BACKGROUND AND PURPOSE: Some retrospective studies have found that the aneurysm wall enhancement on high-resolution MR vessel wall postgadolinium T1WI has the potential to distinguish unstable aneurysms. This study aimed to identify hemodynamic characteristics that differ between the enhanced and nonenhanced areas of the aneurysm wall on high-resolution MR vessel wall postgadolinium T1WI. MATERIALS AND METHODS: TOF-MRA and high-resolution MR vessel wall T1WI of 25 patients were fused to localize the enhanced area of the aneurysm wall. Using computational fluid dynamics, we studied the aneurysm models. Mean static pressure, mean wall shear stress, and oscillatory shear index were compared between the enhanced and nonenhanced areas. RESULTS: The aneurysmal enhanced area had lower wall shear stress (P Ͻ .05) and a lower oscillatory shear index (P ϭ .021) than the nonenhanced area. In addition, the whole aneurysm had lower wall shear stress (P Ͻ .05) and a higher oscillatory shear index (P ϭ .007) than the parent artery. CONCLUSIONS: This study suggests that there are hemodynamic differences between the enhanced and nonenhanced areas of the aneurysm wall on high-resolution MR vessel wall postgadolinium T1WI. ABBREVIATIONS: HR-VWI ϭ high-resolution MR vessel wall imaging; OSI ϭ oscillatory shear index; P ϭ mean static pressure; WSS ϭ wall shear stress
Introduction: Reports have suggested that high blood flow pulsatility in aneurysms may predict a higher risk of rupture, however, it is unclear whether similar flow dynamics also predict aneurysm growth. The objective of this study is to investigate differences in shape and blood flow characteristics between unruptured growing and stable aneurysms of comparable sizes. Hypothesis: Growing and stable aneurysms of comparable sizes exhibit different flow characteristics across different aneurysm regions. Method: We studied 4 growing aneurysms located at the posterior communicating artery (size ranged from 1.8mm to 11.4mm). Patient-specific aneurysm flow analysis and 3D aneurysm shape analysis were performed to investigate the flow changes during follow-up imaging. Specifically, we compared the shape parameters including aneurysm size, volume, and surface changes. We also compared the aneurysm flow properties including flow velocity, wall shear stress, pulsatility, and flow oscillatory characteristics. The growing aneurysms were analyzed against stable-matching aneurysms which were selected based on similar dome and neck size to find the predictive factors for aneurysm growth. These stable-matching aneurysms exhibiting no size changes for 2 years during follow-up were analyzed as a baseline. Results: We found that blood flow pulsatility through the parent artery was similar across all growing and stable aneurysms, averaging 0.58±0.003. Regardless of aneurysm size, blood flow pulsatility through the aneurysm neck was at the level of 0.66 (0.66±0.06) for growing aneurysms. We also found a clear trend of that blood flow pulsatility increased from the neck to dome in growing aneurysms. Blood flow pulsatility, however, decreased from the aneurysm neck to dome in the stable aneurysms (P<0.05). The rate of increase of blood flow pulsatility through the dome also appears to have an exponential correspondence with the aneurysm volume increase, with a R^2 value of 0.94. Conclusion: We found that increasing blood flow pulsatility from the aneurysm neck to dome may be indicative of aneurysm growth, which may be useful in identifying aneurysms that will potentially grow into high-risk aneurysms.
Introduction: Hemodynamics is thought to play an important role in the pathogenesis, progression, and rupture of aneurysms. Reports have suggested that aneurysm rupture, regardless of aneurysm size, may be due to the collision of incoming flow forming a prominent jet stream directed towards the aneurysm head. The objective of this study was to gain insight into the effect of aneurysm neck, body, and dome cross section geometries on local flow rates. Hypothesis: Aneurysm neck, body, and dome cross section geometries affect local flow rates within the aneurysm head. Methods: Blood flow through the aneurysm neck, body, and dome were evaluated with respect to the cross section size of each region in 33 cases of ruptured posterior communicating artery aneurysms. Computational fluid dynamic analysis was performed and quantitative hemodynamic variables were extracted from the simulation results. Results: All aneurysms generally experienced similar incoming systole volumetric flow rates regardless of the inlet cross-section geometry. Aneurysms with smaller necks experienced greater and more uniform flow reductions than medium or large sized necks. The overall reductions of flow volume through the neck for small, medium, and large necks were 97.8 ±1.4%, 90.0 ±2.7%, and 41.1±22.4%, respectively. Blood flow through the aneurysm body was not affected by body size in small and medium cross sections but still appeared to have some dependence on the aneurysm neck size. Aneurysms with large body geometries, however, further experienced flow reductions of 99.1 ±0.43%. Aneurysm dome cross section size was not found to have a significant effect on volumetric flow rate. Conclusion: Regardless of shape, we found that certain aneurysm neck, body, and dome cross section sizes may have a large influence on flow reduction and energy transmission to the aneurysm apex. By analyzing a group of ruptured aneurysm cases, we found small aneurysms necks have the most drastic flow changes, indicating that aneurysm neck shape may be important for clinical assessment of rupture risk.
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