Development of PET detectors using monolithic scintillation crystals processed with sub-surface laser engraving technique

New monolithic scintillation detectors for PET have been developed, where the crystals are processed using internal focused laser processing technique, which is called subsurface laser engraving (SSLE) technique. When high intensity light pulses of short duration from a laser are focused into a scintillation crystal, they induce multi-photon absorption at the focal point and result in refractive index changes or micro-cracks inside the crystal. By applying the SSLE technique to a monolithic scintillation block, fine segmentation in the crystal can be formed without inter-pixel gaps. We have fabricated 2D segmented arrays engraved various patterns of micro-cracks inside monolithic LYSO crystal blocks by using a Nd:YAG laser. The processed crystal array segmented to 12 × 12 with 1.67 mm pitch have been evaluated by coupling to a position-sensitive photomultiplier tube (PS-PMT). The 2D position histograms were measured for uniform irradiation of gamma-rays and each crystal segment was clearly separated. The average energy resolution was 9.7%, similar to that of the conventional arrays, so that the laser processed LYSO crystals have kept their primary scintillation properties. We have also evaluated the laser processed crystals by using multi-pixel photon counters (MPPCs) to investigate the possibilities as a future PET detector. These results suggest that it is possible to fabricate high performance PET detectors using the SSLE technique.