Two Radiographic Teaching Models

Abstract

While it is possible to teach theoretically the effect of the divergent beam on the projection of the body shadows at different levels, yet it is of definite advantage to be able to demonstrate this problem in a practical way to students. The reproduction on a film of shadows, whose sizes and positions on the film are not identical representations of the actual sizes or positions of the objects, is due to two factors: the one ordinary magnification, the other distortion due to magnification of the shadows of objects situated at different planes between tube and film. The separation of these two factors in the mind makes for a clearer conception. To illustrate the first, a flat board (Model I) was used with rows of drawing-pins inserted in a series of vertical and horizontal rows exactly 1 in. apart (Fig. 1). The distance between the pins in the horizontal and vertical was therefore 1 in. By placing this board at varying distances both from tube and film, with the board vertical at right-angles to the cent...