Methods, devices, and apparatus, including computer programs encoded on a computer storage medium for reconstructing image are provided. In one aspect, a method of reconstructing image includes obtaining scanning data for a subject in a continuous incremental scanning of medical equipment including real crystals for detection, associating each of the real crystals with one or more virtual crystals in a virtual scanning system, determining delay random coincidence data of two virtual crystals connected by a response line in the virtual scanning system, obtaining random coincidence data by denoising the delay random coincidence data based on crystal receiving efficiency for each of the real crystals, and reconstructing an image with the scanning data by taking the random coincidence data into account.