Radioactive substances that emit positrons are used in scans.

PET scans use radioactive sustances that emit positrons.

Explanation:

PET scans are scan imaging systems that help the technique and medic identify the tissue and organs activity by the reaction of a radioactive drug under the scan effects. It can provide amazingly useful information/data or diseases that might be developing in early stages. This is one of the most common first imaging systems that are suggested by medics in rare and very dangerous diseases.

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light-years

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it should be briana that has it to me