Particle image velocimetry (PIV) evaluation of flow modification in aneurysm phantoms using asymmetric stents.

Asymmetric stents are promising new devices for endovascular treatment of cerebrovascular aneurysms. For in vitro experiment a patch made of stainless steel mesh is directly attached onto a standard stent and deployed so that the patch is placed over the aneurysm orifice. Thus we modify substantially the flow into the aneurysm and decrease the shear stress on the aneurysm walls. We used mesh-patches having different permeabilities and evaluated the flow using Particle Image Velocimetry. PIV provides instantaneous velocity vector measurements in a cross-section of flow containing reflective micro-particles. A pulsed-laser light sheet illuminates the flow in the target area and images are acquired using a CCD camera. By registering the position of the particles in two successive images the fluid velocity vectors components are calculated. From the 2D velocity field a best polynomial fit is made to obtain a smooth function of each velocity with respect to the coordinates. Using the fit, we derived the values of quantities of interest in the plane of acquisition such as: tangent shear stress, vorticity and inflow. We used four meshes of different permeabilities. We found out that by using lower permeability meshes we create better conditions for the embolization of the aneurysm.