title: Reliability of assessing percentage of diffusion-perfusion mismatch.
abstract: OBJECTIVE
  Emergent neurovascular imaging holds promise in identifying new and optimum target populations for thrombolysis in stroke. Recent research has focused on patients with diffusion-weighted MRI (DWI)-perfusion-weighted MRI (PWI) mismatch as a marker of tissue at risk of infarction and a means to select the most suitable candidates for thrombolysis. The present study sought to estimate the reliability of assessing the percentage of DWI-PWI mismatch.
  
  
  METHODS
  Thirteen patients with acute strokes had DWI and PWI within 7 hours of symptom onset. Six raters independently created relative mean transit time (rMTT) maps and then compared them with DWI images to assess the percentage of mismatch (PWI>DWI) in 10% increments. The MR scans were reassessed by 4 raters, tracing around the lesions to calculate the volume percentage of mismatch.
  
  
  RESULTS
  Visual assessment had an interrater reliability of 0.68 (95% CI, 0.52 to 1.0; SEM=21.6%) and an intrarater reliability of 0.80 (95% CI, 0.47 to 1.0; SEM=16.9%). Hand-drawn assessment had an interrater reliability of 0.66 (95% CI, 0.45 to 1.0; SEM=26.2%) and an intrarater reliability of 0.94 (95% CI, 0.81 to 1.0; SEM=10.9%).
  
  
  CONCLUSIONS
  Results from the present study suggest that quantifying mismatch by the human eye is reproducible but not reliable among observers. This raises doubts about using mismatch for clinical decision making and clinical trial enrollment.
authors.affiliation: Seaman Family MR Research Centre, Foothills Medical Centre, Calgary Health Region, Calgary, Alberta T2N 2T9, Canada. shelagh.coutts@calgaryhealthregion.ca
authors.forename: Shelagh B
authors.initials: SB
authors.lastname: Coutts
authors.forename: Jessica E
authors.initials: JE
authors.lastname: Simon
authors.forename: Anna I
authors.initials: AI
authors.lastname: Tomanek
authors.forename: Philip A
authors.initials: PA
authors.lastname: Barber
authors.forename: Jean
authors.initials: J
authors.lastname: Chan
authors.forename: Mark E
authors.initials: ME
authors.lastname: Hudon
authors.forename: J Ross
authors.initials: JR
authors.lastname: Mitchell
authors.forename: Richard
authors.initials: R
authors.lastname: Frayne
authors.forename: Michael
authors.initials: M
authors.lastname: Eliasziw
authors.forename: Alastair M
authors.initials: AM
authors.lastname: Buchan
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Demchuk
mesh_terms: D000208:Acute Disease; D000368:Aged; D000369:Aged, 80 and over; D002543:Cerebral Hemorrhage / Q000139:chemically induced / Q000517:prevention & control; D020000:Decision Support Systems, Clinical; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D018810:Magnetic Resonance Angiography; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D020521:Stroke / Q000175:diagnosis* / Q000188:drug therapy; D015912:Thrombolytic Therapy / Q000009:adverse effects; D013997:Time Factors; D010959:Tissue Plasminogen Activator / Q000009:adverse effects / Q000627:therapeutic use
chemical_list: D010959:Tissue Plasminogen Activator