A method is disclosed for generating a PET or SPECT image dataset. In an embodiment, the method includes acquiring a plurality of PET or SPECT measurement signals from an examination region; acquiring a plurality of anatomy image datasets that show the examination region using a second imaging modality at the same time as acquiring the PET or SPECT measurement signals; determining the similarity of a reference anatomy image dataset acquired at a time point t′ using the second imaging modality to at least one anatomy image dataset acquired at a different time point and/or predetermining a temporal weighting function; and generating a PET or SPECT image dataset taking into account the similarity of the anatomy image datasets and/or weighting the PET measurement signals temporally. A hybrid imaging modality is also disclosed.