Cinefluorography employing split-image television type image amplifiers.

Abstract

In September 1955 Russell Morgan read (1), and in January 1956 published (2) a paper concerning the history and theory of image amplification. He dealt particularly with his own system that employs an RCA Image Orthicon but mentioned research that was in progress on television type amplifiers that are directly sensitive to x-rays without the necessity of first converting them into visible light. The x-ray image amplifier developed recently for General Electric by their Mr. John E. Jacobs is an instrument of this latter type. This report will describe its construction and operation and point out certain important differences between it and the amplifiers of Westinghouse, Philips, Morgan, and Moon. Preliminary cineradiographic results using the General Electric amplifiers will be presented. The Westinghouse (3) and Philips (4) amplifiers (Figs. 1 and 2) have been shown repeatedly at radiological meetings in recent years, are available commercially, and have enjoyed some clinical use in Europe and the United States. They are so similar in construction and operation that a description of one serves for both. An x-ray beam, having passed through the part that is being examined and the glass wall of the tube, falls on a cathode “sandwich” consisting of a thin, spherically curved disk of radiolucent material (such as aluminum or magnesium) coated with a fluorescent salt (such as activated zinc cadmium sulfide) surfaced with a photoelectric layer (such as activated cesium oxide). The x-ray quanta are converted into photons of visible light by the fluoroscopic screen, and the light causes electrons to be emitted by the surface layer of photoelectric material. These electrons are focused, accelerated, and delivered to a small anode that is coated with a phosphor (such as activated zinc cadmium sulfide), where they are converted back into a visible image many times brighter than the original. Such amplifiers are simple to construct and operate and could be produced cheaply if volume sales could be attained, but they have several faults, including the need for three conversions from one type of energy to another, with considerable loss at each conversion. 1. An invisible x-ray image is converted into a visible light image 2. This visible light image is converted into an invisible electron image 3. The invisible electron image is converted back into a visible light image Moon's method, which employs a scanning x-ray tube (Figs. 3 and 4), constitutes an entirely different approach to the problem (5, 6). A sharply focused, high-energy, electron beam scans a water-cooled tungsten target, producing x-rays at each of its myraid points of impingement. A tiny beam of these x-rays emerging from a pinhole in a lead baffle sweeps through space in synchronism with the scanning electron beam and falls on a large, dense, “water-clear” crystal of calcium fluoride, which absorbs it almost completely and converts it into light.