Performance of the X’tal cube PET detector using 1 mm thick scintillator plates segmented to 1 × 1 mm² by laser processing

Objectives X’tal cube is a 3D position sensitive radiation detector we have developed for PET. Its structure is that multi-pixel photon counters (MPPCs) are coupled on all surfaces of the scintillation crystal block segmented 3 dimensionally into cubes. No reflector is inserted into the crystal block so that scintillation light spreads to all surfaces and detected by all MPPCs. Previously, we presented the study about the crystal block condition by comparing the block composed of small cubic scintillator elements and the block consisted of a monolithic scintillator segmented by laser processing technique. As a new condition, we have tried to compose the block with stacking scintillator plates segmented 2 dimensionally by laser. Because we got sufficient performance for the segmentation into 2 × 2 × 2 mm³, as the next step, we evaluated performance of the X’tal cube using scintillator plates having the segmentation into 1 × 1 × 1 mm³.

Methods We stacked 18 of the LYSO plates with dimensions of 18 × 18 × 1 mm³ for the crystal block. Each plate was segmented to 18 × 18 array using laser by Hamamatsu Photonics K.K., Japan. Between plates were air gaps. 4 × 4 MPPCs of 50 μm type were coupled onto each surface of the crystal block. We used ²²Na sources and selected the events caused by 511 keV gamma-rays by setting energy window. Segment identification performance was evaluated in a 3D position histogram in which each segment response is appeared as the results of Anger-type calculation with all MPPC signals.

Results Some segment responses overlapped, however, most responses could be identified.

Conclusions For easy production of the X’tal cube, we used scintillator plates segmented by laser. As a result of performance evaluation, 1 mm³ detector spatial resolution was obtained most part of the X’tal cube except some outer segments.

Research Support Funds from the Japan Society for the Promotion of Science for a Grant-in-Aid for Scientific Research (no. 23602017).