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A bone scan poses no greater risk than do conventional X-ray procedures. The tracers used in a bone scan produce very little radiation exposure — less than half that of a CT scan.

You don't need to restrict your diet or avoid particular activities in preparation for a bone scan. Immediately before the test, though, you may be asked to remove jewelry or other metal objects.

Bone scans aren't usually performed on pregnant women or nursing mothers because of concerns about radiation exposure to the baby. Tell your doctor if you're pregnant — or think you might be pregnant — or if you're nursing.

A bone scan is a nuclear imaging procedure. In nuclear imaging, tiny amounts of radioactive materials (tracers) are injected into a vein and taken up in varying amounts at different sites in the body.

Areas of the body where cells and tissues are repairing themselves most actively take up the largest amounts of tracer. Nuclear images highlight these areas, suggesting the presence of abnormalities associated with disease or injury.

A bone scan includes both an injection and the actual scan.

The injection

Tracers will be injected into a vein in your arm. The amount of time between the injection and scan varies, depending on the reason your doctor has ordered the scan.

Some images may be taken immediately after the injection. You will need to wait for two to four hours, however, before the main images are taken, to allow the tracer to circulate and be absorbed by your bones. Your doctor may recommend that you drink several glasses of water while you wait.

The scan

You'll be asked to lie still on a table while an armlike device supporting a tracer-sensitive camera passes back and forth over your body. The procedure is painless.

A scan of your entire skeleton usually takes less than 30 minutes. Scanning a limited area of your body takes less time.

Your doctor might order a three-phase bone scan, which includes a series of images taken at different times. A number of images are taken as the tracer is injected, then shortly after the injection, and again two to four hours later.

To better see some bones in your body, your doctor might order additional imaging called single-photon emission computerized tomography (SPECT). This imaging can help analyze conditions that are especially deep in your bone or in places that are difficult to see.

For a SPECT scan, the camera rotates around your body, taking images as it rotates. The additional SPECT images take about 35 minutes.

After the test

A bone scan generally has no side effects, and no follow-up care is needed. The radioactivity in the tracers is mostly removed from your body after one day and completely eliminated by two days.

A doctor who specializes in reading images (radiologist) will look for evidence of abnormal bone metabolism on the scans. These areas appear as darker "hot spots" and lighter "cold spots" where the tracers have or haven't accumulated.

Although a bone scan is very sensitive to abnormalities in bone metabolism, it's less helpful in determining the exact cause of the abnormality. If you have a bone scan that shows hot spots, more testing may be needed to determine the cause.