AN EXPERIMENTAL-METHOD FOR EVALUATING CONSTITUTIVE MODELS OF MYOCARDIUM IN IN-VIVO HEARTS

A new experimental method for the evaluation of myocardial constitutiv e models combines magnetic resonance (MR) radiofrequency (RF) tissue-t agging techniques with iterative two-dimensional (2-D) nonlinear finit e element (FE) analysis. For demonstration, a nonlinear isotropic cons titutive model for passive diastolic expansion in the in vivo canine h eart is evaluated. A 2-D early diastolic FE mesh was constructed with loading parameters for the ventricular chambers taken from mean early diastolic-to-late diastolic pressure changes measured during MR imagin g. FE solution was performed for regional, intramyocardial ventricular wall strains using small-strain, small-displacement theory. Correspon ding regional ventricular wall strains were computed independently usi ng MR images that incorporated RF tissue tagging. Two unknown paramete rs were determined for an exponential strain energy function that maxi mized agreement between observed (from MR) and predicted (from FE anal ysis) regional wall strains. Extension of this methodology will provid e a framework in which to evaluate the quality of myocardial constitut ive models of arbitrary complexity on a regional basis.