Design of a Firewire based data acquisition system for use in animal PET scanners

The University of Washington is building two different animal PET imaging systems-one optimized for mice and one for larger animals. To support both of these systems, our laboratory is designing and building a data acquisition system based on the IEEE 1394a (Firewire) serial bus standard. This bus standard currently allows up to 63 devices per bus with an overall bandwidth of 400 megabits per second transfer rate. The acquisition system is based on a layered electronics design (analog, digital, and transport) for each detector module. The analog card processes signals from the photomultiplier tube (4 to 64 signals depending on the scanner system). The digital board includes circuitry to digitize the analog signals, latch a clock word used for determining coincidence timing, and logic for a coarse timing window. The digitized data is then latched into the Firewire transport card which adds the detector module number and type to the data block. All of the data is collected event by event (list mode) with a Macintosh computer. Initial analysis indicates that the expected count rates for our animal systems can be accommodated with a Firewire based system. The current design makes no assumptions about the geometry of the system. The different scanner designs can all use the same transport card and only require different analog and digital cards as needed for the number of signals being processed. The advantages of a data acquisition system based on the 1394a standard include considerable flexibility in the design of animal PET imaging systems and taking advantage of inexpensive, but powerful desktop computers with a consumer interface that has been developed for high speed data transfer.