Bracamonte Johane H, Wilson John S, Soares Joao S
Department of Mechanical and Nuclear Engineering, Virginia Commonwealth University, 401 West Main Street, Richmond, VA 23284.
Department of Biomedical Engineering and Pauley Heart Center, Virginia Commonwealth University, 601 West Main Street, Richmond, VA 23284.
J Biomech Eng. 2020 Dec 1;142(12). doi: 10.1115/1.4047721.
The establishment of in vivo, noninvasive patient-specific, and regionally resolved techniques to quantify aortic properties is key to improving clinical risk assessment and scientific understanding of vascular growth and remodeling. A promising and novel technique to reach this goal is an inverse finite element method (FEM) approach that utilizes magnetic resonance imaging (MRI)-derived displacement fields from displacement encoding with stimulated echoes (DENSE). Previous studies using DENSE MRI suggested that the infrarenal abdominal aorta (IAA) deforms heterogeneously during the cardiac cycle. We hypothesize that this heterogeneity is driven in healthy aortas by regional adventitial tethering and interaction with perivascular tissues, which can be modeled with elastic foundation boundary conditions (EFBCs) using a collection of radially oriented springs with varying stiffness with circumferential distribution. Nine healthy IAAs were modeled using previously acquired patient-specific imaging and displacement fields from steady-state free procession (SSFP) and DENSE MRI, followed by assessment of aortic wall properties and heterogeneous EFBC parameters using inverse FEM. In contrast to traction-free boundary condition, prescription of EFBC reduced the nodal displacement error by 60% and reproduced the DENSE-derived heterogeneous strain distribution. Estimated aortic wall properties were in reasonable agreement with previously reported experimental biaxial testing data. The distribution of normalized EFBC stiffness was consistent among all patients and spatially correlated to standard peri-aortic anatomical features, suggesting that EFBC could be generalized for human adults with normal anatomy. This approach is computationally inexpensive, making it ideal for clinical research and future incorporation into cardiovascular fluid-structure analyses.
建立体内、非侵入性、针对患者个体且能分辨区域的技术来量化主动脉特性，是改善临床风险评估以及增进对血管生长和重塑的科学理解的关键。实现这一目标的一种有前景的新技术是逆有限元法（FEM），它利用磁共振成像（MRI）从刺激回波位移编码（DENSE）获得的位移场。先前使用DENSE MRI的研究表明，肾下腹主动脉（IAA）在心动周期中变形不均匀。我们假设，在健康主动脉中，这种不均匀性是由区域外膜束缚以及与血管周围组织的相互作用所驱动的，这可以使用弹性基础边界条件（EFBCs）进行建模，该条件使用一组具有不同刚度且呈周向分布的径向弹簧。使用先前获取的患者个体成像以及稳态自由进动（SSFP）和DENSE MRI的位移场，对九条健康的IAA进行建模，随后使用逆有限元法评估主动脉壁特性和不均匀的EFBC参数。与无牵引边界条件相比，规定EFBC可将节点位移误差降低60%，并重现DENSE得出的不均匀应变分布。估计的主动脉壁特性与先前报道的实验双轴测试数据合理相符。归一化EFBC刚度的分布在所有患者中是一致的，并且在空间上与标准的主动脉周围解剖特征相关，这表明EFBC可推广应用于解剖结构正常的成年人群。这种方法计算成本低，非常适合临床研究以及未来纳入心血管流固分析。
