Studies on sub-millimeter LYSO:Ce, Ce:GAGG, and a new Ce:GFAG block detector for PET using digital silicon photomultiplier

The spatial, timing, and energy resolutions of a detector affect the image quality of a positron emission tomography (PET) system. These parameters are in turn dependent on various factors, such as the choice of scintillator, photodetectors, reflector material, and surface treatment (rough or polished) of the scintillators. In this study, we investigated the performances of sub-millimeter scintillator array, LYSO:Ce (polished and rough surfaces with BaSO4reflector or enhanced specular reflector (ESR)), a gadolinium aluminum gallium garnet (Ce:GAGG, rough surface with BaSO4reflector), and a new gadolinium fine aluminum gallate (Ce:GFAG, rough surface with BaSO4reflector) detectors. The outer dimension of each scintillator block was ∼12 × 12 mm with a 12 × 12 matrix of 0.9 ×0.9× 6 mm3 crystal elements. These blocks were optically coupled to a digital silicon photomultiplier (dSiPM, DPC-3200-22-44) with a 1 mm thick optical guide. Experiments were conducted at a sensor temperature of ∼15 °C, and a two-dimensional position histogram for 22Na gamma photons showed that all pixels were clearly resolved for all block detectors (peak-to-valley ratios ranging from 5.3 to 11.1). The average energy resolutions for the LYSO (ESR, rough), LYSO (ESR, polished), LYSO (BaSO4, rough), LYSO (BaSO4, polished), GAGG (BaSO4, rough), and GFAG (BaSO4, rough) arrays were measured as 11.3%, 10.2%, 18.7%, 10.3%, 10.0%, and 13.2% full width at half maximum (FWHM), respectively. The coincidence resolving times (with 3 × 3 × 5 mm3 LYSO crystal as reference) for the LYSO (ESR, rough), LYSO (ESR, polished), LYSO (B aSO4, rough), LYSO (BaSO4, polished), GAGG (BaSO4, rough), and GFAG (BaSO4, rough) arrays were 209 ps, 222 ps, 197 ps, 230 ps, 321 ps, and 276 ps, respectively. In conclusion, the new GFAG scintillator may be a promising candidate for future high-resolution time-of-flight (ToF) PET systems, considering the tradeoff between its performance and potential to be grown at a lower cost.