Current guidelines for abdominal aortic aneurysm (AAA) repair are primarily based on the maximum diameter. Since these methods lack robustness in decision making, new image-based methods for mechanical characterization have been proposed. Recently, time-resolved 3D ultrasound (4D US) in combination with finite element analysis was shown to provide additional risk estimators such as patient-specific peak wall stresses and wall stiffness in a non-invasive way. The aim of this study is to: 1) assess the reproducibility of this US-based stiffness measurement in vitro and in vivo, and 2) verify this 4D US stiffness using the gold standard: bi-axial tensile testing of the excised aortic tissue.

For the in vitro study, 4D US data were acquired in an idealized inflation experiment using porcine aortas. The full aortic geometry was segmented and tracked over the cardiac cycle, and afterwards finite element analysis was performed by calibrating the finite element model to the measured US displacements to find the global aortic wall stiffness. For verification purposes, the porcine tissue was subjected to bi-axial tensile testing. Secondly, four AAA patients were included and 4D US data were acquired before open aortic surgery was performed. Similar to the experimental approach, the 4D US data were analyzed using the iterative finite element approach. During surgery, aortic tissue was harvested and the resulting tissue specimens were analyzed using bi-axial tensile testing. Finally, reproducibility was quantified for both methods.

A high reproducibility was observed for the wall stiffness measurements using 4D US, i.e., an ICC of 0.91 (95% CI: 0.78–0.98) for the porcine aortas and an ICC of 0.98 (95% CI: 0.84–1.00) for the AAA samples. Verification with bi-axial tensile testing revealed a good agreement for the inflation experiment and a moderate agreement for the AAA patients, partially caused by the diseased state and inhomogeneities of the tissue.

The performance of aortic stiffness characterization using 4D US revealed overall a high reproducibility and a moderate agreement with ex vivo mechanical testing. Future research should include more patient samples, to statistically assess the accuracy of the current in vivo method, which is not trivial due to the low number of open surgical interventions.

当前的腹主动脉瘤（AAA）修复指南主要基于最大直径。由于这些方法在决策中缺乏鲁棒性，因此提出了新的基于图像的机械表征方法。最近，时间分辨3D超声（4D US）与有限元分析相结合显示出可以以无创方式提供其他风险评估工具，例如患者特定的峰值壁应力和壁刚度。这项研究的目的是：1）在体外和体内评估这种基于US的刚度测量的可重复性，和2）使用金标准验证这种4D US刚度：切除主动脉组织的双轴拉伸测试。

对于体外在一项研究中，使用猪主动脉的理想充气实验获得了4D US数据。在整个心动周期上对整个主动脉几何结构进行分段和跟踪，然后通过将有限元模型校准为所测得的US位移来进行有限元分析，以找到整体主动脉壁硬度。为了验证目的，对猪组织进行双轴拉伸测试。其次，纳入四名AAA患者，并在进行开腹主动脉手术之前获取4D US数据。与实验方法类似，使用迭代有限元方法分析了4D US数据。在手术过程中，收集主动脉组织，并使用双轴拉伸试验分析所得的组织标本。最后，对两种方法的重现性进行了定量。

使用4D US进行壁刚度测量时，观察到了很高的可重复性，即猪主动脉的ICC为0.91（95％CI：0.78–0.98），AAA的ICC为0.98（95％CI：0.84–1.00）样品。通过双轴拉伸试验的验证表明，对于充气实验而言，它具有良好的一致性，而对于AAA患者而言，则具有适度的一致性，这部分是由疾病状态和组织的不均匀性引起的。

使用4D US进行主动脉僵硬度表征的性能显示，总体上具有很高的重现性，并且与离体机械测试的一致性适中。未来的研究应包括更多的患者样本，以统计学方式评估当前体内方法的准确性，由于开放手术干预的数量较少，因此这并非易事。