Aortic aneurysm is associated with aberrant blood flow and wall shear stress (WSS). This can be studied by coupling magnetic resonance imaging (MRI) with computational fluid dynamics (CFD). For patient-specific simulations, extra attention should be given to the variation in segmentation of the MRI data-set and its effect on WSS.

We performed CFD simulations of blood flow in the aorta for ten different volunteers and provided corresponding WSS distributions. The aorta of each volunteer was segmented four times. The same inlet and outlet boundary conditions were applied for all segmentation variations of each volunteer. Steady-state CFD simulations were performed with inlet flow based on phase-contrast MRI during peak systole.

We show that the commonly used comparison of mean and maximal values of WSS, based on CFD in the different segments of the thoracic aorta, yields good to excellent correlation (0.78–0.95) for rescan and moderate to excellent correlation (0.64–1.00) for intra- and interobserver reproducibility. However, the effect of geometrical variations is higher for the voxel-to-voxel comparison of WSS. With this analysis method, the correlation for different segments of the whole aorta is poor to moderate (0.43–0.66) for rescan and poor to good (0.48–0.73) for intra- and interobserver reproducibility.

Therefore, we advise being critical about the CFD results based on the MRI segmentations to avoid possible misinterpretation. While the global values of WSS are similar for different modalities, the variation of results is high when considering the local distributions.

主动脉瘤与异常血流和壁切应力（WSS）相关。可以通过将磁共振成像（MRI）与计算流体动力学（CFD）耦合来进行研究。对于特定于患者的模拟，应特别注意MRI数据集的分割变化及其对WSS的影响。

我们对十名不同的志愿者进行了主动脉血流的CFD模拟，并提供了相应的WSS分布。每个志愿者的主动脉被分割四次。将相同的入口和出口边界条件应用于每个志愿者的所有细分变体。在峰值收缩期，通过基于相差MRI的入口流量执行稳态CFD模拟。

我们显示，基于CFD在胸主动脉的不同节段中，常用的WSS均值和最大值的比较对于重新扫描产生良好至极好的相关性（0.78–0.95），而对于再次扫描则产生中等至极好的相关性（0.64–1.00）。观察者之间和观察者之间的可重复性。但是，对于WSS的体素与体素比较，几何变化的影响更高。使用这种分析方法，整个主动脉不同部分的相关性对于再扫描而言差于中度（0.43-0.66），而对于观察者内和观察者间的再现性则差于良好（0.48-0.73）。

因此，我们建议对基于MRI分割的CFD结果持批评态度，以避免可能的误解。虽然对于不同的模式，WSS的全局值相似，但是当考虑局部分布时，结果的差异很大。