Finite Element Guide Point Modelling

Finite element modeling is a numerical procedure used to solve problems of mechanics, electrophysiological activity, and fluid flow in engineering applications. Finite element models of cardiac function enable estimation of wall stress, muscle stiffness properties, fluid structure interaction, and predict response to resynchronization therapy [33]. Finite element models have also been used to interactively customize models to patient geometry and motion, through a procedure called guide-point modeling. The model represents the beating heart surfaces as a patchwork of splines (elements) connected at nodes, with constrained continuity of shape and motion. These models were initially applied to biplane coronary cineangiograms [34] and extended to quantify right and left ventricular interaction in mitral regurgitation [35]. In the guide-point modeling procedure, a real time interactive optimization process is employed to iteratively customize the finite element model to user-defined surface guide points, as well as computer generated edge features and feature tracking to deform the model from frame to frame (non-rigid registration) [36]. Initially validated in the left ventricle [37], the method has been extended to biventricular models and validated in CHD patients [38]. The model is customized by least squares optimization of the surface locations to landmarks provided interactively on short and long axis cine images. Using these methods, all four valves can be included (if present). The mass and volume of both ventricles can be obtained, new pathological shapes can be generated which are not already in the database, and all frames in the cine sequence analyzed, resulting in 3D+time motion of the surfaces and valves, and thereby the basal extent of the ventricles, throughout the cardiac cycle. In this method, individual contours of each image are not required since they are provided by the intersections of the model with the image plane. Figure 1 shows short and long axis images and the model-image intersections, together with a 3D view of the model and the image planes.