title: Field inhomogeneity correction for gradient echo myelin water fraction imaging.
abstract: Recently, the multi-echo gradient echo (MGRE) sequence has been proposed for multicomponent T2* (MC T2*) based myelin water fraction (MWF) mapping. This approach has appeal because it can provide fast whole-brain coverage, has low specific absorption rate, and short echo spacing. However, the MGRE signal requires correction for accurate MWF mapping, because of its sensitivity to magnetic field inhomogeneities (ΔB0). We propose a ΔB0correction method for 2D MGRE data obtained for MWF mapping.
  
  
  
  Latter-echo MGRE data were fit to estimate B0gradients in the slice-select direction ( Gz). The decay signal was corrected for the effects of Gz, and MC T2* analysis was performed using nonnegative least-squares fitting. The method was evaluated using simulations and its performance demonstrated in healthy volunteers.
  
  
  
  Simulations showed that MWFs are significantly biased in the presence of Gz and that our correction method leads to accurate MWF estimates. In vivo MWF maps obtained from corrected data showed recovery of MWF estimates in areas of high ΔB0,and overall good agreement with literature values obtained with the reference MC T2-based method.
  
  
  
  A new algorithm was presented for ΔB0correction of 2D MGRE echo data acquired for MWF imaging. Simulations and in vivo data showed an improvement in MWF estimates. Magn Reson Med 78:49-57, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Medical Physics Unit, McGill University, 3801 University Street, Montreal, QC, H3A 2B4, Canada.|McConnell Brain Imaging Centre, McGill University, 3801 University Street, Montreal, QC, H3A 2B4, Canada.
authors.forename: Eva
authors.initials: E
authors.lastname: Alonso-Ortiz
authors.affiliation: Medical Physics Unit, McGill University, 3801 University Street, Montreal, QC, H3A 2B4, Canada.|Department of Oncology, McGill University, 3801 University Street, Montreal, QC, H3A 2B4, Canada.|Research Institute of the McGill University Health Centre, McGill University, 3801 University Street, Montreal, QC, H3A 2B4, Canada.
authors.forename: Ives R
authors.initials: IR
authors.lastname: Levesque
authors.affiliation: Siemens Canada, Montreal, QC, H1Z 4J2, Canada.
authors.forename: Raphaël
authors.initials: R
authors.lastname: Paquin
authors.affiliation: Medical Physics Unit, McGill University, 3801 University Street, Montreal, QC, H3A 2B4, Canada.|McConnell Brain Imaging Centre, McGill University, 3801 University Street, Montreal, QC, H3A 2B4, Canada.|Department of Radiology and Hotchkiss Brain Institute, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada.
authors.forename: G Bruce
authors.initials: GB
authors.lastname: Pike
mesh_terms: D000328:Adult; D016477:Artifacts; D001834:Body Water / Q000737:chemistry* / Q000000981:diagnostic imaging; D003337:Corpus Callosum / Q000737:chemistry*; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D008297:Male; D057054:Molecular Imaging / Q000379:methods*; D009186:Myelin Sheath / Q000737:chemistry*; D009413:Nerve Fibers, Myelinated / Q000737:chemistry*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted
keywords: field inhomogeneities; gradient echo imaging; multicomponent 
  T2*; myelin water