A bone scan is a test that uses nuclear imaging to helps diagnose and track several types of bone disease. Nuclear imaging involves using small amounts of radioactive substances (radiotracers), a special camera that can detect the radioactivity and a computer to see structures such as bones inside the body.
The tracer is absorbed more by cells and tissues that are changing. As a result, a bone scan can be used to find the source of unexplained skeletal pain, a bone infection or a bone injury that can't be seen on a standard X-ray.
A bone scan can also be an important tool for detecting cancer that has spread (metastasized) to the bone from the tumor's original location, such as the breast or prostate.
Why it's done
Scan A shows hot spots (dark areas) in both knees, a sign of arthritis, and a possible fracture in the second toe of the right foot. Otherwise, it shows typical bone metabolism. Scan B shows numerous bone hot spots, a result of cancer that has spread to multiple locations.
A bone scan might help determine the cause of unexplained bone pain. The test is sensitive to differences in bone metabolism, which are highlighted in the body by the radioactive tracer. Scanning the whole skeleton helps in diagnosing a wide range of bone disorders, including:
- Paget's disease of bone
- Cancer originating in bone
- Cancer that has metastasized to bone from a different site
- Infection of the joints, joint replacements or bones
Although the test relies on radioactive tracers to produce the images, these tracers produce little radiation exposure — less than a CT scan.
How you prepare
You typically don't need to restrict your diet or restrict activities before a bone scan. Let your health care provider know if you've taken a medicine containing bismuth, such as Pepto-Bismol, or if you've had an X-ray test using barium contrast material within the past four days. Barium and bismuth can interfere with bone scan results.
Wear loose clothing and leave jewelry at home. You might be asked to wear a gown for the scan.
Bone scans aren't usually performed on pregnant women or nursing mothers because of concerns about radiation exposure to the baby. Tell your health care provider if you're pregnant — or think you might be pregnant — or if you're nursing.
What you can expect
A bone scan procedure includes both an injection and the actual scan.
Tiny amounts of radioactive materials (tracers) are injected into a vein in the hand or arm. The amount of time between the injection and scan varies, depending on the reason for the scan.
Some images might be taken immediately after the injection. But the main images are taken 2 to 4 hours later to allow the tracer to circulate and be absorbed by your bones. You might be asked to drink several glasses of water while you wait.
You'll likely be asked to empty your bladder before the scan to remove the unabsorbed tracer from your body.
You'll lie still on a table while an armlike device supporting a tracer-sensitive camera passes back and forth over your body. The scan itself can take up to an hour. The procedure is painless.
Your health care provider 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 3 to 5 hours after the injection.
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 with conditions that are especially deep in your bone or in places that are difficult to see. During a SPECT scan, the camera takes images as it rotates around your body.
After the test
A bone scan generally has no side effects, and no follow-up care is needed. You might be asked to drink a lot of water for the next day or two to flush the tracer from your system. The radioactivity from the tracers is usually completely eliminated two days after the scan.
A specialist in reading images (radiologist) looks for evidence of unusual 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 sensitive to differences in bone metabolism, it's less helpful in determining the cause of the differences. If you have a bone scan that shows hot spots, you might need more tests to determine the cause.