While antimatter might sound like science fiction, it's very real – and very useful. To image tissue and organs with a positron emission tomography (PET) scan, radioactive isotopes are attached to a material, like sugar, which gathers in cells that use more energy, such as cancer cells. The isotopes decay, producing positrons – the antimatter partner of electrons. When the positrons encounter electrons, they annihilate and produce radiation that can be imaged.