Fluid Structure Interaction Modeling of Abdominal Aortic Aneurysms: The Impact of Patient Specific Inflow Conditions and Fluid/Solid Coupling

Abstract

Rupture risk assessment of abdominal aortic aneurysms (AAA) by means of biomechanical analysis is a viable alternative to the traditional clinical practice of using a critical diameter for recommending elective repair. However, an accurate prediction of biomechanical parameters, such as mechanical stress, strain, and shear stress, is possible if the AAA models and boundary conditions are truly patient specific. In this work, we present a complete fluidstructure interaction (FSI) framework for patientspecific AAA passive mechanics assessment that utilizes individualized inflow and outflow boundary conditions. The purpose of the study is twofold: (1) to develop a novel semiautomated methodology that derives velocity components from phasecontrast magnetic resonance images (PCMRI) in the infrarenal aorta and successfully apply it as an inflow boundary condition for a patientspecific fully coupled FSI analysis and (2) to apply a oneway–coupled FSI analysis and test its efficiency compared to transient computational solid stress and fully coupled FSI analyses for the estimation of AAA biomechanical parameters. For a fully coupled FSI simulation, our results indicate that an inlet velocity profile modeled with three patientspecific velocity components and a velocity profile modeled with only the axial velocity component yield nearly identical maximum principal stress (دƒ1), maximum principal strain (خµ1), and wall shear stress (WSS) distributions. An inlet Womersley velocity profile leads to a 5% difference in peak دƒ1, 3% in peak خµ1, and 14% in peak WSS compared to the threecomponent inlet velocity profile in the fully coupled FSI analysis. The peak wall stress and strain were found to be in phase with the systolic inlet flow rate, therefore indicating the necessity to capture the patientspecific hemodynamics by means of FSI modeling. The proposed oneway–coupled FSI approach showed potential for reasonably accurate biomechanical assessment with less computational effort, leading to differences in peak دƒ1, خµ1, and WSS of 14%, 4%, and 18%, respectively, compared to the axial component inlet velocity profile in the fully coupled FSI analysis. The transient computational solid stress approach yielded significantly higher differences in these parameters and is not recommended for accurate assessment of AAA wall passive mechanics. This work demonstrates the influence of the flow dynamics resulting from patientspecific inflow boundary conditions on AAA biomechanical assessment and describes methods to evaluate it through fully coupled and oneway–coupled fluidstructure interaction analysis.