Hemodynamics Analysis Of Intracranial Aneurysms-patient-specific 3-D Model CFD Simulation

Part?Establishment of patient-specific intracranial aiieurysm 3D rigid wall CFD modelObjective Through 3D-DSA and CTA data, a patient-specific intracranial aneurysms rigid wall CFD model was established to analyze aneurysm hemodynamic characteristics. Investigate the possible factors; include grid density, the fluid characteristics and appropriate interception of the parent artery, which may affect the results. Determine the appropriate conditions to reconstracte the model. Methods Two cases of intracranial aneurysms diagnosed by 3D-DSA or CTA were reconstructed. The commercial CFD software ANSYS CFX 12.0 and finite element method to numerical simulate was used. Select 1-2 cases of intracranial aneurysm to simulate and compared the influence of different grid density, fluid characteristics and parent artery interception methods to the aneurysms flow field. Results Two cases of intracranial aneurysm model were simulated and the flow velocity, flow lines, WSS of the model was calculated. Different grid density had great effect on aneurysm hemodynamics factors. With the increase of grid density, the average WSS increased too. When the maximum diameter of grid was within 0.4mm-0.25mm, the size of grid decreased about 0.05mm and WSS raised 8%-15%. If the size of grid was smaller than 0.25mm, the change of WSS was less than 5%. The differences of streamline and flow velocity between Newtonian and non-Newtonian fluid model were very minor. The biggest difference of the average WSS in a whole cardiac cycle was only about 3.59%. If the inlet interception was presetted too short, the complexity of the flow streamlines in aneurysm region would be underestimated, reduce the scope of the impact of aneurysm, and the flow rate slowed down, which leads to miscalculate the WSS in the impact ion zone. The outlet interception has little impact to the model hemodynamics parameters, such as streamlines, WSS distribution. Conclusion Patient-specific 3-D computational fluid dynamic model of intracranial aneurysm can show the hemodynamic features of the parent artery and aneurysms, which can be used to further analysis hemodynamic. The model reconstruction by 3D-DSA has higher resolution and easier to simplified, and smooth. CTA can reconstruct of whole cerebral blood vessels in one check. For the existence of bilateral artery aneurysms, such as the anterior communicating artery (ACom artery) and the basilar artery aneurysm, CTA is the better choice. The different sizes of the grid have significant influences on the intracranial aneurysms hemodynamic. In intracranial aneurysm model, ino rder to ensure the stability of the results, the grid size should be less than 0.25mm. Newtonian and non-Newtonian fluids have little effect on the intracranial aneurysm flow field, so instead of non-Newtonian fluid, using Newtonian fluid to simulate the aneurysms hemodynamic is reliable. The parent artery interception methods may affect the CFD results singnificently; modeling should consider how to correct the interception model. The inlet of the model should locate in the straight sections of the parent artery. The inlet to the aneurysm should be of sufficient length to ensure blood flow would fully development in the parent artery. The retention of outlet have little impact to the CFD model.Part?Comparison of hemodynamics factors between ruptureand and unrupture intracranial aneurysms.Objective To investigate the impacts of hemodynamic factors on rupture of mirror intracranial aneurysms with 3D reconstruction model computational fluid dynamic (CFD) simulation. Methods Rotation digital subtraction angiography (RDSA) was performed in nine pairs of mirror aneurysms (MANs). Each pair was divided into two groups, the ruptured group and unruptured group. The hemodynamic factors of parent arteries and aneurysms were compared. Results There was significant difference between wall shear stress (WSS) spatially averaged at peak systole of parent artery and average WSS of aneurysm region in the reptured group, i.e,8.78±3.57Pa VS 6.49±3.48pa (P=0.015), but not significant difference in the unruptured group, i.e,9.80±4.12Pa VS 10.17±7.48pa (P=0.678). The average proportion of low WSS area to whole area of aneurysm was 12.20±18.08% in the ruptured group VS 3.96±6.91% in the unruptured group, the difference between them was statistical significance (P=0.015). Average oscillatory shear index (OSI) was 0.0879±0.0764 in the ruptured group, which is significantly higher than that of the unruptured group, i. e,0.0183±0.0191 (P=0.008). Conclusions MANs may be a useful disease model to investigate possible reasons linked to ruptured aneurysms. The ruptured group manifested wider range of low WSS, higher proportion of low WSS area to whole area of aneurysm and higher OSI compared with the unruptured group.Part?Establishment of patient-specific intracranial aneurysm 3D FSI CFD modelObjective A 3D transient fluid-solid coupling model of the blood flow in arteries has been developed in order to study the influence of fluid solid interaction on intracranial aneurysm. Methods A case of intracranial aneurysm was reconstracted by 3D-DSA. The commercial CFD software ANSYS Workbench 12.0, CFX 12.0 and finite element method to numerical simulate was used to FSI. Blood is assumed to be incompressible, Newtonian fluid and laminar flow in the patient-specific intracranial aneurysm. Two cases were selected to established FSI model(assuming the different arterial elastic modulus E=2MPa, 10MPa,40MPa) and rigid wall model. ANSYS Workbench 12.0, CFX 12.0, and FEA was used to simulate, then the differences of hemodynamic parameters between various elastic modulus models and rigid wall model were compared. Results The 3-dimensional elastic aneurysm wall model was created and simulation was performed. The artery wall and fluid field parameters were calculated, such as the vessel wall, Von Mises stress, deformation, flow field. In the model, the largest deformation regional was in the meddle of aneurysms, and high stress concentrated in areas of aneurysm neck. The difference between various elastic modulus models and rigid wall modelshow with the elastic modulus increases, the model deformation decreases, and elastic wall modelhas limited impact to the WSS distribution. The difference average WSS between rigid wall model and the elastic wall (E=2MPa) was less than 5%. Conclusions Patient-specific intracranial aneurysm 3D FSI model was initial establishment and the hemodynamic paratemers were calculated. Deformation of the vascular wall associated with the model geometry. Elastic wall model may have significant impact in the velocity distribution of aneurysm neck. Rigid wall model may overestimate the risk of aneurysm rupture. Elastic wall model have less impact the WSS distribution in the arterial wall.