Visualization of cardiac dynamics using physics-based deformable model

Modeling of moving anatomic structures is complicated by the complexity of motion intrinsic and extrinsic to the structures. However when motion is cyclical, such as in heart, effective dynamic modeling can be approached using modern fast imaging techniques which provide three-dimensional structural data. Data may be acquired as a sequence of 3-D volume images throughout the cardiac cycle. To model the intricate non-linear motion of the heart, we created a physics-based surface model which can realistically deform between successive time points in the cardiac cycle, yielding a dynamic four-dimensional model of cardiac motion. Sequences of fifteen 3-D volume images of intact canine beating hearts were acquired during complete cardiac cycles using the Dynamic Spatial Reconstructor (DSR) and the Electron Beam CT (EBCT). The chambers of the heart were segmented at successive time points, typically at 1/15-second intervals. The left ventricle of the first time point (near end-diastole) was reconstructed as an initial triangular mesh. A mass-spring physics-based deformable model, which can expand and shrink with local contraction and stretching forces distributed in an anatomically accurate simulation of cardiac motion, was applied to the initial mesh and allowed the initial mesh to deform to fit the left ventricle in successive time increments of the sequence. The resultant 4-D model can be interactively transformed and displayed with associated regional electrical activity mapped onto the anatomic surfaces, producing a 5-D model, which faithfully exhibits regional cardiac contraction and relaxation patterns over the entire heart. The beating heart model can be interactively transformed and viewed from different angles, showing regional cardiac contraction and relaxation over the entire heart. For acquisition systems that may provide only limited 4-D data, (e.g., only images at end-diastole and end-systole) the model can provide interpolated anatomic shapes between time points. This physics-based deformable model accurately represents dynamic cardiac structural changes throughout the cardiac cycle. Such models provide the framework for minimizing the number of time points required to usefully depict regional motion of myocardium and allowing quantitative assessment of regional myocardial dynamics. The electrical activation mapping provides spatial and temporal correlation within the cardiac cycle. In procedures such as intra-cardiac catheter ablation, visualization of the dynamic model can be used to accurately localize the foci of myocardial arrhythmias and guide positioning of catheters for effective ablation.