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 defin ed in terms of the scintillator's X-ray luminescence efficiency and th e scintillator-photodetector spectral matching and geometrical configu ration, was studied for various X-ray imaging applications. Four scint illator materials Gd2O2S:Tb, Y2O2S:Tb, ZnSCdS:Ag and CsI:Na were used to prepare test screens. They were evaluated in relation to Various ph otodetectors used in X-ray imaging, such as radiographic films: photoc athodes, and photodiodes. Effective luminescence efficiency was determ ined 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-photodete ctor combinations resulting in higher image brightness level were dete rmined for different X-ray imaging systems. Findings indicate that CsI :Na is very efficient with orthochromatic radiographic films, Gd2O2S:T b could be useful in conventional or digital fluoroscopy and in CT and ZnSCdS:Ag could be employed in some medium to low voltage digital rad iography applications.