CT colonography:: automatic measurement of polyp diameter compared with manual assessment -: an in-vivo study

AIM: To investigate whether automated diameter assessment was feasible for CT colonography. MATERIALS AND 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 -1.1 mm (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 1.3 mm, 2.5 mm 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). CONCLUSION: 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. (C) 2006 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.