Patent Publication Number: US-8971498-B2

Title: Contour collimator and adaptive filter having a magnetic fluid absorbing x-ray radiation and associated method

Description:
This application claims the benefit of DE 10 2012 201 855.7, filed Feb. 8, 2012, which is hereby incorporated by reference. 
     BACKGROUND 
     The present embodiments relate to a contour collimator or an adaptive filter and to an associated method for adjusting a contour in a ray path in x-ray radiation. 
     A contour collimator is used in radiation therapy for the treatment of tumors. In radiation therapy, a tumor is irradiated with energy-rich radiation (e.g., with high-energy x-ray radiation of a linear accelerator). In such treatment, the contour collimator is brought into the ray path of the x-ray radiation. The contour collimator has an opening, through which radiation may pass. The contour of the opening is intended to correspond to the contour of the tumor. The contour thus forms an aperture for the passage of the x-ray radiation. This provides that the tumor, and not the adjoining healthy body tissue, is irradiated with the x-ray radiation. By embodying the contour collimator in a suitable manner, almost any given contour of a tumor may be mapped. 
     Collimators widely used for radiation therapy are multi-leaf collimators, as described, for example, in patent DE 10 2006 039793 B3. The multi-leaf collimator has a number of leaves (e.g., 160 leaves) able to be moved by motors in relation to one another to form the opening. The leaves include a material absorbing the x-ray radiation. Two packages of leaves are disposed opposite one another so that the leaves may be moved with end face sides towards one another or away from one another. 
     Each of the leaves is able to be displaced individually by an electric motor. Since there may be slight deviations in the positioning of the leaves between a required specification and the actual position of the leaves currently set, each leaf has a position measurement device, with which the position currently set may be determined. 
     In examinations with the aid of x-rays, it often occurs that the patient or organs of the patient exhibit a greatly differing absorption behavior with respect to the applied x-ray radiation in the area under examination. For example, in images of the thorax, the attenuation in the area in front of the lungs is very large, as a result of the organs disposed there, while in the area of the lungs, the attenuation is small. Both to obtain an informative image and also to protect the patient, the applied dose may be adjusted as a function of the area so that more x-ray radiation than necessary is not supplied. This provides that a larger dose is to be applied in the areas with high attenuation than in the areas with low attenuation. In addition, there are applications in which only a part of the area under examination is to be imaged with high diagnostic quality (e.g., with little noise). The surrounding parts are of importance for orientation but not for the actual diagnosis. These surrounding areas may thus be mapped with a lower dose in order to reduce the overall applied dose. 
     Filters are used to attenuate the x-ray radiation. Such a filter is known, for example, from DE 44 22 780 A1. This has a housing with a controllable electrode matrix, by which an electrical field that acts on a fluid connected to the electrode matrix, in which x-ray radiation-absorbing ions are present, is able to be generated. The x-ray radiation-absorbing ions are freely movable and move around according to the field applied. In this way, by forming an appropriate field, many or few irons may be correspondingly accumulated in the area of one or more electrodes in order to change the absorption behavior of the filter locally. 
     SUMMARY AND DESCRIPTION 
     The present embodiments may obviate one or more of the drawbacks or limitations in the related art. For example, a further contour collimator and a further adaptive filter that may map a contour robustly and rapidly are provided. In a further example, an appropriate method for forming a contour is provided. 
     An aperture forming the contour is generated with the aid of a magnetic fluid absorbing x-ray radiation or with a fluid impermeable to x-ray radiation (e.g., a ferrofluid). In a magnetic field, magnetic moments of the particles of the ferrofluid tend to travel in a direction and achieve macroscopic magnetization. Magnet elements generating magnetic fields are used to magnetize the fluid or parts of the fluid. 
     Ferrofluids are magnetic fluids that react to magnetic fields without solidifying. The ferrofluids are attracted by magnetic fields. The ferrofluids includes magnetic particles a few nanometers in size that are suspended in a colloidal manner in a carrier fluid. The particles may be stabilized with a polymer surface coating. True ferrofluids are stable dispersions, which provides that the solid particles do not break off over time and do not themselves accumulate on one another in extremely strong magnetic fields or separate from the fluid as another phase. Ferrofluids are supermagnetic and have a very low hysteresis. 
     A contour collimator or an adaptive filter for adjusting a contour of a ray path of x-ray radiation is provided. The apparatus includes a magnetic fluid impermeable to x-ray radiation and switchable magnet elements, by which an aperture forming the contour may be formed in the magnetic fluid by the magnetic fluid being attracted by the magnetic fields of the magnet elements. The contour forms the aperture (i.e., an opening in the contour collimator or the filter). An aperture may be a free opening or the diameter of the free opening, through which x-rays may be emitted or received. The embodiment offers the advantage of a robust collimator or filter, with which rapidly changing contours may be adjusted precisely 
     In a further embodiment, the magnetic fluid may be a ferrofluid. 
     In one development, the magnetic fluid may be arranged in the form of a layer with limited expansion. 
     Furthermore, the apparatus may include at least one second layer, in which the magnet elements are arranged. The second layer may be arranged above or below the first layer. Alternatively, a second layer may be arranged above or below the first layer in each instance. 
     In a further embodiment, an electric grid structure formed from conductor paths is embodied in the second layer. The magnet elements are arranged at the points of intersection of the conductor paths. 
     In a development, the magnet elements may include coils, through which current passes. 
     The contour collimator or the filter may include an electric control unit, with the aid of which the magnet elements may be switched on and off according to the contour to be formed. 
     A number of first and second layers may also be stacked in order to form the contour collimator. 
     In one embodiment, a method for adjusting a contour of a ray path of x-ray radiation using a contour collimator or an adaptive filter is provided. Magnetic fields form an aperture forming the contour in a magnetic fluid that is impermeable to x-ray radiation, by the magnetic fields attracting the magnetic fluid. 
     In one embodiment, the magnetic fields may be formed by switchable magnet elements. 
     The magnetic fields may be formed by electric currents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a spatial view of one embodiment of a contour collimator; 
         FIG. 2  shows a spatial view of one embodiment of an adaptive filter; 
         FIG. 3  shows a spatial view of one embodiment of a plate forming the contour collimator or the filter; 
         FIG. 4  shows a sectional view of one embodiment of a plate forming the contour collimator or the filter; and 
         FIG. 5  shows a view of one embodiment of the grid structure in the second layer. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a spatial representation of one embodiment of a contour collimator  1  having a number of stacked contour plates  3 . An aperture  11  forming a contour  10  is embodied in the collimator plates  3 . The aperture  11  allows x-ray radiation  12  to pass through to an object  13  (e.g., a tumor). Except for the aperture  11 , the collimator plates  3  are impermeable to x-ray radiation  12 . The layers absorbing x-ray radiation  13  are formed by a magnetic fluid  9 . Where the magnetic fluid  9  is absent, the aperture  11  is formed. 
       FIG. 2  shows a spatial representation of one embodiment of an adaptive filter  2  having three stacked filter plates  3 . An aperture  11  forming the contour  11  is embodied in the filter plates  3 . The aperture  11  allows x-ray radiation  12  to pass through. Except for the aperture  11 , the filter plates  3  are impermeable to x-ray radiation  12 . The layers absorbing x-ray radiation  12  are formed by a magnetic fluid  9 . Where the magnetic fluid  9  is absent, the aperture  11  is formed. 
       FIG. 3  shows a spatial view of one embodiment of a collimator plate and/or a filter plate  3 . The plate  3  includes a first layer  4  that is formed by a magnetic fluid  9  that is impermeable to x-ray radiation. Magnetic fields may be generated by magnet elements (not shown in  FIG. 3 ) arranged in second layers  5  using a second layer  5  including material transparent for x-ray radiation arranged thereabove and below. At the location of the aperture  11 , the magnetic fluid  9  is “drawn in” (e.g., attracted) through the magnetic fields lying outside of the aperture, and x-ray radiation may pass therethrough unhindered. 
       FIG. 4  shows one embodiment of the plate  3  from  FIG. 3  in a sectional view. The two second layers  5  including the material that is transparent to x-ray radiation are visible. A plurality of magnet elements  6  (e.g., coils) is embodied in the second layers  5 . The more magnet elements  6  there are available, the more precisely a contour  10  and/or the aperture  11  forming the same may be mapped. The first layer  4  with the magnetic fluid  9  that is not transparent for x-ray radiation is located between the two second layers  5  and is, for example, a ferrofluid. At the locations, at which the magnet elements  6  are active (e.g., generate a magnetic field H), the magnetic fluid  9  is attracted (e.g., removed from the area of the aperture  11  to be formed). As a result, the aperture  11  is produced. 
       FIG. 5  shows a schematic representation of one embodiment of a grid structure  9  embodied in the second layer. The grid structure  8  is formed by conductor paths  7 . Magnet elements  6  are disposed at points of intersection of the conductor paths  7  (e.g., two coils connecting conductor paths). The magnet elements  6  generate a magnetic field H at right angles to the second layer when current is flowing through the conductor paths. A control unit  14  is able to switch each magnet element  6  on and/or off at each point of intersection. The more points of intersection there are available, the more precisely the contour may be mapped. 
     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.