Patent Number: 047440996
Section: summary

BACKGROUND OF THE INVENTION The invention relates to an x-ray diagnostic apparatus, comprising positioning means for the shifting of a selected radiation filter of a plurality of radiation filters into the path of an x-ray beam. An x-ray diagnostic apparatus of this type is described in U.S. Pat. No. 3,976,889. In this x-ray diagnostic apparatus the adaptation of the x-radiation to the respective radiography subject proceeds through shifting of one of a plurality of radiation filters into the radiation path in advance of the radiography subject. The radiation filters are arranged on a rotatably mounted disc whose axis of rotation is offset relative to the central ray of the x-ray beam, said disc being capable of being manually rotated. A parameter which determines the respective filter to be shifted into the ray path is the density of the examination subject. In the case of the known x-ray examination apparatus the operating individual must estimate this density and select the corresponding filter. SUMMARY OF THE INVENTION An example of a commercial mammography apparatus is disclosed in a brochure of Siemens AG entitled "MAMMOMAT B," Kompakter Mammographie-Arbeitsplatz, PIR 87-022, M-R 87 7318, January 1982. In this commercial apparatus, the application of compression to the examination subject is accomplished by a motor driven compression plate, the motion of which is controlled by a foot petal. The maximum exertible pressure can be set in a range from 87 newtons per unit of area to 150 newtons per unit of area during assembly. An x-ray spot film device is described in German OS No. 23 56 276, wherein the speed of the drive motor is switched in steps in dependency upon the force acting on the patient. The object underlying the invention resides in automating the filter selection and positioning in that the density of the radiography subject is automatically detected and the filter adjustment proceeds correspondingly. Accordingly, this object is achieved in that means are present for the formation of an electric density signal which is dependent upon the density of the examination subject, and that the adjustment means contains an electromotor activated by a control circuit to which the density signal is supplied and which activates the motor, corresponding to the respective density signal, for the purpose of selection of the respective filter. The invention is particulalry suitable for apparatus for the preparation of mammography exposures where a compression of the respective examined mamma is a necessary part of the procedure. The density signal can be formed from the respective compression force and/or the respective length of the compression path. The invention will be explained in greater detail in the following on the basis of an exemplary embodiment illustrated on the accompanying drawing sheet; and other objects, features and advantages will be apparent from this detailed disclosure and from the appended claims.