, and remote blood pressure devices are described. Additional aspects of patient monitoring and support, e.g., electrocardiogram and pressure infusion, are also discussed.

    View details for Web of Science ID A1988N908700008

    View details for PubMedID 3398768

  • VERTEBRAL MINERAL DETERMINATION BY QUANTITATIVE COMPUTED-TOMOGRAPHY (QCT) - ACCURACY OF SINGLE AND DUAL ENERGY MEASUREMENTS JOURNAL OF COMPUTER ASSISTED TOMOGRAPHY Gluer, C. C., REISER, U. J., Davis, C. A., Rutt, B. K., Genant, H. K. 1988; 12 (2): 242-258

    Abstract

    Quantitative CT (QCT) studies of trabecular vertebral bone tissue have been carried out in vitro on a GE CT/T 9800 scanner. Results of both single energy (SE) 80 kVp and dual energy (DE) 80/140 kVp QCT data are compared with chemical mineral analysis to determine accuracy. We examined 62 vertebral specimens, from 28 cadavers (19 male and 9 female with an age range of 19-93 years, mean = 60.4). Averaging the results of all vertebral bodies of the same individual for SEQCT versus ashweight, we found a correlation coefficient (r) of 0.94 (p less than 0.0001), a standard error of the estimate (SEE) of 12.2 mg/cm3 (calibrated to K2HPO4), with a coefficient of variation (CV) of 13.2% and an average underestimation of bone mineral content of 18.7 mg/cm3. The corresponding DEQCT results were r = 0.98 (p less than 0.0001), SEE = 7.4 mg/cm3, CV = 7.0%, and an average underestimation of 4.9 mg/cm3. The SE and DE results are correlated with r = 0.98 (p less than 0.0001), SEE = 8.0 mg/cm3, and CV = 8.7%. From our SEQCT data and the results of the chemical analysis of bone mineral and fat content we calculated a fat sensitivity of 7.7 mg/cm3 K2HPO4 per 100 mg/cm3 fat change for our scanner. Using an average fat variability of 87.5 mg/cm3, this leads to a fat-related uncertainty for the normative SEQCT data of 6.7 mg/cm3, which is far lower than the normal biological variation of 29.4 mg/cm3. Using tabulated normative data on fat content versus age and versus mineral content of 188 vertebral specimens from five collaborating centers, we derived a correction algorithm for QCT measurement that reduces our average underestimation to 0.88 mg/cm3 with an SEE of 12.1 mg/cm3. Hence, this correction procedure can be used to estimate the fat corrected absolute mineral density for research purposes or for scanners with high fat sensitivity. For the GE CT/T 9800 scanner, with a relatively low fat to mineral sensitivity at 80 kVp, the correction procedure is generally not recommended for clinical studies since it minimizes the average fat induced error but does not reduce the residual, partially fat related uncertainty. Finally, since the fat related uncertainty is small compared to biological variation, the correlation is high between SEQCT and DEQCT, and the radiation dose is lower and the precision higher for SEQCT, we suggest that most clinical diagnostic studies using the GE CT/T 9800 scanner for bone mineral determination employ SEQCT at 80 kVp.

    View details for Web of Science ID A1988M543100013

    View details for PubMedID 3351039

  • SELECTIVE IODINE IMAGING USING LANTHANUM-K FLUORESCENCE MEDICAL PHYSICS Rutt, B. K., Cunningham, I. A., Fenster, A. 1983; 10 (6): 801-808

    Abstract

    Time-dependent subtraction techniques have tremendously improved the visualization of iodinated vessels. These techniques suffer from motion artifacts, however, since the mask image is acquired several seconds prior to the contrast image. A K-edge subtraction technique for selectively imaging iodine using the characteristic x rays from a lanthanum secondary target is presented. The K alpha lines of lanthanum closely straddle the K edge of iodine. A prepatient iodine filter will alter the ratio of K alpha 1 to K alpha 2 intensities; by subtracting two images made with different K alpha 1/K alpha 2 ratios, iodinated structures can be isolated. Since the method requires no mask image, motion artifacts are reduced. Preliminary images acquired with an image intensifier/photodiode array detector system are shown. Theoretical performance of this method is compared to other iodine-selective imaging techniques on the basis of exposure and dose. The feasibility of using lanthanum K fluorescence for rapid clinical iodine-selective imaging is discussed.

    View details for Web of Science ID A1983RW00600006

    View details for PubMedID 6361506

  • A XENON IONIZATION DETECTOR FOR SCANNED PROJECTION RADIOGRAPHY - THEORETICAL CONSIDERATIONS MEDICAL PHYSICS Rutt, B. K., Drost, D. J., Fenster, A. 1983; 10 (3): 284-292

    Abstract

    Xenon ionization detectors have been used successfully in computed tomography (CT) scanners; however, the detector design used in CT scanners does not provide sufficient spatial resolution for scanned projection radiography. We have been investigating a new design of xenon detector with individual element widths of 0.5 mm. In this design, there are no metal septa separating individual elements. As a result, detection efficiency is better than the design with septa, and construction of an array with submillimeter element widths is simpler; however, crosstalk will now occur between elements. Theoretical calculations of efficiency and resolution for our septaless design of xenon detector are presented. Results of these calculations indicate that for a spectrum of 100 kVp, element dimensions of 0.5 mm X 0.5 mm X 10 cm, a front window of 0.5-mm aluminum, and a xenon pressure of 20 atm, quantum efficiency will be greater than 95%, detective quantum efficiency (DQE) will be approximately 75%, and both energy and conversion efficiencies will be limited to 50% by K-fluorescent escape. The calculations also predict that for the same design, the reduction in lesion contrast induced by crosstalk will be less than 10% for all typical spectra. These theoretical results have encouraged us to pursue the construction of a prototype septaless xenon detector for scanned projection radiography.

    View details for Web of Science ID A1983QT47400002

    View details for PubMedID 6877174

  • SPLIT-FILTER COMPUTED-TOMOGRAPHY - A SIMPLE TECHNIQUE FOR DUAL ENERGY SCANNING JOURNAL OF COMPUTER ASSISTED TOMOGRAPHY Rutt, B., Fenster, A. 1980; 4 (4): 501-509

    Abstract

    A simple technique for obtaining dual energy information from a single computed tomography (CT) scan is described. The method involves filtering the two halves of the X-ray fan beam differently. It is shown that during a 360 degree scan, this split-filtration geometry results in dual energy noise analysis, valid for polychromatic X-ray beams, is presented and used to determine the optimal parameters for the split-filter scans. Using the theoretically optimal split-filter design installed on a commercial CT scanner, photoelectric and Compton images of a head phantom were obtained. Recombination of the photoelectric and Compton components of attenuation at arbitrary energies demonstrates the ability to remove spectral artifacts from conventional CT images.

    View details for Web of Science ID A1980JX88600015

    View details for PubMedID 7391293

Conference Proceedings


  • Acoustic noise reduction in a 4 T MRI scanner Mechefske, C. K., Geris, R., Gati, J. S., Rutt, B. K. SPRINGER. 2002: 172-176

    Abstract

    High-field, high-speed magnetic resonance imaging (MRI) can generate high levels of noise. There is ongoing concern in the medical and imaging research communities regarding the detrimental effects of high acoustic levels on auditory function, patient anxiety, verbal communication between patients and health care workers and ultimately MR image quality. In order to effectively suppress the noise levels inside MRI scanners, the sound field needs to be accurately measured and characterized. This paper presents the results of measurements of the sound radiation from a gradient coil cylinder within a 4 T MRI scanner under a variety of conditions. These measurement results show: (1) that noise levels can be significantly reduced through the use of an appropriately designed passive acoustic liner; and (2) the true noise levels that are experienced by patients during echo planar imaging.

    View details for Web of Science ID 000173319000007

    View details for PubMedID 11755093

  • Simultaneous MRI measurement of blood flow, blood volume, and capillary permeability in mammary tumors using two different contrast agents Henderson, E., Sykes, J., Drost, D., Weinmann, H. J., Rutt, B. K., Lee, T. Y. JOHN WILEY & SONS INC. 2000: 991-1003

    Abstract

    A technique for the simultaneous measurement of three vascular parameters: blood flow (Frho), blood volume (v(b)), and the capillary permeability-surface area product (PSrho) in breast tumors using dynamic contrast-enhanced magnetic resonance imaging (MRI) is presented. Features of the technique include measurement of precontrast tumor T(1), rapid temporal sampling, measurement of the arterial input function, and use of a distributed parameter tracer kinetic model. Parameter measurements are compared that were determined using two contrast agents of different molecular weights, gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA; 0.6 kDa) and Gadomer-17 (17 kDa), in 18 spontaneous canine mammary tumors. Measurements of Frho and v(b) corresponded well with literature values, and the mean PSrho measured using Gd-DTPA was a factor of 15 higher than that measured using Gadomer-17. J. Magn. Reson. Imaging 2000;12:991-1003.

    View details for Web of Science ID 000171295600026

    View details for PubMedID 11105041

  • Anthropomorphic carotid bifurcation phantom for MRI applications Smith, R. F., Rutt, B. K., Holdsworth, D. W. JOHN WILEY & SONS INC. 1999: 533-544

    Abstract

    Anthropomorphic carotid bifurcation flow phantoms that incorporate different stenotic geometries within the internal carotid artery have been developed. This technique produces high-fidelity, life-size vascular flow models that are compatible with magnetic resonance techniques. The models, in conjunction with a computer-controlled flow pump, address the need for a complex vascular geometry that can be used to verify magnetic resonance angiography (MRA) techniques that quantify stenosis severity and blood flow. Stenotic geometries, with up to 80% diameter reduction, have been fabricated in two different phantom materials. Plastic phantoms provide a durable, rigid geometry where the absolute dimensions of the model are well known. Agar gel phantoms provide tissue-like signal (T1, T2) up to the lumen boundary and are also compatible with ultrasound techniques. In this paper the technique to produce vascular flow phantoms is outlined and the compatibility of these phantoms with MRA techniques is demonstrated. J. Magn. Reson. Imaging 1999;10:533-544.

    View details for Web of Science ID 000087572000006

    View details for PubMedID 10508320

  • Combined analysis of spatial and velocity displacement artifacts in phase contrast measurements of complex flows Steinman, D. A., Ethier, C. R., Rutt, B. K. JOHN WILEY & SONS INC. 1997: 339-346

    Abstract

    MR phase contrast (PC) velocity imaging is a promising tool for quantifying blood flow velocity in vivo. PC velocity imaging is, however, susceptible to artifacts that result from the displacement of spins during the finite duration pulse sequences. Such displacement artifacts can lead to errors in velocity measurements, especially in the presence of oblique and accelerating flows, which are common throughout the cardiovascular system. By tracking particles (representing spins) through a computed velocity field, and assuming that spatial and velocity encodings occur at discrete times during the pulse sequence, we simulate the separate and combined effects of oblique and acceleration artifacts on PC velocity images. We demonstrate, both by simulation and MR measurement, the errors associated with such artifacts in PC velocity measurements in a representative flow geometry. Using example particle trajectories, we provide a fluid dynamic basis for characteristic phase-velocity image distortions that can arise when imaging complex, physiologically relevant flows.

    View details for Web of Science ID A1997WP11800013

    View details for PubMedID 9090588

  • AN IN-VITRO MULTIMODALITY VASCULAR PHANTOM Frayne, R., GOWMAN, L. M., Rickey, D. W., Holdsworth, D. W., Picot, P. A., Drangova, M., Chu, K. C., Fenster, A., Rutt, B. K. CANADIAN MEDICAL & BIOLOGICAL ENGINEERING SOC. 1992: 180-181
  • AORTIC-VALVE ROOT INTERACTIONS IN PORCINE HEARTS - IMPLICATIONS FOR BIOPROSTHETIC VALVE SIZING Vesely, I., Menkis, A. H., Rutt, B., Campbell, G. FUTURA PUBL CO. 1991: 482-489

    Abstract

    The implantation of aortic allografts as well as stentless, freehand porcine xenograft valves requires proper sizing of the graft for the recipient aortic root. To visualize the aortic valve in motion and measure the cyclic expansion of the aortic root, we developed an isolated porcine heart model and a computerized three-dimensional reconstruction technique. Dynamic and static expansions of the aortic root were obtained from beating and arrested porcine hearts, and additional static expansions at varying pressures were measured from reconstructed three-dimensional models of valves obtained with high-resolution magnetic resonance imaging. Measurements of aortic root expansion have shown that it is highly dependent upon the pressures imposed on the heart. Although the aortic root expanded by only 5% between systolic pressures of 60 and 100 mmHg, the total expansion was up to 40% between rest and cyclic pressurizing to 100 mmHg. This data suggest that unstented xenograft valves should be sized 30% to 40% larger than the collapsed size of the recipient aorta. Proper sizing of valves on stents should also be attempted to reduce the large amount of leaflet redundancy that current stenting techniques produce.

    View details for Web of Science ID A1991GX17000008

    View details for PubMedID 1815773

  • WHOLE-BODY CT SCANNER FOR ULTRAPRECISE, ULTRAACCURATE DETERMINATION OF BONE-DENSITY Rutt, B. K., STEBLER, B. G., Cann, C. E., Boyd, D. P., Genant, H. K., Manatt, S. L. LIPPINCOTT-RAVEN PUBL. 1985: 609-610

    View details for Web of Science ID A1985AGZ4800049

    View details for PubMedID 11540867

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