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

摘要

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 ℃, 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_3Ga_3Al_2O_(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).