title: Reproducibility of in vivo magnetic resonance imaging-based measurement of myelin water.
abstract: OBJECTIVE
  To evaluate the reproducibility of multicomponent quantitative T(2) (QT2) measurements, in particular the myelin water fraction (MWF), to determine the sensitivity of this method for monitoring myelin changes in longitudinal studies and to provide a basis for correctly powering such studies.
  
  
  METHODS
  The de facto standard 32-echo spin-echo imaging sequence was used throughout, and data were analyzed using regularized non-negative least squares (NNLS) to produce T(2) distributions. Three studies were conducted in healthy subjects. First, two acquisition protocols were compared in 10 subjects. Second, variability of QT2 was evaluated over same-day scan-rescan experiments in 6 subjects. Finally, variability was quantified in a longitudinal study of 5 subjects.
  
  
  RESULTS
  A within-subject coefficient of variation (CoV) of 12% (range 4-25%) was observed for the MWF in brain white matter (WM) regions of interest (ROIs). The geometric mean T(2) was more stable, with a longitudinal CoV of 4% (range 1-6%). The choice of the geometry and repetition time of the acquisition protocol influenced the estimates of the MWF and T(2) values. The choice of integration range for the short-T(2) component had a significant effect on MWF estimates, but not on reproducibility.
  
  
  CONCLUSIONS
  The reproducibility of QT2 measurements using existing methods is moderate and the method can be used in longitudinal studies, with careful consideration of the methodologic variability and an appropriate group size.
authors.affiliation: McConnell Brain Imaging Centre, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada. ives@stanford.edu
authors.forename: Ives R
authors.initials: IR
authors.lastname: Levesque
authors.forename: Charmaine L L
authors.initials: CL
authors.lastname: Chia
authors.forename: G Bruce
authors.initials: GB
authors.lastname: Pike
mesh_terms: D000328:Adult; D001834:Body Water; D001923:Brain Chemistry; D001931:Brain Mapping / Q000379:methods; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009186:Myelin Sheath / Q000737:chemistry*; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult