Left ventricular phantoms with inclusions simulating transmural and non-transmural infarctions: FEM and EchoPAC study

Abstract

The cardiac elastography evolves to enable local strain estimation and identification of non-transmural infarctions. Below we compare the strain values obtained using EchoPAC in physical left ventricular phantoms made of PVA with results of the Finite Element Modelling (FEM) studies on their counterparts. Models had the form of half of an ellipsoid with 15 mm wall thickness. The homogenous model, transmural inclusion model and nontransmural inclusion (5mm thickness) model were designed. The inclusions were located in the mid segment. The material of the ventricle in the FEM studies was modeled as a hyperelastic, isotropic one. The material parameters came from measurements of the PVA samples for the homogenous case and were extrapolated to obtain stiffer inclusions. The model was deformed by applying 36 kPa pressure load to its inner surface. Peak systolic strain values were close to those observed in healthy subjects. A dedicated setup, the Vivid 6 scanner, probe M4S-RS and EchoPAC BT13 software were used in experiments. The values of strains from FEM models were averaged over nodes corresponding to the layers used in the EchoPAC software. The circumferential strain (CS) values from the FEM simulation and the physical experiment are qualitatively very close and correlate well with the clinical data. The experimental CS results also agree with expectations in terms of slope across the wall and effect of the inclusion. Segmental radial strains obtained from EchoPAC and FEM are close. The proposed approach (phantoms, setup) may be used for development of methods for identification of nontransmural infarctions.