Knochenszintigraphie

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.

Der Computer erstellt ein Bild, indem er die unterschiedlichen Intensitäten der ausgesandten Radioaktivität in verschiedene Farben oder Graustufen umwandelt. Zum Beispiel können Bereiche des Zielorgans oder -gewebes, die viele Gammastrahlen aussenden, als rote Flecken ('heiße Stellen') auf dem Bild auf dem Computerbildschirm angezeigt werden.

Bereiche mit niedrigen Gamma-Strahlungswerten können als Blau ('kalte Stellen') dargestellt werden. Verschiedene andere Farben können für die Zwischenstufen der ausgestrahlten Gamma-Strahlen verwendet werden.

How long does a bone scan usually take?

In total, you should allow about four to six hours for everything required for the scan.

An injection of radionucleotides is given via a drip (cannula) into your vein. This takes about 2 to 4 hours to circulate around the body. Sometimes, a few scans might be taken straightaway. You will have the main part of the bone scan after a waiting period of a few hours.
Once enough time has passed, you'll have the main scan. This can take between 30 minutes and 1.5 hours; the radiographers doing the scan will be able to tell you how long to expect.

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 amount 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.

• It takes about 24 hours for the radionucleotide to leave your body completely. The risk to other people is very, very low (and might even be zero), but, as a precaution, you'll often be advised to avoid prolonged close contact with children or pregnant women for 24 hours.

• Rarely, some people have had allergic reactions to the injected chemical. Tell your doctor if you are allergic to iodine.

• Theoretisch ist es möglich, eine Überdosis zu erhalten, wenn die Substanz injiziert wird. Das ist sehr selten.

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:

• Krebs that has spread to the bones.

• Infection of the bone, including infections around joint replacements.

• Broken bones that can't be seen on other tests.

• Bone damage.

• Other causes of unexplained bone pain.

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 'Ausdünnung' der Knochen (Osteoporose). (See the separate leaflet called DEXA Scan for information about this other kind of bone scan.)

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. You may also be asked to empty your bladder of urine before the scanning begins. You will be asked to drink several glasses of water between the injection and the scan.

When you arrive, a radiographer (a specially trained person who operates the radiology machines to get the scan images) will explain what will happen, and will ask you to sign a consent form to indicate that you understand and agree to go ahead. You can, and should, ask any questions you have about the procedure at this point.

The injection

In a bone scan a small amount of a radioactive substance (radionuclide tracer) is injected into a vein in your arm. It then takes some time after injection of the tracer - 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.

The scan

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 move slowly through the whole scanner and the picture is taken continuously.

After the 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.