Physics of Medical Scans
Image Source: NHS
What's a PET scan?
A PET scan is a way of looking inside of the body. It can find out how well parts of the body are working, as well as how they look. A PET scan is a little like an x-ray but uses a special liquid to enable doctors to look at certain activities happening in the body, like what is happening in the brain. A PET scanner looks like a big donut connected to a computer. You lie on a cushioned table that slides into the hole in the scanner, and the detector is made up of multiple rings around your body. [1]
What is it like to have a PET scan?
PET scans don’t hurt at all, and usually you won’t need to stay at the hospital if you have one. People who are suspected of having different medical problems with the brain or other organs in the body are sometimes given a PET scan. The scan allows doctors to find out what the problem is and then they can decide what they need to do to treat it.
Often, there are rules about what you can eat and drink before you have a scan. This depends on where in the body is being scanned, and what doctors are actually using the scan for. Your doctor would always tell you about any special rules on diet leading up to the scan.
After the special liquid is injected, doctors will have you sit and wait for up to an hour for it to be carried around the body to the place that needs scanning. You will then be scanned for up to an hour. [2] You won't feel anything during the scan, even though doctors are using it to look inside of you!
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Sometimes you will be asked to stay away from really young children or pregnant women for a few hours after the scan. This is because, although the radiation in the special liquid is completely safe for you, it might not be safe for young children or unborn babies who are more vulnerable to radiation. [2]
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How does it work?
The special liquid that is injected into the body contains very small amounts of radioactive molecules. This is safe and is carried to the part of the body that is being tested, just like blood is carried around the body. The liquid sends signals that are read by the PET scanning machine which makes images of the inside of the body that doctors can look at. [3]
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References:
[1] Positron Emission Tomography. Available at http://www.cyberphysics.co.uk/topics/radioact/PET.html [Accessed 20/02/19]
[2] PET Scans. Available at: https://www.nhs.uk/conditions/pet-scan/. [Accessed 12/01/19]
[3] Positron Emission Tomography (PET) Scans: Helpful information for parents and children. Available at: http://www.chp.edu/our-services/brain/neurology/patient-procedures/pet-scan. [Accessed 12/01/19]
[4] HSE (2017). The Ionising Radiations Regulations 2017 (Sections 3 and 4).
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Why do all the doctors go outside?
Sometimes, if the PET scan is combined with other scans, the radiologists will go outside because, whilst the scans are perfectly safe to have once, repeated exposure would raise the radiation dose for radiologists to unsafe levels. [4]
How do I look?
What makes the special liquid radioactive?
Radioactive means the special liquid is unstable and lets out particles to try and become more stable.