Figure 1. (a) A true coincidence through the detection (1) of two 511 keV photons (3) resulting from an annihilation (2) between an atomic electron and a positron emitted by the injected radiopharmaceutical; (b) a scattered coincidence with at least one of the two annihilation photons undergoing Compton scatter interaction(s) prior to their detection; (c) a random coincidence registered through the detection of two annihilation photons that have originated from two different sites of annihilation.