| 摘要 |
PURPOSE:To reduce the dose to be exposed and to set accurately the X-ray voltage by providing a microcomputer to an A/D converter, a frame memory, etc. and therefore decreasing the number of test exposures down to two for decision of the photographing conditions. CONSTITUTION:The video level voltage value of an applied X-ray tube 10 to the voltage value KV is detected by a microcomputer 36 connected to a keyboard 38 from the output data of an A/D converter 26 or frame memories 28 and 30 of a digital subtraction system. A switch SW1 which selects a logarithmic amplifier 24 is provided at the output side of a camera control unit 20 of the subtraction system together with a switch SW2 which is used in a photographing mode. Then the voltage values KV1 and KV2 obtained by two test exposures and their corresponding voltages V21 and V22 are supplied from an input means 38. Then a coefficient X0 is equal to (logV21/V22)/(logKV1/KV2). This coefficient and the optimum tube voltage KVopt (equation I ) are operated by an arithmetic means. Thus the X-ray voltage is accurately set.
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