S474 Poster P-101 Modelling

COMPARISON BETWEEN CFD, CFD-FSI AND SOLID MECHANICS IN PATIENT-SPECIFIC CEREBRAL ANEURYSMS

Alvaro Valencia(1), Sebastian Araya(1) , Francisco Muñoz(1), Rodrigo Rivera(2), Eduardo Bravo(2), Marcelo Galvez(2).

1. Department of Mechanical Engineering, Universidad de Chile, Santiago, Chile. 2. Neuroradiology Department, Instituto de Neurocirugía Asenjo, Santiago, Chile.

Introduction Cerebral aneurysms are pathological dilatations that frequently occur in the principal arteries of the circle of Willis. They are usually located near bifurcations and on arteries with high curvatures. The stresses induced by the hemodynamics control the aneurysm growth and rupture. The oscillatory and low wall shear stress (WSS) on aneurysm surface changes endothelial cell remodelling and the pulsatile blood pressure produces aneurysm enlargement. To study patient-specific cerebral aneurysms different approach can be taken, as in-vivo, in vitro and numerical simulations in simplified models. Computational Fluid dynamics (CFD) has been performed in 34 models with rigid walls, [Valencia, 2007]. CFD including fluid-structure interaction (FSI) has been reported in [Torii, 2007]. The mechanical study of isolated aneurysm models including hyperelastic and anisotropic wall reported maximum effective stress around 1 MPa, [Ma, 2007], Considering that breaking stress of cerebral aneurysms ranged from 073 to 1.9 MPa has been measured by [MacDonald, 2000], can be concluded the high relevance of the mechanical load in the aneurysm rupture risk. In this work, we compare results obtained with CFD with CFD-FSI; mechanical models that include aneurysm and artery with isolated aneurysm models. In the mechanical models results with elastic and hyperelastic artery walls are also reported. Methods For this study, 12 lateral cerebral aneurysms including unruptured and with previous rupture aneurysms were obtained, using three-dimensional rotational angiography in format VRML. Using a reconstruction methodology described in [Valencia 2007], simplified models in Parasolid format are obtained, see Fig. 1. The fluid model is non-Newtonian, the mean inlet velocity is physiological realistic and the Womersley profile is imposed at inlet. For CFD-FSI the artery was simplified as an elastic shell. For the solid mechanics simulations, 3D elastic and hyperelastic walls were considered; the artery thickness was also in one case varied.

Figure 1: Original VRML file and reconstructed model of lateral cerebral aneurysm. For the simulations the commercial finite element package ADINA were used. The optimal grid densities were obtained in previous works for the fluid and solid models and here used. Results The wall pressure on aneurysm fundus and the vortex structure inside the aneurysm predicted with CFD and CFD-FSI were similar, however the WSS distribution on aneurysm showed differences between CFD and CFD-FSI simulations. The effective stress on aneurysm wall predicted with CFD-FSI was different as the predictions with the solid model exclusive, also elastic and hyperelastic solid models produce different wall stress and displacement distributions. Important differences were found between isolated aneurysm models and solid models including the arteries in prediction of stress and displacement distributions on the aneurysms. Discussion The importance to perform CFD-FSI simulations is showed in this work. For the solid mechanics exclusive simulations the inclusion of arterial vasculature around the aneurysm and hyperelastic wall models are relevant. References Valencia et al, Med Eng Phys, in Press, 2007. Torii et al, Comput Fluids, 36, 160-168, 2007 Ma et al, J of Biomech Eng-T ASME, 129, 88-96, 2007. MacDonald et al, Ann Biomed Eng, 28, 533-542, 2000.

Journal of Biomechanics 41(S1) 16th ESB Congress, Posters