The correct answer is: barium enema.
Barium enema is technique used for detection of changes or abnormalities in the large intestine-colon via X-rays so it is often called colon X-ray. Barium envelops the lining of the colon so it is clear to see silhouette of the colon. This type of diagnosis is used in the case of abdominal pain, rectal bleeding, chronic diarrhea..