Effects of Casson Rheology on Aneurysm Wall Shear Stress

Marcelo A. Castro, María C. Ahumada Olivares, Christopher Putman, Juan Cebral


It is widely accepted that wall shear stress plays an important role in cerebral aneurysm initiation, progress and rupture. Previous works have shown strong evidence in support of the high wall shear stress as a risk factor associated to those biomechanical processes. Patient-specific imagebased
computational hemodynamic modeling of vascular systems harboring cerebral aneurysms has demonstrated to be a fast and reliable way to compute quantities difficult or impossible to be measured in-vivo. The accuracy of the simulation results have been successfully validated in the past.
Additionally, most model assumptions have shown no impact on the flow characterization whose association with the mentioned processes was investigated. Particularly, the incorporation of the blood rheology in large arterial systems containing aneurysms resulted in similar hemodynamic
characterizations for most aneurysms. However, large aneurysms, especially those containing blebs are expected to have flow rates in the range where Newtonian and non-Newtonian models exhibit the largest differences. In order to study the impact of blood rheology in vascular systems harboring
specific intracranial aneurysms, unsteady finite element blood flow simulations were carried out over patient-specific models. Those models were reconstructed from rotational angiographic images using region growing and deformable model algorithms. Unstructured finite element meshes were generated using and advancing front technique. Walls were assumed as rigid, traction-free boundary conditions were imposed at the outlets of the models, and a flow rate wave form was imposed at the inlets after scaling according to the Murray's Law for optimal arterial networks. The Casson model was
incorporated as a velocity gradient dependent apparent viscosity and the results were compared to those using the Newtonian rheology. Regions with differentiated wall shear stress values and orientations were studied.

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