title: Derivation and evaluation of thresholds for core and tissue at risk of infarction using CT perfusion.
abstract: OBJECTIVE
  Computed tomography perfusion provides information on tissue viability according to proposed thresholds. We evaluated thresholds for ischemic core and tissue at risk and subsequently tested their accuracy in independent datasets.
  
  
  METHODS
  Tissue at risk was evaluated in patients with persistent arterial occlusions, and ischemic core thresholds in patients with recanalization and major clinical improvement. Scans were randomly allocated to derivation or validation groups for tissue at risk and core analysis. Optimum thresholds using mean transit time (MTT), cerebral blood flow (CBF), cerebral blood volume, and delay time (DT) were assessed.
  
  
  RESULTS
  Absolute MTT, relative MTT and DT were best derived predictors of tissue at risk with thresholds of ≥ 7 seconds, ≥ 125%, and ≥ 2 seconds respectively. DT ≥ 2 seconds was the best predictor in the validation dataset (95% agreement levels = -44 to +30 mL, Bias = -6.9). Absolute and relative MTT were the best derived predictors of infarct volume in the core group (8 seconds and 125% respectively) but relative CBF of ≤ 45% performed best in the core validation dataset.
  
  
  CONCLUSIONS
  Time-based perfusion thresholds perform well as predictors of tissue at risk of infarction with DT the best predictor. Relative CBF was the best predictor of ischemic core. Evaluation in larger populations is needed to confirm the performance of tissue viability thresholds.
authors.affiliation: Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Ferghal
authors.initials: F
authors.lastname: McVerry
authors.affiliation: Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Krishna Ashok
authors.initials: KA
authors.lastname: Dani
authors.affiliation: Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Niall J J
authors.initials: NJJ
authors.lastname: MacDougall
authors.affiliation: Department of Medicine and Therapeutics, University of Aberdeen, United Kingdom.
authors.forename: Mary Joan
authors.initials: MJ
authors.lastname: MacLeod
authors.affiliation: Division of Clinical Neurosciences, Western General Hospital, Edinburgh, United Kingdom.
authors.forename: Joanna
authors.initials: J
authors.lastname: Wardlaw
authors.affiliation: Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Keith W
authors.initials: KW
authors.lastname: Muir
mesh_terms: D000368:Aged; D001783:Blood Flow Velocity; D002533:Cerebral Angiography / Q000379:methods*; D002544:Cerebral Infarction / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D018570:Risk Assessment / Q000379:methods; D012606:Scotland; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: Stroke; computed tomography; imaging; perfusion