Real time coincidence detection system for digital high resolution APD-based animal PET scanner

A centralized, fully digital, FPGA-based coincidence detection system has been developed for the LabPET APD-based scanner. The digital flexibility allows excellent timing resolution using digital signal processing and high precision crystal identification. In this digital architecture, fast AND-gate coincidence detection is no longer possible due to signal analysis delay. Timestamp based coincidences must be carried out by a central digital process that handles huge amounts of data. A 45 MHz system clock is used by free running ADCs and reference time counters. Event timestamp is refined to ~0.7 ns resolution with digital analysis. A real-time digital coincidence detection system capable of processing 32 million single events per second is proposed to support a fully digital APD-based architecture. The coincidence engine retains a technology independent structure, making it easily reusable in subsequent generation architectures. The system detects prompt coincidences and evaluates random coincidences using both a delayed-window coincidence and the singles count rate. Finally, it supports dynamic adaptive coincidence windowing for multi-crystal PET scanners, ranging from 0 to 100 ns in 0.7 ns increments