Colonoscopy is one of the least invasive endoscopic investigations of the large colon and the distal section of the small bowel with a CCD camera or a fiber optic camera on a tube that is flexible enough to be inserted through the anus. It may give a visual diagnosis (for example ulceration, polyps) and gives the opportunity for biopsy or the removal of any suspected lesions. Before a colonoscopy, patients have to under colonoscopy prep or colonoscopy preparation. Virtual colonoscopy, which makes use of 2 dimensional and 3 dimensional images reconstructed using CT scans or from MR scans, is also an option, as an entirely non-invasive test, although it is not regarded as standard and still requires investigation in relation to its diagnostic capabilities. In addition to this, virtual colonoscopy restricts therapeutic maneuvers including the removal of polyp and/or tumors or biopsy nor visualisation of any lesions smaller in size than 5 millimeters. Once detected, a standard colonoscopy would be performed on a growth of polyp. Colonoscopy can be carried out to remove polyps that are smaller than one millimeter. Once a polyp is removed, further study can be carried out on it using a microscope. This will help to determine wether or not if the polyp is precancerous. Colonoscopy has some similaries to sigmoidoscopy, but they are no the same. The difference is that the procedures are carried out on the same parts of the colon. However, Sigmoidsocopy only allows for the viewing of the final 2 feet of the colon, whilst colonoscopy allows for the examination of the whole colon. This is often 4 to 5 feet in length.