title: Comparison of methods for obtaining longitudinal whole-brain magnetization transfer measurements.
abstract: OBJECTIVE
  To investigate whether the method of applying image masks can alter quantifiable measures determined from whole-brain MTR calculations.
  
  
  METHODS
  Thirty-five T1/MT image pairs were obtained from five normal volunteers. For each pair a mask was used to specify the regions to be analyzed. Using these regions, a histogram was used to calculate seven global MTR metrics. This process was performed three ways: 1) using a unique mask for each T1/MT pair, 2) sharing a single mask for each subject and registering all intrasubject images to the image corresponding to their mask, and 3) sharing a single mask for each subject and transforming that mask into alignment with each of their original T1/MT image pairs.
  
  
  RESULTS
  With respect to the first method, the latter two methods caused small but significant differences in several parameters.
  
  
  CONCLUSIONS
  The method of applying image masks can affect whole-brain MTR values.
authors.affiliation: Laboratory of Diagnostic Radiology Research, National Institutes of Health, Bethesda, Maryland, USA. ostuni@helix.nih.gov
authors.forename: John L
authors.initials: JL
authors.lastname: Ostuni
authors.forename: Nancy
authors.initials: N
authors.lastname: Richert
authors.forename: Ruth
authors.initials: R
authors.lastname: Wisniewski
authors.forename: Bobbi K
authors.initials: BK
authors.lastname: Lewis
authors.forename: Thomas
authors.initials: T
authors.lastname: Howard
authors.forename: Jay
authors.initials: J
authors.lastname: Patel
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Frank
mesh_terms: D000328:Adult; D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged