Characterization of flow structure and wall shear stress in patient-specific healthy and aneurysmal abdominal aorta phantoms using particle image velocimetry

Date

2023-9-06

Author

Susar, Mehmet Anıl

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Abdominal Aortic Aneurysm (AAA) is an irreversible dilatation of the abdominal aorta, which can lead to rupture without proper screening and treatment, with an over 80% mortality rate for specific age groups. The enlargement of the abdominal aorta causes significant changes of hemodynamics in AAA with clear indications of flow separation and vortical structures. It is generally accepted that growth and rupture mechanisms of AAA are correlated with the disturbed hemodynamics and wall shear stress metrics such as time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and endothelial cell activation potential (ECAP). In the present study, the flow structure and wall shear stress of patient specific healthy and aneurysmal abdominal aorta phantoms are characterized in physiological flow circulatory set-up using quantitative velocity measurement technique, particle image velocimetry (PIV). A method has been developed and implemented to calculate the wall shear stress (WSS) from PIV, which basically overcomes the difficulties of PIV both in extracting the exact wall location and in predicting the velocity gradients on the wall. The results of the study show that the hemodynamics inside a dilated abdominal aorta differs from the healthy aorta significantly. The peak vorticity magnitude of the formed vortices in the AAA is approximately two times that of the healthy aorta. Considering the wall shear stresses, TAWSS values in the AAA sac are close to 0 Pa mainly due to flow separation, whereas it is about 0.1 Pa for most portions of the healthy aorta. There are two zones in the aneurysm, corresponding to separation and reattachment regions, with OSI values of 0.5, which is the maximum value the OSI can have. In addition, a substantial portion of the aneurysm has relatively larger ECAP values. On the contrary, the OSI and ECAP values are roughly 0 for the whole healthy aorta.

Subject Keywords

Abdominal aortic aneurysm, Hemodynamics, Wall shear stress parameters, Vortex identification, Particle image velocimetry

URI

https://hdl.handle.net/11511/105365

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Graduate School of Natural and Applied Sciences, Thesis