CENTRIC ORDERING IS SUPERIOR TO GRADIENT MOMENT NULLING FOR MOTION ARTIFACT REDUCTION IN EPI

Echo-planar imaging [EPI] is sensitive to motion despite its rapid dat a acquisition rate. Compared with traditional imaging techniques, it i s more sensitive to motion or now in the phase-encode direction, which can cause image artifacts such as ghosting, misregistration, and loss of spatial resolution. Consequently, EPI of dynamic structures (eg, t he cardiovascular system) could benefit from methods that eliminate th ese artifacts. In this paper, two methods of artifact reduction for mo tion in the phase-encode direction are evaluated. First, the k-space t rajectory is evaluated by comparing centric with top-down ordered sequ ences. Next, velocity gradient moment nulling (GMN) of the phase-encod e direction is evaluated for each trajectory. Computer simulations and experiments in now phantoms and rabbits in vivo show that uncompensat ed centric ordering produces the highest image quality. This is probab ly due to a shorter readout duration, which reduces T2 relaxation los ses and off-resonance effects, and to the Linear geometry of phantoms and vessels, which can obscure centric blurring artifacts.