The invention provides a positron emission tomography (PET) system. The PET system includes a plurality of annular detector units, a plurality of logical circuits and a calculating device, wherein the detector units are sequentially arranged in the axial direction and used for counting single events, the logical circuits are connected with one or more corresponding detector units and used for counting coincidence events, the coincidence events includes the coincidence events obtained by the single detector unit or the coincidence events obtained by two detector units meeting the pairing rule, and the calculating device includes several calculating nodes and is used for randomly receiving the number, obtained after counting, of the coincidence events and conducting image reconstruction.
Positron emission tomography system and image reconstruction method