A bone scan uses radionuclides to create images of bones. Radionuclides are chemicals which emit radioactivity that can be detected by special scanners.
Note: the information below is a general guide only. The arrangements, and the way tests are performed, may vary between different hospitals. Always follow the instructions given by your doctor or local hospital.
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.
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.
This type of radionuclide bone scanning is also called bone scintigraphy. It is a totally different type of procedure to the DEXA bone scan which is used to measure density of bones in conditions such as 'thinning' of the bones (osteoporosis). (See separate leaflet called DEXA Scan for information about this other kind of bone scan.)
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 30 minutes or more. The number of pictures taken, and the time interval between each picture, vary depending on what is being scanned. For a whole body bone scan, you slide very slowly through the whole scanner and the picture is taken continuously.
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 breast-feeding, as special precautions may be necessary. You may also be asked to empty your bladder of urine before the scanning begins. You will be asked to drink plenty of water between the injection and the scan.
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 also passes out of your body through your urine over about 24 hours. You may be instructed to take special precautions after urinating, to flush the toilet twice and to wash your hands thoroughly.
You will be advised to drink plenty of water for a day after the scan to help flush the radionuclide out of your system.
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 a bone scan?
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.
Dr Rachel Hoad-Robson
Dr Mary Harding
Dr John Cox