Abstract

Novel electronic readout schemes of analog silicon photomultipliers (SiPMs) have shown impressive timing performance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula> -detectors in positron emission tomography (PET). However, transferring these novel concepts to the system level is a key to exploit the improved coincidence time resolution (CTR) in (pre-)clinical imaging. In this study, the commercially available TOFPET2 application-specific integrated circuits (ASICs) from PETsys Electronics S.A. is tested in terms of the best achievable CTR. The measurable CTR limits will be obtained by state-of-the-art high-frequency (HF) readout, minimizing the impact of the electronic front end on the time resolution. We achieved (73 ± 1) ps with the HF readout and (134 ± 10) ps with the TOFPET2 ASIC for a Ce-, and Ca-doped lutetium-oxyorthosilcate (LYSO) crystal of 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 3 mm2 size. We show that SiPM signal amplification and an effectively reduced TOFPET2 input stage impedance boost the CTR of a 20-mm high LYSO:Ce crystal to 187 ± 8 ps. Our studies also lead to the observation of side peaks in the coincidence time difference spectrum. These peaks are studied in depth and a conclusion on the ASIC for 100-ps PET applications is drawn.

Highlights

  • In time-of-flight positron emission tomography (TOFPET), digitizing coincident γ-events with high-precision timestamps is key to improve the signal-to-noise ratio (SNR) of PET images [1]–[5]

  • We further established a combination of the HF readout with the TOFPET2 application-specific integrated circuits (ASICs) with the aim to boost the performance of the ASIC and to take the essential step to investigate improved signal formation on system level

  • We have shown the feasibility of applying a similar highspeed amplification before the TOFPET2 ASIC, which leads to improved coincidence time resolution (CTR) and single-photon resolution in corresponding staircase plots for all tested silicon photomultipliers (SiPMs)

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Summary

Introduction

In time-of-flight positron emission tomography (TOFPET), digitizing coincident γ-events with high-precision timestamps is key to improve the signal-to-noise ratio (SNR) of PET images [1]–[5]. 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]. This ASIC is under investigation by many research groups, making limitations of its electronic front end a subject with a large impact [17]–[21]. We investigate the timing limits of the ASIC front end by the means of comparing the TOFPET2 performance to a HF readout approach. We will exploit the possibility of encoding the signals of a single SiPM with multiple timestamps

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