title: Multicenter measurements of myelin water fraction and geometric mean T2 : intra- and intersite reproducibility.
abstract: OBJECTIVE
  To assess the reproducibility of myelin water fraction (MWF) and geometric mean T2 (GMT2 ), which are in vivo markers of pathological changes underlying disability and progression in diseases such as multiple sclerosis.
  
  
  METHODS
  Five healthy volunteers were scanned twice within 24 hours at six different sites using the same manufacturer's 3T magnetic resonance (MR) system. T2 distributions were produced by fitting multiecho 3D T2 data using non-negative least squares, with stimulated echo correction. MWF, the fraction of signal with T2 between 15 and 40 msec to the entire signal, and GMT2 , the mean T2 on a logarithmic scale from T2 between 40 and 200 msec, were examined in white matter.
  
  
  RESULTS
  Intrasite coefficients of variation (COVs) were low (mean 3.99% for MWF and 0.51% for GMT2 ), as were intersite COVs (mean 4.68% for MWF, 0.31% for GMT2 ). Scan-rescan intraclass correlation coefficients (ICCs) (0.76 for MWF and 0.93 for GMT2 ) and Bland-Altman plots indicated good agreement between single site scans. Intersite ICCs were relatively high (0.69 for MWF and 0.92 for GMT2 ), revealing good intersite reliability.
  
  
  CONCLUSIONS
  MWF and GMT2 measures are reproducible between scans and across sites with an equivalent MR scanner and sequence protocol. Multicenter clinical trials using quantitative T2 relaxation are feasible.
authors.affiliation: Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Sandra M
authors.initials: SM
authors.lastname: Meyers
authors.forename: Irene M
authors.initials: IM
authors.lastname: Vavasour
authors.forename: Burkhard
authors.initials: B
authors.lastname: Mädler
authors.forename: Trudy
authors.initials: T
authors.lastname: Harris
authors.forename: Eric
authors.initials: E
authors.lastname: Fu
authors.forename: David K B
authors.initials: DK
authors.lastname: Li
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Traboulsee
authors.forename: Alex L
authors.initials: AL
authors.lastname: MacKay
authors.forename: Cornelia
authors.initials: C
authors.lastname: Laule
mesh_terms: D000328:Adult; D001834:Body Water / Q000378:metabolism*; D001921:Brain / Q000033:anatomy & histology* / Q000378:metabolism*; D001955:British Columbia; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009186:Myelin Sheath / Q000378:metabolism*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: T2 relaxation; coefficients of variation; intersite; magnetic resonance imaging; myelin water fraction; reproducibility