Abstract:
The invention relates to a gantry for an x-ray device. According to the invention at least one screening device used to reduce interactions with electromagnetic disturbance fields is provided for the at least one transmitter for the non-contact power or signal transmission between a stationary part and a rotatable part of the gantry.

Description:
The present patent document is a 371 of PCT Application Serial Number PCT/EP2005/053413, filed Jul. 15, 2005, designating the United States, which is hereby incorporated by reference. This application also claims the benefit of DE 10 2004 035 603.3, filed Jul. 22, 2004, which is hereby incorporated by reference. 
   BACKGROUND 
   The present embodiments relate to a gantry for an X-ray device. 
   In radiation therapy and in many computed tomography systems, signals are transmitted from a stationary part to a rotatable part of a gantry using a contactless transmitter for example, by induction. As a result, spark development and high wear in such transmission types as wiper rings are avoided. German Patent DE 28 55 379 C2 discloses a contactless power transmission. 
   As shown in  FIG. 2 , a contactless power transmitter for power transmission includes a primary coil on the stationary part of the gantry, a secondary coil on the rotatable part of the gantry, and at least one transmitter core. A plurality of transmitters for different system components to be supplied with power may also be present on one gantry. 
   For structural reasons, an air gap between the stationary part and the rotatable part of the gantry is unavoidable. A magnetic stray field develops around the air gap. The size of the magnetic stray field is in proportion to its size. The magnetic stray field of a transmitter can enter into interaction with the magnetic stray field of a different transmitter, with capacitive coupling paths for data transmission, or with electronic system components. The result of the interaction with other magnetic stray fields can be mutual interference with transmission, to the point of damage to system components. 
   If there are two transmitters side by side, of which the first is responsible for supply to the X-ray tube and the second is responsible for voltage supply otherwise, the interaction at the X-ray tube, despite the first transmitter having been switched off, can permanently cause a voltage of up to several kV. This can lead to unwanted radiation generation. 
   The interaction may possibly be reduced by creating a sufficient distance from the stray fields or between the stray fields. For example, for an air gap of approximately 1 mm, to attain any improvement the distance between two inductive transmitters would have to be at least 10 cm, but for structural reasons that is often not possible. 
   SUMMARY 
   The present embodiments may obviate one or more of the drawbacks or limitations of the related art. For example, in one embodiment, a simple and inexpensive way to reduce the effect on system components of magnetic stray fields that are caused for instance by the contactless inductive power transmission or other signal transmission, or by other electromagnetic interference fields, is provided. 
   In one embodiment, a gantry for an X-ray device is provided for receiving an X-ray tube and/or measurement value detection. A stationary part of the gantry is disposed in stationary fashion, and relative to the stationary part is a rotatable part of the gantry. The gantry is provided for receiving at least one transmitter for power transmission and/or signal transmission between the stationary part and the rotatable part. The power transmission and/or signal transmission between the stationary part and the rotatable part is provided in contactless fashion, in particular inductively and/or capacitively. At least one shielding device for the at least one transmitter is provided for shielding against electromagnetic interference fields. 
   In one embodiment, not only protection of the particular transmitter against electromagnetic interference fields from other transmitters or from external interference fields but also protection of other equipment components against the electromagnetic interference fields of that particular transmitter are assured using a shielding device for the at least one transmitter. 
   In one embodiment, at least one shielding device for the at least one transmitter is provided. The at least one shielding device shields against electromagnetic interference fields that occur as a result of the contactless power transmission and/or signal transmission. To enable assuring comprehensive mutual protection of at least two transmitters, expediently at least one shielding device for at least one transmitter is provided for shielding against electromagnetic interference fields, occurring as a result of the contactless power transmission and/or signal transmission, of the other transmitter or transmitters, respectively. 
   In one embodiment, at least one annular transmitter is provided. In this embodiment, the shielding device is formed by at least one annular shield element that is concentric with the respective transmitter. In this embodiment, the shielding device can be mounted at little expense and does not hinder the operation of the equipment. In one embodiment, at least one annular transmitter is provided. The shielding device is formed by at least one stationary annular shield element that is concentric to the stationary part of the respective transmitter and at least one rotatable annular shield element that is concentric with the rotatable part of the respective transmitter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a front view of an X-ray device with a gantry according to the prior art; 
       FIG. 2  shows a side view of a section through a gantry with an inductive power transmitter according to the prior art; 
       FIG. 3  shows a side view of a section through a gantry with two inductive power transmitters according to the prior art; 
       FIG. 4  shows a side view of one embodiment of a section through a gantry with two inductive power transmitters and shield elements; 
       FIG. 5  shows a side view of one embodiment of a section through a gantry with two inductive power transmitters and overlapping shield elements; 
       FIG. 6  shows a side view of one embodiment of a section through a gantry having an inductive power transmitter and shield elements. 
   

   DETAILED DESCRIPTION 
   As shown in  FIG. 1 , an X-ray diagnosis device produces transverse slice images of a patient  1 . One such system is known as a computed tomography system. The device has a gantry  3  provided in a frame  2 . The gantry  3  has one part that is rotatable by a motor  4  about an axis  5  that extends perpendicular to the plane of the drawing. The gantry  3  includes an X-ray tube  7  and a detector  8  for X-raying the patient lying on a support  6 . 
   the X-ray tube  7  emits a fan-shaped X-ray beam  9 . The size of the X-ray beam  9  is selected such that the entire transverse slice to be examined of the patient  1  is penetrated by X-radiation. Perpendicular to the plane of the slice, the thickness of the X-ray beam  9  is equal to the slice thickness. For X-raying the patient  1 , the assembly comprising the X-ray tube  7  and the detector  8  is rotated about the patient  1  by an angle of approximately 360°. A set of output signals of the detector  8  is called up at predetermined projections, for example, at each degree of angle. 
   The high voltage to the X-ray tube  7  from an X-ray generator  20  is transmitted in contactless fashion. Contactless signal transmission allows the measurement assembly  7 ,  8  to rotate constantly and have very short scanning times. Contactless signal transmission can be from a rotating part to a fixed part, for example, also inductively or via a stationary ring, curved around the pivot axis  5 , of fiber optical material in a manner not described in further detail. 
   As shown in  FIG. 2 , a gantry  3  of the related art includes a single inductive transmitter  27 . The transmitter  27  is disposed annularly around the opening  19  that serves to receive an object  1  and has a pivot axis  5 . The stationary part of the transmitter  27  includes a primary coil  21  and a U-shaped transmitter core part  23 . The rotatable part of the transmitter  27  includes a secondary coil  22  and a U-shaped transmitter core part  24 . For structural reasons, there is an air gap L between the stationary part and the rotatable part of the transmitter  27 . Magnetic stray fields  25  and  26  form around the air gap in both the inner and outer peripheral regions of the transmitter  27 . The magnetic stray field  25  extends into the opening  19 . 
     FIG. 3  shows a scanning unit as in  FIG. 2 , with two transmitters  27  and  37  of different radii. Each transmitter has one stationary part, with primary coils  21  and  31  as well as U-shaped transmitter core parts  23  and  33 , and one rotatable part, with secondary coils  22  and  32  and U-shaped transmitter core parts  24  and  34 . Magnetic stray fields  25 ,  26 ,  35  and  36  form in the region of the air gap L in both transmitters  27  and  37 . The outward-oriented stray field  36  of the inner transmitter  37  and the inward-oriented stray field  25  of the outer transmitter  27  overlap, and the result can create wrong couplings. 
   As shown in  FIG. 4 , in one embodiment, a gantry  3 . 2  includes two annular transmitters  27  and  37  and annular shield elements  41  and  42 . The annular shield elements  41  and  42  are disposed between the annular transmitters  27  and  37  to shield against the magnetic stray fields. The annular shield elements  41  and  42  are concentric to the respective transmitters  27  and  37  and can comprise different materials. In one embodiment, the annular shield elements  41 ,  42  are embodied as magnetostatic shielding, in particular of ferrite. Using materials such as ferrites that are poor electrical conductors, magnetic stray fields  25 ,  36 , as shown in  FIG. 3 , can be statically shielded against. Using this type of shielding, no losses of electrical power occur. 
   The shield elements  41 ,  42  may also be constructed of different materials. In one embodiment, the annular shield elements  41 ,  42  are embodied for eddy current damping. In this embodiment, the annular shield elements  41 ,  42  include electrically conductive material, in particular iron. For the eddy current damping, it is appropriate for the shield elements to form a closed surface. The way the eddy current damping works is that the stray field induces eddy currents in the conductive shielding rings. This creates a contrary field, which acts counter to the original stray field and leads to its compensation. The eddy current damping can effectively shield against stray fields with even only very thin shield elements. 
   As shown in  FIG. 5 , in one embodiment, a gantry  3 . 3  includes annular shield elements  43 - 48 . At least partial mutual axial overlap (parallel to the pivot axis  5 ) of the shield elements  43 - 48  is provided for more than one of the annular shield elements  43 - 48 . In one embodiment, at least one transmitter  27 ,  37  and one shielding device  47 ,  48  is provided outside the outer contour of the largest transmitter  27 , and one shielding device  45 ,  46  is provided inside the inner contour of the smallest transmitter  37 . In this embodiment, equipment components located outside and inside the gantry  3 . 3 , and persons as well, are protected against the stray fields, and the tolerance levels permitted are adhered to. The transmitters are also protected against damaging electromagnetic stray fields. 
   As shown in  FIG. 6 , in one embodiment, a gantry  3 . 4  includes a single transmitter  27  and annular shield elements  45 - 48 . The thickness of the shield elements  41 - 48  is oriented to the penetration depth of the induced currents and may be in the range of 1 mm, for example. 
   In one embodiment, a gantry for an X-ray device includes at least one transmitter for contactless power transmission and signal transmission between a stationary part and a rotatable part of the gantry, and at least one shielding device for reducing interactions with electromagnetic interference fields.