What is Positron Emission
developed in the mid- 1970s, and it was the first scanning method
to give functional information about the brain. PET measures the
emission of positrons from the brain after a small amount of radioactive
isotopes, or tracers, have been injected into the blood stream.
A common example is a glucose-relative with embedded fluor-18.
With this molecule, the activity of different regions of the brain can
be measured. The result is a three-dimentional map with the brain
activity represented by colors.
This technique has proven extremely useful in finding out just how we think, and it is used in research on brain functioning. However, the half-lives of the isotopes used are very short, meaning that on-site production is required. This can be done by the help of physicists and a cyclotron, but few institutions can afford these facilities. There are therefore not more than 100 or so PET laboratories around the world.
The major advantage of PET is that it can show changes that occur fairly quickly, on the order of seconds. The isotopes used can also be embedded in certain substances in order to measure the uptake of that part in different regions of the brain. This way, specific binding of neurotransmitters can be mapped out.
situations which a PET scan can help diagnose are:
To prepare for a PET scan, a patient should eat a light meal the evening before. No food or drink should be ingested on the morning of the scan. Depending on the medical reason for the scan, other preparations may also be needed. During the procedure, a small amount of radioactive material will be injected into one of the patient's veins. The patient will then be asked to lie down on a table that slides into the PET machine so that pictures of the brain can be taken. There is no real risk involved with the radioactivity of the isotope. However, there is a possiblity an individual will show allergic reactions to the substances injected. A patient with known allergies should discuss this with a doctor before undergoing the PET scan.
What is Single Photon-Emission