Standards for measurement of brightness intensification in fluoroscopic image intensifiers

It is convenient to characterize devices for production of intensified X-ray fluoroscopic images in terms of their brightness as compared with conventional fluoroscopic screens. Thus, an X-ray image intensifier is described having an intensification factor of 200 or 500 or 1,000 meaning that the image presented to the viewer is 200 or 500 or 1,000 times brighter than the image would be if he used a conventional X-ray screen. These figures, although widely used today, are meaningless unless all variables are defined and standardized in their measurement. Furthermore, the same term has been used to express the brightness relationship between a light image from a phosphor at the input end of an image device and the light image output. In the case of a fluorescent screen contiguous to a photoelectric surface in a vacuum, the input light image used as the base point can be quite different from, and is usually less bright than, the conventional fluoroscopic screen image under equal stimulus. However, to the best of the author's knowledge, no previous attempt has been made to propose a set of standard conditions on which to base a figure of merit for X-ray image intensifiers.