Bone Scan

Alternative Names:Scintigraphy – bone

Definition:
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 order a procedure called a bone scan. A radiologist will look for evidence of abnormal metabolism on images from your bone scan.

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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. It is a test that detects areas of increased or decreased bone metabolism (turnover). The test is performed to identify abnormal processes involving the bone such as tumor, infection, or fracture.
…...Nuclear Scan->
This is a nuclear scan, also called a radionuclide scan. In a bone scan, a radioactive tracer accumulates in places in your bones with a lot of repair activity. In this way, the tracer is used to identify areas that might be injured due to a fracture, bone infection, arthritis, or invading cancer. The tracer gives off gamma rays, which can be detected using a specialized camera. The camera relays information to a computer to produce images of the bones being scanned. In the images, bright spots appear in the areas where the tracer has collected. Bone scans are most frequently done for people with cancer to see if the cancer has spread to bones.

Why Bone Scan is Done:
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 the Test is Performed
A radiotracer (a bone-seeking radioactive material) is injected into vein, so it travels through the bloodstream. As the material wears away, it gives off radiation. This radiation is detected by a camera that slowly scans your body. The camera takes pictures of how much radiotracer collects in the bones.

If a bone scan is done to see if you have a bone infection, images will be taken shortly after the radioactive material is injected, as well as 3 to 4 hours later, when it has collected in the bones. This is called a 3-phase bone scan.

To evaluate metastatic bone disease, images are taken only after the 3 to 4 hour delay.

The scanning part of the test will last about 1 hour and may require you to change positions.

How do you prepare for the test?
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. You may be asked to wear a hospital gown.

What happens when the test is performed?
The test is performed in the radiology department of a hospital. You will be given a radionuclide. A machine with a specialized camera moves around you. The procedure is painless, but the machine can be noisy. The scan usually takes less than an hour.

There is a small amount of pain when the needle is inserted. During the scan there is no pain. You must remain still during the examination, and you will be instructed when to change positions by the technologist.

You may experience some discomfort due to lying still for a prolonged period of time.

Risk Factor.
The radioactivity you are exposed to is too small to cause side effects or complications except to a fetus. The small amount of radioactivity rapidly diminishes.If you are pregnant or nursing, the test may be postponed to prevent exposing the fetus to radiation.

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The amount of radioactivity in the injection is very small, and virtually all activity is gone from the body within 2-3 days.

Although it is extremely rare with bone scanning agents, a person may develop rash, swelling, or anaphylaxis (severe allergic response).

There is a slight risk of infection or bleeding with any intravenous injection. The risk of an allergic reaction to the tracers is extremely rare.

You might find the injection and the need to lie still during the scanning procedure mildly uncomfortable.

Must you do anything special after the test is over?
Nothing.

How long is it before the result of the test is known?
Results are usually available within a few days.

What you can expect
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.

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 shortly after the injection, and again 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:
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.
Normal Results
Normal distribution areas appear uniform and gray throughout all the bones in your body.

What Abnormal Results Mean
The images should show that the radioactive material has been evenly distributed throughout the body. There should be no

areas of increased or decreased distribution. “Hot spots” are areas where there is an increased accumulation of the radioactive material. “Cold spots” are areas that have taken up less of the radioactive material.

Resources:
https://www.health.harvard.edu/diagnostic-tests/bone-scan.htm
http://www.mayoclinic.com/health/bone-scan/
http://www.nlm.nih.gov/medlineplus/ency/article/003833.htm

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