title: Real-time motion correction using gradient tones and head-mounted NMR field probes.
abstract: OBJECTIVE
  Sinusoidal 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.
  
  
  METHODS
  Benchmarking 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.
  
  
  RESULTS
  For observation windows of 4.8 ms, the precision of probe position determination was found to be 35 to 62 µm, and the maximal measurement error was 595 µm 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.
  
  
  CONCLUSIONS
  NMR 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.
authors.affiliation: Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Haeberlin
authors.affiliation: Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland.|Translational Neuromodeling Unit, Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland.
authors.forename: Lars
authors.initials: L
authors.lastname: Kasper
authors.affiliation: Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland.|Skope Magnetic Resonance Technologies, Zurich, Switzerland.
authors.forename: Christoph
authors.initials: C
authors.lastname: Barmet
authors.affiliation: Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland.
authors.forename: David O
authors.initials: DO
authors.lastname: Brunner
authors.affiliation: Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland.
authors.forename: Benjamin E
authors.initials: BE
authors.lastname: Dietrich
authors.affiliation: Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland.
authors.forename: Simon
authors.initials: S
authors.lastname: Gross
authors.affiliation: Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland.
authors.forename: Bertram J
authors.initials: BJ
authors.lastname: Wilm
authors.affiliation: Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Kozerke
authors.affiliation: Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland.
authors.forename: Klaas P
authors.initials: KP
authors.lastname: Pruessmann
mesh_terms: D000465:Algorithms; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging
keywords: external; field monitoring; head motion; marker; position tracking; prospective