Uses radioactive tracers that travel to the brain and burned as part of the brain’s metabolism.
The substance used can be something like fluorodeoxyglucose which can be used by the brain just like glucose during metabolic activity.
This metabolic activity can be measured by the radioactive substance when used up because a positron is released and, when colliding with an electron, gives off photons which we can pick up
![error] The substance must be radioactive/positron-emitting AND also a derivative of a chemical that the brain actively uses (glucose, dopamine, etc. They just have to connect to the right receptors)