title: Human acute cerebral ischemia: detection of changes in water diffusion anisotropy by using MR imaging.
abstract: OBJECTIVE
  To (a) determine the optimal choice of a scalar metric of anisotropy and (b) determine by means of magnetic resonance imaging if changes in diffusion anisotropy occurred in acute human ischemic stroke.
  
  
  METHODS
  The full diffusion tensor over the entire brain was measured. To optimize the choice of a scalar anisotropy metric, the performances of scalar indices in simulated models and in a healthy volunteer were analyzed. The anisotropy, trace apparent diffusion coefficient (ADC), and eigenvalues of the diffusion tensor in lesions and contralateral normal brain were compared in 50 patients with stroke.
  
  
  RESULTS
  Changes in anisotropy in patients were quantified by using fractional anisotropy because it provided the best performance in terms of contrast-to-noise ratio as a function of signal-to-noise ratio in simulations. The anisotropy of ischemic white matter decreased (P = .01). Changes in anisotropy in ischemic gray matter were not significant (P = .63). The trace ADC decreased for ischemic gray matter and white matter (P < .001). The first and second eigenvalues decreased in both ischemic gray and ischemic white matter (P < .001). The third eigenvalue decreased in ischemic gray (P = .001) and white matter (P = .03).
  
  
  CONCLUSIONS
  Gray matter is mildly anisotropic in normal and early ischemic states. However, early white matter ischemia is associated with not only changes in trace ADC values but also significant changes in the anisotropy, or shape, of the water self-diffusion tensor.
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Boston, USA. sorensen@nmr.mgh.harvard.edu
authors.forename: A G
authors.initials: AG
authors.lastname: Sorensen
authors.forename: O
authors.initials: O
authors.lastname: Wu
authors.forename: W A
authors.initials: WA
authors.lastname: Copen
authors.forename: T L
authors.initials: TL
authors.lastname: Davis
authors.forename: R G
authors.initials: RG
authors.lastname: Gonzalez
authors.forename: W J
authors.initials: WJ
authors.lastname: Koroshetz
authors.forename: T G
authors.initials: TG
authors.lastname: Reese
authors.forename: B R
authors.initials: BR
authors.lastname: Rosen
authors.forename: V J
authors.initials: VJ
authors.lastname: Wedeen
authors.forename: R M
authors.initials: RM
authors.lastname: Weisskoff
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016880:Anisotropy; D001929:Brain Edema / Q000175:diagnosis*; D002545:Brain Ischemia / Q000175:diagnosis*; D001931:Brain Mapping; D002544:Cerebral Infarction / Q000175:diagnosis*; D004058:Diffusion; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D012016:Reference Values