A noise correction double time-over-threshold technique for multiplexed read-outs

One of the main challenges in developing MR compatible, SiPM based PET inserts is minimizing the amount of electronics inside the MR bore, in order to optimize space occupancy and avoid electromagnetic interference due to their material and switching activity. Efforts to simplify the data acquisition infrastructure, which is necessary for signal integrity and measurement precision and is, to a large extend, digital, are mostly based on two approaches. These are multiplexing the SiPM outputs or treating individual channels by time-over-threshold (ToT) signal processing, in order to lower the data throughput. In this study, we set the theoretical framework for quality assessment and examine the feasibility of the combination of those two designs. While a straight-forward combination significantly deteriorates signal quality, we developed and present a novel statistical algorithm of double threshold ToT, which takes advantage of the unavoidable, yet measurable noise in order to better estimate the energy content of multiplexed channels. Using datasets from a prototype developed in our laboratory, we demonstrate that such combination can be made possible without significant loss of signal quality, as the overall signal quality deterioration is limited to 1.25%±0.5% per channel and less than 1% for energy and event position estimation. Furthermore, such algorithm can be directly implemented in the back-end of a two stage PET insert design, away from the MR bore, minimising interference between the imaging modalities, while requiring only a very limited amount of passive electronics and ASICs in the front-end. Such approach, in combination with other designs developed in our laboratory, opens the way for the construction of a miniaturized, low-consumption, cost-effective, digital-free PET insert front-end.