To measure the activity of the human brain during certain thought processes, a short-lived radioactive sugar is injected in the carotid artery and is utilized by those cells that are most active. This shows up on a PET scan and demonstrates the detection of ___.

The correct answer is: isotopes.

Explanation:

PET scan (positron emission energy) is an imaging technique that is used to help in the diagnosis of a disease by observing metabolic processes in the body.

PET scans, although very expensive, are of great utility in the fields of Oncology, Neurology and Cardiology.

Isotopes are atoms that share the same number of protons and electrons but differ in the number of neutrons. This gives the isotopes different properties than regular atoms. In PET, isotopes are radiotracers used to discern the biologic pathway of any compound.