The disclosure relates to PET imaging systems and methods. The systems may execute the methods to obtain an anatomical image of a subject acquired when the subject remains in a breath-hold status； obtain PET data of the subject, the PET data corresponding to a respiration signal with a plurality of respiratory phases of the subject, the respiratory phases including a first respiratory phase and a second respiratory phase； gate the PET data； reconstruct a plurality of gated PET images, the plurality of gated PET images including a first gated PET image corresponding to the first respiratory phase and a second gated PET image corresponding to the second respiratory phase； determine a first motion vector field between the first gated PET image and the second gated PET image； determine a second motion vector field between the anatomical image and the second gated PET image； and reconstruct an attenuation corrected PET image.
