We developed a depth of interaction (DOI) detector for positron emission tomography (PET) using different
kinds of reflectors. The detector module consists of two layers of scintillator arrays, which was composed of 4 ×
4 Gadolinium Aluminum Gallium Garnet (GAGG) crystals of size 3 mm × 3 mm × 10 mm, and 4 × 4 silicon
photomultiplier (SiPM) arrays. The bottom layer optically coupled to the SiPM used a diffuse reflector and the
top layer used a specular reflector. The layer interacted with gamma ray and crystal could be determined by
analyzing the signal size because it obtained for each layer is different by using different reflectors for the crystals
for each layer. The detector performance was analyzed by the flood image, energy spectrum with two photoelectric
peaks, and energy resolution. In the experiment for the detector module performance, all pixels in the
flood map were well decoded, and the energy spectrum of each pixel is measured with two photo peaks.