GRADIENT MOMENT SMOOTHING - A NEW FLOW COMPENSATION TECHNIQUE FOR MULTISHOT ECHO-PLANAR IMAGING

This work identifies an additional source of phase error across k(y) i n multi-shot echo-planar imaging resulting from flow or motion along t he phase-encoding direction, A velocity-independent flow compensation technique, gradient moment smoothing, is presented that corrects this error by forcing the phase to have smooth quadratic behavior, The corr ection is implemented, without compromising scan time, by changing the first moment of a bipolar prephaser pulse on a shot-by-shot basis, In phantom and in vivo experiments, gradient moment smoothing effectivel y eliminates ghosting and signal loss due to phase-encoding flow, When used in conjunction with a ''flyback'' echo-planar readout, which com pensates for flow in the frequency-encoding direction, gradient moment smoothing renders multi-shot echo-planar imaging relatively insensiti ve to in-plane flow. This can make multi-shot echo-planar imaging a vi able technique for accurately imaging inplane flow and may desensitize it to the otherwise serious problem of in-plane motion.