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INNOVATIVE METHODOLOGY

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

¹Department of Biomedical Engineering, Indiana University-Purdue University, Indianapolis, Indiana; ²Laboratory of Cardiac Energetics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland; ³Department of Surgery, Hospital of the University of Pennsylvania, and ⁴Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania; ⁵Department of Cardiac Surgery, University of California, Los Angeles, California; and Departments of ⁶Radiology, ⁷Surgery, and ⁸Cellular and Integration Physiology, Indiana University-Purdue University, Indianapolis, Indiana

Submitted 22 January 2009 ; accepted in final form 23 June 2009

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.

magnetic resonance imaging; displacement-encoding with stimulated echo; heart motion analysis; finite element