Study On Hemodynamics Of Cerebral Aneurysm Based On Patient-Specific Models Of The Circle Of Willis

The annual incident of subarachnoid hemorrhage (SAH) is5-20in100,000people in China, among which52%are caused by aneurysm. Internal carotid artery-ophthalmic artery aneurysm appears at the bifurcation of internal carotid artery and ophthalmic artery, accounting for0.47%-9.26%of the intracranial aneurysms and its treatment has been a neurosurgical challenging problem due to its narrow operative space. On the other hand, as many concurrent factors appear to underline the occurrence and development of cerebral aneurysm, an integrated approach for revealing global and local features of blood flow in the cerebral circulation is required to understand the interaction between the different factors.Aiming at studying the mechanism of aneurysm occurrence and its effect on the blood flow supplying to the brain tissue, the in-vitro patient-specific models of the circle of Willis with and without an aneurysm were developed based on computerized tomography images by biomechanical approaches. The characteristics of flow and solution transport were further investigated in the models by in-vitro and numerical simulations.This work consists of three sections as follows:Three-dimensional computer reconstruction of complex blood vessels. A computer model of the circle of Willis was first reconstructed based on medical images using the commercial software SIMPLEWARE. Moreover, an algorithm for image processing and structured hexahedral mesh generation was developed and successfully applied in the reconstruction of bifurcated vessels and a rat kidney, which provides a valuable image-based modeling method for analyzing hemodynamics in vasculars with real geometries.Development of in-vitro patient-specific models. An approach for making a transparent silicone phantom containing a vessel network was developed. The real geometric in-vitro model was manufactured by stacking plexiglas templates and combining different thermal physical and optical materials. The developed approach is low-costed, fast, and valid compared to three-dimensional printers.Experimental and numerical validations of the flow characteristics in the circle of Willis. In-vitro perfusion experimental platform was made and the methods for measuring pressure, flow, and temperature were confirmed by using a U-tube ultrasound phantom. The flow characteristics in the circle of Willis were explored by a particle image velocimetry (PFV) visualization experiment whose tracer particles are made of special dyed resin. Meanwhile the solution transport characteristics in the circle of Willis were investigated by the injection of ink solution from the left and right carotid artery and the basilar artery.The results of the solution experiment show that different feeding arteries have different roles in the cerebral circulation. The solution from the internal carotid artery is mainly distributed to the regions of the middle cerebral artery, anterior cerebral artery, and ophthalmic artery, whereas the solution from the basilar artery can be distributed to the whole circle of Willis. On the other hand, the supplied regions of the solution are changed under the same experiment when an aneurysm appears in the circle of Willis.The result of PIV experiment further show that the flows in the left and right side of the circle of Willis become more balanced except those in the bilateral ophthalmic arteries after the aneurysm occurs. It is found that the average velocities in the three communicating arteries increase significantly in the circle of Willis with an aneurysm, which means there are more flows from the communicating arteries to compensate the flow in the collateral side. Moreover, the occurrence of the aneurysm causes the flow difference in the left and right ophthalmic artery to become larger. It is interesting to note that there exists back-flow in the posterior communicating arteries during every cycle of the pump in the two vessel structures.These results suggest that the characteristics of the flow and mass transfer in the entire circle of Willis are significantly changed with the occurrence of the aneurysm in the carotid-ophthalmic artery, thus the distribution of blood flow to the brain tissue will be changed. This study provides more knowledge about the effect of aneurysm on the cerebral circulation and will be helpful for knowing the mechanism of its occurrence.