| 摘要 |
An X-ray examination apparatus comprises an X-ray source, an X-ray detector (3) and an X-ray filter arranged between the X-ray source and the X-ray detector. The X-ray filter comprises a plurality of filter elements each comprising a vessel containing an X-ray absorbing liquid, the liquid level in each vessel determining the X-ray absorptivity of the respective filter element. Control means is provided for applying electric voltages to the individual filter elements to change the liquid levels within an adjust time period. The control means is arranged to apply a respective control voltage to each individual filter element a repeat number of times within the adjust time period, the repeat number being selected so as substantially to maximize the rate of change of liquid level of the filter elements. This enables patient examination times to be reduced, by reducing the times between sequential images.
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