Efficient bloch-siegert B1 (+) mapping using spiral and echo-planar readouts.
Magnetic resonance in medicine
2013; 70 (6): 1669-1673
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
Three-Dimensional Dixon Fat-Water Separated Rapid Breathheld Imaging of Myocardial Infarction
JOURNAL OF MAGNETIC RESONANCE IMAGING
2013; 38 (6): 1362-1368
PURPOSE: To develop a breathhold three-dimensional (3D) Dixon technique for fat suppressed imaging of myocardial infarction. MATERIALS AND METHODS: A pulse sequence was developed that uses a radial fan-beam k-space segmentation scheme for efficient coverage of k-space, enabling 3D scans in a single breathhold. The sequence uses a dual-echo bipolar readout to enable Dixon fat-water separation for improved visualization of epicardial and pericardial delayed enhancement. The 3D Dixon method was compared with a conventional 2D fast gradient recalled echo (FGRE) -based technique in 25 patients. RESULTS: Pericardial visualization scores and confidence were higher while overall image quality and artifacts were slightly worse for 3D Dixon compared with 2D FGRE. Robust fat suppression was achieved in 21 of 25 cases using the 3D Dixon method. CONCLUSION: A 3D breathhold method for fat-water separated imaging of myocardial delayed enhancement was developed and validated. J. Magn. Reson. Imaging 2013;. © 2013 Wiley Periodicals, Inc.
View details for DOI 10.1002/jmri.24113
View details for Web of Science ID 000327756800008
View details for PubMedID 23559381
Shared vulnerability of two synaptically-connected medial temporal lobe areas to age and cognitive decline: a seven tesla magnetic resonance imaging study.
journal of neuroscience
2013; 33 (42): 16666-16672
The medial temporal lobe (MTL) is the first brain area to succumb to neurofibrillary tau pathology in Alzheimer's disease (AD). Postmortem human tissue evaluation suggests that this pathology propagates in an ordered manner, with the entorhinal cortex (ERC) and then CA1 stratum radiatum and stratum lacunosum-moleculare (CA1-SRLM)-two monosynaptically connected structures-exhibiting selective damage. Here, we hypothesized that, if ERC and CA1-SRLM share an early vulnerability to AD pathology, then atrophy should occur in a proportional manner between the two structures. We tested this hypothesis in living humans, using ultra-high field 7.0 T MRI to make fine measurements of MTL microstructure. Among a pool of age-matched healthy controls and patients with amnestic mild cognitive impairment and mild AD, we found a significant correlation between ERC and CA1-SRLM size that could not be explained by global atrophy affecting the MTL. Of the various structures that contribute axons or dendrites into the CA1-SRLM neuropil, only ERC emerged as a significant predictor of CA1-SRLM size in a linear regression analysis. In contrast, other synaptically connected elements of the MTL did not exhibit size correlations. CA1-SRLM and ERC structural covariance was significant for older controls and not patients, whereas the opposite pattern emerged for a correlation between CA1-SRLM and episodic memory performance. Interestingly, CA1-SRLM and ERC were the only MTL structures to atrophy in older controls relative to a younger comparison group. Together, these findings suggest that ERC and CA1-SRLM share vulnerability to both age and AD-associated atrophy.
View details for DOI 10.1523/JNEUROSCI.1915-13.2013
View details for PubMedID 24133269
Improvement of gadoxetate arterial phase capture with a high spatio-temporal resolution multiphase three-dimensional SPGR-dixon sequence.
Journal of magnetic resonance imaging
2013; 38 (4): 938-945
PURPOSE: To determine whether a multiphase method with high spatiotemporal resolution (STR) by means of a combination of parallel imaging, pseudorandom sampling and temporal view sharing improves the capture and intensity of gadoxetate arterial phase images as well as lesion enhancement. MATERIALS AND METHODS: Thirty-seven patients were imaged with a conventional spoiled gradient echo acquisition and 48 with a high STR multiphase acquisition after the administration of gadoxetate. Arterial phase capture, image quality, and quality of fat suppression were qualitatively graded. Fourteen lesions in the conventional group and 28 in the high STR multiphase group were imaged, including 34 focal nodular hyperplasias. The ratio of lesion to parenchyma enhancement as well as relative hepatic artery enhancement were calculated. Chi-squared, Mann-Whitney U and student t-tests were used to compare differences. RESULTS: The high STR multiphase acquisition included the arterial phase more frequently than conventional acquisitions (P < 0.001), with the arterial phase missed in 17% (95% CI of 4-28%) of patients with conventional acquisition compared with 2% (95% CI of 0-6%) with the high STR multiphase acquisition. There was no loss of image quality or degree of fat saturation. Additionally, there was increased relative intensity of the hepatic arteries (P < 0.001) as well as lesion enhancement (P = 0.01). CONCLUSION: The high STR multiphase acquisition resulted in more reliable gadoxetate arterial phase capture compared with a conventional acquisition while preserving image quality with robust fat saturation J. Magn. Reson. Imaging 2013. © 2013 Wiley Periodicals, Inc.
View details for DOI 10.1002/jmri.24048
View details for PubMedID 23371926
- Simultaneous T-1 and B-1(+) Mapping Using Reference Region Variable Flip Angle Imaging MAGNETIC RESONANCE IN MEDICINE 2013; 70 (4): 954-961
Breath-held MR Cholangiopancreatography (MRCP) using a 3D Dixon fat-water separated balanced steady state free precession sequence
MAGNETIC RESONANCE IMAGING
2013; 31 (8): 1263-1270
A novel 3D breath-held Dixon fat-water separated balanced steady state free precession (b-SSFP) sequence for MR cholangiopancreatography (MRCP) is described and its potential clinical utility assessed in a series of patients. The main motivation is to develop a robust breath-held alternative to the respiratory gated 3D Fast Spin Echo (FSE) sequence, the current clinical sequence of choice for MRCP. Respiratory gated acquisitions are susceptible to motion artifacts and blurring in patients with significant diaphragmatic drift, erratic respiratory rhythms or sleep apnea. A two point Dixon fat-water separation scheme was developed which eliminates signal loss arising from B0 inhomogeneity effects and minimizes artifacts from perturbation of the b-SSFP steady state. Preliminary results from qualitative analysis of 49 patients demonstrate robust performance of the 3D Dixon b-SSFP sequence with diagnostic image quality acquired in a 20-24s breath-hold.
View details for DOI 10.1016/j.mri.2013.06.008
View details for Web of Science ID 000324609000002
View details for PubMedID 23876262
Musculoskeletal MRI at 3.0 T and 7.0 T: A comparison of relaxation times and image contrast
EUROPEAN JOURNAL OF RADIOLOGY
2013; 82 (5): 734-739
The purpose of this study was to measure and compare the relaxation times of musculoskeletal tissues at 3.0 T and 7.0 T, and to use these measurements to select appropriate parameters for musculoskeletal protocols at 7.0 T.We measured the T? and T? relaxation times of cartilage, muscle, synovial fluid, bone marrow and subcutaneous fat at both 3.0 T and 7.0 T in the knees of five healthy volunteers. The T? relaxation times were measured using a spin-echo inversion recovery sequence with six inversion times. The T? relaxation times were measured using a spin-echo sequence with seven echo times. The accuracy of both the T? and T? measurement techniques was verified in phantoms at both magnetic field strengths. We used the measured relaxation times to help design 7.0 T musculoskeletal protocols that preserve the favorable contrast characteristics of our 3.0 T protocols, while achieving significantly higher resolution at higher SNR efficiency.The T? relaxation times in all tissues at 7.0 T were consistently higher than those measured at 3.0 T, while the T? relaxation times at 7.0 T were consistently lower than those measured at 3.0 T. The measured relaxation times were used to help develop high resolution 7.0 T protocols that had similar fluid-to-cartilage contrast to that of the standard clinical 3.0 T protocols for the following sequences: proton-density-weighted fast spin-echo (FSE), T?-weighted FSE, and 3D-FSE-Cube.The T? and T? changes were within the expected ranges. Parameters for musculoskeletal protocols at 7.0 T can be optimized based on these values, yielding improved resolution in musculoskeletal imaging with similar contrast to that of standard 3.0 T clinical protocols.
View details for DOI 10.1016/j.ejrad.2011.09.021
View details for Web of Science ID 000317335800012
View details for PubMedID 22172536
Hippocampal CA1 apical neuropil atrophy and memory performance in Alzheimer's disease
2012; 63 (1): 194-202
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
- Accelerated breast MRI with compressed sensing. European journal of radiology 2012; 81: S54-5
- High resolution images of the breast. European journal of radiology 2012; 81: S101-3
DIfferential subsampling with cartesian ordering (DISCO): A high spatio-temporal resolution dixon imaging sequence for multiphasic contrast enhanced abdominal imaging
JOURNAL OF MAGNETIC RESONANCE IMAGING
2012; 35 (6): 1484-1492
To develop and evaluate a multiphasic contrast-enhanced MRI method called DIfferential Sub-sampling with Cartesian Ordering (DISCO) for abdominal imaging.A three-dimensional, variable density pseudo-random k-space segmentation scheme was developed and combined with a Dixon-based fat-water separation algorithm to generate high temporal resolution images with robust fat suppression and without compromise in spatial resolution or coverage. With institutional review board approval and informed consent, 11 consecutive patients referred for abdominal MRI at 3 Tesla (T) were imaged with both DISCO and a routine clinical three-dimensional SPGR-Dixon (LAVA FLEX) sequence. All images were graded by two radiologists using quality of fat suppression, severity of artifacts, and overall image quality as scoring criteria. For assessment of arterial phase capture efficiency, the number of temporal phases with angiographic phase and hepatic arterial phase was recorded.There were no significant differences in quality of fat suppression, artifact severity or overall image quality between DISCO and LAVA FLEX images (P > 0.05, Wilcoxon signed rank test). The angiographic and arterial phases were captured in all 11 patients scanned using the DISCO acquisition (mean number of phases were two and three, respectively).DISCO effectively captures the fast dynamics of abdominal pathology such as hyperenhancing hepatic lesions with a high spatio-temporal resolution. Typically, 1.1 × 1.5 × 3 mm spatial resolution over 60 slices was achieved with a temporal resolution of 4-5 s.
View details for DOI 10.1002/jmri.23602
View details for Web of Science ID 000304035100028
View details for PubMedID 22334505
Inversion-recovery-prepared dixon bSSFP: Initial clinical experience with a novel pulse sequence for renal MRA within a breathhold
JOURNAL OF MAGNETIC RESONANCE IMAGING
2012; 35 (4): 875-881
To evaluate the capability of a new breathhold non-contrast-enhanced MRA method (Non-contrast Outer Radial Inner Square k-space Scheme, NORISKS) to visualize renal arteries by comparing the method with a routine clinical but significantly longer non-contrast-enhanced (non-CE) MRA technique.Eighteen subjects referred for abdominal MRI were examined with NORISKS and a routine non-contrast-enhanced MRA technique. Two versions of NORISKS were evaluated: with and without ECG gating. The images were then scored independently and in blinded manner by two radiologists on 5-point scales for visualization of the proximal and distal renal arteries and quality of fat suppression.No statistically significant difference was detected between NORISKS and routine clinical non-CE MRA in all categories except for visualization of the distal renal arteries where ungated NORISKS performed poorer than the routine non-CE MRA (P < 10(-4) ).We have demonstrated a promising non-CE MRA method for acquiring renal angiograms within a breathhold without any compromise in spatial resolution or coverage. ECG-gated NORISKS is able to acquire renal angiograms that are comparable to a routine clinical non-CE MRA method (Inhance IFIR, GE Healthcare), which requires approximately seven times the scan time of NORISKS.
View details for DOI 10.1002/jmri.23503
View details for Web of Science ID 000301712400015
View details for PubMedID 22095672
A 3D balanced-SSFP Dixon technique with group-encoded k-space segmentation for breath-held non-contrast-enhanced MR angiography
MAGNETIC RESONANCE IMAGING
2012; 30 (2): 158-164
A three-dimensional balanced steady-state free precession (b-SSFP)-Dixon technique with a novel group-encoded k-space segmentation scheme called GUINNESS (Group-encoded Ungated Inversion Nulling for Non-contrast Enhancement in the Steady State) was developed. GUINNESS was evaluated for breath-held non-contrast-enhanced MR angiography of the renal arteries on 18 subjects (6 healthy volunteers, 12 patients) at 3.0 T. The method provided high signal-to-noise and contrast renal angiograms with homogeneous fat and background suppression in short breath-holds on the order of 20 s with high spatial resolution and coverage. GUINNESS has potential as a short breath-hold alternative to conventional respiratory-gated methods, which are often suboptimal in pediatric subjects and patients with significant diaphragmatic drift/sleep apnea.
View details for DOI 10.1016/j.mri.2011.09.013
View details for Web of Science ID 000299453200002
View details for PubMedID 22055852
Composite MR image reconstruction and unaliasing for general trajectories using neural networks
MAGNETIC RESONANCE IMAGING
2010; 28 (10): 1468-1484
In rapid parallel magnetic resonance imaging, the problem of image reconstruction is challenging. Here, a novel image reconstruction technique for data acquired along any general trajectory in neural network framework, called "Composite Reconstruction And Unaliasing using Neural Networks" (CRAUNN), is proposed. CRAUNN is based on the observation that the nature of aliasing remains unchanged whether the undersampled acquisition contains only low frequencies or includes high frequencies too. Here, the transformation needed to reconstruct the alias-free image from the aliased coil images is learnt, using acquisitions consisting of densely sampled low frequencies. Neural networks are made use of as machine learning tools to learn the transformation, in order to obtain the desired alias-free image for actual acquisitions containing sparsely sampled low as well as high frequencies. CRAUNN operates in the image domain and does not require explicit coil sensitivity estimation. It is also independent of the sampling trajectory used, and could be applied to arbitrary trajectories as well. As a pilot trial, the technique is first applied to Cartesian trajectory-sampled data. Experiments performed using radial and spiral trajectories on real and synthetic data, illustrate the performance of the method. The reconstruction errors depend on the acceleration factor as well as the sampling trajectory. It is found that higher acceleration factors can be obtained when radial trajectories are used. Comparisons against existing techniques are presented. CRAUNN has been found to perform on par with the state-of-the-art techniques. Acceleration factors of up to 4, 6 and 4 are achieved in Cartesian, radial and spiral cases, respectively.
View details for DOI 10.1016/j.mri.2010.06.021
View details for Web of Science ID 000284816400010
View details for PubMedID 20850243