Methods, devices, and systems for reconstructing Positron Emission Computed Tomography (PET) images are provided. In one aspect, a method includes: for each of coincidence events including at least one true coincidence event and at least one scattering coincidence event, determining an emission path of the coincidence event according to photon information of the coincidence event, the photon information of the coincidence event including time data, position data, and angle data of each of two photons involved in the coincidence event, determining an annihilation position of the coincidence event according to the emission path of the coincidence event and the time data of each of the two photons involved in the coincidence event, and reconstructing a PET image according to the annihilation position, the emission path and the photon information of each of the coincidence events.
