Methods, systems, and machine-readable storage mediums for determining response lines for reconstructing images are provided. An example imaging method includes: receiving single event signals in a detector module and associated with a single event, determining a crystal in the detector module and corresponding to a maximum single event signal of the single event signals, determining an actual energy weighting factor of the crystal, determining an actual depth position corresponding to the actual energy weighting factor of the crystal according to associations between depth positions of the crystal and respective reference energy weighting factors for the crystal, as an acting position in the detector module for the single event, determining a response line of a coincidence event according to respective acting positions in the detector module for two single events constituting the coincidence event, the two single events including the single event, and reconstructing an image according to the response line.