“…PET is based on coincident detection of antiparallel g-rays (1808) with an energy of 511 keV, produced by the annihilation of an electron (e À ) and a positron (b + ), the latter being emitted by a short-lived radionuclide tracer upon decay ( Figure 1A) [21,81]. The most important short-lived radionuclides used in biological studies are 11 C, 13 N, 15 O, and 18 F (Table 1) [21,25,80]. These isotopes have a short half-life (t 1/2 ), which makes them ideal for studying short-term processes (minutes to hours) because of their high signal output during the short time-period they exist.…”