An FPGA-based Time Sampling Charge Measurement Method for TOF-PET Detectors

Abstract

The front-end electronics for detectors of time- of-flight positron emission tomography (TOF-PET) is required to read out the time and energy of detected $\gamma$-events simultaneously. To simplify the circuits for high integration, we propose an amplitude based time-sampling method with a novel algorithm to precisely extract the energy information from time measurement. Therefore, traditionally two independent measuring circuits can be merged without losing measurement precision for each item. A prototype with the method was implemented fully with a field programmable gate array (FPGA), and applied to a TOF-PET detector consisted of a silicon photomultiplier (SiPM) coupled with a LYSO crystal. The energy resolution and the coincidence time resolution of the detector were measured as 14.18% and 316 ps respectively, which are comparable with traditional separate measurements. The contribution of our new method to the energy resolution is measured as 5.9%, which is much small than the intrinsic energy resolution of detectors. The FPGA based prototype design demonstrates not only its effectiveness, but also its practicality. Instead of ASIC technology, using modern FPGA chips, the front-end electronics for TOF-PET scanners can be equally compact and power-efficient.