Patent Number: 051704250
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to an x-ray diagnostics installation having a primary radiation diaphragm disposed in the beam path of an x-ray tube, wherein the x-rays attenuated by an examination subject are processed by an image intensifier video chain which includes an image memory. 2. Description of the Prior Art Primary radiation diaphragms are used in x-ray diagnostics installations to blank portions of the radiation image for reducing stray radiation and for reducing the image brightness. Various types of primary radiation diaphragms are known, such as contour diaphragms, semi-transparent contour diaphragms, finger diaphragms having specific profile absorptions adapted to the subject, etc. A primary radiation diaphragm is disclosed in German Patent 1 800 879 for use in x-ray examination equipment, the primary radiation diaphragm being formed by two semitransparent diaphragm plates. These diaphragm plates can be adjusted in the transillumination image with operating elements, until they assume a desired position. As a result, however, the attending personnel as well as the examination subject are exposed to undesired, additional radiation because the adjustment of the diaphragm does not form a part of the actual diagnostic exposure. SUMMARY OF THE INVENTION It is an object of the present invention to provide an x-ray diagnostics installation having a primary radiation diaphragm disposed in the beam path of an x-ray tube wherein it is possible to achieve an optimum setting of the diaphragm without an additional radiation load. The above object is achieved in accordance with the principles of the present invention in an x-ray diagnostics installation having a primary radiation diaphragm which is provided with sensors which supply an electrical signal corresponding to the position of the individual data parts of the diaphragm to a processing stage. The processing stage acts on the data signals stored on the image memory so that the effect of the primary radiation diaphragm on the stored image is simulated, so that the simulated diaphragm effect can be displayed in the image on a monitor. A simulation of the diaphragm by transparency matching in the displayed image with an absorption matching read-out from the image store can be obtained. A simple structure is obtained in an embodiment wherein the processing stage includes a control computer connected to the sensors, and a simulation circuit connected to the image memory for simulating the effect of the primary radiation diaphragm. The control computer calculates the position and coordinates of the individual diaphragm parts from the sensor signals, and causes an attenuation of the video signal in the region of the diaphragm part in accord with the amount of attenuation which that diaphragm part contributes to the x-ray image. Preferably the simulation circuit includes a circuit for amplitude matching of the video signal, with the absorption factors of the primary radiation diaphragm causing a corresponding attenuation of the video signal. A complete blanking of the image portions attenuated by the diaphragm plates of the primary radiation diaphragm can be achieved if the simulation circuit includes a blanking circuit, which effects a blanking of the video signal in that region of the overall image in registry with the diaphragm plate, so that no video signal at all appears in that region in the displayed image. The absorption behavior of semi-transparent diaphragm plates can be achieved by including a logarithmizing circuit at the input to the simulation circuit, and a delogarithmizing at the output of the simulation circuit. A precise amplitude reduction in the video signal domain can be implemented even in the case of superimposed diaphragm lamellae. It has proven advantageous to supply the output of the simulation circuit to a summing circuit to which the output signal from a further blanking circuit is supplied, the further blanking circuit also being connected to the image memory and to the control computer. The further blanking circuit operates generally in a complementary manner to the blanking or attenuation which takes place in the simulation circuit, so that the signal outside the region of the primary radiation diaphragm can be supplied unattenuated by the further blanking circuit to the summing circuit, with the simulation circuit supplying only that part of the total image which is within the region of the primary radiation diaphragm.