Nuclear medicine imaging is a multi-disciplinary speciality that develops and uses instrumentation (positron emission tomography, single-photon emission computed tomography) and radiopharmaceuticals to investigate physiological processes.  It also can be used to diagnose and treat diseases non-invasively.  A radiopharmaceutical is either a radionuclide such as iodine-131 or a radionuclide that is attached to a carrier molecule (e.g. drug) or particle.  The radiopharmaceutical can be introduced into the human body by injection, swallowing or inhalation and accumulates in the organ or tissue of interest.  In a nuclear medicine scan, a radiopharmaceutical is administered to the patient, and an imaging instrument that detects radiation is used to show biochemical changes in the body. Nuclear medicine imaging provides valuable quantitative functional information about the status of healthy or disease tissues in the body.  This is in contrast to other imaging techniques that primarily show anatomy, for example, conventional ultrasound, magnetic resonance imaging (MRI) or computed tomography (CT).  However, for cancer treatment, a highly targeted radiopharmaceutical can be used to deposit lethal radiation at the tumour site.