Virtual colonoscopy: A method for examining the colon by taking a series of x-rays and then using a computer to reconstruct three-dimensional pictures (a CT scan) of the interior surfaces of the colon from these x-rays. The pictures can be saved, manipulated to better viewing angles, and reviewed after the procedure. The procedure requires a 48-hour low-fiber diet and a complete bowel cleansing. If something suspicious is noted, a regular colonoscopy is needed to biopsy or remove it. Virtual colonoscopy results in about 15% false positives (misleading readings that unnecessarily require a regular colonoscopy). It is also not yet known whether virtual colonoscopy can reliably detect flat adenomas which, like polyps, can give rise to colon cancer. Also called computed tomography or CT colography.