A novel gamma-ray detector with submillimeter resolutions using a monolithic MPPC array with pixelized Ce:LYSO and Ce:GGAG crystals

We have developed a large-area monolithic Multi-Pixel Photon Counter (MPPC) array consisting of 4×4 channels with a three-side buttable package. Each channel has a photosensitive area of 3×3 mm2 and 3600 Geiger mode avalanche photodiodes (APDs). For typical operational gain of 7.5×105 at +20 °C, gain fluctuation over the entire MPPC device is only ±5.6%±5.6%, and dark count rates (as measured at the 1 p.e. level) amount to ≤400kcps per channel. We first fabricated a gamma-ray camera consisting of the MPPC array with one-to-one coupling to a Ce-doped (Lu,Y)2(SiO4)O (Ce:LYSO) crystal array (4×4 array of 3×3×10 mm3 crystals). Energy and time resolutions of 11.5±0.5%11.5±0.5% (FWHM at 662 keV) and 493±22ps were obtained, respectively. When using the charge division resistor network, which compiles signals into four position-encoded analog outputs, the ultimate positional resolution is estimated as 0.19 mm in both X and Y   directions, while energy resolution of 10.2±0.4%10.2±0.4% (FWHM) was obtained. Finally, we fabricated submillimeter Ce:LYSO and Ce-doped Gd3Ga3Al2O12Gd3Ga3Al2O12 (Ce:GGAG) scintillator matrices each consisting of 1.0×1.0, 0.7×0.7 and 0.5×0.5 mm2 pixels, to further improve the spatial resolution. In all types of Ce:LYSO and Ce:GGAG matrices, each crystal was clearly resolved in the position histograms when irradiated by a 137Cs source. The energy resolutions for 662 keV gamma-rays for each Ce:LYSO and Ce:GGAG scintillator matrix were ≤14.3%≤14.3%. These results suggest excellent potential for its use as a high spatial medical imaging device, particularly in positron emission tomography (PET).

► We developed a newly designed large-area monolithic MPPC array.
► We obtained fine gain uniformity, and good energy and time resolutions when coupled to the LYSO scintillator.
► We fabricated gamma-ray camera consisting of the MPPC array and submillimeter pixelized LYSO and GGAG scintillators.
► In the flood images, each crystal of scintillator matrices was clearly resolve.
► Good energy resolutions for 662 keV gamma-rays for each LYSO and GGAG scintillator matrices were obtained.