Elsevier

Academic Radiology

Volume 13, Issue 7, July 2006, Pages 850-859
Academic Radiology

Original investigation
CT Colonography: Effect of Colonic Distension on Polyp Measurement Accuracy and Agreement—In Vitro Study

https://doi.org/10.1016/j.acra.2006.03.018Get rights and content

Rational and Objectives

To investigate the effect of colonic distension on polyp measurement accuracy and reader agreement.

Materials and 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.

Conclusion

3D polyp measurement is more accurate than 2D. However, in the presence of suboptimal distension, inter- and intraobserver agreement is superior using 2D.

Section snippets

Materials and methods

Full ethical committee approval was obtained for the study. A 16-year-old male with familial adenomatous polyposis coli scheduled to undergo elective colectomy was identified from the polyposis registry database at our institution and approached by the study coordinator before colectomy. Full written consent for use of the colectomy specimen was obtained from the patient and his parents. Throughout the study, care was taken to ensure that the experiment did not interfere with subsequent

Results

A total of 23 polyps (4 mm [x1], 5 mm [x11], 6 mm [x6], 7 mm [x2], 8 mm [x2], and 15 mm [x1]) were visible on both datasets and included in the analysis. All polyps were classified as sessile.

Discussion

Validation of polyp size measurement accuracy and quantification of inter- and intraobserver measurement agreement is vital if CTC is to become established as a primary screening modality, with an active role in polyp follow-up.

Recent data have questioned the reliability of measurements using CTC (10), but have used mainly endoscopic estimates of polyp size, rather than exclusively pathologic measurement as their reference. To our knowledge, this is the first study exclusively using human

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