Final answer:
Polyps are well visualized by a double contrast barium enema, which is a procedure used to identify and allow for the removal of precancerous polyps in the colon.
Step-by-step explanation:
A double contrast barium enema is a radiologic procedure that is used to visualize the inner surface of the colon and can be very effective in identifying abnormalities. Among the pathologies listed, polyps are well visualized by a double contrast barium enema. This procedure helps in identifying precancerous polyps, which can then be removed to prevent the development of colorectal cancer. However, a double contrast barium enema is not the preferred method for visualizing a gastrointestinal bleed, hemorrhoids, or a bowel obstruction. GI bleeds are better diagnosed through endoscopy or specialized imaging tests, hemorrhoids are usually diagnosed via physical examination and endoscopy, and bowel obstruction is more effectively identified with other imaging modalities such as CT scans.