The progression of a cerebral aneurysm involves degenerative arterial wall remodeling. Various hemodynamic parameters are suspected to be major mechanical factors related to the genesis and progression of vascular diseases. Flow alterations caused by the insertion of coils and stents for interventional aneurysm treatment may affect the aneurysm embolization process. Therefore, knowledge of hemodynamic parameters may provide physicians with an advanced understanding of aneurysm progression and rupture, as well as the effectiveness of endovascular treatments. Progress in medical imaging and information technology has enabled the prediction of flow fields in the patient-specific blood vessels using computational analysis. In this paper, recent computational hemodynamic studies on cerebral aneurysm initiation, progress, and rupture are reviewed. State-of-the-art computational aneurysmal flow analyses after coiling and stenting are also summarized. We expect the computational analysis of hemodynamics in cerebral aneurysms to provide valuable information for planning and follow-up decisions for treatment.
Hemodynamics including flow pattern, shear stress, and blood viscosity characteristics has been believed to affect the development and progression of arterial stenosis, but previous studies lack of realistic physiological considerations such as irregular surface geometry, non-Newtonian viscosity characteristics and flow pulsatility. The effects of surface irregularities and non-Newtonian viscosity on flow fields were explored in this study using the arterial stenosis models with 48% arterial occlusions under physiological flow condition. Computational flow dynamics based on the finite volume method was employed for Newtonian and non-Newtonian fluid. The wall shear stresses (WSS) in the irregular surface model were higher compared to those in the smooth surface models. Also, non-Newtonian viscosity characteristics increase the peak WSS significantly. The dimensionless pressure drop and the time averaged WSS in pulsatile flow were higher than those in steady flow. But pulsatility effects on pressure and WSS were less significant compared to non-Newtonian viscosity effects. Therefore, irregular surface geometry and non-Newtonian viscosity characteristics should be considered in predicting pressure drop and WSS in stenotic arteries.
Previous investigations of morphology for human carotid artery bifurcation from infancy to young adulthood found substantial growth of the internal carotid artery with advancing age, and the development of the carotid sinus at the root of the internal carotid artery during teen age years. Although the reasons for the appearance of the carotid sinus are not clearly understood yet, it has been hypothesized that the dilation of the carotid sinus serves to support pressure sensing, and slows the blood flow to reduce pulsatility to protect the brain. In order to understand this interesting evolvement at the carotid bifurcation in the aspects of fluid mechanics, we performed in vitro phase-contrast MR flow experiments using compliant silicone replicas of age-dependent carotid artery bifurcations. The silicone models in childhood, adolescence, and adulthood were fabricated using a rapid prototyping technique, and incorporated with a bench-top flow mock circulation loop using a computer-controlled piston pump. The results of the in vitro flow study showed highly complex flow characteristics at the bifurcation in all age-dependent models. However, the highest magnitude of kinetic energy was found at the internal carotid artery in the child model. The high kinetic energy in the internal carotid artery during childhood might be one of the local hemodynamic forces that initiate morphological long-term development of the carotid sinus in the human carotid bifurcation.
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