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Indium is a soft, silvery metal discovered in 1863 and named for the indigo light it emits when heated. Indium-111 is a synthetic radioisotope produced for medical imaging, with a half-life of about 2.8 days.
Indium-111 decays by electron capture, emitting gamma photons suited to SPECT imaging along with short-range Auger electrons. Its multi-day half-life is its key advantage, allowing it to follow slow biological processes, over the days needed to build a complete picture.
This long window has made indium-111 the isotope of choice for labelling white blood cells to locate hidden infection, and for imaging with antibodies and peptides.
Indium-111 is produced in a cyclotron by proton bombardment of enriched cadmium targets. It requires a relatively high-energy cyclotron and costly enriched target material, so supply rests with a limited number of producers.
StandardX is developing accelerator-based production to provide a more reliable and accessible supply of indium-111.