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Fluoroscopy and fluoroscopic procedures were performed within months after the discovery of x-rays in 1895. These procedures were conducted with a fluoroscopic screen which the examiner viewed directly in a darkened room under conditions of rod vision. When I entered the field of medical physics in the late 1940's, this approach to fluoroscopy was still being used, and it was a rather poor method of obtaining information about the patient. Nevertheless, a considerable amount of help in the diagnosis of disease was achieved with this conventional mode of fluoroscopy. In the early 1950's, image intensif-ied fluoroscopes became available, and immediately there was a spectacular increase in brightness and realizable resolution and a correspogding spectacular increase in information retrieval from the fluoroscopic process. The major factor in these advances was conversion to the use of cone vision rather than rod vision. Although the image intensifier provided a spectacular increase in information retrieval, there was not a startling decrease in patient dose, although there was some; perhaps a factor of two or three. Most of the signal amplification provided by the image intensifier was used to create a brighter image and improve information retrieval, and little was applied towards the reduction in patient dose. Perhaps never again in the medical use of x-rays will we obtain such a spectacular improve-ment in information retrieval with an accompanying reduction in patient dose. Of course, initially there was some opposition to image intensified fluoroscopy. One objection was to the small field; early intensifiers had only a 5 inch input screen and radiologists had been used to a big rectangular screen for viewing. Some radiologists had difficulty identifying where they were anatomically during the examination. Incidentally, this problem no longer seems to exist, as evidenced by the fact that the sale of 6 inch intensifiers far exceeds that of 9 inch intensifiers. At present there does not seem to be much interest in larger intensifiers. One factor that did cause concern with the advent of image intensifiers was the constant need to vary machine parameters such as kVp, mA, etc., to maintain an image of constant brightness with changes in patient thickness and density. This problem stimulated the development of image intensified fluoroscopy with automatic brightness control (ABC). This development occurred in the mid 60's.
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