Final answer:
An x-ray of a joint taken after the injection of a contrast medium into the joint is called an arthrogram. Arthrography uses a contrast agent to visualize the soft tissue structures of joints.
Step-by-step explanation:
An x-ray of a joint taken after the injection of a contrast medium into the joint is called an arthrogram. Arthrography is a type of medical imaging that uses a contrast agent to visualize the soft tissue structures of joints, such as cartilage, tendons, and ligaments. It differs from a regular x-ray by showing the surface of soft tissues lining the joint in addition to joint bones, allowing early degenerative changes in joint cartilage to be detected before bones become affected.