Abstract:
A magnetic resonance imaging apparatus comprising: a magnet configured to form a static magnetic field in an imaging area; a cylindrical structure having a guide; a radio frequency coil configured to receive a nuclear magnetic resonance signal generated by transmitting a radio frequency signal into a object set in the static magnetic field; and a radio frequency coil drive structure configured to adjust a distance between the radio frequency coil and a body surface of the object by using a moving structure configured to move along with the guide, a wire configured to move the moving structure and a motor connected to the wire.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a magnetic resonance imaging apparatus and a magnetic resonance imaging method which reconstruct an image using a NMR (nuclear magnetic resonance) signal generated by transmitting a RF (radio frequency) signal with a Larmor frequency into an object and forming a gradient magnetic field inside a magnet for a static magnetic field by a gradient coil, and more particularly, to a magnetic resonance imaging apparatus and a magnetic resonance imaging method which allow an image with more satisfactory quality to be obtained by adjusting a distance between a radio frequency coil for receiving the nuclear magnetic resonance signal and a body surface of the object.  
         [0003]     2. Description of the Related Art  
         [0004]     Conventionally, a magnetic resonance imaging (MRI) apparatus is used as a monitoring apparatus in the medical field.  
         [0005]     The magnetic resonance imaging apparatus is an apparatus which reconstructs a tomographic image of an object using an NMR signal generated with excitation by transmitting a RF signal with a Larmor frequency from a RF coil so as to resonate a nuclear spin in the object magnetically and forming a gradient magnetic field changing temporally with a gradient coil on a imaging area of the object set to the inside of a cylindrical magnet for generating a static magnetic field.  
         [0006]     In the magnetic resonance imaging apparatus as described above, a local RF coil having a size matching with an imaging area is used as a RF coil for receiving a NMR signal for obtaining a tomographic image of a specific part in a object with high sensitivity. For example, a WB (whole-body) coil which is one of RF coils is used as one for receiving on imaging a large area having a field of view about 50 cm around. On the other hand, a local RF coil matching with a size of an imaging area, such as a coil for a head, a genicula or a vertebra, is used as one for receiving when an imaging area for a tomographic image is limited in advance, i.e. on imaging a part, such as a head, a genicula or a vertebra.  
         [0007]     Each local RF coil is optimized every imaging part. Hence, using a local RF coil specialized for receiving a NMR signal from a specific part allows a local image to be imaged with high sensitivity on each imaging area.  
         [0008]     To the contrary, a WB coil allows a more large area to be imaged. However it is difficult to obtain a tomographic image with high sensitivity since a distance from a body surface of an object is farther than that in a case where a local RF coil is used.  
         [0009]     To this situation, a case where it is important on clinical to image a large area with high sensitivity using local RF coils often occurs. However, it is necessary to use a plurality of local RF coils each specified for imaging each specific part in an object on in cases where a large area is imaged using local RF coils. Therefore, it is necessary to take out an object from the bed and reset local RF coils on each change of imaging part, thereby imposing a burden on an object and an operator. That is, conventional local RF coils are preferable for obtaining a local image of an object while imaging a large area needs complicated operations due to moving of the object and changing to other local RF coils.  
         [0010]     In order to solve such a problem, the so called moving-bed method which is conducted by imaging during moving a bed is devised for keeping a more large imaging area using a single local RF coil or a limited number of local RF coils (see, for example, Japanese Patent Application (Laid-Open) No.2002-10992).  
         [0011]      FIG. 9  is a diagram explaining a method for imaging a large area by a single local RF coil with moving the bed in a conventional magnetic resonance imaging apparatus.  
         [0012]     More specifically, as a magnetic resonance imaging apparatus  1  shown in  FIG. 9 , a local RF coil unit  3  is arranged in an imaging area formed in a magnet  2  in which a not shown gradient coil unit is built. A large area is imaged by combining tomographic images obtained through imaging over a plurality of times each imaging range S of the local RF coil unit  3  with moving a bed  4  setting an object P.  
         [0013]     However, on imaging with the conventional moving-bed method, the distance between the local RF coil unit  3  and the bed  4  is constant without being dependent on a position of the bed  4  as shown in  FIG. 9 . Therefore, a distance between an object P having an uneven surface and the local RF coil unit  3  varies depending on a position of the bed  4 . For example, the distance A 1  between the abdominal part of the object P and the local RF coil unit  3  is different from the distance A 2  between the leg part of the object P and the local RF coil unit  3 .  
         [0014]     In other words, a distance between a body surface of an object P and the local RF coil unit  3  is not constant. Hence, the sensitivity of the local RF coil unit  3  becomes uneven, thereby being difficult to obtain a tomographic image with more even sensitivity. This situation leads to reduce quality of a tomographic image.  
       SUMMARY OF THE INVENTION  
       [0015]     The present invention has been made in light of the conventional situations, and it is an object of the present invention to provide a magnetic resonance imaging apparatus and a magnetic resonance imaging method which allow an image with more satisfactory quality to be obtained by adjusting a distance between a local radio frequency coil for receiving the nuclear magnetic resonance signal and a body surface of the object so as to be a more appropriate distance.  
         [0016]     The present invention provides a magnetic resonance imaging apparatus comprising: a magnet configured to form a static magnetic field in an imaging area; a cylindrical structure having a guide; a radio frequency coil configured to receive a nuclear magnetic resonance signal generated by transmitting a radio frequency signal into a object set in the static magnetic field; and a radio frequency coil drive structure configured to adjust a distance between the radio frequency coil and a body surface of the object by using a moving structure configured to move along with the guide, a wire configured to move the moving structure and a motor connected to the wire, in an aspect to achieve the object.  
         [0017]     The present invention also provides a magnetic resonance imaging apparatus comprising: a magnet configured to form a static magnetic field in an imaging area; a radio frequency coil configured to receive a nuclear magnetic resonance signal generated by transmitting a radio frequency signal into a object set in the static magnetic field; and a radio frequency coil drive structure configured to adjust a distance between the radio frequency coil and a body surface of the object by moving a position of the radio frequency coil with a wire, in an aspect to achieve the object.  
         [0018]     The present invention also provides a magnetic resonance imaging apparatus comprising: a magnet configured to form a static magnetic field in an imaging area; a cylindrical structure having a guide; a radio frequency coil configured to receive a nuclear magnetic resonance signal generated by transmitting a radio frequency signal into a object set in the static magnetic field; and a radio frequency coil drive structure configured to adjust a distance between the radio frequency coil and a body surface of the object by moving a position of the radio frequency coil along the guide serving as a moving locus, in an aspect to achieve the object.  
         [0019]     The present invention also provides a magnetic resonance imaging apparatus comprising: a magnet configured to form a static magnetic field in an imaging area; a radio frequency coil configured to receive a nuclear magnetic resonance signal generated by transmitting a radio frequency signal into a object set in the static magnetic field; and a radio frequency coil drive structure configured to adjust a distance between the radio frequency coil and a body surface of the object by moving a position of the radio frequency coil and return the position of the radio frequency coil to a regular position with stability of an elastic body, in an aspect to achieve the object.  
         [0020]     The present invention also provides a magnetic resonance imaging apparatus comprising: a magnet configured to form a static magnetic field in an imaging area; a radio frequency coil configured to receive a nuclear magnetic resonance signal generated by transmitting a radio frequency signal into a object set in the static magnetic field; and a radio frequency coil drive structure configured to adjust a distance between the radio frequency coil and a body surface of the object and a direction of the radio frequency coil by moving positions of at least two points on the radio frequency coil, in an aspect to achieve the object.  
         [0021]     The present invention also provides a magnetic resonance imaging method comprising steps of: forming a static magnetic field in an imaging area; adjusting a distance between a radio frequency coil and a body surface of a object set in the static magnetic field by using a moving structure configured to move along with a guide included in a cylindrical structure, a wire configured to move the moving structure and a motor connected to the wire; and receiving a nuclear magnetic resonance signal generated by transmitting a radio frequency signal into the object with the radio frequency coil, in an aspect to achieve the object.  
         [0022]     The present invention also provides a magnetic resonance imaging method comprising steps of: forming a static magnetic field in an imaging area; adjusting a distance between a radio frequency coil and a body surface of a object set in the static magnetic field by moving a position of the radio frequency coil by a wire; and receiving a nuclear magnetic resonance signal generated by transmitting a radio frequency signal into the object with the radio frequency coil, in an aspect to achieve the object.  
         [0023]     The present invention also provides a magnetic resonance imaging method comprising steps of: forming a static magnetic field in an imaging area; adjusting a distance between a radio frequency coil and a body surface of a object set in the static magnetic field by moving a position of the radio frequency coil along a guide of a cylindrical structure serving as a moving locus; and receiving a nuclear magnetic resonance signal generated by transmitting a radio frequency signal into the object with the radio frequency coil, in an aspect to achieve the object.  
         [0024]     The present invention also provides a magnetic resonance imaging method comprising steps of: forming a static magnetic field in an imaging area; adjusting a distance between a radio frequency coil and a body surface of a object set in the static magnetic field by moving a position of the radio frequency coil; receiving a nuclear magnetic resonance signal generated by transmitting a radio frequency signal into the object with the radio frequency coil; and returning the position of the radio frequency coil to a regular position with stability of an elastic body, in an aspect to achieve the object.  
         [0025]     The present invention also provides a magnetic resonance imaging method comprising steps of: forming a static magnetic field in an imaging area; adjusting a distance between a radio frequency coil and a body surface of an object set in the static magnetic field and a direction of the radio frequency coil by moving positions of at least two points on the radio frequency coil; and receiving a nuclear magnetic resonance signal generated by transmitting a radio frequency signal into the object with the radio frequency coil, in an aspect to achieve the object.  
         [0026]     The magnetic resonance imaging apparatus and the magnetic resonance imaging method as described above make it possible to allow an image with more satisfactory quality to be obtained by adjusting a distance between a local radio frequency coil for receiving the nuclear magnetic resonance signal and a body surface of the object so as to be a more appropriate distance. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     In the accompanying drawings:  
         [0028]      FIG. 1  is a diagram showing a magnetic resonance imaging apparatus according to a first embodiment of the present invention;  
         [0029]      FIG. 2  is a front view of an example of detailed structure of the RF coil drive structure  18  in the magnetic resonance imaging apparatus  10  shown in  FIG. 1 ;  
         [0030]      FIG. 3  is an A-A sectional view shown in  FIG. 2 ;  
         [0031]      FIG. 4  is a diagram explaining an example of method for driving the movable RF coil  16  of the magnetic resonance imaging apparatus  10  shown in  FIG. 1 ;  
         [0032]      FIG. 5  is a diagram showing a magnetic resonance imaging apparatus according to a second embodiment of the present invention;  
         [0033]      FIG. 6  is a sectional view showing an example of a detailed structure of the power transmission structure  22  in the magnetic resonance imaging apparatus  10 A shown in the area B of  FIG. 5 ;  
         [0034]      FIG. 7  is an expanded sectional view of the C area shown in  FIG. 6 ;  
         [0035]      FIG. 8  is a diagram showing a magnetic resonance imaging apparatus according to a third embodiment of the present invention; and  
         [0036]      FIG. 9  is a diagram explaining a method for imaging a large area by a single local RF coil with moving the bed in a conventional magnetic resonance imaging apparatus. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0037]     A magnetic resonance imaging apparatus and a magnetic resonance imaging method according to embodiments of the present invention will be described with reference to the accompanying drawings.  
         [0038]      FIG. 1  is a diagram showing a magnetic resonance imaging apparatus according to a first embodiment of the present invention.  
         [0039]     A magnetic resonance imaging apparatus  10  includes a magnet  11  and a RF coil unit  12 . The magnet  11  housing gradient coils (not shown) is used for forming a static magnetic field. The magnet  11  is formed cylindrical. An imaging area is set in the inside of the magnet  11 . The RF coil unit  12  and a bed  13  for setting an object are also arranged in the inside of the magnet  11 .  
         [0040]     The RF coil unit  12  has a WB coil  14  and a local RF coil set  15 . The WB coil  14  may not provided. The WB coil  14  images the large area of an about 50 cm view for example. The local RF coil set  15  including a coil for use in a heads, a genicula and a spine images a specific part including a heads, a genicula and a spine.  
         [0041]     The WB coil  14  is formed cylindrical. An arbitrary number of the local RF coils  15  each having a predetermined shape are arranged at arbitrary positions in the inside of the WB coil  14 . For example, the local RF coil set  15  includes a pair of a movable RF coil  16  and an immobile RF coil  17  which are arranged so as to counter mutually.  
         [0042]     The immobile RF coil  17  is settled to the inside of the WB coil  14  for example. A RF coil drive structure  18  is provided with the movable RF coil  16  which allows the movable RF coil  16  to move to the predetermined direction, e.g. to the immobile RF coil  17  side countering to the movable RF coil  16 . The RF coil drive structure  18  and the RF coil unit  12  form a RF coil unit.  
         [0043]     The RF coil drive structure  18  can include an arbitrary element. For example, the RF coil drive structure  18  includes motors  19 , wires  20  having non-conductivity and pulleys  21 .  
         [0044]     More specifically, the wires  20  are laid on output shafts  19   a  of the motors  19  respectively so that powers of the motors  19  is transmitted to the wires  20  respectively. The pulleys  21  are provided in various places of the wires  20  so that the each direction of the wires  20  is set to a predetermined one. A power transmission structure  22  having a link construction is provided with the movable RF coil  16  so that the power transmission structure  22  transmits the power from the wires  20  to the movable RF coil  16 . Therefore, since the powers of the motors  19  are transmitted to the movable RF coil  16  via the wires  20 , the movable RF coil  16  can be moved to the immobile RF coil  17  side with driving of the motors  19 .  
         [0045]     In addition, wire adjusting structures  23  are provided with the RF coil drive structure  18 . Each of the wire adjusting structures  23  has a function to adjust tensions of the wires  20 . Therefore, even if the wires  20  are extended by a variation per hour or the wires  20  have relaxations, the wire adjusting structures  23  adjust the tensions of the wires  20  so that the effect of extensions or relaxations of the wires  20  is reduced.  
         [0046]     Furthermore, a bed driving structure  24  is provided with the bed  13  so that the bed driving structure  24  allows the bed  13  to move to a predetermined direction, e.g. to a body axis Z direction of the object which is set as the axis direction in the magnet  11 . Therefore, each of the WB coil  14 , the immobile RF coil  17  and the movable RF coil  16  can change a position in the body axis Z direction relatively to the bed  13  and the object. In addition, since the movable RF coil  16  can be moved to the immobile RF coil  17  side by the power transmission structure  22 , the movable RF coil  16  can change a position in the two directions of a direction vertical to the body axis Z as well as the body axis Z direction relatively to the bed  13  and the object.  
         [0047]      FIG. 2  is a front view of an example of detailed structure of the RF coil drive structure  18  in the magnetic resonance imaging apparatus  10  shown in  FIG. 1 .  FIG. 3  is an A-A sectional view shown in  FIG. 2 .  
         [0048]     As shown in  FIGS. 2 and 3 , the bed  13 , the movable RF coil  16  and the immobile RF coil  17  are arranged in the cylindrical WB coil  14 . Furthermore, the RF coil drive structure  18  allows the movable RF coil  16  to move.  
         [0049]     The power transmission structure  22  of the RF coil drive structure  18  has a structure as shown in  FIG. 2  for example. That is, the power transmission structure  22  has rollers  30  each serving as an example of a moving structure, arms  31 , rotating shafts  32  and springs  33  each serving as an example of an elastic body. For example, the two rotating shafts  32  (of the total of four rotating shafts  32 ) are arranged at each end of the movable RF coil  16  respectively so that the two rotating shafts of each end are in horizontal positions each other. Each of the rollers  30  is arranged on each one end of the four bar-shaped arms  31 . On the other hand, each of the rotating shafts  32  is rotatably inserted in a hole arranged on each of the other ends of the arms  31 . In other word, the four arms  31  arranged on all sides support the movable RF coil  16  via the rotating shafts  32 .  
         [0050]     Each of the springs  33  is mounted on each of the rotating shafts  32  so that stability of each spring  33  acts on each of the arms  31  in the direction in which the each position of the arms  31  relative to the movable RF coil  16  returns to the regular position. For example, a force acts on each of the arms  31  in the direction in which each longitudinal direction of the arms  31  goes horizontally. Therefore, the two arms  31  on the same side of the movable RF coil  16  go horizontally so as to open mutually by the given forces. On the other hand, the forces given from the two arms  31  constantly act perpendicularly on the movable RF coil  16 .  
         [0051]     Furthermore, the WB coil  14  generally has WB bobbins  34  so as to form grooves  35  on the both side of the WB coil  14 . The wires  20  and the rollers  30  which are element of the RF coil drive structure  18  as well as cables  36  for transmitting electric power and signals to the movable RF coil  16  are put in the grooves  35  of the WB bobbins  34 . That is, the grooves  35  of the WB bobbins  34  function as guides for the wires  20 , the rollers  30  and the cables  36  for transmitting control signals to the movable RF coil  16 . The each opposite side of the arms  31  to the movable RF coil  16  is linked with each of the rollers  30  movably arranged in the grooves  35  of the WB bobbins  34 . The cables  36  are settled with the wires  20  and/or the arms  31 , as needed. The ends of the cables  36  passing through the grooves  35  of the WB bobbins  34  are connected to external circuits (not shown).  
         [0052]     On the other hand, the pulleys  21  are arranged on the installation surface side of both end of the WB coil  14 . Each one end of the nonconductive wires  20  which are guided with the grooves  35  of the WB bobbins  34  is connected with the arms  31  near the rollers  30  while each other end of the wires  20  which are respectively guided for the installation surface side of the WB coil  14  with the pulleys  21  is linked with one of the output shafts  19   a  included in the motors  19 . The two wires  20  respectively linked with the two rollers  30  put in the common groove  35  of the WB bobbin  34  cross mutually.  
         [0053]     Furthermore, the wire adjusting structures  23  are contacted with arbitrary positions on the wires  20 , e.g. the positions near the motors  19  respectively. For example, each of the wire adjusting structures  23  includes a pulley and an elastic body, such as a spring. One end of the elastic body is fixed while the other end is linked with the pulley. Each of the pulleys of the wire adjusting structures  23  is contacted with each of the wires  20  so that each elastic force of the elastic bodies keep each tension of the wires  20  constant. In this way, powers of the motors  19  constantly are transmitted to the movable RF coil  16  via the wires  20 .  
         [0054]     Hereby, when the power of the motor  19  moves the two wires  20  put on the common the groove  35  of the WB bobbin  34  to the installation surface side of the WB coil  14 , the two rollers  30  respectively linked with the two arms  31  roll and move on the inner surface of the groove  35  of the WB bobbin  34  so as to approach mutually. Herewith, the two arms  31  opposing the stability of the springs  33  become V-shaped, thereby the movable RF coil  16  approaching the immobile RF coil  17 .  
         [0055]     Furthermore, a sensor  37  for detecting a position of the movable RF coil  16  is provided with the movable RF coil  16 . For example, the sensor  37  has a micro switch. The sensor  37  detects a distance between the movable RF coil  16  and a body surface of an object or the movable RF coil  16  and the immobile RF coil  17 . The sensor  37  outputs a detection signal to a motor control unit  38 .  
         [0056]     The motor control unit  38  has a function to control the motors  19  by giving control signals to the motors  19  based on the detection signal from the sensor  37 . More specifically, the motor control unit  38  controls the motors  19  in accordance with the detection signal from the sensor  37  so that the distance between the movable RF coil  16  and a body surface of an object or the movable RF coil  16  and the immobile RF coil  17  becomes a target one.  
         [0057]     With this structure, powers of the motors  19  controlled by the motor control unit  38  is transmitted from the output shafts  19   a  to the wires  20 , the rollers  30 , the arms  31 , the springs  33  and the rotating shafts  32 . Thus, the distance between the movable RF coil  16  and a body surface of an object or the movable RF coil  16  and the immobile RF coil  17  can be set to an arbitrary one by adjusting the amounts of movements of the wires  20  in accordance with the detection signal of the sensor  37  and driving of the motors  19 .  
         [0058]      FIG. 4  is a diagram explaining an example of method for driving the movable RF coil  16  of the magnetic resonance imaging apparatus  10  shown in  FIG. 1 . In  FIG. 4 , illustration of the WB coil  14  and the RF coil drive structure  18  is omitted.  
         [0059]     Referring to  FIG. 4 , an object P is set on the bed  13 . The bed driving structure  24  moves the bed  13  in the body axis Z direction of the object P. With moving the bed  13 , the RF coil drive structure  18  moves the movable RF coil  16  so that the vertical distance between the movable RF coil  16  and the body surface of the object P becomes constant.  
         [0060]     In this way, imaging can be performed with appropriately adjusting the distance between the movable RF coil  16  and the body surface of the object P by moving the movable RF coil  16  in vertical direction every imaging area corresponding to a position of the bed  13 .  
         [0061]     Therefore, with the magnetic resonance imaging apparatus  10  as described above, the single movable RF coil  16  can cover a large imaging area while a highly sensitive image can be obtained on each imaging area without moving of an object P giving a burden and operation of users including a doctor and a technical expert. In addition, the wires  20  which are main elements of the RF coil drive structure  18  are put in the grooves  35  of the WB bobbins  34 , thereby keeping livability of an object P without reduction of a space for the object P.  
         [0062]     Note that, although an example of method for moving the wires  20  by the motors  19  is shown, a structure for moving the wires  20  by hand motion is also applicable. In addition, a structure for moving the movable RF coil  16  by a moving structure, such as the rollers  30 , using guides forming moving loci, such as rails, grooves and so on, provided on another cylindrical body instead of using the WB coil  14 .  
         [0063]      FIG. 5  is a diagram showing a magnetic resonance imaging apparatus according to a second embodiment of the present invention.  
         [0064]     In the magnetic resonance imaging apparatus  10 A shown in  FIG. 5 , a structure and function of the RF coil drive structure  18 A are different from those of the magnetic resonance imaging apparatus  10  shown in  FIG. 1 . Other constructions and operations of the magnetic resonance imaging apparatus  10 A are not different from those of the magnetic resonance imaging apparatus  10  shown in  FIG. 1  substantially. Therefore, attaching same number to a same element as that of the magnetic resonance imaging apparatus  10  and omitting explanation thereof.  
         [0065]     The RF coil drive structure  18 A of the magnetic resonance imaging apparatus  10 A has an arbitrary structure. For example, the RF coil drive structure  18 A includes motors  19 , nonconductive wires  20 , pulleys  21  and a power transmission structure  22 . Then, the powers of the motors  19  are transmitted to the movable RF coil  16  via the power transmission structure  22  and the wires  20  having directions adjusted by the pulleys  21  so that driving of the motors  19  moves the movable RF coil  16  to the immobile RF coil  17  side, like as the RF coil drive structure  18  of the magnetic resonance imaging apparatus  10  shown in  FIG. 1 .  
         [0066]     In addition, the RF coil drive structure  18 A can adjust an angle of the movable RF coil  16 . For example, as shown in  FIG. 5 , amounts of movements and/or directions of movements with regard to the wires  20  for transmitting the powers to both ends of the movable RF coil  16  are controlled to become different mutually, thereby controlling the angle of the movable RF coil  16  so that a distance between the movable RF coil  16  and a body surface of an object P becomes more constant.  
         [0067]      FIG. 6  is a sectional view showing an example of a detailed structure of the power transmission structure  22  in the magnetic resonance imaging apparatus  10 A shown in the area B of  FIG. 5 .  FIG. 7  is an expanded sectional view of the C area shown in  FIG. 6 .  
         [0068]     For example, the power transmission structure  22  of the RF coil drive structure  18 A has a structure as shown in  FIGS. 6 and 7 . More specifically, the power transmission structure  22  includes rollers  30 , arms  31 , rotating shafts  32 , pillow balls (spherical rolling bearings)  40 , and springs  33 . The power transmission structure  22  of the RF coil drive structure  18 A is substantially similar to that of the RF coil drive structure  18  shown in  FIGS. 2 and 3  except for providing the pillow balls  40 . Therefore, explanation will be described with reference to a diagram showing only near the pillow balls  40 .  
         [0069]     The power transmission structure  22  of the RF coil drive structure  18 A has the pillow balls  40 . The pillow ball  40  is a bearing having a spherical reception face and a through-bore. Each of the pillow balls  40  is arranged on a linking part between each arm  31  and rotating shaft  32 . Each of the rotating shafts  32  is inserted in each through-bore of the pillow balls  40  while each spherical reception face of the pillow balls  40  receives each of the arms  31 . Thus, the angle between each arm  31  and rotating shaft  32  provided with the movable RF coil  16 , i.e. the direction of the movable RF coil  16  can be changed arbitrarily. For example, the pillow balls  40  can arbitrarily change the angle of the movable RF coil  16  on a plane parallel to a body axis Z direction and vertical to a horizontal plane as shown in  FIG. 5 .  
         [0070]     The magnetic resonance imaging apparatus  10 A as described above can keep the distance between the movable RF coil  16  and a body surface of an object P more constant as well as obtain advantage similar to that of the magnetic resonance imaging apparatus  10  shown in  FIG. 1  by changing the angle of the movable RF coil  16  in accordance with uneven body surface of the object P which may exist. Particularly, if the apparatus is configured to allow the angle of the movable RF coil  16  on a plane parallel to a body axis Z direction and vertical to a horizontal plane to be changed arbitrarily, the direction of the movable RF coil  16  can be set to one with higher needs along a body surface of an object P. Consequently, an image with highly sensitive and satisfactory can obtained with the single movable RF coil  16 .  
         [0071]     In addition, changeability of the direction of the movable RF coil  16  achieved by adjusting position of each point of at least two points at which the movable RF coil  16  is supported allows positioning of the movable RF coil  16  with high accuracy and stability. In other word, levelness of the movable RF coil  16  to a set direction can be improved.  
         [0072]      FIG. 8  is a diagram showing a magnetic resonance imaging apparatus according to a third embodiment of the present invention.  
         [0073]     In the magnetic resonance imaging apparatus  10 B shown in  FIG. 8 , a structure and function of the RF coil drive structure  18 B are different from those of the magnetic resonance imaging apparatus  10  shown in  FIG. 1 . Other constructions and operations of the magnetic resonance imaging apparatus  10 A are not different from those of the magnetic resonance imaging apparatus  10  shown in  FIG. 1  substantially. Therefore, attaching same number to a same element as that of the magnetic resonance imaging apparatus  10  and omitting explanation thereof.  
         [0074]     The RF coil drive structure  18  of the magnetic resonance imaging apparatus  10 B has a function to park (evacuate) the movable RF coil  16 . That is, the RF coil drive structure  18  also functions as a parking structure. The RF coil drive structure  18 B has coil side rollers  50  corresponding to the wires  20  respectively. The coil side rollers  50  are arranged at positions sufficiently far from the bed  13  on both side of the WB coil  14 . Each one end of the wires  20  whose directions are steered to the movable RF coil  16  side respectively by the coil side rollers  50  is not linked with the roller  30  of the power transmission structure  22 , but fixed with the movable RF coil  16 .  
         [0075]     On the other hand, the WB coil  14  has a hollow, serving as a parking space  51 , according to the shape of the movable RF coil  16 . That is, the parking space  51  of the WB coil  14  also forms the parking structure.  
         [0076]     Each of the springs  33  of the power transmission structure  22  has elastic force acting in the rotative direction in which each longitudinal direction of the arms  31  gets into vertical to the movable RF coil  16 . Therefore, each elastic force of the springs  33  constantly gives to the movable RF coil  16  a force heading for the bed  13  side. Consequently, when driving of the motors  19  reels off the wires  20 , the movable RF coil  16  moves in the direction far from the bed  13  so as to adjust a position of the movable RF coil  16 .  
         [0077]     When the movable RF coil  16  is to be parked, driving of the motors  19  moves the movable RF coil  16  to a position farther from the bed  13 . Then, the movable RF coil  16  moves into the parking space  51  to be parking status. Because of such a situation, a shape of parking space  51  and each position of coil side rollers  50  are designed according to the shape and the parking position of the movable RF coil  16 .  
         [0078]     With the magnetic resonance imaging apparatus  10 B having a structure as described above, the movable RF coil  16  can be parked in a predetermined position on disuse. Then, a RF coil having a desired shape can be used at the same time easily.  
         [0079]     Note that, a parking structure independent form the RF coil drive structure  18 B may be provided in the magnetic resonance imaging apparatus  10 B, not only the example shown in  FIG. 8   
         [0080]     Furthermore, each element of the magnetic resonance imaging apparatuses  10 ,  10 A, and  10 B in embodiments as described above may be combined mutually to constitute a magnetic resonance imaging apparatus. On the other hand, partial element or function of the magnetic resonance imaging apparatuses  10 ,  10 A, and  10 B may be omitted.