An FPGA-Based 64-Channel Readout Electronics for High-Resolution TOF-PET Detectors

Field programmable logic array (FPGA)-based readout electronics has shown its capability of channel-by-channel signal readout for time-of-flight positron emission tomography (TOF-PET) detectors. However, for detectors that rely on light sharing to achieve subpixel resolution, the high-linear measurement dynamic range of the readout electronics is highly required. In this article, the problems with dynamic range in our previously proposed FPGA-based fast linear discharge circuit are investigated and corresponding methods are proposed to enhance its small signal measurement capability and improve the timing performance as well. A practical 64-channel TOF-PET detector module was constructed and evaluated. The readout electronics test results demonstrated a 240x measurement dynamic range with 99.5% conversion linearity. In the case that the $8\times 8$ silicon photomultiplier (SiPM) array in the detector combines with an $8\times 8$ LYSO crystal (each $3.2\times 3.2\times 10$ mm3) array, the average energy and coincidence time resolution of the detector are measured as 10.68% (511 keV) and 364.9 ps, respectively. To demonstrate the benefit of large dynamic range to high-resolution detectors, the crystal array in the detector was replaced by a $24\times 24$ LYSO array (each $1.04\times 1.04\times 15$ mm3) and achieved 1-mm resolution. The test results confirm that the proposed FPGA-based readout circuit is practical for laboratory instrumentation