Time determination of BGO-APD detectors by digital signal processing for positron emission tomography

Coincidence timing resolution in positron emission tomography (PET) can be improved by replacing fast analog pulse shaping and constant fraction discriminator (CFD) with fully digital signal processing. This can be achieved by digitizing the signal from individual detectors using 100-MHz 8-bit analog-to-digital converters (ADC) and processing the data in field programmable gate arrays (FPGA). Various digital implementation of filters and baseline restorers have been combined with numerical least mean square fit to the data to extract the time of interaction and the energy deposited in BGOAPD detectors. Using the same detector and pre-amplifier, a time resolution of 7.2 ns was obtained with digital techniques, as compare to 12.7 ns with the conventional analog method. By reducing the BGO-BGO coincidence time window by more than ∼40 %, an equivalent reduction of the rate of random events can be obtained, which would improve image SNR significantly at high counting rate in a BGO-APD PET scanner. The proposed digital techniques can be readily adapted to other faster detectors.