Patent Number: 051704250
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS An x-ray diagnostics installation constructed in accordance with the principles of the present invention is shown in FIG. 1, which includes a high-voltage generator 1 which feeds an x-ray tube 2 equipped with a primary radiation diaphragm 3 disposed in the beam path of the x-ray tube 2. An examination subject 4 is situated in the beam path as limited by the primary radiation diaphragm 3. The x-rays generated by the x-ray tube 2 which are attenuated by the patient 4 are incident on the input window of an x-ray image intensifier 5. The incident radiation image, intensified by the x-ray image intensifier 5, is reproduced on the output luminescent screen thereof as a visible image. This image is acquired by a video camera 6 via an optics system (not shown) and is converted into a video signal. The video camera 6 is connected via a processing circuit 7 to a monitor 8 for displaying the video signal. A control unit 9 synchronizes the operation of the various components of the installation. In accordance with the invention, the primary radiation diaphragm 3 is connected to one or more sensors 10, which acquire the position of the beam-blocking and/or beam-attenuation parts (i.e., plates, leaves, lamellae, etc.) of the primary radiation diaphragm 3. The sensors 10 generate electrical signals corresponding to the position of these parts of the primary radiation diaphragm 3, which are supplied to the processing circuit 7. On the basis of the position of the parts of the diaphragm 3, the processing circuit 7, as described below, calculates the attenuation of the radiation image caused by the primary radiation diaphragm 3, and this is correspondingly taken into consideration in the reproduced image on the monitor 8. Details of the processing circuit 7 are shown in FIG. 2. The output signal of the video camera 6 is supplied to a video amplifier 11 and is then digitized in an analog-to-digital converter 12 connected to the output of the video amplifier 11, and the digital signals are entered into an image memory 13. The output of the image memory 13 is connected to a logarithmizing circuit 14, which generates an output signal which is supplied to a first blanking stage 15. An amplitude-matching circuit 16 is connected to the first blanking stage 15, having an output connected to a delogarithmizing circuit 17. The output signal of the image memory 13 is also supplied to a second blanking stage 19. The output of the second blanking stage 19 is superimposed with the output signal of the delogarithmizing circuit 17 in a summing stage 18. The output of the summing stage 18 is supplied to a digital-to-analog converter 20. The analog output signal of the converter 20 is reproduced on the monitor 8. As shown in FIG. 1, the sensors 10 generate a signal corresponding to the position of the components of the primary radiation diaphragm 3, which interact with the x-ray beam, such as to completely blank the beam or attenuate the beam. The sensors 10 may, for example, each be in the form of a potentiometer 21 which generates an analog voltage proportional to the position of the diaphragm part, this analog signal being supplied to an analog-to-digital converter connected to a process control computer 23. Data corresponding to the degree of absorption and to the shape of each beam-interacting part of the primary radiation diaphragm 3 are stored in the control computer 23. On the basis of the position signals of the beam-interacting parts of the diaphragm 3 supplied by the sensors 10 to the control computer 23, the control computer 23 calculates, for each picture element, whether this picture element is covered by a beam-interacting part, and the extent of the attenuation of this picture element by that beam-interacting part. On the basis of these calculations, the control computer 23 produces blanking signals which correspond to the diaphragm contour and diaphragm position. These blanking signals are supplied via a first output 24 to the two blanking stages 15 and 19 which effect a corresponding blanking of their respective input signals. The control computer 23 generates a signal at a second output 25 which corresponds to the absorption factor of the beam-interacting parts of the primary radiation diaphragm 3 at the corresponding location in the video signal. Inverse signals are thereby supplied to the two blanking stages 15 and 19. When the video signal conducted through the first blanking stage 15 is blanked, the video signal conducted through the second blanking stage 19 will be supplied unblanked to the summing circuit 18. If, by contrast, a portion of the video signal which would be affected by one of the beam-interacting parts of the diaphragm is read from the image memory 13, the video signal conducted through the second blanking stage 19 will be blanked, whereas the first blanking stage 15 allows the video signal to pass, so that it can be attenuated in the circuit 16 for amplitude matching in accordance with the absorption factor of the particular beam-interacting part. By employing a specific depth diaphragm as the primary radiation diaphragm 3 at the x-ray tube 2 having localization sensors for the various beam-interacting parts of the diaphragm 3, a signal is obtained which the control computer 23 converts into blanking and absorption signals. A plurality of beam-interacting parts can thereby be entirely or partially mechanically superimposed, so that an absorption compensation for different subject dynamics is possible. By means of the control computer 23 and the simulation circuit formed by components 14, 15, 16, 17, 18 and 19, the beam matching in the video signal is simulated dependent on the diaphragms which have been introduced in the stored signal, so that all diaphragm manipulations can take affect in the stored video image. The coordinate signals of the diaphragm setting are supplied by the sensors 10 to the primary radiation diaphragm 3. The absorption factors, or the blanked field, are edited for gating or attenuating the video signal via the control computer 23, wherein diaphragm thickness and contours are stored. The absorption behavior of the semi-transparent diaphragms is simulated by logarithmizing the video signal. For identical semi-transparent diaphragm parts which are superimposed having the same transmission factors, the amplitude reduction is thus implemented in the video signal domain which is covered by those diaphragm parts, for example, after logarithmization of the video signal. On the basis of the above-described circuitry, the primary radiation diaphragm 3 can be set in a desired manner after an overview exposure has been undertaken and without an additional radiation load, so that either another exposure or manipulations of the patient can be subsequently immediately implemented. Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.