MRI Based Quantification of Outflow Boundary Conditions for Computational Fluid Dynamics of Stenosed Human Carotid Arteries

Many studies have been performed to investigate the contribution of wall shear stress (WSS) to pathophysiological processes related to atherosclerosis (Groen, et al., 2007; Kaazempur-Mofrad, et al., 2004; Ku, et al., 1985). To investigate these relationships in stenosed human carotid arteries, accurate assessment of WSS is required. WSS can be calculated in vivo by coupling medical imaging and computational fluid dynamics (CFD). However, often patient specific in- and outflow information is unavailable. Therefore flow through the common (CCA), internal (ICA) and external (ECA) carotid artery needs to be estimated. Murray’s law (Murray, 1926) is often used for that purpose, but it is unclear whether this law holds for stenosed arteries. The goal of this study was to determine outflow boundary conditions for WSS calculations in stenosed carotid bifurcations. Therefore we first quantified the flow (Q) in carotid arteries with different degrees of area stenosis using phase-contrast MRI and determined an empirical relation between outflow-ratios and degree of area stenosis. Secondly we compared the estimated flow ratio based on Murray’s law to the ones measured by MRI. Finally we analyzed the influence of the outflow conditions on the calculated WSS using CFD.