Abstract:
A magnetic resonance apparatus has a gradient coil unit, which can be displaced on a guide device disposed inside an examination chamber of the magnetic resonance apparatus, an auxiliary device that is displaceable in relation to the examination chamber, and which can be docked on the guide device in order to extend the displacement of the gradient coil unit. The extension device may continue the course of the guide device along a curved path outside of the examination chamber. A positioning device may be displaced on the guide device, extended by the extension device, to displace a subject relative to the examination chamber.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a magnetic resonance imaging apparatus, of the type having a mobile (movable) gradient coil unit.  
           [0003]    2. Description of the Prior Art  
           [0004]    Magnetic resonance is a known technique for generating images of the inside of a body of an examination subject. For this purpose, rapidly switched gradient fields are superimposed onto a static basic magnetic field in a magnetic resonance apparatus, the static basic magnetic field being generated by a basic field magnet. The magnetic resonance apparatus also has a radio-frequency system which irradiates radio-frequency signals into the examination subject in order to trigger magnetic resonance signals and which accepts the triggered magnetic resonance signals. Magnetic resonance images are produced on the basis of the magnetic resonance signals.  
           [0005]    The magnetic resonance apparatus has an examination chamber in which a port of the examination subject to be imaged is positioned for producing magnetic resonance images of the area to be imaged. For this purpose, the magnetic resonance apparatus normally has at least one movable positioning device on which the examination subject is borne. Positioning of the area to be imaged in the examination chamber is possible by displacing the positioning device with the examination subject thereon.  
           [0006]    For example, U.S. Pat. No. 5,185,576 discloses a local gradient coil unit that is combined with a local radio-frequency antenna. The local gradient coil unit has an integrated local radio-frequency antenna is configured for a specific area of the examination subject such as a head of a patient. In contrast to a firmly installed gradient coil system which is dimensioned for the entire patient, the local gradient coil unit, therefore, can be smaller which has advantages concerning obtainable gradient intensities and power requirements with respect to a gradient amplifier feeding the gradient coil unit. The local gradient coil unit having an integrated local radio-frequency antenna can be mounted on the positioning device such that the local gradient coil unit does not move toward the positioning device even given the operation of the magnetic resonance apparatus and the forces acting on it.  
           [0007]    Furthermore, U.S. Pat. No. 5,311,134 discloses a magnetic resonance apparatus having a cylindrical stationary base unit with a basic field magnet and a gradient coil system that cannot be displaced vis-a-vis the basic field magnet. The magnetic resonance apparatus has a track-like guiding device which is partially arranged in a hollow space of the base unit, and extends beyond the hollow space and on which an essentially cylindrical movable gradient coil unit can be displaced, whereby an antenna unit is firmly connected to it in one embodiment. The magnetic resonance apparatus also has a patient bed with which the patient thereon cannot only be positioned in the hollow space of the base unit but also in a hollow space of the gradient coil unit.  
         SUMMARY OF THE INVENTION  
         [0008]    An object of the invention is to provide an improved magnetic resonance apparatus having a mobile gradient coil unit wherein the gradient coil unit can be handled in a simple manner.  
           [0009]    This object is achieved in accordance with the present invention in a magnetic resonance apparatus has a gradient coil unit, which can be displaced on a guide device disposed inside an examination chamber of the magnetic resonance apparatus, an auxiliary device that is displaceable in relation to the examination chamber, and which can be docked on the guide device in order to extend the displacement of the gradient coil unit. The extension device may continue the course of the guide device along a curved path outside of the examination chamber. A positioning device may be displaced on the guide device, extended by the extension device, to displace a subject relative to the examination chamber.  
           [0010]    The inventive gradient coil unit, whose weight can be up to 250 kg, does not have to be lifted for inserting or removing the gradient coil unit into or from the examination chamber given a change between an image acquisition operation with or without the mobile gradient coil unit. Since the gradient coil unit does not have to be lifted, a crane or lift, which is usually provided therefor, is not necessary. Rather, the change can occur by smoothly displacing the gradient coil unit on a horizontal plane.  
           [0011]    In an image acquisition operation without the movable gradient coil unit, the gradient coil unit can be positioned next to an opening of the examination chamber such that a maximum extension of a positioning device through this opening is not impaired. Furthermore, additional space behind the opening is not necessary since the gradient coil unit is parked next to the opening—in contrast to the positioning device that is maximally extended through the opening. Therefore, the minimum distance between the opening and the wall of a setup room or a shielding cabin facing the opening is not enlarged. The unimpaired maximum extension of the positioning device is particularly important with for angiography of peripheral vessels of a patient and/or for obtaining images of the entire body, given magnetic resonance apparatuses having a short basic field magnet, in particular. In the inventive apparatus, in particular, the examination chamber can be easily accessed.  
           [0012]    In an embodiment, an enlarged space must be provided behind the opening for a maximum extension of the positioning device through the opening of the examination chamber when the gradient coil unit is not used at the same time, however, a guiding device that is arranged in the examination chamber is used not only for the positioning device but also for the gradient coil unit.  
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 shows a horizontal longitudinal section through a magnetic resonance apparatus having an extension device for a guiding device of a movable gradient coil unit in accordance with invention.  
         [0014]    [0014]FIG. 2 shows a horizontal longitudinal section through a magnetic resonance apparatus having a curved additional device for a guiding device of a movable gradient coil unit in accordance with invention.  
         [0015]    [0015]FIG. 3 and FIG. 4 show horizontal longitudinal sections through a magnetic resonance apparatus having a movable auxiliary device for a movable gradient coil unit in accordance with the invention.  
         [0016]    [0016]FIG. 5, FIG. 6 and respectively FIG. 7 show horizontal longitudinal sections through a magnetic resonance apparatus having a pivotable auxiliary device for a mobile gradient coil unit in accordance with the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    As an exemplary embodiment of the invention, FIG. 1 shows a horizontal longitudinal section through a magnetic resonance apparatus having an extension device  16 . The magnetic resonance apparatus has an essentially cylindrical base unit  10  in whose hollow space an examination chamber  11  is arranged. The base unit  10  has a superconducting basic field magnet in order to generate a static basic magnetic field, a firmly installed gradient coil system in order to generate gradient fields and an antenna system, which is also firmly installed, for transmitting radio-frequency signals and for receiving magnetic resonance signals.  
         [0018]    The magnetic resonance apparatus has a movable positioning device  18  for introducing the examination subject into the examination chamber  11 . The positioning device  18  can be completely moved out of the examination chamber  11  through an opening of the hollow space situated opposite an opening  12  (not shown in FIG. 1) and can be moved from there into the examination chamber  11  and can be maximally extended through the opening  12  up to the position shown in broken lines.  
         [0019]    A guiding device  14 , which is continued beyond the examination chamber by the extension device  16 , is arranged in the examination chamber  11  of the magnetic resonance apparatus. The guiding device  14  and the extension device  16  serve as a glide path for the positioning device  18  and serve the purpose of guiding a movable gradient coil unit  15  on a horizontal plane prescribed by the devices  14  and  16 .  
         [0020]    In order to generate gradient fields, the movable gradient coil unit  15  has at least one or up to three gradient coils and, depending on the utilization requirements, possibly has shielding coils, cooling and shim devices, which belong to the gradient coils, and can be combined with a local radio-frequency antenna. The electric connecting lines and, if present cooling supply lines, which are necessary for supplying the gradient coil unit  15 , are flexibly fashioned and are firmly connected to the gradient coil unit  15  and to a stationary part of the magnetic resonance apparatus.  
         [0021]    The movable gradient coil unit  15  is cylindrically fashioned such that it can accept a head of a patient. For this purpose, the positioning device  18  is fashioned at the plane facing the gradient coil unit  15  such that it can be moved into a hollow space of the gradient coil unit  15  so that a patient correspondingly positioned on the positioning device  18  can be introduced with the head into the gradient coil unit  15  by displacing the positioning device  18 .  
         [0022]    Given an image acquisition operation of the magnetic resonance apparatus without the gradient coil unit  15  and, as shown in FIG. 1, given a positioning device that is maximally extended through the opening  12 , a length of the extension device  16  is selected such that the extension unit  16  is still capable of carrying the gradient coil unit  15  in a position shown by a thick continuous line.  
         [0023]    For an image acquisition operation using the gradient coil unit  15  and given a positioning device  18  which is only moderately introduced into the examination chamber  11  or which is completely moved out of the examination chamber  11 , the gradient coil unit  15 , from the position shown by a thick continuous line, is to be moved into the examination chamber  11  by a horizontal displacing along the extension device  14  and guiding device  16  and is to be fixed in the examination chamber  11  in a position shown by a thick dot-dash line. Subsequently, the head of the patient can be positioned in the gradient coil unit  15  by displacing the positioning device  18  with the correspondingly positioned patient.  
         [0024]    In an exemplary embodiment, a local radio-frequency antenna, particularly for a head of the patient, can be introduced into the gradient coil unit  15  and is fashioned such it can be fixed on the positioning device  18 , so that the radio-frequency antenna, which is fixed on the positioning device  18  at the plane facing the gradient coil unit  15 , can be moved in and out of the gradient coil unit  15 , which is positioned in the examination chamber  11 , by displacing the positioning device  18 .  
         [0025]    In a further exemplary embodiment, the gradient coil unit  15  is cylindrically fashioned having two recesses for accepting a head of a patient including his/her shoulders, so that a neck area of the patient can also be accepted instead of only imaging the head. German Patent 198 29 298 C2 describes such a gradient coil, however, it is not movable.  
         [0026]    As another exemplary embodiment of the invention, FIG. 2 shows a horizontal longitudinal section through a magnetic resonance apparatus having a curved additional device  26 . The magnetic resonance apparatus has an essentially cylindrical base unit  20  that is configured corresponding to the one as shown in FIG. 1. An examination chamber  21  is arranged in a hollow space of the base unit  20 , whereby examination chamber  21  has a guiding device  24  for guiding a mobile gradient coil unit  25  within the examination chamber  21 . For the continuation of the guiding device  24 , the curved additional device docks on an opening  22  of the examination chamber  21  so that the mobile gradient coil unit  25  can be displaced on a horizontal plane defined by the additional device  24  and guiding device  26 .  
         [0027]    For an operation of the magnetic resonance apparatus by using the movable gradient coil unit  25 , the gradient coil unit  25  is positioned as shown by a thick dash-dot line and is correspondingly fixed. For an operation without the gradient coil unit  25 , the gradient coil unit  25  is positioned as shown by a thick continues line and is correspondingly arrested. The additional device  26 , in particular, is fashioned such that a displaceable positioning device (not shown), which is moved inside through an opening of the hollow space (not shown) that is opposite the opening  22 , can be maximally extended through the opening  22  without impairment by the additional device  26 .  
         [0028]    As a further exemplary embodiment of the invention, FIG. 3 and FIG. 4 show horizontal longitudinal sections through a magnetic resonance apparatus having an auxiliary device  36 . The magnetic resonance apparatus has an essentially cylindrical base unit  30  that is fashioned as shown in FIG. 1. An examination chamber  31  is arranged in a hollow space of the base unit  30 , whereby said examination chamber  31  has a guiding device  34  for guiding a movable gradient coil unit  35 .  
         [0029]    In FIG. 3, the gradient coil unit  35  is fastened at the mobile auxiliary device  36  and the auxiliary device  36 , including the gradient coil unit  35 , is parked next to an opening  32  of the hollow space, so that the magnetic resonance apparatus can be operated without the gradient coil unit  35  and without impairment by the gradient coil unit  35 . Given this operating state, a positioning device (not shown) can be moved into and out of the examination chamber  31  without being restricted by the gradient coil unit  35 . The mobile auxiliary device  36  is fashioned such that it can be attached to the guiding device  34  for inserting or removing the gradient coil unit  35 , so that the gradient coil unit  35  can be displaced along a horizontal plane defined by the guiding device  34  and the auxiliary device  36 .  
         [0030]    [0030]FIG. 4 shows the auxiliary device  36  being docked onto the guiding device  34 . After the gradient coil unit  35  has been detached with the auxiliary device, the gradient coil unit  35  can be moved onto the guiding device  34  into the examination chamber  31  smoothly by hand or motor-driven by the auxiliary device  36  and can be fixed there in a prescribed position.  
         [0031]    As a further exemplary embodiment of the invention, FIG. 5 to FIG. 7 show horizontal longitudinal sections through a magnetic resonance apparatus having a pivotable auxiliary device  56 . The magnetic resonance apparatus has an essentially cylindrical base unit  50  that is fashioned as shown in FIG. 1. An examination chamber  51  is arranged in a hollow of the base unit  50 , whereby said examination chamber  51  has a guiding device  54  for guiding a mobile gradient coil unit  55 . The magnetic resonance apparatus also has a pivotable auxiliary device  56 , which for pivoting about a vertical axis, is connected to the base unit  50  via a hinge  57 . The gradient coil unit  55  can be fastened at the auxiliary device  56 . The auxiliary device  56  is fashioned in a pivotable manner such that the auxiliary device  56  can dock on the guiding device  54  in order to continue said guiding device  54  so that the gradient coil unit  55  can be displaced on a horizontal plane that is defined by the auxiliary and guiding device  54  and  56 . A particular advantage of the pivotable auxiliary device  56  is that the electric connecting lines, which are necessary for supplying the gradient coil unit  55  and possibly cooling supply lines, can be fashioned in a short manner.  
         [0032]    [0032]FIG. 5 shows the auxiliary device  56 , which has the gradient coil unit  55  docked onto it, in a position pivoted next to an opening  52  of the hollow. This position is typical when the magnetic resonance apparatus is operated without using the gradient coil unit  55 . A positioning device (not shown), for example by using the guiding device  54 , can be displaced in the examination chamber  51  without impairment by the gradient coil unit  55 .  
         [0033]    The auxiliary device  56  having the gradient coil unit  55  docked onto it, must be pivoted in the direction of the examination chamber  51  in order to operate the magnetic resonance apparatus with the gradient coil unit  55 . As an example, FIG. 6 shows an intermediate position of the pivot motion.  
         [0034]    [0034]FIG. 7 shows the completed pivot motion with the auxiliary device  56  being docked onto the guiding device  54 . After the lock has been released, the gradient coil unit  55 , proceeding from the auxiliary device  56  can glide onto the guiding device  54 , can be displaced when gliding into the examination chamber  51  and can be fixed in the examination chamber  51  in order to subsequently operate the magnetic resonance apparatus with the gradient coil unit  55 .  
         [0035]    Although modifications and changes may be suggested by those skilled in the art, it is the invention of the inventor to embody within the patent warranted heron all changes and modifications as reasonably and properly come within the scope of his contribution to the art.