Estimation of cardiac hyperelastic material properties from MRI tissue tagging and diffusion tensor imaging.

The passive material properties of myocardium are important in the understanding of diastolic cardiac dysfunction. We determined hyperelastic myocardial material parameters in four isolated arrested pig hearts undergoing passive inflation of the left ventricle. Using geometry from MRI, recorded boundary conditions, muscle fiber architecture from diffusion tensor imaging, and deformation from tissue tagging, finite element models were constructed to solve the finite elasticity stress estimation problem. The constitutive parameters of a hyperelastic transversely isotropic material law were determined by minimizing the difference between the predicted and imaged deformation field. The optimized parameters were in a similar range as those reported by previous studies, showing increased passive stiffness in the muscle fiber direction. The average RMS error was 0.92 mm, similar to the image resolution of 0.80 mm. Optimization of hyperelastic models of myocardial mechanics can thus be performed to extract meaningful biophysical parameters from MRI data.