“Echo-Planar Imaging with Prospective Slice-by-Slice Motion Correction using Active Markers”

Head motion is a fundamental problem in functional MRI, and is often a limiting factor in its clinical implementation. This work presents a rigid-body motion correction strategy for echo-planar imaging (EPI) sequences that uses micro radio-frequency coil “active markers ” for real-time, slice-by-slice prospective correction. Before the acquisition of each EPI-slice, a short tracking pulse-sequence measures the positions of three active markers integrated into a headband worn by the subject; the rigid-body transformation that realigns these markers to their initial positions is then fed back to dynamically update the scan-plane, maintaining it at a fixed orientation relative to the head. Using this method, prospectively-corrected EPI time-series are acquired on volunteers performing in-plane and through-plane head motions, with results demonstrating increased image stability over conventional retrospective image-realignment. Implications of this improvement for BOLD fMRI applications is assessed, as well as the benefit of non-rigid-body distortion-correction to reduce the remaining signal variation. Keywords functional magnetic resonance imaging; fMRI; EPI; motion correction; prospective; real-time; active marker; device tracking; RF-coil; micro-coil; geometric distortio