title: Polyp measurement using CT colonography: agreement with colonoscopy and effect of viewing conditions on interobserver and intraobserver agreement.
abstract: OBJECTIVE
  This article presents inter- and intraobserver agreement for estimates of polyp diameter using CT colonography, including the effects of different visualization displays and prior experience.
  
  
  METHODS
  Four observers, three of whom had prior experience with CT colonography, estimated the maximum diameter of 48 polyps using three different visualization displays: 2D colonography window, 2D abdominal window, and 3D surface rendering. Each re-measured a subset of 10 polyps. Polyps measured 2 to 12 mm according to a colonoscopic reference. Inter- and intraobserver agreement and agreement with the reference measurement were determined using the Bland-Altman method, paired Student's t testing, analysis of variance, and analysis of covariance (ANCOVA), and by calculating the components of variance.
  
  
  RESULTS
  CT measurements overestimated polyp diameter, a phenomenon found least using the 2D abdominal display. Generally, 95% limits of agreement encompassed different size categories for individual polyps: the widest spanned 14.6 mm (-4.6 mm to 10.0 mm) for an experienced observer using the 3D display. When using the 2D abdominal display, no significant difference was found between estimates and the reference value for the other two experienced observers (p = 0.83 and 0.23). All the observers' measurements were significantly different from the reference when using the 3D display (p < 0.001). The novice was significantly different from the experienced observers in some analyses. Inter- and intraobserver agreement were poorest for the 3D display.
  
  
  CONCLUSIONS
  Measurement of polyp diameter from CT colonography is subject to variation contingent on the observer's experience and the viewing display used. Although 3D visualization display is commonly used for polyp detection, it should not be used for measurement.
authors.affiliation: Intestinal Imaging Centre, St. Mark's Hospital, Harrow, Middlesex, England HA1 3UJ.
authors.forename: David
authors.initials: D
authors.lastname: Burling
authors.forename: Steve
authors.initials: S
authors.lastname: Halligan
authors.forename: Stuart
authors.initials: S
authors.lastname: Taylor
authors.forename: Duncan J
authors.initials: DJ
authors.lastname: Brennand
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Altman
authors.forename: Paul
authors.initials: P
authors.lastname: Bassett
authors.forename: Wendy
authors.initials: W
authors.lastname: Atkin
authors.forename: Clive I
authors.initials: CI
authors.lastname: Bartram
mesh_terms: D003111:Colonic Polyps / Q000000981:diagnostic imaging* / Q000473:pathology*; D023881:Colonography, Computed Tomographic / Q000706:statistics & numerical data*; D003113:Colonoscopy / Q000706:statistics & numerical data*; D006801:Humans; D015588:Observer Variation