Flow Visualization Studies of Bifurcation Aneurysm

Abstract

We conducted flow visualization studies and measurements of intraaneurysmal flow volume using a flat three-dimensional acrylic aneurysm model. Flow visualization was done by the tracer particle technique and the particle streamlines were pursued through a charge-coupled device (CCD) camera. Analysis of intraaneurysmal flow volume was carried out by means of dye injection. Monitoring of time-related concentration of the aneurysms allowed calculation of the mean transit time (MTT) using the height-over area method. Fundamental intraaneurysmal flow was composed of inflow, circulation flow, and outflow. These fundamental flow patterns were strongly influenced by the flow ratio into the distal branches. A nearly symmetric flow ratio failed to achieve full intraaneurysmal flow. The critical flow ratio to raise inflow into an aneurysm was considered to be 3:1, and the best flow ratio to develop intraaneurysmal flow in our three-dimensional model was 4:1. An increase of the aneurysmal size and changes in geometrical features such as the daughter formation, the dumbbell shape narrowing and narrowing of the neck led to a stagnant area or very sluggish flow area at the dome side. Geometries favoring aneurysmal rupture are considered to be closely associated with low-flow condition.