Image-based studies for modeling cardiovascular fluid dynamics with applications in congenital heart defects.

摘要

Congenital Heart Defects (CHDs) are defined as structural cardiac defects, which is present at birth. The severity of the defect can lead to the death of the patient. Thanks to the advances in medicine, patients with CHDs now commonly survive into adulthood. However, the procedures are not curative. This makes the management of this population crucial. Towards this aim, image-based modeling has been found to be advantageous in diagnosis and follow-ups of these patients.;Cardiac flow has shown to be related with the condition of the cardiovascular system. The main drawbacks of 4D-Flow MRI, which is the only modality for assessment of cardiac flow in-vivo, is low time resolution. To overcome this, Multiplanar Particle Image Velocimetry (MPPIV), named 4D-Flow Echocardiography, was designed to improve the low temporal resolution of 4D-Flow. MPPIV requires the scan to be done simultaneously in a 2D fashion and in two perpendicular stacks instead of scanning the whole volume. MPPIV applies kriging interpolation and imposes the incompressibility constraint. The performance of MPPIV was examined in analytical and numerical cases. MPPIV was used to experimentally model the flow inside a model of the right ventricle.;Furthermore, a novel fluid dynamics index, axisymmetry index (xi), was developed to quantify axisymmetry of vortex rings. The index was examined in analytical cases and found to be in 100% agreement in terms of axisymmetry (xi=1.000). xi was used for measuring the asymmetry in the vortex ring formed downstream of a model of the mitral valve, whose 3D flow field was quantified using Defocusing Digital Particle Image Velocimetry. The results showed that the anterior leaflet of the mitral valve decreased the asymmetry in the formed vortex ring.;We examined the unsteady Bernoulli equation in the estimation of the pressure drop as in everyday clinical studies, pressure is obtained using simplified Bernoulli equation. The effect of the unsteady term of the Bernoulli equation was investigated for the flow passing through the pulmonary valve. In-vivo data were acquired by 4D-Flow MR. Results showed that ignoring the unsteady term during systole of the cardiac cycle creates a statistically significant difference.