1. A reconstruction apparatus for reconstructing a PET image of an object, the reconstruction apparatus being adapted to reconstruct the PET image based on detection events and detection times assigned to the detection events generated by a PET data acquisition apparatus of a PET system, wherein the PET data acquisition apparatus comprises first detector elements configured to detect photons emitted by a radiation source located within the object and to generate first detection events indicative of the detected photons and detection times assigned to the first detection events, and second detector elements configured to detect photons emitted by the radiation source and generate second detection events indicative of the detected photons and detection times assigned to the second detection events, the reconstruction apparatus including a computer apparatus being configured to: receive a position of the second detector relative to the first detector, determine a first-second timing window including a first-second upper threshold based on the position of the second detector relative to the first detector, generate first-second detection event pairs based on the provided first-second timing window, each first-second detection event pair including a first detection event and a second detection event, to which detection times have been assigned whose detection time difference is equal to or smaller than the first-second upper threshold, and reconstruct the PET image based on the generated first-second detection event pairs.