Identifying Myocardial Mechanical Properties from MRI Using an Orthotropic Constitutive Model

This paper presents a method to characterise the passive orthotropic and contractile properties of left ventricular (LV) myocardial tissue using MRI data of cardiac anatomy, structure and function. Personalised anatomical LV models were fitted to image data from four canine hearts. Diffusion tensor MRI data from the same hearts were parameterised using finite element fitting to provide fibre angle fields that represent longitudinal axes of the myocytes. Fitted fibre angle fields were combined with laminar-sheet orientation data extracted from the Auckland dog heart model and embedded into the customised LV anatomical models. A modified Holzapfel-Ogden orthotropic constitutive relation was parameterised using published data from

ex vivo

shear tests on myocardial tissue blocks. This parameterised constitutive model was scaled for each case in the present study by fitting the individualised LV models to end-diastolic image data. Contractile tension was then estimated by comparing LV model predictions to the end-systolic image data. Personalised models of this kind can be used to predict the 3D deformation and regional stress distributions throughout the LV wall during the entire cardiac cycle.