What is the use of technetium-99m in a SPECT scan?
In: Chemistry
Technetium-99m is radioactive with a half-life of 6 hours, and decays to regular 99Tc by emitting gamma rays.. Gamma rays are very penetrative, and can pass though human tissue. That means that if you have 99mTc gathering in your body at a certain spot, it’s easy to find out where it is from the outside with gamma ray detectors.
SPECT scanning tries to find out where certain kinds of molecules are going in your body. Many diseases can be caused by or identified by things going to the wrong places. To find out where these molecules are going, SPECT scanning injects some molecules (called [Radioligands](https://en.wikipedia.org/wiki/Radioligand)) that have 99mTc mixed in. That 99mTc emits gamma rays, and it’s very easy to see from the outside where those gamma rays are coming from. That means you can see where your molecules are moving or collecting in your body without having to open it up.
Because 99mTc has a short half life (6 hours) essentially all of it is gone after 2 days, and so there’s little worry about long-term effects.
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