A PET detecting module may include a scintillator array configured to receive a radiation ray and generate optical signals in response to the received radiation ray. The scintillator array may have a plurality of rows of scintillators arranged in a first direction and a plurality of columns of scintillators arranged in a second direction. A first group of light guides may be arranged on a top surface of the scintillator array along the first direction. The light guide count of the first group of light guides may be less than the row count of the plurality of rows of scintillators. A second group of light guides may be arranged on a bottom surface of the scintillator array. The light guide count of the second group of light guides may be less than the column count of the plurality of columns of scintillators.
