Development of a large-area monolithic 4×4 MPPC array for a future PET scanner employing pixelized Ce:LYSO and Pr:LuAG crystals

We have developed a new type of large-area monolithic Multi-Pixel Photon Counter (MPPC) array consisting of a 4×4 matrix of 3×3 mm2 pixels. Each pixel comprises 3600 Geiger mode avalanche photodiodes (APDs) that achieve an average gain of 9.68×105 at 71.9 V at 0 °C with variations of only ±7.2% over 4×4 pixels. Excellent uniformity was also obtained for photon detection efficiencies (PDE) of ±6.4%, whilst dark count rates at the single photoelectron (1 p.e.) level amounted to ≃ 2 Mcps / pixel , measured at 0 °C. As the first step toward using the device in scintillation photon detectors, we fabricated a prototype gamma-ray camera consisting of an MPPC array optically coupled with a scintillator matrix, namely a 4×4 array of 3×3 ×10 mm3 crystals. Specifically, we tested the performance with Ce-doped (Lu, Y)2(SiO4)O (Ce:LYSO), Pr-doped Lu3Al5O12 (Pr:LuAG) and “surface coated” Pr:LuAG (Pr:LuAG (WLS)) matrices whereby the emission peak of Pr:LuAG was shifted from 310 to 420 nm via a wavelength shifter (WLS). Average energy resolutions of 13.83%, 14.70% and 13.96% (FWHM) were obtained for 662 keV gamma-rays, as measured at 0 °C with Ce:LYSO, Pr:LuAG and Pr:LuAG (WLS) scintillator matrices, respectively. We confirmed that the effective PDE for Pr:LuAG (WLS) had improved by more than 30% compared to original, non-coated Pr:LuAG matrix. These results suggest that a large-area monolithic MPPC array developed here could be promising for future medical imaging, particularly in positron emission tomography (PET).