FSI simulation of carotid arteries in LS-DYNA

Carotid arteries are responsible for blood supply to the head and the neck, including brain perfusion. At the neck level, the left and right common carotid arteries divide into an internal carotid artery and an external carotid artery, at the so called carotid bifurcation. The carotid bifurcation is particularly prone to the development of atherosclerotic plaques, which can cause relevant clinical events such as transient ischemic attacks and stroke. A vast body of literature has proven that the onset and progression of atherosclerosis at the carotid bifurcation is largely determined by the complex hemodynamic environment. In this context, the in silico investigation of carotid bifurcation hemodynamics can support the identification of atheroprone regions and the prediction of plaques development risk. Various computational studies analyzed blood flow in the carotid bifurcation in terms of wall shear stress (WSS) based descriptors. Nevertheless, in most cases computational fluid dynamics (CFD) simulations were conducted assuming wall rigidity and thus neglecting the impact of wall distensibility on blood flow. The aim of this thesis is to investigate the effect of wall distensibility on carotid bifurcation hemodynamics adopting a fluid-structure interaction (FSI) approach, thus accounting for the mutual interaction between blood flow and the arterial wall. A patient-specific carotid bifurcation geometry, previously reconstructed from magnetic resonance imaging, was considered. A mesh sensitivity analysis was conducted to select an appropriate mesh size for fluid domain discretization. The carotid wall was discretized either with shell or hexahedral elements. Blood was modelled as a Newtonian fluid and a hyperelastic material model was assigned to the carotid wall. Physiologic velocity waveforms were imposed at the inflow section of the CCA and at the outflow section of the ICA, while a steady pressure was imposed at the outflow of the ECA. Three simulations were conducted: a rigid-wall CFD simulation, a FSI simulation with the arterial wall modelled through shell elements and a FSI simulation with the arterial wall modelled through hexahedral elements. Simulations were run using LS-DYNA ICFD solver, which was strongly coupled to the implicit structural solver for FSI. The CFD simulation and the FSI simulation with hexahedral wall elements presented negligible differences in hemodynamic quantities, thus suggesting that the rigid wall assumption does not affect markedly the hemodynamics at the carotid bifurcation. Furthermore, the comparison between the FSI simulations with hexahedral and shell wall elements highlighted quantitative differences in WSS based descriptors. Therefore, further investigations should be conducted to elucidate the effect of wall elements formulation on FSI simulations results. In conclusion, the proposed FSI framework allows for a comprehensive analysis of the fluid dynamics at the carotid bifurcation, accounting for the effect of wall distensibility and enabling the investigation of the complex biomechanical aspects involved in atherosclerosis initiation.