Optical gain signal-to-noise ratio transfer efficiency as an index for ranking of phosphor- photodetector combinations used in X-ray medical imaging

Abstract

Phosphor materials are used in medical imaging combined with radiographic film or other photodetectors. A parameter for choosing a phosphor material is the number of light photons produced per absorbed X-ray energy E, i.e. phosphor gain. Traditionally, a parameter for choosing the best photodetector for a phosphor material is the spectral matching factor, which denotes the percentage of the optical photons detected by the photodetector. However, this factor does not account for the phosphor gain neither in terms of signal strength nor in terms of noise. In this paper a new factor is introduced which evaluates phosphor-photodetector combinations in terms of optical gain signal-to-noise ratio matching. The proposed factor was implemented to some phosphor-photodetector combinations. It was found that for the narrow band emitting phosphors studied the results of the new factor and the matching factor were numerically the same. However, when not narrow bandwidth emitting phosphors were considered the results were numerically different. Additionally, for the case of CsI:Na phosphor different results were obtained in combinations ranking.