FIG. 4.

Phantom study results. a: Motionless scan verified the stability of the motion measurements. b: Rigid body translation validated the accuracy of the measurements and correction. For both (a) and (b), d_x = superior/inferior motion, d_y = right/left motion, and d_z = anterior/posterior motion. In (a), a drift of < 0.25 mm was observed for a span of 170 s; this is negligible compared to actual motion, and could be corrected by polynomial fitting. In (b), the motion was accurately measured as shown in the plot. This measurement successfully corrected for significant motion. Some residual ghosting artifacts remained due to gradient nonlinearity.