Computed tomography (CT) colonoscopy is a noninvasive technique that involves examining the colon by taking multiple CT scans of the patient’s colon and rectum and using computer software to create three-dimensional images. The procedure is used to detect polyps, which are growths of tissue in the colon or rectum. Some types of polyps increase the risk of colon cancer, especially if they are large or if a patient has several polyps. Compared to conventional colonoscopy, CT colonoscopy is less effective in detecting polyps smaller than 5 mm, more effective when the polyps are between 5 and 9.9 mm, and most effective when the polyps are 10 mm or larger. This test may be valuable for patients who have diseases rendering them unable to undergo conventional colonoscopy (e.g., bleeding disorders, lung or heart disease) and for patients who are unable to undergo the sedation required for traditional colonoscopy. The procedure is less invasive than conventional colonoscopy, with little risk of complications and no recovery time. CT colonoscopy can be done as an outpatient procedure, and the patient may return to work or usual activities the same day.

CT colonoscopy and conventional colonoscopy require the bowel to be cleansed before the examination. The patient lies on a table and is moved in and out of a doughnut-like device called a gantry, which houses the x-ray tube and associated electronics. The scanner uses multiple x-ray beams and a series of detectors that rotate around the patient to produce cross-sectional views in a three-dimensional fashion by detecting and recording differences in densities in the colon after having an x-ray beam passed through it. The screening procedure requires no contrast medium injections, but if a suspicious area or abnormality is detected, a repeat series of images may be completed after IV contrast medium is given. These density measurements are sent to a computer that produces a digital analysis of the anatomy, enabling a health-care provider (HCP) to look at slices or thin sections of certain anatomic views of the colon and vascular system. The data can be recorded on photographic or x-ray film or stored in digital format as digitized computer data. A drawback of CT colonoscopy is that polyp removal and biopsies of tissue in the colon must be done using conventional colonoscopy. Therefore, if polyps are discovered during CT colonoscopy and biopsy becomes necessary, the patient must undergo bowel preparation a second time.