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 myocardial deformation, which is an important indicator of viable myocardial tissue. 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 intra-ventricular pressure. A cylindrical model of the left ventricle was developed under both passive loading and active contraction. Some parameters that describe the material properties of the myocardium were estimated by fitting the motion of the cylindrical model to gated SPECT and cine MRI data. Results from the finite element analysis were compared to those from a mathematical cylindrical model. In the future, more realistic meshes derived from imaging data will be used to perform the finite element analysis. The deformation of the mechanical model will be fitted to a complete strain map from tagged MRI or image warping. Finally, it is proposed to introduce electrical propagation into the finite element model.