Friday, April 17, 2009
Thursday, March 19, 2009
LINEAR TOMOGRAPHY
LINEAR TOMOGRAPHY
Tomography is the method of imaging a single plane, or slice, of an object resulting in tomography. There are several forms of tomography. Our main focus is on linear tomography.
Linear tomography: This is the most basic form of tomography. The X-ray tube moved from point "A" to point "B" above the patient, while the cassette holder (or "bucky") moves simultaneously under the patient from point "B" to point "A." The fulcrum, or pivot point, is set to the area of interest. It determines the plane that will be in focus. Two mechanically different types of fulcrums are in common use. In the first , the relationship between the x-ray tube, fulcrum, and film is fixed. The patient is moved up and down on an adjustable table to bring the level of interest to the plane of the fulcrum. The second type has an ajustable fulcrum thaat is moved to the height of the the desired plane, while the patient remains stationary on the table. The higher the fulcrum, the thinner the layer. The broader the focus, the thinner the layer.
In linear tomography, the x-ray tube and the fim holder are linked by a rod mechanism. During the exposure, the tube moves in direction and the film holder moves in the opposite direction. This movement is around a fulcrum.
Linear tomography: This is the most basic form of tomography. The X-ray tube moved from point "A" to point "B" above the patient, while the cassette holder (or "bucky") moves simultaneously under the patient from point "B" to point "A." The fulcrum, or pivot point, is set to the area of interest. It determines the plane that will be in focus. Two mechanically different types of fulcrums are in common use. In the first , the relationship between the x-ray tube, fulcrum, and film is fixed. The patient is moved up and down on an adjustable table to bring the level of interest to the plane of the fulcrum. The second type has an ajustable fulcrum thaat is moved to the height of the the desired plane, while the patient remains stationary on the table. The higher the fulcrum, the thinner the layer. The broader the focus, the thinner the layer.
In linear tomography, the x-ray tube and the fim holder are linked by a rod mechanism. During the exposure, the tube moves in direction and the film holder moves in the opposite direction. This movement is around a fulcrum.
Objects below and above this plane are blurred because they are imaged across the film. Only objects lying in the object plane are properly imaged. The farther from the object plane an anatomical structure is, the more blurred its image will be.
Other aspects of the linear tomographic examination are shown in this diagram. For example, the tomographic angle, which is the movement of the x-ray tube. The larger the tomographic angle, the thinner is the tomographic section. This diagram also illustrates how anatomical structures in the object plane are imaged while structures above and below this plane are not. The tomographic angle is the amplitude of the tube travel and expressed in degrees. The exposure angle is the angle through which the x-ray beam or central ray moves during the exposure.
The purpose of wide-angle tomography is to extend the limits of roentgen visibility to enable us to see objects that are completely obscured by overlying shadows. And one disadvantantage of wide-angle tomography is that it decreases image contrast. The sharpness of all images is decreased by wide-angle technique. The wider the tomographic arc, the more unsharp the images are.
Other aspects of the linear tomographic examination are shown in this diagram. For example, the tomographic angle, which is the movement of the x-ray tube. The larger the tomographic angle, the thinner is the tomographic section. This diagram also illustrates how anatomical structures in the object plane are imaged while structures above and below this plane are not. The tomographic angle is the amplitude of the tube travel and expressed in degrees. The exposure angle is the angle through which the x-ray beam or central ray moves during the exposure.
The purpose of wide-angle tomography is to extend the limits of roentgen visibility to enable us to see objects that are completely obscured by overlying shadows. And one disadvantantage of wide-angle tomography is that it decreases image contrast. The sharpness of all images is decreased by wide-angle technique. The wider the tomographic arc, the more unsharp the images are.
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