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

Abstract 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 mm 2 and 3600 Geiger mode avalanche photodiodes (APDs). For typical operational gain of 7.5×10 5 at +20 °C, gain fluctuation over the entire MPPC device is only ± 5.6 % , and dark count rates (as measured at the 1 p.e. level) amount to ≤ 400 kcps 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 ( SiO 4 ) O (Ce:LYSO) crystal array (4×4 array of 3×3×10 mm 3 crystals). Energy and time resolutions of 11.5 ± 0.5 % (FWHM at 662 keV) and 493 ± 22 ps 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 % (FWHM) was obtained. Finally, we fabricated submillimeter Ce:LYSO and Ce-doped Gd 3 Ga 3 Al 2 O 12 (Ce:GGAG) scintillator matrices each consisting of 1.0×1.0, 0.7×0.7 and 0.5×0.5 mm 2 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 137 Cs source. The energy resolutions for 662 keV gamma-rays for each Ce:LYSO and Ce:GGAG scintillator matrix were ≤ 14.3 % . These results suggest excellent potential for its use as a high spatial medical imaging device, particularly in positron emission tomography (PET).