title: Retrospective correction of physiological field fluctuations in high-field brain MRI using concurrent field monitoring.
abstract: OBJECTIVE
  Magnetic field fluctuations caused by subject motion, such as breathing or limb motion, can degrade image quality in brain MRI, especially at high field strengths. The purpose of this study was to investigate the feasibility of retrospectively correcting for such physiological field perturbations based on concurrent field monitoring.
  
  
  METHODS
  High-resolution T2*-weighted gradient-echo images of the brain were acquired at 7T with subjects performing different breathing and hand movement patterns. Field monitoring with a set of (19) F NMR probes distributed around the head was performed in two variants: concurrently with imaging or as a single field measurement per readout. The measured field fluctuations were then accounted for in the image reconstruction.
  
  
  RESULTS
  Significant field fluctuations due to motion were observed in all subjects, resulting in severe artifacts in uncorrected images. The artifacts were largely removed by reconstruction based on field monitoring. Accounting for field perturbations up to the 1st spatial order was generally sufficient to recover good image quality.
  
  
  CONCLUSIONS
  It has been demonstrated that artifacts due to physiologically induced dynamic field perturbations can be greatly reduced by retrospective image correction based on field monitoring. The necessity to perform such correction is greatest at high fields and for field-sensitive techniques such as T2*-weighted imaging.
authors.affiliation: Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland.
authors.forename: S Johanna
authors.initials: SJ
authors.lastname: Vannesjo
authors.forename: Bertram J
authors.initials: BJ
authors.lastname: Wilm
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Duerst
authors.forename: Simon
authors.initials: S
authors.lastname: Gross
authors.forename: David O
authors.initials: DO
authors.lastname: Brunner
authors.forename: Benjamin E
authors.initials: BE
authors.lastname: Dietrich
authors.forename: Thomas
authors.initials: T
authors.lastname: Schmid
authors.forename: Christoph
authors.initials: C
authors.lastname: Barmet
authors.forename: Klaas P
authors.initials: KP
authors.lastname: Pruessmann
mesh_terms: D000328:Adult; D016477:Artifacts; D001921:Brain / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male
keywords: T2*-weighted imaging; concurrent field monitoring; field fluctuations; magnetic field monitoring; physiological noise