2017 Volume 26 Issue 6 Pages 444-451
Placing a neck bridging stent or a flow diverter has enabled the endovascular treatment for a wide-necked cerebral aneurysm by changes in intra-aneurysmal local hemodynamics. Computer-aided design (CAD) has been applied to an intracranial stent to simulate endovascular treatment effects using computational fluid dynamics (CFD). However, CFD analysis with CAD techniques needs enormous time. The aim of this study was to investigate the hemodynamic changes after placing intracranial stents using CFD with porous media modeling.
The patient-specific geometry models of three unruptured internal carotid artery aneurysms with different sizes were acquired by using three-dimensional (3D) computed tomographic angiography. For each Digital Imaging and Communications in Medicine (DICOM) data, the 3D neck model was made using a Boolean subtraction of aneurysm-deleted model from original geometry model. We obtained 3D stent domain (3DSD) by the transformation in which 3D neck model was offset by a thickness of particle diameter, which corresponds to that of Enterprise VRD (Johnson & Johnson Codman, Miami, FL, USA). Volume coverage ratio (VCR) was defined as the stent volume ratio in 3DSD. Filtration of blood through a virtual 3DSD was described by Darcy’s law (porous media modeling). Hemodynamic parameters such as wall shear stress (WSS), oscillatory shear index (OSI), oscillatory velocity index (OVI), relative residence time (RRT), and flow velocity (FV) at dome were calculated by the CFD analysis. CFD simulation was achieved by changing the VCR every 10% from 0% (VCR 0.00) to 50% (VCR 0.50).
As VCR increased, WSS and FV at dome decreased, and RRT increased in all cases. OSI and OVI in small (Case 1) and medium-sized (Case 2) aneurysms peaked at VCR 0.30 or 0.20 and then decreased, while those in a large aneurysm (Case 3) re-increased at VCR 0.5 after the first peaking and decreasing.
CFD analysis using porous media simulation revealed that an increase in VCR induced stagnant and disturbed blood flow in a short time. However, hemodynamics in a large aneurysm may be different from that of small and medium-sized aneurysms. CFD may be useful to determine the therapeutic strategy for endovascular neurosurgeons.
