The X'tal cube PET detector of isotropic (0.8 mm)3 crystal segments

Depth-of-interaction measurement is essential for PET to reduce the parallax error, resulting in improved spatial resolution with maintaining sensitivity. One of ultimate goals of improvement in DOI detectors is achieving isotopic spatial resolution. For this purpose, we have developed an isotropic 3D position sensitive PET detector named X'tal cube. The X'tal cube is composed of a scintillation crystal block segmented into cubes. Arrays of multi pixel photon detectors (MPPCs) cover all surfaces of the crystal block. In our previous study, we achieved 1.0 mm isotropic spatial resolution. In this study, we finally succeeded to develop the X'tal cube with (0.8 mm)3 isotropic segments. The scintillation crystal block was a 13.6 × 13.6 × 13.6 mm3 monolithic LYSO. 3D segmentation of 17 × 17 × 17 array of 0.8 mm × 0.8 mm × 0.8 mm grids was made by the laser processing. We used 96 MPPCs (S12642-0404PB-50(X)). For each face of the crystal block, monolithic 4 × 4 array of MPPCs with about 0.2 mm gaps was coupled. The position histograms were made by the 3D Anger-type calculation from uniform irradiation data, which showed good identification of each segments. We obtained 9.0% energy resolution for the central part of the crystal block. In conclusion, we succeeded to develop a prototype PET detector with the world's finest segments of (0.8 mm)3 grids.