title: Measuring motion-induced B0 -fluctuations in the brain using field probes.
abstract: OBJECTIVE
  Fluctuations of the background magnetic field (B0 ) due to body and breathing motion can lead to significant artifacts in brain imaging at ultrahigh field. Corrections based on real-time sensing using external field probes show great potential. This study evaluates different aspects of field interpolation from these probes into the brain which is implicit in such methods. Measurements and simulations were performed to quantify how well B0 -fluctuations in the brain due to body and breathing motion are reflected in external field probe measurements.
  
  
  METHODS
  Field probe measurements were compared with scanner acquired B0 -maps from experiments with breathing and shoulder movements. A realistic simulation of B0 -fluctuations caused by breathing was performed, and used for testing different sets of field probe positions.
  
  
  RESULTS
  The B0 -fluctuations were well reflected in the field probe measurements in the shoulder experiments, while the breathing experiments showed only moderate correspondence. The simulations showed the importance of the probe positions, and that performing full 3(rd) order corrections based on 16 field probes is not recommended.
  
  
  CONCLUSIONS
  Methods for quantitative assessment of the field interpolation problem were developed and demonstrated. Field corrections based on external field measurements show great potential, although potential pitfalls were identified.
authors.affiliation: Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Denmark.|Biomedical Engineering Group, DTU Elektro, Technical University of Denmark, Kgs Lyngby, Denmark.
authors.forename: Mads
authors.initials: M
authors.lastname: Andersen
authors.affiliation: Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Denmark.|Biomedical Engineering Group, DTU Elektro, Technical University of Denmark, Kgs Lyngby, Denmark.
authors.forename: Lars G
authors.initials: LG
authors.lastname: Hanson
authors.affiliation: Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Denmark.
authors.forename: Kristoffer H
authors.initials: KH
authors.lastname: Madsen
authors.affiliation: C.J. Gorter Center, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Joep
authors.initials: J
authors.lastname: Wezel
authors.affiliation: Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Vincent
authors.initials: V
authors.lastname: Boer
authors.affiliation: Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Tijl
authors.initials: T
authors.lastname: van der Velden
authors.affiliation: C.J. Gorter Center, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Matthias J P
authors.initials: MJ
authors.lastname: van Osch
authors.affiliation: Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Dennis
authors.initials: D
authors.lastname: Klomp
authors.affiliation: C.J. Gorter Center, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Webb
authors.affiliation: C.J. Gorter Center, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.|Philips Healthcare, Best, The Netherlands.
authors.forename: Maarten J
authors.initials: MJ
authors.lastname: Versluis
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging*; D001931:Brain Mapping; D003198:Computer Simulation; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007091:Image Processing, Computer-Assisted; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D015233:Models, Statistical; D009038:Motion; D019047:Phantoms, Imaging; D012119:Respiration
keywords: 7 Tesla; NMR field probes; dynamic shimming; field fluctuations; field mapping; motion