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By Mayo Clinic staff
During the exam
During a virtual colonoscopy, you'll wear a gown but likely no other garments. Sedation isn't usually necessary, but you may be given an injection of medication to reduce the likelihood of stomach cramps during the exam.
You'll begin the exam lying on your side on the exam table, usually with your knees drawn toward your chest. The doctor will place a small tube (catheter) inside your rectum to fill your colon with air or carbon dioxide. The air or gas — which helps create clear images — may cause a feeling of pressure in your abdomen.
For the next part of the exam, you'll lie on your back. The exam table will be moved into the CT machine, and your body will be scanned. Then you'll turn over to lie on your abdomen or your side, and your body will be scanned again. You may be asked to turn and hold various other positions, as well as hold your breath at times. If necessary, a contrast agent may be given through a vein in your arm (intravenously) to help create clearer images.
A virtual colonoscopy typically takes about 10 minutes.
New computer programs can help doctors examine the many images produced during virtual colonoscopy — ideally calling attention to suspicious areas that deserve a closer look — but more research is needed before computer-assisted virtual colonoscopy is widely available.
After the exam
After the exam, most of the air or gas will be removed from your colon through the catheter in your rectum. You may feel bloated or pass gas for a few hours after the exam as you clear the remaining air or gas from your colon. Walking may help relieve any discomfort, and you can return to your usual diet and activities right away. Consult your doctor if your signs and symptoms don't improve on their own.
- Schilling McCann JA, ed. Diagnostic Tests. Philadelphia, Pa.: Lippincott Williams & Wilkins; 2007:106.
- Virtual colonoscopy. National Digestive Diseases Information Clearinghouse. http://digestive.niddk.nih.gov/ddiseases/pubs/virtualcolonoscopy. Accessed March 18, 2009.
- Cancer imaging. National Cancer Institute. http://imaging.cancer.gov/imaginginformation/cancerimaging/page9. Accessed March 18, 2009.
- Levin B, et al. Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: A joint guideline from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. Gastroenterology. 2008;134:1570.
- Fletcher RH. Screening strategies in patients at average risk for colorectal cancer. http://www.uptodate.com/home/index.html. Accessed March 18, 2009.
- Weinberg DS. In the clinic: Colorectal cancer screening. Annals of Internal Medicine. 2008;148:ITC2-1.
- Kruskal JB. Computed tomographic colonography. http://www.uptodate.com/home/index.html. Accessed March 18, 2009.
- Yee J. Patient preparation for CT colonography. In: Lefere P, ed. Virtual Colonoscopy: A Practical Guide. New York, N.Y.: Springer; 2006:23.
- Johnson CD, et al. Accuracy of CT colonography for detection of large adenomas and cancers. New England Journal of Medicine. 2008;359:1207.
