Marzo Alberto, Singh Pankaj, Reymond Philippe, Stergiopulos Nikos, Patel Umang, Hose Rodney
Department of Medical Physics, School of Biomedical Sciences, University of Sheffield, Sheffield, UK.
Comput Methods Biomech Biomed Engin. 2009 Aug;12(4):431-44. doi: 10.1080/10255840802654335.
Haemodynamics is believed to play an important role in the initiation, growth and rupture of intracranial aneurysms. In this context, computational haemodynamics has been extensively used in an effort to establish correlations between flow variables and clinical outcome. It is common practice in the application of Dirichlet boundary conditions at domain inlets to specify transient velocities as either a flat (plug) profile or a spatially developed profile based on Womersley's analytical solution. This paper provides comparative haemodynamics measures for three typical cerebral aneurysms. Three dimentional rotational angiography images of aneurysms at three common locations, viz. basilar artery tip, internal carotid artery and middle cerebral artery were obtained. The computational tools being developed in the European project @neurIST were used to reconstruct the fluid domains and solve the unsteady Navier-Stokes equations, using in turn Womersley and plug-flow inlet velocity profiles. The effects of these assumptions were analysed and compared in terms of relevant haemodynamic variables within the aneurismal sac. For the aneurysm at the basilar tip geometries with different extensions of the afferent vasculature were considered to study the plausibility of a fully-developed axial flow at the inlet boundaries. The study shows that assumptions made on the velocity profile while specifying inlet boundary conditions have little influence on the local haemodynamics in the aneurysm, provided that a sufficient extension of the afferent vasculature is considered and that geometry is the primary determinant of the flow field within the aneurismal sac. For real geometries the Womersley profile is at best an unnecessary over-complication, and may even be worse than the plug profile in some anatomical locations (e.g. basilar confluence).
血流动力学被认为在颅内动脉瘤的形成、生长和破裂过程中起着重要作用。在此背景下，计算血流动力学已被广泛应用，试图建立血流变量与临床结果之间的相关性。在区域入口处应用狄利克雷边界条件时，通常的做法是根据沃默斯利的解析解将瞬态速度指定为平（塞）流剖面或空间发展剖面。本文提供了三种典型脑动脉瘤的血流动力学对比测量结果。获取了三个常见位置动脉瘤的三维旋转血管造影图像，即基底动脉顶端、颈内动脉和大脑中动脉。利用欧洲@neurIST项目中正在开发的计算工具来重建流体域并求解非定常纳维-斯托克斯方程，依次使用沃默斯利和平流入口速度剖面。根据瘤腔内相关血流动力学变量对这些假设的影响进行了分析和比较。对于基底顶端的动脉瘤，考虑了传入血管不同延伸的几何形状，以研究入口边界处充分发展的轴向流的合理性。研究表明，在指定入口边界条件时对速度剖面所做的假设对动脉瘤内的局部血流动力学影响很小，前提是考虑了传入血管的足够延伸，并且几何形状是瘤腔内流场的主要决定因素。对于实际几何形状，沃默斯利剖面充其量是不必要的过度复杂，在某些解剖位置（如基底汇合处）甚至可能比平流剖面更差。
