Most studies evaluating CTC interpretation have utilized a primary 2D review with 3D for problem solving. Using thin section CT and improved 3D software, endoluminal interpretaion may improve polyp detection. The purpose of this study is to compare primary 2D vs 3D interpretation algorithms for CTC.

30 CTC data sets were retrospectively identified for inclusion in this study. The data sets were chosen such that 15 were normal and 15 showed polyps. Colonoscopy, performed on the same day, served as a reference standard. CTC data were obtained on a four row scanner using 4 X 1 detector configuration, 1.25 mm slice recon q 1 mm, 120 kV and 50 mAs. Data were transferred to a Siemens Leonardo Workstation with CTC software and were analyzed by three radiologists with prior CTC experience of at least 25 cases. The radiologists evaluated the 30 data sets blinded to patient identifiers using either primary 2D or 3D imaging, the method having been randomly predetermined. A minimum of one week elapsed and the 30 data sets were reevaluated using the other primary interpretation (2D or 3D) method. For both interpretaions the time; and size, morphology, and location of polyps was recorded. Mixed model analysis of variance was used to compare 2D and 3D images interpretaion time. Generalized estimating equations were used to compare the 2D and 3D images with respect to per patient specificity and per polyp sensitivity.

The mean evaluation time among all three readers was significantly lower (p < 0.001) utilizing the primary 2D interpretation technique, 10.9 vs. 16.4 minutes. The overall sensitivity of the three readers for polyps measuring 1-5 mm, 5-9 mm, and ≥ 10 mm was 20 and 40%, 50 and 66.7%, and 81 and 81%, for 2D and 3D techniques. The differences were statistically significant only for polyps measuring 1-5 mm (p<.025). The per patient specificity was the same for the 2D and 3D images 93.3% with a 95% confidence interval of [81.7%, 98.6%].

For polyps measuring > 6 mm in size, there was no difference in the sensitivity of CTC using a primary 2D or 3D technique. The mean evaluation time was significantly lower utilizing using a promary 2D technique.