LINEAR TOMOGRAPHY

Tomography otherwise known as body section radiography, planigraphy, laminography or stratigraphy, is the process of using motion of the X-ray focal spot and image receptor (e.g. film) in generating radiographic images where object detail from only one plane or region remains in sharp focus. Linear tomography is one of the most basic techniques. As the tube and film move from the first position to the second, all points in the focal plane project to the same position on X-ray film.Points above or below the focal plane do not project to the same film positions and are blurred. By changing the relative motion of the film and tube, the focal plane can be adjusted upward or downward.

Linear Tomography is a radiographic technique that uses motion to demonstrate anatomy lying in a plane of tissue, while blurring or eliminating structures above and below the plane of interest. This technology led to the development of CT (Computerized Tomography), which is more widely used today. In addition to linear tomography, other types of tube and film motion have been used. These motions include circular, elliptical, hypocycloidal, trispiral. Each of these motions has advantages regarding the way in which out of plane structures are blurred. For example, a linear structure which is aligned with the linear motion of a linear tomograph, will not appear blurred, except at the ends, whereas such a structure will be blurred by the circular motion of a circular tomograph.

PURPOSE

By moving an x-ray source and the film in opposite directions during the exposure structures in the focal plane appear sharper, while structures in other planes appear blurred. By adjusting the direction and range of the movement, operators can select different focal planes which contain the structures of interest.

PRINCIPLE

The tube and the image receptor move during the exposure in opposite directions around a stationary fulcrum, the pivot point.
The tube and the image receptor are attached by a rod as described in the equipment section of this blog.

EQUIPMENT USED

Most features of a tomographic x-ray imaging system appear similar to those of a conventional radiographic imaging system.