The word "Tomography" is derived from the Greek words tome (to cut) and graphein (to write). ** Although Conventional Tomography is almost obsolete and has been replaced in most places with Computerized Tomograpy, it is still used in different procedures.**
Linear Tomography is a very simplistic radiological technique. In a straight line, the x-ray tube moves in one direction while the film moves in the opposite direction. As they move, a fulcrum is created and is the only point that remains stationary. During this occurrence of motion, details from only one region remains in sharp focus. Details from other planes in the object are blurred and effectively removed from the image. At whatever level the fulcrum is located in the part being radiographed, it is the point that remains in sharp focus in the image. The further away from the "Pivot Point" or "fulcrum" ( either above or below) the more motion.
In addition to Linear Tomography, other types of film and tube motions have been used. These motions include circular, elliptical, trispiral, figure 8, and hypocycloidal.
Linear Tomography produces images with excellent diagnostic detail, definition and minimal distortion. Subject contrast of tissue in the tomographic section is enhanced through the process of "blurring". Accuracy and precision are made possible as a result of the inherent exposure area measurement system. (The center picture shows an example of conventional tomography)
The Tomography system is designed for linear movement with a general purpose imaging system. Many of the features of a tomographic x-ray imaging system are similar to features of a conventional radiographic imaging system. The vertical rod that connects the x-ray tube above the table with the image receptor below the patient enables both to move in opposite directions. The fulcrum is the only point in which no movement occurs in either direction.
The image to the left is a Philips Diagnost 94 remote control radiography machine. It is capable of performing general radiographic studies with contrast and linear tomography
Linear Tomography is also used in Dentistry. The image to the left is Planmeca's Proscan Imaging System, which has three complexes including plain film linear tomography
The image below is an example of "True Linear Tomography", involving dentistry. The images are undistorted. The anatomical condition doesn't matter. The images can be cross sectional or longitudinal and are adjustable to any specific angle. There is a constant magnification for diagnostic measurements.
