title: Assessing tissue viability with MR diffusion and perfusion imaging.
abstract: OBJECTIVE
  Diffusion- (DW) and perfusion-weighted (PW) MR imaging reflect neurophysiologic changes during stroke evolution. We sought to determine parameters that distinguish regions of brain destined for infarction from those that will survive despite hypoperfusion.
  
  
  METHODS
  DW and PW images were obtained in 30 patients at 1-12 hours after symptom onset. Relative cerebral blood volume (rCBV), flow (rCBF), mean transit time (MTT), apparent diffusion coefficient (ADC), DW image signal intensity, and fractional anisotropy (FA) lesion-contralateral normal region ratios were obtained in the following regions: 1) infarct core with hyperintensity on DW image, abnormality on rCBF and MTT images, and follow-up abnormality; 2) infarcted penumbra with normal DW image, abnormal rCBF and MTT images, and follow-up abnormality; and 3) hypoperfused tissue that remained viable, with normal DW image, abnormal rCBF and MTT images, and normal follow-up.
  
  
  RESULTS
  rCBF ratios for regions 1, 2, and 3 were 0.32 +/- 0.11, 0.46 +/- 0.13, and 0.58 +/- 0.12, respectively, and were significantly different. DW image intensity and ADC ratios were significantly different among all regions, but were more similar than rCBF ratios. rCBV and FA ratios were not significantly different between regions 2 and 3. No MTT ratios were significantly different. No region of interest with an rCBF ratio less than 0.36, an rCBV ratio less than 0.53, an ADC ratio less than 0.85, a DW image intensity ratio greater than 1.23, or an FA ratio greater than 1.10 remained viable. No region of interest with an rCBF ratio greater than 0.79 infarcted.
  
  
  CONCLUSIONS
  Differences among mean ratios of three regions investigated were greatest for the rCBF ratio. The rCBF ratio may be the most useful parameter in differentiating viable tissue that is likely to infarct without intervention, from tissue that will survive despite hypoperfusion. ADC, DW intensity, FA, and rCBV ratios may provide adjunctive information.
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Pamela W
authors.initials: PW
authors.lastname: Schaefer
authors.forename: Yelda
authors.initials: Y
authors.lastname: Ozsunar
authors.forename: Julian
authors.initials: J
authors.lastname: He
authors.forename: Leena M
authors.initials: LM
authors.lastname: Hamberg
authors.forename: George J
authors.initials: GJ
authors.lastname: Hunter
authors.forename: A Gregory
authors.initials: AG
authors.lastname: Sorensen
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Koroshetz
authors.forename: R Gilberto
authors.initials: RG
authors.lastname: Gonzalez
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001783:Blood Flow Velocity / Q000502:physiology; D001810:Blood Volume / Q000502:physiology; D001921:Brain / Q000098:blood supply*; D002545:Brain Ischemia / Q000175:diagnosis* / Q000503:physiopathology; D002544:Cerebral Infarction / Q000175:diagnosis* / Q000503:physiopathology; D003287:Contrast Media; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D017352:Echo-Planar Imaging / Q000379:methods; D005260:Female; D005500:Follow-Up Studies; D019786:Gadolinium DTPA; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012039:Regional Blood Flow / Q000502:physiology; D015203:Reproducibility of Results; D012189:Retrospective Studies; D014022:Tissue Survival / Q000502:physiology*
chemical_list: D003287:Contrast Media; C064925:gadodiamide; D019786:Gadolinium DTPA