Silicon photomultiplier signal readout and multiplexing techniques for positron emission tomography: a review

Abstract

In recent years, silicon photomultiplier (SiPM) is replacing the photomultiplier tube (PMT) in positron emission tomography (PET) systems due to its superior properties, such as fast single-photon timing response, small gap between adjacent photosensitive pixels in the array, and insensitivity to magnetic fields. One of the technical challenges when developing SiPM-based PET systems or other position-sensitive radiation detectors is the large number of output channels coming from the SiPM array. Therefore, various signal multiplexing methods have been proposed to reduce the number of output channels and the load on the subsequent data acquisition (DAQ) system. However, the large PN-junction capacitance and quenching resistance of the SiPM yield undesirable resistance-capacitance delay when multiple SiPMs are combined, which subsequently causes the accumulation of dark counts and signal fluctuation of SiPMs. Therefore, without proper SiPM signal handling and processing, the SiPMs may yield worse timing characteristics than the PMTs. This article reviews the evolution of signal readout and multiplexing methods for the SiPM. In this review, we focus primarily on analog electronics for SiPM signal multiplexing, which allows for the reduction of DAQ channels required for the SiPM-based position-sensitive detectors used in PET and other radiation detector systems. Although the applications of most technologies described in the article are not limited to PET systems, the review highlights efforts to improve the physical performance (e.g. spatial, energy, and timing resolutions) of PET detectors and systems.

Keywords: Multiplexing; Positron emission tomography (PET); Radiation detector; Silicon photomultiplier (SiPM); Time-of-flight (TOF).

Fig. 1

Comparison between a single channel PMT and an 8 × 8 array of SiPM

Fig. 2

PET detectors with a, monolithic crystal and b pixelated crystal

Fig. 3

Photosensor configurations for scintillation light readout: a single-ended readout, b dual-ended readout, and c lateral side-readout

Fig. 4

Sparse arrangement of a SiPMs and b PET detectors

Fig. 5

Anger logic circuit

Fig. 6

Discretized positioning circuit (DPC): a conventional resistive DPC and b hybrid DPC using the combination of resistor and capacitor pairs

Fig. 7

Row-column summing readout circuit

Fig. 8

Symmetric charge division (SCD) network using: a 1D resistive chains and b weighted summing circuits

Fig. 9

Capacitive multiplexing circuit. a Row-column sum, b cross-strip capacitive multiplexing, and c simplified anger logic

Fig. 10

Delay grid multiplexing circuit based on time-modulation

Fig. 11

Delay line multiplexing circuit using 2-branch splitting and signal combiners

Fig. 12

Schottky diode-based frequency modulation-based multiplexing circuit

Fig. 13

Bipolar multiplexing (Reprint from [153] with permission; © 2014 Institute of Physics and Engineering in Medicine)

Fig. 14

TOT method using bipolar signals

Fig. 15

Digital modulation-based multiplexing using active delay chips

Fig. 16

Digital delay encoding method for ICS event identification. a Concept illustration. b Representative signals from the pulse train outputs: (1) PE absorption event (2) scatter/escape event (3) ICS event, and (4) ICS/escape event (Reprint from [84] with permission; © 2020 Institute of Physics and Engineering in Medicine)

Fig. 17

Pulse-tagging multiplexing using a rectangular and b L-shaped tagging pulses (Reprint from [165] with permission; © Korean Society of Medical and Biological Engineering 2022)

Fig. 18

Automatic gain drift-compensation for SiPM: a conventional SiPM biasing and b SiPM biasing using a temperature sensor with current driving capability

Fig. 19

Bootstrapping methods for SiPM capacitance compensation: a passive method using a balun transformer and b active method using a bootstrapping amplifier