[论文解读] Effect of Foam Insertion in Aneurysm Sac on Flow Structures in Parent Lumen: Relating Vortex Structures with Disturbed Shear

Pawan Kumar Pandey, Malay K. Das|arXiv (Cornell University)|Jun 27, 2021

Intracranial Aneurysms: Treatment and Complications参考文献 77被引用 7

一句话总结

本研究通过涡核线（VCL）拓扑结构，探究了脑动脉瘤中形状记忆聚合物（SMP）泡沫栓塞对母体管腔内涡流结构的影响，揭示了血流动力学紊乱与血流动力学指标之间的关联。泡沫植入显著增加了母体管腔瘤囊底部（SBPL）区域的VCL数量与倾斜度，且与振荡剪切指数（OSI）升高及时间平均壁面剪切应力（TAWSS）降低相关，表明倾斜VCL可能驱动血流紊乱与内皮 dysfuncion。

ABSTRACT

Numerous studies suggest that disturbed shear, causing endothelium dysfunction, can be related to neighboring vortex structures. With this motivation, this study presents a methodology to characterize the vortex structures. Precisely, we use mapping and characterization of vortex structures' changes to relate it with the hemodynamic indicators of disturbed shear. Topological features of vortex core lines (VCLs) are used to quantify the changes in vortex structures. We use the Sujudi-Haimes algorithm to extract the VCLs from the flow simulation results. The idea of relating vortex structures with disturbed shear is demonstrated for cerebral arteries with aneurysms virtually treated by inserting foam in the sac. To get physiologically realistic flow fields, we simulate blood flow in two patient-specific geometries before and after foam insertion, with realistic velocity waveform imposed at the inlet, using the Carreau-Yashuda model to mimic the shear-thinning behavior. With homogenous porous medium assumption, flow through the foam is modeled using the Forcheimmer-Brinkmann extended Darcy model. Results show that foam insertion increases the number of VCLs in the parent lumen. The average length of VCL increases by 168.9% and 55.6% in both geometries. For both geometries under consideration, results demonstrate that the region with increased disturbed shear lies in the same arterial segment exhibiting an increase in the number of oblique VCLs. Based on the findings, we conjecture that an increase in oblique VCLs is related to increased disturbed shear at the neighboring portion of the arterial wall.

研究动机与目标

• 探究SMP泡沫栓塞对脑动脉瘤母体管腔内涡流结构的影响。
• 将涡流拓扑结构的变化与血流动力学紊乱指标（如TAWSS、OSI和TASWSS）关联。
• 开发并应用基于VCL的拓扑表征方法，量化泡沫植入后涡流结构的演化过程。
• 评估倾斜VCL数量的增加是否与血流动力学紊乱区域相关，可能提示内皮功能障碍风险。

提出的方法

• 采用Carreau-Yashuda模型模拟患者特异性脑动脉瘤几何结构中的真实脉动血流，以表征剪切变稀的血液行为。
• 在均匀多孔介质假设下，通过Forchheimer-Brinkman扩展的Darcy模型模拟泡沫引起的血流阻力。
• 利用Sujudi-Haimes算法从仿真数据中提取涡核线（VCLs）以识别涡流。
• 基于平均螺旋度应用后处理滤波，以去除虚假VCLs并提升拓扑精度。
• 通过长度、相对于母体管腔中心线的取向（正常或倾斜）以及在UPL、SBPL和DPL区域的空间分布，量化VCL拓扑特征。
• 将拓扑VCL变化与血流动力学指标（ΔTAWSS、ΔOSI和ΔTASWSS）相关联，以识别血流紊乱区域。

实验结果

研究问题

• RQ1 SMP泡沫植入如何改变脑动脉瘤母体管腔内涡流结构的拓扑特征？
• RQ2 VCL的数量与取向与血流壁面剪切应力指标变化之间存在何种关系？
• RQ3 倾斜VCL数量的增加是否与血流紊乱区域（如TAWSS降低、OSI升高）相关？
• RQ4 在不同血流动力学反应的患者特异性几何结构中，VCL特征有何差异？

主要发现

• 在几何结构-1中，泡沫植入使母体管腔内VCL数量增加了168.9%；在几何结构-2中增加了55.6%。
• 泡沫植入后，几何结构-1中VCL的平均长度增加了168.9%，几何结构-2中增加了55.6%。
• VCL数量的最高增幅，尤其是倾斜VCL，出现在瘤囊底部母体管腔（SBPL）区域，该区域与TAWSS降幅最大和OSI增幅最高的区域一致。
• OSI升高和TAWSS降低的区域——提示血流紊乱——在空间上与倾斜VCL数量增加的区域重合。
• 仅在SBPL区域，ΔTASWSS不为零，表明由于与涡流结构变化相关的方位环流，次级壁面剪切增强。
• 与几何结构-2相比，几何结构-1中倾斜VCL的增幅显著更高，表明下游血管解剖结构可能具有影响。