title: Novel diffusion anisotropy indices: an evaluation.
abstract: OBJECTIVE
  To systematically evaluate diffusion anisotropy (DA) using newly defined indices based on the diffusion deviation and mean diffusivity approach.
  
  
  METHODS
  Measures of amplitude, area, and volume of the DA index (DAI) were measured and compared with regard to their sensitivity to changes in DA, susceptibility to noise in the original diffusion-weighted (DW) images, and contrast-to-noise ratio (CNR) in homogenous regions. Simulations were performed under different levels of noise and DA. Human DTI data were acquired from eight normal volunteers.
  
  
  RESULTS
  Indices of area and volume measures provided improved resolution for characterizing the DA compared to the eigenvalue ratio. The amplitude measure showed consistent performances with good CNR and less susceptibility to noise in the original data.
  
  
  CONCLUSIONS
  These indices are rotationally invariant without the requirement of eigenvalue sorting. At low anisotropy, all indices have a similar CNR. For larger DA, the first index (the deviation tensor divided by the DT) shows improved sensitivity, contrast-to-noise ratio (CNR), and noise immunity compared to the other indices.
authors.affiliation: Department of Medical Imaging and Radiological Sciences, ChangGung University, Kwei-Shan, Tao-Yuan, Taiwan. jwang@mail.cgu.edu.tw
authors.forename: Jiun-Jie
authors.initials: JJ
authors.lastname: Wang
authors.forename: Tsi-Chian
authors.initials: TC
authors.lastname: Chao
authors.forename: Yau-Yau
authors.initials: YY
authors.lastname: Wai
authors.forename: Yuanyu
authors.initials: Y
authors.lastname: Hsu
mesh_terms: D000328:Adult; D000465:Algorithms; D016880:Anisotropy; D001921:Brain / Q000473:pathology*; D004058:Diffusion; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008432:Mathematical Computing; D009010:Monte Carlo Method; D012680:Sensitivity and Specificity