Reduction of background luminance generated in the output screen of x-ray image intensifier tubes

Background luminance of several origins introduced into an X-ray image intensifier tube deteriorates the contrast of its output image. The output screen, which consists of a phosphor layer usually prepared on a transparent substrate, generates influential background luminance in the X-ray image intensifier tube. A theoretical and experimental study on how reduce the background luminance of the output screen by increasing the thickness of the substrate is presented. In evaluating the effect of the background luminance, we calculated and measured the contrast ratio usually used as a characteristic index of the image intensifier tube. The theory and results from the experimental image intensifier tubes show good agreement. This method of background luminance reduction is not only more economical but also superior to the other methods utilizing dark substrates or optical fiber plates. (author)