The Johns Hopkins fluoroscopic screen intensifier.

Abstract

In recent years, considerable attention has been focused upon our need for brighter fluoroscopic screens. It has been pointed out that the clarity of fluoroscopic vision should be improved many times, that the need for dark adaptation before fluoroscopy should be eliminated, and that the radiation dosage delivered to the patient and radiologist during fluoroscopy should be reduced if brighter screens were available to us. A few years ago work was begun in at least three laboratories in this country to develop devices by which fluoroscopic screens may be brightened or intensified. Coltman (1) at the Westinghouse laboratories in East Pittsburgh undertook investigations which have recently culminated in the development of an electronic image tube capable of intensifying the fluoroscopic screen approximately one hundred and fifty times. A short time later, Moon (2), at the University of Chicago, began work directed toward the development of a screen intensifier based on the “flying spot” system used in television. Although practical results have not yet been achieved, Moon (3) anticipates large gains in screen brightness with this system. Early in 1948, studies in screen intensification were undertaken at the Johns Hopkins Hospital. Our first research was concerned with investigation of the fundamental physical and physiological factors influencing fluoroscopic vision (4). Work was then begun on the development of a screen intensifier which, we hoped, would yield gains in screen brightness of 1,000 times or more. This instrument has just been completed and placed under test in our laboratory. It has not been described heretofore. Constructional Details The complete intensifier, arranged for clinical study, is illustrated in Figure 1. It compris es three principal units: (a) a conventional fluoroscopic x-ray generator operating at kilovoltages ranging from 70 to 100 kv.p. and at a tube current of 5 ma.; (b) an x-ray image detector; (c) a fluoroscopic viewing unit. The principles upon which these three units operate together may be visualized in Figure 2. The x-rays produced by the fluoroscopic generator, A, pass through the anatomical structure under examination, B, and enter the x-ray image detector unit. Within this unit, the radiation first passes through a stationary wafer grid, C, and then impinges upon a fluorescent screen of a conventional zinc sulfide type, D. The images appearing on the fluorescent screen are then focused on the sensitive surface of an image orthicon, G, by a folded Schmidt optical system consisting of three plane mirrors, M, a corrector plate, P, and a spherical mirror, F. The image orthicon, an electronic tube used in many television cameras, converts the fluorescent images into an electric current which is amplified many times, first by a preamplifier, H, and after that by a final amplifier, J.