Display modes for CT colonography - Part II. Blinded comparison of axial CT and virtual endoscopic and panoramic endoscopic volume-rendered studies

PURPOSE: To determine the sensitivity of radiologist observers for detectin g colonic polyps by using three different data review (display) modes for c omputed tomographic (CT) colonography, or "virtual colonoscopy." MATERIALS AND METHODS: CT colonographic data in a patient with a normal col on were used as base data for insertion of digitally synthesized polyps. fo rty such polyps (3.5, 5, 7 and 10 mm in diameter) were randomly inserted in four copies of the base data. Axial CT studies, volume-rendered virtual en doscopic movies, and studies from a three-dimensional mode termed "panorami c endoscopy" were reviewed blindly and independently by two radiologists. RESULTS: Detection improved with increasing polyp size. Trends in sensitivi ty were dependent on whether all inserted lesions or only visible lesions w ere considered, because modes differed in how completely the colonic surfac e was depicted. For both reviewers and all polyps 7 mm or larger, panoramic endoscopy resulted in significantly greater sensitivity (90%) than did vir tual endoscopy (68%, P = .014). For visible lesions only, the sensitivities were 85%, or 81%, and 60% for one reader and 65%, 62%, and 28% for the oth er for virtual endoscopy, panoramic endoscopy, and axial CT, respectively. Three-dimensional displays were more sensitive than two-dimensional display s (P < .05). CONCLUSION: The sensitivity of panoramic endoscopy is higher than that of v irtual endoscopy, because the former displays more of the colonic surface. Higher sensitivities for three-dimensional displays may justify the additio nal computation and review time.