Low-cost high-resolution 3rd generation PMT-quadrant- sharing (PQS) BGO block detectors for human and animal PET

The objectives of this work were to investigate the light transport process of Photomultiplier-Quadrant-Sharing (PQS) detector block. The light transport process decides the signal shape and affects detector decoding and timing of detector blocks. We used DETECT2000, a Monte Carlo simulation program of the optical transport process, to study a 52 mm 13times13 crystal array size detector block The crystal was 3.92times3.92times20 mm³ size LSO crystal. Crystals was set to GROUND type surface and 1.8 refraction index. The reflector masks between crystals were set to 0.08 mm thickness, POLISH type surface and 97% reflection rate. The block was coupled to four 51 mm diameter PMT by PQS design. PMT window and optical grease refraction indexes were set to 1.5 and surfaces were set to transparent POLISH type. The PMT photocathode size was set to 47 mm diameter. Both the position and time distribution of the optical photons were got from the simulation. The optical photons were localized on photomultiplier (PMT) photocathode. In the position distribution of detected photons, the half maximum counts region were 17 mm² on block corner and 362 mm² on block center; the tenth maximum counts region were 64 mm² on block corner and 1485 mm² on the center. The region size changed according to reflectors on crystal side. The time spectrum of optical photons showed the rising time were 0.09~0.16 ns. The 95% light collection time were 1.14~1.96 ns.