A previously healthy 61 - year - old woman presents with a 3 - week history of altered bowel habit and rectal bleeding. She refuses to undergo colonoscopy. Which of the following is next best investigation?

CT colonography , CT abdomen and pelvis and barium enema are useful in this situation. But CT colonography is the most accurate of the three, enabling detection of small polyps. The conventional CT will only detect large tumours. The barium enema will only detect large polyps and frank tumours.