What does nuclear medicine mean? What types of things do the doctors do?

Diagnose & Rx . Using isotopes to diagnose and treat thyroid diseases as well as many disorders of the brain, heart, lungs, liver, kidneys and skeleton. Nuclear medicine focuses mostly on function whereas radiology focuses mostly on structure.
RADIOISOTOPES IN MED. Nuclear medicine deals with the application of radioactive materials in the diagnosis and treatment of diseases. The doctors specialized in nuclear medicine administer radioactive material (small amount for diagnosis and large amount for treatment) to patients to diagnose cancer, infection, blood clot in lung, and functions of various organs - heart, gallbladder, kidney, thyroid, stomach etc.
Another answer! I agree with the answer, but i would like to add that the radiation adminstered with one dose of the several technetium phosphates is less than that of a just x-ray. They do not make you radioactive, since most emit gamma rays that go through you. Finally, nuclear imaging is dynamic and live. You can x-ray a corpse, but you can not nuclear image them!
Diagnose and treat. Nuclear medicine docs inject small amounts of radioactivity into patients to take images and interpret them. In addition, for some conditions, larger amounts of radioactivity are used for treatment purposes.
Functional imaging. Nuclear medicine involves radioisotopes which are injected intravenously or subcutaneously, inhaled into lungs, ingested, or instilled into bladder. Gamma rays from isotope form images on gamma camera. Function of organs determined. Includes heart, brain, kidneys, bladder, bones, thyroid, gall bladder, lungs, liver, spleen, lymph nodes etc.Images read by doctors specializing in nuclear medicine.
Resources. Here's a good explaination: http://goo.Gl/scqbf nuclear medicine was called that because it uses energy from the nucleus of an atom (radioactivity) to help diagnosis and treat disease. The more common term now is molecular imaging because of the complexity of issues, where more than just the atomic nucleus is used for imaging. Here's the major organization's site: http://snm.Org/.