if abnormalities are found and the patient needs conventional colonoscopy, it may be performed the same day. Advantages VC may be more comfortable for some individuals, as it does not require the use of a colonoscope. As a result, no sedation is needed, and the patient can return to his/her usual activities or go home after the procedure without the aid of another person. The lack of sedation also lowers the risk of the procedure since some people may have adverse reactions to sedative medications used during conventional colonoscopy. VC provides clearer, more detailed images than a conventional x-ray using a barium enema, sometimes called a lower gastrointestinal (GI) series. Further, about 1 in 10 patients will not have a complete right colon (cecum) evaluation completed with conventional colonoscopy. It also takes less time than either a conventional colonoscopy or a lower GI series. VC provides a secondary benefit of revealing diseases or abnormalities outside the colon. One study of asymptomatic adults undergoing routine VC found that approximately one unsuspected extracolonic cancer was detected per 300 screenings in addition to about one invasive colorectal cancer per 500 screenings, for an overall rate of approximately one unsuspected cancer of any type detected per 200 screenings. Invasive colorectal cancer was the most common malignancy detected, followed by renal cell carcinoma. Disadvantages During virtual colonoscopy, it is not possible to take tissue samples (biopsy) or remove polyps, so a conventional colonoscopy must be performed if abnormalities are found. Also, VC does not show as much detail as a conventional colonoscopy, so polyps smaller than between 2 and 10 millimeters in diameter may not show up on the images. Furthermore virtual colonoscopy performed with CT exposes the patient to ionizing radiation, on the order of a milligray. Some research has demonstrated that ultra-low dose VC can be just as effective in demonstrating bowel disease due to the great difference in x-ray absorption between air and the tissue comprising the inner wall of the colon. Optical colonoscopy is taken as the "gold standard" for colorectal cancer screening by the vast majority of the medical and research communities. However, some radiologists recommend VC as a preferred approach to colorectal screening. Virtual colonoscopy is favored by some professionals because it permits complete visualization of the entire colon, hence providing more opportunity to identify precancerous polyps and cancer, and to then do prompt diagnostic biopsies or therapeutic removal