Final answer:
A barium enema examination is a diagnostic test involving a barium sulfate enema and X-rays to visualize the colon and rectum, helping to diagnose conditions like ulcerative colitis and Crohn's disease.
Step-by-step explanation:
The diagnostic test that requires a barium enema given rectally before taking an X-ray is known as a barium enema examination or lower gastrointestinal (GI) tract radiography. This medical imaging technique is used to visualize the large intestine (including the colon and rectum) and can diagnose various conditions such as acid reflux disease, Crohn's disease, and ulcers. The barium sulfate suspension used in a barium enema coats the lining of the intestinal tract, making it visible on an X-ray due to the high atomic mass of barium which is opaque to x-rays, providing a detailed image that exceeds the clarity of a traditional X-ray.