Bone Scan

How does a bone scan work?

Bone scans use radionuclides to detect areas of the bone which are growing or being repaired. A radionuclide (sometimes called a radioisotope or isotope) is a chemical which emits a type of radioactivity called gamma rays. A tiny amount of radionuclide is put into the body, usually by an injection into a vein. (Sometimes it is breathed in or swallowed, depending on the test.)

There are different types of radionuclides. Different ones tend to collect or concentrate in different organs or tissues. So, the radionuclide used depends on which part of the body is to be scanned.

Cells which are most 'active' in the target tissue or organ will take up more of the radionuclide. So, active parts of the tissue will emit more gamma rays than less active or inactive parts.

Gamma rays are similar to X-rays and are detected by a device called a gamma camera. The gamma rays which are emitted from inside the body are detected by the gamma camera. The rays are then converted into an electrical signal and sent to a computer. The computer builds a picture by converting the differing intensities of radioactivity emitted into different colours or shades of grey. For example, areas of the target organ or tissue which emit lots of gamma rays may be shown as red spots ('hot spots') on the picture on the computer monitor. Areas which emit low levels of gamma rays may be shown as blue ('cold spots'). Various other colours may be used for 'in between' levels of gamma rays emitted.

What is a bone scan used for?

In a bone scan, a radionuclide is used which collects in areas where there is a lot of bone activity (where bone cells are breaking down or repairing parts of the bone). So a bone scan is used to detect areas of bone where there is cancer, infection, or damage. These areas of activity are seen as 'hot spots' on the scan picture.

What happens during a bone scan?

In a bone scan a small quantity of radionuclide is injected into a vein in your arm. It then takes some time - sometimes several hours - for the radionuclide to travel to the target tissue, and to be 'taken' into the active cells. So, after receiving the radionuclide you may have a wait of a few hours. You may be able to go out and come back to the scanning room later in the day.

When it is time to do the scanning, you will need to lie on a couch while the gamma camera detects the gamma rays coming from your body, and the computer turns the information into a picture. You need to lie as still as possible whilst each picture is taken (so it is not blurred). Some pictures can take 20 minutes or more to expose. The number of pictures taken, and the time interval between each picture, varies depending on what is being scanned. Sometimes only one picture is needed. However, for bone scans, two or more pictures are usually needed. Each picture may be taken several hours apart. So, the whole process can take several hours.

What preparation do I need

Usually very little. Your hospital should provide you with information regarding any special arrangements. This test should not be carried out in pregnant women. You should advise your doctor if you are pregnant or, if you think you may be pregnant. You should also inform your hospital if you are breastfeeding, as special precautions may be necessary. For some types of scan you may also be asked to empty your bladder of urine before the scanning begins.

What should I expect after a bone scan?

Bone scans do not generally cause any after effects. Through the natural process of radioactive decay, the small amount of radioactive chemical in your body will lose its radioactivity over time. It may also pass out of your body through your urine or stool (faeces) during the first few hours or days following the test. You may be instructed to take special precautions after urinating, to flush the toilet twice and to wash your hands thoroughly.

If you have contact with children or pregnant women you should let your doctor know. Although the levels of radiation used in the scan are small they may advise special precautions. Your hospital should give you more advice on this.

Are there any risks with radioisotope scans

The term 'radioactivity' may sound alarming. But, the radioactive chemicals used in radionuclide scans are considered to be safe, and they leave the body quickly in the urine. The dose of radiation that your body receives is very small. In many cases, the level of radiation involved is not much different to a series of a few normal X-rays. However:

• As with any other types of radiation (such as X-ray), there is a small risk that the gamma rays may affect an unborn child. So, tell your doctor if you are pregnant or if you may be pregnant.
• Rarely, some people have an allergic reaction to the injected chemical. Tell your doctor if you are allergic to iodine.
• Theoretically, it is possible to receive an overdose when the chemical is injected. This is very rare.