Faculty Bibliography

BACKGROUND AND PURPOSE: Obtaining high-resolution brain MR imaging in patients with a previously implanted deep brain stimulator has been challenging and avoided by many centers due to safety concerns relating to implantable devices. We present our experience with a practical clinical protocol at 1.5T by using 2 magnet systems capable of achieving presurgical quality imaging in patients undergoing bilateral, staged deep brain stimulator insertion. MATERIALS AND METHODS: Protocol optimization was performed to minimize the specific absorption rate while providing image quality necessary for adequate surgical planning of the second electrode placement. We reviewed MR imaging studies performed with a minimal specific absorption rate protocol in patients with a deep brain stimulator in place at our institution between February 1, 2012, and August 1, 2015. Images were reviewed by a neuroradiologist and a functional neurosurgeon. Image quality was qualitatively graded, and the presence of artifacts was noted. RESULTS: Twenty-nine patients (22 with Parkinson disease, 6 with dystonia, 1 with essential tremor) were imaged with at least 1 neuromodulation implant in situ. All patients were imaged under general anesthesia. There were 25 subthalamic and 4 globus pallidus implants. Nineteen patients were preoperative for the second stage of bilateral deep brain stimulator placement; 10 patients had bilateral electrodes in situ and were being imaged for other neurologic indications, including lead positioning. No adverse events occurred during or after imaging. Mild device-related local susceptibility artifacts were present in all studies, but they were not judged to affect overall image quality. Minimal aliasing artifacts were seen in 7, and moderate motion, in 4 cases on T1WI only. All preoperative studies were adequate for guidance of a second deep brain stimulator placement. CONCLUSIONS: An optimized MR imaging protocol that minimizes the specific absorption rate can be used to safely obtain high-quality images in patients with previously implanted deep brain stimulators, and these images are adequate for surgical guidance.

BACKGROUND/AIMS: To assess the usefulness of magnetization-tagged magnetic resonance imaging (MRI) in quantifying cardiac-induced liver motion and deformation in order to predict liver fibrosis. METHODS: This retrospective study included 85 patients who underwent liver MRI including magnetization-tagged sequences from April 2010 to August 2010. Tagged images were acquired in three coronal and three sagittal planes encompassing both the liver and heart. A Gabor filter bank was used to measure the maximum value of displacement (MaxDisp) and the maximum and minimum values of principal strains (MaxP1 and MinP2, respectively). Patients were divided into three groups (no fibrosis, mild-to-moderate fibrosis, and significant fibrosis) based on their aspartate-aminotransferase-to-platelet ratio index (APRI) score. Group comparisons were made using ANOVA tests. RESULTS: The patients were divided into three groups according to APRI scores: no fibrosis (1.5; n=21). The values of MaxDisp were 2.9+/-0.9 (mean+/-SD), 2.3+/-0.7, and 2.1+/-0.6 in the no fibrosis, moderate fibrosis, and significant fibrosis groups, respectively (P<0.001); the corresponding values of MaxP1 were 0.05+/-0.2, 0.04+/-0.02, and 0.03+/-0.01, respectively (P=0.002), while those of MinP2 were -0.07+/-0.02, -0.05+/-0.02, and -0.04+/-0.01, respectively (P<0.001). CONCLUSIONS: Tagged MRI to quantify cardiac-induced liver motion can be easily incorporated in routine liver MRI and may represent a helpful complementary tool in the diagnosis of early liver fibrosis.

Two new 3T MR imaging contrast methods, track density imaging and echo modulation curve T2 mapping, were combined with simultaneous multisection acquisition to reveal exquisite anatomic detail at 7 canonical levels of the brain stem. Compared with conventional MR imaging contrasts, many individual brain stem tracts and nuclear groups were directly visualized for the first time at 3T. This new approach is clinically practical and feasible (total scan time = 20 minutes), allowing better brain stem anatomic localization and characterization.

The aim is to compare tricuspid valve (TV) atrioventricular junction (AVJ) annular motion parameters in unrepaired atrial septal defect (ASD) and repaired Tetralogy of Fallot (TOF) by cardiac magnetic resonance (CMR) imaging. We retrospectively reviewed CMR studies performed between November 2007 and November 2013 in patients 16-45 years of age with unrepaired ASD (with or without partial anomalous pulmonary venous return) and with repaired TOF, who had previous infundibulotomy, but have not undergone pulmonary valve replacement. Longitudinal motion of lateral TV in four-chamber view cine image was tracked through the cardiac cycle with custom software. Twenty TOF patients and 12 ASD patients were included, and values were compared with 80 controls. Right ventricular end-diastolic volume index and right ventricular end-systolic volume index were similar in the ASD and TOF groups and were significantly higher in both groups than in controls. Maximum displacement of the TV in systole, velocity at half-maximal displacement during systole, and velocity at half-maximal displacement during early diastole were all significantly lower in the TOF group than the ASD group [1.39 +/- 0.47 vs. 2.21 +/- 0.46 (cm, p < 0.01), 5.9 +/- 2.1 vs. 10.1 +/- 2.3 (cm/s, p < 0.01), and 7.7 +/- 2.6 vs. 10.9 +/- 3.1 (cm/s, p < 0.05)]. TOF patients have diminished early diastolic TV AVJ velocity compared to patients with an unrepaired ASD, despite similar RV volumes. This observation could suggest diastolic dysfunction or cardiac mechanics unique to the postoperative, volume-overloaded right ventricle in patients with repaired TOF.

INTRODUCTION: Essential tremor can be treated by thalamic stimulation or ablation of the ventral intermediate nucleus (VIM) with good outcomes [1]. Routine magnetic resonance imaging (MRI) cannot distinguish between thalamic nuclei so targeting is based on anatomic atlas-based coordinates. Diffusion MRI-based track density imaging (TDI) can better depict internal thalamic structure [2], but previously has required high-field MRI or long acquisitions that are not clinically practical. We applied multiband diffusion MRI [3] to enable 3-Tesla (3-T) MRI TDI in patients with essential tremor. METHODS: Six patients with essential tremor underwent standard preoperative MRI with an additional multiband diffusion sequence that used 3-slice acceleration factor, 3-mm isotropic image resolution, whole-brain coverage (45 slices) and 256 diffusion gradient directions (b = 2500 s/mm) acquired in 11 minutes. TDI data post-processing generated track density and direction-encoded color maps at 500-micron isotropic super-resolution [2]. RESULTS: Combining TDI and multiband diffusion acquisitions resulted in high-quality images of the human thalamus in typical elderly essential tremor patients using 3-T MRI and clinically feasible scan times. Results also were consistent for repeat imaging in the 3 volunteers. TDI with or without direction-encoding demonstrated some of the internal anatomy of the thalamus, but fiber-orientation maps derived from these data (Fig. 1) were preferred by the 2 participating functional neurosurgeons. CONCLUSION: Multiband diffusion acquisition makes TDI-based parcellation of the thalamus feasible in elderly patients with essential tremor using 3-T MRI. This approach provides at least equivalent data to previous diffusion tractography or TDI approaches for thalamus parcellation, but without long scan times or a 7-Tesla MRI system [4-6]. While planning for gamma knife ablation of VIM for these initial 6 patients still relied on conventional methods, future efforts will focus on validation and careful introduction of TDI-derived thalamic maps to actual surgical planning.

BACKGROUND: Measurement of mitral annulus (MA) dynamics is an important component of the evaluation of left ventricular (LV) diastolic function; MA velocities are commonly measured using tissue Doppler imaging (TDI). This study aimed to examine the clinical potential of a semi-automated cardiovascular magnetic resonance (CMR) technique for quantifying global LV diastolic function, using 3D volume tracking of the MA with conventional cine-CMR images. METHODS: 124 consecutive patients with normal ejection fraction underwent both clinically indicated transthoracic echocardiography (TTE) and CMR within 2 months. Interpolated 3D reconstruction of the MA over time was performed with semi-automated atrioventricular junction (AVJ) tracking in long-axis cine-CMR images, producing an MA sweep volume over the cardiac cycle. CMR-based diastolic function was evaluated, using the following parameters: peak volume sweep rates in early diastole (PSRE) and atrial systole (PSRA), PSRE/PSRA ratio, deceleration time of sweep volume (DTSV), and 50% diastolic sweep volume recovery time (DSVRT50); these were compared with TTE diastolic measurements. RESULTS: Patients with TTE-based diastolic dysfunction (n = 62) showed significantly different normalized MA sweep volume profiles compared to those with TTE-based normal diastolic function (n = 62), including a lower PSRE (5.25 +/- 1.38 s-1 vs. 7.72 +/- 1.7 s-1), a higher PSRA (6.56 +/- 1.99 s-1 vs. 4.67 +/- 1.38 s-1), a lower PSRE/PSRA ratio (0.9 +/- 0.44 vs. 1.82 +/- 0.69), a longer DTSV (144 +/- 55 ms vs. 96 +/- 37 ms), and a longer DSVRT50 (25.0 +/- 11.0% vs. 15.6 +/- 4.0%) (all p < 0.05). CMR diastolic parameters were independent predictors of TTE-based diastolic dysfunction after adjusting for left ventricular hypertrophy, hypertension, and coronary artery disease. Good correlations were observed between CMR PSRE/PSRA and early-to-late diastolic annular velocity ratios (e'/a') measured by TDI (r = 0.756 to 0.828, p < 0.001). CONCLUSIONS: 3D MA sweep volumes generated by semi-automated AVJ tracking in routinely acquired CMR images yielded diastolic parameters that were effective in identifying patients with diastolic dysfunction when correlated with TTE-based variables.

BACKGROUND: We have developed a novel and practical cardiovascular magnetic resonance (CMR) technique to evaluate left ventricular (LV) mitral annular motion by tracking the atrioventricular junction (AVJ). To test AVJ motion analysis as a metric for LV function, we compared AVJ motion variables between patients with hypertrophic cardiomyopathy (HCM), a group with recognized systolic and diastolic dysfunction, and healthy volunteers. METHODS: We retrospectively evaluated 24 HCM patients with normal ejection fractions (EF) and 14 healthy volunteers. Using the 4-chamber view cine images, we tracked the longitudinal motion of the lateral and septal AVJ at 25 time points during the cardiac cycle. Based on AVJ displacement versus time, we calculated maximum AVJ displacement (MD) and velocity in early diastole (MVED), velocity in diastasis (VDS) and the composite index VDS/MVED. RESULTS: Patients with HCM showed significantly slower median lateral and septal AVJ recoil velocities during early diastole, but faster velocities in diastasis. We observed a 16-fold difference in VDS/MVED at the lateral AVJ [median 0.141, interquartile range (IQR) 0.073, 0.166 versus 0.009 IQR -0.006, 0.037, P < 0.001]. Patients with HCM also demonstrated significantly less mitral annular excursion at both the septal and lateral AVJ. Performed offline, AVJ motion analysis took approximately 10 minutes per subject. CONCLUSIONS: Atrioventricular junction motion analysis provides a practical and novel CMR method to assess mitral annular motion. In this proof of concept study we found highly statistically significant differences in mitral annular excursion and recoil between HCM patients and healthy volunteers.

PURPOSE: To assess liver stiffness using magnetization-tagged magnetic resonance imaging (MRI) to measure the cardiac-induced motion in the liver of cirrhosis patients with known Child-Pugh scores. MATERIALS AND METHODS: Tagged MRI was performed using a 3T MR scanner on 52 cirrhosis patients classified into two groups: liver cirrhosis with Child-Pugh A (LCA; n = 39) and liver cirrhosis with Child-Pugh B or C (LCBC; n = 13). We also included 19 healthy controls. Tagged images were acquired encompassing both the liver and the heart. The corresponding displacement and strains were calculated using a Gabor filter bank. The maximum displacement (MaxDisp) was found over the cardiac cycle, as well as the local maximum P1 (MaxP1) and minimum P2 strains (MinP2). Group comparisons were made without and with adjustment for age and gender. RESULTS: In control, LCA, and LCBC groups, the MaxDisp was 3.98 +/- 0.88 mm, 2.52 +/- 0.73 mm, and 1.86 +/- 0.77 mm; the MaxP1 was 0.10 +/- 0.02, 0.04 +/- 0.01, and 0.02 +/- 0.01; and the MinP2 was -0.08 +/- 0.01, -0.05 +/- 0.02, and -0.03 +/- 0.01, respectively. Statistically significant differences were found between groups (P < 0.05 for all). CONCLUSION: This method measures cardiac-induced liver motion and deformation to assess liver stiffness. Significant differences were found in our stiffness measures between control, LCA, and LCBC groups, with more severe disease being associated with greater stiffness. J. Magn. Reson. Imaging 2014;39:1301-1307. (c) 2013 Wiley Periodicals, Inc.