Physical Problems of Fluoroscopy and Spot-Film Radiography

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Abstract
The physical problems of fluoroscopy and spot-film radiography may be divided into two principal categories: (a) those concerned with the radiation hazards to which the patient and radiologist are exposed during the performance of the procedures and (b) those concerned with the poor visibility which prevails during any fluoroscopic examination and especially during the fluoroscopic study of such heavy structures as the abdomen. Radiation Hazards The effects of x-radiation on biological tissues are generally deleterious, and it is therefore important that the radiation to which the patient is exposed during gastro-intestinal study be maintained at a low value. This requires that the study be carried out under conditions in which the field of vision is restricted by the fluoroscopic shutters to the smallest possible size consistent with an adequate appreciation of the anatomical relationships under study and in which the time of exposure is reduced to the shortest possible interval consistent with a complete examination. Although the biophysicists who recently have expressed so much concern over the delivery of even minute quantities of x-radiation to the body are possibly unnecessarily apprehensive, there can be little doubt that fluoroscopic examinations in which the shutters are opened to give an aperture of the order of 200 square inches for periods of ten and fifteen minutes should be condemned. Unfortunately there are a few radiologists, and many more internists whose offices are equipped with fluoroscopic apparatus, who regularly persist in conducting their fluoroscopic procedures in just such a manner. It is therefore hoped that before long the screens with which conventional fluoroscopes are equipped will be reduced in size, either by convention or by regulation, to dimensions consideraly smaller than the 12 x 16 inches now provided. Experience gained at the University of Chicago Clinics and the Johns Hopkins Hospital, where fluoroscopic screens of the order of 30 to 50 square inches have been in regular service for periods of several years, indicates that such small screens constitute no clinical problem in the examination of any anatomical structure. The small field sizes imposed by these screens have done much to reduce the radiation exposure of the patients who have been examined. This is well shown in Figure 1, where the dosage in roentgens, including back-scatter, received at the incident surface of a phantom of tempered masonite presdwood, 20 cm. in thickness, is plotted as a function of the field of observation on the fluoroscopic screen. The measurements were made with a fluoroscope operating at 85 kv.p. and 4 ma., with a filter of 3 mm. of aluminum and with a target-table top distance of 18 inches. It will be observed that the dosage becomes greater as the field size increases. This rise in dosage, however, does not indicate the entire radiation hazard.

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