Real-time motion correction using gradient tones and head-mounted NMR field probes.

PurposeSinusoidal gradient oscillations in the kilohertz range are proposed for position tracking of NMR probes and prospective motion correction for arbitrary imaging sequences without any alteration of sequence timing. The method is combined with concurrent field monitoring to robustly perform image reconstruction in the presence of potential dynamic field deviations. MethodsBenchmarking experiments were done to assess the accuracy and precision of the method and to compare it with theoretical predictions based on the field probe's time-dependent signal-to-noise ratio. An array of four field probes was used to perform real-time prospective motion correction in vivo. Images were reconstructed based on both predetermined and concurrently measured k-space trajectories. ResultsFor observation windows of 4.8 ms, the precision of probe position determination was found to be 35 to 62 mu m, and the maximal measurement error was 595 mu m root-mean-square on a single axis. Sequence update per repetition time on this basis yielded images free of conspicuous artifacts despite substantial head motion. Predetermined and concurrently observed k-space trajectories yielded equivalent image quality. ConclusionNMR field probes in conjunction with gradient tones permit the tracking and prospective correction of rigid-body motion. Relying on gradient oscillations in the kilohertz range, the method allows for concurrent motion detection and image encoding. Magn Reson Med 74:647-660, 2015. (c) 2014 Wiley Periodicals, Inc.