Polyps: linear and volumetric measurement at CT colonography

PURPOSE: To retrospectively determine which of several computed tomographic (CT) colonography-based polyp measurements is most compatible with the linear measurement at optical colonoscopy and which is best for assessing change in polyp size. MATERIALS AND METHODS: This HIPAA-compliant study had institutional review board approval; informed consent was obtained. Prone and supine CT colonography with same-day optical colonoscopy was performed in 216 patients (147 men and 69 women; age range, 46-79 years; mean age, 59.2 years) with 338 polyps detected at CT colonography. Polyp size was measured with three linear measurements and two volume measurements. One linear measurement and one volume measurement were performed by using automated segmentation; remaining measurements were performed manually. Compatibility with linear size at optical colonoscopy and measurement reproducibility were assessed three ways: variation from size measurement at optical colonoscopy, change between prone and supine scans, and variability between observers. Confidence analysis assessed the ability of each measurement to identify polyps with an optical colonoscopy measurement of 1 cm or greater. RESULTS: Two hundred fifty-one segmentable polyps were present on both supine and prone scans. Linear polyp diameter manually measured on a three-dimensional endoluminally viewed surface (L(M3D)) indicated with 95% confidence that a polyp measured as 0.8 cm or smaller was less than 1.0 cm at optical colonoscopy. Prone and supine polyp size difference was smallest for L(M3D) and the linear diameter computed from manual and automated volume measurements, with interquartile ranges smaller than or equal to 0.3, 0.2, and 0.5 cm, respectively. Interobserver and intraobserver variability was smallest for linear polyp diameter measurements on a two-dimensional display, with a mean percentage difference of 2.8% (95% Bland-Altman limits of agreement: -17.8%, 23.4%) and 5.0% (95% Bland-Altman limits of agreement: -28.3%, 38.3%), respectively. CONCLUSION: L(M3D) best approximated polyp size measurements at optical colonoscopy. Linear diameter calculated from automated volume measurements showed the smallest variation between supine and prone scans while avoiding observer variability and may be best for assessing polyp size changes with serial examinations.