The engineering design and construction of an ultra-high resolution high-sensitivity preclinical PET/CT — MuPET

An ultra-resolution high-sensitivity preclinical PET/CT - MuPET is designed and manufactured. The detector system is a triacontagon shape which is very close to a perfect cylindrical ring. The inner diameter of the ring is 165 mm and the axial length is 116 mm. The detector system is using 180 PMT-quadrant-sharing (PQS) blocks - 30 blocks per ring and 6 rings axially with 210 low-cost round PMTs for PQS decoding. Each block consists of 169 LYSO crystals in a 13×13 array. The Slab-Sandwich-Slab (SSS) production methodology is used for the mass production of the 19×19×10 mm³ cuboid blocks. The cuboid blocks are then ground into pentagon shape with a taper angle of 6° at the two side faces, which can eliminate the wedge shape gaps between blocks inside the detector ring to increase the sensitivity. Two crystal widths are used: the small one of 1.32 mm for the 11 crystals in the middle and the large one of 1.76 mm for the 2 crystals on both sides. Using large crystal size can compensate the volume loss due to the grinding, thus improve the uniformity of the individual crystal sensitivities which will benefit the data acquisition and processing. The no-gap detector ring is finished and mounted on the coliseum shape PMT holder with high accuracy. 210 Hamamatsu R1450 19-mm PMTs are selected and sorted base on their gain and dark current, and optical coupled to the detector ring. High voltage dividers and front-end electronics are also mounted inside the PET unit enclosure. The assembled PET module is then inserted into an existing PET/CT gantry which has a cone beam CT installed already. The new PET/CT system is under system debugging and tuning. The preliminary testing results show 5% sensitivity with energy window of 300 to 650 keV, which has the potential to be improved further. The resolution is better than 1.3 mm near the FOV center and the high quality Micro-Deluxe phantom image is obtained.