Improving background suppression of intracranial spiral time-of-flight MRA with phase-sensitive water-fat separation

Motivation: Efficient fat suppression can improve flow visualization in time-of-flight (TOF) MRA. We hypothesize that the phase difference of water and fat may be used for efficient fat suppression for out-of-phase (OP) TOF MRA. Goal(s): To demonstrate the feasibility of fat suppression for spiral TOF with sliding-slice localized quadratic (ssLQ) encoding using the phase-sensitive approach. Approach: After the general reconstruction of ssLQ OP TOF, the global slowly varying phase was estimated and removed. Water and fat voxels were then identified according to their phase. Results: Background suppression was substantially improved with the proposed method, resulting in enhanced visualization of small vessels. Impact: The proposed phase-sensitive approach requires no changes of pulse sequence and negligible computational cost. It might be implemented with a wide range of OP TOF MRA for fat suppression.