Lightguides for improving edge crystal identification and energy resolution in pixelated scintillator detectors

A phoswich depth of interaction (DOI) detector composed by two layers of scintillator arrays (LYSO and BGO) has been proposed. To use this design for building practical systems, a tapered multiple-element glass lightguide is necessary to couple the scintillator arrays to a PSPMT. The complete individual detector module offers an overall dimension of 52×52 mm
²
that matches the external dimensions of the PSPMT package, allowing continuous positioning of the scintillator arrays for creating flat panel detectors without introducing gaps between detector modules. In this work, we define the elements adjacent to the edge in an array as “edge+” elements. Both of the layers of the phoswich detector and the lightguide have such edge+ elements. The lightguide was modified according to the photodetector geometry, aiming at improving edge and corner crystal identification and energy resolution: In an assembled detector, the optimized edge+ lightguide elements superimpose on top of both edge and edge+ anodes of the PSPMT. In that case, the edge+ lightguide elements distribute light onto both the edge and edge+ anodes, while edge lightguide elements primarily distribute light onto the edge anodes. This different light sharing scheme improves the capability of identifying edge+ crystals from edge crystals. In addition, the edge lightguide elements were enlarged to improve the light collection and corresponding energy resolution for the edge crystals. Flood images were acquired and energy resolution was calculated for individual crystals. All the edge and edge+ crystals were clearly resolved. Energy resolution was improved from 24.4 ± 4.4% to 20.0 ± 1.7% for edge crystals. The new proposed lightguide successfully improved edge crystal identification and energy resolution in the proposed pixelated scintillator detector.