Background generation at input screens of x-ray image intensifiers

The background luminance due to the input screen of an X-ray image intensifier (I.I.) was investigated quantitatively as a function of several parameters by means of contrast ratios. The contrast ratio of the input screen increases as the curvature of the screen, the transparency of the photoelectric surface or the reflectance at the inner surface of the electrodes decreases. By comparing measured contrast ratios of actual I.I.s, the contribution of the background luminance at the input screen to that of the I.I. was estimated. The contrast ratio of the input screen ranges from 40 to 200, while those of the ordinary I.I. and the ordinary output screen are 14 and 26 respectively. (author)