The present disclosure provides a positron emission tomography (PET) system and an image reconstruction method thereof. The PET system may include a plurality of annular detector units arranged along an axial direction. Each of the detector units may generate a plurality of single event counts. The PET system may further include a plurality of coincidence logic circuits connected to one or more of the detector units. The coincidence logic circuits may be configured to count coincidence events. Single event data generated by each of the detector units may be transmitted to the corresponding coincidence logic circuit. The plurality of coincidence logic circuits may synchronically generate coincidence counts relating to the plurality of detector units.
