A new data path design for a PET data acquisition system: A packet based approach

We are proposing a new data path design for a position emission tomography (PET) data acquisition system (DAQ). The proposed design can transmit, receive, and process all types of data through a single data stream. Instead of having separate path for data, clock and control signals individually, which is the general case of a conventional DAQ system, the proposed system uses a packet concept to identify and process different data types in a single fast data stream. The proposed design increases flexibility in the design stage and enables an efficient debugging process, which is essential for scaling up channels in a DAQ system. New packets can be defined without changing the existing hardware or logic. Debugging a specific board and a channel in a large system can be efficiently done just by sending a request packet to that channel requesting information to be reported in the same data stream. We defined four different packet types to differentiate information in the data stream: singles packet, coincidence packet, configuration packet, status packet. The length and overhead of these packets are optimized to increase overall throughput. We implemented the algorithm in a Xilinx FPGA board and partitioned the logic in a modular structure. The system consists of a high speed network interface, daisy-chain interface, ADC interface, ADC processor, coincidence processor, and UDP Ethernet interface. The coincidence processor can process single events up to 115 Mevents/sec, and the ADC processor can receive new events locally up to 100 Mevents/sec. Coincidence events are sent to image reconstruction PC with throughput of more than 5.7 Mevents/sec.