New ultra high resolution LYSO pentagon detector blocks for lower-cost murine PET-CT (MuPET/CT)

We developed and built a solid LYSO detector ring for a new MD Anderson Murine PET (MUPET) camera using regular Ø 19 mm photomultipliers in quadrant-sharing (PQS) configuration. 180 PQS pentagon blocks distributed in 6 sub-rings (30 blocks each) constitute the detector system Each block has nominal dimensions of 19 ×x 19 × 10 mm³ in a 13 × 13 crystal array. To form a zero gap solid ring, PQS-blocks were ground into pentagon shapes with a taper angle of 6° on the edge crystals and optical surfaces. Two crystal widths were used for the blocks; a largest width for two edge crystals and, smallest for inner crystals. We explored the possibility of increasing the detectors performance by implementing new design, materials and techniques, testing the detectors response and, measuring the timing resolution. List-mode data were acquired using Ga-68 source with our high yield pileup-event recovery (HYPER) electronics and data acquisition software. Four PQS-blocks were selected to evaluate our detector quality and our mass-production method. The performances of these blocks were quite similar. A typical block is presented in this study. This block has a packing fraction of 95%. All 169 crystal detectors are clearly decoded, peak-to-valley ratio of 2.4, light collection efficiency of 78% and, energy resolution of 14% at 511 keV. Average timing resolution of 430-ps (FWHM) was achieved by single crystal with PQS block-to-block coincidence of 530-ps. This PQS-pentagon block design shows the feasibility of high resolution (~1.2 mm) MuPET-CT detector ring using the lower cost Ø 19 mm PMTs as an alternative to the more expensive position sensitive PMTs or solid state detectors.