Simulations, testing and results for the pixelation of LYSO crystals for gamma detectors using SSLE techniques

One of the most common topologies for the scintillator crystals used in gamma radiation detectors for PET scanners is pixelation. The size of these pixels, the crystal surface treatment and the reflector thickness inserted between crystals directly affects the energy and the spatial resolution as well as the sensitivity of the detector. The fabrication of pixels is laborious, complex and expensive. Here we investigate the possibility of creating pixels within monolithic LYSO scintillators crystals using the proven technique of sub-surface laser engraving with a Nd:YAG laser. To evaluate possible designs considering the limitations of the engraving procedure, we used the simulation software GAMOS to analyze the light propagation inside the crystals engraved with a variety of patterns. We carried out different experimental procedures, including microscopy and laser reflectometry to assess the relative reflective quality of the engraved surfaces. We compared the results of different engraving procedures to a reference reflector commonly used in this type of pixelated crystal matrices. We have configured different engraved surfaces with variable transparency in several pixel geometries including depth-of-interaction encoding patterns. Our results demonstrate that pixels engraved with this method can also be configured to compensate for the multiplexed readout penalties, and at the same time preserve the detector performance requirements. Such modifications of the engraving pattern takes place at practically no cost and constitute a highly promising solution for industrial fabrication, reducing substantially the cost of the detector.