Abstract:
In order to mitigate the feeling of confinement experienced by a subject (patient) and improve the SIN ratio of an MRI coil when used as a head coil, there is provided an MRI coil  10  comprising a pair of opposing coils  1  and  2  whose coil surfaces face each other with an imaging space interposed, and a quadrature coil  3  which has a coil surface orthogonal to the coil surfaces of the opposing coils  1  and  2  and surrounds the imaging space. When the MRI coil  10  is used as a head coil, the quadrature coil  3  is fitted over the eyes of a subject H, and the opposing coils  1  and  2  are positioned near the ears of the subject H.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an MRI (magnetic resonance imaging) coil, and more particularly, to an MRI coil capable of mitigating feeling of confinement experienced by a subject (patient) and improving the S/N ratio when used as a head coil.  
           [0002]    An example of a conventional MRI head coil is shown in FIG. 1.  
           [0003]    The MRI head coil  70  has a cylindrical shape containing an imaging space therein for accommodating the head of a subject H.  
           [0004]    The conventional MRI head coil  70  has the following problems:  
           [0005]    (1) Since the coil has a cylindrical shape enveloping the head of the subject H and has few opening portions, visual and auditory perception of the subject H is extensively restricted and the subject&#39;s exhaled breath fills the coil, giving the subject H a confined feeling.  
           [0006]    (2) Since the coil envelops the head of the subject H, the coil requires a cavity having a greater size than the distance from the tip of the nose to the back of the head, and the coil therefore cannot be significantly reduced in size. Thus, because the distance between the subject H and the coil cannot be reduced, the S/N ratio is lowered.  
         SUMMARY OF THE INVENTION  
         [0007]    It is an object of the present invention to provide an MRI coil capable of mitigating the confined feeling experienced by a subject (patient) and improving the S/N ratio when used as a head coil.  
           [0008]    In accordance with a first aspect of the present invention, there is provided an MRI coil comprising a pair of opposing coils whose coil surfaces face each other with an imaging space interposed, and a quadrature coil which has a coil surface orthogonal to the coil surfaces of the opposing coils and surrounds the imaging space.  
           [0009]    When the MRI coil of the first aspect is used as a head coil, the quadrature coil is fitted over the head of the subject, and the opposing coils are positioned near the ears of the subject. In this condition, the quadrature coil overhangs the eyes of the subject, but does not cover the head top, nose or mouth. The opposing coils are placed near the ears of the subject, but do not completely cover the ears. Moreover, the exhaled breath of the subject does not fill the coil. Hence, the coil does not give the subject a confined feelings Furthermore, since the quadrature coil does not cover the nose, the coil does not require a cavity having a greater size than the distance from the tip of the nose to the back of the subject H&#39;s head, and the coil can be reduced in size. The reduced size shortens the distance between the subject and the coil, thereby improving the S/N ratio.  
           [0010]    In accordance with a second aspect of the present invention, there is provided the MRI coil as described regarding the first aspect, wherein the opposing coils and the quadrature coil are integrally combined so that their positions relative to one another are maintained unchanged, and part of the coil surfaces of the opposing coils are opened outward.  
           [0011]    A coil is preferably disposed as close to the subject as possible in order to improve the S/N ratio. Accordingly, the spacing between the opposing coils is made slightly greater than the size of the subject. However, this may result in difficulties in fitting the coil over the head of the subject when the coil is used as a head coil. The MRI coil of the second aspect has part of the coil surfaces of the opposing coils opened outward, facilitating fitting of the coil over the head of the subject. Moreover, since the opposing coils and the quadrature coil are integrally combined so that their relative positions remain unchanged, the coil requires no pivotal attachment mechanism, thereby simplifying the structure.  
           [0012]    In accordance with a third aspect of the present invention, there is provided the MRI coil as described regarding the first aspect, wherein the opposing toils are pivotally attached to the quadrature coil, and the pair of opposing coils is allowed to be opened in an inverted V-like shape.  
           [0013]    A coil is preferably disposed as close to the subject as possible in order to improve the S/N ratio. Accordingly, the spacing between the opposing coils is made slightly greater than the size of the subject. However, this may result in difficulties in fitting the coil over the head of the subject when the coil is used as a head coil. The MRI coil of the third aspect has the pair of opposing coils that is allowed to be opened in an inverted V-like shape, facilitating fitting of the coil over the head of the subject. Moreover, this eliminates the need to form part of the opposing coils in an opened shape, thereby simplifying the shape of the opposing coils.  
           [0014]    The MRI coil of the present invention may be used as, for example, a knee coil for imaging the knee.  
           [0015]    In accordance with a fourth aspect of the present invention, there is provided an MRI apparatus comprising static magnetic field generating means for generating a static magnetic field to be applied to a subject during image capture, wherein the MRI coil as described regarding any of the first through third aspects is employed to acquire NMR signals from the subject.  
           [0016]    The MRI coil and MRI apparatus of the present invention can thus mitigate feeling of confinement experienced by a subject (patient) and improve the S/N ratio when the coil is used as a head coil.  
           [0017]    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  
       [0018]    [0018]FIG. 1 is a perspective view of a conventional MRI head coil.  
         [0019]    FIGS.  2  ( a ) - ( c ) are views taken from three orthogonal directions of an MRI head coil in accordance with the first embodiment of the present invention.  
         [0020]    [0020]FIG. 3 illustrates the MRI head coil of FIG. 2 prior to being fitted over a subject.  
         [0021]    [0021]FIG. 4 illustrates the MRI head coil of FIG. 2 fitted over the subject.  
         [0022]    [0022]FIG. 5 is a perspective view of an MRI head coil in accordance with the second embodiment of the present invention.  
         [0023]    [0023]FIG. 6 illustrates the configuration of a vertical magnet MRI apparatus in accordance with the third embodiment of the present invention.  
         [0024]    [0024]FIG. 7 illustrates imaging of the head in the vertical magnet MRI apparatus of FIG. 6.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    The present invention will now be described in more detail with reference to its embodiments shown in the accompanying drawings.  
         [0026]    First Embodiment  
         [0027]    FIGS.  2 ( a ) - ( c ) are respectively a front elevational view, a right side view and a plain view of an MRI head coil in accordance with the first embodiment of the present invention.  
         [0028]    The MRI head coil  10  comprises a pair of opposing coils  1  and  2  whose coil surfaces face each other with an imaging space interposed, and a quadrature coil  3  which has a coil surface orthogonal to the coil surfaces of the opposing coils  1  and  2  and surrounds the imaging space.  
         [0029]    The opposing coils  1  and  2  have a generally circularly annular shape as a whole, except that their respective front peripheral portions  1   a  and  2   a  are opened outward.  
         [0030]    The quadrature coil  3  has a generally track-like annular shape (i.e., an annular shape consisting of semicircles and straight lines like a race track for field sports).  
         [0031]    The opposing coils  1  and  2  and the quadrature coil  3  are integrally combined so that their relative positions are maintained unchanged.  
         [0032]    [0032]FIG. 3 illustrates the MRI head coil  10  being fitted over the head of a subject.  
         [0033]    A cradle C is provided with a head rest R for supporting the head of the subject H a certain distance above the cradle C, and a concave portion K for inserting the MRI head coil  10  below the head rest R. The MRI head coil  10  is set behind the head of the subject H.  
         [0034]    First, the subject H is laid on the cradle C at a position such that the head of the subject H is supported by the head rest R.  
         [0035]    The MRI head coil  10  is then slid to be fitted over the head of the subject H. That is, the MRI head coil  10  is slid to a position at which the quadrature coil  3  overhangs the eyes of the subject H.  
         [0036]    [0036]FIG. 4 is a cross sectional view illustrating the MRI head coil  10  fitted over the head of the subject H.  
         [0037]    The opposing coils  1  and  2  are electrically connected so that their currents flow in the same direction (the connection may be either serial or parallel), to constitute so-called Helmholtz coils. This generates a homogeneous magnetic field in the imaging space between the opposing coils  1  and  2 .  
         [0038]    The quadrature coil  3  is “quadrature connected” with respect to the opposing coils  1  and  2 . This achieves effective reception of NMR signals.  
         [0039]    The above-described MRI head coil  10  offers the following advantages:  
         [0040]    (1) The quadrature coil  3  overhangs the eyes of the subject H, but does not cover the head top, nose or mouth. The opposing coils  1  and  2  are placed near the ears of the subject H, but do not completely cover the ears. Moreover, the exhaled breath of the subject H does not fill the coil. Hence, the coil does not give the subject H a confined feeling.  
         [0041]    (2) Since the quadrature coil  3  does not cover the nose, the coil does not require a cavity having a greater size than the distance from the tip of the nose to the back of the subject H&#39;s head, and the coil may be reduced in size. The reduced size shortens the distance between the subject H and the coil, thereby improving the S/N ratio.  
         [0042]    (3) Since the front peripheral portions  1   a  and  2   a  of the opposing coils  1  and  2  are opened outward, the coil is easy to fit over the head of the subject H.  
         [0043]    (4) Since the opposing coils  1  and  2  and the quadrature coil  3  are integrally combined so that their relative positions are maintained unchanged, the coil requires no pivotal attachment mechanism, thereby simplifying the structure.  
         [0044]    Second Embodiment  
         [0045]    [0045]FIG. 5( a ) is a perspective view of coils in an MRI head coil in accordance with the second embodiment of the present invention.  
         [0046]    The MRI head coil  20  comprises a pair of opposing coils  4  and  5  whose coil surfaces face each other with an imaging space interposed, and a quadrature coil  6  which has a coil surface orthogonal to the coil surfaces of the opposing coils  4  and  5  and surrounds the imaging space.  
         [0047]    The opposing coils  4  and  5  have a generally circularly annular shape.  
         [0048]    The quadrature coil  6  has a generally track-like annular shape.  
         [0049]    The opposing coils  4  and  5  and the quadrature coil  6  are integrally combined by means of covers  14  -  16  as will be described hereinafter.  
         [0050]    [0050]FIG. 5 (b) is a perspective view of the covers for the MRI head coil  20 .  
         [0051]    The opposing coil  4  is contained in a left cover  14 . The opposing coil  5  is contained in a right cover  15 . The quadrature coil  6  is contained in a central cover  16 .  
         [0052]    The left and right covers  14  and  15  are pivotally attached to the central cover via hinges, and are allowed to be opened in an inverted V-like shape. That is, the opposing coils  4  and  5  are allowed to be opened in an inverted V-like shape.  
         [0053]    [0053]FIG. 5 ( c ) is a perspective view of the MRI head coil  20  with its covers  14  and  15  opened.  
         [0054]    While the opposing coils  4  and  5  shown in FIG. 5 ( c ) are opened in an inverted V-like shape in the horizontal direction, the opposing coils can instead be configured to be opened in a V-like shape in the upward or downward direction.  
         [0055]    The above-described MRI head coil  20  offers the following advantages:  
         [0056]    (1) Since the coil has a large opening portion, the coil intercepts only a small portion of the field of view of the subject H and is not filled with the exhaled breath of the subject H, thereby giving the subject H no feeling of confinement.  
         [0057]    (2) Since the quadrature coil  6  does not cover the nose, the coil does not require a cavity having a greater size than the distance from the tip of the nose to the back of the subject H&#39;s head, and the coil can be reduced in size. The reduced size shortens the distance between the subject H and the coil, thereby improving the S/N ratio.  
         [0058]    (3) Since the opposing coils  4  and  5  are opened in an inverted V-like shape, the coil is easy to fit over the head of the subject H.  
         [0059]    (4) The opposing coils  4  and  5  can have a simple shape.  
         [0060]    Third Embodiment  
         [0061]    [0061]FIG. 6 illustrates the configuration of a vertical magnet MRI apparatus employing the MRI head coil of the present invention.  
         [0062]    The vertical magnet MRI apparatus  100  comprises a vertical magnet apparatus  30 , a movable chair  40  and a movable table (not shown).  
         [0063]    The vertical magnet apparatus  30  has a vertical opposing magnet  31  whose opposing surface is vertically disposed, another vertical opposing magnet  32  (not shown) which is disposed opposite to the magnet  31 , a rail  33  ( 34 ) provided on the opposing surface of the vertical opposing magnet  31  ( 32 ), a table stopper apparatus (not shown) and a chair stopper apparatus  35 .  
         [0064]    The rail  33  ( 34 ) is provided for supporting the cradle coming out of the movable table.  
         [0065]    The table stopper apparatus and the chair stopper apparatus  35  are provided with connectors for establishing electrical connection with the movable table or the movable chair  40 .  
         [0066]    The movable chair  40  has a supporting panel  41  for supporting the MRI head coil  10  slidably in the vertical direction.  
         [0067]    In imaging operation, the subject H is seated on the movable chair  40  with the movable chair  40  drawn out of the vertical magnet apparatus  30  as shown in FIG. 6. At this time, the MRI head coil  10  is raised. Then the MRI head coil  10  is lowered to be fitted over the head of the subject H. Subsequently the movable chair  40  is moved into the space between the opposing surfaces of the vertical magnet apparatus  30  as shown in FIG. 7. Thereafter, the imaging is performed.  
         [0068]    The above-described vertical magnet MRI apparatus  100  allows imaging of the head to be easily done with a subject seated on a chair.  
         [0069]    Many widely different embodiments of the invention may be configured 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.