Effect of CsI(Tl) micro-conical-frustums on the performance of the pixelated CsI(Tl) scintillation screen in X-ray imaging

Abstract

The pixelated CsI(Tl) scintillation screen based on oxidized silicon micro-pore array template with CsI(Tl) micro-conical-frustums (CMCF) was proposed. The effect of the CMCF on the performance of the pixelated CsI(Tl) scintillation screen in X-ray imaging was studied by using Geant4 Monte Carlo simulation code. The variations of the light output (LO), modulation transfer function (MTF) and detective quantum efficiency (DQE) for the screen with the cone angle β of the CMCF in X-ray imaging were revealed. The results show that the LO of the pixelated scintillation screen with CMCF is superior to that of the screens with CsI(Tl) micro-cylinders (CMC) or with reversed CsI(Tl) micro-conical-frustums (RCMCF), but the spatial resolution of the X-ray imaging system by using the pixelated scintillation screen with RCMCF is better than that by using the screens with CMCF or with CMC. At low frequency, the cone angle β corresponding to DQEs from good to bad are 2.40°, 0.00°and -2.40°. But at high frequency, the cone angle β corresponding to DQEs from good to bad change to 2.40°, -2.40°and 0.00°. The reason is that, for a pixelated scintillation screen, the DQE for the screen not only depends on the efficiency of X-ray absorption, but also depends on the number of scintillation photons exiting the bottom the screen per interacting X-ray photon and its Poisson excess, and MTF. The simulated results of DQEs show that the comprehensive performance of the pixelated CsI(Tl) screen with CMCF in X-ray imaging is better than that of the screens with CMC or with CRMCF.