title: Interexaminer difference in infarct volume measurements on MRI: a source of variance in stroke research.
abstract: OBJECTIVE
  The measurement of ischemic lesion volume on diffusion- (DWI) and perfusion-weighted MRI (PWI) is examiner dependent. We sought to quantify the variance imposed by measurement error in DWI and PWI lesion volume measurements in ischemic stroke.
  
  
  METHODS
  Fifty-eight consecutive patients with DWI and PWI within 12 hours of symptom onset and follow-up MRI on >or= day-5 were studied. Two radiologists blinded to each other measured lesion volumes by manual outlining on each image. Interexaminer reliability was evaluated by intraclass correlation coefficients (ICC) and relative paired difference or RPD (ratio of difference between 2 measurements to their mean). The ratio of between-examiner variability to between-subject variability (variance ratio) was calculated for each imaging parameter.
  
  
  RESULTS
  The correlation (ICC) between examiners ranged from 0.93 to 0.99. The median RPD was 10.0% for DWI, 14.1% for mean transit time, 18.9% for cerebral blood flow, 21.0% for cerebral blood volume, 16.8% for DWI/MTT mismatch, and 6.3% for chronic T2-weighted images. There was negative correlation between RPD and lesion volume in all but chronic T2-weighted images. The variance ratio ranged between 0.02 and 0.10.
  
  
  CONCLUSIONS
  Despite high correlation between volume measurements of abnormal regions on DWI and PWI by different examiners, substantial differences in individual measurements can still occur. The magnitude of variance from measurement error is primarily determined by the type of imaging and lesion volume. Minimizing this source of variance will better enable imaging to deliver on its promise of smaller sample size.
authors.affiliation: Stroke Service, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, 149 13th Street, Room 2301, Charlestown MA 02129, USA. hay@partners.org
authors.forename: Hakan
authors.initials: H
authors.lastname: Ay
authors.forename: E Murat
authors.initials: EM
authors.lastname: Arsava
authors.forename: Mark
authors.initials: M
authors.lastname: Vangel
authors.forename: Banu
authors.initials: B
authors.lastname: Oner
authors.forename: Mingwang
authors.initials: M
authors.lastname: Zhu
authors.forename: Ona
authors.initials: O
authors.lastname: Wu
authors.forename: Aneesh
authors.initials: A
authors.lastname: Singhal
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Koroshetz
authors.forename: A Gregory
authors.initials: AG
authors.lastname: Sorensen
mesh_terms: D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002544:Cerebral Infarction / Q000000981:diagnostic imaging / Q000473:pathology*; D038524:Diffusion Magnetic Resonance Imaging / Q000592:standards* / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D018810:Magnetic Resonance Angiography / Q000592:standards / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009485:Neuroradiography / Q000592:standards / Q000706:statistics & numerical data; D015588:Observer Variation; D012189:Retrospective Studies; D020521:Stroke / Q000000981:diagnostic imaging / Q000473:pathology*