In this study, we propose a simple gain compensation technique for silicon photomultiplier (SiPM)-based positron emission tomography detectors, using a temperature sensor that automatically controls the bias voltage of the SiPM depending upon the ambient temperature. The temperature sensor output, for which the temperature coefficient can be controlled by the input voltage, is used as one end of the bias voltage. By adjusting the temperature coefficient, the proposed gain compensation method can be applied to various SiPMs with different breakdown voltages. As a proof of concept, the proposed method was evaluated for two scintillation detector setups. Applying the proposed method to a single-channel SiPM (ASD-NUV3S-P; AdvanSiD, Italy) coupled with a 3 mm × 3 mm × 20 mm LGSO crystal, the 511 keV photopeak position in the energy histogram changed by only 1.52% per 10 °C while, without gain compensation, it changed by 13.27% per 10 °C between 10 °C and 30 °C. On a 4 × 4 array MPPC (S14161-3050HS-04; Hamamatsu, Japan), coupled with a 3.12 mm × 3.12 mm × 15 mm 4 × 4 LSO array, the photopeak changes with and without gain compensation were 2.34% and 20.53% per 10 °C between 10 °C and 30 °C, respectively. On the wider range of temperature, between 0 °C and 40 °C, the photopeak changes with and without gain compensation were 3.09% and 20.89%, respectively. The energy resolution degradation of SiPM-based scintillation detectors operating at temperatures was negligible when the proposed gain compensation method was applied.

Objective. Identifying the inter-crystal scatter (ICS) events and recovering the first interaction position enables the accurate determination of the line-of-response in positron emission tomography (PET). However, conventional silicon photomultiplier (SiPM) signal multiplexing methods based on two-dimensional (2D) charge-division circuits do not allow the detection of multiple gamma-ray interaction positions in a scintillation array coupled with a SiPM array. In this study, we propose a novel multiplexing method that can restore all the individual channel data from a smaller number of multiplexed channels using high-pass filters and neural networks. Approach.The number of output channels is reduced by summing the SiPM signals that have passed through high-pass filters with different time constants. Then, the signal amplitude of each SiPM channel is restored from the combined signal using an artificial neural network. This study explains the principle of this method in detail and demonstrates the results using 4:1 multiplexing as an example. The usefulness of this method was also demonstrated by its application in the identification of ICS events in 1-to-1 coupled LSO-SiPM PET detectors. Main results. The artificial neural network enabled accurate energy estimation for each SiPM channel. One of the high-pass filter sets with the lowest Cramér–Rao lower bound provided the best results, yielding R2 value of 0.99 between the true and estimated signals. The energy and flood histograms generated using the best-estimated signals were in good agreement with the ground truth. Additionally, the proposed method accurately estimated 2D energy deposit distribution in the LSO crystal array, allowing ICS event identification. Significance. The proposed method is potentially useful for ICS event recovery with a reduced number of array signal readout channels from a SiPM array.

The multiple thresholds used in multi-voltage threshold (MVT) method provide more detailed information about the pulse amplitude of the input analog pulses than the simple time-over-threshold (TOT) method, thus allowing for better energy estimation and pulse reconstruction capabilities. However, as the number of thresholds increases, the number of comparators and digital signal readout channels required for MVT also increases. This requirement owing to the increased number of thresholds is the main disadvantage of MVT implementation using field-programmable gate array (FPGA)-based time-to-digital converters (TDCs) because the FPGA resources required for TDC implementation are substantial and FPGAs have a limited number of input/output ports. Therefore, we propose a new single-line MVT method to improve the integrity of the FPGA-only data acquisition system without analog-to-digital converters by reducing the FPGA input channels required for the MVT method. The proposed method, which applies three different levels of thresholding, reduces the digital output signal line in the MVT by employing a 3-input XOR logic gate. The XOR gate integrates the output signals from the comparators and generates 1-bit line digital pulse train. We evaluated the energy performance of the proposed single-line MVT method using three different energy estimators. The energy estimates were compared with the ground truth energy calculated using domino-ring-sampler 4 (DRS4)-sampled analog pulses. The proposed method showed virtually equivalent energy resolution to that of DRS4-based pulse digitization method and better energy linearity than the conventional TOT method. Among the energy estimation methods used in single-line MVT, the crossing-point triangular sum method showed the best energy linearity. The proposed single-line MVT method will be useful when data acquisition systems without ADCs are implemented using FPGA-based TDCs. This is because the proposed method alleviates the problem of limited input ports and the numerous resources required for TDCs in FPGAs.