Beyin anevrizmalarına yerleştirilen akım değiştirici stentin hemoreolojik etkilerinin incelenmesi

Flow diverter stents (FDS) are one of the most effective methods in treating cerebral aneurysms to prevent rupture and therefore cerebral hemorrhage that can cause deteriorating or fatal incidents for the patients. Implanting an external medium to the human body causes inevitable hemodynamic changes. Even though the FDS method is quite an efficient treatment method, there are some studies which point out complications of delayed hemorrhage following FDS treatment within 30 days. These complications were found to be occurring in patients with inherited and acquired von Willebrand Disease (vWD). The von Willebrand factor (vWF) activity gets reduced as a result of supraphysiological forces acting on the blood flow leading to an excessive increase in shear stress and shear strain rate. The threshold shear stress and shear strain rate values are known to be as 10 Pascal (Pa) and 5000 s-1, respectively. The objective of this thesis is to prove the implantation of a FDS leading to a pathological increase in shear stress and shear strain rate through numerical simulations. As FDS treatment is a once in a lifetime surgery, conducting virtual surgeries and simulations are of impeccable importance. The majority of the cerebral aneurysms occur on internal carotid artery (ICA) and middle cerebral artery (MCA). Six patients with three ICA and MCA aneurysms each were chosen. Digital subtraction angiography (DSA) images were processed through various methods to prepare patient specific cases. Before treatment cases were prepared for each patient and virtual stent implantation was conducted on each model, where every patient had received both 48 and 64 wire FDS treatments in separate cases. Conclusively, 18 simulations were solved with each patient having three simulations. Blood was modeled as a non-Newtonian fluid, patient specific Womersley velocity profile was generated and inserted for each patient as boundary conditions. The dramatic increase in both shear stress and shear strain rate values were observed with the numerical simulations of post FDS implantations . Shear stress and shear strain rate values were above 10 Pa and 5000 s-1 for all patients after treatment. Supplementary parameters pointed out indications of FDS effect on delayed parenchymal microhemorrhages after inspecting distal of every patient artery through oscillatory shear index (OSI) and time-averaged wall shear stress (TAWSS).