Laser-Doppler velocimetry measurements and flow visualization were complementarily made in pulsatile and steady flow in a cerebrovascular aneurysm model with bifurcation angles of 60, 90, and 140 deg, and volume-flow rate ratios between the branches of 1 to 1 and 3 to 1. The mean, peak, and minimal Reynolds numbers based on the bulk average velocity and diameter of the parent vessel were 600, 800, and 280, respectively. For uneven branch flow, it is found that the flow activity inside the aneurysm and the stresses acting on the aneurysmal wall increase with increasing bifurcation angle. More importantly, the present angle suggests the presence of a critical bifurcation angle below which the aneurysm is prone to thrombosis, whereas above which the aneurysm is susceptible to progression or rupture. For evenly distributed branch flow, the intra-aneurysmal flow is sluggish and therefore prone to thrombosis for all studied bifurcation angles.

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