Abstract:
A gradient coil assembly and a method for manufacturing the gradient coil assembly is provided. The gradient coil assembly includes a first tube extending along an axis including a first conductor. The assembly further includes a second tube disposed generally concentrically about the first tube wherein an inner space is defined between the first and second tubes. The second tube includes a second conductor. Finally, the assembly includes a fiber composite structure disposed in the inner space operatively associated with the first and second tubes to increase a stiffness of the assembly.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of a priority under 35 U.S.C. 119 to Great Britain Patent Application No. 0329669.6 filed Dec. 22, 2003, the entire contents of which are hereby incorporated by reference.  
       BACKGROUND OF INVENTION  
       [0002]     The invention relates to a gradient coil assembly utilized in a Magnetic Resonance Imagining (MRI) machine and a method for assembling the gradient coil assembly.  
         [0003]     MRI machines utilize gradient coils to generate magnetic field gradients along three desired orthogonal axes. The gradient coils, however, undergo significant Lorentz forces during coil energization that can cause the coils to vibrate and generate undesirable noise and image degradation. The inventors herein have recognized that there is a need for a gradient coil assembly that is stiffer than other gradient coil assemblies, which can reduce coil vibrations and thus undesirable noise and image degradation.  
       SUMMARY OF INVENTION  
       [0004]     The foregoing problems and disadvantages are overcome by a gradient coil assembly and method for manufacturing assembly in accordance with the exemplary embodiments disclosed herein.  
         [0005]     A gradient coil assembly in accordance with exemplary embodiments includes a first tube extending along an axis including a first conductor. The gradient coil assembly further includes a second tube disposed generally concentrically about the first tube wherein an inner space is defined between the first and second tubes. The second tube includes a second conductor. Finally, the assembly includes a fiber composite structure disposed in the inner space operatively associated with the first and second tubes to increase a stiffness of the assembly.  
         [0006]     A method for assembling a gradient coil assembly for use in an MRI device in accordance with exemplary embodiments is provided. The method includes disposing a first gradient tube generally concentrically about a second gradient tube wherein an inner space is defined between the first and second gradient tubes. The method further includes disposing a fiber composite structure in the inner space defined by the first and second gradient tubes.  
         [0007]     Other systems and/or methods according to the embodiments will be or become apparent to one with skill in the art upon review of the following drawings and detailed description. It is intended that at all such additional systems, methods, and/or computer program products be within the scope of the present invention, and be protected by the accompanying claims. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0008]      FIG. 1  is a block diagram of an MRI imaging system.  
         [0009]      FIG. 2  is a schematic of an outer gradient tube.  
         [0010]      FIG. 3  is a schematic of an inner gradient tube.  
         [0011]      FIG. 4  is a schematic illustrating an inner gradient tube being disposed within an outer gradient tube.  
         [0012]      FIG. 5  is an exploded view of a first embodiment of a gradient coil assembly.  
         [0013]      FIG. 6  is a cross-sectional view of the first embodiment of a gradient coil assembly.  
         [0014]      FIG. 7  is a schematic of a fiber composite fin.  
         [0015]      FIG. 8  is an exploded view of a second embodiment of a gradient coil assembly.  
         [0016]      FIG. 9  is a cross-sectional view of the second embodiment of a gradient coil assembly.  
         [0017]      FIG. 10  is a schematic of a portion of a fiber composite tube used in the second embodiment of a gradient coil assembly.  
         [0018]      FIGS. 11-1  and  11 - 2  are a flowchart of a method of assembling the first embodiment of the gradient coil assembly.  
         [0019]      FIG. 12  is a flowchart of a method of assembling the second embodiment of the gradient coil assembly 
     
    
     DETAILED DESCRIPTION  
       [0020]     Referring to the drawings, identical reference numerals represent identical components in the various views. Referring to  FIG. 1 , an exemplary MRI system  10  is provided for generating images of a person  18 . MRI system  10  may comprise a magnetic assembly  12 , a gradient amplifier unit  14 , and a system controller  16 .  
         [0021]     Magnetic assembly  12  is provided to generate magnetic fields that will be propagated to person  18 . Assembly  12  may comprise a housing  15  defining a chamber  17  for receiving person  18 . Assembly  12  may further comprise polarizing magnets  20 , and a gradient coil assembly having (X) coils, (Y) coils, and (Z) coils. Gradient coil assembly  22  generate magnetic fields in response to signals received from the (Gz) amplifier, (Gy) amplifier, and (Gz) amplifier, respectively, contained in gradient amplifier unit  14 .  
         [0022]     Controller  16  is provided to generate control signals for controlling the gradient amplifier unit  14 . In particular, controller  16  may generate control signals that induce gradient amplifier unit  14  to energize gradient coil assembly  22 .  
         [0023]     Referring to  FIGS. 2-4 , a brief discussion of the inner gradient tube  30  and an outer gradient tube  28  utilized in gradient coil assembly  22  will be discussed. Outer gradient tube  28  is provided to hold the remainder of the gradient coil assembly components therein. Gradient tube  28  may be constructed from a fiber composite material comprising one or more layers wherein each layer comprises a plurality of fibers such as glass fibers, carbon fibers, Kevlar fibers, and aluminum oxide fibers, for example, coated with the epoxy resin. Gradient tube  28  may further include saddle coils  32 ,  34 ,  36 ,  38  disposed on an exterior surface of tube  28 . Saddle coils  32 ,  34 ,  36 ,  38  may be constructed from copper conductors and are provided to generate a magnetic field. Saddle coils  32 ,  34 ,  36 ,  38  are electrically connected either in series or in parallel to each other. Coils  32 ,  34 ,  36 ,  38  may be adhesively applied to tube  28  with adhesives such as epoxy resin. As shown tube  28  is disposed about an axis  48  and includes a centerline  52  that extends through tube  28 .  
         [0024]     Inner gradient tube  30  is disposed within outer gradient tube  28 . Gradient tube  30  may be constructed from a fiber composite material comprising one or more layers wherein each layer comprises a plurality of fibers such as glass fibers, carbon fibers, Kevlar fibers, and aluminum oxide fibers, for example, coated with the epoxy resin. Gradient tube  30  may further include saddle coils  40 ,  42 ,  44 ,  46  constructed from one or more copper conductors that are disposed on the exterior surface of tube  30 . Saddle coils  40 ,  42 ,  44 ,  46  are provided to generate a magnetic field and are electrically coupled together. Saddle coils  40 ,  42 ,  44 ,  46  may be adhesively applied to tube  30  with adhesives such as epoxy resin for example. As shown tube  30 , is disposed about an axis  50  and includes a centerline  54  that extends through tube  30 .  
         [0025]     It should be noted that the combination of saddle coils  32 ,  34 ,  36 ,  38  and saddle coils  40 ,  42 ,  44 ,  46  comprise an (X) coil. Further, although magnetic assembly  12  includes a (Y) coil and a (Z) coil, the (Y) and (Z) coils will not be discussed in any further detail for purposes of simplicity.  
         [0026]     Referring to  FIG. 4 , inner gradient tube  30  may be disposed within outer gradient tube  28 . Further, the axes  48 ,  50  are preferably coincident with one another after final assembly thereof. Further, centerlines  52 ,  54  are preferably coincident with one another after final assembly thereof.  
         [0027]     Referring to  FIG. 5A , an exploded view of a gradient coil assembly  22  in accordance with the first embodiment of the present invention is provided. Gradient coil assembly  22  may include outer gradient tube  28 , inner gradient tube  30 , a viscoelastic sheet  56 , a viscoelastic sheet  58 , and tubular fin assemblies  60 ,  60 ′,  60 ″.  
         [0028]     Viscoelastic sheet  56  is provided to dampen vibrations within assembly  22  during energization of the saddle coils in assembly  22 . Viscoelastic sheet  56  may be wrapped around inner gradient tube  30 . Sheet  56  may be constructed from a plurality of materials including rubber composites.  
         [0029]     Viscoelastic sheet  58  is provided to dampen vibrations within assembly  22  during energization of the saddle coils in assembly  22 . Viscoelastic sheet  58  may be wrapped around an inner surface of outer gradient tube  28 . Sheet  58  may be constructed from a plurality of materials including rubber composites for example.  
         [0030]     Referring to  FIG. 6 , the configuration of tubular fin assembly  60  will now explained. Tubular fin assembly  60  may comprise a plurality of fins  66  disposed circumferentially about a diameter (D). The diameter (D) being at least as large as the diameter of inner gradient tube  30 . Fins  66  are provided to stiffen assembly  22  to reduce vibrations during energization of the saddle coils of assembly  22 . Each of the fins  66  may have a rectangular cross-sectional area (A) and may have a substantially similar length (L). It should be noted that fins  66  could be constructed using other cross-sectional geometries. Further, each of fins  66  may be constructed from a fiber composite material comprising one or more layers wherein each layer comprises a plurality of fibers such as glass fibers, carbon fibers, Kevlar fibers, and aluminum oxide fibers, for example, coated with the epoxy resin. The fiber direction within each fin  66  can be chosen to be parallel to axis  48  of assembly  22 , or perpendicular to axis  48 , or at a predetermined angle relative to axis  48 . The direction of the fibers and the number of fibers may be varied based upon desired vibration characteristics of assembly  22 . Further, the fiber to resin ratio in fins  66  may be equal to or greater than 90%.  
         [0031]     As shown, tubular fin assembly  60  may further include a plurality of viscoelastic fins  68  intermittently disposed between one or more fins  66 . Viscoelastic fins  68  are provided to dampen vibrations in assembly  22  during energization of the saddle coils in assembly  22 . Viscoelastic fins  68  may be constructed from a plurality of materials including rubber composites. It should be noted that the number of fins  66  and fins  68  may vary depending upon the desired operational characteristics of assembly  22 . Further, the cross-sectional shape of fins  66 ,  68  may vary depending upon the desired operating characteristics of assembly  22 . For example, fins  66 ,  68  could be substantially wedge shaped. Tubular fin assemblies  60 ′ and  60 ″ may have a substantially similar configuration as assembly  60 .  
         [0032]     Referring to  FIG. 5A , tubular viscoelastic sheets  62 ,  64  may be provided to dampen vibrations in gradient coil assembly  22  during energization of saddle coils in assembly  22 . As shown, tubular viscoelastic sheet  62  may be disposed between assemblies  60 ,  60 ′. Tubular viscoelastic sheet  64  may be disposed between assemblies  60 ′,  60 ″. Sheets  62 ,  64  may be constructed from a plurality of materials including rubber composites.  
         [0033]     Referring to  FIGS. 11-1  and  11 - 2 , a method for assembling gradient coil assembly  22  will now be explained. At step  90 , saddle coils  40 ,  42 ,  44 ,  46  of the (X) coil are affixed to an outer surface of inner gradient tube  30 . It should be noted that inner (Y) coils (not shown) and inner (Z) coils (not shown) could also be disposed on inner gradient tube  30 .  
         [0034]     Next at step  92 , saddle coils  32 ,  34 ,  36 ,  38  of the (X) coil are affixed to an outer surface of outer gradient tube  28 . It should be noted that outer (Y) coils (not shown) and outer (Z) coils (not shown) could also be disposed on outer gradient tube  28 .  
         [0035]     Next at step  94 , viscoelastic sheet  56  is wrapped over the outer surface of inner gradient tube  30  and saddle coils  40 ,  42 ,  44 ,  46 , and sheet  56  is affixed to tube  30 .  
         [0036]     Next at step  96 , viscoelastic sheet  58  is affixed to an inner surface of outer gradient tube  28 .  
         [0037]     Next at step  98 , a first plurality of radially extending fiber composite fins  66  and viscoelastic fins  68  are disposed around a predetermined diameter (D) corresponding substantially to an outer diameter of inner gradient tube  30  plus a thickness of sheet  56 . Further, the first plurality of fins  66 ,  68  are affixed together to form tubular fin assembly  60 .  
         [0038]     Next at step  100 , a second plurality of radially extending fiber composite fins  66  and viscoelastic fins  68  are disposed around predetermined diameter (D). Further, the second plurality of fins  66 ,  68  are affixed together to form tubular fin assembly  60 ′.  
         [0039]     Next at step  102 , a third plurality of fiber composite fins  66  and viscoelastic fins  68  are disposed around predetermined diameter (D). Further, the third plurality of fins  66 ,  68  are affixed together to form tubular fin assembly  60 ″.  
         [0040]     Next at step  104 , the tubular fin assembly  60 , tubular viscoelastic sheet  62 , tubular fin assembly  60 ′, the viscoelastic sheet  64 , and tubular fin assembly  60 ″ are disposed substantially concentrically around inner gradient tube  30  to form an inner assembly  69 .  
         [0041]     Next at step  106 , inner assembly  69  is disposed within an interior of outer gradient tube  28  to form gradient coil assembly  22 .  
         [0042]     Next at step  108 , saddle coils  40 ,  42 ,  44 ,  46  of inner gradient tube  30  are aligned with respect to saddle coils  32 ,  34 ,  36 ,  38  of outer gradient tube  28 .  
         [0043]     Next at step  110 , gradient coil assembly  22  is vacuum impregnated with epoxy resin (not shown).  
         [0044]     Referring to  FIG. 8 , an exploded view of a gradient coil assembly  22 ′ in accordance with a second embodiment of the present invention is provided. Gradient coil assembly  22 ′ may include outer gradient tube  28 , inner gradient tube  30 , viscoelastic sheet  56 , viscoelastic sheet, and fiber composite tube  70 . It should be noted that the primary difference between gradient coil assembly  22 ′ in gradient coil assembly  22  is that assembly  22 ′ utilizes a fiber composite tube  70  instead of tubular fin assemblies  60 ,  60 ′, and  60 ″.  
         [0045]     Because the structure of outer gradient tube  28 , inner gradient tube  30 , viscoelastic sheet  56 , and viscoelastic sheet  58  were discussed above with respect to gradient coil assembly  22 , the structure of these components will not be discussed in any further detail below.  
         [0046]     Fiber composite tube  70  is provided to increase the stiffness of assembly  22 ′ to prevent deformation of assembly  22 ′ during energization of the saddle coils of assembly  22 ′. Fiber composite tube  70  may be constructed from a fiber composite material comprising one or more layers wherein each layer comprises a plurality of fibers such as glass fibers, carbon fibers, Kevlar fibers, and aluminum oxide fibers, for example, coated with the epoxy resin. Further, the fiber to resin ratio in the tube  70  may be equal to or greater than 90%. Further, referring to  FIG. 10 , a first plurality of fibers  74  being disposed substantially perpendicular to a second plurality of fibers  76  in tube  70  in the illustrated embodiment. It should be noted, however, that the orientation of the first plurality of fibers  74  with respect to the second plurality of fibers  76  may vary depending upon the desired operational characteristics of tube  70 . Further, the ratio of fibers  74  with respect to fibers  76  may vary depending upon the desired operational characteristics of tube  70 .  
         [0047]     Referring to  FIG. 12 , a method for assembling gradient coil assembly  22 ′ will now be explained. At step  120 , saddle coils  40 ,  42 ,  44 ,  46  of the (X) coil are affixed to an outer surface of inner gradient tube  30 . It should be noted that inner (Y) coils (not shown) and inner (Z) coils (not shown) could also be disposed on inner gradient tube  30 .  
         [0048]     Next at step  122 , saddle coils  32 ,  34 ,  36 ,  38  of the (X) coil are fixed to an outer surface of outer gradient tube  28 . It should be noted that outer (Y) coils (not shown) and outer (Z) coils (not shown) could also be disposed on outer gradient tube  28 .  
         [0049]     Next at step  124 , viscoelastic sheet  56  is wrapped over both an outer surface of inner gradient tube  30  and saddle coils  40 ,  42 ,  44 ,  46  and is affixed to tube  30 .  
         [0050]     Next at step  126 , viscoelastic sheet  58  is affixed to an inner surface of outer gradient tube  28 .  
         [0051]     Next at step  128 , fiber composite tube  70  is disposed substantially concentrically around inner gradient tube  30 .  
         [0052]     Next at step  130 , a combination of fiber composite tube  70  and inner gradient tube  30  is disposed within an interior of outer gradient tube  28  to form gradient coil assembly  22 ′.  
         [0053]     Next at step  132 , saddle coils  40 ,  42 ,  44 ,  46  of inner gradient tube  30  are aligned with respect to saddle coils  32 ,  34 ,  36 ,  38  of outer gradient tube  28 .  
         [0054]     Next at step  134 , gradient coil assembly  22 ′ is vacuum impregnated with epoxy resin (not shown).  
         [0055]     The inventive gradient coil assembly and method for manufacturing the assembly provide substantial advantages over other assemblies and methods. In particular, the inventive gradient coil assembly utilizes a fiber composite structure disposed between the inner and outer gradient tubes to provide a stiffer assembly as compared to other gradient coil assemblies. In particular, the fiber composite structure utilized in the inventive gradient coil assembly does not become elastic during relatively high operating temperatures of assembly  14  which provides a stiffer assembly as compared to other assemblies which utilize epoxy resin between the inner and outer gradient tubes. As a result, the stiffer inventive gradient coil assembly results in decreased noise being generated during energization of the saddle coils as compared to other systems. Still further, the inventive gradient coil assembly may utilize viscoelastic members optimally disposed within the assembly to further dampen vibrations and noise that occur during energization of the saddle coils in the gradient coil assembly.  
         [0056]     While the invention is described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made an equivalence may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to the teachings of the invention to adapt to a particular situation without departing from the scope thereof. Therefore, is intended that the invention not be limited the embodiments disclosed for carrying out this invention, but that the invention includes all embodiments falling with the scope of the intended claims. Moreover, the use of the term&#39;s first, second, etc. does not denote any order of importance, but rather the term&#39;s first, second, etc. are us are used to distinguish one element from another.