Methods, devices and apparatus for reconstructing an image are provided. In an aspect, a method includes: obtaining coincidence events detected by crystal pairs in a detector of a PET device by scanning a phantom, reconstructing a phantom image according to the coincidence events, and obtaining a time calibration amount of each of crystals in the detector by determining a crystal based source position deviation and a crystal based source time difference of a crystal pair including the crystal according to the phantom image, determining a time difference of the crystal pair according to respective time differences for the crystal pair detecting a plurality of coincidence events, pre-calibrating the time difference of the crystal pair with the crystal based source time difference, and obtaining the time calibration amount of the crystal according to the pre-calibrated time difference of the crystal pair.