title: CT colonography: effect of colonic distension on polyp measurement accuracy and agreement-in vitro study.
abstract: OBJECTIVE
  To investigate the effect of colonic distension on polyp measurement accuracy and reader agreement.
  
  
  METHODS
  Institutional review board permission was obtained. A sealed colectomy specimen from a patient with familial adenomatous polyposis was scanned using a four-detector-row computed tomography (CT) after half and full air distension. A histopathologist measured the maximum dimension of all polyps in the opened specimen. Digital photographs and line drawings were used to individually match polyps visible in the CT datasets. Two observers (radiologist, technician) independently estimated the maximum polyp diameter using both two-dimensional (2D) and three-dimensional (3D) surface rendering. Full-distension measurements were repeated 1 week later. Accuracy was analyzed using paired t-test. Observer agreement was assessed using Bland Altman limits of agreement.
  
  
  RESULTS
  Twenty-three polyps (4-15 mm) were identified. 2D measurements were significantly smaller than histologic size at both half distension (radiologist first): mean difference [md] -1.1 mm, md -1.7 mm, and full distension md -1.1 mm, md 1.4 mm (all P < .001). 3D measurements were not significantly different from true size other than after half distension for the technician (md -0.7 mm, P = .01). 95% Bland Altman limits for interobserver agreement were narrower after full distension, and better using 2D (half-distension span of agreement approximately 4.7 mm and 6 mm for 2D and 3D, respectively). 2D intraobserver span of agreement between half and full distension was approximately 3.8 mm and 3.2 mm for the radiologist and technician, respectively, compared with 6.2 mm and 5.5 mm using 3D.
  
  
  CONCLUSIONS
  3D polyp measurement is more accurate than 2D. However, in the presence of suboptimal distension, inter- and intraobserver agreement is superior using 2D.
authors.affiliation: Department of Imaging, University College Hospital, 235 Euston Road, London, NW1 2BU, UK. csytaylor@yahoo.co.uk
authors.forename: Stuart
authors.initials: S
authors.lastname: Taylor
authors.forename: Andrew
authors.initials: A
authors.lastname: Slater
authors.forename: Leslie
authors.initials: L
authors.lastname: Honeyfield
authors.forename: David
authors.initials: D
authors.lastname: Burling
authors.forename: Steve
authors.initials: S
authors.lastname: Halligan
mesh_terms: D011125:Adenomatous Polyposis Coli / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000601:surgery; D000293:Adolescent; D000388:Air; D003111:Colonic Polyps / Q000000981:diagnostic imaging* / Q000473:pathology*; D023881:Colonography, Computed Tomographic / Q000379:methods*; D004106:Dilatation; D006801:Humans; D021621:Imaging, Three-Dimensional; D066298:In Vitro Techniques; D007327:Insufflation; D008297:Male; D015588:Observer Variation; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity