 Single photon absorptiometry

Single photon absorptiometry (SPA) is a nuclear medicine technique used to measure the density of various substances within a material, most commonly bone mineral density (BMD). The technique is based on the principle of photon absorption, where a single photon emitted from a radioactive source is absorbed by the material being studied. In the context of bone density measurement, a radioactive source typically emits gamma rays, and the amount of radiation that passes through the bone is measured.