Inclusion Criteria:  - people with referral sheets for surveillance colonoscopies : meaning 3 or 5 years after the initial colonoscopy.  Exclusion Criteria:  known or suspected acute diverticulitis ulcerative colitis Crohn's disease toxic megacolon acute abdominal pain familial polyposis syndrome coagulopathy poor general health (defined as an American Society of Anaesthesiologists class >3) patients presenting for emergency colonoscopies patients incapable of lying flat on their back for the duration of the CT colonography due CHF or other predispositions patients with a personal history of CRC patient undergoing colonoscopy for surveillance after EMR or ESD procedures patients diagnosed with a CRC or a metastatic cancer patients with a history of contrast allergies Patients referred for polypectomy