title: Perfusion thresholds in acute stroke thrombolysis.
abstract: OBJECTIVE
  Perfusion-weighted MRI has been shown to be useful in the early identification of cerebral tissue at risk of infarction during acute ischemia. Identification of threshold perfusion measures that predict infarction may assist in the selection of patients for thrombolysis.
  
  
  METHODS
  Mean transit time (MTT), regional cerebral blood flow (rCBF), and regional cerebral blood volume (rCBV) maps were generated in 35 acute stroke patients (17 treated with tissue plasminogen activator and 18 control patients) imaged within 6 hours from symptom onset. Day 90 outcome infarcts (T2-weighted MRI) were superimposed on acute MTT, rCBF, and rCBV maps. Perfusion-weighted MRI measures were then calculated for 2 regions: infarcted and salvaged tissue.
  
  
  RESULTS
  MTT was prolonged by 22% in infarcted regions relative to salvaged tissue (P<0.001). rCBF was 10% lower in infarcted tissue than in salvaged regions (P<0.01). rCBV did not differ significantly between infarcted and salvaged regions. When reperfusion occurred, tissue with more severely prolonged MTT was salvaged from infarction relative to patients with persistent hypoperfusion (P<0.05). In contrast, rCBF in salvaged regions did not differ between patients with and without reperfusion. In reperfused patients, an inverse correlation (R=0.93, P<0.001) was found between time of initial MRI scan and MTT delay in salvaged tissue.
  
  
  CONCLUSIONS
  Both increases in MTT and decreases in rCBF predict infarction. Differences in MTT also predict salvage in more severely hypoperfused tissue after reperfusion, suggesting that it is the most clinically useful quantitative perfusion measure. Perfusion thresholds for infarction need to be assessed in the context of symptom duration.
authors.affiliation: Department of Neurology, Royal Melbourne Hospital, Parkville, Victoria 3050, Australia. Kenneth.butcher@mh.org.au
authors.forename: K
authors.initials: K
authors.lastname: Butcher
authors.forename: M
authors.initials: M
authors.lastname: Parsons
authors.forename: T
authors.initials: T
authors.lastname: Baird
authors.forename: A
authors.initials: A
authors.lastname: Barber
authors.forename: G
authors.initials: G
authors.lastname: Donnan
authors.forename: P
authors.initials: P
authors.lastname: Desmond
authors.forename: B
authors.initials: B
authors.lastname: Tress
authors.forename: S
authors.initials: S
authors.lastname: Davis
mesh_terms: D000208:Acute Disease; D000368:Aged; D001783:Blood Flow Velocity; D001810:Blood Volume; D001931:Brain Mapping / Q000379:methods; D002544:Cerebral Infarction / Q000175:diagnosis; D002560:Cerebrovascular Circulation; D017352:Echo-Planar Imaging; D005260:Female; D005343:Fibrinolytic Agents / Q000627:therapeutic use; D006801:Humans; D018810:Magnetic Resonance Angiography; D008297:Male; D011237:Predictive Value of Tests; D012044:Regression Analysis; D020521:Stroke / Q000175:diagnosis* / Q000503:physiopathology* / Q000628:therapy; D015912:Thrombolytic Therapy; D013997:Time Factors; D010959:Tissue Plasminogen Activator / Q000627:therapeutic use
chemical_list: D005343:Fibrinolytic Agents; D010959:Tissue Plasminogen Activator