Stroke Prediction Using Carotid Artery CFD Simulations

One out of every twenty deaths in the United States are caused by stroke, which may happen when flow to the carotid artery is hindered by plaque deposition. Traditionally, if blockage is above 70%, surgeons perform a carotid stenting. This surgery is invasive, thus presenting a need for predictive models to help medical decisions. To aid with this, this project aims to investigate velocity profiles and pressure gradients in the carotid artery to better understand the biological significance of the carotid sinus and its relation to stroke risk.

Computational Fluid Dynamics (CFD) simulations are used to analyze blood flow in the carotid. ANSYS Fluent, the commercial CFD software, allows for the discretization of the governing equations of fluid flow using finite volume methods that solve the Navier Stokes equations numerically via iterative procedures. This allows for analysis of flow patterns in patient’s carotid artery scans paying specific attention to the geometry, velocity profiles, streamlines, and pressure gradients. Physiological boundary conditions and models that define blood and artery wall density, blood viscosity, body temperature, and peak systolic and end diastolic velocities are employed. User-Defined functions for blood viscosity dependent on hematocrit levels, and a pulsatile flow model are also utilized. A solution is generated once residual limits are met. For now, 14 carotid arteries from patients with different stroke outcomes (stroke or no stroke) have been analyzed. Patient-specific blood velocities from ultrasound measurements and carotid artery CT scans were provided by the Department of Neurosurgery.

Results from carotid artery simulations showed higher velocities towards the middle portion of the carotid bulge, zero velocity at the walls due to the no-slip boundary condition, and flow reversal closer to the walls. Validation of the model confirmed that mass conservation is obeyed. A scaled ratio was created in which the maximum velocity obtained in the CFD measurements at the peak of the velocity profile at the carotid bulge was compared to the lowest velocity at the reversal region. This scaled ratio ranged from 1.65 to 4.66 for no stroke patients and 9.40 to 10.33 in stroke patients. Thus, the ratio of reverse flow is higher for stroke patients. Improvements to the model include incorporating a fluid-structure interaction between the artery and the blood, in which the vessel wall is modelled as a homogenous, isotropic, viscoelastic material.