A DOI PET detector having extended X'tal cube structure

We developed a new PET depth-of-interaction (DOI) detector in which the scintillation crystal array is extended in one direction. It can be utilized as a PET detector having, for instance, long axial direction. The detector has the "crystal cube (X'tal cube)" structure and the extension was enabled by the feature of the X'tal cube that some MPPCs are always placed close to an originating position of the scintillation photons. X'tal cube is a DOI PET detector we have developed and it can provide isotropic spatial resolution. X'tal cube consists of a scintillation crystal block segmented into cubes and multi-pixel photon counters (MPPCs). A number of MPPCs are coupled on all six sides of the crystal block to detect scintillation photons near their originating position. In a preliminary experiment previously carried out, we confirmed sufficient detector performance of X'tal cube using a prototype composed of a 6 × 6 × 6 array of Lu_2SGd₂(_1-S)SiO₅:Ce (LGSO, x=0.9) crystals with dimensions of 3.0 × 3.0 × 3.0 mm and MPPCs of 3.0 × 3.0 mm active area. In this study, the crystal block was extended in one direction from 6 crystals to 14 crystals. The results of performance evaluation proved that the 6 × 6 × 14 crystals could be identified with the structure. Although MPPCs were coupled on all sides of the crystal block in the extended X'tal cube, at the central part, the detected radiation position would be calculated with mainly the signals of close MPPCs on the four surfaces. That means the detector can be long as considered appropriate for a system while keeping the isotropic spatial resolution.