Flow investigation inside a cerebral giant aneurysm

Cerebral aneurysms are dangerous dilatations of the intracranial vasculature. As these aneurysms are located in the Circle of Willis, which is the essential vessel structure supplying the brain with blood, a rupture leads to drastic consequences for the patient. Physicians are faced with the decision to leave the aneurysm untouched or to intervene. This decision is strongly related to the assessment of rupture risk. It is assumed that hemodynamic factors, i.e. forces resulting from the blood flow itself, play an important role. Thus, a full understanding of correlations between blood flow characteristics and rupture risk is the long-term, ambitious objective of our research. A second aspect that has to be considered is the method of treatment. Several options (clip, coil, flow diverter stenting) are available. A patientspecific analysis and optimization of interventional devices would be ultimately very advantageous. Fluid dynamical simulations provide the most promising tool to reach such ambitious objectives, but require validation. In this contribution, image-based flow investigations of a steady flow through the silicone phantom model of an anatomically realistic giant aneurysm are presented and used as validation source for computational fluid dynamics (CFD). Therefore, the vessel geometry was segmented and reconstructed from angiography data delivering a geometry suitable for simulations as well as for casting a silicone block with included hollow vessels for optical measurements. A stereoscopic particle image velocimetry (PIV) arrangement featuring an index-matched artificial blood liquid is used to obtain averaged velocity vectors in ten parallel planes through the aneurysm sac. From this data streamlines and isocontours of velocity are presented, which show the three-dimensional rolling motion inside the sac. Several PIV planes are compared to their simulation counterparts and show excellent agreement proving the ability of CFD and its assumptions to reliably capture the essential flow features in such cases. As an outlook, the stereo-PIV setup has been slightly modified to enable 3D Particle Tracking Velocimetry (PTV) at low seeding concentrations.