The "X´tal cube" PET detector: 3D scintillation photon detection of a 3D crystal array using MPPCs

We have proposed a depth of interaction (DOI) PET detector named X´tal cube, in which a number of Multi-Pixel Photon Counters (MPPCs) are coupled on various positions of six surfaces of a segmented scintillation crystal block. There are no reflectors within the block, and the areas among MPPCs on the surface are covered with reflector. The MPPC is thin and light solid-state photo-detector so that it is possible to set the MPPCs on the subject side in the detector ring of a PET scanner and the crystal blocks can be closely placed each other in the PET detector ring. To study the characteristics of the X´tal cube, we constructed a segmented crystal block consisting of six layers of a 6 × 6 crystal array with Lu_2xGd_2(1-x)SiO₅: Ce (LGSO, x=0.9) crystals. Each crystal is 3.0 × 3.0 × 3.0 mm³ in dimensions. We examined crystal identification performance for different arrangements of photo-detector elements on the block surfaces. The preliminary experiments showed the possibility of realizing a 3D detector having isotropic resolutions.