Patient specific fluid structure interaction (FSI) modeling: Anticipating the growth of abdominal aortic aneurysm (AAA) by considering the effects of hypertension and aorta wall material properties with intraluminal thrombus (ILT)
An abdominal aortic aneurysm (AAA) occurs when there is a bulge formed in the large blood vessels that supply blood to the abdomen, pelvis, and legs. Abdominal aortic aneurysms pose a serious risk of rupture and can be life-threatening. Diagnosis of a life-threatening AAA is based on measuring the diameter of the enlarged aorta. The diseased aortic wall is characterized by an intraluminal thrombus (ILT), which is deposition of fatty acids, leads to narrowed aorta blood vessel, and creates high pressure in the aneurysm sac. The objective of this study was to model the growth of the aneurysm, by combining medical imaging and computational fluid dynamics (CFD) in a time dependent study to determined wall stress, deformation, and fluid flow dynamics over a certain period of time. This model may aid in clinical decision making to determine the optimum time for surgical intervention by providing patient specific aneurysm growth-rate data to avoid potential premature aneurysm rupture. A Computed Tomography (CT) scan from an AAA patient was reconstructed into a 3D Computer Aided Design (CAD) file, exported into a multi-physics simulation software and simulated as a fluid structure interaction model. Hypertensive blood-flow was simulated in the aorta wall, modeled with degradation of aorta wall material properties over time using the Ogden strain energy equation. The maximum growth rate of the aneurysm model was found to be 0.014 cm/year with an increase of 1.4% in the aortic diameter. This growth rate may vary according to patient specific physiological data and geometry, with higher growth rate indicating the risk to rupture. Besides, including ILT in the AAA model increases the accuracy of estimating the growth of the aneurysm and illustrates that it reduces the oxygen supply to the AAA wall with hypoxia induced strains in the arterial walls. The study also demonstrates that oxygen supply reduced around 80% in the lumen near ILT wall and there was a 40% difference in oxygen concentration between ILT and non-ILT wall.