Proper tangential vector field for the wall shear stress evaluation in numerical blood flow simulations in human carotis tree

In numerical simulations of the cardiovascular system the realistic depiction of the blood vessel is essential. The vessel morphology plays a critical role in the underlying hemodynamical computation, for which 3D geometries are obtained via imaging techniques from patients CTA or MRI scans. To evaluate the patients current risks suffering vessel wall damage or an ischaemic stroke, areas of interest are closely observed. A main indicator for these defects is the stress the blood is exerting on the surrounding vessel tissue. The wall shear stress (WSS) and its cyclic evaluation as the oscillatory shear index (OSI) can be used as an indicator for future medical procedures. As a result of low resolution imaging and craggy stenotic surface areas, the geometry model's mesh is often non smooth on the surface areas. The automatically generated tangential vector fields of such a surface topology are therefore corrupted. Making an interpretation of the orientation dependent WSS not only difficult but partially unreliable. In order to smooth out the erratic surface tangential field we apply a projection of the vessel's center-line tangents of the to the surface, based on a method introduced by Morbiducci et al. The validation of our approach is made by comparing the orientation focused evaluation of the WSS to the generic method with automatically generated tangential vectors. The results of this work focus on the carotid bifurcation area and a distal stenosis area in the internal carotid artery.