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 vi ability of myocardial tissue when evaluating the prognosis of vascular bypa ss surgery. A finite-element mechanical model of the left ventricular myoca rdium was developed to evaluate mechanical properties of the myocardium, wh ich is an important indicator of viable myocardial tissue and of several as pects 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 hyperelas tic material of a specified helical fiber structure configuration. Contract ion of the myocardium was replicated by simulating active contractions alon g the helical fibers, then solving (quasi-statically) for the associated bo undary 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 sof tware package ABAQUS was used to determine the deformation of the left vent ricle, which was loaded by intraventricular pressure. An ellipsoidal and a cylindrical model of the left ventricle were developed under both passive l oading and active contraction. Parameters that describe the material proper ties of the myocardium were estimated for the cylindrical model by fitting the radial motion described by the model to gated SPECT and eine MRI data. We found that the estimation was sensitive to the measurement of the motion . Results from the finite-element analysis were compared to those from a pu rely mathematical description of the cylindrical model.