Abstract:
There is provided a magnetic resonance imaging apparatus, including a gantry which has a gradient magnetic coil generating a gradient magnetic field to be applied to a subject in a magnetostatic field, a bed which allows a top board, on which the subject is placed, to slide in a longitudinal direction, a pulse applying unit which applies a high-frequency pulse to the subject, and a high-frequency coil which detects a magnetic resonance signal generated from the subject by applying the gradient magnetic field and the high-frequency pulse, in which the gradient magnetic coil includes a plurality of line members wounded in a predetermined winding pattern, a first resin material filled in gaps between the plurality of line members, and a second resin material which has higher thermal conductivity than that of the first resin material and is filled in gaps formed between the line members by winding at least one line member of the plurality of line members.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2006-138040, filed May 17, 2006, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a gradient magnetic coil having resin material infiltrated thereto, a method of manufacturing the gradient magnetic coil, and a magnetic resonance imaging (MRI) apparatus having the gradient magnetic coil. 
         [0004]    2. Description of the Related Art 
         [0005]    A medical MRI apparatus generally includes a gantry. The gantry generally includes magnetostatic magnets, gradient magnetic coils, cooling pipes, and the like. 
         [0006]    The gradient magnetic coils include a plurality of coils and generate gradient magnetic field when electric current flows through the plurality of coils. The coils are formed of conductive line members wounded in a winding pattern corresponding to a gradient magnetic field pattern to be generated. Resin materials are filled into gaps between identical line members or gaps between line members of different coils. The resin materials serve to provide insulation between the line members and maintain the winding state of the line members which are wounded in the above-mentioned winding pattern. 
         [0007]    However, recent MRI apparatuses require greater gradient magnetic field and fast initial start-up. For this reason, it is necessary to supply a large amount of current to the gradient magnetic coils. Accompanied by the large current supply, the coils are more likely to emit increasing amount of heat. Thus, cooling of the gradient magnetic coil is becoming important (see, U.S. Pat. No. 6,741,152, for example). 
         [0008]    As the resin material, an epoxy resin has been used so far. Since the epoxy resin has low viscosity at high temperature, it can be suitably used in spreading it into all the corners of the coil gaps, but it has extremely low heat conductivity. Accordingly, in a gradient magnetic coil in which the epoxy resin is filled into the gaps of the coils, the epoxy resin acts as a barrier preventing the heat generated in the coil from being dissipated toward the cooling pipes, thereby lowering the cooling performance. 
         [0009]    In view of those circumstances, it is required to improve heat dissipation efficiency of the gradient magnetic coil. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    According to a first aspect of the invention, there is provided a magnetic resonance imaging apparatus, including a gantry which has a gradient magnetic coil generating a gradient magnetic field to be applied to a subject in a magnetostatic field, a bed which allows a top board, on which the subject is placed, to slide in a longitudinal direction, a pulse applying unit which applies a high-frequency pulse to the subject, and a high-frequency coil which detects a magnetic resonance signal generated from the subject by applying the gradient magnetic field and the high-frequency pulse, wherein the gradient magnetic coil includes a plurality of line members wounded in a predetermined winding pattern, a first resin material filled in gaps between the plurality of line members, and a second resin material which has higher thermal conductivity than that of the first resin material and is filled in gaps formed between the line members by winding at least one line member of the plurality of line members. 
         [0011]    According to a second aspect of the invention, there is provided a method of manufacturing a gradient magnetic coil having a plurality of coils formed by winding the line members in a predetermined winding pattern, the method including: filling a resin material of a clay type into gaps between the line members formed by winding the line member of at least one coil of the plurality of coils; arranging the plurality of coils; allowing a liquid resin material to flow into the gaps between the plurality of coils; and curing the liquid resin material. 
         [0012]    According to a third aspect of the invention, there is provided a gradient magnetic coil including a plurality of line members wound in a predetermined winding pattern, a first resin material which is filled into gaps between the plurality of line members, and a second resin material which has higher thermal conductivity than that of the first resin material and is filled into the gaps formed between the line members by winding at least one line member of the plurality of line members. 
         [0013]    Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
     
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0014]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
           [0015]      FIG. 1  is a partial schematic view illustrating a MRI apparatus according to an embodiment of the invention. 
           [0016]      FIG. 2  is a partial sectional view illustrating a gradient magnetic coil shown in  FIG. 1 . 
           [0017]      FIG. 3  is a perspective view illustrating an X-main coil included in the gradient magnetic coil shown in  FIG. 1 . 
           [0018]      FIG. 4  is a diagram illustrating a temperature simulation result of the gradient magnetic coil shown in  FIG. 1 . 
           [0019]      FIG. 5  is a diagram illustrating a temperature simulation result of the existing gradient magnetic coil. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Hereinafter, an embodiment of the invention will be described with reference to the accompanying drawings. 
         [0021]      FIG. 1  is a partial schematic view illustrating a MRI apparatus according to an embodiment of the invention. 
         [0022]    The MRI apparatus according to the present embodiment includes a gantry  10 , a magnetostatic magnet  11 , a gradient magnetic coil  12 , a magnetostatic field source supply  21 , a gradient magnetic power supply  22 , a high frequency coil (RF coil)  23 , a transmitter  24 , a receiver  25 , a sequencer  26 , a host controller  27 , an input unit  28 , an operation unit  29 , a memory unit  30 , and a display unit  31 . In addition, the MRI apparatus includes a bed (not shown) which is disposed adjacent to the gantry  10 . The sequence  26 , the host controller  27 , the operation unit  29 , and the memory unit  30  are included in a control processing unit (computer system). 
         [0023]    The gantry  10  is generally formed with a substantially cylindrical photographing space  10   a  that is formed in the central portion of the inner space of the gantry  10 . Assuming that the axial direction of the photographing space is the Z direction, the remaining two directions which are perpendicular to the Z direction and with each other are defined as the X direction (left and right direction) and the Y direction (up and down direction). The gantry  10  shown in  FIG. 1  corresponds to only one-half of the whole gantry  10  broken by the YZ plane. 
         [0024]    The magnetostatic magnet  11  and the gradient magnetic coil  12  are accommodated in the gantry  10 . The magnetostatic magnet  11  is supplied with a current from the magnetostatic field source supply  21  and generates magnetostatic field HO in the photographing space. A superconductor magnet is generally used as the magnetostatic magnet  11 . The whole shape of the magnetostatic magnet  11  is in a substantially cylindrical shape. In the inner space of the magnetostatic magnet  11 , a magnet bore  11   a  is formed (hereinafter, referred to as bore). The central axis of the bore  11   a  corresponds to the central axis of the photographing space  10 a. The gradient magnetic coil  12  is disposed in the bore  11   a . The gradient magnetic coil  12  includes three sets of coils which receive driving currents corresponding to the X, Y, and Z axis respectively from the gradient magnetic power supply  22  and generate the gradient magnetic fields respectively corresponding to the X, Y, and Z axis. 
         [0025]    At the time of photographing, the RF coil  23  is placed in the inside of the photographing space  10   a . The RF coil  23  is connected to the transmitter  24  and the receiver  25 . The transmitter  24  supplies a pulse current vibrating at Lamor frequency to the RF coil  23  under the control of the sequencer  26 . The receiver  25  receives a magnetic resonance (MR) signal through the RF coil  23  and performs various signal processing treatments, thereby generating the corresponding digital signals. A top board  32  of the bed can be moved toward and away from the photographing space  10   a  in the gantry  10 , an inspection object  100  is placed on the top board  32 . 
         [0026]    The sequencer  26  operates under the control of the host controller  27  that controls the whole MRI apparatus. The input unit  28  is connected to the host controller  27 . The operator can select a desirable pulse sequence from a plurality of pulse sequences using a method such as a spin echo (SE) method or an echo planner (EPI) method by operating the input unit  28 . The host controller  27  sets a selected pulse sequence to the sequencer  26 . The sequencer  26  controls the application timing and strength of the gradient magnetic field in each of the X, Y and Z axis directions and the application timing, amplitude and duration of high-frequency magnetic field, in accordance with the set pulse sequence. 
         [0027]    The operation unit  29  inputs an MR signal (digital data) generated by the receiver  25  and performs a Fourier transform for arranging actual measurement data in a two-dimensional Fourier space to reorganize images using an internal memory, thereby generating image data or spectrum data. The memory unit  30  stores the operated image data. The display unit  31  displays the image. 
         [0028]      FIG. 2  is a partial sectional view of the gradient magnetic coil  12  and shows an enlarged view of a portion surrounded by the circle CA in  FIG. 1 . 
         [0029]    As shown in  FIG. 2 , the gradient magnetic coil  12  includes a main coil unit  13  and a shield coil unit  14 , and the entire surfaces of the gradient magnetic coil are covered with an epoxy resin  15 . The epoxy resin  15  can be replaced by a room-temperature curable resin of a different kind, which has a low viscosity in a liquid state. 
         [0030]    The main coil unit  13  includes an X-main coil  131 , a Y-main coil  132 , a Z-main coil  133 , and a cooling pipe  134 . The X-main coil  131 , Y-main coil  132 , and Z-main coil  133  are formed of the conductive line members  16  which are respectively wound in patterns suitable for generating gradient magnetic fields corresponding to the X, Y, and Z axis. Compound material  17  is filled into the gaps between the identical line members  16 . The X-main coil  131 , the Y-main coil  132  and the Z-main coil  133  are laminated onto each other in this order in a direction away from the inside of the gradient magnetic coil  12  with a gap therebetween. Outside the Z-main coil  133 , the cooling pipes  134  are disposed in a spiral shape. The gaps between the cooling pipe  134  are filled with the compound material  17 . In addition, the epoxy resin  15  is filled into a surface of the X-main coil  131  disposed in the inner side of the gradient magnetic coil  12 , a gap between the X-main coil  131  and the Y-main coil  132 , a gap between the Y-main coil  132  and the Z-main coil  133 , and a gap between the Z-main coil  133  and the cooling pipe  134 . 
         [0031]    The shield coil unit  14  includes a Z-shield coil  141 , an X-shield coil  142 , a Y-shield coil  143 , and a cooling pipe  144 . The Z-shield coil  141 , the X-shield coil  142 , and Y-shield  143  are formed of the conductive line members  16  which are respectively wound in patterns suitable for shielding gradient magnetic fields corresponding to the X, Y, and Z axis. The compound material  17  is filled into the gaps between the same line members  16 . The Z-shield coil  141 , the X-shield coil  142  and the Y-shield coil  143  are laminated onto each other in this order in a direction away from the inside of the gradient magnetic coil  12  with a gap therebetween. Inside the Z-shield coil  141 , the cooling pipes  144  are disposed in a spiral shape. The gaps between the cooling pipes  144  are filled with the compound material  17 . The cooling pipes  134  and  144  are connected to a circulation device (not shown), and cooling liquid circulates through the pipes  134  and  144 . 
         [0032]    As the compound material  17 , a mixture of a filler such as silica to the epoxy resin may be used. Aluminum can be used as the filler for the silica. However, it is preferable that the filler have higher thermal conductivity than the epoxy resin and insulating and non-magnetic properties. 
         [0033]    A gap G between the main coil unit  13  and the shield coil unit  14  is formed. In the gap G, an adjustment tray (now shown) which has a plurality of pockets for having a steel shim is inserted when it is necessary. The adjustment tray is inserted to the gap G and an intensity distribution of the magnetostatic field in an inside of the photographing spate  10   a  is adjusted by the effect of the steel shim inserted to the pockets according to need. 
         [0034]      FIG. 3  is a perspective view illustrating the X-main coil  131 . In  FIG. 3 , the X-main coil  131  is shown as the gantry  10  viewed from the diagonal below in  FIG. 1 . 
         [0035]    As shown in  FIG. 3 , the line member  16  having a spiral shape is wound, which forms the X-main coil  131 . In addition, the compound material  17  is filled into the gaps between the line members  16 . 
         [0036]    Although other coils  132 ,  133 ,  141 ,  142 , and  143  have different winding patterns of the line member  16  from the X-main coil  131 , the coils  132 ,  133 ,  141 ,  142 , and  143  have the same configuration as the X-main coil  131 . 
         [0037]    Next, the gradient magnetic coil  12  as mentioned-above will be described hereinafter. 
         [0038]    Firstly, the line member  16  is wound in accordance with the pattern of the coils  131 ,  132 ,  133 ,  141 ,  142 , and  143  and the compound material  17  is applied to the gaps between the line members  16 . Since the compound material  17  mixes the filler, the compound material  17  has a higher viscosity than the epoxy resin. Accordingly, the compound material  17  has clay shape. Since the compound material  17  is directly applied to the gaps between the line members  16 , the operation is easily performed. 
         [0039]    Next, the compound material  17  is applied to the coils  131 ,  132 ,  133 ,  141 ,  142 ,  143 , the cooling pipes  134 , and  144  and the coils are inserted into a mold. Then, the epoxy resin  15  which is in a liquid state is filled into an inside of the mold. As shown in  FIG. 2 , the mold supports the coils  131 ,  132 ,  133 ,  141 ,  142 ,  143 , the cooling pipes  134 , and  144 . The inserted coils  131 ,  132 ,  133 ,  141 ,  142 ,  143 , the cooling pipes  134 , and  144  may be fixed by using a glass tape, and the like, before the epoxy resin  15  is inserted into the mold. Since the epoxy resin has a low viscosity in a liquid state, the epoxy resin is easily infiltrated into the gaps between the coils or the gaps between the each coil and the cooling pipes  134 ,  144 . Since the compound material  17  is cured at room temperature, in a process of inserting the epoxy resin  15 , the compound material  17  may not be flowed from the coils  131 ,  132 ,  133 ,  141 ,  142 , and  143 . 
         [0040]    In addition, after the epoxy resin  15  and the compound material  17  is solidified, the coils  131 ,  132 ,  133 ,  141 ,  142 ,  143 , the cooling pipes  134 , and  144  are taken out with the epoxy resin  15 . Accordingly, the gradient magnetic coil  12  is made. 
         [0041]    According to the above-mentioned embodiments, in the gradient magnetic coil  12 , the compound material  17  is filled into a part of area in which the epoxy resin  15  has been filled conventionally. Since the compound material  17  has filler of which thermal conductivity is higher than that of the epoxy resin, the compound material  17  has a higher thermal conductivity than the epoxy resin  15 . In addition, the epoxy resin  15  has a thin layer in gaps between the different coils and gaps between the coils and the cooling pipes  134  and  144 . Accordingly, the heat generated from the each line member  16  of the coils  131 ,  132 ,  133 ,  141 ,  142 , and  143  are more efficiently transferred to the cooling pipes  134 ,  144  than the known method and is efficiently cooled by the cooling liquid. 
         [0042]    When the heat-discharging efficiency is increased, it is possible to fill the compound material  17  into all the gaps without using the epoxy resin  15 . Since the compound material  17  has a high viscosity, it is difficult to infiltrate the compound material  17  into gaps between the different coils and gaps between the coils and the cooling pipes  134 ,  144 . Accordingly, it is difficult to manufacture the product. According to the embodiment, manufacturing process may be simple by using separately the epoxy resin  15  and the compound material  17  and the heat-discharging efficiency may be increased as mentioned above. 
       Simulation Result 
       [0043]      FIG. 4  is a diagram illustrating a simulation result in accordance with a temperature rise by using the gradient magnetic coil  12  on YZ surface.  FIG. 5  is a diagram illustrating a simulation result in accordance with a temperature rise of the known gradient magnetic coil on YZ surface.  FIG. 4  and  FIG. 5  are a simulation result, where the gradient magnetic coil  12  and the known gradient magnetic coil is operated with the same conditions (e.g., supply the current of 15 kW) for the same time. In addition, the known gradient magnetic coil is a gradient magnetic coil in which the epoxy resin  15  is filled into an area having the compound material  17  in the gradient magnetic coil  12 . 
         [0044]    In  FIGS. 4 and 5 , a hatching illustrates a difference of temperature. In  FIGS. 4 and 5 , the same hatching illustrates the same temperature area. The temperature is lowest in an area indicated by a symbol “Ta” and highest in an area indicated by a symbol “Te”. That is, the temperatures in each area are different from each other with a relationship, “Ta&lt;Tb&lt;Tc&lt;Td&lt;Te”. In  FIGS. 4 and 5 , configurations of the coils  131 ,  132 ,  133 ,  141 ,  142 , and  143  are not shown. 
         [0045]    Comparing  FIGS. 4 and 5 , in the gradient magnetic coil  12 , it is known that the high temperature area denoted by the symbol “Te” is sufficiently smaller than that of the known gradient magnetic coil, and it is difficult to increase the temperature of the gradient magnetic coil  12  more than that of the known gradient magnetic coil. 
         [0046]    According to the simulation result, it is obvious that the gradient magnetic coil  12  of the embodiment is more efficiently emit the heat than the known gradient magnetic coil. 
         [0047]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.