Nuclear medicine was developed to study the function of internal organs. This imaging test differs from conventional X-ray, which determines the presence of disease based on structural appearance. Nuclear medicine can often determine abnormalities too challenging for conventional x-ray. The bone, heart, lungs, thyroid, gallbladder and liver are the organs most often studied. Nuclear medicine is often used to gauge the blood supply; diseases of the bone; certain lung and abdominal abnormalities; infections; and thyroid problems. Nuclear medicine relies on a small amount of radioactive material called a tracer and a special camera to capture an image. The tracer may be injected, inhaled or swallowed.