Design and performance of a data acquisition system for VUB-PET

A flexible and high-speed VME-based data acquisition system (DAQ) has been designed to process data from the University of Brussels (VUB) small-animal positron emission tomography (PET) system. The core tasks of the system ar e performed by two custom VME modules: a trigger module and a Fast Readout module (FRO), Following the detection of a valid coincidence event by the t rigger unit, the raw data from all analog-to-digital converter channels inv olved are read out simultaneously via a FRO. An onboard digital signal proc essor (DSP) processor checks and calibrates these data. To increase the tra nsfer throughput of the list mode data to a SUN Ultra Spare 1 workstation, the DSP processor compresses the data format to a 6-byte data packet per ev ent. The maximum average sustained acquisition rate of the system is 200 00 0 counts per second (cps), while peak rates up to 2 Mcps can be handled. Th e DAQ also provides online measurement of the random event rate, the single event rate and event losses due to electronic dead time.