Biomechanical Study Of The Effect Of Variations Of Anterior Cerebral Artery On The Formation And Rupture Of Cerebral Aneurysms

The cerebral aneurysm is one of the recurrent cerebrovascular diseases. It is important to study the initiation and rupture of cerebral aneurysms. The Circle of Willis (CoW) is the most important collateral pathway of the cerebral artery, which has the critical function in balancing blood pressure and supply. Due to its special anatomical shape, most of cerebral aneurysms form in the CoW. Unfortunately, more than 50% of the general population have an uncomplete CoW, which leads to a higher morbidity of cerebral aneurysm. So in this thesis, using the computational fluid dynamics (CFD) and medical imaging technology, we first built patient-specific geometry models to simulate and assess the hemodynamic factors. The relationship between different anatomical variations in CoW and morbidity of cerebral aneurysms were discussed. Secondly, by selecting the ruptured and the unruptured aneurysms as comparison group, some numercial suggestions can be proposed to prevention and treatment of cerebral aneurysm by studying their morphology and hemodynamics.First of all,30 patient-specific 3D models are reconstructed based on different anatomical variations in the anterior circulation of CoW, including the normal group, absence and hypoplasia of antirior cerebral artery (ACA) groups (10 models per group). Six typical hemodynamics parameters are chosen for comparison, namely average wall shear stress (AWSS), average wall shear stress gradient (AWSSG), oscillatory shear index (OSI), aneurysm formation index (AFI), gradient oscillatory number (GON) and blood pressure. The contours suggest that the two variations groups have lager high-value areas than the normal group and higher parameters values, like AWSS (5.71,7.41 and 5.44 Pa, repectively), AWSSG (2.31e+4,1.97e+4 and 1.55e+4 Pa/m), AFI (0.9956,0.9959 and 0.9945) and pressure (1.24e+4,1.22e+4 and 1.19e+4 torr), especially on the anterior communicating artery (AComA) and bifurcate area. The non-parametric T-test data show that AWSS and AFI have significant differences between the normal group and the hypoplasia group (P=0.029,0.037).The other parameters have no significant differences. Therefore, the anatomical variation in the anterior circulation of CoW might affect the hemodynamic environment of cerebral arteries. This may lead to a higher morbidity of cerebral aneurysm.Secondly,42 ruptured aneurysm models and 27 unruptured aneurysm models are reconstructed to discuss the differences between two groups. Four morphological and four hemodynamic parameters were evaluated. At the same time, based on different anatomical variation in the anterior circulation of CoW, the two groups were each divided into the normal group, absence and hypoplasia of ACA groups. The results show that there was no significant morphological differences between the ruptured aneurysms and the unruptured aneurysms. But in the terms of hemodynamics, the parameters value of unruptured aneurysm are obvious higher than ruptured aneurysm, like AWSS (36.63 and 23.95 Pa), AWSSG (2.0e+5 and 1.2e+5 Pa/m), OSI (0.028 and 0.021) and pressure (6.78e+4 and 3.31e+4 torr). The non-parametric test data show that AWSS, average wall shear stress gradient (AWSSG) and pressure have significant differences (P=0.026,0.006,0) between the two groups. However, as for different type of the CoWgroup, only OSI and pressure had significant differences (P=0.012,0.012) in the absence group. Obviously, different types of the CoW have some impact on ruptured aneurysms.