In view of what is to follow there is a well known fact to be called to mind, and that is that in a roentgenogram all structures capable of absorbing the roentgen beam cast their shadows. The intensity or depth of these shadows is dependent on the density of the structures traversed and their distance from the film. Thus, a composite image of all the structures lying in the path of the roentgen beam is produced. These interfering images greatly limit the usefulness of roentgenograms. It has been found that the interference can be overcome to a remarkable degree by imparting a coordinated, synchronized movement of x-ray tube and film about a fixed point during the exposure. All objects in the plane about which movement takes place are, so to speak, "in focus," and those outside the plane are "out of focus" and are blurred because the shadows are displaced.
MOORE S, CONE AJ, DEAN LW, BURTON WY. USE OF LAMINAGRAMS IN LARYNGOLOGY. Arch Otolaryngol. 1941;33(5):776–794. doi:https://doi.org/10.1001/archotol.1941.00660030786011
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