PET Scans
What is it?
A positron emission tomography (PET) scan is a way to produce a 3D image of structures inside the body. It is a useful diagnostic tool as it can detect cancer, problems in blood flow and it can be used to examine brains to diagnose multiple disorders.
​
They consist of a ring of detectors which pick up the gamma rays from each angle, which means a 3D picture can be built up of the target.[G10]
​
The machinery is a similar set up to the gamma knife, as it relies on similar principles.
Image 1: Top down view of a PET scan. Source (Hyperphysics)
How does it work?
Similarly to tracers, the patient is injected with a source and a drug that will collect in the specific area that needs to be imaged. However, the source is of positrons and not gamma rays directly.
A positron is essentially an electron but with one key difference, where electrons have a negative charge a positron has a positive charge. Positrons are anti matter, which means that when it comes into contact with its corresponding matter particle (an electron) the pair will annihilate each other and this will then give off gamma rays.[G12] Click here to learn more about antimatter and how it annihilates with matter.
The position of these gamma rays is picked up from a series of gamma cameras and used to build up a 3D image of the body, as seen in image 1. Click here to learn more about gamma cameras.
Safety
The amount of radiation you receive from this procedure is 20mSv or around 200000 bananas.[G13] This is a large amount and it is not recommended to have this procedure if it is not necessary, though the information you can get from it far outweighs the risk involved.
​
Patients may also experience claustrophobia during this process. Another possible risk factor is that the patient will be a source of gamma rays until the source activity decreases, as they have ingested a positron source.[G14]
