A modular waveform-sampling data acquisition system for time-of-flight PET

Paper presents design and initial performance of ROCSTAR - a waveform data acquisition board that is being developed to instrument a dedicated high spatial resolution time-of-flight capable breast PET scanner. The PET detector is PMT-based, uses LYSO scintillation crystals with a cross-section of 1.5 x 1.5 mm
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& has an average coincidence timing resolution of ~350 ps. The data acquisition design relies on our previous experience in developing a waveform-sampling DAQ based on the Domino Ring Sampler (DRS) integrated circuit. While the core architecture is generalizable, the ROCSTAR board has been customized for the breast scanner detector that has a single dynode and 64 anode signals. To maximize data throughput, the board uses a combination of waveform sampling and traditional flash ADCs. Anode sums are used for event positioning and digitized by flash ADCs, while the dynode signal is used to calculate the energy & timing information and is digitized by the DRS4 chip. Data from both the signal digitization paths are collected by an FPGA which packages & transfers it to a DAQ computer over a Gigabit link. The ROCSTAR board has been designed, and the first boards have been fabricated and assembled. Initial tests indicate the ability to successfully communicate with all the analog & digital portions of the board, simultaneously digitize anode and dynode signals, trigger readout, package, and transmit waveform data to the acquisition computer over Ethernet.