Giulia Soloperto

Flow pattern analysis in a highly stenotic patient-specific carotid bifurcation model using a turbulence model.

The aim of this study is to investigate the blood flow pattern in carotid bifurcation with a high degree of luminal stenosis, combining in vivo magnetic resonance imaging (MRI) and computational fluid dynamics (CFD). A newly developed two-equation transitional model was employed to evaluate wall shear stress (WSS) distribution and pressure drop across the stenosis, which are closely related to plaque vulnerability. A patient with an 80% left carotid stenosis was imaged using high resolution MRI, from which a patient-specific geometry was reconstructed and flow boundary conditions were acquired for CFD simulation. A transitional model was implemented to investigate the flow velocity and WSS distribution in the patient-specific model. The peak time-averaged WSS value of approximately 73 Pa was predicted by the transitional flow model, and the regions of high WSS occurred at the throat of the stenosis. High oscillatory shear index values up to 0.50 were present in a helical flow pattern from the outer wall of the internal carotid artery immediately after the throat. This study shows the potential suitability of a transitional turbulent flow model in capturing the flow phenomena in severely stenosed carotid arteries using patient-specific MRI data and provides the basis for further investigation of the links between haemodynamic variables and plaque vulnerability. It may be useful in the future for risk assessment of patients with carotid disease.

Advanced Computational Models for Disturbed and Turbulent Flow in Stenosed Human Carotid Artery Bifurcation

In this study, newly developed two-equation transitional and turbulence models are employed for the prediction of blood flow patterns in diseased carotid artery where the growth, progression and structure of plaque at rupture are closely linked to low and oscillating wall shear stresses. Moreover, laminar-turbulent transition in the post-stenotic zone can alter the separation zone length, wall shear stress and pressure distribution over the plaque, with potential implications for stresses within the plaque. A separate validation study was carried out with well established experimental measurements and numerical studies. Laminar flow, Menter’s hybrid k-e/k-ω Shear Stress Transport model and its transitional version were implemented in pulsatile simulations from which analyses of velocity profiles, wall shear stress and turbulence intensity were conducted. It was found that the transitional version of SST gave better overall agreement with experimental data for pulsatile flow in an axisymmetric stenosed tube and this is further highlighted in the patient-specific geometry simulation results. A magnetic-resonance (MR) image based model of the carotid bifurcation with 70% stenosis was reconstructed and simulated using patient-specific boundary conditions. The laminar flow assumption was found to be inadequate when the differences occurred in the wall shear stress analysis of the patient-derived model.

Plaque Rupture in the Carotid Artery: A Combined Imaging, Computational and Histological Analysis

Cerebro-vascular events are often related to the rupture of vulnerable atherosclerotic plaques and thrombus formation in the carotid arteries. Haemodynamically significant stenoses experience increased wall shear stress (WSS) in the entrance region but in the post-stenotic region, instead the flow decelerates and tends to become unstable, with separation and recirculation. The high WSS tends to promote processes leading to matrix degradation, with potential rupture, whilst processes stimulated in the post-stenotic zone might be expected to promote further plaque development [1].Copyright