X’tal cube PET detector composed of a stack of scintillator plates segmented by laser processing

We have developed a 3-dimensional (3D) position-sensitive radiation detector named X’tal cube, which can be applied to a PET detector. The X’tal cube is composed of a scintillation crystal block and multi-pixel photon counters (MPPCs). The crystal block is segmented 3-dimensionally into small cubes by optical discontinuity (3D segmentation) and no reflector is inserted inside. Scintillation light originating in a segment then spreads 3-dimensionally so that the MPPCs are set on all six surfaces of the crystal block to detect the light. Regarding the 3D segmentation of the crystal block, we have already succeeded in getting the segmentation inside of a monolithic scintillator block by a laser processing technique instead of the general way, arranging small cubic scintillator elements into a 3D array. We have confirmed that utilizing the laser processing technique not only eliminates the difficulty of handling the small scintillator elements but also improves detector performance.As a new trial, we considered fabrication of the crystal block by stacking the scintillator plates which were segmented 2-dimensionally by the laser processing technique (2D segmentation). Plates are also easier to handle and for the laser processing, 2D segmentation is simpler than 3D segmentation. In this study, we prepared the X’tal cube with the scintillator plates (Plate-XC) and evaluated its performance to confirm its technical feasibility. For the Plate-XC, we segmented 18 mm × 18 mm × 2.0 mm LYSO plates 2-dimensionally by laser processing so as to make a 9 × 9 array of 2.0 mm × 2.0 mm segments. The crystal block was composed of 9 stacked LYSO plates without using coupling material but with air gaps. The Plate-XC showed sufficient crystal identification performance when 662 keV gamma-rays were irradiated. Furthermore, to understand the characteristics of the Plate-XC, we also analyzed the scintillation light distribution in the crystal block. Results indicated that light spread from outer segments was influenced by the segment boundary conditions, air gaps or laser-processed gaps, while the spread from the center segment did not seem to have such an influence. Regarding energy performance, we obtained around 10% energy resolution for the outer segments as well as for the center segment