SUBTRACTION (Latin subtractio from subtrahere to take away; synonym sustraktion) — a method of photographic or electronic processing of the x-ray image for the purpose of strengthening of contrast of its separate elements.
By page by means of photographic processing of roentgenograms it is offered in 1934 Mr. Tsidzes de Plantom (V. to Ziedses des Plantes). Methods of electronic processing of the image suggested to use in 1964 Mr. Holmen (S. Holman).
Pages apply at cerebral angiography (see) when on roentgenograms of the image of small vessels are badly distinguishable against the background of dense bone structures of a skull. For this purpose at first roentgenograms of a skull without contrasting of vessels make the negative copy, then on it impose the positive copy of the picture with the contrasted vessels executed in the same projection. During the imposing of pictures picture contrast of bone structures due to subtraction of optical density of a positive and a negative sharply decreases, and the contrasted vascular network of a brain, on the contrary, accurately appears on this background (fig).
S. radiographic is based on the same principle. images by transformation a video body-vizionnogo of a signal on special television devices — the subtraskopa allowing to eliminate the disturbing background and to select diagnostically important information due to subtraction (subtraction) of one image «stored in memory», from another, made at present.
Villages use also to emphasize contrast of important structures in the diagnostic relation on pneumoencephalograms (see. Pnevmoentsefalografiya ), miyelogramma (see. Miyelografiya ), Urogramums and piyelogramma (see. Piyelografiya , Urography ).
Bibliography: Pancakes H. N, etc. Television methods of processing x-ray and gamma images, M., 1982; The M is scarlet e e in N. and d river. The equipment and a method on the izsledvena in a rentgenolo-giyat, page 144, Sofia, is modern 1974; Lehrbuch der Rontgendiagnostik, hrsg. v. H. Schinz, Bd 1, S. 38, Stuttgart, 1979.
V. V. Kitayev.