False-colour scintigram (gamma camera scan) of the hands of a person with extensive rheumatoid arthritis affecting the wrists & fingers. Arthrit- ic joints appear as brighter areas; the right-side hand is particularly severely affected. The image records the distribution & intensity of gamma rays emitted by a tiny amount of a radioisotope inject- ed into the patient; the radioisotope concentrates in the joints. The gamma rays are detected by a scintillating material in which they generate small flashes of light; the flashes are amplified by photomultiplier tubes & processed into an image by a computer. Inflamed tissue around arthritic joints increases radioisotope concentration.