Magnetic Resonance Elastography (MRE) of the liver is a novel noninvasive clinical diagnostic tool to stage fibrosis based on measured stiffness. The purpose of this study is to design, evaluate and validate a rapid MRE acquisition technique for noninvasively quantitating liver stiffness which reduces by half the scan time, thereby decreasing image registration errors between four MRE phase offsets. In vivo liver MRE was performed on 16 healthy volunteers and 14 patients with biopsy-proven liver fibrosis using the standard clinical Gradient Recalled Echo (GRE) MRE sequence (MREs) and a developed rapid GRE MRE sequence (MREr) to obtain the mean stiffness in an axial slice. The mean stiffness values obtained from the entire group using MREs and MREr were 2.72±0.85kPa and 2.7±0.85kPa, respectively, representing an insignificant difference. A linear correlation of R2=0.99 was determined between stiffness values obtained using MREs and MREr. Therefore, we can conclude that MREr can replace MREs, which reduces the scan time to half of that of the current standard acquisition (MREs), which will facilitate MRE imaging in patients with inability to hold their breath for long periods.

Purpose To determine alteration in left ventricular (LV) myocardial stiffness (MS) with hypertension (HTN). Cardiac magnetic resonance elastography (MRE) was used to estimate MS in HTN induced pigs and MRE-derived MS measurements were compared against LV pressure, thickness and circumferential strain. Materials and Methods Renal-wrapping surgery was performed to induce HTN in 8 pigs. LV catheterization (to measure pressure) and cardiac MRI (1.5T; gradient echo-MRE and tagging) was performed pre-surgery at baseline (Bx), and post-surgery at month 1 (M1) and month 2 (M2). Images were analyzed to estimate LV-MS, thickness and circumferential strain across the cardiac cycle. The associations between end-diastolic (ED) and end-systolic (ES) MS and i) mean LV pressure; ii) ED and ES thickness respectively; and iii) circumferential strain were evaluated using Spearman’s correlation method. Results From Bx to M2, mean pressure, MRE-derived stiffness, and thickness increased while circumferential strain decreased significantly (slope test, p≤0.05). Both ED and ES MS had significant positive correlation with i) mean pressure (ED MS: ρ =0.56; p=0.005 and ES MS: ρ =0.45; p=0.03); ii) ED thickness (ρ =0.73; p<0.0001) and ES thickness (ρ =0.84; p<0.0001) respectively; but demonstrated a negative trend with circumferential strain (ED MS: ρ =0.31 and ES MS: ρ =0.37). Conclusion This study demonstrated that in HTN porcine model, MRE-derived MS increased with increase in pressure and thickness.

Purpose Aortic stiffness plays an important role in evaluating and predicting the progression of systemic arterial hypertension (SAH). The aim of this study is to determine the stiffness of aortic wall using magnetic resonance elastography (MRE) in a hypertensive porcine model and compare it against invasive aortic pressure measurements. Methods Renal wrapping surgery was performed on eight pigs to induce SAH. Aortic MRE was performed at baseline and two months post-surgery using a retrospectively pulse-gated gradient-echo MRE sequence on a 1.5T scanner. Mechanical waves of 70Hz were introduced into the aorta. Invasive central aortic pressure measurements were obtained prior to each scan to calculate mean arterial pressure (MAP). MRE data were analyzed to obtain effective aortic stiffness. Spearman’s rank correlation analysis was performed to assess the relationship between MAP and MRE-derived aortic stiffness. Results Significant increase in effective aortic stiffness was observed between baseline and two months post-surgery measurements (paired t-test; p=0.004). The average MAP by pooling all animals was 65.24±9.42mmHg at baseline and 92.57±11.80mmHg two months post-surgery with p<0.0001. Moderate linear correlation was observed between MAP and effective aortic stiffness (ρ=0.52; p=0.046). Conclusion This study demonstrated that in SAH porcine model, MRE-derived aortic stiffness increased with increase in MAP.