To improve the spatial resolution of preclinical positron emission tomography (PET), a detector consisting of a
two-layer scintillator pixel array was designed. A light guide was inserted between the arrays of scintillators to
change the distribution of light generated in each layer. By analyzing the different light distributions, it is possible
to track where the gamma rays interacted. To this end, a gamma ray event was generated at the center of
the flashing pixel and a lookup table was created based on the signal obtained from the light sensor. The optimal
position of the scintillation pixel was tracked through comparison and analysis of the newly detected signal
with the look-up table through maximum likelihood position estimation. As a result, excellent accuracy was
shown. If this detector is used in a preclinical PET system, it is expected to show excellent spatial resolution,
and since an optical sensor that is not affected by magnetic fields is used, it is considered that it can be applied
to PET/MRI in the future.