Nuclear medicine uses small amounts of radioactive pharmaceuticals (radiopharmaceuticals) to diagnose or treat benign and malignant disease. Radiopharmaceuticals may be administered to patients by injection into a vein or skin, ingested in tablet or liquid form, or by inhalation. After administration, the radiopharmaceutical accumulates in the tissue or organ under investigation.

In diagnostic nuclear medicine imaging, the radiation emitted from the patient's body after the administration of a radiopharmaceutical is detected by a Gamma camera. It produces an image by looking at the pattern of radiopharmaceutical absorption in the body. Nuclear medicine imaging is unique because it provides clinicians with information about both structure and function. Diagnostic nuclear medicine images often identify abnormalities at a very early stage of disease, sometimes before other types of diagnostic tests.

Positron Emission Tomography (PET) uses short-lived radiopharmaceuticals to image cells that are more metabolically active than normal. PET-CT is most commonly used to diagnose or stage cancer and to show response to treatment. Cancer cells metabolise glucose about ten times faster than normal cells so they can be identified, even in low concentrations. PET images are often combined with CT images - both scans are taken at the same time - to give accurate localisation of increased cell metabolism. Combining PET and CT images allows clinicians to give a more accurate diagnosis than using PET or CT images alone.

In nuclear medicine therapy, radiopharmaceuticals that emit beta particles are often used because they are absorbed locally within the target tissue or organ. Nuclear medicine therapies are used to treat a range of cancers and some non-cancerous conditions. After some nuclear medicine treatments, patients are required to follow a few simple precautions to restrict the radiation exposure given to their family and friends. Advice is tailored to each individual patient and is provided by the hospital staff who administer the treatment.