Real time digital implementation of the high-yield-pileup-event-recover (HYPER) method

We have proposed a high-yield-pileup-event- recover (HYPER) method that can process scintillation signals in very high count-rate situations where multiple-event pileups are normal, and successfully used this method in our BGO animal PET and human PET systems. In the first generation HYPER electronics, the integration and weight-sum circuits were implemented using analog signal. However, the same idea can be implemented in full digital mode. In the digital HYPER method, the input signal is digitized with a free run ADC, and then processed in a field programmable gate array (FPGA). Recent improvement in integrated circuit technology makes it possible to do digitization and real-time processing with clock frequency over 200 MHz. The dead time is reduced because there's no dead-time for discharging the integration value. The analog delay line used to balance the trigger delay is removed, which will reduce the signal distortion, and in turn increase the measurement resolution. The processing in the FPGA includes digital integration, weight-sum, and dynamic pile-up correction. Simulation shows a possible working frequency of 320 MHz with a low-cost FPGA, the Altera CY2C35F484C6. Energy spectrum of LSO with count rate up to 20 MCPS has been studied. The energy resolution of 1, 2, 4, 8, 12, 16 and 20 MCPS is 10.6%, 11.1%, 12.4%, 14.1%, 16.2%, 18.4% and 23.0%, respectively.