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Bone scan: Using nuclear medicine to find bone abnormalities
From MayoClinic.com
Special to CNN.com

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.

This 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 specific problems. To get a picture of your bone metabolism, your doctor may use a procedure called a bone scan.

What is a bone scan?

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

  • Bone cancer
  • Bone infections
  • Arthritis
  • Causes of unexplained bone pain

A bone scan falls under the category of nuclear medicine, 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 gamma waves of radiation, 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.

When is a bone scan ordered?

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 bone (osteomyelitis)
  • Osteomalacia or rickets
  • Fibrous dysplasia
  • Avascular necrosis
  • Unexplained pain

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

How do you prepare?

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 performed on pregnant women because of concerns about radiation exposure to the fetus.

How is a bone scan done?

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. You'll then wait about two to four hours to allow the tracers to circulate and be absorbed by your bones. You may be allowed to leave the health care facility during this time. Your doctor will ask you to drink several glasses of water so you'll urinate frequently to remove unabsorbed radioactive material from your system.
  • The scan. During the scan, you'll be asked to lie very 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 about 30 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 two to four hours later.

For certain conditions your doctor might order a single photon emission computerized tomography (SPECT) scan. This can help analyze conditions that are especially deep in your bone or in places that are difficult to see. A SPECT scan takes about 45 minutes to an hour.

After the test

Once inside your body, the tracers don't remain active for long. The radioactivity disappears within one to three days.

You should feel no side effects after the procedure, and no aftercare is necessary. If you're breast-feeding, your doctor might ask you to stop for 24 hours after the tracer injection.

Results

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 cause of the abnormality, such as a fracture, infection or bone tumor. Other tests are often performed to help establish the diagnosis. In order to rule out bone cancer, for instance, your doctor may need further imaging studies or a biopsy, which is a sample of bone tissue that's removed for examination.

Pros and cons

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 conventional X-ray procedures. The tracers used in a bone scan produce very little radiation.

You might find the injection and the need to lie still during the scanning procedure unpleasant. Your risk of an allergic reaction to the tracers is rare.

December 14, 2005

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