Key result
Prescription of elastic foundation boundary conditions reduced the nodal displacement error by 60% compared to traction-free boundary conditions and reproduced heterogeneous strain distribution.
Why the study?
Establishing in vivo, noninvasive, patient-specific techniques to quantify aortic properties is needed to improve clinical risk assessment, specifically evaluating whether heterogeneous deformation in healthy aortas is driven by perivascular tissue interactions modeled by elastic foundation boundary conditions.
An inverse finite element method using DENSE MRI and elastic foundation boundary conditions accurately models patient-specific aortic wall properties and peri-aortic tethering.
May enable patient-specific aortic assessment; leaves open validation for clinical risk stratification.
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.
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Bracamonte et al. (2020) studied Healthy infrarenal abdominal aortas (n=9). Inverse finite element method with elastic foundation boundary conditions vs. Traction-free boundary condition was evaluated on Nodal displacement error. Prescription of elastic foundation boundary conditions reduced the nodal displacement error by 60% compared to traction-free boundary conditions and reproduced heterogeneous strain distribution.
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