Position, Form, and Thickness of the Image Layer in Narrow Beam Rotation Radiography

Abstract

Narrow beam rotation radiography is essentially based on a specific projection technique (HECKMANN 1939, 1967, WELANDER 1974. The rotation centre of the continuously moving beam acts as the functional focus of the projection of the object, usually the jaws. Incorporated in the technique is also the formation of a layer, which, although not tomographic according to definitions given by EDHOLM (1960) and by WELANDER (1975), has certain similarities to a tomographic layer.It was empirically put forward by TAMMISALO & NIEMINEN (1964) that the position of the centre of the sharply depicted object plane is dependent on the ratio between the velocity of the film in relation to the beam and the velocity of the beam in relation to the object. With this as the basis TAMMISALO (1964) analysed mathematically the position and form of the image layer in images exposed with one specific equipment, the Orthopantomograph 2. A mathematical deduction, later on confirmed by ex perimental tests, has shown that the empirical postulation quoted above is correct

The orthopantomogram, an aid in diagnosis of temporomandibular joint problems. I. The factor of vertical magnification

“…The vertical dimension of the beam thereby allows a large area of -v ,*;-:: ;:;\ an object to be sharply projected. At the centre of the sharply depicted layer, the magnification factors are the same in both dimensions (Welander, 1974;Sjoblom & Welander, 1978;Welander, 1978). The increased clinical recognition of the high prevalence of craniomandibular disorders has increased the demand for early temporomandibular joint diagnosis.…”