Principles of Computed Tomography

Abstract

U sing conventional radiologic techniques it is not possible to produce an image of one plane of section. This is due to the projection mode, in which all planes of the irradiated body segment are projected on top of each other. A tomogram is a sectional roentgenogram, an image of one selected plane of section, and is made in the following manner. By giving the x-ray tube a curvilinear motion during exposure synchronous with the recording plate but in the opposite direction, the shadow of the selected plane remains stationary on the moving film while the shadows of all other planes have a relative displacement on the film and are therefore obliterated or blurred. U sing this tomographic study with the patient in the recumbent position one obtains frontal sections. In transverse tomography the x-ray tube remains stationary and the seated patient and the film plate are rotated around the longitudi’rial axis of the patient. This type of tomography was replaced by computed tomography.