Realtime photo-peak searching method implemented on digital circuit

Although GAPD has been reported to provide good performance as a PET photosensor, it has significant temperature-dependent gain variations causing the drifting of photo-peaks and hence deteriorating the detection sensitivity. Therefore, it is necessary to develop a realtime photo-peak searching method to ensure to apply proper energy window and to sustain uniform sensitivity. This study presented a new realtime photo-peak search method implemented on FPGA. The method used detected gamma-ray energy information to search photo-peak without calculation of direction and step size. The direction was determinated by acquiring a gamma-ray count that has energy within a search range nearby a searching point, and the step size was fixed. The method used two searching points, valley point and peak point, which could be stored in a few registers in FPGA. The performance was evaluated with the simulated energy spectrum and the experimental data acquired with LYSO-MPPC detector. The photo-peak searching error was 3.1±5.5 keV with the simulated energy spectrum with 11% energy resolution, 7.0±7.1 keV with the experimental data. The proposed method successfully found the photo-peak in both the simulation and the experimental study. It is expected that the method could be a powerful realtime searching method to implement on digital circuit for radiation counting system. Since the performance of the searching method depended on searching step size, energy detection range and initial searching point, additional experimental study for the optimization of the parameter will be performed.