Nuclear medicine imaging shows not only the anatomy of an organ or body part, but the function of the organ, as well. This functional information can show if the organ is working properly. This is due to the fact that the radionuclides (low-level radioactive chemicals used in nuclear medicine studies) are absorbed by or taken up at varying rates (or in different concentrations) by different tissue types.
While nuclear medicine images may show less detail than other types of imaging, the functional information they provide can be valuable (and in some cases, may not be available from other types of imaging). A diseased or poorly functioning tissue will emit a different signal than healthy tissue, thus giving the physician an indication of how the tissue or organ is functioning. So the functional image of the bone may show the disease sooner than the anatomic image provided by an X-ray or CT scan.