Abstract:
The present invention aims to provide an RF coil assembly capable of eliminating the need for connecting and disconnecting an electric path at decoupling portions and is an RF coil assembly including: a plurality of coil loops that are adjacent to each other in sequence and construct a phased array; and a plurality of decoupling device that cancel electromagnetic coupling between adjacent coil loops, respectively, wherein at least two of the plurality of coil loops are two coil loops that are adjacent to each other across a boundary where they can be decoupled from each other, and wherein at least one of the plurality of decoupling device is two coils that are connected in series to the two coil loops, respectively, and are opposed to each other across the boundary and form a pair of coils for decoupling.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Japanese Application No. 2005-316187 filed Oct. 31, 2005. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an RF coil assembly (radio frequency coil assembly) and, in particular, to a phased array type RF coil assembly for an MRI (magnetic resonance imaging) apparatus. 
     In an MRI apparatus performing parallel imaging and the like, a magnetic resonance signal from an object is received by a plurality of RF coils. The signals received by the plurality of RF coils are received by a plurality of receivers. 
     The plurality of RF coils construct a phased array. In the phased array, there is provided a decoupling means in order to prevent the adjacent RF coils from being magnetically coupled to each other (refer to, for example, a patent document 1) 
     [Patent document 1] Japanese Unexamined Patent Publication No. 2002-119495 (pages 3 and 4, FIGS. 1 and 2) 
     In the case of constructing an RF coil assembly in the shape of a cylinder, in order to enhance a filling factor and at the same time to facilitate mounting and dismounting the RF coil assembly on and from an object, there are cases where the RF coil assembly can be decoupled, for example, in an anterior and posterior direction. In this case, it is desired to eliminate the need for connecting and disconnecting an electric path including a decoupling means at decoupling portions. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to realize an RF coil assembly that eliminates the need for connecting and disconnecting an electric path at decoupling portions. 
     The present invention to solve the above problem is an RF coil assembly including: a plurality of coil loops that are adjacent to each other in sequence and construct a phased array; and a plurality of decoupling means that cancel electromagnetic coupling between adjacent coil loops, respectively, and characterized in that at least two of the plurality of coil loops are two coil loops that are adjacent to each other across a boundary where they can be decoupled from each other, and in that at least one of the plurality of decoupling means is two coils that are connected in series to the two coil loops and are opposed to each other across the boundary and form a pair of coils for decoupling. 
     It is preferable in terms of decoupling the RF coil assembly into two parts that two of the plurality of coil loops are two coil loops that are adjacent to each other across a first boundary where they can be decoupled from each other and form a first pair of coil loops, that one of the plurality of decoupling means is two coils that are respectively connected in series to the two coil loops forming the first pair of coil loops, and are opposed to each other across the first boundary and form a first pair of coils for decoupling, that other two of the plurality of coil loops are two coil loops that are adjacent to each other across a second boundary where they can be decoupled from each other and form a second pair of coil loops, and that another of the plurality of decoupling means is two coils that are respectively connected in series to the two coil loops forming the second pair of coil loops, and are opposed to each other across the second boundary and form a second pair of coils for decoupling. 
     It is preferable in terms of decoupling the RF coil assembly into the respective coil loops that all of the remainder of the plurality of coil loops are coil loops that are adjacent to each other across a boundary where they can be decoupled from each other, and that the all of the remainder of the plurality of decoupling means are two coils that are respectively connected in series to the two coil loops forming the pair of coil loops, and are opposed to each other across the boundary and form a pair of coils for decoupling. 
     It is preferable in terms of carrying out decoupling with ease that a decoupling means except the pair of coils for decoupling is two coils that are connected in series to two adjacent coil loops, respectively, and are opposed to each other and form a pair of coils for decoupling. 
     It is preferable in terms of eliminating the need for providing a coil for decoupling that a decoupling means except the pair of coils for decoupling is a decoupling means using an overlap between adjacent coil loops. 
     It is preferable in terms of constructing a cylindrical RF coil assembly that the plurality of coil loops are a plurality of coil loops that are adjacent to each other in sequence along a periphery of a cylinder. 
     According to the present invention, an RF coil assembly is an RF coil assembly including: a plurality of coil loops that are adjacent to each other in sequence and construct a phased array; and a plurality of decoupling means that cancel electromagnetic coupling between adjacent coil loops, respectively, wherein at least two of the plurality of coil loops are two coil loops that are adjacent to each other across a boundary where they can be decoupled from each other, and wherein at least one of the plurality of decoupling means is two coils that are connected in series to the two coil loops, respectively, and are opposed to each other across the boundary and form a pair of coils for decoupling. As a result, it is possible to realize an RF coil assembly capable of eliminating the need for connecting and disconnecting an electric path at decoupling portions. 
     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 
         FIG. 1  is a diagram showing the basic construction of an RF coil assembly. 
         FIG. 2  is a diagram showing the construction of a supporting body of a coil loop. 
         FIG. 3  is a diagram showing the equivalent circuit of an RF coil assembly that focuses attention on two adjacent coil loops. 
         FIG. 4  is a diagram showing the equivalent circuit of two adjacent coil loops provided with a decoupling means. 
         FIG. 5  is a diagram showing the construction of an RF coil assembly that is one example of the best mode for carrying out the present invention. 
         FIG. 6  is a diagram showing another example of an RF coil assembly. 
         FIG. 7  is a diagram showing still another example of an RF coil assembly. 
         FIG. 8  is a diagram showing the construction of a supporting body of a coil loop. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In this regard, it is not intended to limit the present invention to the best mode for carrying out the present invention. The basic construction of an RF coil assembly is shown in  FIG. 1 . As shown in  FIG. 1 , the RF coil assembly has four coil loops  10 ,  20 ,  30 , and  40 . Each coil loop is actually constructed of an LCR circuit but is here simply expressed by the loop of a conductor, and ditto for the following. 
     The coil loops  10 ,  20 ,  30 , and  40  are placed on a supporting body  50  shaped like an elliptic cylinder as shown in  FIG. 2  in such a way as to be adjacent to each other in sequence along the periphery of the supporting body  50 . The supporting body  50  is constructed of a combination of an anterior supporting body  502  shaped like a semi-elliptic cylinder and a posterior supporting body  504  shaped like a semi-elliptic cylinder. 
     The coil loops  10 ,  40  are supported by the anterior supporting body  502  and the coil loops  20 ,  30  are supported by the posterior supporting body  504 . The anterior supporting body  502  and the posterior supporting body  504  can be coupled to and decoupled from each other at boundary portions  512 ,  534 . 
     The equivalent circuit of the RF coil assembly that focuses attention on two adjacent coil loops is shown in  FIG. 3 . As shown in  FIG. 3 , two coil loops typified by a port  1  and a port  2  are expressed by LCR circuits, respectively, and are electromagnetically coupled to each other by mutual induction M. 
     In a phased array, there is provided a decoupling means so as to cancel this electromagnetic coupling. The equivalent circuit of two coil loops provided with the decoupling means is shown in  FIG. 4 . As shown in  FIG. 4 , inductors L′, L′ as a decoupling means are added to two coil loops and the electromagnetic coupling by the mutual induction M is cancelled by the use of the mutual induction M′ of opposite polarity between the inductors. 
     In  FIG. 5  is shown the schematic construction of an RF coil assembly having a decoupling means. This RF coil assembly is one example of the best mode for carrying out the present invention. One example of the best mode for carrying out the present invention relating to an RF coil assembly is shown by the construction of this RF coil assembly. 
     This RF coil assembly corresponds to an RF coil assembly in which in the basic construction shown in  FIG. 1 , a decoupling means is added to the coil loops  10 ,  20 ,  30 , and  40 . The respective coil loops of this RF coil assembly are also placed on the decoupling type supporting body  50  shaped like an elliptic cylinder as shown in  FIG. 2  in such a way as to be adjacent to each other in sequence along its periphery. 
     That is, the coil loops  10 ,  40  are supported by the anterior supporting body  502  and the coil loops  20 ,  30  are supported by the posterior supporting body  504 . With this, the coil loops  10 ,  40  are placed on an anterior side and the coil loops  20 ,  30  are placed on a posterior side. Each of the coil loops  10 ,  20 ,  30 , and  40  is one example of the coil loop in the present invention. 
     The decoupling of the coil loop  10  from the coil loop  20  is carried out by a decoupling means  12 . The decoupling means  12  is constructed of a coil  121  provided in series to the coil loop  10  and a coil  122  provided in series to the coil loop  20 . 
     The coil  121  and the coil  122  are opposed to each other in a direction perpendicular to the central axis of the supporting body  50  in a state where their coil planes are horizontal. Both coils are opposite to each other in winding directions and hence develop mutual induction of opposite polarity. Here, each of the coils  121 ,  122  is shown as a coil of one turn, but each of them can have an appropriate number of turns, ditto for the following. 
     The decoupling of the coil loop  20  from the coil loop  30  is carried out by a decoupling means  23 . The decoupling means  23  is constructed of a coil  232  provided in series to the coil loop  20  and a coil  233  provided in series to the coil loop  30 . 
     The coil  232  and the coil  233  are opposed to each other in a direction parallel to the central axis of the supporting body  50  in a state where their coil planes are vertical. Both coils are opposite to each other in winding directions and hence develop mutual induction of opposite polarity. 
     The decoupling of the coil loop  30  from the coil loop  40  is carried out by a decoupling means  34 . The decoupling means  34  is constructed of a coil  343  provided in series to the coil loop  30  and a coil  344  provided in series to the coil loop  40 . 
     The coil  343  and the coil  344  are opposed to each other in a direction perpendicular to the central axis of the supporting body  50  in a state where their coil planes are horizontal. Both coils are opposite to each other in winding directions and hence develop mutual induction of opposite polarity. 
     The decoupling of the coil loop  40  from the coil loop  10  is carried out by a decoupling means  41 . The decoupling means  41  is constructed of a coil  414  provided in series to the coil loop  40  and a coil  411  provided in series to the coil loop  10 . 
     The coil  414  and the coil  411  are opposed to each other in a direction parallel to the central axis of the supporting body  50  in a state where their coil planes are vertical. Both coils are opposite to each other in winding directions and hence develop mutual induction of opposite polarity. 
     The decoupling means  12 ,  23 ,  34 , and  41  are examples of the decoupling means in the present invention. The coils  121 ,  122 ,  232 ,  233 ,  343 ,  344 ,  414 , and  411  are examples of the coil for decoupling in the present invention. 
     A boundary portion  512  between the anterior supporting body  502  and the posterior supporting body  504  is between the coil loops  10  and  20 . For this reason, the coils  121 ,  122  constructing the decoupling means  12  between the coil loops  10  and  20  are opposed to each other across the boundary portion  512 . The boundary portion  512  is one example of a boundary where the coil loops can be decoupled from each other in the present invention and one example of a first boundary. 
     A boundary portion  534  between the anterior supporting body  502  and the posterior supporting body  504  is between the coil loops  30  and  40 . For this reason, the coils  343 ,  344  constructing the decoupling means  34  between the coil loops  30  and  40  are opposed to each other across the boundary portion  534 . The boundary portion  534  is one example of a boundary where the coil loops can be decoupled from each other in the present invention and one example of a second boundary. 
     This construction eliminates the need for disconnecting an electric path when the RF coil assembly is decoupled into an anterior part and a posterior part. Moreover, this construction eliminates the need for connecting the electric path when the anterior part is coupled to the posterior part. 
     Another example of the construction of an RF coil assembly is shown in  FIG. 6 . In this RF coil assembly, a partial overlap of coil loops  40  and  10  is used as a decoupling means between the coil loops  40  and  10 , and a partial overlap of coil loops  20  and  30  is used as a decoupling means between the coil loops  20  and  30 . Except this construction, this RF coil assembly is the same as the RF coil assembly shown in  FIG. 5 . Even this construction can eliminate the need for disconnecting an electric path when the RF coil assembly is decoupled into an anterior part and a posterior part and can eliminate the need for connecting the electric path when the anterior part is coupled to the posterior part. Further, this construction is preferable in terms of eliminating the need for providing a coil for decoupling between the coil loops  40  and  10  and a coil for decoupling between the coil loops  20  and  30 . 
     Still another example of the construction of an RF coil assembly is shown in  FIG. 7 . In this RF coil assembly, the decoupling of the coil loop  20  from the coil loop  30  is carried out by a decoupling means  23 ′. The decoupling means  23 ′ is constructed of a coil  232 ′ provided in series to the coil loop  20  and a coil  233 ′ provided in series to the coil loop  30 . 
     The coil  232 ′ and the coil  233 ′ are opposed to each other in a direction perpendicular to the central axis of the supporting body  50  in a state where their coil planes are vertical. Both coils are opposite to each other in winding directions and hence develop mutual induction of opposite polarity. 
     The decoupling of the coil loop  40  from the coil loop  10  is carried out by a decoupling means  41 ′. The decoupling means  41 ′ is constructed of a coil  414 ′ provided in series to the coil loop  40  and a coil  411 ′ provided in series to the coil loop  10 . 
     The coil  414 ′ and the coil  411 ′ are opposed to each other in a direction perpendicular to the central axis of the supporting body  50  in a state where their coil planes are vertical. Both coils are opposite to each other in winding directions and hence develop mutual induction of opposite polarity. 
     Except this construction, this coil assembly is the same as the RF coil assembly shown in  FIG. 5 . Even this construction can eliminate the need for disconnecting an electric path when the RF coil assembly is decoupled into an anterior part and a posterior part and can eliminate the need for connecting the electric path when the anterior part is coupled to the posterior part. 
     Moreover, as shown in  FIG. 8 , this construction can eliminate the need for connecting and disconnecting the electric path even when the supporting body  50  can be decoupled into the respective coil loops at the boundary portions  512 ,  523 ,  534 , and  541 . 
     While examples of the RF coil assembly having four coil loops have been described above, the number of the coil loops is not limited to four but may be an appropriate plural number. Moreover, the cylindrical supporting body for supporting the plurality of coil loops is not limited to being elliptic in cross section but may be circular or appropriately polygonal in cross section. 
     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.