Improve conspicuity of distal small vessels in velocity-selective ASL MRA using variable flip angle readout

Motivation: The conventional velocity-selective ASL-based (VSASL) MRA's acquisition efficiency is low since a long waiting time is used for blood refreshing. A large turbo factor for acquisition window can be used, but will lead to image blurring and degraded depiction of small vessels. Goal(s): To explore the potential of variable flip angle (VFA) strategy for improving conspicuity of distal small vessels in VSASL MRA. Approach: Four VFA strategies were designed and compared with constant FA in vessel visualization. Vessel sharpness of ACA, MCA and PCA was calculated. Results: Compared to constant FA, VFA has higher sharpness and can reduce the blurring of small vessels. Impact: The sharpness was higher for VFA than constant FA, suggesting the effectiveness of the VFA strategy in reducing blurring and improving the conspicuity of distal small vessels for VSASL MRA.