Analysis of wall shear stress parameters for patient-specific carotid bifurcations

Modelling of the blood flow in the carotid artery bifurcation is of interest with regards to the genesis and diagnosis of atherosclerotic plaques. In the present study, six haemodynamic wall stress parameters are utilised to evaluate regions of possible atherogenesis within the domain. The arterial geometry was extracted from patient CT scans using AMIRA. The surface mesh quality was then improved through application of in-house meshing software based on the Delaunay method. To resolve the high near-wall velocity gradients inside a carotid bifurcation, boundary layers were employed. A locally conservative Galerkin (LCG) spatial discretisation was applied along with an artificial compressibility characteristic based split scheme to solve the incompressible Navier-Stokes equations. A no-slip boundary condition was applied to the vessel wall. A Womersley profile, which assumes fully developed unsteady flow was applied to the inflow and outflow boundaries. Blood was approximated as a Newtonian fluid. A convergence study was undertaken to ensure solution independence. The healthy right carotid geometry from Patient 1 was analysed. The results show that time-averaged wall shear stress (WSS) was high (6-15Pa) at the apex, along with a small region where WSS exceeded 20Pa. However, low WSS occurred in the common carotid artery (CCA). High oscillatory shear occurred in the CCA distal to a local narrowing of the internal carotid artery (ICA) and along the outer wall, indicating a potential region of atherogenesis. The highest values of wall shear stress angle deviation (WSSAD) and wall shear stress angle gradient (WSSAG) occur at the apex. The wall shear stress temporal gradient (WSSTG) reached 4000 Pa/s near the apex. Wall shear stress spatial gradient (WSSG) values corresponded with the WSS, with a maximum occurring at the apex. Further patient-specific arterial geometries, derived from patients that have been clinically diagnosed with a stenosis, will be evaluated during the presentation