Patent Number: 062529390
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows diagrammatically an X-ray examination apparatus 1 according to the invention. The X-ray source 2 emits an X-ray beam 3 for irradiating an object 4. Due to differences in X-ray absorption within the object 4, for example a patient to be radiologically examined, an X-ray image is formed on an X-ray sensitive surface 15 of the X-ray detector 5 which is arranged opposite the X-ray source. A high-voltage power supply 51 supplies the X-ray source 2 with an electric high voltage. The X-ray detector 5 of the present embodiment is formed by an image intensifier/pick-up chain which includes an X-ray image intensifier 16 for converting the X-ray image into an optical image on an exit window 17 and a video camera 18 for picking up the optical image. The entrance screen 19 acts as the X-ray sensitive surface of the X-ray image intensifier which converts incident X-rays into an electron beam which is imaged on the exit window by means of an electron optical system 20. The incident electrons generate the optical image on a phosphor layer 21 of the exit window 17. The video camera 18 is coupled to the X-ray image intensifier 16 by way of an optical coupling 22, for example a lens system or a fiber-optical coupling. The video camera 18 extracts an electronic image signal from the optical image; this image signal is applied to a monitor 23 in order to visualize the image information in the X-ray image. The electronic image signal may also be applied to an image processing unit 24 for further processing. Between the X-ray source 2 and the object 4 there is arranged the X-ray filter 6 for local attenuation of the X-ray beam. The X-ray absorptivity of individual filter elements 7 of the X-ray filter is adjusted by means of an adjusting unit 50. The X-ray absorptivity of the individual filter elements is controlled by adjustment of the quantity of X-ray absorbing liquid 14 present in the individual filter elements. The quantity of X-ray absorbing liquid 14 in such a filter element is adjusted on the basis of the electric voltage applied to the relevant filter element. The adjusting unit 50 is coupled to the high voltage supply 51 so that the X-ray filter 6 can be adjusted on the basis of the intensity of the X-ray beam 3 emitted by the X-ray source. The adjusting unit 51 is also connected to the video camera. Consequently, the X-ray filter can be adjusted on the basis of the electronic image signal, so on the basis of image information in the X-ray image. FIG. 2 is a diagrammatic perspective view of a first embodiment of the X-ray filter of the X-ray examination apparatus according to the invention. The filter elements 8 in the embodiment shown in FIG. 2 are constructed as capillary tubes. The capillary tubes 8 are formed as spaces between the wall foils 9 which are locally attached to one another along bonding seams 10. The wall foils 9 are preferably plastic foils, polyester foils or polyethylene terephthalate foils (PETP foils). PETP foils of this kind can be readily fused locally by thermal compression, so that the bonding seams are simply formed by narrow strips along which the neighboring PETP foils are fused. It has also been found that bonding seams of this kind are so strong that the PETP foils are not torn loose when the stack of PETP foils is stretched. Each of the capillary tubes 8 is provided with an electrically conductive electrode 11, for example in the form of an aluminium track across the wall of the relevant capillary tube 8. Furthermore, the X-ray filter includes an electronic control unit 12 for controlling the electric voltages applied to the individual capillary tubes 8. To this end, the electronic control unit 12 includes an electronic switching system with thin-film transistors. The electrodes 11 of the capillary tubes 8 are connected to the electronic control unit 12 by way of the voltage lines 13. The voltage lines 13 are electrically conductive tracks, for example aluminium tracks, deposited on the surface of the wall foils 9. The voltage lines 13 spatially separate the electronic switching system from the capillary tubes 8. The electronic control unit 12 is arranged at such a distance from the capillary tubes 8 that the X-ray beam 3 does not pass through the control unit 12 during operation of the X-ray examination apparatus. Because the voltage lines 13 extend across the wall foils 9, they occupy hardly any additional space between the capillary tubes 8. Furthermore, the wall foils 9 are partly separated from one another by intermediate foils 31. The intermediate foils 31 are arranged between the wall foils 9 in the part between the control unit 12 and the part of the wall foils 9 where the capillary tubes 8 are formed. A plurality of intermediate foils are provided between neighboring wall foils 9, so that in the direction transversely of the longitudinal axis of the capillary tubes 8 the distances between the voltage lines 13 on the relevant separate wall foils 9 are in this example substantially larger than the distances between neighboring capillary tubes 8. Furthermore, voltage lines 13 on one and the same wall foil 9 fan out relative to one another in the region where the relevant wall foil 9 is separated from the neighboring wall foils 9 by intermediate foils 31. Because of the fanning out of the voltage lines 13, in the direction parallel to the capillary tubes 8 the distance between the voltage lines on the same wall foil becomes larger at the area where they emerge from the stack of wall foils 9 than the distance between the voltage lines 13 at the area of the capillary tubes. As a result of the intermediate foils 31 and the fanning out, the distances between the voltage lines 13 at the area where they leave the stack become exactly equal to the distances between contact points 40 on the electronic control unit 12. The voltage lines 13 can thus be readily connected to the contact points 40 of the electronic control unit 12. The electronic control unit 12 forms part of the adjusting unit 50. The stack of wall foils 9 with the intermediate foils 31 is provided with a mechanical reinforcement 41 at the area of the control unit 12. For example, the reinforcement 41 is formed by cured epoxy resin which is provided between the foils. FIG. 3 shows a second embodiment of an X-ray filter of the X-ray examination apparatus according to the invention. In the X-ray filter shown in FIG. 3 intermediate foils 31 are inserted between the wall foils 9. The intermediate foils 31 are provided in a part of the stack of wall foils 9 in which no capillary tubes are formed. Furthermore, in the direction parallel to the longitudinal axis of the capillary tubes several or even all intermediate foils 31 extend as far as the outside of the stack of wall foils 9. Like in the embodiment shown in FIG. 2, voltage lines 13 extend across the wall foils to the electrodes 11 of the capillary tubes 8. In the embodiment of FIG. 3, furthermore, supply lines 32 are provided on the intermediate foils. The supply lines are electrically conductive, like the voltage lines 13; for example, the supply lines are formed as aluminium tracks. Respective supply lines 32 are connected to respective voltage lines 13 by way of supply contact pads 34 of the supply lines 32 and voltage contact pads 35 of the voltage lines 13. An individual supply line is provided with a supply contact pad 34 at an end where the supply line 32 reaches the relevant individual voltage line 13. Furthermore, an individual voltage line is provided with a voltage contact pad 35 at an end which is remote from the capillary tube 8 whereto the relevant voltage line 13 is connected. A supply contact pad 34 and a voltage contact pad 35 each time form a respective electrical connection between the relevant supply line 32 and the relevant voltage line 13. For example, each of the individual capillary tubes 8 is connected to a single voltage line 13 by way of its electrode 11, and each one of the voltage lines 13 is connected to a respective one of the supply lines 33. The individual capillary tubes 8 in another embodiment are individually provided with two electrodes 11 and per capillary tube the two electrodes 11 are connected to two individual voltage lines 33. Preferably, in that case the two voltage lines are provided on oppositely situated wall foils. Furthermore, the pair of voltage lines 13 for individual capillary tubes 8 is connected to a single supply line 32. Thus, two voltage lines and one supply line are used for each capillary tube 8. The electrical contact is established notably by pressing or clamping the respective supply contact pads 34 and voltage contact pads 35 mechanically onto one another. It is notably easy to press or clamp the voltage contact pads 35 and supply contact pads 34 together by pressing or clamping the stack of wall foils with the inserted intermediate foils 31 at the area where the intermediate foils 31 are provided. It is notably possible to press a large number of supply contact pads 34 and voltage contact pads together in pairs; each such pair then consists of a supply contact pad and a voltage contact pad of the relevant supply line and voltage line to be connected to one another. The supply and voltage contact pads 35 are preferably constructed as electrically conductive pads at the end of the relevant supply or voltage line. Such a supply or voltage contact pad then actually consists of a widened portion of the relevant supply or voltage line. It is notably possible to press a large number of supply contact pads 34 and voltage contact pads 35 together in pairs; each such pair then consists of a supply contact pad 34 and a voltage contact pad 35 of the relevant supply and voltage line 13 which are to be connected to one another. It is thus readily possible to establish more than 16,000 connections which are necessary when the X-ray filter according to the invention comprises 128.times.128 capillary tubes 8, all of which have to be connected to the control unit 12. The supply contact pads 34 and voltage contact pads 35 are preferably constructed as an electrically conductive pad at the end of the relevant supply or voltage line 13. The supply and voltage lines have a width of, for example from 10 .mu.m or 50 .mu.m to 150 .mu.m. The width of the supply and voltage contact pads then amounts to, for example from one and a half to two times the width of the supply and voltage lines. Such a supply or voltage contact pad then actually constitutes a widened portion of the relevant supply or voltage line at the relevant end of such a supply voltage line. The stack of intermediate foils 31 in the embodiment shown in FIG. 3 projects from the stack of wall foils 9. The control unit 12 is arranged at the end of the stack of intermediate foils 31 which is outside the stack of wall foils. Between the intermediate foils 31, supporting the supply lines 32, if desired, additional foils may be provided in order to adapt the distances between the supply lines 32 in the direction transversely of the plane of the intermediate foils 31. Furthermore, in order to adapt the distances between the supply lines 32 in the plane of the relevant intermediate foils 31, the supply lines 32 on the intermediate foils 31 may fan out in the region where the supply lines 32 emerge from the stack of intermediate foils 31. At the area where they emerge from the stack of intermediate foils 31 the spacing of the supply lines 32 can thus be accurately adapted to the spacing of the contact points 40 of the control unit 12. FIG. 4 shows a further embodiment of an X-ray filter of an X-ray examination apparatus according to the invention. In the embodiment shown in FIG. 3 an integrated control circuit 36 (driver IC) is provided on the intermediate foils 31. This control circuit provides the selection of the voltage lines which are to receive electric voltages and the voltage lines which are not to receive electric voltages. The integrated control circuit has a multiple output whereto the supply lines are connected. The input of the integrated control circuit is connected, for example to the video camera 18 or to the high-voltage supply 51 in order to adjust the X-ray filter on the basis of the electronic image signal or the intensity of the X-ray beam, respectively. All references cited herein, as well as the priority document European Patent Application 98203898.6 filed Nov. 17, 1998, are incorporated herein by reference in their entirety and for all purposes to the same extent as if each individual publication or patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety for all purposes.