Radionuclides are naturally occurring or artificially produced atoms with unstable nuclei. Therefore radionuclides undergo a radioactive decay, and emit gamma ray(s) and/or subatomic particles.
Radionuclides are used as agents in nuclear medicine and to destroy tumors in cancer therapy.

See Isotope and Radioactive Decay.

Whole body scintigraphy is the measurement of radioactivity in the entire body.
Whole body scintigraphy is useful for example in detection of tumors, infections, evaluation of metastases, and diseases with multiple organ involvement.
Different whole body scan techniques include: