Development of a high-resolution and depth-of-interaction capable detector for time-of-flight PET

PET with its quantitative powers is becoming increasingly popular in the clinic. While the detector spatial resolution and sensitivity directly affect its ability, it has been shown that including the time-of-flight information further enhances its powers. Currently numerous approaches are being pursued to improve spatial resolution and timing, but most involve trade-offs. We describe here the development of a high-resolution PET detector with time-of-flight capabilities. The detector design is based on our previously developed pixelated Anger-logic detector where an array of individual crystals is readout by an array of larger photomultiplier tubes (PMTs) coupled to it via a light-guide. Depth-of-interaction (DOI) measurement in this design is accomplished by making use of a dual crystal-layer offset relative to each other. With a target spatial resolution of 1-2 mm, we have carefully evaluated the performance of several 1.5 × 1.5 and 2.0 × 2.0 mm² and 10-20 mm long LYSO crystals readout by several appropriately sized PMTs. Experiments and simulations were used to investigate the design, and optimize performance of the detector. An experimental prototype using a single 8 × 7 array of 1.5 × 1.5 × 12 mm³ LYSO crystals readout by a 7-PMT array of the Hamamatsu R4124 PMTs was developed. A high-speed waveform sampling data acquisition system based on the DRS4 switched-capacitor that digitizes data at 5 GS/s was also built. Experimental evaluations demonstrate that the detector provides very good timing and also successfully discriminates 1.5 × 1.5 mm² cross-section scintillation crystals. Bench-top timing measurements with a dual-layer detector demonstrate that relatively good timing can be maintained in a stacked crystal arrangement, suggesting the feasibility for extending the approach to incorporate DOI with this design.