Assessing the information content of phosphor produced medical images:: application to Zn2SiO4:Mn phosphor

In this study a method to assess the information content of medical images produced by phosphors is described. The optical signal emitted by the phosphor after X-ray excitation, the detective quantum efficiency (DQE), expressing the signal-re-noise ratio (SNR) transfer efficiency, and the information;capacity were experimentally determined. The method was based on light flux and modulation transfer function (MTF) measurements and was used to assess the imaging performance of the Zn2SiO4:Mn phosphor. The latter was employed in the form of laboratory prepared phosphor layers (test screens). Results showed that high values for optical signal emission and DQE were obtained for medium thickness phosphor layers (56 and 89 mg/cm(2)) at 20 kVp X-ray tube voltage. The information capacity was found to decrease continuously with phosphor coating weight. (C) 2000 Elsevier Science Ltd, All rights reserved.