Reproducibility of Cardiac Multifrequency MR Elastography in Assessing Left Ventricular Stiffness and Viscosity

Abstract

Background: Cardiac magnetic resonance elastography (MRE) shows promise in assessing the mechanofunctional properties of the heart but faces clinical challenges, mainly synchronization with cardiac cycle, breathing, and external harmonic stimulation.

Purpose: To determine the reproducibility of in vivo cardiac multifrequency MRE (MMRE) for assessing diastolic left ventricular (LV) stiffness and viscosity.

Study type: Prospective.

Subjects: This single-center study included a total of 28 participants (mean age, 56.6 ± 23.0 years; 16 male) consisting of randomly selected healthy participants (mean age, 44.6 ± 20.1 years; 9 male) and patients with aortic stenosis (mean age, 78.3 ± 3.8 years; 7 male).

Field strength/sequence: 3 T, 3D multifrequency MRE with a single-shot spin-echo planar imaging sequence.

Assessment: Each participant underwent two cardiac MMRE examinations on the same day. Full 3D wave fields were acquired in diastole at frequencies of 80, 90, and 100 Hz during a total of three breath-holds. Shear wave speed (SWS) and penetration rate (PR) were reconstructed as a surrogate for tissue stiffness and inverse viscous loss. Epicardial and endocardial ROIs were manually drawn by two independent readers to segment the LV myocardium.

Statistical tests: Shapiro-Wilk test, Bland-Altman analysis and intraclass correlation coefficient (ICC). P-value <0.05 were considered statistically significant.

Results: Bland-Altman analyses and intraclass correlation coefficients (ICC = 0.96 for myocardial stiffness and ICC = 0.93 for viscosity) indicated near-perfect test-retest repeatability among examinations on the same day. The mean SWS for scan and re-scan diastolic LV myocardium were 2.42 ± 0.24 m/s and 2.39 ± 0.23 m/s; the mean PR were 1.24 ± 0.17 m/s and 1.22 ± 0.14 m/s. Inter-reader variability showed good to excellent agreement for myocardial stiffness (ICC = 0.92) and viscosity (ICC = 0.85).

Data conclusion: Cardiac MMRE is a promising and reproducible method for noninvasive assessment of diastolic LV stiffness and viscosity.

Level of evidence: 2 TECHNICAL EFFICACY: 1.

Keywords: left ventricle; magnetic resonance elastography; noninvasive; tissue stiffness; tomoelastography.

Figure 1

Placement of four air‐driven actuators inducing high‐frequency mechanical waves (yellow) to the heart.

Figure 2

Pulse‐sequence timing diagram depicting the synchronization of imparted motion, motion‐encoding gradients, and the cardiac cycle.

Figure 3

Example case of an 87‐year‐old male participant showing acquired SAX T2‐weighted magnitude images of the MMRE scan, SWS map, and PR map in the mid ventricle for both examinations. MMRE = multifrequency magnetic resonance elastography; SWS = shear wave speed; PR = penetration rate.

Figure 4

Bland–Altman plots of agreement between both examinations for SWS and PR for healthy participants (purple) and patients with aortic stenosis (green). Single red bold dashed line = mean difference; paired blue bold dash‐dotted lines = ±1.96 standard deviations (SD). SWS = shear wave speed; PR = penetration rate.

Figure 5

Bland–Altman plots of agreement between three examinations with different actuator positioning for SWS and PR. Green = differences between scan and re‐scan1; blue = differences between scan and re‐scan2; red = differences between re‐scan1 and re‐scan2. SWS = shear wave speed; PR = penetration rate.

Figure 6

Bland–Altman plots of agreement between both readers for SWS and PR. Single red bold dashed line = mean difference; paired blue bold dash‐dotted lines = ±1.96 standard deviations (SD). SWS = shear wave speed; PR = penetration rate.

Figure 7

Correlations between SWS (a) and PR (b) and age in healthy participants. SWS = shear wave speed; PR = penetration rate.