Experimental investigation of the optical signal, gain, signal-to-noise ratio and information content characteristics of X-ray phosphor screens

In this study, the quality of medical images produced by X-ray phosphor scr eens is described by a model based on the light generation and emission pro perties of the phosphor material. Combined detector gain (CDG), modulation transfer function (MTF), detective quantum efficiency (DQE) and information capacity (IC) of the screens were expressed and evaluated as functions of emitted optical fluence, incident X-ray fluence and emitted optical spectru m. Phosphor screens with coating thickness ranging from 21 mg/cm(2) to 137 mg/cm(2) were prepared in the laboratory and were irradiated by X-rays with X-ray voltages from 50 to 140 kVp. Experimental data were obtained in both transmission and reflection modes of measurement (light emission from both screen sides). Results showed that most image quality parameters (CDG, MTF DQE) depend strongly on phosphor screen thickness. CDG and DQE also depend on X-ray tube voltage. However, the total quantity of information (IC), wh ich depends on both the incident X-ray fluence and phosphor material type, was not found to be significantly affected by phosphor thickness.