Abstract:
An adaptive x-ray filter for changing a local intensity of x-rays includes an x-ray absorbing first fluid and electrically deformable control elements. The electrically deformable control elements change a layer thickness of the first fluid at a site of a respective electrically deformable control element by at least partially displacing the x-ray absorbing first fluid.

Description:
[0001]    This application claims the benefit of DE 102012209150.5, filed on May 31, 2012, which is hereby incorporated by reference. 
       BACKGROUND 
       [0002]    The present embodiments relate to an adaptive x-ray filter for changing a local intensity of x-rays. 
         [0003]    In examinations with the aid of x-rays, a patient and/or organs of the patient in a region to be examined may exhibit a very different absorption behavior with respect to the applied x-rays. For example, with thorax imaging, the attenuation in the mediastinum (i.e., in the region in front of the lungs) is very great due to the organs arranged there. In the region of the lungs, the attenuation is very low. To obtain a useful image and to protect the patient, the applied dose may be set depending on the region, so that no more x-rays than are needed are supplied. In other words, a greater dose is to be applied in regions with greater attenuation than in regions with less attenuation. In some applications, only part of the examined region is to be imaged with significant diagnostic quality (e.g., with little noise). The surrounding parts may be important for orientation but not for the actual diagnosis. These surrounding regions may be mapped with a lower dose in order to reduce the entire dose applied. 
         [0004]    Filters are used in order to attenuate x-rays. A filter of this type is known, for example, from DE 44 22 780 A1. The filter has a housing with a controllable electrode matrix that generates an electric field. The electric field acts on a fluid connected to the electrode matrix, in which ions absorbing x-rays are present. The ions absorbing x-rays are freely moveable and roam around as a function of the applied field. With such a corresponding electric field embodiment, correspondingly more or fewer ions may be accumulated in the region of one or more electrodes to change the absorption behavior of the filter locally. 
         [0005]    Electroactive polymers (EAP) that change form based on application of an electrical voltage are known from the prior art. One example of an electroactive polymer is a dielectric elastomer. A dielectric elastomer converts electrical energy directly into mechanical work. An actuator based on a dielectric elastomer may be constructed, for example, by coating an elastomer film on both sides with electrodes. An electric voltage may be applied to the elastomer film. The applied voltage compresses the elastomer film in the thickness direction, where the elastomer film extends laterally. With this process, the elastomer film may perform work and thus act as an actuator. If the voltage between the electrodes is removed again, the elastomer film reassumes an original form. 
       SUMMARY AND DESCRIPTION 
       [0006]    The present embodiments may obviate one or more of the drawbacks or limitations in the related art. For example, a further adaptive x-ray filter for changing the local intensity of x-rays is provided. 
         [0007]    In one example, orthogonally arranged, electrically deformable molding elements locally able to change the layer thickness of an x-ray absorbing first fluid in a plane are provided. The local absorption behavior of the filter changes as a result. When the layer thickness is minimal, more x-rays reach an object than when the layer thickness is greater. The x-rays may therefore be modulated in two dimensions. 
         [0008]    In one embodiment, an adaptive x-ray filter for changing the local intensity of x-rays is provided. The x-ray filter includes an x-ray absorbing first fluid (e.g., Galinstan) and electrically deformable control elements. The control elements change the layer thickness of the first fluid at a site of the respective control element by at least partially displacing the first fluid. Control elements are also known under the term actuators and refer to converters with which electronic signals are converted into mechanical movement or other physical variables. One or more of the present embodiments are advantageous in that the radiation field of x-rays may be modulated simply, precisely and rapidly using the adaptive x-ray filter. 
         [0009]    In another example, the control elements may be arranged in a plane that is at right angles to the x-rays. 
         [0010]    In one embodiment, the x-ray filter includes a flexible membrane that is transparent for x-rays. The flexible membrane separates the first fluid from the control elements. The membrane may be moved by the control elements. The control elements may be arranged on the membrane. The layer thickness of the first fluid is therefore changed locally with the aid of the membrane. 
         [0011]    In another embodiment, the x-ray filter includes a second fluid arranged below the membrane. The second fluid is transparent for x-rays. The second fluid includes an x-ray absorption characteristic that is similar to the x-ray absorption characteristic of the control elements. As a result, unwanted structures in the x-ray images are prevented by the control elements. The control elements may be surrounded by the second fluid. 
         [0012]    In one embodiment, the control elements may include at least one electroactive element. When a voltage is applied, electroactive elements constrict (e.g., contract) or extend (e.g., expand). As a result, a deflection of the membrane may be achieved, and thus, the x-ray-absorbing length of the first fluid may be modulated. As a result, a non-uniform x-ray field may be set. 
         [0013]    In another embodiment, the control elements may also include an electroactive polymer. A control element based on an electroactive polymer (e.g., in the form of a dielectric elastomer) may be constructed by an elastomer film coated with electrodes on both sides. An electric voltage is applied to the elastomer film. When the voltage is applied, the elastomer film constricts in the thickness direction, whereby the elastomer film extends laterally. This extension produces a deflection of the membrane. When the voltage between the electrodes is removed again, the elastomer film reassumes an original form. 
         [0014]    In another embodiment, a lifting apparatus may be arranged on a control element. The lifting apparatus increases a travel (e.g., a deflection) of the control element. 
         [0015]    In one embodiment, a method for changing the local intensity of x-rays using an adaptive x-ray filter is provided. Control elements of the adaptive x-ray filter arranged in a plane are electrically deformed and/or changed in terms of length by an electrical cause. As a result, the layer thickness of an x-ray absorbing first fluid irradiated by the x-rays is changed at a site of the respective control element by the control elements being able to at least partially displace the first fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows a schematic representation of the functional principle of one embodiment of an adaptive x-ray filter; 
           [0017]      FIG. 2  shows a cross-sectional view through one embodiment of an adaptive x-ray filter having control elements; 
           [0018]      FIG. 3  shows a cross-sectional view through one embodiment of an adaptive x-ray filter having differently adjusted control elements; 
           [0019]      FIG. 4  shows a cross-sectional view through one embodiment of a control element with electroactive elements; 
           [0020]      FIG. 5  shows a cross-sectional view through one embodiment of a control element having an electroactive polymer in an extended state; and 
           [0021]      FIG. 6  shows a cross-sectional view through one embodiment of a control element with a lifting apparatus. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  shows the functional principle of an adaptive x-ray filter. A location-dependent attenuation of x-rays  2  may be achieved by use of an adaptive x-ray filter  1 . The x-rays  2  are generated by an x-ray source  3 , penetrate the adaptive x-ray filter  1  and a patient  4 , and are measured by an x-ray detector  5 . The local attenuation of the x-rays  2  is controlled with a control unit  6  by the adaptive x-ray filter  1 . 
         [0023]    An intensity profile  7  of the x-rays  2  upstream of the adaptive filter  1  is shown schematically in the top right in  FIG. 1 . The intensity y is shown via axis x, which specifies the location. An approximately uniform course of the intensity y is shown. An intensity profile  8  of the x-rays  2  is shown schematically in the bottom right in  FIG. 1  after passing through the adaptive x-ray filter  1 . The change in local intensity y specified by the adaptive x-ray filter  1  is shown by the form of the intensity profile  8 . 
         [0024]      FIG. 2  shows a cross-section through one embodiment of an adaptive x-ray filter having control elements. The adaptive x-ray filter  1  includes a housing  9  that is separated into a first chamber  11  with a first fluid  15 , and a second chamber  12  with a second fluid  16 , by a flexible membrane  10 . Each of the chambers  11 ,  12  has an inflow/outflow  13 ,  14 , by which the fluids  15 ,  16  may be supplied/drained off. The first fluid  15  is an x-ray absorbing fluid. The second fluid  16  is a fluid transparent for x-rays. 
         [0025]    Control elements  17  such as, for example, actuators are arranged on a lower side of the membrane  10 . The control elements  17  and the second fluid  15  include, for example, comparable x-ray absorption properties. Thus, no unwanted structures are visible in a created x-ray image. The first and second fluids  15 ,  16  may be filled through the inflows/outflows  13 ,  14 , and a differential pressure may be applied to the membrane  10 . The fluids  15 ,  16  may be supplied or drained off through the inflow/outflow openings  13 ,  14  depending on the deflection of the membrane  10 . Control signals such as, for example, a voltage may be sent via activation lines  18  to the control elements  17 . The control elements  17  constrict (e.g., contract) or extend (e.g., expand), thereby causing the membrane  10  to deflect. 
         [0026]      FIG. 3  shows a cross-section through one embodiment of an adaptive x-ray filter with differently adjusted control elements. An adaptive x-ray filter  1  with the same structure to that in  FIG. 2  is shown. Control signals such as, for example, a voltage may be sent via the activation lines to the control elements  17 . The control elements  17  extend very differently as a. A deflection of the membrane  10  and thus a modulation of the absorbing length of the first fluid  15  are thus achieved. As a result, a non-uniform x-ray image may be set. 
         [0027]      FIG. 4  shows a cross-section through one embodiment of a control element having electroactive elements. A control element  17  includes a number of electroactive elements  19  that extend when a voltage is applied. If the voltage is removed again, the electroactive elements  19  reassume an original form of the electroactive elements  19 . In order to prevent unwanted structures on an x-ray image to be created, the electroactive elements  19  have an x-ray transparent property that is similar to the surrounding materials (e.g., a fluid (not shown) that surrounds the electroactive elements  19 ). 
         [0028]      FIG. 5  shows a cross-section through one embodiment of a control element having an electroactive polymer in the extended state. A control element  17  includes a dielectric elastomer film  20  coated on both sides with electrodes (not shown), to which an electric voltage may be applied. The dielectric elastomer film  20  is compressed in the thickness direction by the applied voltage, whereby the dielectric elastomer film  20  extends laterally. This extension enables a deflection of a membrane (not shown). When the voltage between the electrodes is removed, the dielectric elastomer film  20  reassumes an original 2-dimensional form. 
         [0029]      FIG. 6  shows a cross-section through one embodiment of a control element with a lifting apparatus. A control element  17  includes an electroactive element  19  that shortens when an electric voltage is applied. The electroactive element  19  is actively connected to a lifting apparatus  21 . The lifting apparatus  21  is arranged in the control element  17  such that a shortening of the electroactive element  19  results in a deflection  22 . Due to the lifting effect, the deflection is greater than the shortening of the electroactive element  19 . The materials used for the lifting apparatus  21 , the electroactive element  21 , a fluid (not shown) surrounding the electroactive element  19 , and the lifting apparatus  21  all include a similar x-ray-transparent property. As a result, unwanted structures on an x-ray image to be created are avoided. 
         [0030]    While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.