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Diagnostic tests

PET (Positron Emission Tomography)

Positron Emission Tomography (also called PET or PET imaging) is a diagnostic exam that shows metabolic activity of your brain. Positrons are tiny particles released from a radioactive substance administered to you.

Why the test is performed?

PET scans help to show what area of your brain may be the origin of seizures. They are used in patients who have not responded to medicine and may be candidates for epilepsy surgery.

How does the test work?

• PET measures how intensely different parts of your brain use up glucose, oxygen, or other substances.
• A small amount of a radioactive substance is injected into one of your veins.
• This substance attaches itself to glucose (sometimes ammonia or water) and is taken up by areas of your brain.
• Positrons are released from the tagged glucose, which is detected by the PET scanner. The images that result are helpful in diagnosing a variety of conditions and diseases, including epilepsy.
• The PET images show different colors or levels of brightness. The seizure area may appear darker in the brain tissue, however during a seizure it will temporarily collect more glucose than other brain tissue and will appear brighter.

What does the PET scanner look like?

The PET scanner looks like a large doughnut. Around the central hole of the machine are rings of detectors that record the emission of positrons. As you lie on a cushioned table, you will be moved into the central hole of the machine.

How should I prepare for the test?

• The test will take about 90 minutes.
• You should not eat for at least 6 hours before the PET scan.
• You will be encouraged to drink several glasses of water before the test.
• You should wear comfortable loose-fitting clothing.

What will I feel during the test?

• The PET scan itself will cause you no discomfort.
• You may feel a small pinprick when the radioactive substance is injected into one of your veins.
• You will be asked to lie in a cushioned examination table and to rest quietly and remain still during the exam. You will need to avoid significant movement or talking, because this may change where the attached glucose localizes in your brain.
• Some patients who are claustrophobic (afraid of closed-in spaces) may feel anxious while positioned in the PET scanner.
• Some patients may find it uncomfortable to hold one position for more than a few minutes.

What are the benefits and the risks?

• The PET exam allows your doctor to study your brain. It can show where your seizure starts and help determine if you are a candidate for surgery.
• The radioactivity is very short-lived, so your radiation exposure is low. The amount of the substance given to you is so small it does not affect the normal processes of the body.
• Pregnant and Nursing Women: The radioactive substance may expose the fetus or infants who are breast-feeding to radiation. The risk to the fetus or infant should be considered in relation to the potential information gained from the result of the PET examination. If you are pregnant or think you are pregnant, you should inform the PET imaging staff before the examination is performed.
• Potential side effects may be slight burning at the site of where the radioactive substance is injected.

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Please discuss with your doctor any questions or concerns you may have.