Maximization of Digital Photon Counter efficiency when using Neighbor Logic

Digital Photon Counters (DPCs) are a new technology capable of detecting light similar to a Silicon Photomultiplier. In previous work we characterized the Philips DPC-3200-22_C DPC array for use in small-animal PET. Among other performance aspects studied was a reduction in detector efficiency from Neighbor Logic (NL) malfunction. NL forces neighboring DPC elements into a readout cycle after the first DPC is triggered, and was found to be necessary to readout a finely pixelated array of scintillator crystals. In previous work a detected event was discarded from the data set when NL malfunctioned for the Anger Logic coordinate could not be properly calculated. When the missing DPC is sufficiently far from the crystal of interaction, the Anger Logic coordinate is altered by enough that it cannot be identified using the crystal identification map (CIM; segmented histogram of Anger Logic coordinates) created from events in which all DPCs reported. However, the event may still hold enough information to accurately identify the crystal of interaction through using a CIM generated solely using events where that particular DPC malfunctioned. Here we propose that separate CIMs be used for each permutation of missing DPC elements when NL malfunction occurs. We found that detection efficiency is improved for all combinations of device settings tested. For easier to pass trigger schemes (TSs, which set a statistical minimum threshold of cell breakdowns to trigger the DPC) where NL count loss was significant, there was a very large improvement in efficiency (i.e. 87 to 52% loss for the easiest scheme). This method of event recovery leads to no degradation in timing resolution and a minimal degradation in energy resolution. Use of this method could allow one to use lower TSs which have excellent timing resolution compared to TS4, which was previously found to be necessary to preserve efficiency.