Rotational Tomography of the Face

Abstract

Rotational tomography is a specialised form of sectional or differential tomography. From the very outset, X-ray examination of any region of the body, however limited in area, has resolved itself into contact radiography. Each object has its own thickness and the final radiographic shadow on the sentitised surface is always a composite picture of numerous layers of that dense object. The image must therefore represent many superimposed body layers making it impossible for the radiologist to decide to which layer the seat of the disease belongs. In many cases, the actual lesion may be obscured by shadows of other body layers. In addition to superimposition, the incidence of distortion is ever present. Although the film is placed behind the object, anatomical considerations may make close apposition impossible and any contour of the region, other than one geometrically flat, prevents the axes of film and object from being parallel to each other. In such circumstances, the X-ray beam cannot be directed at right angles to the film and the object, which are not in the same plane. These obvious shortcomings of contact radiography were in part overcome, about 27 years ago, when an apparatus was devised whereby a selected layer or number of layers could be demonstrated in specified regions of the body. It entailed a linked movement in the X-ray tube and the film, in an agreed plane of the body or object, in opposite directions at a proportional rate.