title: Apparent diffusion coefficient thresholds do not predict the response to acute stroke thrombolysis.
abstract: OBJECTIVE
  Apparent diffusion coefficient (ADC) thresholds for tissue infarction have been identified in acute stroke. IV tissue plasminogen activator (tPA) is associated with tissue salvage. We hypothesized that tPA would lower the ADC threshold for infarction.
  
  
  METHODS
  ADC and mean transit time (MTT) maps were generated for 26 patients imaged within 6 hours of stroke onset (12 tPA and 14 conservatively managed controls). MTT maps and day-90 T2-weighted images were coregistered to ADC maps. Relative ADC (rADC) values were calculated for initial diffusion-weighted imaging (DWI) lesions, infarct growth regions (final infarct volume-the acute DWI lesion volume), and hypoperfused salvaged regions (HS; MTT map abnormality-the final infarct volume). When relevant, the DWI lesion was subdivided into DWI reversal and DWI infarct regions.
  
  
  RESULTS
  Mean DWI lesion rADC was 0.79 in tPA and 0.74 in untreated patients (P=0.097). Mean rADC in HS and infarct growth regions were similar in tPA patients (0.950 and 0.946) and untreated patients (0.957, P=0.76; 0.970, P=0.08, respectively). The rADC in HS tissue was directly correlated with the time to treatment with tPA (r=0.685; P=0.029). DWI reversal was seen in 67% of tPA-treated patients and in 36% of those conservatively managed (Fisher exact test; P=0.238). In the 13 patients with DWI reversal, the mean rADC in these regions (0.81+/-0.07) was significantly higher than in the acute DWI region that infarcted (0.74+/-0.07; P=0.02), although no absolute thresholds could be identified.
  
  
  CONCLUSIONS
  The peri-DWI lesion region contains tissue with intermediate ADC values. The fate of this tissue is variable and cannot be predicted based on the ADC alone. DWI expansion occurs in bioenergetically normal tissue, and this is attenuated by tPA in a time-dependent fashion.
authors.affiliation: Department of Neurology, Royal Melbourne Hospital, Melbourne, Victoria, Australia.
authors.forename: Poh-Sien
authors.initials: PS
authors.lastname: Loh
authors.forename: Ken S
authors.initials: KS
authors.lastname: Butcher
authors.forename: Mark W
authors.initials: MW
authors.lastname: Parsons
authors.forename: Lachlan
authors.initials: L
authors.lastname: MacGregor
authors.forename: Patricia M
authors.initials: PM
authors.lastname: Desmond
authors.forename: Brian M
authors.initials: BM
authors.lastname: Tress
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Davis
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002545:Brain Ischemia / Q000175:diagnosis* / Q000209:etiology; D038524:Diffusion Magnetic Resonance Imaging; D005343:Fibrinolytic Agents / Q000627:therapeutic use*; D006801:Humans; D008875:Middle Aged; D011237:Predictive Value of Tests; D011994:Recombinant Proteins; D020521:Stroke / Q000150:complications / Q000175:diagnosis* / Q000188:drug therapy*; D010959:Tissue Plasminogen Activator / Q000627:therapeutic use*; D016896:Treatment Outcome
chemical_list: D005343:Fibrinolytic Agents; D011994:Recombinant Proteins; D010959:Tissue Plasminogen Activator