II. The Present Medical Applications

Abstract

There is no difficulty in obtaining a xeroradiograph of a thin part of the body such as the hand. Over a comparatively wide range of charge and development time the picture is immediately recognisable even though the appearance of the plate as viewed by reflected light is quite different from that of an ordinary radiograph. Careful comparison of the results with the radiograph shows that bone detail readily visible in the latter is not always visible on the xeroradiograph. Rather unexpectedly soft tissue frequently shows clearly and with greater contrast on the xeroradiograph than on a radiograph. Relative to film the xerographic plate is slow and requires significantly greater exposures. Any assessment of the present possibilities and the most fruitful line of future development of the process is necessarily contingent upon a careful comparison between it and the conventional film techniques. Present knowledge indicates that there are three variables to be considered, viz. (i) the time for which the plate is charged; (ii) the X-ray exposure; and (iii) the time for which the exposed plate is subjected to the powder cloud. The effects of changes in these have been studied, bone (a metacarpal) being used as a phantom. Precautions were taken to ensure precise positioning of the phantom with respect to xerographic plate and the X-ray tube. As the work involved taking many pictures each of these was recorderd photographically so that comparison could be mde without having to use large numbers of plates.