Evaluation of the PETsys TOFPET2 ASIC in multi-channel coincidence experiments

Abstract

Background Aiming to measure the difference in arrival times of two coincident γ-photons with an accuracy in the order of 200ps, time-of-flight positron emission tomography systems commonly employ silicon photomultipliers (SiPMs) and high-resolution digitization electronics, application specific integrated circuits (ASICs). This work evaluates the performance of the TOFPET2 ASIC, released by PETsys Electronics S.A. in 2017, dependent on its configuration parameters in multi-channel coincidence measurements. Methods SiPM arrays fabricated by different vendors (KETEK, SensL, Hamamatsu, Broadcom) were tested in combination with the ASIC. Scintillator arrays featuring different reflector designs and different configurations of the TOFPET2 ASIC software parameters were evaluated. The benchtop setup used is provided with the TOFPET2 ASIC evaluation kit by PETsys Electronics S.A. Results Compared to existing studies featuring the TOFPET2 ASIC, multi-channel performance results dependent on a larger set of ASIC configuration parameters were obtained that have not been reported to this extend so far. The ASIC shows promising CRTs down to 219.9 ps in combination with two Hamamatsu S14161-3050-HS-08 SiPM arrays (128 channels read out, energy resolution 13.08%) and 216.1 ps in combination with two Broadcom AFBR-S4N44P643S SiPM arrays (32 channels read out, energy resolution 9.46%). The length of the trigger delay of the dark count suppression scheme has an impact on the ASIC performance and can be configured to further improve the coincidence resolution time. The integrator gain configuration has been investigated and allows an absolute improvement of the energy resolution by up to 1% at the cost of the linearity of the energy spectrum. Conclusion Measuring up to the time-of-flight performance of state-of-the-art positron emission tomography (ToF-PET) systems while providing a uniform and stable readout for multiple channels at the same time, the TOFPET2 ASIC is treated as promising candidate for the integration in future ToF-PET systems.

A Comprehensive Study on the Timing Limits of the TOFPET2 ASIC and on Approaches for Improvements

“…A promising candidate for multi-channel readout is the TOFPET2 ASIC developed by PETsys Electronics S.A., a 64-channel integrated circuit which can process data rates of up to 600 kcps per individual channel, featuring a threethreshold trigger logic for dark count rejection [13]. The TOFPET2 ASIC consumes a maximum power of 8.2 mW per channel (including signal digitization) and has shown promising performance results in prior studies [14]- [16]. In addition, this ASIC is under investigation by many research groups, making limitations of its electronic front end a subject with a large impact [17]- [21].…”

Performance evaluation of side‐by‐side optically coupled monolithic LYSO crystals

“…Several methods have been developed to mitigate border effects, some of them are based on weighted centroid methods 16 or squared‐charge (SC) centroids 17 . Recently, the development of multichannel photosensor‐readout application‐specific integrated circuits combined with silicon photomultipliers (SiPMs) enabled the possibility to build highly granular, scalable, and large arrays for position sensitive gamma‐ray detectors 18–20 . These developments allowed for an exhaustive characterization of the 3D spatial detector response, paving the way for new positioning algorithms, such as maximum‐likelihood (ML) methods, 21,22 nonlinear data fit, 23 k‐NN technique, 24,25 Voronoi‐based calibration methods, 26 and machine‐learning artificial neural‐network (NN) algorithms 27–29 .…”

Advances in Detector Instrumentation for PET

“…ASIC readouts possess a small footprint and can be used to read, preprocess, and digitize each SiPM photodetector element independently or the resulting channels after multiplexing. Because of the customized design of ASICs for a specific type of detector and requirement, they often can yield performance parameters superior to those from readout circuits built using discrete components (23).…”