COMPUTED TOMOGRAPHIC COLONOGRAPHY (VIRTUAL COLONOSCOPY) - A NEW METHOD FOR DETECTING COLORECTAL NEOPLASMS

Computed tomographic (CT) colonography is an exciting new technique th at uses volumetric CT data combined with advanced imaging software to create two-dimensional and three-dimensional images of the colon. The technique uses both three-dimensional images that simulate the endolum inal perspective of the colonoscope, as web as axial and reformatted t wo-dimensional images. The two-dimensional and three-dimensional image s are complementary, and in combination offer the most robust performa nce for the detection of colorectal polyps. Currently, CT colonographi c examinations are performed in the fully cleansed and air-inflated co lon using a slice thickness of 5 mm, a reconstruction interval of 3 mm , a pitch of 1.3, and 70 mA. In a blinded, prospective study of 70 pat ients (half with a known lesion, and half from a surveillance populati on with a low disease prevalence) the sensitivity for the detection of polyps of 1 cm or more is 75%, and the specificity is 90%. The most c ommonly encountered problems include retained colonic fluid and stool, suboptimally distended colonic segments, and long interpretation time s. Many of these problems ran be solved using both supine and prone im aging. It is expected that the performance of this examination with im prove, and that a new era of colorectal screening will begin.