Evaluation of the SensL SPMMatrix for use as a detector for PET and gamma camera applications

The SPMMatrix from SensL (SensL, Cork, Ireland) is a large area photodetector consisting of a 4 × 4 array of SensL SPMArray4 detectors, each a 4 × 4 array of silicon photomultiplier (SiPM) pixels, giving a total of 256 SiPM pixels. In addition, the device has 32 amplifiers and analog-to-digital conversion (ADC) channels and a FPGA-based data acquisition board The anodes of the SiPMs are chained together according to an array/pixel wiring scheme developed by SensL to reduce the number of readout electronics channels to 32. In this work we conducted a preliminary evaluation of the SPMMatrix device to assess its suitability for PET and gamma camera applications. One commercially manufactured 4×4 array of 3.17 × 3.17 × 10 mm³ LYSO crystals was coupled to one of the 4×4 SiPM pixel arrays, effectively giving a one-to-one coupling of the scintillator crystal and SiPM pixels. A custom data acquisition program that allowed acquisition of all 32 ADC channels was used to acquire data from the device. A ⁶⁸Ge source was used for all testing. High quality flood images were obtained from the SPMMatrix device, with all crystals being well resolved Two methods were investigated for determining the energy resolution. The better method, using the hardware sum of the pixels in one SPMArray4 detector, gave an energy resolution of 17%. The resolution degraded to 21% when the energy value was calculated by a software sum of the pixel values. This decrease in energy resolution is likely due to the contribution of dark noise from the pixels in the other arrays and due to the array/pixel multiplexing strategy. In comparison, the same L YSO array tested with a single SPMArray4 detector and NIM electronics gave an energy resolution of 14.6%.