Glaser, Kevin J.

PurposeMR elastography (MRE) is a phase‐contrast MRI technique that is used to quantitatively assess liver stiffness for staging hepatic fibrosis. The current approach requires manual selection of a region of interest (ROI) with good wave quality from which to measure stiffness. The purpose of this work was to develop and evaluate a fully automated approach for measuring hepatic stiffness from MRE images to further reduce measurement variability.Materials and MethodsAn automated liver elasticity calculation (ALEC) algorithm was developed to address reader stiffness measurement variability. ALEC has three stages: initial tissue estimation, segmentation, and ROI cleanup. Stiffnesses measured by the algorithm were compared with technicians and an expert radiologist in a set of 121 clinical cases acquired at 1.5 Tesla. Intra‐class correlation (ICC), Bland‐Altman analysis, and a noninferiority test were performed to evaluate whether the algorithm can be used in place of manual analysis by technicians.ResultsThe stiffness measurement difference with the expert was 1.42% ± 11.17% (mean ± standard deviation) for the algorithm and 1.82% ± 13.65% for the technicians. The ICCs were 0.981 and 0.984, respectively. Both the algorithm and technicians were equivalent to the expert within a 5% significance margin (P < 0.01). The algorithm had no failures in the 119 cases that were considered analyzable by the human readers.ConclusionThe results of this study show that the newly developed automated algorithm is able to measure stiffness in clinical liver MRE exams with an accuracy that is equivalent to that of an expert radiologist. ALEC may be useful for analysis of archived data and suitable for performing multi‐center studies. J. Magn. Reson. Imaging 2016;43:1055–1063.

PurposeTo investigate the feasibility of utilizing brain stiffness as a potential biomarker for behavioral variant frontotemporal dementia (bvFTD) patients. Magnetic resonance elastography (MRE) is a noninvasive technique for evaluating the mechanical properties of brain tissue in vivo. MRE has demonstrated decreased brain stiffness in patients with Alzheimer's disease.Materials and MethodsWe examined five male subjects with bvFTD and nine cognitively normal age‐matched male controls (NC) with brain 3T MRE. Stiffness was calculated in nine regions of interest (ROIs): whole brain (entire cerebrum excluding cerebellum), frontal lobes, occipital lobes, parietal lobes, temporal lobes, deep gray matter / white matter (GM/WM; insula, deep gray nuclei and white matter tracts), cerebellum, sensorimotor cortex (pre‐ and postcentral gyri), and a composite region labeled FT (frontal and temporal lobes excluding the pre‐ and postcentral gyri).ResultsSignificantly lower stiffness values were observed in the whole brain (P = 0.007), frontal lobe (P = 0.001), and temporal lobes (P = 0.005) of bvFTD patients compared to NC. No significant stiffness differences were observed in any other ROIs of bvFTD patients compared to NC (P > 0.05). These results demonstrate that statistically significant brain softening occurs in the frontal and temporal lobes of bvFTD patients, which corresponds to the expected pathophysiology of bvFTD.ConclusionFuture studies evaluating the feasibility of brain MRE for early disease detection and monitoring disease progression could shed new insights into understanding the mechanisms involved in bvFTD. J. Magn. Reson. Imaging 2016;43:474–478.

BackgroundTo evaluate the reliability of MRE using a spin‐echo echo‐planar imaging (SE‐EPI) renal MRE technique in healthy volunteers.MethodsInstitutional review board approved prospective study in which all participants provided written informed consent. Sixteen healthy volunteers comprising seven males and nine females with a median age of 35 years (age range: 23 to 59 years) were included. Coronal 90 Hz and 60 Hz MRE acquisitions were performed twice within a 30‐min interval between examinations. Renal MRE reliability was assessed by (i) test–retest repeatability, and (ii) inter‐rater agreement between two independent readers. The MRE‐measured averaged renal stiffness values were evaluated using: intraclass correlation coefficient (ICC), Bland‐Altman and the within‐subject coefficient of variation (COV).ResultsFor test–retest repeatability, Bland‐Altman showed a mean stiffness difference between examinations of 0.07 kPa (95% limits of agreement: −1.41, 1.54) at 90 Hz and 0.01 kPa (95% limits of agreement: −0.51, 0.53) at 60 Hz. Coefficient of repeatability was 1.47 kPa and 0.52 kPa at 90 Hz and 60 Hz, respectively. The within‐subject COV was 13.6% and 7.7% at 90 Hz and 60 Hz, respectively. ICC values were 0.922 and 0.907 for test–retest repeatability and 0.998 and 0.989 for inter‐rater agreement, respectively (P < 0.001).ConclusionSE‐EPI renal MRE is a reliable technique. J. Magn. Reson. Imaging 2015;42:844–850.

Purpose To evaluate the feasibility of using three‐dimensional (3D) MR elastography (MRE) to determine the stiffness of the pancreas in healthy volunteers. Materials and Methods Twenty healthy volunteers underwent 1.5 Tesla MRE exams using an accelerated echo planar imaging (EPI) pulse sequence with low‐frequency vibrations (40 and 60 Hz). Stiffness was calculated with a 3D direct inversion algorithm. The mean shear stiffness in five pancreatic subregions (uncinate, head, neck, body, and tail) and the corresponding liver stiffness were calculated. The intrasubject coefficient of variation (CV) was calculated as a measure of the reproducibility for each volunteer. Results The mean shear stiffness (average of values obtained in different pancreatic subregions) was (1.15 ± 0.17) kPa at 40 Hz, and (2.09 ± 0.33) kPa at 60 Hz. The corresponding liver stiffness was higher than the pancreas stiffness at 40 Hz ([1.60 ± 0.21] kPa, mean pancreas‐to‐liver stiffness ratio: 0.72), but similar at 60Hz ([2.12 ± 0.23) kPa, mean ratio: 0.95). The mean intrasubject CV for each pancreatic subregion was lower at 40 Hz than 60 Hz ( P < 0.05 for all subregions, range: 11.9–15.7% at 40 Hz and 16.5–19.6% at 60 Hz). Conclusion The 3D pancreatic MRE can provide promising and reproducible stiffness measurements throughout the pancreas, with more consistent data acquired at 40 Hz. J. Magn. Reson. Imaging 2015;41:369–375. © 2013 Wiley Periodicals, Inc .

Purpose To develop a rapid proton MR elastography (MRE) technique that can quantify the absolute shear stiffness of lung parenchyma, to investigate the ability to differentiate respiration‐dependent stiffness variations of the lung, and to demonstrate clinical feasibility. Materials and Methods A spin‐echo echo planar imaging MRE sequence (SE‐EPI MRE) with a very short echo time was developed and tested in a series of five healthy volunteers at three different lung volumes: (i) residual volume (RV), (ii) total lung capacity (TLC), (iii) and midway between RV and TLC (MID). At each volume, lung density was quantified using a MR‐based density mapping sequence. For reference, data were acquired using the previously described spin‐echo lung MRE sequence (SE‐MRE). MRE data were also acquired in a patient with proven Idiopathic Pulmonary Fibrosis (IPF) to test clinical feasibility. Results The SE‐EPIMRE sequence reduced total acquisition time by a factor of 2 compared with the SE‐MRE sequence. Lung parenchyma median shear stiffness for the 5 volunteers quantified with the SE‐EPI MRE sequence was 0.9 kPa, 1.1 kPa, and 1.6 kPa at RV, MID, and TLC, respectively. The corresponding values obtained with the SE‐MRE sequence were 0.9 kPa, 1.1 kPa, and 1.5 kPa. Absolute shear stiffness was also successfully measured in the IPF patient. Conclusion The results indicate that stiffness variations due to respiration could be measured with the SE‐EPIMRE technique and were equivalent to values generated by the previously described SE‐MRE approach. Preliminary data obtained from the patient demonstrate clinical feasibility. J. Magn. Reson. Imaging 2014;40:1230–1237 . © 2013 Wiley Periodicals, Inc .

PurposeTo investigate the influence of portal pressure on the shear stiffness of the liver and spleen in a well‐controlled in vivo porcine model with magnetic resonance elastography (MRE). A significant correlation between portal pressure and tissue stiffness could be used to noninvasively assess increased portal venous pressure (portal hypertension), which is a frequent clinical condition caused by cirrhosis of the liver and is responsible for the development of many lethal complications.Materials and MethodsDuring multiple intraarterial infusions of Dextran‐40 in three adult domestic pigs in vivo, 3D abdominal MRE was performed with left ventricle and portal catheters measuring blood pressure simultaneously. Least‐squares linear regressions were used to analyze the relationship between tissue stiffness and portal pressure.ResultsLiver and spleen stiffness have a dynamic component that increases significantly following an increase in portal or left ventricular pressure. Correlation coefficients with the linear regressions between stiffness and pressure exceeded 0.8 in most cases.ConclusionThe observed stiffness–pressure relationship of the liver and spleen could provide a promising noninvasive method for assessing portal pressure. Using MRE to study the tissue mechanics associated with portal pressure may provide new insights into the natural history and pathophysiology of hepatic diseases and may have significant diagnostic value in the future. J. Magn. Reson. Imaging 2013;38:809–815. © 2013 Wiley Periodicals, Inc.

PurposeTo investigate the feasibility of using MR elastography (MRE) for the evaluation of the stiffness of in vivo aortic wall.Materials and MethodsTo validate the experimental approach for imaging the aorta in vivo, a gel phantom with an embedded porcine aorta was imaged in the presence of fluid flow within the aorta. The potential changes in the elasticity of the vessel wall with changes in pressure were investigated. The feasibility of performing MRE of abdominal aorta was assessed in five volunteers (age, 22–40 years; body mass index, 21.5–25.2 kg/m2). The pulse‐gated cine MRE technique was used to study the wave propagation along the aorta throughout the cardiac cycle and provide estimates of aortic stiffness in diastole.ResultsIn the phantom study, the wave propagation was well visualized within the porcine aorta embedded in the gel phantom. An increase of the Young's modulus‐wall thickness (E*t) product with the increase in static pressure was observed. In the in vivo study, the waves were well visualized within the lumen of abdominal aorta in the five volunteers in diastolic phase, but they were not well visualized during systole.ConclusionMRE is feasible for noninvasively assessing the stiffness of the abdominal aorta and merits further investigation. J. Magn. Reson. Imaging 2013;38:1549–1553. © 2013 Wiley Periodicals, Inc.