A computed tomography colonography, also known as virtual colonoscopy, uses X-ray scanning to produce cross-sectional images of the colon's interior, RadiologyInfo.org explains. The scanner rotates X-ray emitters and detectors around the body to measure variations in radiation absorption, which a computer translates into three-dimensional images. The procedure involves inserting a tube into the patient's rectum and pumping air, carbon dioxide or an inflated balloon inside the colon to expand its interior, giving the doctor a clear view of all surfaces.
A major benefit of virtual colonoscopy is that the compiled images enable doctors to view a detailed simulation that mimics traveling along the colon's interior, RadiologyInfo.org states. The patient undergoes bowel cleansing in advance to clear out the colon, and the examination usually lasts no more than 15 minutes.
Doctors typically use virtual colonoscopy for colorectal cancer screening and monitoring polyps, according to WebMD. The procedure is also useful for examining patients with colon obstructions that prevent a traditional colonoscopy or for further assessment of abnormal colon test results. Virtual colonoscopy is faster and less invasive than a regular procedure, but it is less accurate at detecting polyps smaller than 0.4 inches. As of 2015, virtual colonoscopy is still a new procedure, and a traditional colonoscopy is usually necessary to confirm the growth of polyps or remove them.