PET Scans
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17-02-2011, 09:45 AM

.ppt   PET Scans.ppt (Size: 711 KB / Downloads: 79)
What is a PET Scan?
A Positron emission tomography (PET) scan is a nuclear medical imaging technique which produces a three-dimensional image of functional processes in the body
History of the P.E.T scan
• The concept of emission and transmission tomography was introduced by David E. Kuhl and Roy Edwards in the late 1950s at the University of Pennsylvania.
• In the 1970s, Tatsuo Ido at the Brookhaven National Laboratory was the first to describe the synthesis of 18F- FDG, the most commonly used PET scanning isotope carrier.
• As you can see there is not one person who developed the PET scan but a whole collection of people have made what it is today.
How it works
1. A short-lived radioactive tracer isotope, is injected into the living subject (usually into blood circulation). The tracer is chemically incorporated into a biologically active molecule.
2. There is a waiting period while the active molecule becomes concentrated in tissues of interest.
3. As the radioisotope undergoes positron emission decay (also known as positive beta decay), it emits a positron, an antiparticle of the electron with opposite charge.
4. After traveling up to a few millimeters the positron encounters an electron.
5. The encounter annihilates them both, producing a pair of (gamma) photons moving in opposite directions.
6. These are detected when they reach a scintillator in the scanning device, creating a burst of light which is detected by photomultiplier tubes.
7. The technicians can then create an image of the parts of your brain, for example which are overactive.
The Tracer
• The radioisotopes used in PET scans are isotopes of carbon, nitrogen, oxygen and 18F used as a substitute for hydrogen.
• These are the only radioactive forms of natural elements that will pass safely through your body and be detected by the scanner.
• The type of tracer used depends on what your doctor wants to measure. For example, if your doctor is looking at a tumor, he might use radio labeled glucose (FDG) and watch how it is metabolized by the tumor.
Comparison with a MRI scan
• When people go in for a ‘scan’ it is most likely a Magnetic Resonance Imaging scan.
So what’s the difference between the two scans?
• A MRI scan does not use nuclear medicine, it creates an image using magnets.
• A MRI scan can assess the size and shape of body organs and tissue. However, they cannot assess function. A PET scan looks at function.
• In other words, MRI scans tell you what something looks like, while a PET scan can tell you how it is working.
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22-02-2011, 12:13 PM

PET scanning is a very specialised but useful tool in cancer imaging, diagnosing diseases of the brain such as dementia and for treating heart disease. It works in an entirely different way to other imaging techniques such as X-rays, CT scanning or MRI scanning.
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03-03-2011, 02:14 PM

How to Prepare for the Test

You must sign a consent form before having this test. You will be told not to eat anything for 4 - 6 hours before the PET scan, although you will be able to drink water.

Tell your health care provider if you are pregnant or think you might be pregnant.

Also tell your health care provider about any prescription and over-the-counter medicines that you are taking, because they may interfere with the test.

Be sure to mention if you have any allergies, or if you've had any recent imaging studies using injected dye (contrast).

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