Bone scan of legs and feet. Coloured radionuclide bone scan (gamma scan) of a patient's lower legs and feet. This image was made with a gamma camera, which detects gamma rays emitted by a radioactive tracer that concentrates in bone. The tracer - a phosphate complex linked to the radioactive isotope technetium-99m - is injected into the body before the scan is taken. Bone scans are often used to screen cancer patients for evidence of secondary disease after they have received treatment for their primary cancers. Bone metastases (secondary bone cancers) absorb the tracer in greater amounts than normal bone and show up as hot spots on the image.