Tomography of the lamina dura

Tomographic technics are based on the principle that when the X-ray source is moved in relation to the object the speed of the projection of different parts of the object on a plane will be different. By selecting the projections which have a certain speed, an image of a selected plane of the object can be obtained. Two principles have to be considered: 1. the image of a curved surface will only show the surface area where the rays form a tangent to the surface; 2. in tomography the blurring of the image increases with an increase of the tomographic angle and the distance of the object to the plane in focus. The image formation of curved bony surfaces, such as the lamina dura, is discussed in detail. The specific properties of the spatial model of the lamina dura requires another approach to explain the image formation. Diagrams and graphs illustrate the effect of the tomographic movement of the X-ray source on the movement of the projected image. Limits for the misalignment permitting an interpretable image are given, as well as an explanation of the images obtained when these limits are exceeded.