Faculty Bibliography

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.

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.

A 32-year-old female with relapsing-remitting multiple sclerosis (MS) presented with severe new onset ataxia and diplopia. MRI showed a new inflammatory MS lesion that involved the right dorsal pons and extended into the adjacent superior cerebellar peduncle. The patient improved with aggressive immunotherapy; however, repeat MRI 3 months later revealed a new non-enhancing lesion in the left inferior medullary olive. The differential diagnosis for this new lesion included an MS lesion vs hypertrophic olivary degeneration, with infarct or neoplasm as the less likely considerations. We used track density imaging, which provides unprecedented anatomic details based on probabilistic tractography streamlines, to demonstrate apparent changes in the integrity of the dentato-rubro-olivary pathway (Guillain-Mollaret triangle) that were consistent with the diagnosis of hypertrophic olivary degeneration from the antecedent MS lesion involving the right superior cerebellar peduncle. Further medical therapy was avoided, and follow-up MRI 1 year later showed interval involution of the left olivary lesion. This case demonstrates the potential clinical utility of using track density imaging to detect lesion-induced alterations in brainstem connectivity and characterize neurodegeneration in patients.

PURPOSE: Perfusion analysis from first-pass contrast enhancement kinetics requires modeling tissue contrast exchange. This study presents a new approach for numerical implementation of the tissue homogeneity model, incorporating flexible distance steps along the capillary (NTHf). METHODS: The proposed NTHf model considers contrast exchange in fluid packets flowing along the capillary, incorporating flexible distance steps, thus allowing more efficient and stable calculations of the transit of tracer through the tissue. We prospectively studied 8 patients (62 +/- 13 years old) with suspected CAD, who underwent first-pass perfusion CMR imaging at rest and stress prior to angiography. Myocardial blood flow (MBF) and myocardial perfusion reserve index (MPRI) were estimated using both the NTHf and the conventional adiabatic approximation of the TH models. Coronary artery lesions detected at angiography were clinically assigned to one of three categories of stenosis severity ('insignificant', 'mild to moderate' and 'severe') and related to corresponding myocardial territories. RESULTS: The mean MBF (ml/g/min) at rest/stress and MPRI were 0.80 +/- 0.33/1.25 +/- 0.45 and 1.68 +/- 0.54 in the insignificant regions, 0.74 +/- 0.21/1.09 +/- 0.28 and 1.54 +/- 0.46 in the mild to moderate regions, and 0.79 +/- 0.28/0.63 +/- 0.34 and 0.85 +/- 0.48 in the severe regions, respectively. The correlation coefficients of MBFs at rest/stress and MPRI between the NTHf and AATH models were r = 0.97/0.93 and r = 0.91, respectively. CONCLUSIONS: The proposed NTHf model allows efficient quantitative analysis of the transit of tracer through tissue, particularly at higher flow. Results of initial application to MRI of myocardial perfusion in CAD are encouraging.

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.

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.

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.