A procedure used to find out if cancer has spread to the bone. A small amount of a radioactive substance called fluorine F 18 sodium fluoride 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 fluorine F18 sodium fluoride than normal bones do. Also called F-18 NaF PET and fluorine F 18 sodium fluoride PET.