Nuclear medicine is a division of medicine and medical imaging that uses the nuclear properties of substance in diagnosis and therapy. Many procedures in nuclear medicine use radionuclide, or pharmaceuticals that have been labeled with radionuclide (radiopharmaceuticals). In diagnosis, radioactive substances are administered to patients and the radiation emitted is calculated. The bulk of these diagnostic tests involve the configuration of an image using a gamma camera. Imaging may also be referred to as radionuclide imaging or nuclear scintigraphy. Other diagnostic tests use probes to obtain measurements from parts of the body, or counters for the measurement of samples taken from the patient. In therapy, radionuclides are administered to luxury disease or provide palliative pain relief. For instance, administration of Iodine-131 is often used for the action of thyrotoxicosis and thyroid cancer.

Nuclear medicine imaging tests vary from most other imaging modalities in that the tests mainly show the physiological function of the system being investigated as divergent to the anatomy. In several centers, the nuclear medicine images can be superimposed on images from modalities such as CT or MRI to highlight which division of the body the radiopharmaceutical is concentrated in. This practice is frequently referred to as image fusion.

Nuclear medicine diagnostic tests are typically provided by a dedicated department within a hospital and may include services for the preparation of radiopharmaceuticals. The exact name of a department can differ from hospital to hospital, with the most ordinary names being the nuclear medicine department and the radioisotope department.

The end effect of the nuclear medicine imaging process is a "dataset" comprising one or additional images. In multi-image datasets the array of images may symbolize a time sequence (i.e. cine or movie) often called a "dynamic" dataset, a cardiac gated time sequence, or a spatial series where the gamma-camera is moved qualified to the patient. SPECT (single photon release computed tomography) is the procedure by which images acquired from a rotating gamma-camera are reconstructed to create an image of a "slice" through the patient at an exacting position. A compilation of parallel slices form a slice-stack, a three-dimensional symbol of the distribution of radionuclide in the patient.