Echo‐planar imaging with prospective slice‐by‐slice motion correction using active markers

Abstract

Head motion is a fundamental problem in functional magnetic resonance imaging and is often a limiting factor in its clinical implementation. This work presents a rigid-body motion correction strategy for echo-planar imaging sequences that uses micro radiofrequency coil "active markers" for real-time, slice-by-slice prospective correction. Before the acquisition of each echo-planar imaging-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 echo-planar imaging 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. The benefit of this improved image stability is assessed in a blood oxygenation level dependent functional magnetic resonance imaging application. Finally, a non-rigid-body distortion-correction algorithm is introduced to reduce the remaining signal variation.