Continuous LYSO-SSPM array based PET detectors for clinical and small volume imaging studies

We are developing a large area thick continuous LYSO-solid state photomultiplier (SSPM) array based PET detectors to exploit the potential applications in clinical and small volume imaging studies. The PET detector design for clinical applications consists of a 47×47×14 mm³ slab of LYSO crystal sandwiched between two 8×8 element SSPM arrays with 5×5 mm² elements. The detector module for higher resolution, small volume imaging studies consists of a thin sheet ~5-10mm of LYSO scintillator sandwiched between two 12×12 element SSPM arrays with 1.5×1.5 mm² elements. Towards addressing this goal, here we present the construction and evaluation of 8×8 element SSPM array with each element being 5mm × 5mm in size. The SSPM array with an imaging area of 47×47 mm² was created by close-tiling RMD´s 2×2 array of 5×5 mm² SSPM chips in a 4×4 format. Pixel uniformity, energy resolution and timing resolution for individual pixels in the 8×8 array was studied by coupling a single LYSO crystal measuring 3×3×15 mm³ to each SSPM pixel in the array. The measured photopeak amplitude for 511 keV gamma-rays varied from 66 to 100 over the array. The energy resolution for all pixels in the array ranged from 10% to 12.5% (FWHM). The measured timing resolution for all pixels was in 700ps to 800ps range. Continuous crystal based PET module was also built by coupling a 47×47×8 mm³ slab of polished LYSO crystal to the 8×8 SSPM array. The energy resolution measured in the center of the crystal was 16.4% (FWHM) and at the edge it was 16.8% (FWHM). The coincidence timing resolution measured against LYSO-PMT detector was 1.1ns in the center and 1.3ns at the edge of the crystal. We also discuss the performance of a monolithic 6×6 SSPM array with each element 1.5mm × 1- 5mm for smaller volume, higher resolution PET detectors. The energy resolution for all pixels in the array ranged from 13% to 15%. The measured timing resolution for all pixels was in the range of 500ps to 550ps.