The effect of the grain size distribution (GSD) on the light emission performance of phosphor-based X-ray detectors

Abstract The light emission performance of indirect, phosphor-based, X-ray detectors has significantly affected image quality and diagnostic validity of the medical imaging examinations. This issue has been investigated by examining and further understanding the optical anisotropy in optical diffusion mechanisms. One crucial parameter of phosphor's structural properties that remarkably changes light distribution is the size of the phosphor particles. Up to now, the vast majority of studies have been carried out considering phosphor materials consisted of grains of equal size. In the present article an attempt is made to investigate the influence of grain size distribution (GSD) on light emitting characteristics and compare it with the condition of mean values assumptions. Our investigation was based on LIGHTAWE Monte Carlo simulation code with purpose to examine the Gd2O2S:Tb phosphor layer extracted from a mammographic Kodak Min-R 2 Cassette. The GSD was determined via scanning electron microscopy (SEM). Three cases of mean values were taken into account: (i) 1.48 μm obtained calculations of the aforementioned GSD, (ii) 2.50 μm and 7.00 μm taken from previous articles and manufacturer datasheets. Light emission was performed under different irradiation conditions (i. e., light quanta are produced by light source or an X-ray beam) and in terms of light amount and distribution. Our investigation showed that the optical distribution in real GSD was found: (a) sharper than the calculated mean value of the GSD and (b) broader than the mean value taken from the manufacturer datasheet. In particular, the deviation of GSD was found significantly high compared to 7.00 μm mean value. Examining the spatial resolution properties of both conditions, the deviation was around 16.5%, 18.2%, 14.8% assuming that the light source is situated within the phosphor mass, an X-ray beam of 20 keV and X-ray beam of 30 keV, respectively.