Flow in an intracranial aneurysm model: effect of parent artery orientation

Flow in an artery with an intracranial saccular aneurysm is investigated under steady and pulsatile flow conditions. Experiments have been carried out using a PIV system that images the instantaneous flow distribution over a selected plane cutting through the bulge. Simulations of the 3D Navier-Stokes equations have been carried out using a finite-volume method. Three models (M1-M3) resembling diseased portions of intracranial aneurysm are considered. These differ in the manner in which the connecting inlet artery is oriented with respect to the bulge. In experiments, a blood mimicking fluid is circulated through the model and dynamic similarity with simulation is achieved under physiological conditions (Re=426 and Wo=4.7). Experimental data are reported on the medial plane and compared against the numerical solution. The three-dimensional flow field is mapped in detail by examining the numerically generated data. The present study reveals distinct flow patterns within the aneurysm at varying orientations of the inlet parent artery. Depending on its orientation, flow may impinge on the distal neck before entering the aneurysm, mix with the primary recirculation pattern, or may entirely bypass it. These flow patterns significantly influence pressure and wall shear stress, and have a bearing on the deformation and aging of the biological tissue. In the three configurations, flow within the bulge reveals a persistent three-dimensional vortex, whose core shifts spatially during the pulsatile cycle. The vortex has a primary component on the medial plane that drives secondary flow on an orthogonal plane within the aneurysmal sac. A vertical cross plane reveals contra-rotating circulation patterns nestled in the neck region that strengthens during the pulsatile cycle, while horizontal planes above the connecting arteries show stagnant secondary flow structures. Vortex strength, measured using the Q-criterion, increases from model M1 to M3 and changes with the phase of the flow rate waveform. Wall shear stress (WSS) and wall pressure are high in regions of flow impingement and WSS is low within the aneurysm, thus generating a region of wall shear stress gradient. Variations in WSS and pressure are shown to be sensitive to the orientation of the inlet parent artery.