title: B1mapping for bias-correction in quantitative T1imaging of the brain at 3T using standard pulse sequences.
abstract: B1mapping is important for many quantitative imaging protocols, particularly those that include whole-brain T1mapping using the variable flip angle (VFA) technique. However, B1mapping sequences are not typically available on many magnetic resonance imaging (MRI) scanners. The aim of this work was to demonstrate that B1mapping implemented using standard scanner product pulse sequences can produce B1(and VFA T1) maps comparable in quality and acquisition time to advanced techniques.
  
  
  
  Six healthy subjects were scanned at 3.0T. An interleaved multislice spin-echo echo planar imaging double-angle (EPI-DA) B1mapping protocol, using a standard product pulse sequence, was compared to two alternative methods (actual flip angle imaging, AFI, and Bloch-Siegert shift, BS). Single-slice spin-echo DA B1maps were used as a reference for comparison (Ref. DA). VFA flip angles were scaled using each B1map prior to fitting T1; the nominal flip angle case was also compared.
  
  
  
  The pooled-subject voxelwise correlation (ρ) for B1maps (BS/AFI/EPI-DA) relative to the reference B1scan (Ref. DA) were ρ = 0.92/0.95/0.98. VFA T1correlations using these maps were ρ = 0.86/0.88/0.96, much better than without B1correction (ρ = 0.53). The relative error for each B1map (BS/AFI/EPI-DA/Nominal) had 95thpercentiles of 5/4/3/13%.
  
  
  
  Our findings show that B1mapping implemented using product pulse sequences can provide excellent quality B1(and VFA T1) maps, comparable to other custom techniques. This fast whole-brain measurement (∼2 min) can serve as an excellent alternative for researchers without access to advanced B1pulse sequences.
  
  
  
  1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1673-1682.
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Boudreau
authors.affiliation: Cerebral Imaging Centre, Douglas Mental Health University Institute, Montreal, Canada.
authors.forename: Christine L
authors.initials: CL
authors.lastname: Tardif
authors.affiliation: Ecole Polytechnique de Montreal, Montreal, Quebec, Canada.|Montreal Heart Institute, University of Montreal, Montreal, Quebec, Canada.
authors.forename: Nikola
authors.initials: N
authors.lastname: Stikov
authors.affiliation: Hospital for Sick Children, Toronto, Ontario, Canada.|Department of Medical Biophysics, University of Toronto, Ontario, Canada.
authors.forename: John G
authors.initials: JG
authors.lastname: Sled
authors.affiliation: Department of Medical Biophysics, University of Toronto, Ontario, Canada.
authors.forename: Wayne
authors.initials: W
authors.lastname: Lee
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada.|Hotchkiss Brain Institute and Department of Radiology, University of Calgary, Calgary, Alberta, Canada.
authors.forename: G Bruce
authors.initials: GB
authors.lastname: Pike
mesh_terms: D000328:Adult; D001921:Brain / Q000033:anatomy & histology*; D001931:Brain Mapping / Q000379:methods*; D017352:Echo-Planar Imaging / Q000379:methods; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D012016:Reference Values; D015203:Reproducibility of Results
keywords: B1 mapping; Bloch-Siegert shift; T1 mapping; actual flip angle imaging; double angle method; echo planar imaging