Your doctor may order a bone scan if you have unexplained skeletal pain suggesting bone loss, bone infection or a bone injury undetectable on a standard X-ray. A bone scan is also an important tool for detecting cancer that has spread (metastasized) to the bone from a tumor that started in a different organ, such as the breast or prostate. Similarly, a bone scan can detect some abnormalities related to leukemia and lymphoma.
Your doctor may order a bone scan to determine whether you have any bone abnormalities that may be related to one of the following symptoms and conditions:
- Paget’s disease of bone
- Cancer originating in bone
- Cancer that has spread (metastasized) to bone from a different primary site, such as the prostate, lung or breast
- Infection of the joints, joint replacements or bones (osteomyelitis)
- Fibrous dysplasia
- Avascular necrosis or impaired blood supply to bones
- Unexplained bone pain
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 mildly uncomfortable. The risk of an allergic reaction to the tracers is extremely rare.
How 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 usually performed on pregnant women because of concerns about radiation exposure to the fetus.
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 imaging 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 mostly removed after one day and completely eliminated by two days. You should feel no side effects after the procedure, and no aftercare is necessary.
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.