Experimental and simulation studies on various models of intracranial lateral aneurysms.

摘要

Hemodynamic forces are long thought to have a significant effect on vascular walls. The focus of this dissertation is to investigate the effects of hemodynamic forces on the walls of intracranial lateral aneurysms which are known to lead to cerebral hematoma or hemorrhage. There are two aspects of the present research. One is a computer simulation of the flow field in the vicinity of such abnormalities and the other is an experimental verification of the computer simulation. Computer simulations were carried out on the CFD software Fluent and the experiments were done with the help of a two dimensional particle image velocimetry (PIV) apparatus.; Two dimensional computer simulations were carried out on three different shapes of aneurysms, namely hemi-spherical, spherical and pear. Each of them were composed of two different ostium (entrance) widths (R and 2R where R is the radius of the parent artery on which the aneurysm is located). In addition, an aneurysm attached to the parent artery was considered both with and without a neck. The parent artery was investigated without any curvature, and also as a curved artery with an aneurysm. The flow in cranial arteries is characterized by a certain range of Reynolds numbers. Therefore, Reynolds numbers of 100, 400 and 700 were considered for the flow through these models. Post processing of the CFD solution to the flow field with user subroutines was employed to determine the shear rate, stress tensor and the inflow into the aneurysmal area, in order to characterize the model.; Experimental work involved designing and testing a particle image velocimetry (PIV) apparatus which was then used to measure two dimensional velocities in glass models. A laser light sheet was used to illuminate the flow field. This was obtained from a continuous wave (CW) ion laser and suitable optics. The laser was shuttered to give controlled exposure of light to the fluid medium. A CCD camera, used to capture the images for analysis, drove the shutter for synchronization while capturing the flow field pictures. Two-frame-cross-correlation done on the successive frames which were a known time apart, yielded the velocity vectors in the exposed two dimensional field.; Some of the findings of this study are: (a) the aneurysm is characterized by increased pressures and shear forces in the neck and base regions, (b) the neck area is important in determining how the fluid striking it is redirected into the aneurysmal volume. This shift of flow can result in increased shear on the walls of dome, (c) at flows characterized by higher Reynolds numbers, the dome experiences greater hemodynamic forces that push or bend the aneurysm towards the parent artery or make it oscillate between two extremities and (d) wide ostium widths of aneurysms cause higher inflows and greater hemodynamic forces due to the entering fluid.