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

A theoretical description of the effect of light generation and light atten uation properties on the imaging performance of phosphor materials used in radiation detectors of medical imaging systems is presented. The descriptio n is based on a theoretical model employing analytical expressions for the detector optical gain (DOG) (emitted optical quanta per incident X-ray), th e modulation transfer function (MTF) and the detective quantum efficiency ( DQE) as functions of optical properties of phosphors. The model was used to Bt experimental DOG-data and to estimate the values of two important param eters:(l) the intrinsic X-ray to light conversion efficiency, expressing th e property of light generation within the phosphor material, (2) the recipr ocal diffusion length, expressing the property of light attenuation within the phosphor material. For this study, La2O2S:Tb, Y2O2S:Tb, Y2O2S:Eu, and Y 2O3:Eu phosphor materials were employed. Additionally, the sensitivity of D OG, MTF, and DQE on the variation of the intrinsic X-ray to light conversio n efficiency and of the optical attenuation coefficient within the phosphor was theoretically studied. It was found that (1)DOG increases with increas ing intrinsic X-ray to light conversion efficiency and decreases with incre asing optical attenuation coefficient: (2) MTF increases with increasing op tical attenuation while it remains unaltered by varying the intrinsic X-ray to tight conversion efficiency and (3) DQE decreases with increasing optic al attenuation and remains constant with increasing X-ray to light conversi on efficiency. (C) 2001 Elsevier Science B.V. All rights reserved.