Initial stress and nonlinear material behavior in patient-specific AAA wall stress analysis

Area of Science:

• Biomedical Engineering
• Computational Mechanics
• Cardiovascular Research

Background:

• Current abdominal aortic aneurysm (AAA) rupture risk assessment relies on maximum diameter.
• AAA wall stress analysis offers a more critical approach but often neglects initial stresses from blood pressure during imaging.
• Finite element analysis (FEA) is used for AAA wall stress computation.

Purpose of the Study:

• To evaluate the effect of neglecting initial stresses (IS) on patient-specific AAA wall stress.
• To assess the contribution of nonlinear material behavior of the AAA wall in stress analysis.
• To determine the necessity of including IS and nonlinear material models in AAA wall stress computations.

Main Methods:

• CT data from 30 patients with AAA diameters below surgical criteria were used for AAA segmentation.
• Mean arterial blood pressure (MAP) was measured post-CT to compute initial stresses (IS) for the CT geometry.
• Wall stress was computed with and without IS, using both linear and nonlinear material models for comparison.

Main Results:

• AAA wall stresses were, on average, higher when computed with initial stresses (IS) compared to without.
• Stresses computed using a nonlinear material model were higher than those from a linear model.
• Omitting IS and material nonlinearity had varied effects on individual AAA wall stress results.

Conclusions:

• Initial stresses (IS) cannot be disregarded in patient-specific AAA wall stress analyses.
• Nonlinear material models should be incorporated for more accurate AAA wall stress computations.
• Accurate AAA rupture risk assessment requires considering both initial stresses and nonlinear material properties.