Stress-Strain Characterization of a Dynamically-Controlled Cardiac Phantom with Fluid and Structural Dynamics

Nicolas Charalambous¹, Kristis Michaelides¹, Elias Psimolofitis², Vasilis Tzangarakis³, Demos Michaelides³, Stelios Angeli⁴, Christakis Constantinides⁴

Myocardial tissue characterization, pre- and post-implantation or following therapy, has becoming an elusive and active research area in clinical practice and basic science work. Prior efforts have focused on the invasive [Stuyvers 1997] and non-invasive MRI characterization of the left ventricular (LV) muscle elasticity [Kolinpaka 2010] to document energetic status, rates and extent of filling and relaxation [Aletras 1999, Wen 2005]. Diastolic filling, in particular, is regarded as the dynamic outcome of myocardial re-lengthening post-contraction and ventricular flow. The pressure fields developed within the intra-ventricular cavity are the determinants of wall stress and the transmural strain gradients. The temporal evolution of such gradients is ultimately dependent on tissue viscoelasticity and its mechanical material properties. Transmural stress and strain, are therefore, direct manifestations of structure-function, the muscles material properties, and the active and passive fiber force generation, as a result of sarcomeric contraction-relaxation, intra-cavity blood pressure changes, and their effects on the endocardial wall [Hu 2003]. This work develops a comprehensive noninvasive imaging protocol for computational modeling, and estimation of global cardiac stress and strain fields of an elastomeric heart of a dynamically controlled cardiac phantom using ex-vivo testing, functional MRI and computational fluid dynamics (CFD). The elicited results are validated based on the computational solutions of the Navier-Stokes (NS) equations for the elastomer and flow velocity fields, in comparison with bench experimentation and phase contrast (PC) MRI.