http://www.triumf.ca/welcome/petscan.html

What is PET?
The name "PET" comes from Positron Emission Tomography. It is a new scanning technique in medical research.

Each patient is given a minute amount of a radioactive pharmaceutical that closely resembles a natural substance used by the body. One example of such a pharmaceutical produced at TRIUMF is 2-fluoro-2-deoxy-D-glucose (FDG), which is similar to a naturally occurring sugar, glucose, with the addition of a radioactive fluorine atom. Gamma radiation produced from the positron-emitting fluorine is detected by the PET scanner and shows in fine detail the metabolism of glucose in the brain.

How does it feel to have a PET scan?
During a scan the patient reclines on a comfortable couch with his or her head inside the large, doughnut-shaped Positron Emission Tomograph. While the patient’s head must be kept very still, the only real discomfort involved may be the pinprick of a hypodermic needle as a minute amount of radiopharmaceutical is injected. The radiopharmaceutical could be administered as an intravenous injection or inhaled as a gas. How it is administered depends on the radiopharmaceutical. Which one is chosen depends on what function the scientist wants to study.

What does a PET scan show?
The brain function being studied during a PET scan determines which radiopharmaceutical is used. Oxygen-15 can be used to label oxygen gas for the study of oxygen metabolism, carbon monoxide for the study of blood volume, or water for the study of blood flow in the brain. Similarly, fluorine-18 is attached to a glucose molecule to produce FDG for use in the observation of the brain’s sugar metabolism. Many more PET radiopharmaceuticals exist, and research is under way to develop still more to assist in the exploration of the working human brain. For example, dopa, a chemical active in brain cells, is labelled with positron-emitting fluorine or carbon and applied in research on the communication between certain brain cells which are diseased, as in dystonia, Parkinson’s disease, or schizophrenia.

PET radioisotopes produced at TRIUMF
Labelling agent
        Half-life
carbon-11
        20.3 minutes
oxygen-15
        2.03 minutes
fluorine-18
        109.8 minutes
bromine-75
        98.0 minutes

How much radiation does a patient get?
PET scans using radioactive fluorine in FDG would result in patients receiving exposures comparable to (or less than) those from other medical procedures, such as the taking of X-rays. Other scanning agents - for instance, 6-F-dopa or radioactive water - normally cause even less exposure.