Medical Tracers
What are they?
Image 1: Medical image of a mouse. Source (Nature)
Medical tracers are a diagnostic technique, which allow for the imaging of the internal structures of the body. A medical tracer is usually composed of a radioactive isotope and a chemical compound that collects in the place of interest. The source of radiation used normally is not radioactive for long and the most common one used is technetium-99m.[G9]
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Click here to learn how technetium produces gamma rays.
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Image 1 shows the tracer collecting in the organs of a mouse. It looks similar to a heat map, where the red spots have the most of the tracer and the blue have the least.
How do they work?
The patient is injected with the medical tracer (or sometimes it is taken orally) and it is left for some time to develop and allow the best pictures to be seen, without leaving it too long (as the source could decrease in activity to nothing).
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The radioactive isotope (thanks to the chemical it’s paired with) makes its way to the parts of the body you want to image. The gamma rays are produced by the isotope and they are picked up by a gamma camera. Click here to learn more about gamma cameras.
More specifically, the camera picks up the location from which they are produced so you can look at specific organs or biological processes to see if they are going wrong. he gamma camera picks up the position from different angles to build up a complete picture of what’s happening.[G10]
For example, the brain will take up lots of glucose so, if combined with a tracer, you can look at blood flow to the brain and pinpoint any problems.
Safety
The mean dose of radiation received by a procedure is 3.5mSv, or as seen on the scale 35000 bananas.[G11] This is fairly high and the cumulative effect of having many of these procedures could be harmful to your health, so it is only used when necessary. Care is taken to have the least amount of radiation possible to get a useful diagnostic picture and sources are chosen that remain radioactive for the least amount of time that is practically viable.
