Nuclear medicine is a specialty which utilizes radioactive drugs to diagnose and treat disease. Images of the patient after the administration of radioactive tracers is done to evaluate many conditions. The bone scan may be done to diagnose metastatic disease, fractures, infections, etc. PET scans are utilized to evaluate cases of lymphoma, non-small cell bronchogenic carcinoma, melanoma, recurrent colorectal carcinoma, and head and neck cancer, etc. The hepatobiliary scan is usually done to evaluate the gall bladder but can diagnose other conditions as well. There are many types of renal scans to help diagnose diseases of the kidneys such as infection and obstruction. Cardiac studies may be done to detect the presence of scar or ischemia of the heart or abnormal wall motion. Other nuclear medicine studies include calculating the rate of gastric emptying and finding the site of occult infection. The most common condition treated is hyperthyroidism, associated with Graves disease, for which an oral dose of radioactive iodine may be given, if indicated. Some other forms of hyperthyroidism may also be treated this way. Some thyroid cancers can also be treated. There are many other indications for nuclear medicine studies. The radiation exposure a patient receives from most nuclear medicine procedures is less than that of one chest x-ray.