Scintigraphie au gallium

What is a gallium scan?

A gallium scan is a type of nuclear medicine, or radionuclide scan.

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.

Gallium tends to concentrate in areas of the body where there is rapid cell division. This is seen on pictures taken with the gamma camera. Where large amounts are seen, this can be a sign of infection, inflammation, injury or possible cancer. The image below shows how sarcïdose may be diagnosed by gallium scan.

Gallium scan image

© By A B Allard, J Buscombe, D P Kidd [CC BY-SA 4.0], via Wikimedia Commons

The test is normally done in two parts. In the first part you will receive an injection of the gallium citrate, usually into your arm. This may be a little uncomfortable as the needle is inserted but after that you will normally feel no effects. Usually, you can go home after the injection - to allow the gallium to work its way around your body.

The second part of the test involves coming back to hospital for the pictures to be taken (the scan). Depending on your hospital and the reason for doing the test, you may be asked to return for the scans to be done one day, two days, or three days after the injection.

When it is time to do the scanning, you lie on a couch while the gamma camera detects the gamma rays coming from your body. 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 camera does not produce any radiation, so you are not exposed to any additional radiation while the scan is being done.

The number of pictures taken, and the time interval between each picture, varies depending on what is being scanned. So, the whole process can take several hours. During the scan you are NOT enclosed in a tunnel.

You will not have to undress for the scan. You may be asked to remove metal objects such as keys or coins from your pockets. You may be asked to remove belts with buckles, or large necklaces.

A gallium scan can be used to:

• Detect the source of an infection that is causing a high temperature (fever), called a fever of unknown origin.

• Find an abscess or certain infections. This is particularly used to detect infection in the bones (osteomyelitis).

• Monitor the response to un traitement antibiotique.

• Diagnose inflammatory conditions such as fibrose pulmonaire ou sarcïdose - as image above.

• Detect certain types of cancer (such as lymphoma). A gallium scan also may be done to see if cancer has spread (metastasised) to other areas of the body, or to watch how well a cancer treatment is working. Nowadays gallium scans are used less to detect cancer. Positron-emission tomography (PET) scans are most commonly used for cancer.

Usually very little. Your local hospital should give you information to help you prepare for the test. As a gallium scan involves a small amount of radiation, pregnant women should not have it done. Let your doctor know if you are, or think you could be, pregnant. You should also let your doctor know if you are breastfeeding. You may be asked to stop breastfeeding for a certain length of time before and after the test.

If pictures of your tummy (abdomen) are needed, you may be given some laxative tablets before the scan. These tablets will make you go to the toilet. This helps to make the pictures clearer. If you need these tablets, you will be given them by hospital staff. You will also be given advice about when to take them.

Radionuclide scans such as a gallium scan 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 poo (faeces) during the first few hours or days following the test. You may be instructed to take special precautions when urinating. These may include flushing 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, your doctor may advise special precautions. Your hospital should give you more advice on this.

If you are travelling abroad in the three months after your scan, ask your doctor for further advice. Ports and airports have very sensitive radiation detectors which may pick up tiny amounts of radioactivity remaining after your scan. Usually, it is possible for your hospital to provide you with a letter that you can show to officials at ports or airports. Or you could take your appointment letter with you to show you have had this scan done.

The term 'radioactivity' may sound alarming. But, the radioactive chemicals used in radionuclide scans such as a gallium scan are considered to be safe. They start to leave the body in the urine during the first 24 hours and through the gut after that. Drink plenty to help your body remove the gallium. The half life of gallium is 78 hours and it is excreted relatively slowly from the body. The average retained dose is 65% after seven days, so it will take a few weeks to be removed from your body.

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 radiographie), il existe un faible risque que les rayons gamma puissent affecter un enfant à naître. Informez donc votre médecin si vous êtes enceinte ou si vous pourriez l'être.

• Rarement, certaines personnes ont une réaction allergique au produit chimique injecté.

The first part of the test involves an injection of a chemical called gallium citrate into the bloodstream. Gallium citrate behaves rather like iron and some of it attaches to proteins in your blood, particularly to the protein called transferrin. It then circulates around your body with your blood and begins to collect in different parts of your body. The gallium will naturally concentrate in areas where there is inflammation or where white blood cells have collected. It can take several days for the gallium to build up, which is why the second part of the scan is done a few days later.

Gallium emits gamma rays, a type of radioactive wave. 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, are converted into an electrical signal and are 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 ('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.