Preliminary results of a data acquisition sub-system for distributed, digital, computational, APD-based, dual-modality PET/CT architecture for small animal imaging

A new highly integrated data acquisition (DAQ) system for a combined, APD-based, dual-modality PET/CT scanner, implementing both analog and digital electronics on the same board, has been fabricated and tested. The DAQ system was designed to achieve high-precision (<1 ns) coincidence detection in PET and high-rate event counting in CT imaging using the same detectors and electronics. One DAQ board holds 64 parallel detector channels that can be sampled directly at the output of the charge-sensitive preamplifiers (CSP) at a rate of 100 MHz with free-running analog-to-digital converters (ADC) from Maxim. Digital signal processing is performed in field programmable gate arrays (FPGAs) from Xilinx. Independent 500 V voltage regulators are mounted on board for optimum biasing of individual APDs coupled to phoswich detectors. The DAQ board has been fabricated on a 12 copper layers printed circuit board (PCB). The low-noise analog front-end is directly interfaced on board through differential CSP outputs to the high-speed digital circuits for optimum coupling and noise immunity. The board shows excellent electrical characteristics with all circuitry powered up, featuring a mean signal to noise and distortion ratio (SINAD) of 47.7 dB over all 64 channels when supplied with a 10 MHz sine waveform at its input. Initial performance characteristics with BGO/LSO phoswich detectors are reported.