MR elastography as a method for the assessment of myocardial stiffness: comparison with an established pressure-volume model in a left ventricular model of the heart

Abstract

Magnetic resonance elastography (MRE) measurements of shear stiffness (mu) in a spherical phantom experiencing both static and cyclic pressure variations were compared to those derived from an established pressure-volume (P-V)-based model. A spherical phantom was constructed using a silicone rubber composite of 10 cm inner diameter and 1.3 cm thickness. A gradient echo MRE sequence was used to determine mu within the phantom at static and cyclic pressures ranging from 55 to 90 mmHg. Average values of mu using MRE were obtained within a region of interest and were compared to the P-V-derived estimates. Under both static and cyclic pressure conditions, the P-V- and MRE-based estimates of mu ranged from 98.2 to 155.1 kPa and 96.2 to 150.8 kPa, respectively. Correlation coefficients (R(2)) of 0.98 and 0.97 between the P-V and MRE-based estimates of shear stiffness measurements were obtained. For both static and cyclic pressures, MRE-based measures of mu agree with those derived from a P-V model, suggesting that MRE can be used as a new, noninvasive method of assessing mu in sphere-like fluid-filled organs such as the heart.

Figure 1

Experimental setup showing the connections between the driver, flow pump, pressure transducer and plythesmograph.

Figure 2

A gradient echo MRE schematic pulse sequence indicating the RF pulse; X, Y, and Z gradients with flow-compensating gradients shown on X and Z; the first moment nulled MEG which can be applied along any axis; and the mechanical excitation.

Figure 3

Radial displacement image (left) of the phantom obtained under cyclic pressure conditions using the GRE MRE sequence at a pressure of 55.6 mmHg and corresponding stiffness map (right) with a mean stiffness of 96.2±16.2 kPa for a region of interest shown with the dotted line.

Figure 4

Plot of MRE and P-V stiffness estimates versus pressure during cyclic pressure changes.

Figure 5

Plot of MRE and P-V stiffness estimates versus pressure using static infusion pressures.

Figure 6

Correlation between shear stiffness measurements from the P-V method and MRE during static pressure infusions.

Figure 7

Correlation between shear stiffness estimates obtained during cyclic and static pressure infusions using MRE.