FPGA/DSP-based coincidence unit and data acquisition system for the Sherbrooke animal PET scanner

The use of field programmable gate arrays (FPGA) is a natural step in the evolution of modern PET scanners to improve system flexibility, increase design speed, and reduce electronic circuit size and cost. Hybrid high-performance programmable digital interfaces integrating an on-board FPGA and digital signal processor (DSP) were used to rebuild the coincidence units and data acquisition system of the Sherbrooke animal PET scanner. Logic was implemented within the FPGA to process singles and coincidence events, both trues and randoms. Coincidence validation is realized directly in the FPGA by an AND gate of the time signals generated by the scanner CF triggers. Twelve coincidence units from eight groups of detectors were equally divided between four FPGA/DSP modules to evenly distribute the event rate from the detectors. The event data is streamingly transmitted to the DSP for real-time histogramming into host memory or list mode data storage on disk. Event rates in excess of 10⁷/second can be achieved, which allows ultra-fast calibration and single-photon transmission measurements to be performed. The whole system occupies three full-length PCI slots in a standard PC computer