Fully-Coupled FSI Computational Analyses in the Ascending Thoracic Aorta Using Patient-Specific Conditions and Anisotropic Material Properties

Abstract

Computational hemodynamics has become increasingly important within the context of precision medicine, providing major insight in cardiovascular pathologies. However, finding appropriate compromise between speed and accuracy remains challenging in computational hemodynamics for an extensive use in decision making. For example, in the ascending thoracic aorta, interactions between the blood and the aortic wall must be taken into account for the sake of accuracy, but these fluid structure interactions (FSI) induce significant computational costs, especially when the tissue exhibits a hyperelastic and anisotropic response. The objective of the current study is to use the Small On Large (SOL) theory to linearize the anisotropic hyperelastic behavior in order to propose a reduced-order model for FSI simulations of the aorta. The SOL method is tested for fully-coupled FSI simulations in a patient-specific aortic geometry presenting an Ascending Thoracic Aortic Aneurysm (aTAA). The same model is also simulated with a fully-coupled FSI with non-linear material behavior, without SOL linearization. Eventually, the results and computational times with and without the SOL are compared. The SOL approach is demonstrated to provide a significant reduction of computational costs for FSI analysis in the aTAA, and the results in terms of stress state distribution are comparable. The method is implemented in ANSYS and will be further evaluated for clinical applications.

An image-based approach for the estimation of arterial local stiffness in vivo

“…It was plausible to expect this behavior, also considering the lower strain values encountered from the analysis of the different cardiac phases. Considering all three cases, the estimated values of Young's modulus were always contained within the 0.5-3.0 MPa range, which is in line with already reported physiological values from the state of the art (Lin et al (2022); Vignali et al (2021b)).…”

“…Stiffness estimation —The definition of stiffness from the evaluation of strain and stress is, at last, performed. To evaluate the stiffness, the model was assumed as linearized, given the possibility to assume small deformations occurring between diastolic and systolic phase ( Vignali et al (2021b) ; Roccabianca et al (2014) ). The assumption allowed for the adoption of the Hooke law as a constitutive equation to relate stress and strain.…”

Introduction of a Novel Image-Based and Non-Invasive Method for the Estimation of Local Elastic Properties of Great Vessels

“…With respect to limitations of the study, the method presented in this study was calibrated to provide an estimation of the Young's modulus, modeling the vessel wall as an isotropic linear elastic material, thus neglecting the established hyperelastic and anisotropic properties of vascular tissues [18,49,50]. The E value computed from the χ-method is referred not only to a specific section of the vessel, providing local information on the wall stiffness, but also to the environment surrounding the vessel of interest, i.e., other vascular structures and anatomical constraints.…”

“…The lack of such crucial information results in approximations in material modeling [14][15][16], thus strongly limiting the reliability of numerical tools. The mechanical response of vessels, as a result of blood flowing [17,18] or device interaction [19], depends not only on the material properties of the vessel itself, but also on the surrounding structures and tissues [20], thus, in some cases, reducing the value of ex vivo data [21]. Given the importance of non-invasively extrapolating in vivo material information relating to cardiovascular structures, several approaches have been investigated over recent years, such as inverse numerical methodologies and image-based techniques [22][23][24].…”

The Hemodynamic Effect of Modified Blalock–Taussig Shunt Morphologies: A Computational Analysis Based on Reduced Order Modeling

“…In light of this necessity, the exploration of new tools for MBTS fluid dynamic analysis appears to be very challenging. In recent years, Computational Fluid Dynamic (CFD) techniques have been increasingly used to study cardiovascular systems and procedures within both the systemic [12][13][14] and pulmonary circulation [15][16][17]. In this clinical context, the goal is to develop valuable engineering tools for the evaluation of post-and preoperative information.…”