Iodine-123 (123I) is a radioactive isotope of iodine used in nuclear medicine imaging, including single photon emission computed tomography (SPECT).

Iodine-123 is produced in a cyclotron by proton irradiation of enriched xenon. Its half-life is 13.22 hours; the decay emits gamma radiation with predominant energies of 159 keV and 27 keV. In medical applications this radiation can be detected by a gamma camera.

Medical applications

Iodine-123 is supplied as a solution of sodium iodide. This is administered to a patient by intravenous injection or as a drink1. The iodine is taken up by the thyroid gland and a gamma camera is used to form functional images of the thyroid for diagnosis. Quantitative measurements of the thyroid can be performed to calculate the iodine uptake for the diagnosis of hypothyroidism.

Iodine-123 is also used as a label in other radiopharmaceuticals e.g.metaiodobenzylguanidine (MIBG).

See also

* Isotopes of iodine


1. Sharp PF, Gemmell HG, Smith FW (eds). Practical nuclear medicine 2nd edition. 1998 Oxford University Press.

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