Patent Publication Number: US-2022221538-A1

Title: Rf coil assembly and mri apparatus

Description:
FIELD OF THE INVENTION 
     The invention relates to a RF (radio frequency) coil assembly. More particularly, the present invention relates to a RF coil assembly adapted to be used with a magnetic resonance imaging (MRI) apparatus. The present invention also relates to a MRI apparatus comprising the RF coil assembly. 
     RF coil assemblies are used in MRI apparatus. In addition to “flat” coil assemblies, which are lightweight and would be used for MRI scans on a region of a subject such as the abdomen, there are “curved” coil assemblies, which take a non-planar form. The “curved” coil assemblies have typically a hard plastic housing for enclosing a flexible coil to hold the coil assembly in the desired configuration. The “curved” coil assemblies would be used for MRI scans on the region of the subject such as the head, the shoulder or the ankle where a substantially flat coil assembly is not appropriate. This kind of “curved” coil assemblies is usually cumbersome and fairly heavy. If the size and shape of a “curved” coil assembly required for a particular subject is not available, it can be time-consuming to replace a “curved” coil assembly for that subject. In addition, different “curved” coil assemblies are usually required for different “curved” regions of a subject such as the head, the shoulder or the ankle, which not only increases the cost but also results in difficulty in storage and management of the “curved” coil assemblies. 
     US2008/007250A1 describes an MRI RF coil array comprised of a large number of separate coil elements supported on a substrate shaped to the contour of the anatomy being imaged. However, it requires a contoured substrate and an array of polygonal tiles drawn on the surface of the contoured substrate to position the coil array on the substrate surface, which results in a complicated coil array manufacturing and also makes the positioning and fastening of the coil array to the anatomy burdensome. U.S. Pat. No. 7,526,330B describes an RF coil for imaging parts of a human head which includes upper and lower pairs of RF coils respectively supported by rigid lower and upper supporting structures. WO2019/097863A1 describes a mirror assembly for a RF head coil with a hard plastic housing. 
     Thus, there is a need to make improvements on the known non-planar “curved” coil assemblies. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide non-planar “curved” coil assemblies that are not only lighter and better match the regions of different subjects to be imaged than prior coil assemblies but are also applicable to different “curved” regions of the subject to be imaged. 
     According to one aspect of the present invention, there is provided a RF coil assembly comprising a first rigid frame, and a flexible coil in a naturally planar shape having a first end, a second end opposite the first end and a longitudinal axis extending from the first end to the second end, the first end is attached to the first rigid frame and the second end is away from the first rigid frame, wherein upon attaching the first end of the flexible coil to the first rigid frame, the first rigid frame is shaped to bend the flexible coil to form a shape of the RF coil assembly which conforms to a shape of a region of a subject with multiple contours. According to the present invention, the RF coil assembly is not only lighter and better matches the regions of different subjects but it also may be used as a multiple purpose coil assembly that is applicable to different “curved” regions of the subjects. Furthermore, the RF coil assembly made of a flexible coil attached to a rigid frame can assume the desired shape and can be maintained therein for immediate use instead of having to achieve the desired shape by an operator attaching the flexible coil to body regions. Therefore, the positioning and fastening of the RF coil assembly is much easier and faster as compared to the conventional flexible coil, and the workflow of MRI scanning is enhanced. 
     According to one embodiment of the present invention, the shape of the RF coil assembly comprises a concave contour that conforms to a convex contour of the region of the subject and a half tubular contour that conforms to a half tubular contour of the region of the subject. According to another embodiment of the present invention, the region of the subject comprises any one of anterior part of head, shoulder and ankle. Advantageously, the concave contour portion and the half tubular contour portion of the flexible coil formed as a result of attaching the flexible coil to the first rigid frame can conform to multiple regions of a subject, thereby providing a multiple purpose RF coil assembly. The resulting shape of the RF coil assembly is conceived from the inventor&#39;s observation that the scan regions like the head, the shoulder and the ankle exhibit similar patterns of contours, which include a convex contour and a half tubular contour. The RF coil assembly with the concave contour portion and the half tubular contour portion is designed to conform to the scan regions with such contour patterns. Moreover, the rigid frame allows easier and faster positioning of the RF coil assembly as compared to the conventional flexible coils. 
     According to another embodiment of the present invention, the shape of the first rigid frame conforms to the shape of an anterior part of the top of the head and the flexible coil is bent to conform to the shape of the other portions of the anterior part of the head upon attachment of the flexible coil to the first ridge frame ( 3 ). In this way, the first rigid frame can match the anterior part of the top of the head of the subject to improve the subject&#39;s comfort and the rigidness of the frame allows easy placement of the RF coil assembly on the body regions. 
     According to another embodiment of the present invention, the flexible coil is bent in a first bending region to a substantially concave contour and in a second bending region to a substantially half tubular contour upon attaching the first end of the flexible coil to the first rigid frame, the second bending region being spaced away from the first end and the first bending region extending from the first end to the second bending region. 
     According to another embodiment of the present invention, the first end is curved as a result of the bending along a first bending axis and a second bending axis, the first bending axis is parallel to the longitudinal axis and the second bending axis is perpendicular to the longitudinal axis and in the proximity of the first end, the second end is curved as a result of the bending along the first bending axis, a portion of the sides of the flexible coil in the proximity of the first end is curved as a result of the bending along the second bending axis, wherein a curve bending line is formed in the flexible coil as a result of the bending along the second bending axis, the first bending region is bounded by the curved first end, the curved portion of the sides and the curve bending line, and the second bending region is bounded by the curve bending line, the straight portion of the sides and the curved second end. 
     According to another embodiment of the present invention, the flexible coil comprises a flexible printed circuit board, which is partially covered with foam while a first exposed portion of the flexible printed circuit board projects from the foam, said first exposed portion of the flexible printed circuit board being attached to the first rigid frame. As a result, the RF coil assembly can be assembled easily. 
     According to another embodiment of the present invention, the first rigid frame comprises a first part and a second part that are buckled together to retain the first exposed portion. The first part has a convex surface on a side facing the second part, a plurality of positioning studs project from the convex surface, a plurality of positioning holes are formed in the first exposed portion of the flexible printed circuit board, and the positioning studs pass through the respective positioning holes in the first exposed portion of the flexible printed circuit board, the contour of the convex surface and the distribution of the positioning studs on the convex surface and the positioning holes in the first exposed portion are configured in such a way that the flexible coil has the concave contour in the proximity of the first end and the half tubular contour in the remaining portion of the flexible coil. As a result, it is unnecessary to perform any complicated operation during assembly of the RF coil assembly. 
     According to another embodiment of the present invention, the RF coil assembly further comprises a second rigid frame attached to the second end of the flexible coil. The second rigid frame helps maintain the shape of the RF coil assembly and is convenient for an operator to hold the RF coil assembly. 
     According to another embodiment of the present invention, the RF coil assembly further comprises a control board and a pre-amplifier housed between the first part and the second part. The control board and the pre-amplifier housed within the rigid frame are not damaged easily. 
     According to another embodiment of the present invention, the RF coil assembly further comprises a hinge mechanism to hinge detachably the first rigid frame to a support. The hinge mechanism allows the RF coil assembly to pivot relative to the support to receive the region of the subject. 
     According to another embodiment of the present invention, the hinge mechanism comprises a pair of movable blocks each having a pivot shaft, a spring for acting on the movable blocks to move the movable blocks away from each other, and an operating plate for abutting against the movable blocks to move the movable blocks toward each other to retract the pivot shafts. In this way, the RF coil assembly may be detached easily from the support. 
     According to another embodiment of the present invention, the RF coil assembly can be hinged detachably to a base coil assembly to form together a head coil assembly, the base coil assembly comprising a pair of support ribs for supporting the flexible coil of the RF coil assembly when the RF coil assembly is in a closed position. In this way, the RF coil assembly can be used as (?) a top coil assembly of a head coil assembly. 
     According to another embodiment of the present invention, the second end is flexible so that the sides of the flexible coil at the second end can be compressed toward each other to pivot the flexible coil into a space between the pair of support ribs. In this way, the flexible coil may better match a small size of the subject&#39;s head, thereby obtaining a high quality image. 
     According to another aspect of the present invention, it is an object to provide a MRI apparatus comprising the RF coil assembly. 
     These and other objects, features and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a RF coil assembly according to a preferred embodiment of the present invention. 
         FIG. 2  is another perspective view of the RF coil assembly as shown in  FIG. 1 . 
         FIG. 3  is a perspective view showing a first part of a first rigid frame of the RF coil assembly as shown in  FIG. 1 . 
         FIG. 4  is another perspective view of the first part of the first rigid frame as shown in  FIG. 3 . 
         FIG. 5  is a perspective view showing a second part of a first rigid frame of the RF coil assembly as shown in  FIG. 1 . 
         FIG. 6  is another perspective view of the second part of the first rigid frame as shown in  FIG. 5 . 
         FIG. 7  is a perspective view showing a flexible coil of the RF coil assembly as shown in  FIG. 1 . 
         FIG. 8  is a partial perspective view showing the flexible coil attached to the first part of the first rigid frame. 
         FIG. 9  is a perspective view similar to  FIG. 8  with a positioning pad disposed on the flexible coil. 
         FIG. 10  is an exploded perspective view showing a hinge mechanism of the RF coil assembly as shown in  FIG. 1 . 
         FIG. 11  is a partial cross section showing the hinge mechanism as shown in  FIG. 10 . 
         FIG. 12  is a perspective view showing the hinge mechanism as shown in  FIG. 10  in a first position. 
         FIG. 13  is a perspective view showing the hinge mechanism as shown in  FIG. 10  in a second position. 
         FIG. 14  is a perspective view showing the RF coil assembly as shown in  FIG. 1  and a base coil assembly on which the RF coil assembly can be mounted. 
         FIG. 15  is a perspective view showing the RF coil assembly as shown in  FIG. 1  mounted on the base coil assembly being in a closed position. 
         FIG. 16  is another perspective view showing the RF coil assembly as shown in  FIG. 1  mounted on the base coil assembly being in a closed position. 
         FIG. 17  is a side view showing the RF coil assembly as shown in  FIG. 1  mounted on the base coil assembly being in an opened position. 
         FIG. 18  is a top view showing the RF coil assembly as shown in  FIG. 1 , used as part of a head coil assembly. 
         FIGS. 19 and 20  are perspective views showing the RF coil assembly well matching the head of different subjects while being used as part of a head coil assembly. 
         FIG. 21  is a top view showing the RF coil assembly as shown in  FIG. 1 , used as a shoulder coil assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
       FIG. 1  is a perspective view showing a RF coil assembly according to a preferred embodiment of the present invention.  FIG. 2  is another perspective view of the RF coil assembly as shown in  FIG. 1 . As shown in  FIGS. 1 and 2 , a RF coil assembly  1  according to the present invention comprises a first rigid frame  3  and a flexible coil  5  attached to the first rigid frame  3 .  FIG. 7  is a perspective view showing a flexible coil of the RF coil assembly in a naturally planar shape. The flexible coil  5  has a first end  5   a , a second end  5   b  opposite the first end  5   a , and two opposite sides  5   c ,  5   d  between the first end  5   a  and the second end  5   b . The flexible coil  5  has a longitudinal axis L extending substantially from the first end  5   a  to the second end  5   b  and a traverse axis T perpendicular to the longitudinal axis L. The flexible coil  5  substantially extends in a plane defined by the longitudinal axis L and the traverse axis T and thus is initially in a planar shape before the flexible coil  5  is attached to the first rigid frame  3 . That is, when no external force acts on the flexible coil  5 , a natural shape of the flexible coil  5  is planar as shown in  FIG. 7 . The flexible coil  5  has an inner surface  5   e  configured to be placed over a region of subject and an external surface  5   f  opposite the inner surface  5   e . The first rigid frame  3  is shaped to bend the flexible coil  5  along a first bending axis Y parallel to the longitudinal axis L and to further bend the flexible coil  5  along a second bending axis X perpendicular to the longitudinal axis L (or parallel to the traverse axis T) when the first end  5   a  of the flexible coil  5  is attached to the first rigid frame  3 . The bending along the first bending axis Y forms approximately a 180 degree bend, giving the initially planar flexible coil  5  a substantially half tubular shape. A bending angle produced by bending along the second bending axis X is determined to conform to any of the bending angle of the curve of the anterior part of the top of the head, for example the curve running from the top of the head to the forehead, the bending angle of the curve of the shoulder point and the bending angle of the curve of the heel. Since the bending angles of these curves have a close resemblance, the bending angle as determined above can conform to any of these curves. In addition, as the flexible coil  5  is attached to the first rigid frame  3  at the first end  5   a , the second bending axis X is a in the proximity of the first end  5   a  and only the region of the flexible coil  5  in the proximity of the first end  5   a  experiences the bending along the second bending axis X. As a result of the bending along the second axis X, the first end  5   a  is pushed inward towards the second end  5   b  of the flexible coil  5  to further bend a portion of the flexible coil  5  at the first end  5   a  so that a substantially semicircular shape is formed in the proximity of the first end  5   a  and a bending line B is formed in the flexible coil  5 . 
     As such, a first bending region bounded by the curved first end  5   a , the curved portion of the sides  5   c ,  5   d  of the flexible coil  5  and the bending line B is formed into a substantially concave contour as a result of the bending actions along the first and second bending axes X and Y. The concave contour conforms to the curve of the anterior part of the top of the head, the shoulder point and the heel. A second bending region bounded by the bending line B, the straight portion of the sides of the flexible coil  5  and the curved second end  5   b  is formed into a substantially half tubular contour as a result of the bending along the first bending axis Y. The half tubular contour conforms to the curve of the face, the upper arm and lower leg. The longitudinal length and the transverse width of the flexible coil  5  are sized such that the regions of the subject can be received in the first bending region and the second bending region. Advantageously, the flexible coil  5  is bent into a curvature with multiple curve contours, e.g., the concave contour and the half tubular contour, to conform to the complicated curvature of the region of the subject. Moreover, the contour pattern of the concave contour and half tubular contour combination of the RF coil assembly  1  conforms to that of multiple regions of the subject, e.g., the anterior of the head, the shoulder and the ankle. Therefore, the RF coil assembly shaped into the specific curvature can be used as a multiple purpose coil. 
       FIG. 3  is a perspective view showing a first part of a first rigid frame of the RF coil assembly as shown in  FIG. 1 .  FIG. 4  is another perspective view of the first part of the first rigid frame as shown in  FIG. 3 .  FIG. 5  is a perspective view showing a second part of a first rigid frame of the RF coil assembly as shown in  FIG. 1 .  FIG. 6  is another perspective view of the second part of the first rigid frame as shown in  FIG. 5 . As shown in  FIGS. 3-6 , in one embodiment, the first rigid frame  3  comprises a first part  7  and a second part  9  that are separately injection moulded. The first part  7  and the second part  9  can be buckled together to form the first rigid frame  3 . The first part  7  has a concave surface  7   b  configured to be placed over the region of the subject and a convex surface  7   a  opposite the concave surface  7   b . A plurality of positioning studs  11  and a plurality of threaded studs  13  project from the convex surface  7   a . The second part  9  has a concave surface  9   a  which corresponds to the convex surface  7   a  of the first part  7  and a hinge mechanism seat  15  on a convex surface  9   b  opposite the concave surface  9   a.    
     As the concave surface  7   b  is configured to be placed over the region of the subject, e.g., the anterior part of the top of the head, it can be shaped to slope downwards from the top of the head towards the forehead. As the curve of the top of the head has a close resemblance to the curve of the shoulder and posterior end of the foot, the concave surface  7   b  as shaped above is readily applicable to the other regions, e.g., the shoulder and the posterior end of the foot. The flexible coil  5  is attached to the corresponding convex surface  7   a  to form the first bending region which extends smoothly from the convex surface  7   a  and slopes down to the bending line B. As such, the concave surface of the first rigid frame  3  and the inner concave surface of the first bending region of the flexible coil  5 , which are placed over the region of the subject, can better conform to the convex contour, e.g., the curve from the top of the head down to the forehead. The inner half tubular surface of the second bending region conforms to the half tubular contour of the face. Advantageously, the overall RF coil assembly results in the concave contour and half tubular contour which conform to the region of the subject comprised of multiple contours, e.g., the convex contour and the half tubular contour of the head, shoulder or ankle. 
     Alternatively, the first rigid frame  3  is shaped into half of a spherical cap to be placed over the upper top of the head. When the flexible coil  5  is attached to the convex surface  7   a  in the hemispherical cap shape, the flexible coil  5  is shaped into the concave bending region and the half tubular bending region. The overall RF coil assembly thereby better conforms to the region of the subject which comprises the convex contour and half tubular contour. Similarly, the concave surface  7   b  can also be shaped into a half bowl shape for the purpose of producing the overall RF coil assembly which better conforms to the region of the subject comprised of multiple contours. It is contemplated by those skilled in the art that the shapes described herein, e.g., the semicircular, the concave, the half tubular, the convex, the hemispherical cap, the half bowl, etc., are not precise but include the shape with a close resemblance to the described shape. 
     Advantageously, the overall RF coil assembly can conform to multiple regions which have similar but complex contours, e.g., the convex and the half tubular contour of the head, shoulder and ankle. Moreover, the first rigid frame  3  makes the positioning and fastening of the RF coil assembly easier and faster as compared to the conventional flexible coil. When used as the head top coil, the RF coil assembly can replace the conventional rigid head top coil to be attached directly to the conventional head base, resulting in an upgrade of the conventional rigid head coil to the head coil of the present invention with minimum cost and effort. Furthermore, the second end  5   b  distal to the first rigid frame  3  is still kept flexible, allowing it to be deformed to better conform to subjects of various sizes or the different regions of the subject. 
       FIG. 7  is a perspective view showing a flexible coil of the RF coil assembly as shown in  FIG. 1 . As shown in  FIG. 7 , the flexible coil  5  is flat before being attached to the first rigid frame  3 . The flexible coil  5  comprises a flexible printed circuit board  17 . The flexible printed circuit board  17  is partially covered with biocompatible foam  19 , while a first exposed portion  21  of the flexible printed circuit board  17  projects from the foam  19  at the first end  5   a  of the flexible coil  5 . The foam  19  can be applied by a thermoforming method using moulds or by a layered method using foam and adhesives. There are a plurality of positioning holes  23  in the first exposed portion  21  of the flexible printed circuit board  17 . In one embodiment, there is a second exposed portion  25  at a second end  5   b  of the flexible coil  5  opposite the first end  5   a . A few openings  27  are formed in the flexible coil  5  to allow the subject&#39;s eyes, ears, nose and mouth not to be covered by the flexible coil  5 , while the RF coil assembly is used as a top of the head coil assembly, thereby improving the subject&#39;s comfort. 
       FIG. 8  is a partial perspective view showing the flexible coil attached to the first part of the first rigid frame.  FIG. 9  is a perspective view similar to  FIG. 8  with a positioning pad disposed on the flexible coil. When the RF coil assembly is assembled, as shown in  FIG. 8 , the flexible coil  5  is first attached to the first part  7  of the first rigid frame  3 , with the positioning studs  11  on the convex surface  7   b  of the first part  7  passing through the respective positioning holes  23  in the first exposed portion  21  of the flexible printed circuit board  17 . The contour of the convex surface  7   b  and the distribution of the positioning studs  11  on the convex surface  7   a  of the first part  7  and the positioning holes  23  in the first exposed portion  21  are configured in such a way that the flexible coil  5  is bent into the concave contour in the proximity of the first end  5   a  and the half tubular contour in the remaining portion of the flexible coil after the flexible coil  5  is attached to the first part  7  of the first rigid frame  3 . By means of the positioning studs  11  on the convex surface  7   a  of the first part  7  and the positioning holes  23  in the first exposed portion  21 , it is very easy to attach the flexible coil  5  to the first part  7  and maker the flexible coil  5  have the desired contour. 
     A positioning pad  29  may be disposed on the first exposed portion  21  of the flexible printed circuit board  17  attached to the first part  7  to prevent the first exposed portion  21  from shifting relative to the first part  7 . After other possible electronic devices, such as a control board and a pre-amplifier of the RF coil assembly, are connected with the first exposed portion  21 , the second part  9  is buckled onto the first part  7 . Then, the first part  7  and the second part  9  are fastened together by screws passing through the second part  9  and threaded into the threaded studs  13  on the first part  7  so that the first exposed portion  21  of the flexible printed circuit board  17  and the other possible electronic devices of the RF coil assembly are securely retained between the first part  7  and the second part  9  to form the RF coil assembly  1 . The control board and the pre-amplifier are housed within the rigid frame  3  so that they are not damaged easily. Preferably, the RF coil assembly  1  may comprise a second rigid frame  30  at the second end  5   b  of the flexible coil  5  to securely retain the second exposed portion  25 . The second rigid frame  30  may be in a handle shape so that it helps to maintain the shape of the RF coil assembly  1  and it is convenient for an operator to hold the RF coil assembly  1 . Of course, it is feasible that the second rigid frame  30  is disposed at the foam-covered portion of the flexible coil  5  without the second exposed portion at the second end  5   b.    
     The RF coil assembly  1  according to the present invention may further comprise a retractable hinge mechanism  31  mounted onto the hinge mechanism seat  15  of the second part  9  and an interface  32  provided at the second part  9  of the first rigid frame  3  in electrical communication with the flexible coil  5 .  FIG. 10  is an exploded perspective view showing a hinge mechanism of the RF coil assembly as shown in  FIG. 1 . As shown in  FIG. 10 , the retractable hinge mechanism  31  comprises a bracket  33  and a pair of movable blocks  35 . The bracket  33  has a pair of side plates  33   a  facing each other. Each of the movable blocks  35  has a pivot shaft  35   a  projecting from a side of the main body of the movable block and a blind hole  35   b  formed in the main body opposite the pivot shaft  35   a . The movable blocks  35  each have a skewed slot  35   c  having a bevel  35   d . The movable blocks  35  are disposed between the pair of side plates  33   a  of the bracket  33 , with the pivot shaft  35   a  extending through a through hole  33   b  in the side plates  33   a . Two ends of a spring  37  are received within the blind hole  35   b  of the movable blocks  35  so that the movable blocks  35  always move away from each other. The hinge mechanism  31  further comprises an operating plate  39  having an operating button  39   a  formed at one end and two projections  39   b  at the other end.  FIG. 11  is a partial cross section showing the hinge mechanism as shown in  FIG. 10 . After the operating plate  39  is mounted in place by a fixing plate  41  which is fastened onto the bracket  33  by screws  43 , the operating button  39   a  of the operating plate  39  extends through an opening  33   d  in the bracket  33  to be accessible from outside and two projections  39   b  extend into the skewed slot  35   c  of the respective movable blocks  35  to abut against the bevel  35   d , as shown in  FIG. 11 . 
       FIG. 12  is a perspective view showing the hinge mechanism as shown in  FIG. 10  in a first position.  FIG. 13  is a perspective view showing the hinge mechanism as shown in  FIG. 10  in a second position. In a usual state, the pivot shaft  35   a  of each movable block  35  projects from the through hole  33   b  in the side plates  33   a  under an action of the spring  37 , as shown in  FIG. 12 . When the operating button  39   a  of the operating plate  39  is pulled upward relative to the bracket  33 , the two projections  39   b  abut against the bevel  35   d  of the respective movable blocks  35  and move the movable blocks  35  toward each other so that the pivot shaft  35   a  of each movable block  35  retracts relative to the bracket  33 , as shown in  FIG. 13 . When the operating button  39   a  of the operating plate  39  is released, the spring  37  pushes the pivot shafts  35   a  of the movable blocks  35  to project from the through hole  33   b  in the side plates  33   a  again, as shown in  FIG. 12 . It should be understood that the hinge mechanism  31  can be implemented in other ways. For example, the movable blocks  35  and the operating plate  39  may be configured in such a way that the pivot shaft  35   a  of each movable block  35  retracts relative to the bracket  33  when the operating plate  39  moves downward relative to the bracket  33 . Further, the bracket  33  may be omitted and a portion of the first rigid frame  3  may function as the bracket  33 . 
       FIG. 14  is a perspective view showing the RF coil assembly as shown in  FIG. 1  and a base coil assembly on which the RF coil assembly can be mounted. The base coil assembly  45  is configured to support the subject&#39;s head when the subject&#39;s head is imaged and comprises a coil disposed within a rigid housing. There are a pair of support arms  47  on the base coil assembly  45 . A hole  49  for receiving the pivot shaft  35   a  of the movable block  35  is formed in each of the support arms  47  so that the RF coil assembly  1  may be mounted detachably onto the base coil assembly  45 . Specifically, when it is necessary to mount the RF coil assembly  1  onto the base coil assembly  45 , the operating button  39   a  of the operating plate  39  is pulled upward so that the pivot shaft  35   a  of each movable block  35  retracts. While the pivot shaft  35   a  of each movable block  35  is in alignment with the hole  49  in the support arms  47 , the operating button  39   a  of the operating plate  39  is released and the pivot shaft  35   a  extends into the respective hole  49 . As a result, the RF coil assembly  1  is mounted pivotally onto the base coil assembly  45  to form together a head coil assembly. When the operating button  39   a  of the operating plate  39  is pulled upward again, the RF coil assembly  1  is detachable from the base coil assembly  45 . There are a pair of support ribs  51  on the base coil assembly  45 . The support ribs  51  support the flexible coil  5  of the RF coil assembly  1  when the RF coil assembly  1  is in a closed position, as shown in  FIGS. 15 and 16 . There is an interface  53  in electrical communication with an Analog to Digital Converter of a MRI apparatus.  FIG. 15  is a perspective view showing the RF coil assembly as shown in  FIG. 1  mounted on the base coil assembly  45  being in a closed position.  FIG. 16  is another perspective view showing the RF coil assembly as shown in  FIG. 1  mounted on the base coil assembly  45  being in a closed position.  FIG. 17  is a side view showing the RF coil assembly as shown in  FIG. 1  mounted on the base coil assembly  45  being in an opened position. By grasping the second rigid frame  30 , it is very easy for the operator to pivot the RF coil assembly from the closed position to the opened position or from the opened position to the closed position.  FIG. 18  is a top view showing the RF coil assembly  1  used as a part of a head top coil assembly to scan the subject&#39;s head. It should be understood that the RF coil assembly  1  can be detachably attached to another support such as a subject support couch. 
       FIGS. 19 and 20  are perspective views showing the RF coil assembly matching the head of different subjects while being used as a part of a head top coil assembly. Generally, in the closed position, the flexible coil  5  of the RF coil assembly  1  is supported on the support ribs  51  on the base coil assembly  45  to match the shape and size of a majority of subjects. However, as shown in  FIG. 19 , since the second end  5   b  always has flexibility, by compressing the sides  5   c ,  5   d  of the flexible coil  5  at the second end  5   b  toward each other and pivoting the flexible coil  5  down into a space between the support ribs  51 , the flexible coil  5  may better match a subject&#39;s head of a small size, thereby obtaining a high quality image. Compared with  FIG. 19 , the flexible coil  5  as shown in  FIG. 20  is pivoted down much more to match a child&#39;s head. 
       FIG. 21  is a top view showing the RF coil assembly as shown in  FIG. 1  used as a shoulder coil assembly. As shown in  FIG. 21 , the RF coil assembly  1  is detached from the base coil assembly  45  and used as a shoulder coil assembly. The RF coil assembly  1  according to the present invention also matches well a subject&#39;s shoulder. Of course, the RF coil assembly  1  also matches well a subject&#39;s ankle and thus may be used as an ankle coil assembly. 
     Although the invention has been described in detail for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims.