X’tal Cube PET Detector Composed of a Stack of Scintillator Plates Segmented by Laser Processing

We have developed a three-dimensional (3-D) 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 three-dimensionally into small cubes by optical discontinuity (3-D segmentation) and no reflector is inserted inside. Scintillation light originating in a segment then spreads three-dimensionally so that the MPPCs are set on all six surfaces of the crystal block to detect the light. Regarding the 3-D 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 3-D 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 two-dimensionally by the laser processing technique (2-D segmentation). Plates are also easier to handle and for the laser processing, 2-D segmentation is simpler than 3-D 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 two-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.