Circle of Willis Flow Analysis

Overview

The Circle of Willis (CoW) is located at the base of the brain providing the primary vascular link to the heart. The communicating arteries of the CoW form a bridge between the cerebral arteries and are thought to maintain the blood supply should problems occur. However, congenital variations can lead to uncertainty with this hypothesis. In this case study realistic numerical representations of the vessels of interest are obtained using ScanIP+FE to convert contrast enhanced MRI scan images into accurate CFD meshes. The role of the communicating arteries is then investigated with blood flow simulation.

Characteristics:

  • Segmentation of contrast enhanced MRI data and generation of downstream vascular disease
  • Generation of CFD model with specified inlets and outlets in ScanIP+FE
  • Mesh sensitivity analysis
  • CFD simulation with COMSOL Multiphysics®
  • Analysis of flow velocities and pressure fields

Thanks to

ISIFC - University of Franche-Comté:
N. Messaoudi

Image Processing

A contrast enhanced MRI scan of an adult male head was used to provide the image data required to generate the model of the CoW. A variety of ScanIP semi-automated and manual segmentation tools were used to isolate the complex structure and provide the baseline CoW model. A number of problematic downstream vascular features (aneurism and stenosis) were then created using ScanIP 3D editing tools, providing a set of models with which to analyse their effect on blood flow through the communicating arteries.

Meshing

For comparative simulation, CFD meshes where produced directly from the CoW model. All meshes were of equally high quality, with maximum element aspect ratios of less than 2. Mesh sensitivity analyses were carried out on a range of mesh densities to determine the optimum number of elements to be used for the simulation. Meshes were exported in the dedicated COMSOL format provided by ScanIP+FE allowing their straightforward import into the solver.

Simulations

The meshes were exported to COMSOL Multiphysics®, where the blood flow model was set up. The blood flow was simulated using the creeping flow solver under time-dependent conditions. The materials of the model were defined according to properties taken from literature.

The simulations confirmed the role of the communicating arteries. Increased blood flow within these vessels was observed with the presence of downstream vascular anomalies, suggesting that the lack of blood flow in these areas was offset by the flow in the communicating arteries.