title: Observer reliability of CT angiography in the assessment of acute ischaemic stroke: data from the Third International Stroke Trial.
abstract: BACKGROUND
  CT angiography (CTA) is often used for assessing patients with acute ischaemic stroke. Only limited observer reliability data exist. We tested inter- and intra-observer reliability for the assessment of CTA in acute ischaemic stroke.
  
  
  METHODS
  We selected 15 cases from the Third International Stroke Trial (IST-3, ISRCTN25765518) with various degrees of arterial obstruction in different intracranial locations on CTA. To assess inter-observer reliability, seven members of the IST-3 expert image reading panel (>5 years experience reading CTA) and seven radiology trainees (<2 years experience) rated all 15 scans independently and blind to clinical data for: presence (versus absence) of any intracranial arterial abnormality (stenosis or occlusion), severity of arterial abnormality using relevant scales (IST-3 angiography score, Thrombolysis in Cerebral Infarction (TICI) score, Clot Burden Score), collateral supply and visibility of a perfusion defect on CTA source images (CTA-SI). Intra-observer reliability was assessed using independently repeated expert panel scan ratings. We assessed observer agreement with Krippendorff's-alpha (K-alpha).
  
  
  RESULTS
  Among experienced observers, inter-observer agreement was substantial for the identification of any angiographic abnormality (K-alpha = 0.70) and with an angiography assessment scale (K-alpha = 0.60-0.66). There was less agreement for grades of collateral supply (K-alpha = 0.56) or for identification of a perfusion defect on CTA-SI (K-alpha = 0.32). Radiology trainees performed as well as expert readers when additional training was undertaken (neuroradiology specialist trainees). Intra-observer agreement among experts provided similar results (K-alpha = 0.33-0.72).
  
  
  CONCLUSIONS
  For most imaging characteristics assessed, CTA has moderate to substantial observer agreement in acute ischaemic stroke. Experienced readers and those with specialist training perform best.
authors.affiliation: Division of Neuroimaging Sciences, University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh, EH4 2XU, UK.
authors.forename: Grant
authors.initials: G
authors.lastname: Mair
authors.forename: Rüdiger
authors.initials: R
authors.lastname: von Kummer
authors.forename: Alessandro
authors.initials: A
authors.lastname: Adami
authors.forename: Philip M
authors.initials: PM
authors.lastname: White
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Adams
authors.forename: Bernard
authors.initials: B
authors.lastname: Yan
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Demchuk
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Farrall
authors.forename: Robin J
authors.initials: RJ
authors.lastname: Sellar
authors.forename: Rajesh
authors.initials: R
authors.lastname: Ramaswamy
authors.forename: Daisy
authors.initials: D
authors.lastname: Mollison
authors.forename: Elena V
authors.initials: EV
authors.lastname: Boyd
authors.forename: Mark A
authors.initials: MA
authors.lastname: Rodrigues
authors.forename: Karim
authors.initials: K
authors.lastname: Samji
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Baird
authors.forename: Geoff
authors.initials: G
authors.lastname: Cohen
authors.forename: Eleni
authors.initials: E
authors.lastname: Sakka
authors.forename: Jeb
authors.initials: J
authors.lastname: Palmer
authors.forename: David
authors.initials: D
authors.lastname: Perry
authors.forename: Richard
authors.initials: R
authors.lastname: Lindley
authors.forename: Peter A G
authors.initials: PA
authors.lastname: Sandercock
authors.forename: Joanna M
authors.initials: JM
authors.lastname: Wardlaw
mesh_terms: D000208:Acute Disease; D002545:Brain Ischemia / Q000000981:diagnostic imaging* / Q000188:drug therapy; D002533:Cerebral Angiography; D002983:Clinical Competence; D006801:Humans; D015588:Observer Variation; D011446:Prospective Studies; D015203:Reproducibility of Results; D020521:Stroke / Q000000981:diagnostic imaging* / Q000188:drug therapy; D015912:Thrombolytic Therapy; D014057:Tomography, X-Ray Computed