Description: Publication date: January 2015 Source: Magnetic Resonance Imaging, Volume 33, Issue 1 Author(s): Hironori Shimizu , Hiroyoshi Isoda , Tsuyoshi Ohno , Rikiya Yamashita , Seiya Kawahara , Akihiro Furuta , Koji Fujimoto , Aki Kido , Hiroshi Kusahara , Kaori Togashi Purpose To compare and evaluate images of non-contrast enhanced magnetic resonance (MR) portography and hepatic venography acquired with two different fat suppression methods, the chemical shift selective (CHESS) method and short tau inversion recovery (STIR) method. Materials and methods Twenty-two healthy volunteers were examined using respiratory-triggered three-dimensional true steady-state free-precession with two time-spatial labeling inversion pulses. The CHESS or STIR methods were used for fat suppression. The relative signal-to-noise ratio and contrast-to-noise ratio (CNR) were quantified, and the quality of visualization was scored. Results Image acquisition was successfully conducted in all volunteers. The STIR method significantly improved the CNRs of MR portography and hepatic venography. The image quality scores of main portal vein and right portal vein were higher with the STIR method, but there were no significant differences. The image quality scores of right hepatic vein, middle hepatic vein, and left hepatic vein (LHV) were all higher, and the visualization of LHV was significantly better (p 〈 0.05). Conclusion The STIR method contributes to further suppression of the background signal and improves visualization of the portal and hepatic veins. The results support using non-contrast-enhanced MR portography and hepatic venography in clinical practice.

Description: Publication date: Available online 12 December 2014 Source: Magnetic Resonance Imaging Author(s): Urša Mikac , Ana Sepe , Igor Serša Magnetic resonance microscopy (MRM) was used to study water distribution and mobility in common bean ( Phaseolus vulgaris ) seed during soaking at room temperature (20°C) and during the cooking of presoaked and dry bean seed in near-boiling water (98°C). Two complementary MRI methods were used to determine the total water uptake into the seed: the T 2 -weighted 3D RARE method, which yielded an increased signal from regions of highly mobile (bulk) water and a suppressed signal from regions of poorly mobile (bound) water; and the 3D SPI method, which yielded an increased signal from regions of water restricted in motion and a suppressed signal from the bulk water regions owing to the short repetition time of the method. Based on these results, it can be concluded that during soaking water enters the bean through the micropyle, migrating below the seed coat. The raphe and hypocotyl are hydrated first, while the cotyledon tissue is hydrated next. It was also observed that the imbibition rate increases with an increasing soaking temperature.

Description: Publication date: January 2015 Source: Magnetic Resonance Imaging, Volume 33, Issue 1 Author(s): Xiaoxu Wang , Ting Chen , Shaoting Zhang , Joël Schaerer , Zhen Qian , Suejung Huh , Dimitris Metaxas , Leon Axel Tagged magnetic resonance imaging (TMRI) provides a direct and noninvasive way to visualize the in-wall deformation of the myocardium. Due to the through-plane motion, the tracking of 3D trajectories of the material points and the computation of 3D strain field call for the necessity of building 3D cardiac deformable models. The intersections of three stacks of orthogonal tagging planes are material points in the myocardium. With these intersections as control points, 3D motion can be reconstructed with a novel meshless deformable model (MDM). Volumetric MDMs describe an object as point cloud inside the object boundary and the coordinate of each point can be written in parametric functions. A generic heart mesh is registered on the TMRI with polar decomposition. A 3D MDM is generated and deformed with MR image tagging lines. Volumetric MDMs are deformed by calculating the dynamics function and minimizing the local Laplacian coordinates. The similarity transformation of each point is computed by assuming its neighboring points are making the same transformation. The deformation is computed iteratively until the control points match the target positions in the consecutive image frame. The 3D strain field is computed from the 3D displacement field with moving least squares. We demonstrate that MDMs outperformed the finite element method and the spline method with a numerical phantom. Meshless deformable models can track the trajectory of any material point in the myocardium and compute the 3D strain field of any particular area. The experimental results on in vivo healthy and patient heart MRI show that the MDM can fully recover the myocardium motion in three dimensions.

Description: Publication date: Available online 6 December 2014 Source: Magnetic Resonance Imaging Author(s): Yu-Chung N. Cheng , Ching-Yi Hsieh , Ronald Tackett , Paul Kokeny , Rajesh Kumar Regmi , Gavin Lawes Purpose The purpose of this work is to develop a method for accurately quantifying effective magnetic moments of spherical-like small objects from magnetic resonance imaging (MRI). A standard 3D gradient echo sequence with only one echo time is intended for our approach to measure the effective magnetic moment of a given object of interest. Methods Our method sums over complex MR signals around the object and equates those sums to equations derived from the magnetostatic theory. With those equations, our method is able to determine the center of the object with subpixel precision. By rewriting those equations, the effective magnetic moment of the object becomes the only unknown to be solved. Each quantified effective magnetic moment has an uncertainty that is derived from the error propagation method. If the volume of the object can be measured from spin echo images, the susceptibility difference between the object and its surrounding can be further quantified from the effective magnetic moment. Numerical simulations, a variety of glass beads in phantom studies with different MR imaging parameters from a 1.5 T machine, and measurements from a SQUID (superconducting quantum interference device) based magnetometer have been conducted to test the robustness of our method. Results Quantified effective magnetic moments and susceptibility differences from different imaging parameters and methods all agree with each other within two standard deviations of estimated uncertainties. Conclusion An MRI method is developed to accurately quantify the effective magnetic moment of a given small object of interest. Most results are accurate within 10% of true values and roughly half of the total results are accurate within 5% of true values using very reasonable imaging parameters. Our method is minimally affected by the partial volume, dephasing, and phase aliasing effects. Our next goal is to apply this method to in vivo studies.

Description: Publication date: Available online 5 December 2014 Source: Magnetic Resonance Imaging Author(s): Matteo Figini , Ileana Zucca , Domenico Aquino , Paolo Pennacchio , Simone Nava , Alessandro Di Marzio , Maria Giulia Preti , Guseppe Baselli , Roberto Spreafico , Carolina Frassoni Diffusion Tensor Imaging (DTI) is a Magnetic Resonance modality that permits to characterize the orientation and integrity of the white matter (WM). DTI-based tractography techniques, allowing the virtual reconstruction of WM tract pathways, have found wide application in preclinical neurological research. Recently, anatomically detailed rat brain atlases including DTI data were constructed from ex vivo DTI images, but tractographic atlases of normal rats in vivo are still lacking. We propose here a probabilistic tractographic atlas of the main WM tracts in the healthy rat brain based on in vivo DTI acquisition. Our study was carried out on 10 adult female Sprague–Dawley rats using a 7 T preclinical scanner. The MRI protocol permitted a reliable reconstruction of the main rat brain bundles: corpus callosum, cingulum, external capsule, internal capsule, anterior commissure, optic tract. The reconstructed fibers were compared with histological data, proving the viability of in vivo DTI tractography in the rat brain with the proposed acquisition and processing protocol. All the data were registered to a rat brain template in the coordinate system of the commonly used atlas by Paxinos and Watson; then the individual tracts were binarized and averaged, obtaining a probabilistic atlas in Paxinos-Watson space of the main rat brain white matter bundles. With respect to the recent high-resolution MRI atlases, the resulting tractographic atlas, available online, provides complementary information about the average anatomical position of the considered WM tracts and their variability between normal animals. Furthermore, reference values for the main DTI-derived parameters, Mean Diffusivity and Fractional Anisotropy, were provided. Both these results can be used as references in preclinical studies on pathological rat models involving potential alterations of WM.

Description: Publication date: Available online 5 December 2014 Source: Magnetic Resonance Imaging Author(s): Khader M. Hasan , John A. Lincoln , Flavia M. Nelson , Jerry S. Wolinsky , Ponnada A. Narayana In this retrospective study we tested the hypothesis that the net effect of impaired electrical conduction and therefore increased heat dissipation in multiple sclerosis (MS) results in elevated lateral ventricular (LV) cerebrospinal fluid (CSF) diffusivity as a measure of brain temperature estimated in vivo using diffusion tensor imaging (DTI). We used validated DTI-based segmentation methods to obtain normalized LV-CSF volume and its corresponding CSF diffusivity in 108 MS patients and 103 healthy controls in the age range of 21-63 years. The LV CSF diffusivity was ~ 2% higher in MS compared to controls that corresponds to a temperature rise of ~ 1 °C that could not be explained by changes in the CSF viscosity due to altered CSF protein content in MS. The LV diffusivity decreased with age in healthy controls (r = -0.29; p = 0.003), but not in MS (r = 0.15; p = 0.11), possibly related to MS pathology. Age-adjusted LV diffusivity increased with lesion load (r = 0.518; p = 1x10 - 8 ). Our data suggest that the total brain lesion load is the primary contributor to the increase in LV CSF diffusivity in MS. These findings suggest that LV diffusivity is a potential in vivo biomarker of the mismatch between heat generation and dissipation in MS. We also discuss limitations and possible confounders.

Description: Publication date: December 2014 Source: Magnetic Resonance Imaging, Volume 32, Issue 10 Author(s): Chen Chen , Junzhou Huang Sparsity has been widely utilized in magnetic resonance imaging (MRI) to reduce k-space sampling. According to structured sparsity theories, fewer measurements are required for tree sparse data than the data only with standard sparsity. Intuitively, more accurate image reconstruction can be achieved with the same number of measurements by exploiting the wavelet tree structure in MRI. A novel algorithm is proposed in this article to reconstruct MR images from undersampled k-space data. In contrast to conventional compressed sensing MRI (CS-MRI) that only relies on the sparsity of MR images in wavelet or gradient domain, we exploit the wavelet tree structure to improve CS-MRI. This tree-based CS-MRI problem is decomposed into three simpler subproblems then each of the subproblems can be efficiently solved by an iterative scheme. Simulations and in vivo experiments demonstrate the significant improvement of the proposed method compared to conventional CS-MRI algorithms, and the feasibleness on MR data compared to existing tree-based imaging algorithms.

Description: Publication date: Available online 11 November 2014 Source: Magnetic Resonance Imaging Author(s): Jeroen J.N. van Schie , Cristina Lavini , Lucas J. van Vliet , Frans M. Vos The Fast Spoiled Gradient Echo (FSPGR) sequence is often used in MRI to create T 1 -weighted images. The signal intensity generated by this sequence depends on the applied flip angle. Knowing the correct flip angle is essential for the determination of T 1 -maps by means of an FSPGR based Variable Flip Angle (VFA) approach. Also, quantitatively determining the concentration of contrast agent in case of Dynamic Contrast Enhanced MRI (DCE-MRI) requires knowledge of the applied flip angle. In both cases, the B 1 -field (in)homogeneity significantly affects the results. In this paper, we present a new method to obtain both the T 1 -map and B 1 -inhomogeneity map using scans that can each be acquired within a breath-hold. We combine two short sequences for T 1 quantification: Variable Flip Angle and Look-Locker (LL). The T 1 -maps obtained from the LL data were used to estimate the B 1 -inhomogeneity inherently present in the VFA data, which was then used to correct for the VFA method’s inaccurate flip angles. This way, a reliable T 1 -map could be computed, which was validated using both in vitro and in vivo scans. The in vitro results show that the procedure yields a substantially smaller mean deviation in T 1 from the T 1 measurement’s gold standard (the Inversion Recovery method), while the in vivo results show both a more accurate estimation of T 1 and a reduction of the influence of the B 1 -inhomogeneity on the signal intensity.

Description: Publication date: Available online 13 November 2014 Source: Magnetic Resonance Imaging Author(s): Bilge Bırlık , Funda Obuz , Funda D. Elibol , Ahmet O. Celik , Selman Sokmen , Cem Terzi , Ozgul Sagol , Sulen Sarioglu , Ilknur Gorken , lhan Oztop Purpose To determine the diagnostic performance of diffusion-weighted MRI and MR volumetry for the assessment of tumor response after preoperative chemoradiotherapy (CRT) in patients with locally advanced rectal cancer. Materials and Methods Forty-three patients with rectal cancer who underwent preoperative CRT were prospectively examined for the study. This prospective study was approved by our Institutional Review Board. DW- and high resolution T2-weighted imaging were performed before and after therapy. Two different diffusion gradients (b = 0 and b = 600, then separately b = 0 and b = 1000) were applied. The mean tumor volume and mean ADC values were measured before and after therapy. To evaluate the responders and nonresponders to neoadjuvant CRT, two criteria, ypT stage determined in the pathologic examination after treatment and histopathologic tumor regression grade (Ryan), were used as reference standards. The patients with a lower ypT stage than T stage in the first MRI before neoadjuvant CRT were evaluated as the responder group, while the patients with a higher or the same ypT stage relative to the first MRI T stage were evaluated as the nonresponder group. According to Ryan tumor regression grade, Grade 1 was evaluated as the responders, whereas grades 2 and 3 were evaluated as the nonresponder group. The percentage ADC increase and percentage tumor volum regression were compared between the responders and nonresponders using two reference standards: T downstaging and tumor regression grade (TRG). Results Before CRT, the mean tumor ADC in the responder group was significantly lower than that in the nonresponder group (p 〈 0.001). At the end of CRT, the mean percentage of tumor ADC change in the responder group was significantly higher than that in the nonresponder group. The percentage tumor volume regression of the responders was significantly higher than that of the nonresponders (p = 0.001). The cut-off ADC value for discriminating between the responders and nonresponders after treatment was determined to be (b = 600) 1.03 × 10 − 3 mm 2 /s and the sensitivity, 71%; specificity, 79%; accuracy, 74%; positive predictive value, 81%; negative predictive value, 68% respectively. The cut-off value for discriminating between the responders and the nonresponders after treatment was determined for b = 1000 as 1.20x10 − 3 mm 2 /s and the sensitivity, 42%; specificity, 84 %; accuracy, 60%; positive predictive value, 77%; negative predictive value, 53 %. Conclusion The increase in the mean tumor ADC and percentage tumor volume regression in patients with rectal cancer treated with preoperative CRT was correlated with good response. DW MR imaging is a promising non-invasive technique that can help predict and monitor early therapeutic response in patients with rectal cancer who undergo CRT.

Description: Publication date: Available online 8 November 2014 Source: Magnetic Resonance Imaging Author(s): R.T. Fitzgerald , X. Ou , J.S. Nix , M.C. Arthur , A.T. Brown , R.D. Skinner , M.J. Borrelli , W.C. Culp Background Dodecafluoropentane emulsion (DDFPe), an oxygen transport agent, has been shown to reduce infarct volume in animal models of acute ischemic stroke (AIS). Our study assesses the effect of DDFPe on MRI markers of infarct evolution in the early hours after vascular occlusion in a rat AIS model. We hypothesized that DDFPe will delay the development of MRI markers of AIS and/or reduce the extent of infarciton. Methods Permanent, unilateral surgical occlusion of the middle cerebral and common carotid arteries was performed in control (n = 4) and treatment (n = 10) rats. The treatment group received 1 IV dose of 2% w/v DDFPe at 0.6 mL/kg at 1 hour post-occlusion verses none. Diffusion-weighted (DWI) and inversion recovery (IR) MRI sequences were obtained over the 4 hours following occlusion. Infarct extent was quantified by number of abnormal MRI slices per sequence for each group and time point. Student’s T-test was applied. Results DDFPe-treated rats demonstrated reduced infarct extent versus controls over combined time points on IR at 5.43 ± 0.40 (mean ± standard error) abnormal slices vs. 7.38 ± 0.58 (P = 0.01) and on DWI at 5.21 ± 0.54 vs. 9.00 ± 0.95 (P 〈 0.01). Development of abnormal MRI signal was delayed in the treatment group. Conclusions DDFPe delays and reduces MRI markers of AIS in the early hours following vascular occlusion in a rat stroke model. Further investigation of DDFPe as a neuroprotectant is warranted.