Image based computational modeling of intracardiac flows
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With continuous advancements in four-dimensional medical imaging technologies, increasing computational speeds, and widespread availability of high performance computing facilities, computational modeling of intracardiac flows is becoming increasingly viable and has the potential to become a powerful non-invasive diagnostic tool for the diagnosis and treatment of cardiovascular disease. The motive of the current study is to develop a modeling framework that facilitates image-based analysis of intracardiac flows in health as well as disease and to use this framework to gain fundamental insights into intracardiac hemodynamics. A procedure is developed for constructing computational fluid dynamics (CFD) – ready models from in vivo imaging data. The key components of this procedure are the registration and segmentation of the 4D data for several (~20) key frames, template based mapping to ensure surface grid conformality and high-fidelity simulations using a sharp-interface immersed boundary solver. A physiologically representative, kinematic model of the mitral valve is also developed for use in these simulations. As a precursor, a comprehensive quantitative validation of the flow solver is performed using experimental data in a simple model of the left ventricle. A quantitative comparison of the phase-averaged velocity and vorticity fields between the simulation and the experiment shows a reasonable agreement. The detailed assessment of this comparison is used to identify and discuss the key challenges and uncertainties associated in conducting such a validation study. The vast majority of computational investigations of intracardiac flows have focused either on the left or the right ventricles while the corresponding atria were modeled in highly simplistic ways. However, the impact of this simplification on the hemodynamics of the ventricular filling has not been clearly understood. Additionally, the surface of the ventricle has been assumed to be smooth although it is well known that the left ventricle is highly corrugated with surface protrusions or trabeculae and papillary muscles extending deep into the ventricular cavity. Hence, separate studies were conducted to understand the effect of complex atrial flows on the intraventricular flow development and also to understand and quantify the impact of the trabeculae and papillary muscles on ventricular hemodynamics Results indicate that the trabeculae and papillary muscles significantly impact ventricular flow resulting in a deeper penetration of the mitral jet into the ventricle during filling. These anatomical features are also found to produce a “squeezing” effect that enhances apical washout. It is also demonstrated that the complex flow dynamics developed inside the left atrium have minimal influence on the flow inside the left ventricle, which is primarily governed by the mitral valve leaflets configuration. The complex vortical structures inside the left atrium are rapidly dissipated due to the complex interaction of multiple vortex rings leading to breakup, annihilation and enhanced viscous dissipation so that the flow is smoothly streamlined as it enters the mitral orifice and produces a near-uniform velocity profile at the level of the mitral annulus. The implications of these findings on the modeling of the intra-ventricular flows are also discussed.