title: Perfusion magnetic resonance imaging maps in hyperacute stroke: relative cerebral blood flow most accurately identifies tissue destined to infarct.
abstract: OBJECTIVE
  In ischemic stroke, perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) provide important pathophysiological information. A PWI>DWI mismatch pattern suggests the presence of salvageable tissue. However, improved methods for distinguishing PWI>DWI mismatch tissue that is critically hypoperfused from benign oligemia are required.
  
  
  METHODS
  We investigated the usefulness of maps of relative cerebral blood flow (rCBF), volume (rCBV), and mean transit time (rMTT) to predict transition to infarction in hyperacute (<6 hours) stroke patients with PWI>DWI mismatch patterns. Semiquantitative color-thresholded analysis was used to measure hypoperfusion volumes, including increasing color signal intensity thresholds of rMTT delay, which were compared with infarct expansion, outcome infarct size, and clinical status.
  
  
  RESULTS
  Acute rCBF lesion volume had the strongest correlation with final infarct size (r=0.91, P<0.001) and clinical outcome (r=0.67, P<0.01). There was a trend for acute rCBF>DWI mismatch volume to overestimate infarct expansion between the acute and outcome study (P=0.06). Infarct expansion was underestimated by acute rCBV>DWI mismatch (P<0.001). When rMTT lesions included tissue with moderately prolonged transit times (mean delay 4.3 seconds, signal intensity values 50% to 70%), infarct expansion was overestimated. In contrast, when rMTT lesions were restricted to more severely prolonged transit times (mean delay 6.1 seconds, signal intensity >70%), these regions progressed to infarction in all except 1 patient, but infarct expansion was underestimated (P<0.001).
  
  
  CONCLUSIONS
  The acute rCBF lesion most accurately identified tissue in the PWI>DWI mismatch region at risk of infarction. Color-thresholded PWI maps show potential for use in an acute clinical setting to prospectively predict tissue outcome.
authors.affiliation: Department of Neurology, The Royal Melbourne Hospital, Parkville Victoria, Australia.
authors.forename: M W
authors.initials: MW
authors.lastname: Parsons
authors.forename: Q
authors.initials: Q
authors.lastname: Yang
authors.forename: P A
authors.initials: PA
authors.lastname: Barber
authors.forename: D G
authors.initials: DG
authors.lastname: Darby
authors.forename: P M
authors.initials: PM
authors.lastname: Desmond
authors.forename: R P
authors.initials: RP
authors.lastname: Gerraty
authors.forename: B M
authors.initials: BM
authors.lastname: Tress
authors.forename: S M
authors.initials: SM
authors.lastname: Davis
mesh_terms: D000208:Acute Disease; D000368:Aged; D001921:Brain / Q000098:blood supply / Q000473:pathology; D020520:Brain Infarction / Q000209:etiology / Q000473:pathology*; D002560:Cerebrovascular Circulation; D003116:Color; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010477:Perfusion / Q000379:methods*; D020521:Stroke / Q000150:complications* / Q000503:physiopathology