Reconstruction of myocardial tissue motion and strain fields from displacement-encoded MR imaging

Abstract

A quantitative analysis of myocardial mechanics is fundamental to understanding cardiac function, diagnosis of heart disease, and assessment of therapeutic intervention. Displacement encoding with stimulated-echo (DENSE) magnetic resonance imaging (MRI) technique was developed to track the three-dimensional (3D) displacement vector of discrete material grid points in the myocardial tissue. Despite the wealth of information gained from DENSE images, the current software only provides two-dimensional in-plane deformation. The objective of this study is to introduce a postprocessing method to reconstruct and visualize continuous dynamic 3D displacement and strain fields in the ventricular wall from DENSE data. An anatomically accurate hexagonal finite-element model of the left ventricle (LV) is reconstructed by fitting a prolate spheroidal primitive to contour points of the epi- and endocardial surfaces. The continuous displacement field in the model is described mathematically based on the discrete DENSE vectors using a minimization method with smoothness regularization. Based on the displacement, heart motion and myocardial stretch (or strain) are analyzed. Illustratory computations were conducted with DENSE data of three infarcted and one normal sheep ventricles. The full 3D results show stronger overall axial shortening, wall thickening, and twisting of the normal LV compared with the infarcted hearts. Local myocardial stretches show a dyskinetic LV in the apical region, dilation of apex in systole, and a compensatory increase in strain in the healthy basal region as a compensatory mechanism. We conclude that the proposed postprocessing method significantly extends the utility of DENSE MRI, which may provide a patient-specific 3D model of cardiac mechanics.

Accurate High-Resolution Measurements of 3-D Tissue Dynamics With Registration-Enhanced Displacement Encoded MRI

“…10. In contrast to the above noted variability of displacements within the imaging plane, the through-plane motion was relatively uniform, in agreement with previous observations of animal cardiac motion [64], [65]. From the 3-D displacement fields, the LV twist angles were measured to be −3.0 ± 3.0° (mean ± SD for the slice), 2.8 ± 3.2°and 8.9 ± 3.8° at the base, mid-ventricle and apex, respectively.…”

Left ventricular torsion and longitudinal shortening: two fundamental components of myocardial mechanics assessed by tagged cine-MRI in normal subjects

“…Given that the global rotation is the average of the rotation angles for all points inside the LV, it summarizes the overall twisting of each short axis cut. As reported by Liu et al [23], it might have a significant diagnostic value, since it is significantly reduced in the presence of LV dysfunction. This is also the case for overall LV shortening (which is the global scaling in the longitudinal direction).…”

Regional Left Ventricular Myocardial Contractility and Stress in a Finite Element Model of Posterobasal Myocardial Infarction

“…Future studies will include the RV geometry and pressure as part of the model. The quality and resolution of the experimental strain could be improved by utilizing a 3T scanner rather than a1.5T scanner, which can produce a more precise gradient of strain in the LV wall [29, 30]. Additionally, it is difficult to quantify the steep transition in the wall thickness at the BZ.…”