Estimation of mechanical properties from gated SPECT and cine MRI data using a finite-element mechanical model of the left ventricle

A significant challenge in diagnosing cardiac disease is determining the viability of myocardial tissue when evaluating the prognosis of vascular bypass surgery. A finite-element mechanical model of the left ventricular myocardium was developed to evaluate mechanical properties of the myocardium, which is an important indicator of viable myocardial tissue and of several aspects of congestive heart failure. The model of the heart muscle mechanics was derived from the passive and active behavior of skeletal muscle, which is considered to be a quasi-incompressible transversely isotropic hyperelastic material of a specified helical fiber structure configuration. Contraction of the myocardium was replicated by simulating active contractions along the helical fibers, then solving (quasi-statically) for the associated boundary valued problem at a sequence of time steps between end-diastole and end-systole of the cardiac cycle. At each time step, the finite-element software package ABAQUS was used to determine the deformation of the left ventricle, which was loaded by intraventricular pressure. An ellipsoidal and a cylindrical model of the left ventricle were developed under both passive loading and active contraction. Parameters that describe the material properties of the myocardium were estimated for the cylindrical model by fitting the radial motion described by the model to gated SPECT and cine MRI data. The authors found that the estimation was sensitive to the measurement of the motion. Results from the finite-clement analysis were compared to those from a purely mathematical description of the cylindrical model.