Evaluation of powder/granular Gd2O2S:Pr scintillator screens in single photon counting mode under 140 keV excitation

Abstract

The aim of this paper is the evaluation of analternative, low cost solution for the gamma detector in planar imaging. Itis based on a powder scintillator, well established in X-ray imaging, andcould be further exploited in simultaneous bimodal imaging systems. For thispurpose, we have examined the performance of Gd2O2S:Pr powderscintillator, in the form of thick granular screens easily produced in thelaboratory by commercially available Gd2O2S:Pr powder. The screenwas coupled to a round position sensitive photomultiplier tube (R3292PSPMT). The system's evaluation was performed in photon counting mode under99mTc excitation. In all measurements, a general purpose hexagonalparallel collimator was used. Different samples of screens with coatingthickness varying from 0.1 g/cm2 to 1.2 g/cm2 were tested. The 0.6g/cm2 screen, corresponding to ∼ 2 mm actual thickness, was foundmost efficient under 140 keV irradiation. The system`s performance with theproposed screen is reported with the modulation transfer function. Moreoversensitivity, spatial and energy resolution as well as the uniformityresponse using phantoms were measured. The performance of the proposedscreen was compared with two CsI:Tl pixellated crystal arrays with 2 × 2 × 3 mm3 and 3 × 3 × 5 mm3pixel size. A spatial resolution,of 3 mm FWHM, for a 99mTc line source, was achieved at zero source tocollimator distance. In addition, the Gd2O2S:Pr screen showed aslower degradation of the spatial resolution with increasing source tocollimator distance e.g at 20 cm, the Gd2O2S:Pr screen showed aqspatial resolution of 8.4 mm while the spatial resolution of the pixellatedcrystals was 15 mm. Taking into account its easy production, its flexibilitydue to powder form, the very low cost and the good spatial resolutionproperties of the proposed alternative detector, powder scintillators couldpotentially be used for the construction of flexible detector geometries,such as ring type or gamma probes or as a low cost detector solution ineducational photon counting imaging applications, complementary to standardX-ray imaging.