Patent Publication Number: US-11035917-B2

Title: Magnetic resonance imaging apparatus and RF coil device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/246,745 filed Apr. 7, 2014 (now U.S. Pat. No. 10,175,313), which is a continuation of International Application No. PCT/JP2014/50904, filed Jan. 20, 2014, and the PCT application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-10298, filed Jan. 23, 2013, the entire contents of each of which are incorporated herein by reference. 
    
    
     1. Field of the Invention 
     Embodiments described herein relate generally to a magnetic resonance imaging apparatus and an RF coil device. 
     2. Description of the Related Art 
     MRI is an imaging method which magnetically excites nuclear spin of an object (a patient) placed in a static magnetic field with an RF pulse having the Larmor frequency and reconstructs an image on the basis of MR signals generated due to the excitation. The aforementioned MRI means magnetic resonance imaging, the RF pulse means a radio frequency pulse, and the MR signal means a nuclear magnetic resonance signal. 
     Here, an RF (Radio Frequency) coil device is a device which transmits an RF pulse to nuclear spin inside an object by, for example, supplying a coil with an RF pulse electric current and detects generated MR signals. 
     Some of RF coil devices are built-in types included in an MRI apparatus and other RF coil devices are recognized by a control unit of the MRI apparatus by being connected to a connection port of the MRI apparatus such as local RF coil devices, for example. 
     In MRI, multi-channel structure is promoted in acquisition system of MR signals. The above “channel” means each pathway of a plurality of MR signals outputted from each coil element and inputted to an RF receiver of an MRI apparatus. Although the number of the channels is determined to be equal to or smaller than the input reception number of the RF receiver, a large number of RF coil devices can be connected to an MRI apparatus. 
     If the number of cables between an RF coil device and a control side (the above RF receiver side) of an MRI apparatus increases due to promotion of the aforementioned multichannel structure, it is inconvenient because hard-wiring becomes complicated. 
     Therefore, it is desired to unwire transmission and reception of signals between an RF coil device and an MRI apparatus. However, radio communication by an analogue signal has not been achieved, because there are various restrictions such as degradation of dynamic range. 
     More specifically, in order to suppress influence on receiving sensitivity to weak MR signals emitted from an object, it is impossible in an MRI apparatus to enlarge the output of electromagnetic waves used for radio communication between an RF coil device and an MRI apparatus. If it is impossible to enlarge the radio output power, dynamic range degrades due to signal loss caused when transmitted signals travel space. Then, in Japanese Patent Application Laid-open (KOKAI) Publication No. 2010-29664, a digital radio communication method in which MR signals are digitized and then transmitted wirelessly is proposed. 
     The problem of the restriction of the dynamic range can be solved by wirelessly transmitting MR signals after digitalization. 
     However, how to reserve electric power of the RF coil device side has not been sufficiently considered in digital radio communication of MR signals. For example, though a built-in rechargeable battery may be included inside an RF coil device, currently commercially-supplied rechargeable batteries are not sufficient in terms of charging capacity as compared with power consumption of an RF coil device in MRI. Thus, if many pulse sequences are performed, a situation where it has no choice but to exchange the rechargeable battery before performing the next pulse sequence is supposed. 
     Therefore, a novel technology to save electric power of an RF coil device satisfactorily and effectively in structure of wirelessly transmitting MR signals detected by the RF coil device to a control side of an MRI apparatus has been desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a block diagram showing the general structure of the MRI apparatus of the first embodiment; 
         FIG. 2  is a schematic oblique perspective figure showing an example of the structure of the whole body coil of the MRI apparatus of the first embodiment; 
         FIG. 3  is a schematic block diagram showing the structure relevant to the transmission system of RF pulses and the transmission system of electric power of the MRI apparatus of the first embodiment; 
         FIG. 4  is a schematic equivalent circuit diagram showing an example of the structure of the coil elements of the RF coil device of the first embodiment; 
         FIG. 5  is an equivalent circuit diagram in the case of assuming the coil elements EC 1  in  FIG. 4  to be a parallel circuit of impedance Z 1  and impedance Z 2 ; 
         FIG. 6  is a block diagram showing the charging system and the processing system of MR signals in the control system of the RF coil device of the first embodiment; 
         FIG. 7  is a schematic block diagram showing the respective components relevant to the digital radio communication system of the MR signals, in the MRI apparatus of the first embodiment; 
         FIG. 8  is a timing chart showing the first example of transmission of electric power; 
         FIG. 9  is a timing chart showing the second example of transmission of electric power; 
         FIG. 10  is a timing chart showing the third example of transmission of electric power; 
         FIG. 11  is a timing chart showing the fourth example of transmission of electric power; 
         FIG. 12  is a flowchart illustrating an example of a flow of an imaging operation performed by the MRI apparatus of the first embodiment; 
         FIG. 13  is an equivalent circuit diagram of the power transmitting coil of the MRI apparatus of the second embodiment; 
         FIG. 14  is a schematic oblique drawing showing an equivalent circuit of the whole body coil and an example of the layout of the power transmitting coil of the MRI apparatus of the second embodiment; 
         FIG. 15  is an equivalent circuit diagram of the power transmitting coil observed from a direction different from  FIG. 13  in the second embodiment; 
         FIG. 16  is a schematic oblique drawing showing another example of the layout of the power transmitting coil to the whole body coil in the second embodiment, in the same notation as  FIG. 14 ; 
         FIG. 17  is an explanatory diagram showing a comparison between the layout of  FIG. 14  and the layout of  FIG. 16  in terms of existence or non-existence of a coupling effect by the magnetic fluxes passing through the power transmitting coil; 
         FIG. 18  is a schematic cross-sectional diagram showing an example of the layout of the power transmitting coil indicated by the positional relation with the RF coil device, in the second embodiment; 
         FIG. 19  is a block diagram showing the respective components relevant to the transmission system of the RF pulses and the transmission system of electric power in the second embodiment, in the same notation as  FIG. 3 ; 
         FIG. 20  is an equivalent circuit diagram of the power transmitting coil of the MRI apparatus of the third embodiment; 
         FIG. 21  is a schematic oblique drawing showing an example of the layout of the power transmitting coil of the third embodiment, in the same notation as  FIG. 14 ; 
         FIG. 22  is a schematic equivalent circuit diagram showing an example of the structure of the RF coil device of the fourth embodiment; 
         FIG. 23  is a schematic block diagram showing the respective components relevant to the digital radio communication system of the MR signals and the charging system, in the MRI apparatus of the fourth embodiment; 
         FIG. 24  is an explanatory diagram showing a difference in degree of the coupling effect between combinations with the power transmitting coil, in the case of using the eight-letter shaped power transmitting coil in the fifth embodiment; and 
         FIG. 25  is an explanatory diagram showing a difference in degree of the coupling effect between combinations with the power transmitting coil, in the case of using the loop type power transmitting coil in the fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     As methods of transmitting electric power to a wearable type RF coil device, (1) electromagnetic inductive wireless power transfer and capacitive coupling wireless power transfer which are capable of wireless transmission within a short-distance, (2) magnetically coupled resonant type wireless power transfer that is capable of wireless transmission between mutually slightly distant positions and (3) line-coupled wireless power transfer that wirelessly transmits electric power via line, are possible. 
     However, considering the convenience of a user in the structure of wirelessly transmitting MR signals from the RF coil device side to the control side of the MRI apparatus, it is desirable to be able to wirelessly transmit electric power to an RF coil device remotely located to some extent. If it is not achieved, the power transmission side and the power receiving side are closely fixed to each other by any suitable means, and this restricts the arrangement of wearable type RF coil devices. 
     Considering the above, it is considered that the magnetically coupled resonant type wireless power transfer (method) mentioned in the above (2) is preferable. However, in the conventional technology, there is not an idea of wirelessly transmitting electric power to an RF coil device by the magnetically coupled resonant type wireless power transfer. Then, the inventor has worked out a novel technology of wirelessly transmitting electric power satisfactorily and effectively to an RF coil device remotely located to some extent by the magnetically coupled resonant type wireless power transfer. 
     In the magnetically coupled resonant type wireless power transfer of the present embodiments, the resonance frequencies of the respective antenna circuits of the power transmission side and the power receiving side are adjusted so as to become equal. Then, electromagnetic waves of the resonance frequency are generated by supplying a great current to the antenna circuit of the power transmission side, and thereby the antenna circuit of the power receiving side resonates due to the electromagnetic waves. 
     By the electric current flowing to the antenna circuit of the power receiving side in the above manner, a charge/discharge element of the power receiving side can be charged. The charge/discharge element herein refers to a circuit element that can be repeatedly charged and discharged, such as a capacitor, a rechargeable battery and so on. Although examples of a rechargeable battery BAT will be explained in the following embodiments, other charge/discharge elements such as an electric double layer capacitor may be alternatively used. 
     Hereinafter, examples of aspects which embodiments of the present invention can take will be explained per aspect. 
     (1) According to one embodiment, an MRI apparatus obtains an MR signal from an RF coil device that detects the MR signal emitted from an object, and this MRI apparatus includes a power transmitting unit, a signal receiving unit and an image reconstruction unit. 
     The power transmitting unit wirelessly transmits electric power to a power receiving unit of the RF coil device by the magnetically coupled resonant type wireless power transfer. 
     The signal receiving unit wirelessly receives a digitized MR signal wirelessly transmitted from the RF coil device. 
     The image reconstruction unit obtains the digitized MR signal received by the signal receiving unit, and reconstructs image data of the object on the basis of the digitized MR signal. 
     (2) According to another embodiment, an RF coil device includes a coil element, a power receiving unit and a signal transmitting unit. 
     The coil element detects an MR signal emitted from an object. 
     The power receiving unit receives electric power wirelessly transmitted by the magnetically coupled resonant type wireless power transfer. 
     The signal transmitting unit digitizes the MR signal detected by the coil element and wirelessly transmits the digitized MR signal to an MRI apparatus, by consuming the electric power received by the power receiving unit. 
     In the following, embodiments of the RF coil devices, the MRI apparatuses and the MRI methods to which the above new technology is applied will be described with reference to the accompanying drawings. Note that the same reference numbers are given for identical components in each figure, and overlapping explanation is abbreviated. 
     The First Embodiment 
     The difference between the first embodiment and the second to the fifth embodiments is as follows. 
     That is, in the first embodiment, a whole body coil WB 1  combines both functions of transmitting electric power and transmitting RF pulses and each coil element inside an RF coil device  100  combines both functions of detecting MR signals and receiving electric power. 
     On the other hand, the whole body coil of the second embodiment, the third embodiment and the fifth embodiment does not have a function of transmitting electric power. In addition, in the fourth embodiment, a power receiving coil is disposed inside the RF coil device as a separate component from the coil elements. 
     Thus, the whole body coil WB 1  (see  FIG. 2 ) of the first embodiment performs transmission of the RF pulses to an imaging region and wireless transmission of electric power to a wearable type RF coil device. 
     Although the function of detecting MR signals from an object is not indispensable for the whole body coil WB 1 , the whole body coil WB 1  has the function of detecting MR signals as an example in the present embodiment. 
     Therefore, the whole body coil WB 1  has structure of double resonance type (doubly-tuned type), transmits the RF pulses by resonating at the Larmor frequency, and wirelessly transmits electric power to the RF coil device by resonating at a predetermined frequency which is lower than the Larmor frequency. In addition, the whole body coil WB 1  induces (detects) MR signals from the object by resonating at the Larmor frequency. 
     Similarly, each coil element inside the RF coil device has the structure of the double resonance type. 
     In the following, embodiments will be explained in order, starting from the overall structure of the MRI apparatus. 
       FIG. 1  is a block diagram showing the general structure of the MRI apparatus  10  according to the first embodiment. 
     For the sake of avoiding complication,  FIG. 1  does not show all the components of the MRI apparatus  10 , and other components omitted in FIG.  1  such as a high pass filter HPF 1  will be explained with  FIG. 2  to  FIG. 7 . 
     As an example here, the components of the MRI apparatus  10  will be explained by classifying them into three groups which are a bed unit  20 , a gantry  30  and a control device  40 . 
     Firstly, the bed unit  20  includes a bed  21 , a table  22 , and a table moving structure  23  disposed inside the bed  21 . An object P is loaded on the top surface of the table  22 . In addition, a reception RF coil device  24  is disposed inside the table  22 . 
     The bed  21  supports the table  22  in such a manner that the table  22  can move in the horizontal direction (i.e. the Z axis direction of the apparatus coordinate system). 
     The table moving structure  23  adjusts the position of the table  22  in the vertical direction by adjusting the height of the bed  21 , when the table  22  is located outside the gantry  30 . 
     In addition, the table moving structure  23  inserts the table  22  into inside of the gantry  30  by moving the table  22  in the horizontal direction and moves the table  22  to outside of the gantry  30  after completion of imaging. 
     As an example here, a wearable type RF coil device  100  that detects MR signals from the chest part is loaded on the object P. The RF coil device  100  receives wirelessly transmitted electric power by the magnetically coupled resonant type wireless power transfer, and operates by consuming this electric power. The RF coil device  100  digitizes the MR signals detected from the object P, and wirelessly transmits the digitized MR signals to the control side (the later-described radio communication device  36 ) of the MRI apparatus  10 . 
     In the present embodiment, various RF coil devices of digital radio communication type such as a pelvic part RF coil device and a lower limb RF coil device can be used in addition to the above RF coil device  100  for the chest part. Although each of these RF coil devices is assumed to be a part the MRI apparatus  10  in the present embodiment and the later-described second to the fifth embodiments, they may be interpreted as components independent from the MRI apparatus  10 . 
     Secondly, the gantry  30  is shaped in the form of a cylinder, for example, and is installed in an imaging room. The gantry  30  includes a static magnetic field magnet  31 , a shim coil unit  32 , a gradient magnetic field coil unit  33  and an RF coil unit  34 . 
     The static magnetic field magnet  31  is, for example, a superconductivity coil and shaped in the form of a cylinder. The static magnetic field magnet  31  forms a static magnetic field in an imaging space by using electric currents supplied from the later-described static magnetic field power supply  42 . The aforementioned “imaging space” means, for example, a space in the gantry  30  in which the object P is placed and to which the static magnetic field is applied. Note that the static magnetic field magnet  31  may include a permanent magnet which makes the static magnetic field power supply  42  unnecessary. 
     The shim coil unit  32  is, for example, shaped in the form of a cylinder and arranged inside the static magnetic field magnet  31  so as to become coaxial to the static magnetic field magnet  31 . The shim coil unit  32  forms an offset magnetic field that uniforms the static magnetic field by using electric currents supplied from the later described shim coil power supply  44  of the control device  40 . 
     The gradient magnetic field coil unit  33  is, for example, shaped in the form of a cylinder and arranged inside the shim coil unit  32 . The gradient magnetic field coil unit  33  includes an X axis gradient magnetic field coil  33   x , a Y axis gradient magnetic field coil  33   y  and a Z axis gradient magnetic field coil  33   z  (not shown). 
     In this specification, the X axis, the Y axis and the Z axis are assumed to be those of the apparatus coordinate system unless otherwise specifically noted. As an example here, the apparatus coordinate system, whose X axis, Y axis and Z axis are perpendicular to each other, is defined as follows. 
     Firstly, the Y axis direction is defined as the vertical direction, and the table  22  is disposed in such a position that the direction of the normal line of its top surface accords with the Y axis direction. The horizontal moving direction of the table  22  is defined as the Z axis direction, and the gantry  30  is installed in such a manner that its axis direction accords with the Z axis direction. The X axis direction is the direction perpendicular to these Y axis direction and Z axis direction, and is the width direction of the table  22  in the example of  FIG. 1 . 
     The (unillustrated) X axis gradient magnetic field coil forms a gradient magnetic field Gx in the X axis direction in an imaging region in accordance with an electric current supplied from the later-described gradient magnetic field power supply  46 . 
     Similarly, the (unillustrated) Y axis gradient magnetic field coil forms a gradient magnetic field Gy in the Y axis direction in the imaging region in accordance with an electric current supplied from the gradient magnetic field power supply  46 . 
     Similarly, the (unillustrated) Z axis gradient magnetic field coil forms a gradient magnetic field Gz in the Z axis direction in the imaging region in accordance with an electric current supplied from the gradient magnetic field power supply  46 . 
     Thereby, directions of a gradient magnetic field Gss in a slice selection direction, a gradient magnetic field Gpe in a phase encoding direction and a gradient magnetic field Gro in a readout (frequency encoding) direction can be arbitrarily selected as logical axes, by combining the gradient magnetic fields Gx, Gy and Gz in the X axis, the Y axis and the Z axis directions as three physical axes of the apparatus coordinate system. 
     The above “imaging region” means, for example, at least a part of an acquisition range of MR signals used to generate one image or one set of images, which becomes an image. The imaging region is three-dimensionally defined as a part of the imaging space in terms of range and position by the apparatus coordinate system, for example. For example, when MR signals are acquired in a range wider than a region made into an image in order to prevent wraparound artifact, the imaging region is a part of the acquisition range of MR signals. On the other hand, in some cases, the entire acquisition range of MR signals becomes an image, and the imaging region accords with the acquisition range of MR signals. In addition, the above “one set of images” means, for example, a plurality of images when MR signals of the plurality of images are acquired in a lump in one pulse sequence such as multi-slice imaging. 
     The RF coil unit  34  is, for example, shaped in the form of a cylinder and arranged inside the gradient magnetic field coil unit  33 . The RF coil unit  34  includes the aforementioned whole body coil WB 1 . Details of the whole body coil WB 1  will be described later with  FIG. 2 . In addition, the RF coil unit  34  may further include a power transmitting coil that exclusively performs transmission of electric power. 
     The radio communication device  36  receives digitized MR signals wirelessly transmitted from the RF coil device  100 , and inputs the received MR signals into the RF receiver  50 . 
     Thirdly, the control device  40  includes the static magnetic field power supply  42 , the shim coil power supply  44 , the gradient magnetic field power supply  46 , an RF transmitter  48 , a power transmitter  49 , an RF receiver  50 , a system control unit  61 , a system bus SB, an image reconstruction unit  62 , an image database  63 , an image processing unit  64 , an input device  72 , a display device  74  and the storage device  76 . 
     The gradient magnetic field power supply  46  supplies the respective electric currents for forming the gradient magnetic field Gx, the gradient magnetic field Gy and the gradient magnetic field Gz to the X axis gradient magnetic field coil, the Y axis gradient magnetic field coil and the Z axis gradient magnetic field coil, respectively. 
     The power transmitter  49  transmits alternating-current power of a predetermined frequency for wireless transmission to the whole body coil WB 1 . As to details of this operation, it will be later explained with  FIG. 2  and  FIG. 3 . 
     The RF transmitter  48  generates RF pulse electric currents of the Larmor frequency for causing nuclear magnetic resonance in accordance with control information inputted from the system control unit  61 , and transmits the generated RF pulse electric currents to the RF coil unit  34 . The RF pulses in accordance with these RF pulse electric currents are transmitted from the RF coil unit  34  to the object P. 
     The whole body coil WB 1 , the reception RF coil  24  and the RF coil device  100  detect MR signals generated due to excited nuclear spin inside the object P by the RF pulses and the detected MR signals are inputted to the RF receiver  50  by wire. 
     The RF receiver  50  generates raw data of MR signals by performing predetermined signal processing on the MR signals inputted from the whole body coil WB 1 , the reception RF coil  24  or the RF coil device  100 , then performing A/D (analogue to digital) conversion on them, and then performing processing such as filtering. The raw data are digitized into complex number data of digitized MR signals. 
     Because the signals from the radio communication device  36  have been already digitized by A/D conversion, only necessary data processing is performed. The RF receiver  50  inputs the raw data of the MR signals into the image reconstruction unit  62 . 
     The system control unit  61  performs system control of the MRI apparatus  10  in setting of imaging conditions of a main scan, an imaging operation and image display after imaging through interconnection such as the system bus SB. 
     The aforementioned term “imaging condition” refers to under what condition RF pulses or the like are transmitted in what type of pulse sequence, or under what condition MR signals are acquired from the object P, for example. 
     As parameters of the imaging conditions, for example, there are the imaging region as positional information in the imaging space, the number of slices, an imaging part and the type of the pulse sequence such as spin echo and parallel imaging. The above “imaging part” means a region of the object P to be imaged, such as a chest and an abdomen. 
     The aforementioned “main scan” is a scan for imaging an intended diagnosis image such as a T1 weighted image, and it does not include a scan for acquiring MR signals for a scout image or a calibration scan. 
     A scan is an operation of acquiring MR signals, and it does not include image reconstruction processing. 
     The calibration scan is a scan for determining unconfirmed elements of imaging conditions, conditions and data used for image reconstruction processing and correction processing after the image reconstruction, and the calibration is performed separately from the main scan. 
     As a calibration scan, there are a sequence of calculating the center frequency of the RF pulses of the main scan and so on. Out of calibration scans, a prescan is a scan performed before the main scan. 
     In addition, the system control unit  61  makes the display device  74  display screen information for setting imaging conditions, sets the imaging conditions on the basis of command information from the input device  72 . In addition, the system control unit  61  makes the display device  74  display images indicated by the generated display image data after completion of imaging. 
     The input device  72  provides a user with a function to set the imaging conditions and image processing conditions. 
     The image reconstruction unit  62  arranges and stores the raw data of MR signals inputted from the RF receiver  50  as k-space data, in accordance with the phase encode step number and the frequency encode step number. The above k-space means a frequency space. The image reconstruction unit  62  generates image data of the object P by performing image reconstruction processing including such as two-dimensional Fourier transformation and so on. The image reconstruction unit  62  stores the generated image data in the image database  63 . 
     The image processing unit  64  takes in the image data from the image database  63 , performs predetermined image processing on them, and stores the image data after the image processing in the storage device  76  as display image data. 
     The storage device  76  stores the display image data after adding accompanying information such as the imaging conditions used for generating the display image data and information of the object P (patient information) to the display image data. 
     Note that, though the components of the MRI apparatus  10  are classified into three groups (the gantry  30 , the bed unit  20  and the control device  40 ), this is only an example of interpretation. 
     For example, the table moving structure  23  may be interpreted as a part of the control device  40 . 
     Alternatively, the RF receiver  50  may be included not outside the gantry  30  but inside the gantry  30 . In this case, for example, an electronic circuit board that is equivalent to the RF receiver  50  may be disposed in the gantry  30 . Then, the MR signals, which are electrical signals converted from the electromagnetic waves by the reception RF coil  24  and so on, may be amplified by a pre-amplifier in the electronic circuit board, then the amplified signals may be outputted to the outside of the gantry  30  as digital signals and inputted to the image reconstruction unit  62 . In outputting the signals to the outside of the gantry  30 , for example, an optical communication cable is preferably used to transmit the signals in the form of optical digital signals. This is because the effect of external noise is reduced. 
       FIG. 2  is a schematic oblique perspective figure showing an example of the structure of the whole body coil WB 1  of the MRI apparatus  10  of the first embodiment. 
     Note that, the conducting wires of the circuit of the whole body coil WB 1  located on the plus side (near side) in the X axis direction are indicated by bold lines and the conducting wires located on the minus side (remote side) in the X axis direction are indicated by fine lines in order to make the respective wires distinguishable. In addition, as to each of the points where one conducting wire intersects with another conducting wire, electrically connected points are indicated by filled circle and non-connected points are distinguished from the electrically connected points by semicircularly indicating no connection between the conducting wires. 
     The whole body coil WB 1  includes the first loop conductor  200 , the second loop conductor  202 , eight connecting conductors (rungs)  204 , sixteen parallel resonance capacitors Ca and eight series resonance capacitors Cb. 
     In  FIG. 2 , the first loop conductor  200  corresponds to the two rings on the left side in parallel with an X-Y plane, and the second loop conductor  202  corresponds to the two rings on the right side in parallel with an X-Y plane. 
     The connecting conductors  204  correspond to eight straight lines extending along the Z axis direction as an example in  FIG. 2 , five of them are indicated by bold lines and three of them are indicated by fine lines. Each of the eight connecting conductors  204  is connected to the first loop conductor  200  on its one end and is connected to the second loop conductor  202  on its other end. That is, the whole body coil WB 1  is of a bird cage type by the first loop conductor  200 , the second loop conductor  202  and the eight connecting conductors  204 . 
     In the middle of each of the connecting conductors  204  (for example, in the center), one series resonance capacitor Cb is inserted in series. 
     In the first loop conductor  200 , the ring on the side of the second loop conductor  202  includes eight connection nodes connecting itself to the eight connecting conductors  204 , and eight parallel resonance capacitors Ca are connected (inserted) between two of the eight connection nodes one by one, so as to be in parallel with the rings of the first loop conductor  200 . 
     Similarly, in the second loop conductor  202 , the ring on the side of the first loop conductor  200  includes eight connection nodes connecting itself to the eight connecting conductors  204 , and eight parallel resonance capacitors Ca are connected (inserted) between two of the eight connection nodes one by one, so as to be in parallel with the rings of the second loop conductor  202 . 
     That is, if the wires between connection nodes of the connecting conductors  204  and the first loop conductor  200  or the second loop conductor  202  are interpreted as inductance components, an LC circuit is partially established between the wires and the parallel resonance capacitors Ca. 
     Thus, the whole body coil WB 1  of the first embodiment has the structure obtained by changing the element number (of the ladder type delay circuit) of the double resonance RF coil in FIG. 1 of Japanese Patent No. 2714044 from six to eight, in terms of circuit. The number of elements herein is equal to the number of the connecting conductors  204 . 
     Therefore, because the whole body coil WB 1  resonates at two different frequencies, the higher resonance frequency is defined as the first resonance frequency f 1  and the lower resonance frequency is defined as the second resonance frequency f 2 . 
     The circuit constants of the whole body coil WB 1  are set in such a manner that the first resonance frequency f 1  becomes the Larmor frequency and the second resonance frequency f 2  becomes the frequency for transmitting electric power. In the present specification, it is assumed that the Larmor frequency is the same as the magnetic resonance frequency. 
     The above circuit constants are (1) the capacitance value of the parallel resonance capacitor Ca, (2) the capacitance value of the series resonance capacitor Cb, (3) the inductance between the connection nodes in the first loop conductor  200  (each connection node connects the ring to one of the connecting conductors  204 ), (4) the inductance between the connection nodes in the second loop conductor  202  (each connection node connects the ring to one of the connecting conductors  204 ), and so on. 
     As to the second resonance frequency f 2  for transmitting electric power, though the frequency bands restricted by the regulations of the country where the MRI apparatus  10  is installed are avoided, 6 MHz band and 13 MHz band can be used in Japan at the filing time of this application, for example. 
     However, in the case of wirelessly transmitting electric power to an RF coil device continuously regardless of a transmission period of an RF pulse and a detection period of MR signals (see later-described  FIG. 8 ), it is safer to set the second resonance frequency f 2  avoiding frequencies obtained by dividing the Larmor frequency by a natural number. 
     In addition, because the equations for obtaining the first resonance frequency f 1  and the second resonance frequency f 2  are written in page three of the aforementioned Japanese Patent No. 2714044, detailed explanation is omitted here. 
     Because the whole body coil WB 1  is a bird cage type of eight elements, as an example in  FIG. 2 , it is supplied with electric power by a QD (quadrature phase) system from the respective connection nodes whose angles are mutually different by 90 degrees. This is so that the transmitted energy effectively contributes to rotation (excitation) of nuclear spin in consideration of the generation direction of magnetic fields. 
     More specifically, the high frequency transmitting and receiving cables  210  and  212  are respectively connected to positions having mutually different angles by 90 degrees in the first loop conductor  200 . That is, between the one parallel resonance capacitor Ca whose both ends are connected to the high frequency transmitting and receiving cable  210  and the other parallel resonance capacitor Ca whose both ends are connected to the high frequency transmitting and receiving cable  212 , another parallel resonance capacitor Ca is sandwiched. 
     In addition, the power transmission cable  220  is connected to both ends of the series resonance capacitor Cb of one connecting conductor  204 , and the power transmission cable  222  is connected to both ends of the series resonance capacitor Cb of another connecting conductor  204 . 
     If the whole body coil WB 1  is observed from a cross-section of an X-Y plane, it is interpreted as the QD system because the number of the connecting conductors  204  is eight and one connecting conductor  204  is interposed between the connecting conductor  204  connected to the power transmission cable  220  and the connecting conductor  204  connected to the power transmission cable  222 . 
     Note that, the connection wires of these high frequency transmitting and receiving cables  210  and  212  and the power transmission cables  220  and  222  to the whole body coil WB 1  are respectively indicated by dashed lines in  FIG. 2  in order to distinguish them from the conducting wires of the whole body coil WB 1 . 
       FIG. 3  is a schematic block diagram showing the structure relevant to the transmission system of the RF pulses and the transmission system of the electric power of the MRI apparatus  10  of the first embodiment. GND in  FIG. 3  indicates a ground line. 
     As shown in  FIG. 3 , the MRI apparatus  10  further includes phase dividers  230 ,  232 , high pass filters HPF 1 , HPF 2 , and low pass filters LPF 1 , LPF 2 . The high pass filters HPF 1  and HPF 2  are respectively inserted in the high frequency transmitting and receiving cables  210  and  212  in series. The low pass filters LPF 1  and LPF 2  are respectively inserted in the power transmission cables  220  and  222  in series. 
     The RF transmitter  48  sets the first resonance frequency f 1  to the Larmor frequency inputted from the system control unit  61 , and supply high-frequency electric power of the first resonance frequency f 1  to the phase divider  230 . 
     The phase divider  230  amplifies the inputted high-frequency electric power, and two-divides the amplified electric power into RF pulses (high-frequency pulses) whose phases are mutually different by 90 degrees. 
     The phase divider  230  supplies one of the two-divided RF pulses whose phase is 0 degree to both ends of one parallel resonance capacitor Ca of the whole body coil WB 1 , via the high frequency transmitting and receiving cable  210 . In addition, the phase divider  230  supplies the other of the two-divided RF pulses whose phase is 90 degrees to both ends of another parallel resonance capacitor Ca of the whole body coil WB 1 , via the high frequency transmitting and receiving cable  212 . 
     Thereby, because the whole body coil WB 1  resonates at the first resonance frequency f 1 , the RF pulses are transmitted from the whole body coil WB 1  to an imaging region by the QD system. 
     Note that, the high pass filters HPF 1  and HPF 2  prevent the second resonance frequency f 2  which is lower than the first resonance frequency f 1  from invading into the phase divider  230  side via the whole body coil WB 1 . 
     On the other hand, the power transmitter  49  sets the second resonance frequency f 2  to the frequency for electric power transmission inputted from the system control unit  61 , and supplies alternating-current power of the second resonance frequency f 2  to the phase divider  232 . The phase divider  232  amplifies the inputted alternating-current power, and two-divides the amplified alternating-current power in such a manner that one of the two-divided alternating-current powers has a phase being different by 90 degrees from the other of the two-divided alternating-current powers. 
     The phase divider  232  supplies one of the two-divided alternating-current power whose phase is 0 degree to both ends of one series resonance capacitor Cb of the whole body coil WB 1 , via the power transmission cable  220 . 
     In addition, the phase divider  232  supplies the other of the two-divided alternating-current powers whose phase is 90 degrees to both ends of another series resonance capacitor Cb of the whole body coil WB 1 , via the power transmission cable  222 . 
     Thereby, because the whole body coil WB 1  resonates at the second resonance frequency f 2 , electromagnetic waves of the second resonance frequency f 2  are transmitted from the whole body coil WB 1  by the QD system. That is, electric power is wirelessly transmitted to the RF coil device  100 . 
     Note that, the low pass filters LPF 1  and LPF 2  prevent the first resonance frequency f 1  from invading into the phase divider  232  side via the whole body coil WB 1 . 
     In addition, it is not necessary to compose the power transmission side under the QD system, and the power transmission cable  222  in  FIG. 2  and the phase divider  232  in  FIG. 3  may be omitted. 
       FIG. 4  is a schematic equivalent circuit diagram showing an example of the structure of the coil elements of the RF coil device  100  of the first embodiment. Although only four coil elements EC 1  to EC 4  are shown in  FIG. 4  for the sake of avoiding complication, the number of the coil elements may be three, less than three, five or more than five. 
     As shown in  FIG. 4 , each of the coil elements EC 1  to EC 4  includes a switch SW 1 , capacitors C 1 , C 2 , CS and a coil L 1 . Each of the coil elements EC 1  to EC 4  is a double resonance type. 
     That is, in each of the coil elements EC 1  to EC 4 , the respective capacitance values of the capacitors C 1 , C 2  and CS and the inductance value of the coil L 1  are matched, in such a manner that the first resonance frequency f 1  becomes the Larmor frequency and the second resonance frequency f 2  becomes the transmission frequency of the alternating-current power. This point will be further explained with the next  FIG. 5 . In addition, as to ON/OFF switching of the switch SW 1 , it will be explained with the later-described  FIG. 7 . 
     In addition, the RF coil device  100  includes the same number of coaxial cables  104  as the coil elements so as to respectively correspond to the coil elements EC 1  to EC 4 . One end of each of the coaxial cables  104  is connected to both ends of the capacitor C 2  of each of the coil elements EC 1  to EC 4 . The other end of each of the coaxial cables  104  is connected to the control system  102  of the RF coil device  100 . The capacitor C 3  is inserted in one end side of each of the coaxial cables  104 . 
     The capacitance value of the capacitor C 2  of each of the coil elements EC 1  to EC 4  and the capacitance value of the capacitor C 3  inserted inside each of the coaxial cables  104  are selected in such a manner that these components function as an impedance matching circuit. Note that, as to the antennas  106   a  to  106   d  connected to the control system  102  in  FIG. 4 , they will be explained with the later-described  FIG. 7 . 
       FIG. 5  is an equivalent circuit diagram in the case of assuming the coil element EC 1  in  FIG. 4  to be a parallel circuit of the impedance Z 1  and the impedance Z 2 . 
     The inductance component LS in  FIG. 5  corresponds to the inductance of the hard-wiring of each of the coil elements EC 1  to EC 4  excluding the portion between the two connection nodes connected to the coaxial cable  104  in  FIG. 4 . That is, the inductance component of the hard-wiring that starts from the connection node of the capacitor C 2  and the capacitor C 3 , passes through the switch SW 1  and ends at the connection node of the capacitor C 1 , the capacitor C 2  and the coaxial cable  104  is LS. 
     Thus, the impedance Zt of each of the coil elements EC 1  to EC 4  corresponds to the impedance Zt of the parallel circuit of the part of the impedance Z 1  surrounded by a dashed line frame and the part of the impedance Z 2  surrounded by a chain line frame. 
     Then, if the capacitance values of the capacitors C 1 , C 2  and CS are respectively defined as C 1 , C 2  and Cs, the inductance value of the coil L 1  is defined as L 1  and the inductance value of the inductance component LS is defined as Ls, the first resonance frequency f 1  and the second resonance frequency f 2  are respectively calculated by the following equation (1) and equation (2). 
     
       
         
           
             
               
                 
                   
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       FIG. 6  is a block diagram showing the charging system and the processing system of the MR signals in the control system  102  of the RF coil device  100  of the first embodiment. As shown in  FIG. 6 , the control system  102  includes a rechargeable battery BAT. Furthermore, the control system  102  includes duplexers (splitters) DP 1  to DP 4 , preamplifiers PA 1  to PA 4 , A/D convertors AD 1  to AD 4  and rectifiers RC 1  to RC 4  so as to respectively correspond to the respective coil elements EC 1  to EC 4 . 
     Because  FIG. 6  becomes complicated if all the wires of the coil elements EC 1  to EC 4  are shown, only the wires of the connection destination of the coil elements EC 1  and EC 2  are shown in  FIG. 6 . Thus, the duplexers DP 3  and DP 4 , the preamplifiers PA 3  and PA 4  and the A/D convertors AD 3  and AD 4  are not illustrated in  FIG. 6 . 
     Each of the duplexers (splitters) DP 1  to DP 4  is connected to each of the coil elements EC 1  to EC 4  via the coaxial cable  104 . Here, because each of the coil elements EC 1  to EC 4  resonates at the first resonance frequency f 1  that is tuned to the frequency (the Larmor frequency) of MR signals emitted from the object P, each of the coil elements EC 1  to EC 4  detects weak MR signals. 
     In addition, each of the coil elements EC 1  to EC 4  wirelessly receives alternating-current power by receiving the electromagnetic wave of the second resonance frequency f 2  emitted from the whole body coil WB 1  so as to resonate. The MR signals and alternating-current power received by each of the coil elements EC 1  to EC 4  are respectively taken in the duplexers DP 1  to DP 4  of the control system  102  via the coaxial cables  104 . 
     The duplexers DP 1  to DP 4  extract electric current components of the first resonance frequency f 1  (MR signals), and respectively input them into the preamplifiers PA 1  to PA 4 . 
     In addition, the duplexers DP 1  to DP 4  extract electric current components of the second resonance frequency f 2  (alternating-current power), and respectively input them to the rectifiers RC 1  to RC 4 . 
     Each of the rectifiers RC 1  to RC 4  converts the alternating electric current respectively inputted from the duplexers DP 1  to DP 4  into direct-current electricity, and supplies the direct-current electricity to the rechargeable battery BAT as a charging current. 
     Each of the preamplifiers PA 1  to PA 4  amplifies the MR signals of the first resonance frequency f 1  respectively inputted from the duplexers DP 1  to DP 4 , and respectively inputs the amplified MR signals into the A/D convertors AD 1  to AD 4 . 
     The A/D convertors AD 1  to AD 4  digitize the inputted analogue MR signals, and input the digitized MR signals into the subsequent stage (see  FIG. 7 ). 
       FIG. 7  is a schematic block diagram showing the respective components relevant to the digital radio communication system of the MR signals, in the MRI apparatus  10  of the first embodiment. In  FIG. 7 , only the wires of the connection destination of the coil elements EC 1  and EC 2  are shown while the wires of the connection destination of the other coil elements EC 3  and EC 4  are omitted as to the RF coil device  100  in the way similar to  FIG. 6 . This is because  FIG. 7  becomes complicated if all the wires of the coil elements are illustrated. 
     As shown in  FIG. 7 , the control system  102  of the RF coil device  100  further includes a CPU (Central Processor Unit)  110 , a P/S (Parallel/Serial) converter PSC, a data transmitting unit  116 , a reference signal receiving unit  118 , an ID (Identification Information) transmitting unit  122  and a gate signal receiving unit  124 . 
     In addition, the radio communication device  36  includes antennas  306   a  to  306   d , a data receiving unit  316 , a reference signal transmitting unit  318 , an ID (Identification Information) receiving unit  322  and a gate signal transmitting unit  324 . 
     In addition, (the control device  40  of) the MRI apparatus  10  further includes a frequency upconversion unit  402 , a pulse waveform generation unit  404 , a fixed frequency generation unit  406  and a variable frequency generation unit  408 . 
     In addition, the RF receiver  50  includes a frequency downconversion unit  410  and a signal processing unit  412 . 
     As an example in the first embodiment, there are four radio communication pathways between the RF coil device  100  and the radio communication device  36 . In the following, the four radio communication pathways will be explained in order. 
     Firstly, in the pathway between the antennas  106   c  and  306   c , the identification information of the RF coil device  100  is wirelessly transmitted. 
     More specifically, for example, the ID transmitting unit  122  preliminarily stores the above identification information or obtains it from the CPU  110 . The ID transmitting unit  122  adjusts the radio output power of the digital signal of the above identification information to a level appropriate for the remote radio communication, and inputs this to the antenna  106   c . The antenna  106   c  radiates the electromagnetic waves of the digital signal of the identification information. 
     The antenna  306   c  of the radio communication device  36  detects the carrier waves radiated from the antenna  106   c , and inputs them to the ID receiving unit  322 . The ID receiving unit  322  extracts the identification information of the RF coil device  100  from the inputted carrier waves, and inputs the identification information to the system control unit  61 . Thereby, the system control unit  61  recognizes information on an RF coil device such as which of various types of RF coil devices (for example, a chest part RF coil device) is currently connected. 
     Secondly, in the pathway between the antennas  106   d  and  306   d , a digital gate signal is continuously wirelessly transmitted from the radio communication device  36  to the RF coil device  100  during imaging. The gate signal is a control signal of the switch SW 1  that switches ON/OFF state of each of the coil elements EC 1  to EC 4 . 
     More specifically, the gate signal transmitting unit  324  adjusts the level of radio output power of the gate signal to a level appropriate for remote radio communication, and inputs it to the antenna  306   d . The antenna  306   d  radiates electromagnetic waves of the gate signal. The antenna  106   d  of the RF coil device  100  detects the carrier waves radiated from the antenna  306   d , and inputs them to the gate signal receiving unit  124 . 
     The gate signal receiving unit  124  extracts the gate signal from the inputted carrier waves, and inputs the extracted gate signal to the CPU  110 . The CPU  110  switches ON/OFF state of each of the coil elements EC 1  to EC 4  by the switch SW 1 , on the basis of the gate signal. 
     Note that, as an alternative configuration, the trigger signal may be transmitted from the gate signal transmitting unit  324  to the gate signal receiving unit  124 , and the gate signal may be generated inside the gate signal receiving unit  124  on the basis of the trigger signal. 
     As to timing of wirelessly transmitting electric power to the RF coil device  100 , four examples will be explained with the next  FIG. 8  to  FIG. 11 . Here, consider a case where the wireless transmission of electric power is not performed in a period during which an RF pulse is transmitted to the object P (see  FIG. 10 ). 
     In a period during which an RF pulse is transmitted to the object P, the gate signal inputted from the antenna  306   d  to the RF coil device  100  is set to, for example, on-level. During the on-level span of the gate signal, the above switch SW 1  becomes off-state so as to disconnect the loop of each of the coil elements EC 1  to EC 4  and thereby each of the coil elements EC 1  to EC 4  cannot detect MR signals nor receive alternating-current power. 
     Except in the span during which RF pulses are transmitted to the object P, the gate signal adjusted to off-level is wirelessly transmitted. While the gate signal is off-level, the above switch SW 1  becomes on-state and each of the coil elements EC 1  to EC 4  can detect MR signals and receive alternating-current power. 
     Thirdly, in the pathway between the antennas  306   b  and  106   b , a digital reference signal is continuously wirelessly transmitted from the radio communication device  36  to the RF coil device  100  during imaging. The reference signal is a signal that synchronizes the RF coil device  100  as a transmission side of the MR signals with a basic frequency of system based on the fixed frequency generation unit  406 . The reference signal transmitting unit  318  generates the reference signal by performing processing such as modulation, frequency conversion, amplification and filtering on the criterion clock signal inputted from the fixed frequency generation unit  406 . 
     The fixed frequency generation unit  406  generates the criterion clock signal whose frequency is constant. The fixed frequency generation unit  406  includes a crystal controlled oscillator with high degree of stability and so on, in order to generate the criterion clock signal. 
     The fixed frequency generation unit  406  inputs the criterion clock signal to the reference signal transmitting unit  318  and the variable frequency generation unit  408 . In addition, the fixed frequency generation unit  406  inputs the criterion clock signal to respective components performing clock synchronization inside the MRI apparatus  10  such as the image reconstruction unit  62  and the pulse waveform generation unit  404 . 
     The variable frequency generation unit  408  includes PLL (Phase-Locked Loop), DDS (Direct Digital Synthesizer), and a mixer. The variable frequency generation unit  408  operates on the basis of the above criterion clock signal. 
     The variable frequency generation unit  408  generates a local signal (clock signal) of variable frequency that accords with a setting value inputted from the system control unit  61  as a center frequency of RF pulses. 
     In order to achieve this, the system control unit  61  inputs a default value of the center frequency of the RF pulses to the variable frequency generation unit  408  before a prescan. In addition, the system control unit  61  inputs a corrected value of the center frequency of the RF pulses to the variable frequency generation unit  408  after the prescan. 
     The variable frequency generation unit  408  inputs the above local signal of variable frequency to the frequency downconversion unit  410  and the frequency upconversion unit  402 . 
     In addition, a trigger signal (A/D conversion start signal) that determines the timing of sampling in each of the A/D converters AD 1  to AD 4  of the RF coil device  100  is inputted from the system control unit  61  to the reference signal transmitting unit  318 . The above sampling means, for example, to extract intensity of an analog signal at regular time intervals so as to enable digital record. 
     As an example here, the reference signal transmitting unit  318  wirelessly transmits both the reference signal and the trigger signal by superimposing the trigger signal on the reference signal. 
     More specifically, the reference signal transmitting unit  318  adjusts the level of radio output power of the reference signal on which the trigger signal is superimposed to a level appropriate for remote radio communication, and inputs it to the antenna  306   b . The antenna  306   b  radiates electromagnetic waves of the reference signal on which the trigger signal is superimposed. The antenna  106   b  of the RF coil device  100  detects the carrier waves radiated from the antenna  306   b , and inputs them to the reference signal receiving unit  118 . 
     The reference signal receiving unit  118  extracts the trigger signal and the reference signal from the inputted carrier waves, and inputs them to each of the A/D convertors AD 1  to AD 4 . 
     Fourthly, in the pathway between the antennas  106   a  and  306   a , the digitized MR signals are wirelessly transmitted from the RF coil device  100  to the radio communication device  36 . 
     More specifically, analogue MR signals detected by the coil elements selected for detecting MR signals (for at least one of the coil elements EC 1  to EC 4 ) are subjected to removal of an alternating-current power component via the duplexers (DP 1  to DP 4 ), then amplified by the preamplifiers (PA 1  to PA 4 ) and then inputted to the A/D convertor (AD 1  to AD 4 ), as explained with  FIG. 6 . 
     Each of the A/D convertors (AD 1  to AD 4 ) converts the inputted analogue MR signals into digital signals, by starting sampling and quantization on the basis of the reference signal (sampling clock signal) in synchronization with the timing when the trigger signal is transmitted. 
     If at least one of the coil elements (EC 1  to EC 4 ) is not selected for detecting MR signals, the preamplifier(s) (PA 1  to PA 4 ) and the A/D converter(s) (AD 1  to AD 4 ) corresponding to the non-selected coil element(s) do not operate as an example in the present embodiment. 
     Each of the A/D convertors (AD 1  to AD 4 ) inputs the digitized MR signals to the P/S converter PSC. If a plurality of the coil elements (EC 1  to EC 4 ) are selected for detecting MR signals, the MR signals which have been detected by these coil elements and have respectively undergone A/D conversion are plural. 
     In this case, the P/S converter PSC converts these plural MR signals from parallel signals into a serial signal for radio transmission, and inputs the serial signal to the data transmitting unit  116 . This is because the number of antenna for transmitting the MR signals is only one (the antenna  106   a ) in the example of the present embodiment. 
     However, the present embodiment is not limited to an aspect of wirelessly transmitting the MR signals as a serial signal. For example, the MR signals may be wirelessly transmitted as parallel signals by increasing the number of antennas for transmitting and receiving MR signals. 
     The data transmitting unit  116  generates the MR signal for radio transmission (which is a serial and digital signal) by performing processing such as error correction encoding, interleave, modulation, frequency conversion, amplification, and filtering on the inputted serial MR signal. 
     The data transmitting unit  116  adjusts the level of radio output power of the MR signal for wireless transmission to a level appropriate for remote radio communication, and inputs the MR signal to the antenna  106   a . The antenna  106   a  radiates electromagnetic waves of the MR signal. The antenna  106   b  of the RF coil device  100  detects the carrier waves radiated from the antenna  306   b , and inputs them to the reference signal receiving unit  118 . 
     The antenna  306   a  of the radio communication device  36  detects the carrier waves radiated from the antenna  106   a , and input them to the data receiving unit  316 . The data receiving unit  316  performs processing such as amplification, frequency conversion, demodulation, deinterleave and error correction decoding on the MR signal inputted from the antenna  306   a . Thereby, the data receiving unit  316  extracts the original digitized MR signals from the MR signal for radio transmission, and inputs the extracted MR signals to the frequency downconversion unit  410  of the RF receiver  50 . 
     The frequency downconversion unit  410  multiplies the MR signals inputted from the data receiving unit  316  by the local signal inputted from the variable frequency generation unit  408 , and makes an arbitrary signal band get through by filtering. Thereby, the frequency downconversion unit  410  performs frequency conversion (downconversion) on the MR signals, and inputs the MR signals whose frequency is lowered to the signal processing unit  412 . 
     The signal processing unit  412  generates raw data of the MR signals by performing predetermined signal processing on the above MR signals whose frequency is lowered. The raw data of the MR signals are inputted to the image reconstruction unit  62 , and converted into k-space data and stored in the image reconstruction unit  62 . 
     Note that, as to the gate signal, it may be superimposed on the reference signal in the way similar to the trigger signal. In this case, because the number of radio communication pathways can be decreased by one by omitting components such as the antennas  106   d  and  306   d , configuration of the radio communication device  36  and the RF coil device  100  can be streamlined. 
     In addition, as to the respective frequencies of the signals (carrier waves) for the remote radio communication generated by the data transmitting unit  116 , the ID transmitting unit  122 , the reference signal transmitting unit  318  and the gate signal transmitting unit  324 , it is preferable to avoid frequencies which are equal to numbers obtained by dividing the frequency of RF pulses transmitted to the object P by a natural number (in the first embodiment, the respective frequencies of the carrier waves are set in such a manner). 
     In addition, the RF coil device  100  and the radio communication device  36  perform frequency separation of the carrier waves of the remote radio communication. More specifically, the respective radio frequency values used in the four carrier waves of the remote radio communication generated by the data transmitting unit  116 , the ID transmitting unit  122 , the reference signal transmitting unit  318  and the gate signal transmitting unit  324  are widely separated. 
     The foregoing is an explanation of the four radio communication pathways. 
     In  FIG. 7 , the system control unit  61  determines the imaging conditions such as a repetition time, a type of RF pulses, a center frequency of the RF pulses and a band width of the RF pulses in a pulse sequence, on the basis of the imaging conditions inputted by an operator via the input device  72  (see  FIG. 1 ). The system control unit  61  inputs the imaging conditions determined in the above manner to the pulse waveform generation unit  404 . 
     The pulse waveform generation unit  404  generates a pulse waveform signal of baseband by using the criterion clock signal inputted from the fixed frequency generation unit  406 , depending on the imaging conditions inputted from the system control unit  61  in the above manner. The pulse waveform generation unit  404  inputs the pulse waveform signal of baseband to the frequency upconversion unit  402 . 
     The frequency upconversion unit  402  multiplies the pulse waveform signal of baseband by the local signal inputted from the variable frequency generation unit  408 , then makes an arbitrary signal band pass by filtering, and thereby performs frequency conversion (upconversion). The frequency upconversion unit  402  inputs the pulse waveform signal of baseband whose frequency is raised to the RF transmitter  48 . 
     The RF transmitter  48  generates the RF pulses on the basis of the inputted pulse waveform signal. 
       FIG. 8  to  FIG. 11  are timing charts showing the first to fourth examples of transmission of electric power. In  FIG. 8  to  FIG. 11 , each horizontal axis indicates elapsed time t. 
     In addition, each timing chart in the upper part of each of  FIG. 8  to  FIG. 11  shows timing of transmitting the RF pulses for imaging, and each period of the protruded triangle-shaped bold line is the transmission span of the RF pulse. 
     In addition, each timing chart in the middle part of each of  FIG. 8  to  FIG. 11  shows timing of detecting MR signals, and each period during which the bold line protrudes to form a rectangular shape is the detection span of MR signals by the coil elements (EC 1  to EC 4 ) of the RF coil device  100 . 
     In addition, each timing chart in the bottom part of each of  FIG. 8  to  FIG. 11  shows timing of wirelessly transmitting electric power, electric power is transmitted in each period during which the bold line on the chart is ON-level, and electric power is not transmitted in each period during which the bold line on the chart is OFF-level. 
       FIG. 8  corresponds to a case where electric power is wirelessly transmitted from the whole body coil WB 1  to the RF coil device  100  on a steady basis. The “on a steady basis” herein means that electric power is continuously wirelessly transmitted regardless of a transmission span of an RF pulse, a detection span of MR signals or the like of a pulse sequence. 
       FIG. 9  corresponds to a case where electric power is wirelessly transmitted to the RF coil device  100  by avoiding only detection spans of MR signals. Such control can be achieved by outputting alternating-current power from the power transmitter  49  by avoiding only detection spans of MR signals under the control of the system control unit  61 , for example. 
     Here, in the first embodiment, the coil elements EC 1  to EC 4  of the RF coil device  100  perform both detection of MR signals and reception of electric power, and the whole body coil WB 1  performs both transmission of RF pulses and wireless transmission of electric power. However, this is only an example, and each function may be separately performed per coil by adding further coils. 
     For example, like the later-described fourth embodiment and the fifth embodiment, detection of MR signals may be performed by a coil exclusively for detection, and reception of electric power may be performed by a coil exclusively for power reception by deposing a further coil exclusively for power reception inside the RF coil device. 
     Alternatively, for example, like the later-described second embodiment and the third embodiment, another coil exclusively for transmitting electric power is disposed inside gantry  30  as an example, so that the whole body coil WB 1  performs transmission of RF pulses and detection of MR signals and the coil exclusively for transmitting electric power wirelessly transmits electric power. 
     Including cases where the respective functions are allotted to different coils by disposing a further coil, for example, in the following first to third cases, it is preferable to wirelessly transmit electric power by avoiding detection spans of MR signals like  FIG. 9 . 
     Firstly, it is a case where a coupling effect is likely to occur between coils for detecting MR signals on the RF coil device side (in the first embodiment, they are the coil elements EC 1  to EC 4 ) and a coil for wirelessly transmitting electric power (in the first embodiment, it is the whole body coil WB 1 ). The coupling effect means that a radiofrequency electric current leaks to a coil system of one side if a radiofrequency electric current is supplied to a coil system of the other side. In order to avoid this, a coil for transmitting electric power is set to off-state at the timing when MR signals are detected. 
     Secondly, it is a case where the coupling effect is likely to occur inside the RF coil device between a coil exclusively for detecting MR signals and a coil exclusively for receiving electric power. In order to avoid this, the coil exclusively for receiving electric power is set to off-state at the timing when MR signals are detected. 
     Thirdly, it is a case where a developmental period of noise overlaps a detection period of MR signals, because a circuit of receiving electric power inside the RF coil device generates noise at the time of wirelessly receiving electric power depending on conditions. In this case, the aspect of  FIG. 9  is preferable because it is possible that noise mixes into detecting and processing system of MR signals. In this third case, it is not necessary to turn off the coil exclusively for receiving electric power inside the RF coil device in the detection period of MR signals, and it may be enough to stop transmission of electric power. 
       FIG. 10  corresponds to a case where electric power is wirelessly transmitted to the RF coil device  100  by avoiding only spans of transmitting RF pulses (from the RF coil unit  34 ). The system control unit  61  can achieve such control by controlling the power transmitter  49  so as to output alternating-current power by avoiding output spans of radio-frequency electric currents from the RF transmitter  48 , for example. 
     Including cases where the respective functions are allotted to different coils as described earlier, for example, in the following first and second cases, it is preferable to wirelessly transmit electric power by avoiding output spans of the RF pulses like  FIG. 10 . 
     Firstly, it is a case where the coupling effect is likely to occur between a coil for transmitting the RF pulses to the object P and a coil for wirelessly transmitting electric power to the RF coil device side. 
     Secondly, it is a case where the coupling effect is likely to occur between a coil for transmitting the RF pulses to the object P and a coil for receiving electric power inside the RF coil device. 
       FIG. 11  corresponds to a case where electric power is wirelessly transmitted to the RF coil device  100  by avoiding spans of transmitting RF pulses and spans of detecting MR signals. As compared with the aspects of  FIG. 8  to  FIG. 10 , the aspect of  FIG. 11  is the most effective in terms of avoiding the coupling effect and noise contamination. More specifically, for example, the aspect of  FIG. 11  is especially preferable in the case where both of the following two conditions are satisfied. 
     The first condition is that the coupling effect is likely to occur between (A) a coil for transmitting the RF pulse to the object P and (B) at least one of a coil for wirelessly transmitting electric power to the RF coil device side and a coil for receiving electric power inside the RF coil device. 
     The second condition is that the coupling effect is likely to occur between (A) a coil for detecting MR signals inside the RF coil device and (B) at least one of a coil for wirelessly transmitting electric power to the RF coil device side and a coil for receiving electric power inside the RF coil device. 
       FIG. 12  is a flowchart illustrating an example of flow of imaging operation performed by the MRI apparatus  10  of the first embodiment. In the following, according to the step numbers in the flowchart shown in  FIG. 12 , an operation of the MRI apparatus  10  will be described by referring to the aforementioned  FIGS. 1 to 11  as required. 
     [Step S 1 ] The RF coil device  100  is loaded on the object P on the table  22  (see  FIG. 1 ). The system control unit  61  performs initial setting of the MRI apparatus  10 . 
     In addition, the system control unit  61  makes the power transmitter  49  and the whole body coil WB 1  (see  FIG. 2 ) start wireless transmission of the alternating-current power at the second resonance frequency f 2 , when it receives a command of starting power supply from the input device  72  by the operation of an operator, for example. Thereby, the coil elements EC 1  to EC 4  inside the RF coil device  100  receive the alternating-current power, and the rechargeable battery BAT is charged. This operation has been already explained with  FIG. 3  to  FIG. 6 . 
     After the power reception, the CPU  110  of the RF coil device  100  makes the ID transmitting unit  122  wirelessly transmit the identification information of the RF coil device  100  to the ID receiving unit  322 , by using the electric power from the rechargeable battery BAT. This operation has been already explained with  FIG. 7 . 
     Thereby, the system control unit  61  recognizes which RF coil device is loaded on the object P and that the wireless connection status with the RF coil device  100  is normal. 
     When the system control unit  61  recognizes that the wireless connection status with the RF coil device  100  is normal, the system control unit  61  outputs permission to communicate with the RF coil device  100  (communication permission) to each component of the MRI apparatus  10 , and then makes the power transmitter  49  and the whole body coil WB 1  continue wireless transmission of electric power. 
     As to the timing of wirelessly transmitting electric power, as an example here, the system control unit  61  sets it to one of the aspects of  FIG. 8  to  FIG. 11 , depending on a type of pulse sequence. 
     In time of receiving electric power, i.e. in time of charging, amount of heat generation of the control system  102  of the RF coil device  100  increases. Thus, it is better to adjust the timing of wirelessly transmitting electric power depending on electric power of the transmitted RF pulses per unit time. 
     As the first example, when the transmitted RF pulses per unit time are few because of reasons such as a long repetition time, the system control unit  61  sets the timing of wirelessly transmitting electric power to the aspect of  FIG. 8  in which electric power is transmitted on a steady basis. 
     As the second example, when the transmitted RF pulses per unit time are many because of reasons such as a short repetition time, the system control unit  61  adjusts the timing of wirelessly transmitting electric power like the aspects of  FIG. 9  to  FIG. 11 . 
     However, the above selection method is only an example for cases where the whole body coil WB 1  and the RF coil device  100  are configured so as to be unlikely to cause the coupling effect and noise contamination mentioned with  FIG. 8  to  FIG. 11 . 
     Thus, as to the timing of wirelessly transmitting electric power, the system control unit  61  may set it to one of the aspects of  FIG. 8  to  FIG. 11  selected by an operator&#39;s operation to the input device  72 . In addition, the four aspects of  FIG. 8  to  FIG. 11  are only examples, and the timing of wirelessly transmitting electric power is not limited to those aspects. 
     The reference signal transmitting unit  318  (see  FIG. 7 ) starts inputting the digital reference signal on which the trigger signal is superimposed to the reference signal receiving unit  118  of the RF coil device  100  through the radio communication pathway between the antennas  306   b  and  106   b , in accordance with the above communication permission (the reference signal is continuously wirelessly transmitted). 
     In addition, the table moving structure  23  (see  FIG. 1 ) moves the table  22  to inside of the gantry  30  in accordance with the control by the system control unit  61 . 
     After this, the process proceeds to Step S 2 . 
     [Step S 2 ] The system control unit  61  sets some of the imaging conditions of the main scan on the basis of the imaging conditions inputted to the MRI apparatus  10  via the input device  72  and information on the currently used RF coil device acquired in Step S 1  (in this example, information indicating that the RF coil devices  100  is used). After this, the process proceeds to Step S 3 . 
     [Step S 3 ] The system control unit  61  makes the MRI apparatus  10  perform prescans by controlling each component of the MRI apparatus  10 . In the prescans, for example, a corrected value of the center frequency of the RF pulses is calculated. 
     After this, the process proceeds to Step S 4 . 
     [Step S 4 ] The system control unit  61  sets the rest of the imaging conditions of the main scan on the basis of the execution results of the prescans. The imaging conditions include information on which of the coil elements EC 1  to EC 4  are used for detecting MR signals in the main scan. 
     Thus, the system control unit  61  inputs the information on the coil elements used for the main scan into the CPU  110  of the RF coil device  100  via any one of the radio communication pathways. This information is, for example, wirelessly transmitted from the gate signal transmitting unit  324  to the gate signal receiving unit  124 , and then inputted into the CPU  110  from the gate signal receiving unit  124 . 
     After this, the process proceeds to Step S 5 . 
     [Step S 5 ] The system control unit  61  makes the MRI apparatus  10  perform the main scan by controlling each component thereof. 
     More specifically, a static magnetic field is formed in the imaging space by the static magnetic field magnet  31  excited by the static magnetic field power supply  42 . In addition, electric currents are supplied from the shim coil power supply  44  to the shim coil  32 , and thereby the static magnetic field formed in the imaging space is uniformed. 
     Note that, during the implementation term of the main scan, the aforementioned gate signal is continuously wirelessly transmitted between the antennas  306   d  and  106   d  from the gate signal transmitting unit  324  to the gate signal receiving unit  124 . 
     After this, when the system control unit  61  receives a command of start of imaging from the input device  72 , the MR signals from the object P are acquired (collected) by repeating the following processes of &lt;1&gt; to &lt;4&gt; in series. 
     &lt;1&gt; The system control unit  61  drives the gradient magnetic field power supply  46 , the RF transmitter  48  and the RF receiver  50  in accordance with the pulse sequence, thereby the gradient magnetic fields are formed in the imaging region including the imaging part of the object P, and the RF pulses are transmitted from (the whole body coil WB 1  or the like of) the RF coil unit  34  to the object P. 
     When electric power is wirelessly transmitted at the timing shown in  FIG. 10  or  FIG. 11 , the gate signal is adjusted to, for example, on-level only in the period during which an RF pulse is transmitted to the object P. In this case, the gate signal of on-level is inputted from the gate signal receiving unit  124  of the RF coil device  100 , then each of the coil elements EC 1  to EC 4  of the RF coil device  100  becomes off-state and thereby the coupling effect is prevented. 
     When electric power is wirelessly transmitted at the timing shown in  FIG. 8  or  FIG. 9 , the gate signal is kept off-level because electric power is received by the coil elements EC 1  to EC 4  in the period during which an RF pulse is transmitted to the object P. 
     &lt;2&gt; When electric power is wirelessly transmitted at the timing explained with  FIG. 10  or  FIG. 11 , each of the gate signals is switched over to off-level after transmission of the RF pulses, and each of the coil elements (at least one of EC 1  to EC 4 ) selected for detecting MR signals in the Step S 4  detects the MR signals caused by nuclear magnetic resonance inside the object P. 
     When electric power is wirelessly transmitted at the timing explained with  FIG. 8  or  FIG. 9 , the gate signals are kept off-level and the MR signals are detected in the same way as mentioned above. 
     The detected MR signals are inputted to the duplexers (DP 1  to DP 4 ), the preamplifiers (PA 1  to PA 4 ), the A/D convertor (AD 1  to AD 4 ) in order, as explained with  FIG. 6  and  FIG. 7 . 
     &lt;3&gt; Each of the A/D converters (AD 1  to AD 4 ) corresponding to the coil elements (at least one of EC 1  to EC 4 ) selected for detecting MR signals starts sampling and quantization of the MR signals on the basis of the reference signal, in synchronization with the timing when the trigger signal is transmitted. Each of the A/D converters (AD 1  to AD 4 ) inputs the digitized MR signals to the P/S converter PSC. 
     The P/S converter  214  converts the inputted single or plural MR signal(s) into a serial signal, and inputs the serial signal to the data transmitting unit  116 . 
     The data transmitting unit  116  generates the MR signal for radio transmission by performing predetermined processing on the serial signal of the MR signal, and wirelessly transmits the serial signal from the antenna  106   a  to the antenna  306   a.    
     &lt;4&gt; The data receiving unit  316  of the radio communication device  36  extracts the original digital MR signals from the MR signal for radio transmission received by the antenna  306   a , per coil element. 
     The data receiving unit  316  inputs each of the MR signals extracted per coil element to the frequency downconversion unit  410  of the RF receiver  50 . 
     Note that, not only the RF coil device  100  but also the reception RF coil device  24  are used for detecting MR signals, the MR signals detected by the respective coil elements inside the reception RF coil device  24  are inputted to the frequency downconversion unit  410  of the RF receiver  50  by wire. 
     The frequency downconversion unit  410  performs frequency downconversion on the inputted MR signals, and inputs the MR signals whose frequency is lowered to the signal processing unit  412 . 
     The signal processing unit  412  generates raw data of the MR signals by performing predetermined processing on the inputted MR signals. The raw data of the MR signals are inputted to the image reconstruction unit  62 , and converted into k-space data and stored in the image reconstruction unit  62 . 
     After completing the acquisition of the MR signals detected by the coil element(s) of the RF coil device  100  by repeating the above &lt;1&gt; to &lt;4&gt; processes, the process proceeds to Step S 6 . 
     Note that, even in the implementation term of the above &lt;1&gt; to &lt;4&gt; processes, the RF coil device  100  performs the operation of wirelessly receiving electric power continuously (see  FIG. 8 ) or partially intermittently (see  FIG. 9  to  FIG. 11 ). 
     [Step S 6 ] The image reconstruction unit  62  reconstructs image data by performing image reconstruction processing including Fourier transformation on the k-space data. 
     The image reconstruction unit  62  stores the reconstructed image data in the image database  63 . 
     After this, the process proceeds to Step S 7 . 
     [Step S 7 ] The image processing unit  64  obtains the image data from the image database  63  and generates display image data by performing predetermined image processing on the obtained image data. The image processing unit  64  stores the display image data in the storage device  76 . 
     Then, the system control unit  61  transmits the display image data to the display device  74 , and makes the display device  74  display images indicated by the display image data. 
     Note that, as an example in  FIG. 12 , the input of the reference signal starts in Step S 1 . However, this is only an example. For example, the input of the reference signal may start just before the prescans in Step S 3  (i.e. after setting the imaging conditions in Step S 2 ). 
     The foregoing is a description of the operation of the MRI apparatus  10  according to the first embodiment. 
     As just described, in the first embodiment, the whole body coil WB 1  and the coil elements EC 1  to EC 4  are configured as circuits of the double resonance system, their first resonance frequency f 1  is set to the common value, and their second resonance frequency f 2  is also set to the common value. 
     That is, the whole body coil WB 1  transmits an RF pulse to the object P by resonating at the first resonance frequency f 1 , and wirelessly transmits electric power as electromagnetic waves to the RF coil device  100  by resonating at the second resonance frequency f 2 . Then, the coil elements EC 1  to EC 4  detect the MR signals from the object P by resonating at the first resonance frequency f 1 , and receive the wirelessly transmitted electric power by resonating at the second resonance frequency f 2 . 
     Because of the wireless transmission of the alternating-current power on the basis of the magnetically coupled resonant type wireless power transfer, electric power can be transmitted, even if the RF coil device  100  of the power receiving side is located separately from the power transmission side to some extent. 
     That is, according to the MRI apparatus  10  of the first embodiment, electric power can be wirelessly transmitted to the RF coil device satisfactorily and effectively by the magnetically coupled resonant type wireless power transfer, in the structure of wirelessly transmitting MR signals detected by the RF coil device to a control side of an MRI apparatus. 
     In addition, because the whole body coil WB 1  has the double resonance system in the first embodiment, it is not necessary to separately provide another coil for transmitting electric power. That is, as a merit of the first embodiment, it is not necessary to secure space inside the gantry  30  for another coil of transmitting electric power. 
     In addition, because each of the coil elements EC 1  to EC 4  of the RF coil device  100  has the double resonance system in the first embodiment, it is not necessary to separately provide another coil for receiving electric power. That is, without further enlarging the size of the RF coil device  100 , electric power can be received under the magnetically coupled resonant type wireless power transfer. 
     In addition, as described as the first example to the fourth example in Step S 1 , the system control unit  61  sets the timing of wirelessly transmitting electric power depending on a type of pulse sequence. That is, the timing of wirelessly transmitting electric power is set to an appropriate one of  FIG. 8  to  FIG. 11  in accordance with conditions such as a type of pulse sequence, required image quality and so on. 
     The Second Embodiment 
     The difference between the second embodiment and the first embodiment is as follows. That is, in the second embodiment, the whole body coil WB 2  does not have a function of transmitting electric power and another coil for transmitting electric power is separately provided inside the gantry  30 . 
       FIG. 13  is an equivalent circuit diagram of the power transmitting coil PT 1  of the MRI apparatus  10  of the second embodiment. The power transmitting coil PT 1  is composed by inserting a switch SW 2  and the capacitors Cg, Ch and Ci in series in eight-letter shaped hard-wiring. 
     The resonance frequency of the power transmitting coil PT 1  is equal to the frequency for transmitting electric power, i.e. the second resonance frequency f 2  in the first embodiment. The circuit constants of the power transmitting coil PT 1  such as the respective capacitance values of the capacitors Cg, Ch and Ci are selected so as to satisfy the above resonance frequency. 
     Although electric power can be transmitted so as to avoid a predetermined period like  FIG. 9  to  FIG. 11  by the output control of the power transmitter  49 , it can be transmitted so as to avoid a predetermined period by switching ON/OFF state of the switch SW 2 . 
     In addition, one end side of a power transmission cable  250  is connected to both ends of the capacitor Ch. 
     The other end of the power transmission cable  250  is connected to the power transmitter  49  (see later-described  FIG. 19 ). A capacitor Cj is inserted in one end side of the power transmission cable  250 . 
     The respective capacitance values of the capacitor Ch and the capacitor Cj are selected in such a manner that the capacitor Ch and the capacitor Cj function as an impedance matching circuit. 
       FIG. 14  is a schematic oblique drawing showing an equivalent circuit of the whole body coil WB 2  and an example of the layout of the power transmitting coil PT 1  of the MRI apparatus  10  of the second embodiment. 
     In the way similar to  FIG. 2 , the conducting wires of the circuit of the whole body coil WB 2  located on the near side in the X axis direction are indicated by bold lines, and the conducting wires located on the remote side in the X axis direction are indicated by fine lines. 
     In addition, as to each of the points where one conducting wire intersects with another conducting wire, electrically connected points are indicated by filled circle and non-connected points are distinguished from the electrically connected points by semicircularly indicating no connection between the conducting wires. 
     In addition, for the sake of distinction, in  FIG. 14 , the wires of the power transmitting coil PT 1  are indicated by dashed lines and the power transmission cable  250  is omitted in order to avoid complication. 
     The whole body coil WB 2  includes the first loop conductor  254 , the second loop conductor  256 , eight connecting conductors (rung)  258  and sixteen capacitors Ck. 
     In  FIG. 14 , the first loop conductor  254  corresponds to the ring on the left side in parallel with an X-Y plane, and the second loop conductor  256  corresponds to the ring on the right side in parallel with an X-Y plane. 
     The connecting conductors  258  correspond to eight straight lines extending along the Z axis direction as an example in  FIG. 14 . Each of the eight connecting conductors  258  is connected to the first loop conductor  254  on its one end and is connected to the second loop conductor  256  on its other end. 
     In the first loop conductor  254 , the ring includes eight connection nodes connecting itself to the eight connecting conductors  258 , and eight capacitors Ck are inserted between two of the eight connection nodes one by one. The same holds true for the second loop conductor  256 . 
     As just described, the whole body coil WB 2  is a bird cage type, and its circuit constants are selected in such a manner that its resonance frequency becomes the Larmor frequency. The circuit constants herein mean the capacitance value of the capacitor Ck, the inductance value of each wire of the first loop conductor  254 , the second loop conductor  256  and the connecting conductor  258  or the like. 
     Because the whole body coil WB 2  is a bird cage type of eight elements, it is supplied with electric power by the QD system from the respective connection nodes whose angles are mutually different by 90 degrees in the way similar to the first embodiment. More specifically, the high frequency transmitting and receiving cables  210  and  212  are respectively connected to positions having mutually different angles by 90 degrees in the first loop conductor  254 . 
     Note that, the connection wires of these high frequency transmitting and receiving cables  210  and  212  to the whole body coil WB 2  are respectively indicated by dashed lines in  FIG. 14  for distinction. 
     In addition, the power transmitting coil PT 1  is arranged to the interior side of the whole body coil WB 2  (i.e. the interior side of the RF coil unit  34 ) inside the gantry  30 , for example. 
     In the example of  FIG. 14 , the power transmitting coil PT 1  is arranged, in such a manner that its intersection part CRO of the eight-letter shape (the part indicated by a dashed line frame in  FIG. 13 ) becomes in parallel with the Z axis direction (the extending direction of the connecting conductors  258 ). 
     However, as to the layout of the power transmitting coil PT 1 , the layout shown in  FIG. 14  is only an example and its layout direction may be changed like the following  FIG. 15  and  FIG. 16 . 
       FIG. 15  is an equivalent circuit diagram of the power transmitting coil PT 1  observed from a direction different from  FIG. 13 . 
       FIG. 16  is a schematic oblique drawing showing another example of the layout of the power transmitting coil PT 1  to the whole body coil WB 2 , in the same notation as  FIG. 14 .  FIG. 15  describes the intersection part CRO of the eight-letter shape in the vertical direction of the paper in the same manner as  FIG. 16 , for easier comparison with  FIG. 16 . 
     In the layout of  FIG. 16 , the power transmitting coil PT 1  is arranged, in such a manner that its intersection part CRO of the eight-letter shape is orthogonal to the Z axis direction (the extending direction of the connecting conductors  258 ). 
     Although the power transmitting coil PT 1  practically sufficiently functions regardless of whether it is arranged in the direction shown in  FIG. 14  or  FIG. 16 , the power transmitting coil PT 1  is arranged in the direction shown in  FIG. 16  as an example in the second embodiment. This is because the layout of  FIG. 16  is considered to be slightly more effective than the layout of  FIG. 14  for the reason explained with  FIG. 17  as follows. 
       FIG. 17  is an explanatory diagram showing a comparison between the layout of  FIG. 14  and the layout of  FIG. 16 , in terms of existence or non-existence of the coupling effect by the magnetic fluxes passing through the power transmitting coil PT 1 . 
     The upper half of  FIG. 17  corresponds to the layout of  FIG. 14 , and the lower half of  FIG. 17  corresponds to the layout of  FIG. 16 . In  FIG. 17 , the switch SW 2  is omitted under the assumption that the switch SW 2  is in a conduction state. 
     Here, a high frequency magnetic field of the RF pulse transmitted from the whole body coil WB 2  to the object P actually rotates in an X-Y plane, for example. 
     Thus, the direction of magnetic fluxes passing through the power transmitting coil PT 1  is not uniquely determined. 
     Accordingly, the case where the possibility of causing the coupling effect with the whole body coil WB 2  is comprehensively lower is desirable in consideration of various generation patterns of magnetic fluxes. 
     First, consider the layout of  FIG. 14 . 
     As shown in the top part of  FIG. 17 , it is assumed that the direction of the magnetic flux FL 1  on the upper side of the intersection part CRO of the eight-letter shape is the same as the direction of the magnetic flux FL 2  on its lower side. In this case, the electric current Iin 1  in the downward direction of  FIG. 17  is induced by the magnetic flux FL 1  in the upper side of the intersection part CRO, and the electric current Iin 2  in the downward direction of  FIG. 17  is induced by the magnetic flux FL 2  in the lower side of the intersection part CRO. However, because the power transmitting coil PT 1  has eight-letter shaped wiring structure, the flowing direction of the electric current Iin 1  is opposite to that of the electric current Iin 2  in terms of circuit, these two cancel each other flow, and thus the coupling effect is not caused. 
     On the other hand, as shown in the second top part of  FIG. 17 , it is assumed that the direction of the magnetic flux FL 1  on the upper side of the intersection part CRO of the eight-letter shape is opposite to the direction of the magnetic flux FL 2  on its lower side. In this case, the electric current Iin 1  in the downward direction of  FIG. 17  is induced by the magnetic flux FL 1  in the upper side of the intersection part CRO, and the electric current Iin 2  in the upward direction of  FIG. 17  is induced by the magnetic flux FL 2  in the lower side of the intersection part CRO. Because the flowing direction of the electric current Iin 1  is the same as the electric current Iin 2  due to the eight-letter shaped wiring structure, the coupling effect is likely to be caused. 
     Next, consider the layout of  FIG. 16 . 
     As shown in the second bottom part of  FIG. 17 , as to the right side of the intersection part CRO of the eight-letter shape, it is assumed that the magnetic flux FL 3  passes through the upper side and the magnetic flux FL 5  passes through the lower side. 
     Similarly, as to the left side of the intersection part CRO of the eight-letter shape, it is assumed that the magnetic flux FL 4  passes through the upper side and the magnetic flux FL 6  passes through the lower side. 
     Furthermore, it is assumed that these magnetic fluxes FL 3  to FL 6  are in the same direction. 
     In this case, the electric currents Iin 3  and Iin 5  are induced in the same direction in terms of circuit by the magnetic fluxes FL 3  and FL 5 , and the same applies to the electric currents Iin 4  and Iin 6  induced by the magnetic fluxes FL 4  and FL 6 . The flowing direction of the electric current Iin 3  and Iin 5  becomes opposite to the flowing direction of the electric currents Iin 4  and Iin 6 . That is, the electric currents Iin 3  and Iin 5  counterbalance the electric currents Iin 4  and Iin 6 , and thus the coupling effect is not caused. 
     On the other hand, as shown in the bottom part of  FIG. 17 , it is assumed that the direction of the magnetic fluxes FL 3  and FL 4  on the upper side is opposite to the direction of the magnetic fluxes FL 5  and FL 6 . 
     In this case, the electric currents Iin 3  and Iin 6  are induced in the same direction in terms of circuit by the magnetic fluxes FL 3  and FL 6 , and the same applies to the electric currents Iin 4  and Iin 5  induced by the magnetic fluxes FL 4  and FL 5 . The flowing direction of the electric current Iin 3  and Iin 6  becomes opposite to the flowing direction of the electric currents Iin 4  and Iin 5 . That is, the electric currents Iin 3  and Iin 6  counterbalance the electric currents Iin 4  and Iin 5 , and thus the coupling effect is not caused. 
     Thus, the layout of  FIG. 16  does not cause the coupling effect regardless of the direction of the magnetic flux on the upper side of  FIG. 17  and the direction of the magnetic flux on the lower side of  FIG. 17  are the same or opposite to each other. Accordingly, the layout of  FIG. 16  is less likely to cause the coupling effect than the layout of  FIG. 14 . Thus, it is considered that the layout of  FIG. 16  is slightly more preferable than the layout of  FIG. 14 . 
     As just described, the arrangement direction of the power transmitting coil PT 1  has been explained in relation to the Z axis direction (the extending direction of the connecting conductor  258 ). 
     Next, the layout of the power transmitting coil PT 1  will be explained in relation to the position of the RF coil device  100 . 
       FIG. 18  is a schematic cross-sectional diagram showing an example of the layout of the power transmitting coil PT 1  indicated by the positional relation with the RF coil device  100 , in the second embodiment. When the RF coil device  100  is loaded on the upper side of the object P in the Y axis direction (the vertical direction), it is preferable that the power transmitting coil PT 1  is disposed to the upper side in the vertical direction inside the gantry  30  as shown in  FIG. 18 . 
     This is because electric power can be wirelessly transmitted more effectively if the power transmission side and the power receiving side are close to each other. 
       FIG. 19  is a block diagram showing the respective components relevant to the transmission system of the RF pulses and the transmission system of electric power of the second embodiment, in the same notation as  FIG. 3 . The RF pulses of the Larmor frequency are inputted from the RF transmitter  48  side to the whole body coil WB 2  by the QD system, and MR signals detected by the whole body coil WB 2  are taken in the RF receiver  50  side. This point is the same as the first embodiment. 
     On the other hand, because the power transmitting coil PT 1  is further (separately) provided in the second embodiment, alternating-current power (whose frequency is equal to the second resonance frequency f 2  in the first embodiment) for wireless transmission is supplied from the power transmitter  49  to the power transmitting coil PT 1  without going through a phase divider. 
     The functions of the high pass filters HPF 1  and HPF 2  and the low pass filter LPF 1  shown in  FIG. 19  are respectively the same as the first embodiment. 
     The foregoing is the explanation of the structure of the MRI apparatus  10  of the second embodiment, and imaging operation of the second embodiment is the same as that of the first embodiment explained with  FIG. 12 . That is, the timing of wirelessly transmitting electric power is set to the appropriate one of  FIG. 8  to  FIG. 11 , in accordance with a type of pulse sequence. 
     As just described, the same effects as the first embodiment are obtained in the second embodiment. 
     As compared with the first embodiment, though the layout space for the power transmitting coil PT 1  is further secured, the phase divider  232  in the power transmission side and one of the low pass filters can be omitted in the second embodiment (see  FIG. 3  and  FIG. 19 ). 
     The Third Embodiment 
     The structure of the MRI apparatus  10  of the third embodiment is the same as the second embodiment, except that the structure of the power transmitting coil is changed from eight-letter shape to a loop type. Thus, only the difference between the third embodiment and the second embodiment will be explained. 
       FIG. 20  is an equivalent circuit diagram of the power transmitting coil PT 2  of the MRI apparatus  10  of the third embodiment. The power transmitting coil unit PT 2  is composed by inserting a switch SW 2 , capacitors Cm, Cn and Co in series in loop-shape hard-wiring. 
     The resonance frequency of the power transmitting coil unit PT 2  is equal to the frequency for power transmission (which is equal to the second resonance frequency f 2  of the first embodiment). The circuit constants of the power transmitting coil unit PT 2  such as the respective capacitance values the capacitors Cm, Cn and Co are selected so that the resonance frequency of the power transmitting coil unit PT 2  becomes the above frequency for power transmission. The switch SW 2  functions in the same way as the second embodiment. 
     In addition, one end side of the power transmission cable  250  is connected to both ends of the capacitor Co. The other end side of the power transmission cable  250  is connected to the power transmitter  49 . The capacitor Cp is inserted in the one end side of the power transmission cable  250 . 
     The respective capacitance values of the capacitor Co and the capacitor Cp are selected, in such a manner that the capacitor Co and the capacitor Cp function as an impedance matching circuit. 
       FIG. 21  is a schematic oblique drawing showing an example of the layout of the power transmitting coil PT 2  of the third embodiment, in the same notation as  FIG. 14 . The power transmitting coil unit PT 2  is disposed to the interior side of the whole body coil WB 2  (the interior side of the RF coil unit  34 ) inside the gantry  30  as shown in  FIG. 21 , for example. 
     In addition, similarly to the second embodiment, it is preferable that the power transmitting coil unit PT 2  is disposed to the upper side in the vertical direction if the RF coil device  100  is loaded on the upper side of the object P in the Y axis direction (vertical direction). 
     As just described, the same effects as the second embodiment are obtained in the third embodiment. 
     The Fourth Embodiment 
     The MRI apparatus  10  of the fourth embodiment has the same structure as the MRI apparatus  10  of the first embodiment, except that a power receiving coil is separately provided inside the RF coil device. 
     That is, the structure of the power transmission side is the same as the first embodiment, and only the difference between the fourth embodiment and the first embodiment will be explained as follows. 
       FIG. 22  is a schematic equivalent circuit diagram showing an example of the structure of the RF coil device  100 ′ of the fourth embodiment. Although twelve coil elements EL 1  to EL 12  are shown in  FIG. 22  in order to avoid complication, the number of the coil elements may be thirteen, more than thirteen, eleven of less than eleven. 
     In  FIG. 22 , only the wires of the power receiving coil  140  and the wires of the coaxial cable  160  connected to the power receiving coil  140  are indicated by bold lines in order to distinguish them from the wires of the coil elements EL 1  to EL 12 . 
     The power receiving coil  140  includes a switch SW 3  and capacitors Cr, Ct and Cu. The circuit constants of the power receiving coil  140  such as the respective capacitance values of the capacitors Cr, Ct and Cu are selected, in such a manner that the resonance frequency of the power receiving coil  140  becomes the frequency for power transmission (the second resonance frequency f 2  of the first embodiment). 
     Although electric power can be wirelessly transmitted so as to avoid predetermined periods like  FIG. 9  to  FIG. 11  by the output control of the power transmitter  49 , electric power can be received so as to avoid predetermined periods by ON/OFF switching of the switch SW 3 . 
     In addition, one end side of the coaxial cable  160  is respectively connected to both ends of the capacitor Cu of the power receiving coil  140 . The other end side of the coaxial cable  160  is connected to the control system  102 ′ of the RF coil device  100 ′. The capacitor Cv is inserted in the one end side of the coaxial cable  160 . 
     The respective capacitance values of the capacitor Cu of the power receiving coil  140  and the capacitor Cv inserted in the coaxial cable  160  are selected in such a manner that they function as an impedance matching circuit. 
     Because the general structure of each of the coil elements EL 1  to EL 12  may be the same as coil elements of the conventional technology, detailed explanation is omitted. However, for the sake of obtaining the decoupling effect, the respective coil elements EL 1  to EL 12  are arranged in such a manner that the plane including wires of the power receiving coil  140  becomes in parallel with the plane including the wires of the respective coil elements EL 1  to EL 12 . In addition, each of the coil elements EL 1  to EL 12  is arranged so as to partially overlap each other when they are viewed from above in order for them to have mutual decoupling effect. 
       FIG. 23  is a schematic block diagram showing the respective components relevant to the digital radio communication system of the MR signals and the charging system, in the MRI apparatus  10  of the fourth embodiment. 
     The control system  102 ′ of the RF coil device  100 ′ includes the high pass filters HPF 1  to HPF 12 , the preamplifiers PA 1  to PA 12  and the A/D convertors AD 1  to AD 12 , all of which respectively correspond to the coil elements EL 1  to EL 12 . 
     However, only the connection destinations of the coil elements EL 1  and EL 2  are shown in  FIG. 23 , because illustrating hard-wiring of all the coil elements makes  FIG. 23  complicated. Actually, there are the high pass filters HPF 3  to HPF 12 , the preamplifiers PA 3  to PA 12  and the A/D convertors AD 3  to AD 12 , to which MR signals of the coil elements EL 3  to EL 12  are respectively inputted in the pathway similar to that of the coil element EL 1 . However, they are not illustrated. 
     In addition, the control system  102 ′ further includes a CPU  110 ′, a rectifier RC 1 , the rechargeable battery BAT, the P/S convertor PSC, the data transmitting unit  116 , the reference signal receiving unit  118 , the ID transmitting unit  122  and the gate signal receiving unit  124 . In addition, the RF coil device  100 ′ includes the antennas  106   a  to  106   d , similarly to the first embodiment. 
     Each of the coil elements EL 1  to EL 12  detects the MR signals emitted from the object P, and these MR signals are inputted to the preamplifiers PA 1  to PA 12  via the high pass filters HPF 1  to HPF 12 . 
     The high pass filters HPF 1  to HPF 12  remove noise such as the frequency component of the wirelessly transmitted alternating-current power. 
     Each of the MR signals inputted to the preamplifiers PA 1  to PA 12  is wirelessly transmitted to the radio communication device  36  and subjected to the processing, in the same way as the first embodiment. 
     On the other hand, the electromagnetic waves of the second resonance frequency f 2  are emitted from the whole body coil WB 1  by the electric power supplied from the power transmitter  49 . 
     The power receiving coil  140  of the RF coil device  100 ′ wirelessly receives the alternating-current power by resonating at this second resonance frequency f 2 . The alternating-current power received by the power receiving coil  140  is taken in the control system  102 ′ via the coaxial cable  160 , and is converted into direct-current electricity by the rectifiers RC 1 . The rectifiers RC 1  charges the rechargeable battery BAT by this direct-current electricity. 
     As just described, in the fourth embodiment, the coil elements EL 1  to EL 12  exclusively for detecting MR signals and the power receiving coil  140  exclusively for receiving electric power are disposed in the RF coil device  100 ′ side. Although the coil arrangement on the RF coil device  100 ′ is different from the first embodiment, the same effects as the first embodiment are obtained in the fourth embodiment. 
     As compared with the first embodiment, though the power receiving coil  140  is separately provided, the number of the rectifiers can be reduced to one and the duplexers can be omitted in the RF coil device  100 ′. 
     Note that, though the power receiving coil  140  is a loop type in the fourth embodiment, this is only an example. The power receiving coil in the RF coil device  100 ′ may be eight-letter shaped, for example. 
     The Fifth Embodiment 
     The structure of the MRI apparatus  10  of the fifth embodiment is the same as the fourth embodiment, except that a coil exclusively for power transmission is separately provided in the power transmission side like the second embodiment or the third embodiment. 
     Thus, instead of the whole body coil WB 1  of the double resonance system in the first embodiment and the fourth embodiment, (1) the whole body coil WB 2  and (2) one of the power transmitting coil PT 1  (see  FIG. 13  to  FIG. 16 ) and the power transmitting coil unit PT 2  (see  FIG. 20  and  FIG. 21 ) are disposed inside the gantry  30 . 
     That is, the fifth embodiment can be interpreted as combination of the first to the fourth embodiments, and a structure chart for each component of the MRI apparatus  10  of the fifth embodiment is omitted. 
     Here, as to wireless power transmission, transmission efficiency can be improved in a condition in which the power transmitting coil (PT 1  or PT 2 ) easily couples to the power receiving coil. In order to achieve this, it is considered to be preferable if the directions of the magnetic fluxes that respectively pass through both sides are the same. 
       FIG. 24  is an explanatory diagram showing a difference in degree of the coupling effect between combinations with the power transmitting coil, in the case of using the eight-letter shaped power transmitting coil PT 1  in the fifth embodiment. 
     When the power transmitting coil PT 1  of eight-letter shape is disposed to the upper side in the vertical direction (the Y axis direction) inside the gantry  30  like  FIG. 18 , it is preferable that the power receiving coil of the RF coil device  100 ′ loaded on the object P is the power receiving coil  140 ′ of eight-letter shape (see the upper part of  FIG. 24 ). 
     This is because the magnetic fluxes generated from the power transmitting coil PT 1  pass through the hard-wiring of the power receiving coil  140 ′ in a route that easily generates an induced current, if a power transmitting coil of an eight-letter shape and a power receiving coil of an eight-letter shape are arranged so as to face each other. 
     More specifically, as shown in the upper part of  FIG. 24 , the direction of the first magnetic flux passing through the right loop of the power receiving coil  140 ′ of an eight-letter shape and the direction of the second magnetic flux passing through its left loop are opposite to each other in a plane where the hardwiring of the power receiving coil  140 ′ extends. Accordingly, the direction of the electric current induced in the right loop by the first magnetic flux and the direction of the electric current induced in the left loop by the second magnetic flux are the same in terms of circuit, because the right loop and the left loop are wired so as to become the eight-letter shape. 
     On the other hand, consider a case where the power transmitting coil PT 1  of eight-letter shape is disposed to the upper side in the vertical direction inside the gantry  30  like  FIG. 18  and the power receiving coil  140  of a loop type is arranged on the object P (see the lower part of  FIG. 24 ). In this case, as compared with the upper part of  FIG. 24 , it is hard to say that the magnetic fluxes generated from the power transmitting coil PT 1  pass through the hard-wiring of the power receiving coil  140  in a route that easily cause an induced current. The reason is as follows. 
     That is, the direction of the first magnetic flux passing through the right side of the loop wire of the power receiving coil  140  and the direction of the second magnetic flux passing through the left side the loop wire are opposite to each other. Accordingly, the direction of the electric current induced by the first magnetic flux and the direction of the electric current induced by the second magnetic flux become opposite to each other. 
       FIG. 25  is an explanatory diagram showing a difference in degree of the coupling effect between combinations with the power transmitting coil, in the case of using the loop type power transmitting coil PT 2  in the fifth embodiment. 
     It is preferable that the power receiving coil of the RF coil device  100 ′ loaded on the object P is the power receiving coil  140  of a loop type, if the power transmitting coil unit PT 2  of a loop type is disposed to the upper side in the vertical direction inside the gantry  30  (see the upper part of  FIG. 25 ). 
     This is because the magnetic fluxes generated from the power transmitting coil PT 2  pass through the hard-wiring of the power receiving coil  140  in a route that easily generates an induced current, if a power transmitting coil of a loop type and a power receiving coil of a loop type are arranged so as to face each other. The reason is as follows. 
     For example, in the upper part of  FIG. 25 , the direction of the first magnetic flux (indicated by a dashed line) passing through the right side of the loop wire of the power receiving coil  140  and the direction of the second magnetic flux (indicated by a chain line) passing through the left side of the loop wire are the same, when they are viewed from a plane where the wire of the power receiving coil  140  extends. Accordingly, the direction of the electric current induced by the first magnetic flux becomes the same as the direction of the electric current induced by the second magnetic flux. 
     On the other hand, consider a case where the power transmitting coil unit PT 2  of a loop type is disposed to the upper side in the vertical direction inside the gantry  30  and the power receiving coil  140 ′ of an eight-letter shape is loaded on the object P (see the lower part of  FIG. 25 ). In this case, as compared with the upper part of  FIG. 25 , it is hard to say that the magnetic fluxes generated from the power transmitting coil PT 2  pass through the hard-wiring of the power receiving coil  140 ′ in a route that easily causes an induced current. 
     This is because the power receiving coil  140 ′ is wired into an eight-letter shape, and thus the direction of the electric current induced in the right side of the power receiving coil  140 ′ by the right side magnetic flux indicated by a dashed line becomes opposite to the direction of the electric current induced in the left side by the left side magnetic flux indicated by a chain line in terms of circuit in the lower part of  FIG. 25 . 
     Thus, in the fifth embodiment, the power transmitting coil and the power receiving coil are selected so as to accord with the combination of the upper part of  FIG. 24  or the upper part of  FIG. 25 . 
     As just described, the same effects as the first embodiment are obtained in the fifth embodiment. 
     According to each of the aforementioned embodiments, electric power of an RF coil device can be saved satisfactorily and effectively in structure of wirelessly transmitting MR signals detected by the RF coil device to a control side of an MRI apparatus. 
     Supplementary Notes on the Embodiments 
     [1] In the first to fifth embodiments, examples in which only one wearable type RF coil device is used have been explained. However, embodiments of the present invention are not limited to such aspects. 
     In a case where a plurality of wearable type RF coil devices are used, electric power can be wirelessly transmitted to each of the RF coil devices by the magnetically coupled resonant type wireless power transfer and digitized MR signals from each of the RF coil devices can be wirelessly received by the radio communication device  36  on the basis of the aforementioned theory. 
     When a plurality of wearable type RF coil devices are used, electric power may be wirelessly transmitted to at least one of the RF coil devices by the magnetically coupled resonant type wireless power transfer in the above manner, and as to the rest of the RF coil devices, conventional type of RF coil devices each of which is connected to a connection port of an MRI apparatus by wire may be used. 
     [2] Examples in which the radio communication device  36  is disposed to the deep side of the gantry  30  in  FIG. 1  have been explained. However, embodiments of the present invention are not limited to such an aspect. 
     The radio communication device  36  may be disposed to another position such as the entrance of the gantry  30 , for example. 
     In addition, when a plurality of RF coil devices are used, a plurality of the radio communication devices  36  respectively corresponding to the plurality of RF coil devices may be provided, for example. 
     [3] Correspondences between terms used in the claims and terms used in the embodiments described above will be described. Note that the correspondences described below are just some of possible interpretations for reference and should not be construed as limiting the present invention. 
     In the first embodiment and the fourth embodiment, the power transmitter  49  and the whole body coil WB 1  are examples of the power transmitting unit described in the claims. 
     In the second embodiment, the third embodiment and the fifth embodiment, the power transmitter  49  and the power transmitting coil PT 1  (or PT 2 ) are examples of the power transmitting unit described in the claims. 
     In the first embodiment, the second embodiment and the third embodiment, the coil elements EC 1  to EC 4 , the capacitor C 3 , the coaxial cables  104  and the duplexers DP 1  to DP 4  are examples of the power receiving unit described in the claims. 
     In the fourth embodiment, the power receiving coil  140  and the coaxial cables  160  are examples of the power receiving unit described in the claims. 
     The radio communication device  36  is an example of the signal receiving unit described in the claims. 
     The A/D convertors AD 1  to AD 4  (or AD 1  to AD 12 ), the P/S convertor PSC, the data transmitting unit  116  and the antenna  106   a  in the RF coil devices  100  and  100 ′ are examples of the signal transmitting unit described in the claims. 
     The rechargeable battery BAT is an example of the charge/discharge element described in the claims. 
     [4] While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.