Distortion refers to the misinterpretation of the shape or size of the structures under evaluation. In the field of radiography, three forms of distortion exist such as elongation, magnification, and shortening. This paper will explore these forms of radiography throughout its course.
Elongation
Elongation is a type of radiography imaging takes place when the CR becomes angled, and the body part plus the image receptor are in a parallel direction towards each other. The same as magnification, every radiograph shows some quantity of elongation and foreshortening as well. The elongation takes place because of the beam’s divergence (the beam’s edges are ever at a given angle towards each other.
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Concerning the cause of elongation, it usually results from the case of the under graduation of the respective x-ray beam. It is the effect that it takes place through the use of the paralleling type of technique; the angulation of the particular x-ray beam is not more than the long axis of the plane teeth. Angulation is the direction plus the degree where the x-ray tube gets moved from its usual position that is always perpendicular with the image receptor. Meanwhile, the angulation of the x-ray tube is designed to ensure a controlled or expected quantity of shape distortion with the aim of avoiding the superimposition of the anatomical components. At the same time, it also provides changes in the SID that unless under compensation through a new SID, will lead to the production of decrement in the exposure or density.
For the sake of preventing elongation, the operator needs to ensure the increment of the vertical type of angulation so that he can correct the elongation. That is to say; for the case of the maxillary arch, the positive angulation needs to be raised. In the case of the mandibular arch, the negative type of angulation needs to be increased. The error may also take place when it involves the use of the technique of the bisecting angle. Usually, the error brought by the x-ray beam that is perpendicular to the long axis of the particular teeth instead of the bisecting angle that lies between the receptor and the teeth.
Magnification
Magnification is often the result of the distortion size. Sometimes magnification in radiography is known as the Marco-radiography. For sure it remains that it is the mammography where the magnification views are still carried routinely. In the magnification views, a platform that is raised for supporting the breast is put above the holder of the film in a nearly half distance between the cassette and focus. Hence, the image gets magnified by a factor of two. Regardless of this, the overall impact of this is to ensure the significant increment in the un-sharpness such that it is in a position of viewing similar small detail within the magnified views, where the small focus spot needs to be used. This has the impact of ensuring the increment in the time for exposure due to the lower mA. However, it is possible to offset this via the removal of the grid, because of the scatter that is decreased following the introduction of the air gap. In a specific manner, there will be the increment in the patient dose thus this procedure is suitable for the symptomatic types of patients.
In certain occasions, the distance between the image detector and the specimen is always adjusted for the sake of obtaining the image's magnification. Magnification at times is a great value during the inspection of parts. The more the specimen for the test is far from the image detector, the greater the achieved magnification. The quantity of magnification may be established by following the below formula;
M = (a + b) / a
M represents magnification a represents the distance from the source to the object b represents the distance from the object to the detector
Figure 2: Sketch of the geometric variables that affect magnification.
Shortenings
Foreshortening takes place when the body part gets angled, and the image receptor and the CR are perpendicular towards each other. Foreshortening is ever present because of the three-dimensionality of the nation based structures. Shortening may consist of the surrounding components, and the teeth may emerge following the improper vertical type of angulation. On the same note, shortening is the outcome of the overangulation of the x-ray beam. When shortening takes place following the use of the paralleling type of technique, the angulation of the x-ray beam is more significant than the longer axis covering the teeth's plane. For the sake of correcting the shortening by use of the technique of paralleling, the operator needs to ensure the decrement of the positive case of the vertical angulation for the maxillary types of projections and a decrement in the vertical for the mandibular kinds of forecasts. The error may also be corrected in any case the receptor is not in a parallel position to the long axis of the teeth.
