Bone scan: Using nuclear medicine to find bone abnormalities

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Bone scan: Using nuclear medicine to find bone abnormalities

Bone scans — Find bone disorders and hidden fractures.

When you think of bones, you may picture dry, brittle structures similar to what you'd find in a museum or what anthropologists find buried in the desert. But the bones inside your body are anything but static — they're alive and active, providing support for your body and serving as your body's warehouse for important minerals. Inside some of your bones is a soft core called bone marrow that manufactures blood cells.

The process of bone growth and renewal is part of your body's metabolism — natural processes that create and use energy. Changes in your bone metabolism can be caused by a number of problems. To get a picture of your bone metabolism, your doctor may use a procedure called a bone scan.

Your doctor may order a bone scan to help diagnose subtle or hidden bone fractures, such as a stress fracture, that may not show up on a routine X-ray. Bone scans can also help detect other conditions as well.

Who is a bone scan for?

Your doctor may order a bone scan to determine whether you have any bone abnormalities that may signify one of the following disorders:

  • Fractures
  • Arthritis
  • Paget's disease of bone
  • Bone tumors
  • Infection of the joints, joint replacements or bone (osteomyelitis)
  • Fibrous dysplasia
  • Avascular necrosis or impaired bone blood supply
  • Unexplained bone pain

Your doctor may order a bone scan to determine whether cancer, such as prostate, lung or breast cancer, has spread (metastasized) to bone.

How do you prepare for a bone scan?

No special preparation is required on your part before a bone scan, though you may be asked to remove jewelry or other metal objects. You can eat or drink anything you like before the test.

As with most tests, tell your doctor if you're pregnant or think you might be pregnant. Bone scans aren't usually performed on pregnant women because of concerns about radiation exposure to the fetus.

How is a bone scan done?

A bone scan falls under the category of nuclear medicine procedures, which means that it uses tiny amounts of radioactive materials called tracers (radionuclides). These tracers accumulate in certain organs and tissues, such as bones. Once introduced into the body, tracers emit a type of radiation called gamma waves, which are detected by a special camera. This camera produces images that are interpreted by radiologists or nuclear medicine specialists.

In a sense, a nuclear procedure such as a bone scan is the opposite of a standard X-ray examination. An X-ray passes radiation into or through your body to create an image on film placed on the other side of your body. In a nuclear scan, the source of radiation is inside your body and travels to the surface, where a camera detects it.

What can you expect during a bone scan?

A bone scan can be divided into two basic parts:

  • The injection. You will receive an injection of tracers into a vein in your arm, and depending on the reason your doctor orders the scan, images of the injection may be taken immediately. You'll then wait between two and four hours to allow the tracers to circulate and be absorbed by your bones. You may be allowed to leave the radiology department during this time. Your doctor will ask you to drink extra water to remove unabsorbed radioactive material from your system.
  • The scan. During the scan, you'll be asked to lie still on a table while a machine with an arm-like device supporting the gamma camera passes over your body to record the pattern of tracer absorption by your bones. This is painless. A scan of your entire skeleton takes as long as 60 minutes. Scanning a limited area of your body takes less time.

In some cases, 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 again shortly after the injection and three to four hours later.

For certain conditions your doctor might also order additional images called single-photon emission computerized tomography (SPECT). This can help analyze conditions that are especially deep in your bone or in places that are difficult to see with static or two-dimensional (planar) images. The additional SPECT images take approximately 30 minutes.

After the test
Once inside your body, the tracers don't remain active for long. The radioactivity is eliminated within two days. You should feel no side effects after the procedure, and no aftercare is necessary.

Results of a bone scan

The radiologist looks for evidence of abnormal bone metabolism on the scans. These show up 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. However, a thorough medical history often reveals the cause, such as a suspected fracture, infection or bone tumor. Other tests may be performed to help establish the diagnosis. For instance, in order to rule out bone cancer, your doctor may need further imaging studies (computerized tomography or magnetic resonance imaging) or a biopsy, which is a sample of bone tissue that's removed for examination.

Hot spots

Images of bone scans depicting hot spots

Scan A shows hot spots (dark areas) in both knees, a sign of arthritis in this case, and a possible fracture in the second toe of the right foot. Otherwise it shows normal bone metabolism. Scan B shows a number of hot spots, here a result of cancer that has spread to multiple locations.

Risks of a bone scan

A bone scan's sensitivity to variation in bone metabolism and its ability to scan the entire skeleton make it very helpful in diagnosing a wide range of bone disorders. The test poses no greater risk than do conventional X-ray procedures. The tracers used in a bone scan produce very little radiation exposure.

You might find the injection and the need to lie still during the scanning procedure are mildly uncomfortable. The risk of an allergic reaction to the tracers is extremely rare.

Last Updated: 12/14/2007
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