A bone scan is a test that uses nuclear imaging to help diagnose and track several types of bone disease. Nuclear imaging involves using small amounts of radioactive substances, called radioactive tracers, a special camera that can detect the radioactivity and a computer. These tools are used together 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 skeletal pain when the cause isn't clear. The source of pain may be a bone infection or a bone injury that doesn't show up on a standard X-ray.

A bone scan also can be an important tool for detecting cancer that has spread to the bone from the tumor's original location, such as the breast or prostate.

Although the test relies on radioactive tracers to create the images, these tracers produce little radiation exposure — less than a CT scan.

You usually don't need to restrict your diet or restrict activities before a bone scan. Tell your healthcare professional 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 people who are pregnant or nursing because of concerns about radiation exposure to the baby. Tell your healthcare professional if you are pregnant — or think you might be pregnant — or if you're nursing.

A bone scan procedure includes both an injection and the actual scan.

The injection

Tiny amounts of radioactive substances, called radioactive 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 racer from your body that's not absorbed.

The scan

You'll lie still on a table while an armlike device supporting a tracer-sensitive camera passes back and forth over your body. The scanning procedure can take up to an hour. The procedure is painless.

Your healthcare professional 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 healthcare professional might order extra imaging called single-photon emission computerized tomography (SPECT). This imaging can help with conditions that are especially deep in the 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 tracer is usually removed completely two days after the scan.

A specialist in reading images, called a radiologist, looks at the scans for evidence of bone metabolism that's not typical. These areas appear as darker "hot spots" and lighter "cold spots" where the tracers have or haven't collected.

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.