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CT Colonography: Automated Measurement of Colonic Polyps Compared with Manual Techniques—Human in Vitro Study¹

¹ From the Department of Imaging, University College Hospital, 2F Podium, 235 Euston Rd, London NW1 2BU, England (S.A.T., S.H.); Department of Imaging, John Radcliffe Hospital, Oxford, England (A.S.); Medicsight, London, England (L.H., J.D., H.A.); Charing Cross Hospital, London, England (M.E.R.); and St Mark's and Northwick Park Hospitals, London, England (D.B.). From the 2005 RSNA Annual Meeting. Received December 19, 2005; revision requested February 13, 2006; revision received February 17; final version accepted April 7. Address correspondence to S.A.T. (e-mail: csytaylor{at}yahoo.co.uk).

Purpose: To prospectively investigate the relative accuracy and reproducibility of manual and automated computer software measurements by using polyps of known size in a human colectomy specimen.

Materials and Methods: Institutional review board approval was obtained for the study; written consent for use of the surgical specimen was obtained. A colectomy specimen containing 27 polyps from a 16-year-old male patient with familial adenomatous polyposis was insufflated, submerged in a container with solution, and scanned at four-section multi–detector row computed tomography (CT). A histopathologist measured the maximum dimension of all polyps in the opened specimen. Digital photographs and line drawings were produced to aid CT–histologic measurement correlation. A novice (radiographic technician) and an experienced (radiologist) observer independently estimated polyp diameter with three methods: manual two-dimensional (2D) and manual three-dimensional (3D) measurement with software calipers and automated measurement with software (automatic). Data were analyzed with paired t tests and Bland-Altman limits of agreement.

Results: Seven polyps (6-mm diameter) could not be extracted by using the software; 20 polyps (5–15-mm diameter) remained for analysis. Automated measurement was not significantly different from histologic size for the experienced reader (mean difference, 0.63 mm; P = .06) or novice reader (mean difference, 0.58 mm; P = .12). With manual 2D measurement and manual 3D measurement, the experienced reader (1.21-mm mean difference, P < .001, and 0.68-mm mean difference, P = .03, respectively) and novice reader (1.54-mm mean difference, P < .001, and 0.84-mm mean difference, P = .002, respectively) significantly underestimated polyp size. Interobserver agreement was good and similar for all three methods (95% limits of agreement span, approximately 2.5 mm). Intraobserver agreement was related to reader experience, with differences of up to 2.5 mm within expected limits of agreement.

Conclusion: For polyps smaller than 1 cm, measurement differences of up to 2.5 mm are within the expected limits of inter- and intraobserver agreement for all measurement techniques. Automated and manual 3D polyp measurements are more accurate than manual 2D measurements.

© RSNA, 2006