title: Perfusion CT in acute stroke: predictive value of perfusion parameters in assessing tissue viability versus infarction.
abstract: OBJECTIVE
  The aim of this study was to assess the value of computed tomography (CT) perfusion parameters in differentiating tissue viability in acute stoke patients.
  
  
  METHODS
  Thirteen patients (mean age 63.3 years) with nonhaemorrhagic stroke underwent multidetector perfusion CT within 3 h of symptom onset. Images were continuously acquired at the basal ganglia over 40 s during injection of 90 ml of iodinated contrast medium injected at a rate of 9 ml/s with a 9-s delay. Z-axis coverage was 20 mm. All patients underwent diffusion-weighted magnetic resonance imaging (DWI) within 12 h of perfusion CT to define the extent of the infarct. Perfusion CT data were analysed in regions of interests (ROIs) on regional cerebral blood volume (rCBV), regional cerebral blood flow (rCBF) and mean transit time (MTT) maps placed in various parts of the perfusion-deficient territory and in the contralateral hemisphere. Statistical analysis was performed using the analysis of variance (ANOVA) test to assess differences in CT perfusion parameters. Receiver operator characteristics (ROC) analysis was performed to assess possible threshold values that predict tissue infarction vs. viability.
  
  
  RESULTS
  Normal CT findings with abnormal CT perfusion parameters were seen in the region of infarction and in the viable tissue (penumbra) within a 1.5-cm distance from the infarct margin as outlined on DWI images. Infarcted areas demonstrated significant prolongation of MTT values compared with noninfarcted areas (p<0.0001). Average MTT was 9.8 s in areas of infarction, 5.1 s in the viable tissue adjacent to the infarct (penumbra), and 3.4 s in the contralateral control area. An MTT threshold level of 6.05 s has a 100% positive predictive value (sensitivity 84.6%, specificity 100%, accuracy 92.3%) for the presence of infarcted tissue. Average rCBF was 24.6 ml/100 g per min in infarcted tissue, 64.8 in penumbra and 70.8 in normal tissue. Average rCBV was 3.5 ml/100g in infarcted tissue, 3.9 in penumbra and 2.9 in normal tissue.
  
  
  CONCLUSIONS
  Prolongation of MTT was the most frequent CT perfusion finding observed in acute stroke patients. Average MTT values of 5.1 s may distinguish viable tissue, whereas MTT values >6.05 s identify infarcted tissue.
authors.affiliation: DIBIMEL, Sezione di Scienze Radiologiche, Università di Palermo, Via A. Casella 7, I-90145 Palermo, Italy. sparacia@unipa.it
authors.forename: G
authors.initials: G
authors.lastname: Sparacia
authors.forename: A
authors.initials: A
authors.lastname: Iaia
authors.forename: B
authors.initials: B
authors.lastname: Assadi
authors.forename: R
authors.initials: R
authors.lastname: Lagalla
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001479:Basal Ganglia / Q000098:blood supply / Q000000981:diagnostic imaging; D001810:Blood Volume / Q000502:physiology; D001921:Brain / Q000098:blood supply / Q000000981:diagnostic imaging; D002545:Brain Ischemia / Q000000981:diagnostic imaging* / Q000503:physiopathology; D002544:Cerebral Infarction / Q000000981:diagnostic imaging* / Q000503:physiopathology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003287:Contrast Media; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012372:ROC Curve; D011856:Radiographic Image Enhancement / Q000379:methods; D012680:Sensitivity and Specificity; D020521:Stroke / Q000000981:diagnostic imaging* / Q000503:physiopathology; D013997:Time Factors; D014022:Tissue Survival / Q000502:physiology; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media