| Computer modeling and simulation have become an important means for investigating the associations between intra-aneurysmal hemodynamic characteristics and the growth and rupture of cerebral aneurysm.Despite the nature of local pathological changes,blood flow characteristics in cerebral aneurysms may be subject to the influence from systemic blood flow in the cerebral arterial network.However,most previous modeling studies focused on local hemodynamic phenomena in aneurysms,and have not yet addressed the issue in depth.In this context,the thesis applied different modeling methods to represent the relationships between boundary conditions of cerebral aneurysm and hemodynamics in the cerebral arterial network,aiming to clarify the effects of systemic hemodynamics on local intra-aneurysmal blood flow characteristics.We first reconstructed the geometrical model of cerebral aneurysm along with the cerebral arterial network,extracted arterial diameters/lengths,and incorporated the geometrical data into a zero-one dimensional(0-1-D)computational model of the circulatory system to simulate the blood flow waveform in each individual cerebral artery.Subsequently,three modeling methods were applied to represent the three-dimensional(3-D)blood flows in each cerebral aneurysm: 1)model the aneurysm along with the entire cerebral arterial network in fully three dimension(i.e.,Model A,whose solution was considered to be close to the gold standard solution and served as the ‘reference solution’ for examining the reliability of the solutions of other models),2)limit 3-D modeling to the local aneurysm area,with the inlet/outlet boundary conditions of the model being prescribed with the flow waveforms simulated by the 0-1-D model(i.e.,Model B),and 3)adopt the same region of modeling and inlet boundary conditions as Model B,but with the outlets being supported by the free outflow conditions(i.e.,Model C).Numerical simulation experiments on three patients diagnosed with cerebral aneurysm showed that Model B,though being supported by boundary conditions prescribed based on flow waveforms predicted by the 0-1-D circulatory model,could not completely reproduce the solution of Model A,but did brought some improvements over Model C.A cross-sectional comparison of the results for different aneurysms revealed that aneurysms located at bifurcation were most sensitive to the choice of modeling method,which could be attributed to the considerable influence of an aneurysm on flow division among arteries adjacent to the aneurysm.Inspired by these findings,we further constructed idealized models of aneurysm and Y-type adjacent arteries to investigate the influence of the location of aneurysm relative to bifurcation on intra-aneurysmal hemodynamic parameters.Five aneurysms located differently relative to the bifurcation were introduced in sequence in the inflow artery and two outflow arteries(with different diameters),respectively.The results of hemodynamic simulations demonstrated that intra-aneurysmal hemodynamic changes induced by varying the location of aneurysm were small when the aneurysm was present at the inflow artery or the larger outflow artery,while the time-averaged wall shear stress increased considerably as the aneurysm moved away from the bifurcation along the smaller outflow artery.These results implied that the degree of the sensitivity of intra-aneurysmal blood flow characteristics to the location of aneurysm was related to the geometrical dimension of and hemodynamic conditions in the aneurysm carrier artery.In summary,the thesis,through modeling and numerical simulation experiments on several patient-specific and idealized cerebral aneurysms,preliminarily proved the close relationship between intra-aneurysmal flow characteristics and the structure of the cerebral arterial network,systemic hemodynamics and the location of aneurysm,implying the importance of choosing proper modeling methods based on the location of aneurysm in hemodynamic studies on cerebral aneurysm. |
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