Positron Emission Tomography is a scanning technique which detects chemical and physiological changes related to metabolism. This procedure produces three-dimensional images of blood flow, chemical reactions and muscular activity in the body as they occur. It measures the intensity of the use (metabolization) of glucose, oxygen or other substances in the brain.
More active brain areas have increased blood flow and consume more oxygen, thus detecting over- or under- activity in the brain. This allows the neurologist to study the function of the brain. By measuring areas of blood flow and metabolism, the PET scan is used to locate the site from which a seizure originates.
The information provided by a PET scan is valuable in the diagnosis of seizure type and in the evaluation of a potential candidate for surgery. The PET scan tests brain metabolism, chemistry or blood flow by injecting a small amount of radioactive substance into the body. When this substance reaches the brain during the scan, a computer uses the recorded signals to create images of specific brain functions.
A functional image of brain activity is important because functional changes are often present before structural changes in tissues. PET images may therefore demonstrate pathological changes long before they would be evident by other scanning techniques.
The limitations of PET:
- The session cannot last very long because it requires the injection of radioactive material.
- It takes time for active brain cells to absorb the radioactive material takes time to be absorbed. The scan images change too slowly to capture fast-changing brain events.
Before a PET Scan
- Your child should not eat or drink anything four to six hours prior to the exam.
- Dress your child in comfortable clothing.
- Your child should take all prescribed medication(s) as usual unless instructed otherwise by the physician.
During a PET Scan
- Before the scan, your child will either inhale or receive an injection of a small amount of radioactive tracer. The tracer is a compound such as sugar “labelled” with a short-lived radioisotope.
- Following the injection, your child will rest for approximately 30 to 45 minutes while the substance reaches the brain.
- The technologist will place your child on a scanner table.
- Your child will place his/her head in a special headrest. This immobilizes the head using foam blocks or a special mould shaped for your child.
- It is important for your child to lie completely still.
- The scanner table will slowly pass through the PET scanner. Your child’s head will be inside the large, doughnut-shaped machine. The scanner detects the radioactive material to produce a computer image of your child’s brain.
- Scanning time is approximately one to two hours.
After a PET Scan
- There are no after effects from the injection or the PET imaging.
- Your child can resume normal activity immediately after the PET scan is completed.
- A radiologist or nuclear medicine technologist will review the PET scan and report to your child’s physician. The physician will then make a follow-up appointment to discuss the results with you.
- Nuclear Medicine Technologist
- operates cameras which detect and map the radioactive tracer in the patient’s body to create an image on the computer monitor
- explains test procedures to patients
- prepares the radiopharmaceutical and administer it orally or through injection
- interpret the results.
- Pregnant women should not undergo a PET Scan because of the radioactive isotopes used.
- If your child is or may be pregnant, inform your doctor.
Clarke Institute of Psychiatry, Toronto, Ontario
Research grants to the institute cover the cost of the test.
McMaster-Chedoke Hospital, Hamilton, Ontario
The hospital covers the cost of the test.
Montreal Neurological Institute and Hospital, Montreal, Quebec
You must pay $700 for the test, but the Ontario Health Insurance Plan (OHIP) will fully reimburse you.
University of British Columbia, Vancouver, British Columbia
604-822-2211 (general directory)
Epilepsy Foundation (of America) – for locations in the United States
You must pay approximately US$1700 for the test, which insurance does not cover.