Figure 4.

Principle of positron emission tomography (PET) imaging. A tracer labeled with a positron-emitting radionuclide (exemplified by the ¹⁸F-labeled amino acid O-([¹⁸F]fluoroethyl)tyrosine, with fluorine-18, carbon, nitrogen and oxygen atoms shown as orange, grey, blue or red spheres, respectively while hydrogen atoms are omitted for clarity) is injected into the subject. The subject is placed into the PET-scanner consisting of a ring of opposite detectors (indicated as blue trapezoids). The in vivo biodistribution of the tracer is then tracked by detecting the antiparallel γ-quants produced after the decay of the radionuclide and annihilation of the emitted positrons with electrons in surrounding tissues. Adapted from [45] (CC BY 4.0).