Luminance distribution of x-ray image intensifiers

For a number of reasons, the luminance distribution of the output image of an X-ray image intensifier (I.I.) tube is not uniform but has a tendency to decrease toward the periphery. The reasons for this were investigated by measurement and calculation using two types of variable field I.I. with different viewing-field sizes and distances from the focal spot of the X-ray tube to the entrance plane (FED). The most significant cause of the nonuniformity in the luminance distribution is nonuniformity of the local area demagnification ratio (or distortion) of the image and the second is nonuniformity of the local photoelectric sensitivity of the input screen. The nonuniformity of an I.I. can be improved by selecting a smaller viewing field or a larger FED. The distortion of the image is divided into that from the entrance plane to the input screen and that from the input screen to the output screen, the latter being rather more significant. (author)