Description: Publication date: Available online 30 December 2015 Source: Magnetic Resonance Imaging Author(s): Prachi Dubey, Vasileios-Arsenios Lioutas, Rafeeque Bhadelia, Brad Manor, Peter Novak, Magdy Selim, Vera Novak Background Non-infarct zone white matter wallerian degeneration is well-documented in large volume territorial infarctions. However to what extent these abnormalities exist in small volume infarction is not known, particularly since routine T2/FLAIR MR images show minimal changes in such cases. We therefore utilized DTI based quantitative 3D tractography for quantitative assessment of white matter integrity in chronic phase of small volume anterior circulation infarcts. Methods Eleven chronic stroke subjects with small anterior circulation large vessel infarcts (≤ 10 cc volume of primary infarct) were compared with 8 age matched controls. These infarcts had negligible to mild gliosis and encephalomalacia in the primary infarct territory without obvious wallerian degeneration on conventional MRI. Quantitative Diffusion Tensor 3-D tractography was performed for CST, genu and splenium of corpus callosum. Tract based Trace and fractional anisotropy (FA) was compared with age matched controls. Results On univariate analysis, Chronic stroke subjects had significant elevation in Trace measurement in genu of corpus callosum (GCC), ipsilesional and contralesional CST, (p 〈 0.05), compared to controls. After adjusting for smoking, hypertension (HTN) and non-specific white matter hyperintensities, (WMHs), there was significant elevation in trace within the ipsilesional CST (p = 0.05). Contralesional CST FA correlated significantly with walking speed, r = 0.67, p = 0.03. Conclusions Stroke subjects with small volume infarcts demonstrate significant quantitative microstructural white matter abnormalities in chronic phase, which are otherwise subthreshold for detection on routine imaging. Ability to quantify these changes provides an important marker for assessing non-infarct zone neuroaxonal integrity in the chronic phase even in the setting of small infarction.

Description: Publication date: Available online 30 December 2015 Source: Magnetic Resonance Imaging Author(s): Francesco Padormo, Arian Beqiri, Shaihan J. Malik, Joseph V. Hajnal The use of multiple transmission channels (known as Parallel Transmission, or PTx) provides increased control of the MRI signal formation process. This extra flexibility comes at a cost of uncertainty of the power deposited in the patient under examination: the electric fields produced by each transmitter can interfere in such a way to lead to excessively high heating. Although it is not possible to determine local heating, the global Q matrix (which allows the whole-body Specific Absorption Rate (SAR) to be known for any PTx pulse) can be measured in-situ by monitoring the power incident upon and reflected by each transmit element during transmission. Recent observations have shown that measured global Q matrices can be corrupted by losses between the coil array and location of power measurement. In this work we demonstrate that these losses can be accounted for, allowing accurate global Q matrix measurement independent of the location of the power measurement devices.

Description: Publication date: Available online 30 December 2015 Source: Magnetic Resonance Imaging Author(s): Ephraim I. Ben-Abraham, Jun Chen, Joel P. Felmlee, Phil Rossman, Armando Manduca, Kai-Nan An, Richard L. Ehman Low back pain (LBP) is a costly and widely prevalent health disorder in the U.S. One of the most common causes of LBP is degenerative disc disease (DDD). There are many imaging techniques to characterize disc degeneration; however, there is no way to directly assess the material properties of the intervertebral disc (IVD) within the intact spine. Magnetic resonance elastography (MRE) is a MRI-based technique for non-invasively mapping the mechanical properties of tissues in vivo . The purpose of this study was to investigate the feasibility of using MRE to detect shear wave propagation in and determine the shear stiffness of an axial cross-section of an ex vivo baboon IVD, and compare with shear displacements from a finite element model of a IVD motion segment in response to harmonic shear vibration. MRE was performed on two baboon lumbar spine motion segments (L3-L4) with the posterior elements removed at a range of frequencies (1000–1500 Hz) using a standard clinical 1.5 T MR scanner. Propagating waves were visualized in an axial cross-section of the baboon IVDs in all three motion-encoding directions, which resembled wave patterns predicted using finite element modeling. The baboon nucleus pulposus showed an average shear stiffness of 79 ± 15 kPa at 1000 Hz. These results suggest that MRE is capable of visualizing shear wave propagation in the IVD, assessing the stiffness of the nucleus of the IVD, and can differentiate the nucleus and annulus regions.

Description: Publication date: Available online 30 December 2015 Source: Magnetic Resonance Imaging Author(s): Wang Yuan, Li Dan, Bao Faxiu, Guo Chenguang, Ma Shaohui, Zhang Ming Objective To compare cross-sectional area (CSA) and volume (V) between the trigeminal nerves (TGNs) of the affected side and the unaffected side in patients with idiopathic trigeminal neuralgia (ITN), and both nerves in normal controls, and to correlate these morphological data with degree of facial pain and emotional disorder severity in ITN patients. Methods Forty ITN patients and 40 matched healthy volunteers underwent three-dimensional fast imaging employing steady state acquisition (3D-FIESTA) and time-of-flight magnetic resonance angiography (TOF-MRA) focusing on CSA and V of the TGN cisternal segment. Correlations between the morphological results and scores of visual analogue scale (VAS), Hamilton depression rating scale (HAMD), and Hamilton anxiety rating scale (HAMA) were analyzed in two groups. Results CSA and V of the affected TGN were significantly smaller than in the unaffected TGN and both sides in controls. No statistical differences were observed between morphological data of the unaffected TGN and control TGNs. CSA and V of the affected TGN were significantly associated with VAS scores in ITN patients, and intermediate correlations were detected with HAMD and HAMA scores. Conclusion Degree of atrophy in the affected TGN can be effective for evaluating facial pain and assessing emotional deficits in ITN patients.

Description: Publication date: Available online 30 December 2015 Source: Magnetic Resonance Imaging Author(s): Hiroshi Akima, Maya Hioki, Akito Yoshiko, Teruhiko Koike, Hisataka Sakakibara, Hideyuki Takahashi, Yoshiharu Oshida Purpose The purpose of this study was to assess relationships between intramuscular adipose tissue (IntraMAT) content determined by MRI and intramyocellular lipids (IMCL) and extramyocellular lipids (EMCL) determined by 1 H-magnetic resonance spectroscopy ( 1 H-MRS) or echo intensity determined by B-mode ultrasonography of human skeletal muscles. Methods Thirty young and elderly men and women were included. T1-weighted MRI were taken from the right mid-thigh to measure IntraMAT content of the vastus lateralis (VL) and biceps femoris (BF) using a histogram shape-based thresholding technique. IMCL and EMCL were measured from the VL and BF at the right mid-thigh using 1 H-MRS. Ultrasonographic images were taken from the VL and BF of the right mid-thigh to measure echo intensity based on grey-scale level for quantitative analysis. Results There was a significant correlation between IntraMAT content by MRI and EMCL of the VL and BF (VL, r = 0.506, P 〈 0.01; BF, r = 0.591, P 〈 0.001) and between echo intensity and EMCL of the VL and BF (VL, r = 0.485, P 〈 0.05; BF, r = 0.648, P 〈 0.01). IntraMAT content was also significantly correlated with echo intensity of the VL and BF (VL, r = 0.404, P 〈 0.05; BF, r = 0.493, P 〈 0.01). Conclusion Our study suggests that IntraMAT content determined by T1-weighted MRI at 3 T primarily reflects extramyocellular lipids, not intramyocellular lipids, in human skeletal muscles. (230 words)

Description: Publication date: Available online 29 December 2015 Source: Magnetic Resonance Imaging Author(s): Nainesh Parikh, Justin M. Ream, Hoi Cheung Zhang, Kai Tobias Block, Hersh Chandarana, Andrew B. Rosenkrantz Purpose To investigate the feasibility of high temporal resolution quantitative perfusion imaging of bladder tumors performed simultaneously with conventional multi-phase MR urography (MRU) using a novel free-breathing continuously acquired radial MRI sequence with compressed-sensing reconstruction. Methods 22 patients with bladder lesions underwent MRU using GRASP (Golden-angle RAdial Sparse Parallel) acquisition. Multi-phase contrast-enhanced abdominopelvic GRASP was performed during free-breathing (1.4x1.4x3.0mm 3 voxel size; 3:44min acquisition). Two dynamic datasets were retrospectively reconstructed by combining different numbers of sequentially acquired spokes into each dynamic frame: 110 spokes per frame for 25-second temporal resolution (serving as conventional MRU for clinical interpretation) and 8 spokes per frame for 1.7-second resolution. Using 1.7-second resolution images, ROIs were placed within bladder lesions and normal bladder wall, a femoral artery arterial input function was generated, and the Generalized Kinetic Model was applied. Results Biopsy/cystectomy demonstrated 16 bladder tumors (13 stage ≥ T2, 3 stage ≤ T1) and 6 benign lesions. All lesions were well visualized using 25-second clinical multi-phase images. Using 1.7-second resolution images, K trans was significantly higher in tumors (0.38 ± 0.24) than normal bladder (0.12 ± 0.02 = 8, p 〈 0.001) or benign lesions (0.15 ± 0.04, p = 0.033). Ratio between K trans of lesions and normal bladder was nearly double for tumors than benign lesions (4.3 ± 3.4 vs. 2.2 ± 1.6), and K trans was nearly double in stage ≥ T2 than stage ≤ T1 tumors (0.44 ± 0.24 vs. 0.24 ± 0.24), although these did not approach significance (p = 0.180-0.209), possibly related to small sample size. Conclusion GRASP allows simultaneous quantitative high temporal resolution perfusion of bladder lesions during clinical MRU examinations using only one contrast injection and without additional scan time.

Description: Publication date: Available online 29 December 2015 Source: Magnetic Resonance Imaging Author(s): Yu Liu, Gabriella Captur, James C. Moon, Shuxu Guo, Xiaoping Yang, Shaoxiang Zhang, Chunming Limy This paper presents a new level set method for segmentation of cardiac left and right ventricles. We extend the edge based distance regularized level set evolution (DRLSE) model in to a two-level-set formulation, with the 0-level set and k -level set representing the endocardium and epicardium, respectively. The extraction of endocardium and epicardium is obtained as a result of the interactive curve evolution of the 0 and k level sets derived from the proposed variational level set formulation. The initialization of the level set function in the proposed two-level-set DRLSE model is generated from roughly located endocardium, which can be performed by applying the original DRLSE model. Experimental results have demonstrated the effectiveness of the proposed two-level-set DRLSE model.

Description: Publication date: Available online 18 December 2015 Source: Magnetic Resonance Imaging Author(s): Yuechao Zhao, Junlin Chen, Mingjun Yang, Yu Liu, Yongchen Song In this study, magnetic resonance imaging (MRI) was used to dynamically visualize the diffusion process of CO 2 in porous media saturated with liquid hydrocarbon. Based on the assumption of semi-infinite media, effective CO 2 diffusivity was obtained directly by the nonlinear fitting of one MR profile during the diffusion process. These experimental findings obtained based on MRI method showed a close agreement with the conventional pressure–volume–temperature method. The novel MRI-based technique is a time-saving approach that can reduce the duration of CO 2 diffusivity measurement more than 90%, and realize rapid and accurate measurement and estimation of CO 2 diffusivity.

Description: Publication date: Available online 22 December 2015 Source: Magnetic Resonance Imaging Author(s): Ahmed M. Elkady, Hongfu Sun, Alan H. Wilman Quantitative Susceptibility Mapping (QSM) is an emerging area of brain research with clear application to brain iron studies in deep grey matter. However, acquisition of standard whole brain QSM can be time-consuming. One means to reduce scan time is to use a focal acquisition restricted only to the regions of interest such as deep grey matter. However, the non-local dipole field necessary for QSM reconstruction extends far beyond the structure of interest. We demonstrate the practical implications of these non-local fields on the choice of brain volume for QSM. In an illustrative numerical simulation and then in human brain experiments, we examine the effect on QSM of volume reduction in each dimension. For the globus pallidus, as an example of iron-rich deep grey matter, we demonstrate that substantial errors can arise even when the field-of-view far exceeds the physical structural boundaries. Thus, QSM reconstruction requires a non-local field-of-view prescription to ensure minimal errors. When using standard QSM acquisition, axial imaging, centered on the globus pallidus, should encompass at least 60 mm in the superior-inferior direction to conserve susceptibility values from the globus pallidus. This dimension exceeds the physical coronal extent of this structure by at least four-fold. As QSM sees wider use in the neuroscience community, its unique requirement for an extended field-of-view needs to be considered.

Description: Publication date: Available online 19 December 2015 Source: Magnetic Resonance Imaging Author(s): Yinghua Zhu, Yi Guo, Sajan Goud Lingala, R. Marc Lebel, Meng Law, Krishna S. Nayak Purpose To develop and evaluate a novel 3D Cartesian sampling scheme which is well suited for time-resolved 3D MRI using parallel imaging and compressed sensing. Methods The proposed sampling scheme, termed GOlden-angle CArtesian Randomized Time-resolved (GOCART) 3D MRI, is based on golden angle (GA) Cartesian sampling, with random sampling of the k y -k z phase encode locations along each Cartesian radial spoke. This method was evaluated in conjunction with constrained reconstruction of retrospectively and prospectively undersampled in-vivo dynamic contrast enhanced (DCE) MRI data and simulated phantom data. Results In in-vivo retrospective studies and phantom simulations, images reconstructed from phase encodes defined by GOCART were equal to or superior to those with Poisson disc or GA sampling schemes. Typical GOCART sampling tables were generated in 〈 100 ms. GOCART has also been successfully utilized prospectively to produce clinically valuable whole-brain DCE-MRI images. Conclusion GOCART is a practical and efficient sampling scheme for time-resolved 3D MRI. It shows great potential for highly accelerated DCE-MRI and is well suited to modern reconstruction methods such as parallel imaging and compressed sensing.