A procedure used to find out if cancer has spread to the bone. A small amount of a radioactive substance called 18F-NaF is injected into a vein. A PET scan is then used to make detailed pictures of the bones. Bones with cancer in them take up more 18F-NaF than normal bones do. Also called 18F-sodium fluoride positron emission tomography and fluorine F 18-sodium fluoride PET.