Estimating Flow Direction of Circle of Willis Using Dynamic Arterial Spin-Labeling MR Angiography.

Background and purpose: The circle of Willis (COW) is a crucial mechanism for cerebral collateral circulation. This proof-of-concept study aims to develop and assess an analysis method to characterize the hemodynamics of the arterial segments in the COW by using arterial spin-labeling (ASL) based non-contrast-enhanced dynamic MR angiography (dMRA).

Materials and methods: The developed analysis method uses a graph model, bootstrap strategy, and ensemble learning methodologies to determine the time curve shift from ASL dMRA to estimate the flow direction within the COW. The performance of the method was assessed on 52 subjects, by using the flow direction, either antegrade or retrograde, derived from 3D phase-contrast MR imaging as the reference.

Results: A total of 340 arterial segments in the COW were evaluated, among which 30 (8.8%) had retrograde flow according to 3D phase-contrast MRI. The ASL dMRA-based flow direction estimation has an accuracy, sensitivity, and specificity of 95.47%, 80%, and 96.34%, respectively.

Conclusions: Using ASL dMRA and the developed image analysis method to estimate the flow direction in COW is feasible. This study provides a new method to assess the hemodynamics of the COW, which could be useful for the diagnosis and study of cerebrovascular diseases.