Positron Emission Tomatography. A non-invasive means of seeing into the body.

A radioactive dye is injected into your veins. You are placed on a bed and you are slowly moved through a large machine that looks like two huge donuts. The procedure is painless, except for the small needle prick of course. It generally takes 30-45 minutes. The dye congregates in areas of high cellular activity such as in a cancerous tumor. This then shows up as an image on the scan. Its effectiveness has been debated as sometimes it will show false positives as there are other things that also result in high levels of cellular activity.

It is called a PET scan. It's nearly indistinguishable to the patient from an MRI, except that you may be injected with a low-level radioactive isotope solution. The full term is Positron Emission Tomography. The short answer is that a PET scan can pick up real-time brain activity by reading glucose metabolization withing the brain. This will show brain activity deficits. It can also identify anomalous "hot spots" that show runaway cellular growth indicative of tumors. It is also used to examine other parts of the body. Here is the long answer: Positron Emission Tomography: PET. A highly specialized imaging technique that uses short-lived radioactive substances to produce three-dimensional colored images of those substances functioning within the body. These images are called PET scans and the technique is termed PET scanning. PET scanning provides information about the body's chemistry not available through other procedures. Unlike CT (computerized tomography) or MRI (magnetic resonance imaging), techniques that look at anatomy or body form, PET studies metabolic activity or body function. PET has been used primarily in cardiology, neurology, and oncology. The PET scan has been used to assess the benefit of coronary artery bypass surgery, identify causes of childhood seizures and adult dementia, and detect and grade tumors. It is very sensitive in picking up active tumor tissue but does not measure the size of it. In PET the patient receives a short half-lived radiopharmaceutical (produced by a cyclotron or a generator). Because the radioisotope used in a PET scan is short-lived, the amount of radiation exposure the patient receives is about the same as two chest X-rays. The radiopharmaceuticals discharge positrons from wherever they are used in the body. As the positrons encounter electrons within the body, a reaction producing gamma rays occurs. The patient lies on a table that slides into the middle of the scanner. Within the scanner are rings of detectors containing special crystals that produce light when struck by a gamma ray. The scanner's electronics record these detected gamma rays and map an image of the area where the radiopharmaceutical is located. Since the radiopharmaceutical contains a chemical commonly used by the body, PET enables the physician to see the location of the metabolic process. For example, glucose (or sugar, which the body uses to produces energy) combined with a radioisotope will show where glucose is being used in the brain, the heart muscle, or a growing tumor.