Display modes for CT colonography - Part I. Synthesis and insertion of polyps into patient CT data

PURPOSE: To develop and validate a method for the insertion of digitally sy nthesized polyps into computer tomographic (CT) images of the human colon f or use as ground truth for evaluation of virtual colonoscopy. MATERIALS AND METHODS: Spiral CT simulator software was used to generate 10 synthetic polyps in various configurations. Additional software was develo ped to insert these polyps into volume CT scans. Ten polyps in eight patien ts were selected for comparison. Three radiologists evaluated whether two-d imensional (2D) CT images and three-dimensional (3D) volume-rendered CT ima ges showed synthetic or real polyps. RESULTS: Edge-response profiles and noise of simulated polyps matched those of native polyps. Frequency distributions of reviewers' responses were not significantly different for synthetic versus real polyps in either 3D or 2 D images. Responses were clustered around the response of "unsure" if lesio ns were real or synthetic. Receiver operating characteristic curves had are as of 0.54 (95% CI = 0.39, 0.68) for 3D and 0.39 (95% CI = 0.25, 0.53) for 2D images, which were not significantly different from random guessing (P = .70 and .28 for 3D and 2D images, respectively). CONCLUSION: Synthetic polyps were indistinguishable from real polyps. This method can be used to generate ground truth experimental data for compariso n of of CT colonographic display and detection methods.