| 摘要 |
<p>An X-ray examination apparatus comprises an exposure control circuit (20) which supplies a control signal for adjustment of the X-ray source (1). The exposure control circuit (20) determines the control signal from an area of the X-ray image in which no overexposure occurs. To this end, the exposure control circuit comprises a selection unit (23) for determining a measuring part from an electronic image signal, formed from the X-ray image by means of an X-ray detector (5, 8, 7), by comparing the signal level of the electronic image signal with an upper limit value which is dependent on the setting of the X-ray apparatus, for example of the high voltage and the anode current of the X-ray source. The upper limit value preferably amounts to the difference between the overexposure level and a safety margin. The safety margin serves to render the exposure control circuit insensitive to small fluctuations of the intensity and energy of the X-ray beam (3) generated by the X-ray source (1).</p> |
