Positron Emission Tomography (PET) is a nuclear medicine imaging technique that uses a radioactive tracer to visualise the functional process of the body area of interest.
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A PET scan is a functional imaging technique that uses radioactive tracers to measure the biochemical processes taking place within your body. The scan allows analyses of the rate of change of metabolic processes over time. This allows for the study of function in healthy as well as diseased bodies.
PET scans can be used for the following purposes:
A PET scanner looks similar to an MRI scanner; it is a large circular machine with a hole in the centre through which the patient can be moved in and out of the scanner.
As mentioned earlier, PET scans involve the use of radioactive tracers. These tracers are developed by attaching isotopes (which are radioactive atoms) to a chemical substance that your body naturally uses. The most commonly used radioactive tracer is fluorodeoxyglucose (FDG) which is made by attaching the fluorine-18 isotope to glucose which is used by our brain cells during metabolism. Other well known isotopes are oxygen-15, carbon-11 and nitrogen-13.
Before scanning, the tracer is injected into your body via an intravenous line. You will then have to wait 30-60 minutes for it to be uptaken in your body.
Whilst in the scanner, the tracer will undergo radioactive decay. During this process, the tracer releases positrons (which have an electric charge of +1 i.e, the antimatter of electrons). Positrons and electrons in our body come in contact, annihilate each other and in the process emit gamma rays. These rays are detected by the scanner, and sent to the computer where the signals are processed to create the images of the measured area. The higher the consumption of the tracer, the higher the activity in the region and the brighter the image looks. Based on this information, and previous knowledge about the metabolic processes of a region, a doctor can make inferences about the PET image.
PET scan involves exposing you to a small amount of radioactive substances in the form of the tracer. The amount of radioactivity is small, and thus carries very little risk. But, it could cause an allergic reaction in some patients, and is not recommended for pregnant women, babies or children. Additionally, repeated exposure is more harmful and therefore the scan should be performed only when necessary. Lastly, the images provided by the scan are extremely helpful in cases where it is applied, and any small risk of exposure to radiation are definitely outweighed by the gain in information.