We report the development of a compact high-resolution detector for a positron emission tomography (PET) insert in small animal irradiator. The detector consists of 4 sub-detectors; each sub-detector consists of a 15×15 array of 1×1×20 mm3 LYSO scintillators with each array end coupled to an 8×8 array of 2×2 mm2 silicon photomultipliers for depth-of-interaction (DOI) measurement; all sides of scintillators were roughed with a 0.03 mm surface lapping for balanced detector performance. Based on row and column signal readout, only 64-ch electronics is required to process 512-ch output of each detector. A compact 96-ch electronics board was developed to measure the charge, timing, and position of each interaction and convert them into digital output pulses for further processing. The detector performance evaluation study shows an average ~26.3% energy resolution, ~3.2 ns coincidence timing resolution, and ~3.2 mm DOI resolution from all crystals. All scintillators are well identified. The maximum throughput of the detector is ~200 K events/s.