The present disclosure may provide a method. The method may include obtaining a PET dataset relating to a subject acquired, based on a tracer species in the subject, by a PET device. The PET dataset relating to the subject may be acquired for a time period when the subject moves by moving a couch on which the subject is supported. The time period may include a first time segment and a second time segment. The method may also include determining an activity distribution set of the tracer species in the subject within the time period. The activity distribution set may include a plurality of segment activity distributions. Further, the method may include determining an offset of the couch within the second time segment with respect to the first time segment based on the activity distribution set of the tracer species.
