Analysis On Hemodynamic Characteristics In Cerebral Anterior Communicating Artery Aneurysm And The Associated Influential Factors

Cerebral anterior communicating artery(ACoA)is among the cerebral arteries most susceptible to aneurysm development and rupture.However,the pathological mechanisms behind the phenomenon remain unclear.It is well documented that hemodynamic factors play key roles in the development and rupture of aneurysm,and,accordingly,investigating the hemodynamic characteristics in cerebral aneurysm could be expected to provide useful insights into the initialization,progression and prognosis of cerebral aneurysm.Cerebral artery network is featured by a specific anatomical structure(e.g.,the existence of the circle of Willis)and especially presents marked interindividual variations,making hemodynamics in a certain cerebral aneurysm prone to the influence of the systemic hemodynamic environment.However,the majority of existing studies focused on modeling and hemodynamic analysis for local cerebral aneurysms,while simplifying the prescription of boundary flow conditions,which led to potential deviation of computed results from in vivo hemodynamic conditions.In particular,ACoA is located at the junction of multiple cerebral arteries,making flow characteristics in an aneurysm developing in this region highly sensitive to hemodynamic conditions in the surrounding arteries.The main purpose of this thesis was to quantitatively study the influence of boundary conditions on flow characteristics in ACoA aneurysm.For this purpose,we reconstructed the geometric models of several ACoA aneurysms from patient-specific medical imaging data,and subsequently carried out a series of computational fluid dynamic analysis to investigate the effects of varying flow division between the left and right anterior artery(ACA)A1 segments on hemodynamic variables(such as wall shear stress,vortex and streamlines)in the ACoA aneurysms.In the meantime,an experimental model of ACoA aneurysm was manufactured based on anatomical data to perform PIV(Particle Image Velocimetry)experiment so as to validate the numerical method employed to simulate blood flows.Obtained results showed that varying the flow division between the inflow arteries(herein,left and right ACA A1 segments)led to marked changes in intra-aneurysm flow patterns and wall shear stress distribution.The influence of boundary conditions on wall shear stress was location-dependent,exhibiting evident nonlinear variations in some specific regions.In the meantime,it was found that the regions sensitive to boundary conditions were related closely to the anatomical structure of aneurysm and the bearing arteries,implying that the findings from a single patient study might not be applicable to other patients.Hemodynamic computations performed under pulsatile flow conditions further demonstrated that oscillatory shear index was highly sensitive to boundary conditions as well.Moreover,the comparisons between PIV experiments and hemodynamic computations showed that the adopted numerical method was able to reasonably reproduce the main flow characteristics observed in the experiments.In summary,the present study demonstrated the marked influence of boundary conditions on flow characteristics computed for an ACoA aneurysm,implying that it would be necessary to fully take into account the anatomy of the cerebral artery network and systemic hemodynamic environment when studying blood flows in or assessing the risk of an ACoA aneurysm.