ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

the hemodynamics in cerebral aneurysms. Two patient-specific models of a cerebral
aneurysm corresponding to patients treated by our local Department of Neuroradiology
are investigated. Up to now, most studies have tried to predict parameters that increase
the rupture probability without knowing exactly where the rupture sets in [5,6]. In
contrast, of great importance in this study is the fact, that in both cases a rupture
occurred during the medical examination without any manipulation. Due to this rare
incident the region of interest (ROI) is known, unlike in usual analyses. Thereby,
specific evaluations in this area are possible. Li et al. [7] investigated a ruptured cerebral
aneurysm by means of CFD methods as well, but due to their simplifying assumptions
of a steady, Newtonian flow no characteristic patterns in the ROI could be extracted.
The hemodynamic simulations are carried out on high-quality block-structured grids to
minimize the computational costs and to achieve an excellent convergence behavior.
Blood is treated as an incompressible, isothermal and Newtonian fluid. To provide a
realistic inflow condition a flow rate generated by a complex Fourier series is
implemented.
In order to determine the flow behavior in the ROI, most widely used indicators e.g.
velocity magnitude, pressure distribution and wall shear stresses are analyzed and
compared against each other.
3. METHODS
3.1 Vascular model
Before the desired blood flow simulations can be carried out, it is necessary to generate
a suitable geometry model. Therefore, a 3D rotational angiography (3DRA) technique
was used for obtaining models with highest local resolution. The investigated cerebral
aneurysms, presented in Figure 1 (a-b), were located on the middle cerebral artery
(MCA) and the anterior communicating artery (ACA), respectively. In both cases the
flow directs from the bottom to the top. To improve the surface quality and the realistic
approximation respectively, a seeded region-growth algorithm was used for
segmentation followed by a smoothing procedure [8].
In order to achieve a good convergence behavior, block-structured meshes were
generated using the commercial meshing software ANSYS ICEM-CFD® 13.0 (Ansys
Inc., Canonsburg, PA, USA). The meshes consist of roughly 2 to 2.5 million hexahedral
elements and a mesh independence study was performed in advance in order to identify
the necessary grid density. An element height of 14 µm for the first layer and a growth
ratio of 1.3 towards the lumen were defined (see Fig. 1 c-d).
Fig. 1: Geometries of the two patient-specific cerebral aneurysms (a-b) and exemplary
presentation of a block-structured hexahedral mesh (c-d)