title: Effects of gradient non-linearity correction and intensity non-uniformity correction in longitudinal studies using structural image evaluation using normalization of atrophy (SIENA).
abstract: OBJECTIVE
  To evaluate the effects of gradient nonlinearity correction and intensity nonuniformity correction on longitudinal (two-year) changes in global and regional brain volumes.
  
  
  METHODS
  A total of 208 subjects (70 females and 138 males, age range = 38.1-83.0 years) were included in this study. Each subject was scanned twice, at an interval of approximately two years (range = 1.5-2.3 years). Three-dimensional fast spoiled-gradient recalled acquisition in the steady state (3D-FSPGR) images corrected for gradient nonlinearity and/or intensity nonuniformity were compared with uncorrected 3D-FSPGR images with use of structural image evaluation using normalization of atrophy 2.6 (SIENA).
  
  
  RESULTS
  The mean absolute deviations of percentage brain volume change (PBVC) values in the gradient nonlinearity +/- intensity nonuniformity corrected images were significantly less than that in the uncorrected images, and the difference in the mean absolute deviation of PBVC was the most significant between the uncorrected images and the images corrected for both gradient nonlinearity and intensity nonuniformity. Voxel-wise comparisons showed large significant differences between the uncorrected images and the corrected images.
  
  
  CONCLUSIONS
  Correction for gradient nonlinearity and intensity nonuniformity reduces the variance of measured longitudinal changes in brain volumes and will improve accuracy for detecting subtle brain changes.
authors.affiliation: Department of Radiology, Graduate School of Medicine, University of Tokyo, Bunkyo-ku, Tokyo, Japan. takaoh-tky@umin.ac.jp
authors.forename: Hidemasa
authors.initials: H
authors.lastname: Takao
authors.forename: Osamu
authors.initials: O
authors.lastname: Abe
authors.forename: Naoto
authors.initials: N
authors.lastname: Hayashi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kabasawa
authors.forename: Kuni
authors.initials: K
authors.lastname: Ohtomo
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001284:Atrophy / Q000473:pathology*; D001921:Brain / Q000473:pathology*; D001931:Brain Mapping; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012984:Software