The application provides a three-dimensionally heterogeneous PET system comprising at least two heterogeneous detector modules, each comprising at least two kinds of crystal strips closely arranged to form different detection performances levels for different kinds of crystal strips and same detection performances levels for same kind of crystal strips. Parameters of detection performances of crystal strips comprise energy resolution, density, size and light output, wherein different detection performances levels for crystal strips comprise one or more of parameters of detection performances of crystal strips being in different levels. Compared with a high spatial resolution PET system, the application effectively reduces manufacturing costs of a PET system without significantly reducing spatial resolution thereof. Compared with an ordinary spatial resolution PET system, it improves spatial resolution of a PET system by slightly increasing its cost, and can also provide imaging field of view with high spatial resolution in radial direction.
