gms | German Medical Science

Objective: Hemodynamic parameters and the flow situation inside intracranial aneurysms have great influence on the risk of rupture. Therefore, computational fluid dynamics (CFD) is a frequently used tool for rupture risk assessment [1]. However, there are great differences between different studies regarding CFD strategy, like spatial and temporal resolution or the extent of considered geometry.

Methods: 3D rotational angiography data of a middle cerebral artery (MCA) aneurysm was segmented using a threshold-based method. For the first investigation, five meshes with different spatial resolution were created. The second study applied a modular meshing approach to investigate the impact of increasing inlet vessel lengths.

Frequency analyses was conducted to ensure, that the applied time step size of 0.001 s is sufficient. Wall shear stress (WSS) and oscillatory shear index (OSI) as defined by Xiang et al. (2011) were calculated, since they were identified as significant parameters for aneurysm rupture [2]. CFD computations were performed using ANSYS Fluent V18.2.

Results: Table 1a [Tab. 1] shows the mesh statistics and the resulting WSS and OSI for the first study. While the coarsest mesh seems to be sufficient for an accurate computation of the WSS, this is not applicable to the OSI. A comparison of the OSI distribution between the coarsest and the finest mesh can be seen in Figure 1 [Fig. 1].

The results of the inlet vessel variation study are shown in Table 1b [Tab. 1]. It is noticeable, that including the carotid siphon in the geometry greatly influences the resulting OSI.

Frequency analyses showed, that the highest occurring frequencies were at approximately 150 Hz. Furthermore, it was found, that including the carotid siphon greatly increases the occurrence of higher frequencies.

Conclusion: The presented results show the great importance of including enough inlet vessel geometry and choosing a sufficient mesh resolution, in order to calculate hemodynamic parameters reliably. Especially the OSI shows a great dependence of mesh resolution and the presence of the carotid siphon, since it induces flow instabilities.