(… FLOOR-oh-MY-soh-NIH-duh-zole) A radioactive substance being studied as an imaging agent in head and neck cancer and other types of cancer. It binds to large molecules in cancer cells that have a low level of oxygen. Radiation given off by 18F-fluoromisonidazole is detected by a positron emission tomography (PET) scan. Knowing the amount of 18F-fluoromisonidazole in the cancer cells may help plan the best treatment and help predict whether the cancer will come back after treatment. Also called 18F-MISO, fluorine F 18-fluoromisonidazole, and FMISO.