CT colonography: examination prerequisites.

CT colonography is likely to play an important role in colorectal cancer screening. The ability of this new technique to detect colorectal polyps and cancer is predicated on an optimally cleansed and distended colon. Whereas the most common reported colonic cleansing regimen employed for CT colonography is polyethylene glycol lavage solution, saline cathartics such as sodium phosphate and magnesium citrate offer the advantage of a drier cleansed colon. Positive labeling of residual stool and fluid combined with electronic substraction of tagged material is under investigation. This new technique would eliminate purgative bowel cleansing and increase patient acceptance of CT colonography. Colonic distention is easily and reliably achieved with atmospheric air, although carbon dioxide is being evaluated as a more comfortable alternative. The use of antispasmodics for CT colonography is controversial. Glucagon is no longer used at centers where a clear benefit has not been found. Intravenous contrast may be useful in a specific subset of patients undergoing CT colonography, although it is doubtful that it will be used routinely for CT colonography.