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This is the image that a PET scan produces- each COLOR indicates a different level of activity in that area of the brain. Positron Emmission Tomography (PET) was the first scanning method to show the brain as it actually worked. 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. 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. With this test, 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 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 shows changes that occur quickly, 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.
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