X-Ray diagnostic installation comprising means for the formation of a transparency signal

Claim 1

An x-ray diagnostic installation comprising an x-ray tube for producing radiation at a location for receiving a radiography subject (2), an x-ray tube power supply for supplying operating power to the x-ray tube, an x-ray image means (5) for disposition behind the location for receiving a radiography subject (2) for recording a radiation image, an exposure terminating switch for effecting a termination of an x-ray exposure operation of said x-ray tube, means for the formation of an electric signal which corresponds to the radiation transparency of the radiography subject, said means comprising two radiation detectors (6, 7) arranged in respective radiation paths behind the location for receiving a radiography subject (2) for supplying detector output signals, filter means (8) being present for providing a different radiation attenuation along the respective radiation paths of the respective detectors (6, 7), and a quotient forming circuit (10) connected with said radiation detectors (6, 7) for forming a quotient of said detector output signals as said electric signal, the detectors (6, 7) being disposed adjacent one another, and said filter means comprising a radiation filter (8) arranged in front of one of the detectors (7), an automatic exposure control circuit controlling said exposure terminating switch and comprising a switching stage (17) for actuation to effect termination of an x-ray exposure operation, said quotient forming circuit being disconnection dose value, in dependence upon the radiation transparency and thickness of the radiography subject, a memory (13) for storing information associated with a mean radiation transparency and specific exposure values, a comparator (11) whose inputs are coupled with said memory and with the quotient forming circuit (10) for comparing the information of the memory (13) which information corresponds to the selected exposure values with the electric signal from said quotient forming circuit and a correction memory (15) connected with the output of the comparator (11) such that the correction memory (15) supplies a correction value to said switching stage in accordance with the difference signal supplied to the correction memory by said comparator as a function of the x-ray tube high voltage.