Hemodynamic analysis of flow near cerebral aneurysms: Insight into aneurysm formation and effects of intervention
The purpose of this study is to investigate the role of hemodynamics in the initiation and progression of cerebral aneurysms. It is composed of two major sections, where the first part attempts at understanding the hemodynamic cause and effect linkages leading to aneurysm formation and it is shown that low and oscillatory shear could lead to aneurysm initiation. The second part consists of hemodynamic analysis inside the aneurysm. It is shown that stable flow patterns exist inside the aneurysm with distinct influx and efflux zones that remain unchanged during the cardiac cycle; application of this knowledge will aid in better design of flow diverting devices. In my Master’s thesis, it was demonstrated that low and oscillatory wall shear stresses (WSS) correlated with the aneurysm sites. This work is summarized and then a careful critique of some newer aneurysm formation theories involving high WSS and wall shear stress gradients (WSSG) and how they relate to the AFI (aneurysm formation indicator, proposed by our group) is presented. Second, a numerical experiment is performed to demonstrate the potential drawbacks of using WSSG and its variations as a hemodynamic indicator. Effects of various meshing schemes and resolutions are investigated systematically and the sensitivity of WSSG to image acquisition and reconstruction is demonstrated, along with its potential for misleading interpretation. Third, robustness and sensitivity of the proposed AFI is demonstrated by analyzing the effects of ageing reflected by the change in waveform shape as a result of degeneration of arterial tone. It is shown that AFI indeed captures the differences in the waveforms of an older and a younger adult. Fourth, hemodynamic influences on aneurysm stability under realistic physiological conditions are explored, and contrary to what has been reported in the literature, we have shown that flow patterns inside the aneurysm are relatively stable and insensitive to pulsatility. Two aneurysm types were considered: sidewall (paraclinoid) and bifurcation (basilar tip), with three specimens of each obtained from human patients via clinical 3D digital subtraction angiography. We identified stable large-scale flow patterns in the aneurismal flows. This knowledge of flow patterns is applied towards better design of stents and other flow diverting devices. In addition, potential use of hemodynamic simulations in clinical application is also established.