Abstract:
For the purpose of always keeping the positional relationship fixed between a support section for supporting a supported object and a base section for receiving the support section, the present apparatus comprises: a support section  500  for horizontally supporting a supported object; a base section  112  having a horizontal plane on its top; and a position adjusting section  300  provided between the support section and the base section, for moving the support section forward/backward between a position above the horizontal plane and a position off the horizontal plane while keeping the support section at a level higher than the horizontal plane, and for moving the support section upward/downward between a position higher than the horizontal plane and a position lower than the horizontal plane at the position off the horizontal plane.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a support apparatus, magnet system and magnetic resonance imaging apparatus, and particularly to a support apparatus capable of placing a support plate, which horizontally supports a supported object, either over a base or off the base, a magnet system for a magnetic resonance imaging apparatus comprising such a support apparatus, and a magnetic resonance imaging apparatus comprising such a magnet system.  
           [0002]    In a magnetic resonance imaging (MRI) apparatus, a subject to be imaged is carried into an internal space of a magnet system, i.e., an imaging space; a static magnetic field, gradient magnetic fields and a high frequency magnetic field are applied to excite spins within the subject to generate magnetic resonance signals; and an image is reconstructed based on the received signals.  
           [0003]    One type of the magnet system is the open magnet system. The open magnet system has a structure in which a pair of magnets vertically facing each other across the imaging space are supported by a C-shaped yoke. The magnet system having such a structure provides high openness because the vertical yoke is disposed only on one side.  
           [0004]    The subject to be imaged is carried into the imaging space of such a magnet system, being rested on a movable bed having wheels. The carrying is achieved by horizontal movement of the movable bed from the front of the magnet system. Such a carrying scheme facilitates access to the subject during imaging, and allows efficient use of the internal space of the magnet system.  
           [0005]    In the MRI apparatus employing the movable bed to carry the subject into the imaging space as described above, the bed for supporting the subject and the magnet system for receiving the bed are separate. Therefore, the positional relationship between the bed and the magnet system while receiving the bed is not fixed.  
         SUMMARY OF THE INVENTION  
         [0006]    It is therefore an object of the present invention to provide a support apparatus in which the positional relationship between a support section for supporting a supported object and a base section for receiving the support section is always fixed, a magnet system comprising such a support apparatus, and a magnetic resonance imaging apparatus comprising such a magnet system.  
           [0007]    (1) The present invention, in accordance with one aspect thereof for solving the aforesaid problem, is a support apparatus characterized in comprising: a support section for horizontally supporting a supported object; a base section having a horizontal plane on its top; and a position adjusting section provided between said support section and said base section, for moving said support section forward/backward between a position above said horizontal plane and a position off said horizontal plane while keeping said support section at a level higher than said horizontal plane, and for moving said support section upward/downward between a position higher than said horizontal plane and a position lower than said horizontal plane at said position off said horizontal plane.  
           [0008]    (2) The present invention, in accordance with another aspect thereof for solving the aforesaid problem, is a magnet system for a magnetic resonance imaging apparatus that has a space for receiving a subject to be imaged and generates a static magnetic field, gradient magnetic field and high frequency magnetic field in said space, characterized in comprising: a base section having a horizontal plane on its top; a post section provided on one side of said base section and extending upright beyond said horizontal plane; a hood section supported by said post section, facing said horizontal plane across said space; a support section for horizontally supporting the subject to be imaged; and a position adjusting section provided between said base section and said support section, for moving said support section forward/backward between a position above said horizontal plane and a position off said horizontal plane on the other side of said base section while keeping said support section at a level higher than said horizontal plane, and for moving said support section upward/downward between a position higher than said horizontal plane and a position lower than said horizontal plane at said position off said horizontal plane.  
           [0009]    (3) The present invention, in accordance with still another aspect thereof for solving the aforesaid problem, is a magnetic resonance imaging apparatus having: a magnet system that has a space for receiving a subject to be imaged and generates a static magnetic field, gradient magnetic field and high frequency magnetic field in said space; and image producing means for producing an image based on magnetic resonance signals acquired through said magnet system, characterized in that said magnet system comprises: a base section having a horizontal plane on its top; a post section provided on one side of said base section and extending upright beyond said horizontal plane; a hood section supported by said post section, facing said horizontal plane across said space; a support section for horizontally supporting the subject to be imaged; and a position adjusting section provided between said base section and said support section, for moving said support section forward/backward between a position above said horizontal plane and a position off said horizontal plane on the other side of said base section while keeping said support section at a level higher than said horizontal plane, and for moving said support section upward/downward between a position higher than said horizontal plane and a position lower than said horizontal plane at said position off said horizontal plane.  
           [0010]    In the present invention of the aspects as described regarding (1)-(3), a position adjusting section for moving the support section forward/backward between a position above a horizontal plane at the top of the base section and a position off the horizontal plane while keeping the support section at a level higher than the horizontal plane, and for moving the support section upward/downward between a position higher than the horizontal plane and a position lower than the horizontal plane at the position off the horizontal plane, is provided between the base section and the support section; and therefore, the positional relationship between the support section and the base section for receiving it can be always fixed.  
           [0011]    Preferably, said position adjusting section comprises a pair of link mechanisms respectively provided between two positions of said support section along a direction parallel with said horizontal plane and perpendicular to the direction of said forward/backward movement and the corresponding end portions of said base section, said link mechanisms being pivotally rotatable relative to said base section; and a movement mechanism for moving a portion of said pair of link mechanisms adjacent to said base section in the direction of said forward/backward movement, so that the position adjustment of the support section can be suitably achieved.  
           [0012]    Preferably, each member of said pair of link mechanisms comprises a pair of arms configured to avoid mutual interference involved in said pivotal rotation so that the upward/downward movement can be suitably achieved.  
           [0013]    (4) The present invention, in accordance with still another aspect thereof for solving the aforesaid problem, is a support apparatus characterized in comprising: a support section for horizontally supporting a supported object; a base section having a horizontal plane on its top; and a position adjusting section provided between said support section and said base section, for moving said support section forward/backward between a position above said horizontal plane and a position off said horizontal plane while keeping said support section at a level higher than said horizontal plane.  
           [0014]    (5) The present invention, in accordance with still another aspect thereof for solving the aforesaid problem, is a magnet system for a magnetic resonance imaging apparatus that has a space for receiving a subject to be imaged and generates a static magnetic field, gradient magnetic field and high frequency magnetic field in said space, characterized in comprising: a base section having a horizontal plane on its top; a post section provided on one side of said base section and extending upright beyond said horizontal plane; a hood section supported by said post section, facing said horizontal plane across said space; a support section for horizontally supporting the subject to be imaged; and a position adjusting section provided between said base section and said support section, for moving said support section forward/backward between a position above said horizontal plane and a position off said horizontal plane on the other side of said base section while keeping said support section at a level higher than said horizontal plane.  
           [0015]    (6) The present invention, in accordance with still another aspect thereof for solving the aforesaid problem, is a magnetic resonance imaging apparatus having: a magnet system that has a space for receiving a subject to be imaged and generates a static magnetic field, gradient magnetic field and high frequency magnetic field in said space; and image producing means for producing an image based on magnetic resonance signals acquired through said magnet system, characterized in that said magnet system comprises: a base section having a horizontal plane on its top; a post section provided on one side of said base section and extending upright beyond said horizontal plane; a hood section supported by said post section, facing said horizontal plane across said space; a support section for horizontally supporting the subject to be imaged; and a position adjusting section provided between said base section and said support section, for moving said support section forward/backward between a position above said horizontal plane and a position off said horizontal plane on the other side of said base section while keeping said support section at a level higher than said horizontal plane.  
           [0016]    In the present invention of the aspects as described regarding (4)-(6), a position adjusting section for moving the support section forward/backward between a position above a horizontal plane at the top of the base section and a position off the horizontal plane while keeping the support section at a level higher than the horizontal plane, is provided between the support section and the base section; and therefore, the positional relationship between the support section and the base section for receiving it can be always fixed.  
           [0017]    Preferably, said position adjusting section comprises a pair of extendable arms respectively provided between two positions of said support section along a direction parallel with said horizontal plane and perpendicular to the direction of said forward/backward movement and the corresponding end portions of said base section, said extendable arms being capable of extending relative to said base section, so that the forward/backward movement of the support section can be suitably achieved.  
           [0018]    Preferably, said position adjusting section comprises a pair of arms respectively provided between two positions of said support section along a direction parallel with said horizontal plane and perpendicular to the direction of said forward/backward movement and the corresponding end portions of said base section; and a movement mechanism for enabling a portion of said support arms adjacent to said base section to move in the direction of said forward/backward movement, so that the forward/backward movement of the support section can be suitably achieved.  
           [0019]    Therefore, the present invention can provide a support apparatus in which the positional relationship between a support section for supporting a supported object and a base section for receiving the support section is always fixed, a magnet system comprising such a support apparatus, and a magnetic resonance imaging apparatus comprising such a magnet system.  
           [0020]    Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is a block diagram of an apparatus in accordance with one embodiment of the present invention.  
         [0022]    [0022]FIG. 2 is a schematic view showing the configuration of a magnet system.  
         [0023]    [0023]FIG. 3 is a schematic view showing the configuration of the magnet system.  
         [0024]    [0024]FIG. 4 is a schematic view showing a cross section taken along a line A-A in FIG. 3.  
         [0025]    [0025]FIG. 5 is a schematic view showing the configuration of a magnet body.  
         [0026]    [0026]FIG. 6 is a schematic view showing the configuration of the magnet body.  
         [0027]    [0027]FIG. 7 is a schematic view showing a cross section taken along a line B-B in FIG. 6.  
         [0028]    [0028]FIG. 8 is a schematic view showing the structure of a table position adjusting mechanism.  
         [0029]    [0029]FIG. 9 is a schematic view showing the condition in which the table is pushed out.  
         [0030]    [0030]FIG. 10 is a schematic view showing the condition in which the table is lowered.  
         [0031]    [0031]FIG. 11 is a schematic view showing the configuration of a magnet system.  
         [0032]    [0032]FIG. 12 is a schematic view showing the configuration of the magnet system.  
         [0033]    [0033]FIG. 13 is a schematic view showing the condition in which the table is pushed out.  
         [0034]    [0034]FIG. 14 is a schematic view showing the configuration of a magnet system.  
         [0035]    [0035]FIG. 15 is a schematic view showing the configuration of the magnet system.  
         [0036]    [0036]FIG. 16 is a schematic view showing the structure of the table position adjusting mechanism.  
         [0037]    [0037]FIG. 17 is a schematic view showing the condition in which a table is pushed out. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]    Several embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the present invention is not limited to the embodiments. FIG. 1 shows a block diagram of a magnetic resonance imaging apparatus, which is one embodiment of the present invention. The configuration of the apparatus represents an embodiment of the apparatus in accordance with the present invention.  
         [0039]    As shown in FIG. 1, the present apparatus has a magnet system  100 . The magnet system  100  has a main magnetic field magnet section  102 , a gradient coil section  106  and an RF coil section  108 . The main magnetic field magnet section  102 , gradient coil section  106  and RF coil section  108  each comprise a pair of members facing each other across a space. These sections have a generally disk-like shape and are disposed to have a common center axis. The magnet system  100  will be described in detail later.  
         [0040]    A subject  1  is rested on a table  500  and carried into and out of the internal space (bore) of the magnet system  100 . The table  500  is driven by a table driving section  120 . The relationship between the table  500  and the magnet system  100  will be described in detail later.  
         [0041]    The main magnetic field magnet section  102  generates a static magnetic field in the internal space of the magnet system  100 . The direction of the static magnetic field is generally orthogonal to the direction of the body axis of the subject  1 . That is, a “vertical” magnetic field is generated. The main magnetic field magnet section  102  is constructed using a permanent magnet, for example. It will be easily recognized that the main magnetic field magnet section  102  is not limited to a permanent magnet, but may be made using a super or normal conductive electromagnet or the like.  
         [0042]    The gradient coil section  106  generates three gradient magnetic fields for imparting respective gradients to the static magnetic field strength in directions of three mutually perpendicular axes, i.e., slice axis, phase axis and frequency axis.  
         [0043]    The gradient magnetic field in the slice axis direction is sometimes referred to as the slice gradient magnetic field. The gradient magnetic field in the phase axis direction is sometimes referred to as the phase encoding gradient magnetic field. The gradient magnetic field in the frequency axis direction is sometimes referred to as the readout gradient magnetic field. In order to enable generation of such gradient magnetic fields, the gradient coil section  106  has three gradient coils, which are not shown. The gradient magnetic field will be sometimes referred to simply as the gradient hereinbelow.  
         [0044]    The RF coil section  108  transmits an RF (radio frequency) pulse for exciting spins within the subject  1  in the static magnetic field space. The RF coil section  108  also receives magnetic resonance signals generated by the excited spins. The RF coil section  108  may be a type that conducts transmission and reception by the same coil or by separate coils.  
         [0045]    The gradient coil section  106  is connected with a gradient driving section  130 . The gradient driving section  130  supplies driving signals to the gradient coil section  106  to generate the gradient magnetic fields. The gradient driving section  130  has three driving circuits, which are not shown, corresponding to the three gradient coils in the gradient coil section  106 .  
         [0046]    The RF coil section  108  is connected with an RF driving section  140 . The RF driving section  140  supplies driving signals to the RF coil section  108  to transmit the RF pulse, thereby exciting the spins within the subject  1 .  
         [0047]    The RF coil section  108  is connected to a data collecting section  150 . The data collecting section  150  gathers receive signals received by the RF coil section  108  by sampling them, and collects the signals as digital data.  
         [0048]    The table driving section  120 , gradient driving section  130 , RF driving section  140  and data collecting section  150  are connected with a control section  160 . The control section  160  controls the table driving section  120 , gradient driving section  130 , RF driving section  140  and data collecting section  150  to carry out imaging.  
         [0049]    The control section  160  is constructed using, for example, a computer. The control section  160  has a memory, which is not shown. The memory stores programs for the control section  160  and several kinds of data. The function of the control section  160  is achieved by the computer executing a program stored in the memory.  
         [0050]    The output of the data collecting section  150  is connected to a data processing section  170 . The data collected by the data collecting section  150  is input to the data processing section  170 . The data processing section  170  is constructed using, for example, a computer. The data processing section  170  has a memory, which is not shown. The memory stores programs for the data processing section  170  and several kinds of data.  
         [0051]    The data processing section  170  is connected to the control section  160 . The data processing section  170  is above the control section  160  and controls it. The function of the present apparatus is achieved by the data processing section  170  executing a program stored in the memory.  
         [0052]    The data processing section  170  stores data collected by the data collecting section  150  into the memory. A data space is formed in the memory. The data space constitutes a two-dimensional Fourier space. The Fourier space will be sometimes referred to as a k-space hereinbelow. The data processing section  170  performs a two-dimensional inverse Fourier transformation on the data in the k-space to reconstruct an image of the subject  1 . The data processing section  170  is an embodiment of the image producing means of the present invention.  
         [0053]    The data processing section  170  is connected with a display section  180  and an operating section  190 . The display section  180  comprises a graphic display, etc. The operating section  190  comprises a keyboard, etc., provided with a pointing device.  
         [0054]    The display section  180  displays the reconstructed image and several kinds of information output from the data processing section  170 . The operating section  190  is operated by a user, and the section  190  inputs several commands, information and so forth to the data processing section  170 . The user interactively operates the present apparatus via the display section  180  and operating section  190 .  
         [0055]    [0055]FIGS. 2, 3 and  4  schematically show the configuration of the magnet system  100 . FIG. 2 is a front elevational view, FIG. 3 is a right side-view and FIG. 4 is a cross section taken along a line A-A in FIG. 2. Although not shown, a left side view corresponds to a mirror image of FIG. 3. As shown, the magnet system  100  has a base section  112 , a post section  114  and a hood section  116 .  
         [0056]    The base section  112  is an embodiment of the base section in accordance with the present invention. The post section  114  is an embodiment of the post section in accordance with the present invention. The hood section  116  is an embodiment of the hood section in accordance with the present invention.  
         [0057]    The upper surface of the base section  112  forms a horizontal plane. The post section  114  stands generally upright in the depth of the base section  112  as viewed from the front. The hood section  116  extends generally horizontally from the upper portion of the post section  114  toward the front. The lower surface of the hood section  116  faces the upper surface of the base section  112  across a space.  
         [0058]    The magnet system incorporates a magnet body. FIGS. 5, 6 and  7  schematically show the configuration of the magnet body  110 . FIG. 5 is a front elevational view, FIG. 6 is a right side view and FIG. 7 is a cross section taken along a line B-B in FIG. 5. Although not shown, a left side view corresponds to a mirror image of FIG. 6. As shown, the magnet body  110  has an upper magnetic pole section  111 , a lower magnetic pole section  113  and a yoke  115 .  
         [0059]    The yoke  115  has a generally C-shape structure as viewed from the side. The upper and lower magnetic pole sections  111  and  113  are attached respectively to the lower surface of the upper horizontal limb and to the upper surface of the lower horizontal limb of the C-shaped yoke  115  in a relationship such that they face each other across the space.  
         [0060]    The upper and lower magnetic pole sections  111  and  113  each have a generally short cylindrical shape. The upper and lower magnetic pole sections  111  and  113  each contain the aforementioned main magnetic field magnet section  102 , gradient coil section  106  and RF coil section  108 .  
         [0061]    The upper horizontal limb of the C-shaped yoke and the upper magnetic pole section  111  lie within the hood section  116  of the magnet system  100 . The vertical limb of the C-shaped yoke lies within the post section  114  of the magnet system  100 . The lower horizontal limb of the C-shaped yoke and the lower magnetic pole section  113  lie within the base section  112  of the magnet system  100 .  
         [0062]    Thus, the space across which the base section  112  and the hood section  116  face each other forms a space in which the magnetic fields are generated by the main magnetic field magnet section  102 , gradient coil section  106  and RF coil section  108 .  
         [0063]    The base section  112  of the magnet system  100  is provided with the table  500  for placing the subject to be imaged. The table  500  is mounted on the base section  112  so that the longitudinal dimension of the table  500  extends laterally as viewed from the front of the magnet system  110 . The surface of the table  500  on which the subject to be imaged is placed is parallel with the upper surface of the base section  112 . The table  500  is an embodiment of the support section in accordance with the present invention.  
         [0064]    The mounting of the table  500  on the base section  112  is achieved by a pair of mounting mechanisms  300  respectively provided at the right and left end portions of the base section  112  as viewed from the front of the magnet system  100  and the corresponding portions of the lower surface of the table  500 . The mounting mechanisms  300  form part of the table driving section  120 . The mounting mechanisms  300  represent an embodiment of the position adjusting section in accordance with the present invention.  
         [0065]    The mounting mechanisms  300  are formed by link mechanisms. As exemplarily shown in FIG. 3, each link mechanism is constructed by pivotally attaching respective ends of a pair of arms  304  and  304 ′ to a pair of pivots  302  and  302 ′ that are disposed at a predefined interval on the lower surface of the table  500 , each pivot being parallel with the longitudinal direction of the table  500 , and fixedly attaching respective other ends of the pair of arms  304  and  304 ′ to a pair of pivots  306  and  306 ′ vertically protruding from an end surface of the base section  112  at a predefined interval. The pair of arms  304  and  304 ′ are bent in an L shape.  
         [0066]    The pair of pivots  302  and  302 ′ is disposed so that the pivot  302  lies nearer and the pivot  302 ′ lies farther as viewed from the front of the magnet system  100 .  
         [0067]    The pair of pivots  306  and  306 ′ is disposed so that the pivot  306  lies nearer and the pivot  306 ′ lies farther as viewed from the front of the magnet system  100 .  
         [0068]    The relationship between the pair of pivots  302  and  302 ′ and the pair of pivots  306  and  306 ′ is such that the pair of pivots  302  and  302 ′ lies nearer and the pair of pivots  306  and  306 ′ lies farther as viewed from the front of the magnet system  100 . Moreover, the pair of pivots  302  and  302 ′ is positioned higher than the upper surface of the base section  112 , and the pair of pivots  302  and  302 ′ is positioned lower than the upper surface of the base section  112 .  
         [0069]    The distance between the pivots  302  and  302 ′ is equal to the distance between the pivots  306  and  306 ′. Moreover, a line connecting the centers of the pivots  302  and  302 ′ and a line connecting the centers of the pivots  306  and  306 ′ are parallel with each other. Thus, the link mechanism is identical to a so-called parallel-ruler type link mechanism. It should be noted that the arm  304 ′ connecting the pivots  302 ′ and  306 ′ passes between the arm  304  and the base section  112 , and makes a downward detour avoiding the pivot  306 .  
         [0070]    The arms  304  and  304 ′ will be sometimes referred to as a link mechanism hereinbelow. The link mechanism is an embodiment of the link mechanism in accordance with the present invention. The arms  304  and  304 ′ represent an embodiment of the pair of arms in accordance with the present invention.  
         [0071]    The pair of pivots  306  and  306 ′ protrudes outward through a slit portion  308  from the inside of the base section  112 . The pair of pivots  306  and  306 ′ are torque output axes of actuators provided within the base section  112 . The output torque of the actuators keeps the table  500  at a position above the upper surface of the base  112  at a distance, as shown.  
         [0072]    The slit portion  308  is an elongated hole extending in parallel with the upper surface of the base section  112 . The actuators bearing the pivots  306  and  306 ′ can be linearly moved along the slit portion  308  by a movement mechanism provided within the base section  112 . FIG. 3 shows the condition in which the pivots  306  and  306 ′ are moved farthest as viewed from the front of the magnet system  100 .  
         [0073]    [0073]FIG. 8 schematically shows an exemplary configuration of the actuators and movement mechanism provided within the base section  112 . As shown, actuators  316  and  316 ′ bearing the pivots  306  and  306 ′ are mounted on a carriage  320 .  
         [0074]    The carriage  320  is movable on a rail  322 . The rail  322  runs in parallel with the slit portion  308 . The carriage  320  is joined to a portion of a belt  404  traveling around four pulleys  402 .  
         [0075]    The side of the belt  404  on which the carriage  320  is joined is parallel with the rail  322 , and the span of the side is the same as the length of the rail  322 . At least one of the four pulleys  402  is driven by a motor (not shown) etc. that is reciprocally rotatable.  
         [0076]    Thus, the pivots  306  and  306 ′ of the actuators  316  and  316 ′ can be reciprocally moved along the slit portion  308 , and accordingly, the table  500  supported by the pivots  306  and  306 ′ via the link mechanism  304 / 304 ′ can be reciprocally moved over the base section  112 . A portion comprised of the carriage  320 , rail  322 , pulleys  402  and belt  404  is an embodiment of the movement mechanism in accordance with the present invention.  
         [0077]    [0077]FIG. 9 shows the condition in which the table  500  is moved nearest as viewed from the front of the magnet system  100 . The positions nearer and farther as viewed from the front of the magnet system  100  will be sometimes referred to simply as those nearer and farther hereinbelow.  
         [0078]    As shown in FIG. 9, in this condition, the table  500  is positioned completely out of the space between the base section  112  and the hood section  116 . That is, the table  500  is positioned protruding nearer than the front of the magnet system  100  off the base section  112 .  
         [0079]    In this condition, by rotating the pivots  306  and  306 ′ counterclockwise using the actuators  316  and  316 ′, the link mechanism  304 / 304 ′ rotates counterclockwise.  
         [0080]    The counterclockwise rotation of the link mechanism  304 / 304 ′ lowers the table  500  while keeping the table  500  in a horizontal orientation. In the condition in which the table  500  is lowered to the lowest position, it comes down near the floor, as exemplarily shown in FIG. 10.  
         [0081]    The link mechanism  304 / 304 ′ can lower the table  500  near the floor without interfering with the table  500  because the arm  304  bends at a generally right angle. Moreover, since the arm  304 ′ is configured to pass between the arm  304  and base section  112  and make a downward detour avoiding the pivot  306 , the table  500  can be lowered from a level higher than the upper surface of the base section  112  to a level near the floor without interference between the arms  304  and  304 ′, and the table  500  can be lifted up from the level near the floor to the level higher than the upper surface of the base section  112 .  
         [0082]    By appropriately controlling the actuators  316  and  316 ′, the level of the table  500  can be adjusted to any level between the level shown in FIG. 9 and that shown in FIG. 10. By such level adjustment, the level of the table  500  can be set so that the subject to be imaged can easily get on and off the table  500 .  
         [0083]    For example, the table  500  bearing the subject at the level shown in FIG. 10 is lifted up to the level shown in FIG. 9 by a clockwise rotation of the pivots  306  and  306 ′ by the actuators  316  and  316 ′, and then the table  500  is pulled into the space between the base section  112  and the hood section  116  by movement of the carriage  320 . When the carriage  320  moves farthest, the table  500  reaches a fixed position in the space between the base section  112  and the hood section  116 , as shown in FIG. 3.  
         [0084]    Thus, since the table  500  is mounted on the base section  112  of the magnet system  100  by the mounting mechanism  300 , the positional relationship between the table  500  and the base section  112  for receiving it can be always fixed. Moreover, the level of the table  500  can be appropriately adjusted so that the subject to be imaged can easily get on and off the table  500 .  
         [0085]    [0085]FIGS. 11 and 12 schematically show an exemplary configuration in which the table  500  is mounted on the magnet system  100  by a mounting mechanism different from that described above. FIG. 11 is a front elevational view and FIG. 12 is a right side view. Although not shown, a left side view corresponds to a mirror image of FIG. 12. In FIGS. 12 and 13, members other than the mounting mechanism  310  are the same as those shown in FIGS. 2 and 3, and therefore, they are designated by similar reference symbols and explanations thereof will be omitted.  
         [0086]    The configuration of the mounting mechanism  310  will now be described with reference to FIG. 12. As shown, the mounting mechanism  310  supports the table  500  by arms  314  from the lower side. The table  500  is kept slightly above the upper surface of the base section  112 , as shown. The mounting mechanism  310  forms part of the table driving section  120 . The mounting mechanism  310  is an embodiment of the position adjusting section in accordance with the present invention.  
         [0087]    A portion of each arm  314  that lies farther as viewed from the front of the magnet system  100  is inserted into a cylinder  324  such that the arm  314  can be slidably moved in the horizontal direction. The cylinder  324  is inserted into a cylinder  334  such that the cylinder  324  can be slidably moved in the horizontal direction. The cylinder  324  is inserted into a cylinder  344  such that the cylinder  334  can be slidably moved in the horizontal direction. The cylinder  344  is fixedly attached to a lateral end portion of the base section  112  as viewed from the front of the magnet system  100 . FIG. 12 shows the condition in which the arm  314  and the cylinders  324  and  334  are inserted most deeply into the respective receiving cylinders.  
         [0088]    The cylinders  324 ,  334  and  344  incorporate a mechanism for pushing and pulling the respective inner portions of the arm and cylinders by using, for example, hydraulic pressure. Thus, a portion comprised of the arm  314  and the cylinders  324 ,  334  and  344  forms an arm as a whole that is extendable in the horizontal direction. The portion comprised of the arm  314  and the cylinders  324 ,  334  and  344  will be sometimes referred to as an extendable arm hereinbelow. The extendable arm is an embodiment of the extendable arm in accordance with the present invention.  
         [0089]    [0089]FIG. 13 shows the condition in which the extendable arm is extended most. As shown, in this condition, the table  500  is positioned completely out of the space between the base section  112  and the hood section  116 . That is, the table  500  is positioned protruding nearer than the front of the magnet system  100  off the base section  112 . Thus, the subject to be imaged can get on and off the table  500  without interference from the hood section  116  of the magnet system  100 .  
         [0090]    The table  500  bearing the subject in the condition shown in FIG. 13 is pulled into the space between the base section  112  and the hood section  116  by a retracting operation of the extendable arm. In the condition in which the extendable arm is retracted most, the table  500  reaches a fixed position in the space between the base section  112  and the hood section  116 , as shown in FIG. 12.  
         [0091]    Thus, since the table  500  is mounted on the base section  112  of the magnet system  100  by the mounting mechanism  310 , the positional relationship between the table  500  and the base section  112  for receiving it can be always fixed.  
         [0092]    [0092]FIGS. 14 and 15 schematically show an exemplary configuration in which the table  500  is mounted on the magnet system  100  by a mounting mechanism different from those described above. FIG. 14 is a front elevational view and FIG. 15 is a right side view. Although not shown, a left side view corresponds to a mirror image of FIG. 15. In FIGS. 14 and 15, members other than the mounting mechanism  330  are the same as those shown in FIGS. 2 and 3, and therefore, they are designated by similar reference symbols and explanations thereof will be omitted.  
         [0093]    The configuration of the mounting mechanism  330  will now be described with reference to FIG. 15. As shown, the mounting mechanism  330  supports the table  500  by arms  354  from the lower side. The table  500  is kept slightly above the upper surface of the base section  112 . The mounting mechanism  330  forms part of the table driving section  120 . The mounting mechanism  330  is an embodiment of the position adjusting section in accordance with the present invention. The arm  354  is an embodiment of the support arm in accordance with the present invention.  
         [0094]    A portion of each arm  354  that lies farther as viewed from the front of the magnet system  100  is fixedly attached to pivots  326  and  326 ′. The pivots  326  and  326 ′ are disposed so that the pivot  326  lies nearer and the pivot  326 ′ lies farther as viewed from the front of the magnet system  100 .  
         [0095]    The pivots  326  and  326 ′ protrude outward through a slit portion  308  from the inside of the base section  112 . The pivots  326  and  326 ′ are supported by bearing members provided within the base section  112 .  
         [0096]    The slit portion  308  is an elongated hole extending in parallel with the upper surface of the base section  112 . The bearing members bearing the pivots  326  and  326 ′ are linearly movable along the slit portion  308  by a movement mechanism provided within the base section  112 . FIG. 15 shows the condition in which the pivots  326  and  326 ′ are moved farthest as viewed from the front of the magnet system  100 .  
         [0097]    [0097]FIG. 16 schematically shows an exemplary configuration of the bearing members and movement mechanism provided within the base section  112 . As shown, bearing members  336  and  336 ′ bearing the pivots  326  and  326 ′ are mounted on a carriage  330 .  
         [0098]    The carriage  330  is movable on a rail  332 . The rail  332  runs in parallel with the slit portion  308 . The carriage  330  is joined to a portion of a belt  434  traveling around four pulleys  432 .  
         [0099]    The side of the belt  434  on which the carriage  330  is joined is parallel with the rail  332 , and the span of the side is the same as the length of the rail  332 . At least one of the four pulleys  432  is driven by a motor (not shown) etc. that is reciprocally rotatable.  
         [0100]    Thus, the pivots  326  and  326 ′ can be reciprocally moved along the slit portion  308 , and accordingly, the table  500  supported by the pivots  326  and  326 ′ via the arm  354  can be reciprocally moved over the base section  112 . FIGS. 15 and 16 show the condition in which the arm  354  is moved farthest as viewed from the front of the magnet system  100 . A portion comprised of the carriage  330 , rail  332 , pulleys  432  and belt  434  is an embodiment of the movement mechanism in accordance with the present invention.  
         [0101]    [0101]FIG. 17 shows the condition in which the table  500  is moved nearest as viewed from the front of the magnet system  100 . As shown, in this condition, the table  500  is positioned completely out of the space between the base section  112  and the hood section  116 . That is, the table  500  is positioned protruding nearer than the front of the magnet system  100  off the base section  112 . Thus, the subject to be imaged can get on and off the table  500  without interference from the hood section  116  of the magnet system  100 .  
         [0102]    The table  500  bearing the subject in the condition shown in FIG. 17 is pulled into the space between the base section  112  and the hood section  116  by a retracting operation of the arm  354 . In the condition in which the arm is retracted most, the table  500  reaches a fixed position in the space between the base section  112  and the hood section  116 , as shown in FIG. 15.  
         [0103]    Thus, since the table  500  is mounted on the base section  112  of the magnet system  100  by the mounting mechanism  300 , the positional relationship between the table  500  and the base section  112  for receiving it can be always fixed.  
         [0104]    While the present invention has been described with reference to preferred embodiments, various changes or substitutions may be made on these embodiments by those ordinarily skilled in the art pertinent to the present invention without departing from the technical scope of the present invention. Therefore, the technical scope of the present invention encompasses not only those embodiments described above but all that fall within the scope of the appended claims.  
         [0105]    Many widely different embodiments of the invention may be constructed without departing from the spirit and the scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.