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Changes in bone metabolism may be a sign of several disorders. A bone scan is a nuclear medicine procedure that creates a picture of the metabolism of the bones.
Nuclear medicine uses small amounts of radioactive materials called tracers (radionuclides). These tracers collect in some organs and tissues, including bones. Once they have been absorbed by the body, the tracers emit radiation waves that are detected by a special gamma camera and used to create images.
A bone scan is the opposite of a standard X-ray in the way that it creates an image. During an X-ray, radiation is sent through the body to create an image on film placed behind the body. In a nuclear bone scan, the body is emitting the radiation to the surface, where it can be detected by the gamma camera.
A bone scan is useful for diagnosing:
- Bone cancer or other tumors
- Bone infections (osteomyelitis)
- Subtle or hidden bone fractures that do not show up on an X-ray, such as stress fractures
- Bone disorders, such as osteomalacia (rickets), fibrous dysplasia, avascular necrosis, arthritis or Paget's disease
- The cause of unexplained bone pain
- Prostate, lung, breast or other cancer that has spread to the bone (metastatic disease)
Before you have a bone scan, you will need to remove jewelry or other metal objects. If you are or think you may be pregnant, be sure to tell your doctor and the technician before the scan. Bone scans are done on pregnant women to avoid radiation exposure to the fetus.
To start the bone scan, tracers are injected into a vein in your arm. It takes two to four hours for the tracers to circulate and be absorbed by your bones. During this time, you may be able to leave the Medical Center while you're waiting. You will be asked to drink as much water as possible so that unabsorbed radioactive material will be eliminated from your body in your urine. The radioactivity needed for the bone scan disappears in one to three days. If you are breastfeeding, your doctor may ask you to stop for 24 hours after you have been given the tracers.
During the scan itself, you lie still on a table while a machine with an arm holding the gamma camera passes over your body and records the pattern of radiation waves being emitted by your body. You will not feel anything during the scan. A scan of your entire skeleton takes about 30 minutes; scans of smaller areas of your body can take from 20 to 45 minutes. In some cases, your doctor might order that a series of images be taken at different times - as the tracer is injected, again after the tracer is circulating in your body and finally two to four hours later.
Abnormalities in the bone metabolism show up on the scans as darker "hot spots" and lighter "cold spots" depending on where the tracers have collected. A bone scan is less helpful in showing what caused the abnormality, so other tests may be recommended by your doctor to address these questions.
A bone scan has no greater risk than conventional X-ray procedures. The tracers used in a bone scan produce very little radiation.