Radioisotopes are radioactive elements that have a different number of neutrons than their more stable counterparts. The radioactive nature of some of these atoms have made them extremely useful in the field of nuclear medicine. The following is a list of some common radionuclides used for diagnostic and therapeutic purposes, along with the method by which they are produced, their half-lives, and a few of their medical uses.

Iodine-131 is produced in a nuclear reactor and has a half-life of about 8 days. It is used in the imaging of the thyroid and the treatment of some thyroid disorders.

Technitium-99m is the result of the slow decay of molybdenum-99. Nuclear medicine labs receive regular deliveries of molybdenum-99 encased in lead containers; when the technetium radionuclide is needed, it is washed out of the container with saline. Technitium-99m has a half-life of six hours and binds easily to other molecules, making it ideal for a wide variety of diagnostic purposes. This radiopharmaceutical is used to image such organs as the heart, bones, the lungs, and the liver.

Thallium-201 is produced in a cyclotron. Its half-life is 73 hours. The molecule's strong chemical resemblance to potassium makes it ideal for imaging myocardial perfusion.

In nuclear medicine, the terms radioisotope, radionuclide, radiopharmaceutical, and tracer are used interchangeably.