title: CT colonography: automatic measurement of polyp diameter compared with manual assessment - an in-vivo study.
abstract: OBJECTIVE
  To investigate whether automated diameter assessment was feasible for CT colonography.
  
  
  METHODS
  Two experienced observers independently measured the maximum diameter of 50 polyps (colonoscopic reference size range 5-12 mm) from colonography datasets using conventionally placed software callipers and a variety of two-dimensional (2D) computed tomography (CT) window settings (colon, abdominal, bone, lung), and also three-dimensional (3D) perspective rendering. Polyps were also measured using automated polyp-segmentation software. Agreement between observers and with the colonoscopic reference measurement was determined using Bland-Altman, Wilcoxon, and Mann-Whitney U analyses.
  
  
  RESULTS
  Inter-observer agreement was similar for all window displays: mean difference in millimetres (SD difference; 95% limits of agreement) ranged from 0 (1.7, -3.3, 3.3) for 2D colon to -1.1mm (1.6, -4.3, 2.0) for 3D, compared with -0.5 (2.09, -4.6, 3.6) for automated measurement. When compared to colonoscopy, the largest discrepancy occurred using the 3D display (mean difference 1.3mm, 2.5mm for each observer). There was also a significant difference between estimates and reference size when using the 2D abdominal and 3D displays (p=0.03, <0.001).
  
  
  CONCLUSIONS
  Automated polyp measurement is possible in vivo. Automated and conventional methods have comparable inter-observer agreement. The greatest measurement error is encountered when using a 3D display for estimates of diameter.
authors.affiliation: University College Hospital, London, UK.
authors.forename: D
authors.initials: D
authors.lastname: Burling
authors.forename: S
authors.initials: S
authors.lastname: Halligan
authors.forename: S A
authors.initials: SA
authors.lastname: Taylor
authors.forename: L
authors.initials: L
authors.lastname: Honeyfield
authors.forename: M E
authors.initials: ME
authors.lastname: Roddie
mesh_terms: D003106:Colon / Q000473:pathology; D003111:Colonic Polyps / Q000000981:diagnostic imaging*; D023881:Colonography, Computed Tomographic / Q000379:methods*; D003113:Colonoscopy / Q000379:methods; D005240:Feasibility Studies; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D015588:Observer Variation; D015203:Reproducibility of Results