title: Quantitative diffusion-tensor anisotropy brain MR imaging: normative human data and anatomic analysis.
abstract: OBJECTIVE
  To obtain normative human cerebral data and evaluate the anatomic information in quantitative diffusion anisotropy magnetic resonance (MR) imaging.
  
  
  METHODS
  Quantitative diffusion anisotropy MR images were obtained in 13 healthy adults by using single-shot echo-planar MR imaging and a combination of tetrahedral and orthogonal gradient encoding (whole-brain coverage in about 1 minute). White matter (WM) anatomy was assessed at visual inspection, and values were measured in various brain regions. Different anisotropy measures, including total anisotropy (A sigma), were compared on the basis of information content, rotational invariance, and susceptibility to noise. Partial volume and noise effects were simulated.
  
  
  RESULTS
  Anisotropy MR images depicted WM features not typically seen on conventional MR images (e.g., external capsule, thalamic substructures, basal ganglia, occipital WM, thickness of the internal capsule). Statistically significant anisotropy differences occurred across brain regions, which were reproducible within and across subjects. A sigma was highest in commissural WM and progressively lower in projection and association WM. This order paralleled that of known resistance to spread of vasogenic edema, which suggested that anisotropy may be sensitive to WM histologic structure. Gray matter (GM) A sigma data were consistent with zero anisotropy, and partial volume WM-GM effects were approximately linear. A sigma image quality could be effectively improved by means of averaging.
  
  
  CONCLUSIONS
  Quantitative diffusion anisotropy images can be obtained rapidly and demonstrate subtle WM anatomy. Different histologic types of WM have significant and reproducible anisotropy differences.
authors.affiliation: Mallinckrodt Institute of Radiology, St Louis, MO, USA. shimonyj@npg.wustl.edu
authors.forename: J S
authors.initials: JS
authors.lastname: Shimony
authors.forename: R C
authors.initials: RC
authors.lastname: McKinstry
authors.forename: E
authors.initials: E
authors.lastname: Akbudak
authors.forename: J A
authors.initials: JA
authors.lastname: Aronovitz
authors.forename: A Z
authors.initials: AZ
authors.lastname: Snyder
authors.forename: N F
authors.initials: NF
authors.lastname: Lori
authors.forename: T S
authors.initials: TS
authors.lastname: Cull
authors.forename: T E
authors.initials: TE
authors.lastname: Conturo
mesh_terms: D000328:Adult; D016880:Anisotropy; D001921:Brain / Q000033:anatomy & histology*; D001931:Brain Mapping; D003198:Computer Simulation; D004058:Diffusion; D017352:Echo-Planar Imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D012016:Reference Values