Design and Performance of a Resistor Multiplexing Readout Circuit for a SiPM Detector

Abstract

A silicon photomultiplier (SiPM)-based positron emission tomography (PET) detector was developed using a resistor network charge division multiplexing circuit for detector readout. The detector consists of a lutetium-yttrium oxy-orthosilicate (LYSO) scintillation crystal array, an SiPM array detector (SPMArray 4, SensL Inc., Cork, Ireland) and the resistor multiplexing network implemented in a through-hole package to facilitate changing of resistor values. For purposes of optimizing the readout circuit, the LYSO array used was a 4 4 crystal array with crystal size mm on a pitch of 3.37 mm, matched to the SiPM pixel size. Flood image, energy resolution, photopeak amplitude, timing resolution, and signal time-pickoff measurements were performed using standard NIM electronics. The resistor network values were optimized through an iterative process. The performance of the detector was evaluated over a range of temperatures from 23°C to 60°C by heating the detector. The ability of the detector to resolve crystals smaller than the SiPM pixel pitch was evaluated using a dual-layer LYSO array with crystals of 1.67-mm pitch. The optimal resistor network values were found to be 100 Ω along the rows connecting the SiPM pixels and 56 Ω for the columns. For these resistor value settings, the average energy resolution for the central four crystals in the array at 23.5°C was 13.3% ± 0.3% and degraded to 16.3% ± 0.3% at 60°C. The photopeak amplitude decreased by 2%/°C, and the timing resolution degraded from 3.43 ± 0.22 ns to 4.64 ± 0.25 ns for a 350-750-keV energy window over this temperature range. The signal time-pick-off point shifted earlier by 2.7 ns as the temperature increased, an effect likely due to changes in the signal shape with temperature. The detector was able to resolve all 113 crystals in the dual-layer LYSO array. These results demonstrate that the resistor multiplexing readout circuit functions well for reading out SiPM array based detectors, which use scintillator crystal arrays much smaller than the SiPM pixel pitch. The reduced number of output signals achieved through this signal multiplexing greatly reduces the number of signal cables required. In addition, the ability of this detector to function over a wide range of temperatures offers significant flexibility in defining the system operating temperature set point.