ACCURATE VELOCITY MAPPING WITH FACE

Spin dislocation between the slice selection, phase encoding, and freq uency encoding is a source of image distortions, Two strategies can be pursued to improve the appearance of moving spins in an image. Either the sequence is made equally sensitive to velocity-dependent dislocat ion artifacts for all spatial directions or the sensitivity is reduced with a shorter echo time, The first approach increases the dislocatio n for the phase-encoding direction and is therefore not useful if velo city maps with minimal distortion are the goal, FAcE (FID acquired ech oes) is a sequence with separate sampling of the left and right k-spac e half-planes that allows for very short echo times, It was applied fo r velocity mapping of flow in the slice select direction, Special atte ntion was paid to a compact design of the velocity-encoding select gra dient to achieve short echo times even with high velocity sensitivity. Artifacts introduced by in-plane motion were studied for FAcE and con ventional gradient-echo sequences, both in phantom experiments and sim ulation, FAcE allows for very short echo times with inherent motion co mpensation of the frequency-encoding gradient, Thus, both motion-relat ed dislocation artifacts and signal voids due to coherence loss in reg ions with irregular how are minimal.