ORBITAL NAVIGATOR ECHOES FOR MOTION MEASUREMENTS IN MAGNETIC-RESONANCE-IMAGING

A single ''orbital'' navigator echo, that has a circular k-space traje ctory, is used to simultaneously measure in-plane rotational and multi -axis translational global motion. Rotation is determined from the shi ft in the magnitude profile of the echo with respect to a reference ec ho. Displacements are calculated from the phase difference between the current echo and a reference echo. Phantom studies show that this tec hnique can accurately measure rotation and translations. Preliminary r esults from adaptive motion correction studies on phantom and human su bjects indicate that the orbital navigator echo is an effective method for motion measurement in MRI.