Imaging performance of silicon photomultipliers coupled to BGO and CsI: Na arrays

The aim of this study is to investigate the imaging performance of a silicon photomultiplier array (ArraySL-4) photodetector for possible PET and potentially SPECT applications using BGO and CsI(Na) pixellated scintillators. Our main objectives are: i) the comparison of the ArraySL-4 to the older version SensL's SPMArray4 photo detector in terms of energy resolution and peak to valley ratio of a row profile in the flood image and ii) the study of the effect of different coupling schemes using ultra transmitting glass windows of various thicknesses. We acquired raw images from two pixellated scintillators (BGO with 2 x 2 x 5mm(3) and CsI: Na with 1 x 1 x 5mm(3) pixel sizes) irradiated with 511 keV and 1274.5 keV g -rays from a 22Na source. The SiPM array detector allowed the clear visualization of the discrete 2 x 2mm(2) pixellated BGO and 1 x 1mm(2) CsI: Na scintillator elements at room temperature (no cooling). The energy resolution of the new SensL ArraySL-4 detector for the 2 x 2 x 5mm(3) BGO pixellated scintillator array is improved for rather 6 percentage points (energy resolution improvement equal to 22%) and the peak to valley ratio is measured higher for both scintillator arrays (for BGO 68% (1 : 7 x) and for CsI: Na 154% (2 : 5 x)) compared with SPMArray4. The clear identification of the 1 x 1mm(2) CsI: Na scintillator elements provides evidence that the combination of those SiPMs with even smaller arrays can be used as an efficient imaging detector module. Optical coupling significantly improves image uniformity, while the use of BK7 ultra transmitting glass window with 1.35mm thickness provided the best measure energy resolution equal to 21.5%.