Assessment of the gain transfer function of phosphors for application in medical imaging radiation detectors

Objective: to study various phosphors used in detectors of medical imaging systems by the gain transfer function (GTF), defined in terms of X-ray lumi nescence efficiency, light spectrum and modulation transfer function. Materials and methods: four phosphor materials, La2O2S:Tb, Y2O2S:Tb, Y2O2S: Eu and Y2O3:Eu were used in the form of fluorescent layers prepared in the laboratory. The GTF was determined at 30 kVp and 80 kVp X-ray tube voltages for various phosphor coating weights. Results: La2O2S:Tb, which was the highest density and effective atomic numb er phosphor used, was found to exhibit the best GTF performance at 80 kVp. At 30 kVp, the yttrium based phosphors were found of increased performance. This is mainly due to the proximity of the X-ray energy to the K-absorptio n edge of yttrium at 17 keV. Europium activated phosphors were found to per form very well when combined with the red sensitive film and the silicon ph otodiode. Conclusion: The GTF may be a useful method for comparing and selecting phos phor materials for use in various medical imaging applications. (C) 2000 El sevier Science Ireland Ltd. All rights reserved.