Research on Optimum Design of Stent Used for Interventional Treatment Apparatus of Aneurysms

为了优化设计用于治疗动脉瘤的支架，进行了数值模拟，得到了设计准则。选择囊状动脉瘤作为模型动脉瘤，在瘤颈的载瘤动脉内放置支架。然后，动脉瘤中的血流速度减慢，预计血栓会在动脉瘤内壁产生，导致动脉瘤壁硬化，防止动脉瘤的生长和破裂。从计算结果中得到了以下结果。(1)当血流在动脉瘤内达到最大值时，它从动脉瘤颈上游进入动脉瘤，沿动脉瘤内壁流动，从动脉瘤颈下游排出。(2)动脉瘤内压力基本均匀，但压力随时间脉动，平均动脉瘤上下游侧值。(3)动脉瘤内血流的驱动力是压差…。载瘤动脉边界层内的血流动量撞击支架细丝后由轴向向径向偏转时，动脉瘤上下游之间的血流速度增加。(4)根据血流切变率判断血栓的形成。为了检查支架置入的有效性，有必要测量支架细丝附近和动脉瘤中的流量。我们研制了外径为100μm的导管式激光测速传感器，用于测量血管局部血流速度。通过将这个传感器穿过支架插入到动脉瘤中，就可以测量动脉瘤中的局部血流速度。对传感器周围的流动进行了数值模拟，估算了传感器在待测流场中的存在引起的测量误差。此外，众所周知，血液粘度在流速较低的区域增加。这是由于血液在低流量区域的非牛顿流变性造成的。因此，为了高精度地估计支架的效果，需要通过解决红细胞变形和周围血浆流动之间的耦合问题来对血流的流变性进行准确的建模。提出了一种基于浸没边界法的耦合分析方法，并通过数值模拟验证了方法的有效性。较少

For the purpose of optimum design of stent used for the treatment of aneurysms, numerical simulations were performed to obtain the design criterion. Saccular aneurysm was chose as a model aneurysm and stent was located in the parent artery at the neck of the aneurysm. Then, the speed of blood flow in the aneurysm decreases and it is expected that thrombus generates on the inner wall of aneurysm, resulting in hardening of the aneurysm wall and prevention of aneurysm growth and rupture. The following results were obtained from the calculation results. (1)When the flow becomes maximum in the aneurysm, it enters the aneurysm from upstream side of the aneurysm neck, flows along the inner wall of the aneurysm, and discharges from downstream side of aneurysm neck. (2)The pressure in the aneurysm becomes almost uniform, but the pressure pulsates with time having average the value of upstream and downstream sides of the aneurysm. (3)The driving forces of flow in the aneurysm is pressure differe … More nce between upstream and downstream sides in the aneurysm and momentum of flow in the boundary layer of the parent artery which impinges on the stent filaments and then deflects from axial to radial direction. (4)The generation of the thrombus can be judged based on the wall shear rate of the blood flow. In order to check the effectiveness of the placement of the stent, flow measurement near the stent filaments and in the aneurysm is necessary. We have developed cathetertype LDV-sensor having 100μ m in outer diameter for measuring the local blood flow velocity in blood vessels. By inserting this sensor across the stent into the aneurysm, it is possible to measure the local flow velocity in the aneurysm. Numerical simulation of flow around this sensor was performed to estimate measurement error due to the existence of the sensor in the flow field which is to be measured. Furthermore, it is known that the blood viscosity increases in the region where the flow velocity is low. This is due to non-Newtonian rheological behavior of the blood in the low flow region. Therefore, in order to estimate the effect of the stent with high accuracy, accurate modeling of the rheology of blood flow is necessary by solving the coupled problem between the deformation of the red blood cell and plasma flow around it. A coupled analysis by using immersed boundary method was proposed and the effectiveness of the method was confirmed by numerical simulations. Less