Biomechanics Laboratory, Biomedical Engineering, EE2322, Erasmus MC, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands.
J Biomech. 2010 Aug 26;43(12):2332-8. doi: 10.1016/j.jbiomech.2010.04.039.
Accurate assessment of wall shear stress (WSS) is vital for studies on the pathogenesis of atherosclerosis. WSS distributions can be obtained by computational fluid dynamics (CFD) using patient-specific geometries and flow measurements. If patient-specific flow measurements are unavailable, in- and outflow have to be estimated, for instance by using Murray's Law. It is currently unknown to what extent this law holds for carotid bifurcations, especially in cases where stenoses are involved. We performed flow measurements in the carotid bifurcation using phase-contrast MRI in patients with varying degrees of stenosis. An empirical relation between outflow and degree of area stenosis was determined and the outflow measurements were compared to estimations based on Murray's Law. Furthermore, the influence of outflow conditions on the WSS distribution was studied. For bifurcations with an area stenosis smaller than 65%, the outflow ratio of the internal carotid artery (ICA) to the common carotid artery (CCA) was 0.62+/-0.12 while the outflow ratio of the external carotid artery (ECA) was 0.35+/-0.13. If the area stenosis was larger than 65%, the flow to the ICA decreased linearly to zero at 100% area stenosis. The empirical relation fitted the flow data well (R(2)=0.69), whereas Murray's Law overestimated the flow to the ICA substantially for larger stenosis, resulting in an overestimation of the WSS. If patient-specific flow measurements of the carotid bifurcation are unavailable, estimation of the outflow ratio by the presented empirical relation will result in a good approximation of calculated WSS using CFD.
准确评估壁面切应力（WSS）对于动脉粥样硬化发病机制的研究至关重要。可以使用计算流体动力学（CFD）根据患者特定的几何形状和流量测量来获得 WSS 分布。如果无法获得患者特定的流量测量，则必须通过例如 Murray 定律来估计流入和流出量。目前尚不清楚 Murray 定律在颈动脉分叉处的适用程度，尤其是在存在狭窄的情况下。我们在存在不同程度狭窄的患者的颈动脉分叉处使用相位对比 MRI 进行了流量测量。确定了流出量与面积狭窄程度之间的经验关系，并将流出量测量值与基于 Murray 定律的估计值进行了比较。此外，还研究了流出条件对 WSS 分布的影响。对于面积狭窄程度小于 65%的分叉，颈内动脉（ICA）与颈总动脉（CCA）的流出比为 0.62+/-0.12，而颈外动脉（ECA）的流出比为 0.35+/-0.13。如果面积狭窄程度大于 65%，则 ICA 的流量将以 100%面积狭窄的速度线性降至零。经验关系很好地拟合了流量数据（R(2)=0.69），而 Murray 定律对于较大的狭窄程度会大大高估流向 ICA 的流量，从而高估 WSS。如果无法获得颈动脉分叉处的患者特定流量测量，则通过呈现的经验关系估计流出比将导致使用 CFD 计算得出的 WSS 得到很好的近似。
