Purpose To assess reproducibility in measuring left ventricular (LV) myocardial stiffness in volunteers throughout the cardiac cycle using magnetic resonance elastography (MRE) and to determine its correlation with age. Methods Cardiac MRE (CMRE) was performed on 29 normal volunteers, with ages ranging from 21 to 73 years. For assessing reproducibility of CMRE-derived stiffness measurements, scans were repeated per volunteer. Wave images were acquired throughout the LV myocardium, and were analyzed to obtain mean stiffness during the cardiac cycle. CMRE-derived stiffness values were correlated to age. Results Concordance correlation coefficient revealed good inter-scan agreement with rc of 0.77, with p-value<0.0001. Significantly higher myocardial stiffness was observed during end-systole (ES) compared to end-diastole (ED) across all subjects. Additionally, increased deviation between ES and ED stiffness was observed with increased age. Conclusion CMRE-derived stiffness is reproducible, with myocardial stiffness changing cyclically across the cardiac cycle. Stiffness is significantly higher during ES compared to ED. With age, ES myocardial stiffness increases more than ED, giving rise to an increased deviation between the two.
Purpose To determine magnetic resonance elastography (MRE)-derived stiffness of pancreas in healthy volunteers with emphasis on: 1) short term and midterm repeatability; and 2) variance as a function of age. Methods Pancreatic MRE was performed on 22 healthy volunteers (age range:20-64years) in a 3T-scanner. For evaluation of reproducibility of stiffness estimates, the scans were repeated per volunteer on the same day (short term) and one month apart (midterm). MRE wave images were analyzed using 3D inversion to estimate the stiffness of overall pancreas and different anatomic regions (i.e., head, neck, body, and tail). Concordance and Spearman correlation tests were performed to determine reproducibility of stiffness measurements and relationship to age. Results A strong concordance (ρc=0.99;p-value<0.001) was found between short term and midterm repeatability pancreatic stiffness measurements. Additionally, the pancreatic stiffness significantly increased with age with good Spearman correlation coefficient (all ρ>0.81;p<0.001). The older age group (>45yrs) had significantly higher stiffness compared to the younger group (≤45yrs) (p<0.001). No significant difference (p>0.05) in stiffness measurements was observed between different anatomical regions of pancreas, except neck stiffness was slightly lower (p<0.012) compared to head and overall pancreas at month 1. Conclusion MRE-derived pancreatic stiffness measurements are highly reproducible in the short and midterm and increase linearly with age in healthy volunteers. Further studies are needed to examine these effects in patients with various pancreatic diseases to understand potential clinical applications.
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 To estimate change in left ventricular (LV) end-systolic and end-diastolic myocardial stiffness (MS) in pigs induced with myocardial infarction (MI) with disease progression using cardiac magnetic resonance elastography (MRE) and to compare it against ex-vivo mechanical testing, LV circumferential strain and MRI relaxometry parameters (T1, T2, and extracellular volume fraction (ECV)). Methods MRI (1.5T) was performed on 7 pigs, before surgery (Bx), and 10 (D10) and 21 (D21) days after creating MI. cardiac MRE-derived MS was measured in infarcted region (MIR) and remote region (RR), and validated using mechanical testing-derived MS obtained post-sacrifice on D21. Circumferential strain and MRI relaxometry parameters (T2, T1, and ECV) were also obtained. Multi-parametric analysis was performed to determine correlation between cardiac MRE-derived MS and i) strain, ii) relaxometry parameters, and iii) mechanical testing. Results Mean diastolic (D10:5.09±0.6kPa; D21:5.45±0.7kPa) and systolic (D10:5.72±0.8kPa; D21:6.34±1.0kPa) MS in MIR were significantly higher (p<0.01) compared to mean diastolic (D10:3.97±0.4kPa; D21:4.12±0.2kPa) and systolic (D10:5.08±0.6kPa; and D21:5.16±0.6kPa) MS in RR. The increase in cardiac MRE-derived MS at D21 (MIR) was consistent and correlated strongly with mechanical testing-derived MS (r(diastolic)=0.86; r(systolic)=0.89). Diastolic MS in MIR demonstrated a negative correlation with strain (r=0.58). Additionally, cardiac MRE-derived MS demonstrated good correlations with post-contrast T1 (r(diastolic)= −0.549; r(systolic)= −0.741) and ECV (r(diastolic)=0.548; r(systolic)=0.703), and no correlation with T2. Conclusion As MI progressed, cardiac MRE-derived MS increased in MIR compared to RR, which significantly correlated with mechanical testing-derived MS, T1 and ECV.
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