An experimental method to determine the effective luminescence efficiency of scintillator-photodetector combinations used in X-ray medical imaging systems.

The scintillator effective luminescence efficiency, which may be defined in terms of the scintillator's X-ray luminescence efficiency and the scintillator-photodetector spectral matching and geometrical configuration, was studied for various X-ray imaging applications. Four scintillator materials Gd2O2S:Tb, Y2O2S:Tb, ZnSCdS:Ag and CsI:Na were used to prepare test screens. They were evaluated in relation to various photodetectors used in X-ray imaging, such as radiographic films, photocathodes, and photodiodes. Effective luminescence efficiency was determined for a range of X-ray tube voltages (50-140 kVp) by measuring the light flux emitted per unit of incident exposure rate and the spectra of the light emitted by the four scintillators. Scintillator-photodetector combinations resulting in higher image brightness level were determined for different X-ray imaging systems. Findings indicate that CsI:Na is very efficient with orthochromatic radiographic films, Gd2O2S:Tb could be useful in conventional or digital fluoroscopy and in CT and ZnSCdS:Ag could be employed in some medium to low voltage digital radiography applications.