Magnetic resonance imaging assessment of myocardial elastic modulus and viscosity using displacement imaging and phase‐contrast velocity mapping

Abstract

Approximately half of patients experiencing congestive heart failure present with a normal left ventricular ejection fraction. Perturbations in material properties affecting ventricular pressure/volume relationships likely play an important role in the "stiff heart syndrome" yet noninvasive tools permitting the accurate assessment of myocardial elasticity are extremely limited. We developed an MRI-based technique to examine regional left ventricular stress/strain relationships by incorporating displacement-encoding with stimulated-echoes (DENSE) and phase-contrast (PC) velocity mapping and compared regional elastic moduli (EM) and viscous delay time constants (VDTCs) (N=10) with immediate postmortem direct strain gauge measurements (N=8) and global chamber compliance (literature) in normal dogs. EMs by MRI were significantly greater in papillary muscle columns when compared with lateral wall and septal locations by MRI (7.59+/-1.65 versus 3.40+/-0.87 versus 2.55+/-0.93 kPa, P<0.0001) and were in agreement with direct strain gauge measurements (3.78+/-0.93 and 2.96+/-0.88 kPa for the lateral wall and the septum, P=ns for both versus MRI). MRI-determined VDTCs were similar in the three regions (VDTC=-1.15+/-12.37 versus 3.04+/-7.25 versus 4.17+/-5.76 ms, P=ns) and did not differ from lateral and septal wall strain gauge assessment (VDTC=3.09+/-0.40 and 4.57+/-1.86 ms, P=ns for both versus MRI). Viscoelastic measurements obtained in six normal volunteers demonstrated the feasibility of this technique in humans. Noninvasive, regional assessment of myocardial stiffness using DENSE and PC velocity mapping techniques is accurate in a canine model and feasible in humans.