Modeling the effect of light generation and light attenuation properties on the performance of phosphors used in medical imaging radiation detectors

Abstract

A theoretical description of the effect of light generation and light attenuation properties on the imaging performance of phosphor materials used in radiation detectors of medical imaging systems is presented. The description is based on a theoretical model employing analytical expressions for the detector optical gain (DOG) (emitted optical quanta per incident X-ray), the modulation transfer function (MTF), and the detective quantum efficiency (DQE) as functions of optical properties of phosphors. The model was used to fit experimental DOG-data and to estimate the values of two important parameters: (1) the intrinsic X-ray to light conversion efficiency, expressing the property of light generation within the phosphor material; (2) the reciprocal diffusion length, expressing the property of light attenuation within the phosphor material. For this study, La 2O 2S : Tb, Y 2O 2S : Tb, Y 2O 2S : Eu, and Y 2O 3 : Eu phosphor materials were employed. Additionally, the sensitivity of DOG, MTF, and DQE on the variation of the intrinsic X-ray to light conversion efficiency and of the optical attenuation coefficient within the phosphor was theoretically studied. It was found that (1) DOG increases with increasing intrinsic X-ray to light conversion efficiency and decreases with increasing optical attenuation coefficient; (2) MTF increases with increasing optical attenuation while it remains unaltered by varying the intrinsic X-ray to light conversion efficiency and (3) DQE decreases with increasing optical attenuation and remains constant with increasing X-ray to light conversion efficiency.