CsI(Tl) micro-pixel scintillation array for ultra-high resolution gamma-ray imaging

The aim of this paper is to investigate the intrinsic spatial resolution limit by coupling a CsI(Tl) micro-pixel scintillation array to position sensitive photomultipliers (PSPMTs) for ultra-high resolution gamma-ray imaging. On this purpose, 1 mm thick array with 0.2 mm pixel side, 0.4 mm pitch has been realized by Spectra Physics (Hilger). The present scintillation arrays technology is suitable to produce larger crystal areas. In this paper we present spatial resolution and positioning results obtained by coupling the micro-pixel scintillation array to Hamamatsu square PSPMTs: 1' R8520-C12, 1' R5900-L16 and 2' H8500 Flat panel PMT. Preliminary measurements demonstrate better performance in term of uniformity response when micro-pixel array is coupled to a H8500 PSPMT model. This setup carries out an intrinsic spatial resolution lower limit of about 0.6 mm FWHM at 50% FWHM energy resolution, defining it as the minimum scintillation array pitch detectable at 122 keV. The results obtained by R5900-L16 with a better sampling of the scintillation light has shown an improvement of the position linearity in spite of a worse spatial resolution due to the poor light output of scintillation array. Index Terms--Biomedical nuclear imaging, photomultipliers, scintillation detectors.