Unlike magnetic resonance or computed tomography (CT) imaging, positron emission tomography (PET) measures the distribution of a chemical of interest labeled with a radioactive tag, usually Fluorine 18. After this tracer has been administered, the participant will wait some period of time to let the tracer distribute through the body. The scanner consists of a ring of crystals surrounding the participant. As the tracer undergoes radioactive decay, it emits a positron (positively charged electron) that travels a short distance and combines with an electron to create two particles of light (photons) that propagate in opposite directions. When these photons strike crystals on opposite sides of the scanner they create a brief flash of light that is detected by the scanner electronics and stored. When a sufficient number of these photons have been collected, they can be converted into images showing the relative concentration of the tracer.

The National Intrepid Center of Excellence's PET scanner is a Siemens Biograph mCT PET/CT, and can acquire both PET and CT images.