Patent Number: 046726527
Section: summary

BACKGROUND OF THE INVENTION The invention relates to a radiodiagnostic apparatus with an X-ray tube, a diaphragm which is semitransparent in at least one region and which clears a slit of variable width to let radiation pass, with an x-ray image intensifier and a television camera coupled thereto for the generation of video signals, the camera being connected with a monitor for the reproduction of the video signals. German Offenlegungsschrift No. 1,800,879 discloses a primary ray diaphragm for x-ray examination apparatus. Here, a semitransparent diaphragm consisting of two diaphragm plates attenuates the lateral radiations in the x-ray beam. Otherwise, particularly in the case of extremities, the unattenuated beam would directly strike the x-ray image intensifier input screen. This would produce bright areas which impair the perception of details in the actual viewing area. By the use of the semitransparent diaphragm plates these overradiated (or "bloomed") lateral areas are attenuated, so that the visibility in the area of interest is increased, although high-contrast objects (for example, surgical instruments brought in from the side) are still clearly visible. To properly orient the test object with respect to the radiodiagnostic apparatus, the diaphragm plates are rotatable on a diaphragm disk. For manual adjustment of the width of the non-attenuated ray path, the two diaphragm plates can be moved toward each other, until (in the ideal case) overradiated areas have disappeared. In the normal case of non-rectilinear contours, contour adaptation cannot be achieved with the rectilinear end faces of the diaphragm plates. Either a large portion of the object to be examined is attenuated as well, or else large parts of the television picture are still overradiated, so that the visibility of details continues to be reduced. From German Offenlegungsschrift No. 29 05 202 a viewer ("light viewing box") is further known, where for the observation of transparent, rectangular pictures the image support can be darkened by a plurality of parallel and narrow cover strips. By placing pictures on the edge of the viewer, their size is picked up automatically. Subsequently only those strips which cover the picture are moved by a motor until the film is exposed also at its lower edge. Several films can be exposed simultaneously only if they are of the same vertical size. Adaptation to irregular contours is impossible by using the blades of this viewer. One object of the invention is to provide, for a radiodiagnostic apparatus of the initially mentioned kind, a semi-transparent diaphragm which adapts itself as exactly as possible to the contours of the object to be examined, so that only small areas of the object being examined, or none at all, are covered up, or only small areas in the vicinity of the object are uncovered. SUMMARY OF THE INVENTION According to the invention, the diaphragm comprises a plurality of individual blades, which abut and are parallel to each other. The blades are arranged into two opposed groups which are on both sides of the slit and are individually longitudinally slidable dependent on the size of the object to be viewed. There is connected to the television camera an evaluating circuit which supplies a control signal obtained from the video signal to a setting device for the individual blades. The blades of the diaphragm are automatically moved toward each other until each individual blade reaches the outer contours of the object being examined. Advantageously the longitudinal direction of the blades is perpendicular to the center line of the slit. A better adaptation of the blades to the contour of the object being examined can be obtained when the longitudinal direction of the blades makes an angle of between 20.degree. and 90.degree. with the center line of the slit. It has been found to be advantageous when the angle between the longitudinal direction of the blades and the center line of the slit is 45.degree.. A simple control of the blades results when each individual blade is displaced by a corresponding motor. The mechanical construction can be simplified when there are provided for each side of the diaphragm, i.e. each group of blades, a motor which drives a roller, and at least one coupling magnet, the motor and magnet being controlled by the evaluating circuit, and when the blades can be coupled with the roller by the coupling magnet. Reliable adjusting of the blades is achieved when at least one part of each of the blades is designed as a toothed rack and when the roller is designed as a toothed roller. The mechanical cost can be further reduced when a coupling magnet is provided which is displaced mechanically and couples the blades individually with the roller. Parallel actuation of the blades can be achieved when a coupling magnet is associated with each blade, the coupling magnet being individually actuated by the evaluating circuit. The evaluating circuit is further simplified when the coupling magnets are actuated individually, one after the other. Rapid adjusting of the blades can be achieved when the coupling magnets are actuated by the evaluating circuit alternately in multiplexing. The electronic engineering can be simplified when, in radio diagnostic apparatus in which the diaphragm is arranged on a rotatable diaphragm ring, the television camera and the diaphragm are coupled in their rotation in such a way that the longitudinal direction of the blades always lies in the direction of the television's horizontal scan. Advantageously, the evaluating circuit comprises a circuit for position determination of the blades within the video picture. To the circuit are supplied the clock pulses of the television camera and control signals, which identify the particular blade being actuated. The video signal is supplied to an adaptation stage, and the adaptation stage and the circuit are connected with a gate circuit to which a peak value detector is connected. The output signal of the detector is supplied to a comparator stage which compares the output signal with an adjustable threshold value, and the comparator stage controls the coupling magnets. Optimum control of the blades is achieved if the threshold value is selectable to correspond to the transmission characteristics of the organ under investigation.