Abdominal aortic aneurysm (AAA) is the focal enlargement of the aorta in the abdomen and its rupture is the 3rd leading cause of sudden death in men older than 65 years in the US. More in-depth understanding of the pathophysiology of the disease and patient-specific risk assessment are critically important in reducing AAA- related mortality. Many researchers considered abnormal wall shear stress as a potentially important factor in aneurysm expansion and rupture risk. Most AAAs, however, develop intraluminal thrombus (ILT) layers during the progression. The role of ILT on AAA expansion is controversial and the presence of ILT increases complexity in investigating the effect of wall shear stress on AAA expansion. Recent studies also suggest that hemodynamics in the AAA plays a critical role in thrombus formation and its growth. Previous studies, however, used patient-specific models taken from only one time point and have mostly focused on studying relationships between two factors (e.g., wall shear stress vs. AAA expansion, the presence of ILT vs. AAA expansion), which haven't been successful in fully elucidating relationships between multiple factors. Therefore, the main goal of this project is to systemically study these variables, to examine multiple hypotheses on their relationships, and to possibly develop correlations among them by using longitudinal data from AAA patients.
Specific aims are to i) quantify geometric parameters for ILTs and the local expansion rates of AAAs using CT images taken at multiple times, ii) perform hemodynamic simulations with the geometric model constructed from each patient and use the Lagrangian particle method for computing the shear stress experienced by platelets, and iii) examine three hypotheses on the effect of hemodynamic factors in AAAs by using the results from Aim (i) and (ii) for multiple patients and develop correlations among AAA expansion, ILT formation, and hemodynamic parameters. To advance these goals, we have already initiated collaboration with a clinical research team in South Korea and acquired longitudinal images of small AAAs from eleven patients that have been taken with 6 to 24 month intervals with high resolution CT. We will use these longitudinal patient data for developing the proposed numerical simulations and testing of hypotheses on AAA expansion and thrombus formation using multivariate statistical analysis. In our hemodynamic simulations, we will use the Lagrangian particle method to trace the history of shear stress of platelets and to assess the dynamical effects of high shear for platelet activation at the proximal side of the geometrically complex AAA. The study presented in this proposal is a joint collaborative effort between the departments of Mechanical Engineering and Statistics at Michigan State University and the Department of Radiology at Seoul National University Hospital. The proposed research would help ultimately to determine growth rules for developing better computational models of AAAs, which will become an essential tool in clinical management and surgical treatment of the disease.
The proposed research aims to investigate effects of biomechanical factors such as wall shear stress and intraluminal thrombus on abdominal aortic aneurysm expansion using computational fluid dynamics and longitudinal data from patients.