Abdominal aortic aneurysm (AAA) is a life-threatening condition involving the permanent dilation of the aorta, often detected incidentally through imaging for some other condition. The standard clinical approach to managing AAA follows a one-size-fits-all model based on aneurysm size and growth rate, leading to underestimation or overestimation of rupture risk in individual patients. The widely studied stress-based rupture risk estimation using computational biomechanics requires wall strength information. However, non-invasive methods for local patient-specific wall strength measurement have not yet been developed. Recently, we introduced an image-based approach for patient-specific, in vivo, non-invasive AAA kinematic analysis using time-resolved 3D computed tomography angiography (4D-CTA) images to measure wall strain throughout the cardiac cycle. In the present study, we integrated wall tension computation and strain measurement to develop a novel measure of local structural integrity of AAA wall - Relative Structural Integrity Index (RSII), independent of material properties and thickness of the wall and conditions of blood pressure measurement. Our methods provide a visual map of AAA wall structural integrity for individual patients using only their medical images and blood pressure data. We applied our methods to twelve patients. Additionally, we compared our measure of structural integrity of aneurysmal and non-aneurysmal aortas. Our results show similar values of the wall structural integrity measure across the patients, indicating the reliability of our methods. In line with experimental observations reported in the literature, our analysis revealed that localized low stiffness areas are primarily found in the most dilated AAA regions. Our results clearly demonstrate that the AAA wall is stiffer than the non-aneurysmal aorta.

翻译：腹主动脉瘤（AAA）是一种危及生命的疾病，表现为主动脉的永久性扩张，通常是在因其他病症进行影像学检查时偶然发现。目前临床管理AAA的标准方法采用基于动脉瘤尺寸和生长速率的"一刀切"模式，这导致对个体患者的破裂风险存在低估或高估。基于计算生物力学的应力破裂风险评估方法虽被广泛研究，但需要血管壁强度信息。然而，目前尚未开发出针对患者局部血管壁强度的无创测量方法。最近，我们提出了一种基于影像的个体化、在体、无创AAA运动学分析方法，利用时间分辨三维计算机断层扫描血管造影（4D-CTA）图像测量整个心动周期中的血管壁应变。在本研究中，我们整合了血管壁张力计算与应变测量，开发出一种新型的AAA血管壁局部结构完整性指标——相对结构完整性指数（RSII），该指标独立于血管壁的材料特性、厚度以及血压测量条件。我们的方法仅利用患者的医学影像和血压数据，即可生成个体化的AAA血管壁结构完整性可视化图谱。我们将该方法应用于十二名患者，并比较了动脉瘤段与非动脉瘤段主动脉的结构完整性测量结果。研究显示各患者血管壁结构完整性测量值具有相似性，证明了本方法的可靠性。与文献报道的实验观察结果一致，我们的分析表明局部低刚度区域主要出现在AAA最扩张的区域。结果明确显示AAA血管壁较非动脉瘤主动脉更为僵硬。