Abstract:
A device for installation of a gradient coil unit into a magnetic resonance apparatus has at least one support unit and at least one carrier unit. The carrier unit is fashioned to carry the gradient coil unit, and the at least one support unit is supported thereon such that it can tilt on a connector.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention concerns a device for installation of a gradient coil unit into a magnetic resonance apparatus. 
   2. Description of the Prior Art 
   For the installation of heavier components of a medical apparatus, an auxiliary device is frequently required that assists the technician. The mass of a gradient coil unit of a magnetic resonance apparatus is generally more than 100 kilograms, such that installation thereof into the magnetic resonance apparatus is not possible without auxiliary means. In magnetic resonance apparatuses, the gradient coil unit is supported (mounted) within a basic field magnet. A gap thus exists between the basic field magnet and the gradient coil unit. This gap is only a few millimeters, while the diameter of the receptacle (retainer) for the gradient coil unit is several hundreds of millimeters. It is therefore necessary to exactly position the gradient coil unit. In particular the magnetic center of the gradient coil unit must be positioned at the magnetic center of the basic field magnet with a tolerance of approximately 1 mm. The axes of symmetry of basic field magnet and gradient coil unit must additionally be aligned counter to one another with a tolerance of 0.1°. Once the alignment of the gradient coil unit is achieved exactly, lining parts are installed into the gap with a positive fit and the gradient coil unit is fixed in this manner. 
   To install the gradient coil unit it is known to accommodate the gradient coil unit by means of a carrier device and to insert it into the basic field magnet. The alignment ensues by means of shims (wedges) arranged between the gradient coil unit and the basic field magnets. A rotation ensues utilizing gravity by means of shims that are not centrally mounted, so a tilting of the gradient coil unit is achieved. The described procedure is exceedingly time-consuming and laborious for the implementing technician. 
   A transport cart or carriage for a gradient coil unit is known from EP 0 552 542 A1. The transport cart is fashioned such that different types of gradient coil units can be transported therewith. Spacers can be introduced between the basic field magnet and the gradient coil unit to align the gradient coil unit within the basic field magnet. 
   A method and a device for horizontal mounting of liners in high-pressure tank construction is described in East German PS 119 297. A tube bundle is thereby supported on transport segments. To align the tube bundle within a high pressure jacket, the transport segments are supported on three-point supports that can be vertically adjusted at three points of the floor or base by means of leveling elements. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a device for installation of a gradient coil unit into a magnetic resonance apparatus that allows installation and alignment of the gradient coil unit in a simple manner. 
   This object is achieved in accordance with the invention by a device having at least one support unit and at least one carrier unit that is designed to carry the gradient coil unit and on which the at least one support unit is carried such that it can be tilted via a connector. The support unit is brought into the receptacle (tunnel) of the magnetic resonance apparatus with the gradient coil unit and is aligned. In the installation of the gradient coil unit, it is positioned such that its magnetic center is in or at the magnetic center of the basic field magnet. By the use of a tiltable connector, it is possible in a simple manner to correct the tilt of the gradient coil unit with regard to its axis of symmetry. This avoids the conventional protracted adjustment event with shims within the basic field magnet. 
   In an embodiment, the at least one carrier unit can be tilted relative to an axis that is parallel to a longitudinal axis of the support unit. This enables a simple alignment of the gradient coil unit with regard to this longitudinal axis. This adjustment event is particularly important for a gradient coil unit built in a cylindrical shape, as is common. 
   One possibility for correcting a non-ideally-aligned gradient coil unit is the use of weight elements that are mounted on the carrier unit such that they can be moved and secured. By moving the weight elements the technician can effect an optimization of the angle position of the gradient coil unit in a simple manner. 
   In another embodiment, the carrier unit has a position monitoring unit. The correct (in terms of angle) position for a technician can be directly detected with this position monitoring unit. 
   The at least one support unit has a support segment with a support surface (contact surface) for movable support of the connector. For example, the position of the gradient coil unit can be optimized in a simple manner within the basic field magnet, and the magnetic center of the gradient coil unit thus can be positioned in the magnetic center of the basic field magnet. 
   In a preferred embodiment of the invention, the connector exhibits a tapering at both ends with regard to an axis lying perpendicular to the cross-section. The support surface is planar. Due to the use of barrel-shaped roller, the gradient coil unit (connected, for example, with the carrier unit) automatically aligns within the basic field magnet by gravity. The gradient coil unit thus can be tilted on its axis of symmetry in a limited range, such that the correct (with regard to the angle) position can be adjusted in a simple manner. In this manner, only a little work still needs to be conducted for the alignment of the gradient coil unit. In particular iterative alignments by means of shims is avoided. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal section through a magnetic resonance apparatus showing the installation of a gradient coil unit in accordance with the invention. 
       FIG. 2  is an end sectional view of the magnetic resonance apparatus of  FIG. 1 . 
       FIG. 3  shows an embodiment of a roller (caster) and a support bar in accordance with the invention. 
       FIG. 4  shows an alternative embodiment of a roller and of a support bar. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As shown in  FIG. 1 , a magnetic resonance apparatus has a basic field magnet  2  with a tubular longitudinal opening  4 . A gradient coil unit  6  is installed into the opening  4 . For a better overview, the resulting gap  8  between the gradient coil unit  6  and the basic field magnet  2  is shown over-proportionally large in comparison with the size of the basic field magnet  2 . The gradient coil unit  6  is connected via metal carriers  10  with two carrier units  12  that are supported on a support bar or rail  14  such that they can move along it. The support bar  14  traverses the gradient coil unit  6  and is larger in terms of length than the basic field magnet  2 . The support bar  14  is part of a C-shaped support unit  16 . The support unit  16  has a load arm  18  with an annular receptacle (eye)  20  for attachment to a crane (not shown here). A counterweight  22  that serves for compensation of the asymmetrical (due to the C-shape) weight distribution of the support unit  16  is attached on the load arm  18 . The receptacle  20  is arranged above the center of gravity  24  of the support unit  16 . The length of the support bar  14  is designed such that its center point  26  is situated below the center of gravity  24 . When the support unit  16  is suspended by the crane, the support bar  14  is aligned level due to the counterweight  22 . The gradient coil unit  6  is supported on the support bar  14  such that its center of gravity  28  is situated in a vertical line  30  with the center  26  of the support bar  14 . The level position of the support bar  14  is also maintained with the gradient coil unit  6  supported thereon. Since the gradient coil unit  6  is supported on the support bar  14  such that it can move, the correct position thereof can be adjusted by simple displacement on the support bar  14 . The possible directions of the displacement are indicated by a double arrow  32 . Using the crane it is possible in a simple manner to exactly position the support bar  14  and the gradient coil unit  6  with regard to the basic field magnet  2 . 
   In addition to the correct positioning within the basic field magnet  2 , it is necessary to align the gradient coil unit  6  in a correct angular position with regard to its axis of symmetry  33 . For basic alignment, the carrier units  12  are supported on rollers (not shown in  FIG. 1 ). Two embodiments of the rollers are shown in  FIGS. 3 and 4  and explained in further detail below. Weight elements  34  that are used for fine adjustment of the angular position and whose function is explained further using  FIG. 2  are attached on both carrier units  12 . 
     FIG. 2  shows an end section view of the magnetic resonance apparatus according to  FIG. 1 . Only a part of the basic field magnet  2  with the gradient coil unit  6  inserted into the opening  4  is thereby shown. Receptacle pockets  36  that are used for accommodating shim materials for correction of the magnetic field in the normal operation of the magnetic resonance apparatus are formed in the gradient coil unit  6 . Corresponding receptacle pockets  36  are also provided in the carrier units  12 . Metal carriers  10  that likewise proceed through the carrier units  12  located at both ends of the gradient coil unit  6  are placed through two of the receptacle pockets  36  in the mounting of the gradient coil unit  6 . The metal carriers  10  are longer than the gradient coil unit  6 . In this manner the gradient coil unit  6  is connected with the carrier units  12  in a detachable manner. Each carrier unit  12  has a roller  38  by means of which it can be supported and moved on the support bar  14 . The properties of the roller  38  on the support bar  14  are explained in detail below using the exemplary embodiments shown in  FIGS. 3 and 4 . The embodiments of the roller  38  allows the gradient coil unit  6  to tilt in a limited range. The angular position of the gradient coil unit  6  can thereby be adjusted. The angular position of the gradient coil unit  6  can be monitored simply via a level  42  installed over the carrier unit  12 . A fine adjustment can be effected via the movable weight elements for optimization of the angular position. By simple displacement of the weight elements  34  on a support rod  44 , a technician can correct the angular position of the gradient coil unit  6  until the level  42  indicates the correct angular position. Due to the displacement of the weight elements  34 , the center of gravity of the system made up of gradient coil unit  6  and the carrier units  12  shifts such that the system correspondingly aligns under the effect of gravity. The weight elements  34  can be fixed on the support rods  44  via locking screws (not shown) to maintain an alignment of the gradient coil unit  6 . After the correct alignment of the gradient coil unit  6 , cladding parts or shims are inserted into the gap  8  between the basic field magnet  2  and the gradient coil unit  6  such that the gradient coil unit  6  is fixed in its final position. Now only the metal carrier  10  must be removed from the receptacle pockets  36  of the gradient coil unit  6  and the carrier units  12  must be demounted. After removal of the support bar  14 , the mounting of the gradient coil unit  6  within the basic field magnet  2  is concluded. The time expenditure relative to the laborious alignment of the gradient coil unit  6  by means of shims can be reduced by several hours. 
     FIG. 3  shows an embodiment of the support bar  14   a  and of the roller  38   a.  In this embodiment, the bar  14   a  has a planar support surface  46   a.  The roller  38   a  has the shape of a barrel, with taperings  48  of the cross-section at the ends. The contact surface between the roller  38   a  and the support bar  14   a  is thereby minimized and the roller  38   a  can be tilted in a limited range, as indicated by the double arrow  50 . The gradient coil unit  6  also can be correspondingly tilted via the carrier unit  12  connected with the roller  38   a.    
     FIG. 4  shows an alternative embodiment of the support bar  14   b  and of the roller  38   b.  Here the support bar  14   b  exhibits a tapering towards the support surface  46   b.  The roller  38   b  exhibits a central narrowing  52 . In this embodiment as well, the roller  38   b  can be tilted analogous to the embodiment described in  FIG. 3 . 
   Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.