A virtual colonoscopy (VC), less frequently known as a CT colonography, is a procedure that uses x-rays and other medical imaging technology to detect problems in the colon, bowels and intestines, such as colorectal or sessile polyps considered to be pre-cancerous. It is a less invasive alternative to the regular colonoscopy procedure, during which a patient must be sedated while a long tool called a colonscope or endoscope is inserted into the rectum and large intestine. Virtual colonoscopies are usually performed by a radiologist in a hospital or any medical center with the proper equipment. While this test can be considered an alternative for colonoscopy in screening for colorectal cancer, colonoscopy is still the preferred method as it offers intervention as well as improved sensitivity for small or flat polyps.
Virtual Colonoscopy Procedure
Although a virtual colonoscopy requires much of the same bowel preparation techniques as a regular colonoscopy, it differs because it does not require sedation of any kind. It is a new imaging technique that is minimally invasive. The test is sometimes referred to as a “painless colonscopy.” A virtual colonoscopy is a quick, 10-minute procedure, and patients can usually return to normal activities afterward, whereas assistance is almost always necessary after a patient is sedated during a regular colonoscopy.
When the procedure starts, a radiology specialist will ask the patient to lie on a small table connected to a CT (computed tomography) or MRI (magnetic resonance imaging) machine. In the United States, using a CAT scan is more common than using MRI.
The patient will then need to gather his knees toward his chest while a trained specialist inserts a thin, flexible tube into the patient’s rectum. The purpose of the tube is to pump gas or air into the gastrointestinal (GI) tract—essentially inflating the colon to allow a doctor to see more clearly once a visual image is created.
The table on which the patient is laying will move through a large, cylindrical scanner that takes cross-sectional pictures and puts them together to produce one 3D, animated view of the colon. A doctor will ask patients to remain as still as possible and oftentimes to hold their breath to prevent blurring of the images.
The process must be repeated while the patients lie on their stomachs, face down, before a final image can be made. Since a virtual colonoscopy can only detect pre-cancerous polyps bigger than 5 millimeters, patients whose test results show abnormalities will have to undergo further examination with a regular colonoscopy, and small polyps will not be addressed.
Virtual Colonoscopy Preparation
Both regular and virtual colonoscopies require the same bowel prep. Unfortunately, most patients find this aspect of the process the most discomforting, but thorough cleansing of the colon is essential in order to get accurate results. Any solid matter, such as residual fecal matter, can show up on an x-ray and be confused for unnatural growths.
There are several methods of bowel prep that patients can practice the day before a colonoscopy or virtual colonoscopy exam. The most traditional is the use of an enema or laxatives while adhering to a strict liquids-only diet. Oftentimes a suppository is used to clean the rectum of any residual fecal matter that has not been cleared by prior bowel preparation.
An experimental technique called fecal tagging is also becoming more common. The process involves coating the gastrointestinal tract with a chemical solution that makes residual fecal matter appear “white” on the final x-ray image, distinguishing it from colorectal abnormalities. Fecal tagging can be performed with or without traditional bowel prep, but patients who chose not to cleanse their bowels beforehand must keep a low-fat and low-fiber diet in the several days leading up to a colonoscopy, in addition to ingesting the diluted chemical solution.
Scheduling a Virtual Colonoscopy
If you feel you are in need of a virtual colonoscopy, for either routine or abnormal issues, please contact one of our gastroenterology specialists.
Reviewed 12/12/2011 by David M. Nolan, M.D.
Diplomate of the American Board of Internal Medicine, 2011
Currently a Fellow of Gastroenterology, at UCI 2011-2014