Abstract:
A radio frequency coil unit includes a chassis which has a tubiform inner cylinder, a plurality of flanges arranged apart from each other, each of the plurality of flanges provided in a state of protruding outwards from the inner cylinder while in contact with a whole outer circumference surface of the inner cylinder, and a tubiform external cylinder in which each of the plurality of flanges is provided in a state of contacting an inner surface thereof, wherein the chassis forms a flow path of cooling air as a space surrounded by the inner cylinder, the plurality of flanges and the external cylinder, and a radio frequency coil which is mounted on the inner cylinder or the external cylinder to be positioned in the space surrounded by the inner cylinder, the plurality flanges and the external cylinder.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2008-304643, filed Nov. 28, 2008, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is related to a magnetic resonance diagnostic apparatus which has a radio frequency coil arranged in a gantry, and a radio frequency coil unit used for this magnetic resonance diagnostic apparatus. 
         [0004]    2. Description of the Related Art 
         [0005]    In a magnetic resonance diagnostic apparatus, generally, a radio frequency coil (referred to hereinafter as an RE coil) such as a whole body coil (referred to hereinafter as a WB coil) is arranged inside a gantry. 
         [0006]    The RE coil generates heat by energization. Conventionally, the RE coil was cooled by natural convection of the surrounding. Therefore, generally, no special cooling treatment was applied. 
         [0007]    Therefore, there was a problem that heat generated by the RE coil increased the temperature of the imaging space inside the gantry and made the subject placed in this imaging space uncomfortable. 
         [0008]    In order to deal with this, a cover has been discussed on being arranged leaving a certain space from the RE coil, to prevent heat generated by the RF coil from being transferred to the imaging space. However, in this case, there was a problem that the cover made the imaging space small and may give the subject an oppressive feeling. 
         [0009]    Further, a structure to cool the RF coil by using cooling water is suggested in, for example, Jpn. Pat. Appln. KOKAI Publication No. 11-244255. However, according to the structure known by the reference, the structure of the cooling unit would become elaborate, and the accommodating space thereof would become large. Therefore, there has been a problem that the reduced imaging space may give the subject an oppressive feeling. 
         [0010]    Under such circumstances, the applicant of the present invention suggests in Jpn. Pat. Appln. KOKAI Publication No. 2009-142647 a structure in which a space is formed between a member holding the RE coil (hereinafter referred to as a base portion) and a cover to generate a flow of cooling air in this space, in order to air-cool the RE coil. 
         [0011]    However, sometimes the RE coil is removed from the gantry for maintenance. Therefore, the RF coil is desired to be taken out easily from the gantry. Accordingly, in the invention, an RF coil unit which is independent from the gantry is formed by the RF coil and the base portion holding the RF coil. The RF coil unit is not fixed to the gantry but is used in a state of being fitted in the imaging space. Further, when attaching or detaching the RF coil unit to or from the gantry, the RF coil unit is taken in and out from the imaging space from the opening of the imaging space of the gantry. Therefore, the outer diameter of the RF coil unit should be smaller than the inner diameter of the imaging space. Attachment/detachment of the RF coil unit would become easier as the difference between the outer diameter of the RE coil unit and the inner diameter of the imaging space increases. However, at the same time, as the difference between the outer diameter of the RF coil unit and the inner diameter of the imaging space increases, the base portion becomes less close to the wall surface forming the imaging space. Therefore, the structure suggested by Jpn. Pat. Appln. KOKAI Publication No. 2009-142647 is defective in that, since the cooling air would flow out of the imaging space, cooling efficiency of the RE coil would deteriorate. 
         [0012]    It is considered that by mounting a seal member having resiliency on a position where the base portion is adjacent to the cover, air-tightness formed between the RE coil unit and the cover can be secured to a certain extent while enabling attachment/detachment of the RE coil unit with respect to the gantry. However, it would still be difficult to attach or detach the RE coil unit to or from the gantry as the above mentioned tightness improves. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    From the above mentioned circumstances, it has been desired to facilitate attachment/detachment of the RE coil unit with respect to the gantry while achieving air-tightness of the space formed between the RE coil unit and the cover. 
         [0014]    According to a first aspect of the present invention, there is provided a radio frequency coil unit which is used by being arranged in a magnetic field formed by superimposing a gradient field on a static field in a gantry, wherein the gantry comprises a static field magnet unit which generates the static field, a gradient coil unit which generates the gradient field, and airflow generating unit which causes a flow of cooling air, the radio frequency coil unit comprising: a chassis which has a tubiform inner cylinder, a plurality of flanges arranged apart from each other, each of the plurality of flanges provided in a state of protruding outwards from the inner cylinder while in contact with a whole outer circumference surface of the inner cylinder, and a tubiform external cylinder in which each of the plurality of flanges is provided in a state of contacting an inner surface thereof, wherein the chassis forms a flow path of the cooling air as a space surrounded by the inner cylinder, the plurality of flanges and the external cylinder; and a radio frequency coil which is mounted on the inner cylinder or the external cylinder to be positioned in the space surrounded by the inner cylinder, the plurality of flanges and the external cylinder. 
         [0015]    According to a second aspect of the present invention, there is provided a magnetic resonance diagnostic apparatus comprising: a static field magnet unit which generates a static field; a gradient coil unit which generates a gradient field to be superimposed on the static field; an airflow generating means which cause flow of cooling air; and a radio frequency, wherein the radio frequency coil unit comprises: a chassis which has a tubiform inner cylinder, a plurality of flanges arranged apart from each other and provided in a state of protruding outwards from the inner cylinder while in contact with a whole outer circumference surface of the inner cylinder, and a tubiform external cylinder in which each of the plurality of flanges is provided in a state of contacting the inner surface thereof, wherein the chassis forms a flow path of the cooling air as the space surrounded by the inner cylinder, the plurality of flanges and the external cylinder; and a radio frequency coil mounted on the inner cylinder or the external cylinder to be positioned in a space surrounded by the inner cylinder the plurality of flanges and the external cylinder. 
         [0016]    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 DRAWINGS 
         [0017]    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. 
           [0018]      FIG. 1  shows a configuration of a magnetic resonance diagnostic apparatus according to a first embodiment. 
           [0019]      FIG. 2  is a partially cutaway view of a gantry structure of the magnetic resonance diagnostic apparatus according to the first embodiment. 
           [0020]      FIG. 3  is a perspective view of a body coil unit structure shown in  FIG. 2 . 
           [0021]      FIG. 4  is a partially cutaway view of a structure of a gantry in a magnetic resonance diagnostic apparatus according to a second embodiment. 
           [0022]      FIG. 5  is a partially cutaway view of a structure of a gantry in a magnetic resonance diagnostic apparatus according to a third embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Hereinafter, several embodiments of the present invention will be explained with reference to the drawings. 
       First Embodiment 
       [0024]      FIG. 1  shows a structure of a magnetic resonance diagnostic apparatus  100  according to a first embodiment. As shown in  FIG. 1 , the magnetic resonance diagnostic apparatus  100  includes a static field magnet unit  1 , a gradient coil unit  2 , a gradient power supply  9 , a body coil  4 , a bed  10 , a bed controller  11 , a transmitter  12 , a local coil  13 , a receiver  14 , and a computer system  15 . 
         [0025]    The static field magnet unit  1  is formed in the shape of a hollow cylinder and adapted to generate a uniform static magnetic field within its inside space. As the static field magnet unit  1 , for example, a permanent magnet, a superconducting magnet, or the like is used. 
         [0026]    The gradient coil unit  2  is formed in the shape of a hollow cylinder and placed inside the static field magnet unit  1 . The gradient coil unit  2  is a combination of three types of coils respectively corresponding to the three mutually orthogonal X-, Y-, and Z-axes. When the three coils are individually supplied with currents from the gradient power supply  9 , the gradient coil unit  2  generates gradient magnetic fields each of which has its strength varied along a corresponding one of the X-, Y-, and Z-axes. Suppose that the Z-axis direction coincides with the direction of the static magnetic field. The gradient magnetic fields along the X-, Y-, and Z-axes directions are used as a slice selecting gradient magnetic field Gs, a phase encoding gradient magnetic field Ge, and a readout gradient magnetic field Gr, respectively. The slice selecting gradient magnetic field Gs is used to arbitrarily determine an imaging plane section. The phase encoding gradient magnetic field Ge is used to change the phase of the magnetic resonance signals according to spatial location. The readout gradient magnetic field Gr is used to change the frequency of the magnetic resonance signals according to spatial location. Note that the longitudinal dimension of the gradient coil unit  2  is shorter than that of the static field magnet unit  1 . 
         [0027]    A gantry is formed by covering the static field magnet unit  1  and the gradient coil unit  2  with a gantry housing (not shown). In the gantry housing; a cylindrical opening portion is formed in the gradient coil unit  2 , and an imaging space is formed inside the opening portion. 
         [0028]    A subject  200  is placed on a top board  41  of the bed  10  and moved into the imaging space. Note that the shape of the imaging space is not limited to a cylindrical shape, and may be another shape such as a polygonal column shape. The top board  41  of the bed  10  is driven by the bed controller  11  to move longitudinally and vertically. Usually, the bed  10  is installed so that its longitudinal axis is parallel to the central axis of the static field magnet unit  1 . 
         [0029]    The body coil  4  is placed inside the gradient coil unit  2  and generates a radio-frequency magnetic field in response to a radio-frequency pulse from the transmitter  12 . The body coil  4  is adapted to receive magnetic resonance signals emitted from the subject  200  due to the influence of the radio-frequency magnetic field. The output signal from the body coil  4  is applied to the receiver  14 . 
         [0030]    The transmitter  12  transmits radio-frequency pulses corresponding to Lamar frequency to a transmitting RF coil  6 . 
         [0031]    The local coil  13  is placed inside the gradient coil unit  2  and adapted to receive magnetic resonance signals emitted from the subject  200  due to the influence of the radio-frequency magnetic field. The output signal from the local coil  13  is applied to the receiver  14 . 
         [0032]    The receiver  14  produces magnetic resonance signal data on the basis of the output signal from the body coil  4  or the output signal from the local coil  13 . 
         [0033]    Further, the transmitter  12  transmits RF pulses to the body coil unit  4  only during a transmission period. The receiver  14  inputs output signals from the body coil unit  4  only during a reception period, which is different from the transmission period. 
         [0034]    The computer system  15  includes an interface unit  15   a , a data collection unit  15   b , a reconstruction unit  15   c , a memory unit  15   d , a display unit  15   e , an input unit  15   f , and a main controller  15   g.    
         [0035]    The interface unit  15   a  is connected to the gradient power supply  9 , the bed controller  11 , the transmitter  12 , the local coil  13 , the receiver  14 , and the like. The interface unit  15   a  inputs/outputs signals exchanged between the respective units connected to the interface unit  15   a  and the computer system  15 . 
         [0036]    The data collection unit  15   b  collects via the interface unit  15   a  digital signals output from the receiver  14  and then stores the collected digital signals, i.e., the magnetic resonance signal data, into the memory unit  15   d.    
         [0037]    The reconstruction unit  15   c  performs postprocessing, i.e., reconstruction, such as Fourier transforms, on the magnetic resonance signal data stored in the memory unit  15   d  to obtain spectrum data of desired nuclear spins within the subject  200  or image data. 
         [0038]    The memory unit  15   d  stores magnetic resonance signal data and spectrum data or image data for each patient. 
         [0039]    The display unit  15   e  displays a variety of information, such as spectrum data, image data, and the like, under the control of main controller  15   g . As the display unit  15   e , there is available a display device, such as a liquid crystal display. 
         [0040]    The input unit  15   f  receives commands and information input from an operator. As the input unit  15   f , there is available a pointing device such as a mouse or trackball, a selection device such as a mode changeover switch, or an input device such as a keyboard in accordance with the occasion. 
         [0041]    The main controller  15   g  is equipped with a CPU, a memory, and the like, which are not shown in the block diagram and collectively controls the magnetic resonance diagnostic apparatus  100  of this embodiment. The main controller  15   g  has a variety of controlling functions to implement the known functions in the magnetic resonance diagnostic apparatus  100 . 
         [0042]      FIG. 2  is a partially cutaway view of a gantry structure of the magnetic resonance diagnostic apparatus  100  according to the first embodiment. Further, portions identical to those in  FIG. 1  are applied symbols identical thereto. Detailed explanations thereof are omitted. 
         [0043]    The gantry is provided with a static field magnet unit  1 , a gradient coil unit  2 , a bore tube  3 , a body coil unit  4 , a cover  5  and a bed rail  6 . 
         [0044]    The static field magnet unit  1  is formed in the shape of a hollow cylinder and adapted to generate a uniform static magnetic field within its inside space. As the static field magnet unit  1 , for example, a permanent magnet or a superconductive magnet is used. 
         [0045]    The gradient coil unit  2  is formed in the shape of a hollow cylinder and is arranged inside the static field magnet unit  1  in a state where its axis approximately coincides with the axis of the static field magnet unit  1 . The gradient coil unit  2  is a combination of three types of coils respectively corresponding to mutually orthogonal X-, Y- and Z-axes. When the three types of coils are independently supplied with currents from the gradient power supply  9 , the gradient coil unit  2  generates gradient magnetic fields in which magnetic field strengths are gradient along each of X-, Y- and Z-axes. Suppose that the Z-axis direction coincides with the direction of, for example, the static magnetic field. The gradient magnetic fields along each of X-, Y- and Z-axes are corresponded to, for example, a slice selecting gradient magnetic field Gs, a phase encoding gradient magnetic field Ge and a readout gradient magnetic field Gr, respectively. The slice selecting gradient magnetic field Gs is used to arbitrarily determine an imaging cross section. The phase encoding gradient magnetic field Ge is used to encode the phase of magnetic resonance signals according to spatial location. The readout gradient magnetic field Gr is used to encode the frequency of magnetic resonance signals according to spatial location. As the gradient coil unit  2 , a so called actively shielded gradient coil (ASGC) can be used. 
         [0046]    The bore tube  3  is formed in the shape of a hollow cylinder and arranged inside the gradient coil unit  2  in a state where its axis approximately coincides with the axis of the gradient coil unit  2 . The bore tube  3  forms an imaging space for imaging a subject  200  placed therein. 
         [0047]    The body coil unit  4  is arranged inside the bore tube  3  and includes an inner cylinder  41 , partition members  42  and  43  and an external cylinder  44 . 
         [0048]    The inner cylinder  41  is in the shape of a hollow cylinder and has on both ends flanges  41   a  and  41   b , which protrude outwardly. 
         [0049]    The external cylinder  44  is in the shape of a hollow cylinder. The inner diameter of the external cylinder  44  is approximately equal to the diameter including the ends of flanges  41   a  and  41   b  of the inner cylinder  41 . The external cylinder  44  accommodates the inner cylinder  41  therein and is fixed at the distal ends of flanges  41   a  and  41   b  of the inner cylinder  41 . A material which has translucency along with radiant heat insulation capability is used for the external cylinder  44 . The external cylinder  44  may be formed cylindrical in advance, or formed cylindrical by winding a sheet-like member around the inner cylinder  41 . 
         [0050]    In this manner, a circular belt-like space is formed between the inner cylinder  41  and the external cylinder  44 , and a radio frequency (RF) coil is mounted on the outer surface of the inner cylinder  41 . Here, suppose the RF coil is a bird cage type whole body (WE) coil. In this manner, the WB coil is arranged inside the space formed between the inner cylinder  41  and the external cylinder  44 . Further, in  FIG. 2 , the illustration of the WB coil is omitted. 
         [0051]    The partition members  42  and  43  are formed by using, for example, urethane foam, and are approximately ring-like. The inner diameters of the partition members  42  and  43  are approximately the same as the outer diameter of the inner cylinder  41 . Their widths are approximately the same as the amount of protrusion of flanges  41   a  and  41   b  of the inner cylinder  41 . The partition members  42  and  43  are arranged on the outside of the inner cylinder  41 . In this manner, the partition members  42  and  43  partition the space formed between the inner cylinder  41  and the external cylinder  44  into three spaces,  44   a ,  44   b  and  44   c . However, on each exterior portion of the partition members  42  and  43  is formed a notch which forms openings  42   a  and  43   a  that communicate space  44   a  and space  44   b , and space  44   b  and space  44   c , respectively. Further, as explained later, air is flowed through spaces  44   a ,  44   b  and  44   c , in which each of the spaces functions as a duct. 
         [0052]    The external cylinder  44  is fixed to the inner cylinder  41  with fixing strength which is capable of securing airtightness between the inner cylinder  41  and external cylinder  44  to an extent that air flowing in spaces  44   a ,  44   b  and  44   c  does not leak easily. 
         [0053]    The cover  5  covers the body coil unit  4  so that the subject  200  mounted in the imaging space does not touch the body coil unit  4 . 
         [0054]    The bed rail  6  is arranged in a state which penetrates through the inside of the body coil unit  4 . The bed rail  6  guides the bed top, which is not shown, sent in from the right side of  FIG. 2  to a horizontal direction in  FIG. 2 . In the bed rail  6  is formed an inlet duct and an outlet duct. The inlet duct is communicated through spaces  44   a  and  44   c  and has an opening to introduce air from the outside of the gantry. The outlet duct is communicated through the space  44   b  and is connected to a fan  8  via an extended duct  7 . 
         [0055]      FIG. 3  is a perspective view showing a structure of the body coil unit  4 . In  FIG. 3 , the illustration of partition members  42  and  43  are omitted. 
         [0056]    On the outer surface of the inner cylinder  41  is provided a plurality of conductive patterns  45  and a plurality of circuit elements  46  and  47  which form the body coil. Further, the circuit element  46  is, for example, a condenser. The circuit element  47  is, for example, a pin diode. The plurality of circuit elements  46  are arranged near both side ends of the inner cylinder  41 , in a circumferential direction along the inner cylinder  41 . The plurality of circuit elements  47  are arranged near the center of the base portion, in a circumferential direction along the inner cylinder  41 . Further, the entire body coil which is formed by the conductive pattern  45  and the circuit elements  46  and  47  is positioned in a space formed by the inner cylinder  41  and the external cylinder  44 . 
         [0057]    In the magnetic resonance diagnostic apparatus  100  of the first embodiment configured in the above manner, when the body coil emits RF pulse upon imaging, the circuit elements  46  and  47  generate heat. When the fan  8  causes negative pressure to the outlet duct in the bed rail  6  via the extended duct  7  at this time, air is introduced to the inlet duct in the bed rail  6  from the opening thereof, and flows in the order of spaces  44   a  and  44   c , space  44   b , the outlet duct, the extended duct  7 , and the fan  8 . This air flowing through spaces  44   a ,  44   b  and  44   c  comes in contact with the circuit elements  46  and  47  and air-cools the circuit elements  46  and  47 . Since the inner cylinder  41  and the external cylinder  44  are firmly fixed, high air-tightness can be secured for spaces  44   a ,  44   b  and  44   c . Therefore, since almost no air leakage occurs through gaps between the inner cylinder  41  and the external cylinder  44 , airflow occurs efficiently in spaces  44   a ,  44   b  and  44   c  and cools the circuit elements  46  and  47  efficiently. 
         [0058]    Meanwhile, when assembling the magnetic resonance diagnostic apparatus  100 , or upon maintenance of the body coil unit  4 , the body coil unit  4  is taken in and out with respect to the space inside the bore tube  3 , from the opening of the bore tube  3 . Since the body coil unit  4  itself forms spaces  44   a ,  44   b  and  44   c , the airtightness of the spaces  44   a ,  44   b  and  44   c  is not influenced by whether or not the difference between the outer diameter of the body coil unit  4  and the inner diameter of the bore tube  3  is large. Therefore, the body coil unit  4  is able to have its outer diameter made smaller than the inner diameter of the bore tube  3  to facilitate being taken in and out with respect to the space inside the bore tube  3 . 
         [0059]    The external cylinder  44  is fixed to the inner cylinder  41 . However, for sake of maintenance, it is desirable that the external cylinder  44  can be detached easily from the inner cylinder  41 . Therefore, when fixing the external cylinder  44  to the inner cylinder  41 , it is desirable to use means which can easily unfix the external cylinder  44  from the inner cylinder  41 , such as by using a screw cramp. In the case of using a screw cramp, it is fine to arrange a sealing agent using, such as, urethane foam between the inner cylinder  41  and the external cylinder  44 . It is also fine to use an adhesive agent which is capable of unfixing the external cylinder  44  from the inner cylinder  41  without causing damage to the inner cylinder  41  while securing the above mentioned fixing strength. 
         [0060]    Further, in the first embodiment, the external cylinder  44  is formed by a translucent material. Therefore, a maintenance worker is able to see the body coil without unfixing the external cylinder  44  from the inner cylinder  41 . 
         [0061]    Further, in the first embodiment, the external cylinder  44  is formed by a material having radiant heat insulation capability. Therefore, it is capable of preventing temperatures from rising in spaces  44   a ,  44   b  and  44   c  and the space inside the inner cylinder  41  caused by radiant heat generated by the gradient coil unit  2 . 
       Second Embodiment 
       [0062]      FIG. 4  is a partially cutaway view of a structure of a gantry in the magnetic resonance diagnostic apparatus  100  according to a second embodiment. Further, portions identical to those in  FIGS. 1 to 3  are applied symbols identical thereto. Detailed explanations thereof are omitted. 
         [0063]    This gantry is provided with a static field magnet unit  1 , a gradient coil unit  2 , a bore tube  3 , a cover  5 , a bed rail  6  and a body coil unit  9 . In other words, the gantry in the second embodiment comprises a body coil unit  9  instead of the body coil unit  4  of the gantry in the first embodiment. 
         [0064]    The body coil unit  9  is arranged inside the bore tube  3 . The body coil unit  9  includes partition members  42  and  43 , an external cylinder  44 , inner cylinder  91  and flange forming members  92  and  93 . In other words, the body coil unit  9  comprises an inner cylinder  91  instead of the inner cylinder  41  in the body coil unit  4 , and, additionally, flange forming members  92  and  93 . 
         [0065]    The inner cylinder  91  has a configuration in which flanges  41   a  and  41   b  are removed from the inner cylinder  41 . 
         [0066]    The flange forming members  92  and  93  are formed using, for example, urethane foam, and are formed approximately ring-like. The flange forming members  92  and  93  have inner diameters which are approximately equal to the cuter diameter of the inner cylinder  91  and widths which are approximately equal to the protruding amount of flanges  41   a  and  41   b  of the inner cylinder  41 . The flange forming members  92  and  93  are arranged respectively on both ends on the outside of the inner cylinder  91  and are fixed thereto. In this manner, the flange forming members  92  and  93  form flanges protruding outwards from the inner cylinder  91 . 
         [0067]    The external cylinder  44  is fixed at the distal end of the flange forming members  92  and  93 . 
         [0068]    In this manner, a circular band-like space is formed between the inner cylinder  91 , the flange forming members  92  and  93  and the external cylinder  44 , and a radio frequency (RE) coil is mounted on the outer surface of the inner cylinder  91 . In this manner the WB coil is arranged inside the space formed between the inner cylinder  91 , the flange forming members  92  and  93  and the external cylinder  44 . Further, in  FIG. 4 , the illustration of the WE coil is omitted. 
         [0069]    The partition members  42  and  43  are arranged on the outside of the inner cylinder  91 . 
         [0070]    The flange forming members  92  and  93  are fixed to the inner cylinder  91  and the external cylinder  44  with fixing strength that is capable of securing airtightness between the inner cylinder  91  and external cylinder  44  and the flange forming members  92  and  93  to an extent that air flowing in the spaces  44   a ,  44   b  and  44   c  are not easily leaked. 
         [0071]    In this manner, the body coil unit  9  is different from the body coil unit  4  in that the flange is formed by flange forming members  92  and  93  which are bodies different from the inner cylinder  91 . However, the overall shape of the body coil unit  9  is equivalent to the body coil unit  4 . 
         [0072]    Accordingly, the magnetic resonance diagnostic apparatus  100  of the second embodiment can also achieve an advantage similar to that of the first embodiment. 
       Third Embodiment 
       [0073]      FIG. 5  is a partially cutaway view of a structure of a gantry in the magnetic resonance diagnostic apparatus  100  according to a third embodiment. Further, portions identical to those in  FIGS. 1 to 3  are applied symbols identical thereto. Detailed explanations thereof are omitted. 
         [0074]    This gantry is provided with a static field magnet unit  1 , a gradient coil unit  2 , a body coil unit  4 , a cover  5  and a bed rail  6 . In other words, the gantry in the third embodiment has a configuration in which the bore tube  3  is removed from the gantry in the first embodiment. Further, the body coil unit  4  is formed so that its outer diameter is rather smaller than the inner diameter of the gradient coil unit  2 , and is arranged inside the gradient coil unit  2 . 
         [0075]    When assembling the magnetic resonance diagnostic apparatus  100 , or upon maintenance of the body coil unit  4 , the body coil unit  4  is taken in and out with respect to the space side the gradient coil unit  2  from the opening of the gradient coil unit  2 . Since the body coil unit  4  itself forms spaces  44   a ,  44   b  and  44   c , the airtightness of the spaces  44   a ,  44   b  and  44   c  is not influenced by whether or not the difference between the outer diameter of the body coil unit  4  and the inner diameter of the gradient coil unit  2  is large. Therefore, the outer diameter of the body coil unit  4  can be made smaller than the inner diameter of the gradient coil unit  2  to facilitate the body coil unit  4  being taken in and out with respect to the space inside the gradient coil unit  2 . 
         [0076]    The present invention can be implemented by various modified modes as follows. 
         [0077]    It is fine to omit the flanges  41   a  and  41   b  of the inner cylinder  41  and provide flanges protruding inwards from the external cylinder  44 . Alternatively, in addition to the flanges  41   a  and  41   b  of the inner cylinder  41 , it is also fine to provide flanges protruding inwards from the external cylinder  44 . 
         [0078]    It is also fine to arrange a plurality of conductive patterns  45  and a plurality of circuit elements  46  and  47  forming a body coil on the inside surface of the external cylinder  44 . 
         [0079]    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.