The technical solution as put forth by the present invention comprises a computer imaging system and detectors arranged around the detected object for collecting gamma photons from positron annihilation events. The key is a multi-pinhole plate placed between the detected object and the detectors, and the multi-pinhole plate can be a coded aperture mask coded by using a function h(x,y). The gamma photons generated from the annihilation events inside the detected object are absorbed by the detector after being collimated by the multi-pinhole plate. Accordingly, after the detectors have performed detection at multiple angles, the result is transmitted to the computer imaging system, and quasi three-dimensional images are generated after being processed by the disclosed algorithm. Furthermore, the quasi three-dimensional images generate secondary projection images and, after adjustment, generate sinograms, and finally three-dimensional tomographic images are reconstructed from multiple sinograms.
