Patent Number: 
Section: claims

1. An X-ray apparatus which is provided with an X-ray source ( 1 ) for producing X-rays ( 2 ), an X-ray detector ( 4 ) for detecting the X-rays, and a filter ( 12 ) which is arranged between the X-ray source and the X-ray detector and includes a plurality of tubular filter elements ( 13 ) for receiving an X-ray absorbing and electrically conductive liquid filling ( 22 ), first means ( 140 ) being provided for applying an electric voltage to individual filter elements ( 13 ), an X-ray absorptivity of the individual filter elements being adjustable by control of a quantity of X-ray absorbing liquid filling ( 22 ) present within the individual filter elements ( 13 ), characterized in that the filter ( 12 ) is also provided with a hydrostatic pressure control system ( 160 ) for controlling a hydrostatic pressure in the filter elements, measuring means being provided for measuring a physical quantity related to the height of a column of the X-ray absorbing liquid filling ( 224 ) within the filter elements, and with control means for controlling the hydrostatic pressure control system ( 160 ), the height of the column of the X-ray absorbing liquid filling ( 224 ) in an individual filter element being determined by the combination of the hydrostatic pressure and the electric voltage applied to the filter element. 2. A filter ( 12 ) for use in the X-ray apparatus claimed in  claim 1 , wherein the measuring means are arranged to measure a reference electric voltage ( 300 ,  301 ) in at least one reference filter element ( 135 ). claim 1 3. A filter ( 12 ) for use in the X-ray apparatus claimed in  claim 1 , wherein a common liquid supply duct ( 220 ,  221 ) is provided for all filter elements ( 13 ) and the measuring means are arranged to measure a hydrostatic pressure ( 131 ) in the common liquid supply duct ( 220 ). claim 1 4. A filter ( 12 ) for use in the X-ray apparatus as claimed in  claim 1 , wherein the measuring means are provided with means for measuring an orientation (xcex2) of the filter as a whole relative to a vertical direction (g). claim 1 5. A filter ( 12 ) for use in the X-ray apparatus claimed in  claim 1 , wherein a common liquid duct ( 220 ,  221 ) is provided for all filter elements ( 13 ) and a liquid reservoir is provided for the supply of the X-ray absorbing liquid ( 224 ) via the common supply duct. claim 1 6. A filter ( 12 ) as claimed in  claim 5 , wherein the liquid reservoir ( 150 ,  150 xe2x80x2) includes tubular elements. claim 5 7. A filter ( 12 ) as claimed in  claim 6 , wherein the tubular elements are filter elements ( 13 xe2x80x2,  13 xe2x80x3). claim 6 8. A filter ( 12 ) as claimed in  claim 7 , wherein the first means are arranged to drain the liquid filling ( 22 ) from an internal volume of each filter element ( 13 ) to at least one corresponding filter element ( 13 xe2x80x2,  13 xe2x80x3) in the liquid reservoir ( 150 ,  150 xe2x80x2). claim 7 9. A filter ( 12 ) for use in the X-ray apparatus as claimed in  claim 1 , wherein the filter includes a number of sub-filters ( 212 ,  213 ,  214 ,  215 ) that are hydraulically separated from one another. claim 1