Gain Invariant Coordinate Reconstruction for SiPM-Based Pixelated Gamma Detectors With Multiplexed Readout

Currently, the prevailing high-resolution Positron Emission Tomography (PET) detector architecture consists of pixelated scintillating crystals coupled to a photosensitive layer, such as position sensitive photomultiplier tubes (PS-PMTs) or silicon photomultiplier (SiPM) arrays. In such detector designs, a light guide layer is commonly used between the finely segmented scintillating crystal array and coarsely segmented photosensitive layer to disperse scintillation light over several elements of the photosensitive layer. Such detectors typically rely on some form of analog signal multiplexing to minimize the number of readout electronics channels and employ Center-of-Gravity (CoG) approach to calculate the positions of gamma-ray interactions. In this article, we report on the Truncated Center of Gravity (TCoG) and Raised-To-the-Power (RTP) algorithms for calculation of gamma photon scintillation position as applied to our newly developed small-scale prototype PET system consisting of a pair of opposing detectors based on $24\times24$ LYSO scintillation crystal matrices and $8\times 8$ SiPM arrays with 64:16 multiplexed readout. The major notable advantage of using TCoG or RTP algorithm in contrast to basic CoG is shown to be their independence of photosensor gain variations. An improvement in the calculation of scintillation positions is demonstrated both for TCoG and RTP algorithms, the Field of View (FOV) distortion inherent to CoG reconstruction is eliminated. On average, the Peak-to-Valley Ratio (PVR) is increased at least by a factor of 2.25. The energy resolution for the considered small-scale PET prototype is ~13.5% when using CoG, TCoG, or RTP reconstruction algorithms.