A framework for the fluid structure interaction simulation of the aneurysmatic ascending aorta

In the wide spectrum of cardiovascular diseases (CVD), the ascending thoracic aortic aneurysm (ATAA) is a critical condition, due to its silent progression and the severe complications, such as aortic dissection, rupture, or sudden death. Current clinical guidelines for surgical intervention - typically based on maximum aortic diameter criterion - are not always reliable predictors of individual patient risk, as they do not account for biomechanical and hemodynamic factors that drive aneurysm progression. Although widely employed to investigate blood flow patterns and wall shear stress distribution in the aorta, Computational Fluid Dynamics (CFD) generally assumes a rigid vessel wall. In contrast, Fluid-Structure Interaction (FSI) simulations account for the mechanical interplay between flow-induced forces and wall deformation, thus providing a more realistic representation of the biomechanical environment. This is especially important in the ascending thoracic aorta, where wall compliance significantly influences stress distributions and flow patterns. To address this challenge, this thesis presents the development of a dedicated preprocessing pipeline for the generation of patient-specific models of the ascending thoracic aorta using clinical and imaging data. This pipeline enables advanced FSI simulations that contribute to a deeper understanding of aneurysm biomechanics. The proposed pipeline includes several key steps designed to ensure robustness and reproducibility across patient-specific cases. The geometry is obtained by retrospectively-gated computed tomography angiography (CTA) images at the end-diastolic and peak systolic instant, including the valve orifice plane, aortic root, and supra-aortic vessels. The computational grid is locally refined in the ascending aorta (AAo) to accurately capture relevant flow and structural phenomena. A patient-specific calibration of the wall material properties is then performed through an iterative process, varying the Young’s modulus in a previously reported range. After obtaining the diastolic tensional state through a prestress simulation, the patient’s systolic blood pressure is applied to the aortic wall in a structural simulation. The patient Young’s modulus is identified as the value that minimizes the difference between the simulated and CTA-measured AAo volume. Doppler-derived flow rate is imposed at the inflow, whereas three-element Windkessel (RCR) models at the outlet are calibrated to match patient-specific pressure measurements. Finally, the FSI simulation is executed using the two-way Arbitrary Lagrangian-Eulerian (ALE) method. This pipeline was applied to an exemplary model. Results showed elevated Wall Shear Stress (WSS) values concentrated in the region of the Valsalva sinuses. Pressure values showed a median of 125.53 mmHg, with an interquartile range from 125.16 to 126.03 mmHg. Both pressure and Time-Averaged Wall Shear Stress (TAWSS) exhibited peak values in the anterolateral region, suggesting this area may play a key role in aneurysm progression, with TAWSS showing a median of 0.89 Pa and an interquartile range from 0.45 to 1.39 Pa. The established FSI framework allows simulation of patient-specific ascending thoracic aorta models. This approach enables a comprehensive investigation of coupled hemodynamic and structural stresses on the aortic wall, providing deeper insight into their complementary role in ATAA progression and better supporting clinical decision-making.