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 are 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 trigger unit, the raw data from all analog-to-digital converter channels involved are read out simultaneously via a FRO. An onboard digital signal processor (DSP) processor checks and calibrates these data. To increase the transfer throughput of the list mode data to a SUN Ultra Sparc 1 workstation, the DSP processor compresses the data format to a 6-byte data packet per event. The maximum average sustained acquisition rate of the system is 200000 counts per second (cps), while peak rates up to 2 Mcps can be handled. The DAQ also provides online measurement of the random event rate, the single event rate and event losses due to electronic dead time