Combined CFD/MRI analysis of blood flow in human left ventricle.

The study is to simulate blood flow processes in a human left ventricular (LV) via a combination of computational fluid dynamics (CFD) and magnetic resonance imaging (MRI). Cardiac MR images from normal and patient subjects are segmented and transformed to generate time-resolved two-dimensional (2D) and three-dimensional (3D) moving grids for blood flow using the arbitrary Lagrangian-Eulerian (ALE) formulation of the Navier-Stokes equations. The numerical solution of the Navier-Stokes equations yields pressure gradient in LV which is well correlated with the acceleration and deceleration of the diastolic and systolic flow. The complexity of transient spiral flow produced by the LV dilation and contraction is difficult to analyze and graphically presented. Thus 2D and 3D models of LV have been used to capture the main characteristics of blood flow in LV. The numerical simulation is performed for (i) 2D model of three normal and three heart failure subjects without valve leaflets (ii) 2D model of LV with and without mitral and aortic valve leaflets for a normal case (iii) 3D model of LV for a normal case (iv) 3D model of LV for a patient case before and after surgery. The results of the 2D modeling for three normal and three heart failure cases without valve leaflets show that the number of vortices and pressure difference between basal and apical for normal cases is higher than abnormal cases. The effect of leaflets on fluid patterns during diastole and systole are assessed. The flow patterns are highly altered with presence of valve leaflets. The work-energy equation is well used to quantify the energy transfer from the contraction and dilation of the ventricle to the pulsating flow processes. The results show that the valve leaflets can not change the rate of energy transfer from LV in comparison with LV without valve leaflets. Furthermore, the pressure and vorticity contours in LV associated with net pressure and shear stress on leaflets are derived. The results show low shear stress on leaflets during diastole and systole. In a 3D model of LV, the 3D flow processes are analyzed by calculating the Lagrange stream function on a sequence of longitudinal planes. The net rate of energy transfer from the wall motion to the blood flow in the ventricle is primarily contributed by the rate of kinetic energy. For the normal subject, the work done by shear stresses and the dissipation of energy are rather small. The results of energy characteristics show an optimal filling and ejection for a normal case. Moreover, the kinematic, dynamics and energy characteristics of blood flow in a LV before and after surgery are quantified. All mentioned characteristics are improved for after surgery LV. The Theoretical and numerical assessment of LV blood flow might provide a basic understanding of fluid mechanics of normal and abnormal ventricular dilation and contraction.DOCTOR OF PHILOSOPHY (MAE