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PET Scanning

A type of radionuclide scanning that creates an image based on the function of individual cells within an organ or tissue

Positron emission tomography (PET) scanning is a special form of radionuclide scanning. The technique was originally used as a research tool in the 1970s but is now also used for medical imaging. Unlike certain other techniques, such as CT scanning, PET does not produce good structural images; instead, it gives information about the chemical activity of tissues or organs. It can also be used to assess blood flow.

How does it work?

By measuring the uptake by a tissue or organ of certain molecules, such as glucose or oxygen, doctors can assess how well an organ is functioning. The molecules that are to be taken up by the tissue or organ are labelled with a radioactive substance (radionuclide) before being introduced into the body.

PET uses radionuclides that emit particles called positrons. The radiation that these particles generate is detected by a PET scanner. The number of positrons emitted by an area of tissue or an organ indicates how much radionuclide it has taken up and therefore how chemically active that region is. A PET scanner is a doughnut-shaped machine incorporating detectors that pick up radiation all around the patient. The technique produces cross-sectional images that can be colour coded according to the concentration of radioactivity.

PET scan of brain

This normal PET scan shows high activity on the outside of the brain, the grey matter, and lower activity deeper inside.

What is it used for?

PET is mainly used to study the brain and the heart. The radionuclides used in PET can label the molecules related to blood flow as well as those involved in chemical activity. Consequently, PET can show areas of decreased blood flow while also establishing whether the cells in the area being studied are still chemically active and capable of recovery or whether they are dead. PET scanning is sometimes used to locate the origin of epileptic activity (see Epilepsy) in the brain and to investigate brain function in certain other neurological conditions, such as Alzheimer’s disease. PET may also be used to detect tumours because the level of chemical activity in abnormal tissue is higher than that in healthy tissue.

What are the risks?

Like in other radiation-based imaging techniques, PET scanning carries a risk of cell damage that may lead to cancer later in life. However, radionuclides are used in small amounts and rapidly break down into harmless elements.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

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