title: Diffusion tensor imaging of the brain: effects of distortion correction with correspondence to numbers of encoding directions.
abstract: OBJECTIVE
  The aim of the study was to estimate the effect of distortion correction with correspondence to numbers of encoding directions to acquire diffusion tensor imaging (DTI) of improved quality.
  
  
  METHODS
  Ten volunteers underwent DTI of the head using echo planar imaging with 6, 13, 27, and 55 encoding directions. Fractional anisotropy (FA) maps and apparent diffusion coefficient (ADC) maps were created before and after distortion correction. Regions of interest were placed in the corpus callosum on each map, and standard deviations of FA and ADC were calculated. FA maps were also evaluated visually by experienced neuroradiologists.
  
  
  RESULTS
  Dispersion of standard deviations tended to be reduced after distortion correction, with significant differences found in FA maps with 6 encoding directions, ADC maps with 6 directions, and ADC maps with 13 directions (P < 0.001, P < 0.005, and P < 0.05, respectively). Visual image quality was improved after distortion correction (P < 0.01 for all of the visual comparisons).
  
  
  CONCLUSIONS
  Distortion correction is effective in providing DTI of enhanced quality, notwithstanding the number of encoding directions.
authors.affiliation: Department of Computational Diagnostic Radiology and Preventive Medicine, The University of Tokyo Hospital, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8655, Japan. takeharu-yoshikawa@umin.ac.jp
authors.forename: Takeharu
authors.initials: T
authors.lastname: Yoshikawa
authors.forename: Shigeki
authors.initials: S
authors.lastname: Aoki
authors.forename: Osamu
authors.initials: O
authors.lastname: Abe
authors.forename: Naoto
authors.initials: N
authors.lastname: Hayashi
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Masutani
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Masumoto
authors.forename: Harushi
authors.initials: H
authors.lastname: Mori
authors.forename: Yoshiroh
authors.initials: Y
authors.lastname: Satake
authors.forename: Kuni
authors.initials: K
authors.lastname: Ohtomo
mesh_terms: D000328:Adult; D000465:Algorithms; D016880:Anisotropy; D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging; D001931:Brain Mapping / Q000379:methods*; D003337:Corpus Callosum / Q000000981:diagnostic imaging*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods; D017352:Echo-Planar Imaging; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008297:Male; D017711:Nonlinear Dynamics; D011859:Radiography