Identification of in vivo nonlinear anisotropic mechanical properties of ascending thoracic aortic aneurysm from patient-specific CT scans

Abstract

Accurate identification of in vivo nonlinear, anisotropic mechanical properties of the aortic wall of individual patients remains to be one of the critical challenges in the field of cardiovascular biomechanics. Since only the physiologically loaded states of the aorta are given from in vivo clinical images, inverse approaches, which take into account of the unloaded configuration, are needed for in vivo material parameter identification. Existing inverse methods are computationally expensive, which take days to weeks to complete for a single patient, inhibiting fast feedback for clinicians. Moreover, the current inverse methods have only been evaluated using synthetic data. In this study, we improved our recently developed multi-resolution direct search (MRDS) approach and the computation time cost was reduced to 1~2 hours. Using the improved MRDS approach, we estimated in vivo aortic tissue elastic properties of two ascending thoracic aortic aneurysm (ATAA) patients from pre-operative gated CT scans. For comparison, corresponding surgically-resected aortic wall tissue samples were obtained and subjected to planar biaxial tests. Relatively close matches were achieved for the in vivo-identified and ex vivo-fitted stress-stretch responses. It is hoped that further development of this inverse approach can enable an accurate identification of the in vivo material parameters from in vivo image data.

A Probabilistic and Anisotropic Failure Metric for Ascending Thoracic Aortic Aneurysm Risk Stratification

“…The areas under the curves (AUC), which reflect the discriminative powers of the failure metrics, are 0.5489, 0.8448, 0.7644 and 0.8621, respectively, for Method 1~ Method 4. The diameter criterion has the lowest AUC, while the highest AUC is achieved by FP evaluated under elevated blood pressure using the patient-specific hyperelastic properties, which highlights the potential benefits of incorporating patient-specific hyperelastic properties[53][54][55][56][57][58] in the risk stratification. specific hyperelastic properties, the performance is not improved by evaluating FP under elevated blood pressure by using a representative set of hyperelastic parameters.In general, to evaluate a diagnostic method, an AUC of 0.5 suggests no discrimination, 0.7 to 0.8 is considered acceptable, and 0.8 to 0.9 is considered excellent[59].…”

Medical Image-Based Computational Fluid Dynamics and Fluid-Structure Interaction Analysis in Vascular Diseases

“…Therefore, medical images obtained from various imaging modalities have been combined with inverse FEA to derive in vivo vascular mechanical properties. For example, the in vivo aortic elastic properties of ascending thoracic aortic aneurysm have been identified from gated CT scans using an inverse approach ( Liu et al, 2019a ). An iterative procedure has also been developed to identify coronary artery mechanical properties by matching both maximum and minimum in vivo Cine IVUS lumen circumferences ( Guo et al, 2017 ; Wang et al, 2021 ).…”

Ascending aorta mechanics in bicuspid aortopathy: controversy or fact?

“…Before closing this article, let us emphasize that it is unclear whether the results of in-vitro experimentation on ATAA tissue are representative of the in-vivo failure modes. There have been recent attempts to assess the in-vivo mechanical properties of ATAAs, 50,51 but tissue strength can only be determined through destructive in-vitro testing. Until this obstacle is obviated by noninvasive strength determination, use of clinically measurable parameters as surrogate measures of aortic tissue strength may help to assess the risks of aortic complications based on solely noninvasive clinical data.…”