title: Comparison of myelin water fraction from multiecho T2 decay curve and steady-state methods.
abstract: OBJECTIVE
  Myelin water fraction is conventionally measured from the T2 decay curve. Recently, a steady-state approach entitled multicomponent-driven equilibrium single pulse observation of T1 /T2 (mcDESPOT) was employed for myelin water fraction mapping. However, no direct comparison between the established multiecho T2 relaxation method and mcDESPOT has been performed.
  
  
  METHODS
  Gradient and spin echo (GRASE) acquired T2 decay curve and mcDESPOT measurements were acquired from 10 healthy volunteers using a 3T MRI. We compared myelin water fraction, transmit radio frequency field (B1 ), and T2 's of intra- and extracellular water obtained from both methods.
  
  
  RESULTS
  For all brain regions examined, myelin water fractions from mcDESPOT were significantly higher than those from multiecho GRASE. B1 maps were qualitatively similar between GRASE and mcDESPOT, but multicomponent T2 times were significantly different. To investigate the effect of exchange, mcDESPOT data were analyzed with and without exchange. When exchange was turned off, intra- and extracellular T2 times from mcDESPOT were roughly consistent with GRASE results; however, myelin water fractions derived from mcDESPOT were still significantly higher than those derived from GRASE.
  
  
  CONCLUSIONS
  Myelin water fraction values derived from mcDESPOT cannot be considered to be equivalent to those derived from T2 decay curve approaches.
authors: UBC MRI Research Centre, Department of Radiology, University of British Columbia, Vancouver, BC, Canada.
authors: Jing
authors: J
authors: Zhang
authors: Division of Neurology, Department of Medicine, University of British Columbia, Vancouver, BC, Canada.
authors: Shannon H
authors: SH
authors: Kolind
authors: UBC MRI Research Centre, Department of Radiology, University of British Columbia, Vancouver, BC, Canada.|Department of Pathology & Laboratory Medicine, University of British Columbia, Vancouver, BC, Canada.
authors: Cornelia
authors: C
authors: Laule
authors: UBC MRI Research Centre, Department of Radiology, University of British Columbia, Vancouver, BC, Canada.|Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada.
authors: Alex L
authors: AL
authors: MacKay
mesh_terms: D000328:Adult; D000465:Algorithms; D001834:Body Water / Q000737:chemistry*; D001923:Brain Chemistry; D017352:Echo-Planar Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D057054:Molecular Imaging / Q000379:methods; D009186:Myelin Sheath / Q000737:chemistry*; D009413:Nerve Fibers, Myelinated / Q000737:chemistry*; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution
keywords: T2 relaxation; mcDESPOT; myelin water fraction; steady-state imaging