Linear Tomography

Linear Tomography is an imaging modality in which the x-ray tube is mechanically attached to the image receptor and moves in one direction as the image receptor moves in the opposite direction. Linear Tomography is the simplest tomographic examination. This examination is used to help doctors see anatomical parts of the body that are not able to be seen in normal x-rays, such as the kidney in a x-ray of the abdomen. The most common procedure that uses linear tomography is IVP which eliminates any organs that are obstructing the the kidneys.

In Linear Tomography the fulcrum, which is the imaginary pivot point where the image receptor and x-ray tube move, determines the object plane. Only the anatomical structure lying with in the object plan are clearly imaged. Those objects above or below the fulcrum plan will be blurred because they are moving across the object plan but also because they are moving in opposite directions. the examination starts when the image receptor and the x-ray tubes are on either side of the fulcrum, the exposure will begin when the two move simultaneously in opposite directions.

The Tomographic section which is the thickness of the section that will be imaged is also a very important factor in linear tomography, this is controlled by the tomographic angle.the smaller the Tomographic angle is the larger the section thickness is . so a very small tomographic angle would give an entire tomographic section which would basically come out as a normal x-ray. the larger the tomographic angle is the thinner the tomographic section is, which would give a better view of obscured structures.

Below is a diagram of a Linear Tomography machine it is one of the most basic techniques as the tube and the film move from the first point to the second point. All the point in the focal spot plan project to the same position on the x-ray film. Thus point A,B, and C project to point A', B', and C' in the second position. Point above or below the focal plan do not project to the same film positions and are blurred. by changing the relative motion of the film and tube the focal plan can be adjusted to move up or down