JP5035890B2 - RF coil and MRI apparatus - Google Patents

Description

  The present invention relates to an RF coil (Radio Frequency Coil) and an MRI (Magnetic Resonance Imaging) apparatus. More specifically, the present invention relates to an RF coil comprising two coils (Coil) whose relative positional relationship can be changed and having a mechanism for removing magnetic coupling between them, and an MRI apparatus using the RF coil.

  If there is a magnetic coupling due to mutual inductance between the coils arranged adjacent to each other, the reconstructed image appears as an artifact and the image quality deteriorates. Therefore, the magnetic coupling between the coils is neutralized by the following four methods, for example.

One is a method of overlapping the coil surfaces of adjacent coils by about 10% of the coil area (see, for example, paragraph [0002] and FIG. 13 of Patent Document 1).
The second is a method of generating inductive coupling using a coil so as to remove magnetic coupling (see, for example, Patent Document 2).
The third is a method of generating capacitive coupling using a capacitor so as to remove magnetic coupling (see, for example, Patent Document 3).
Finally, there is a method of cutting a loop of a coil by a high impedance (Impedance) parallel resonance circuit (see, for example, Patent Document 4).

Further, for example, when photographing a patient's shoulder or carotid artery, there are cases where it is desired to change the distance and angle between coils used to transmit an RF pulse (Pulse) and receive a magnetic resonance signal. In such a case, in the method of generating inductive coupling using the above-described coil, a method of changing the degree of overlapping of two coils used for generating inductive coupling has been proposed (for example, , See Patent Document 2).
Japanese Patent Laid-Open No. 11-318851 JP 2005-28141 A JP 2000-166894 A JP 2001-309901 A

  In the method of overlapping the coil surfaces, since the positional relationship between the coils is limited, the distance and angle between the coils cannot be changed.

  Further, the method of cutting the coil loop by the high impedance parallel resonance circuit cannot be used for the plurality of coils when the magnetic resonance signal is simultaneously received by the plurality of coils.

  The method of inductive coupling using a coil is a new magnetic coupling between the coil used to generate inductive coupling and the coil used to transmit RF pulses and receive magnetic resonance signals. , Magnetic coupling becomes complicated. This complexity can be reduced, for example, by placing the coils used to generate inductive coupling and the coils used to transmit RF pulses and receive magnetic resonance signals to be orthogonal to each other. There is a limitation on the arrangement of the coil used to cause sexual coupling and the coil used for transmitting RF pulses and receiving magnetic resonance signals.

  From the above, the distance and angle between the two coils used for RF pulse transmission and magnetic resonance signal reception can be changed, and magnetic coupling is sufficiently removed by the method of generating capacitive coupling using a capacitor. There is a need for an RF coil that can be used and an MRI apparatus using the RF coil.

  The RF coil of the present invention includes a first coil used for transmitting an RF pulse or receiving a magnetic resonance signal, a second coil used for transmitting an RF pulse or receiving a magnetic resonance signal, and the first coil. A first inter-coil connection capacitor that generates a voltage that cancels out a voltage generated by a mutual inductance between the first coil and the second coil, and a coil of the second coil A second inter-coil connecting capacitor that is included in a loop and generates a voltage that cancels a voltage generated by a mutual inductance between the first coil and the second coil; and a first inter-coil connecting capacitor A first neutralizing capacitor that connects the two coils at one end and one end of the second inter-coil connecting capacitor; and the first inter-coil connecting capacitor. A connection line or a second neutralization capacitor for connecting the two coils at the other end of the sensor and the other end of the second inter-coil connection capacitor, and the first coil and the second coil The first coil and the second coil are changed by changing the capacitance of the first neutralization capacitor and / or the second neutralization capacitor in accordance with a change in the mutual distance or angle. The magnetic coupling due to the mutual inductance is removed.

  Preferably, in the RF coil of the present invention, the first coil and the second coil are arranged on the same plane, and the mutual distance can be changed on the same plane.

  Preferably, in the RF coil of the present invention, the first coil and the second coil are arranged to face each other, and the distance to face can be changed.

  Preferably, in the RF coil of the present invention, the first neutralization capacitor and / or the second neutralization capacitor includes at least two chargeable flat plates arranged in parallel, and the flat plates are translated. As a result, the area of the overlapping portion of the flat plates is changed, and the capacitance is changed.

  Preferably, in the RF coil of the present invention, an insulating material having a high dielectric constant is attached to the surface of the flat plate.

  Preferably, in the RF coil of the present invention, the first coil and the second coil are rotated about a rotation axis so that an angle formed by the coil surfaces of the first coil and the second coil is set. Wherein the first neutralization capacitor and / or the second neutralization capacitor includes at least two chargeable curved plates arranged to rotate about the rotational axis; Depending on the angle formed by the coil surfaces of the first coil and the second coil, the curved plate is rotated to change the area of the overlapping portion of the curved plate, thereby changing the capacitance.

  Preferably, in the RF coil of the present invention, an insulating material having a high dielectric constant is attached to the surface of the curved plate.

  The MRI apparatus of the present invention includes a first coil used for transmitting an RF pulse or receiving a magnetic resonance signal, a second coil used for transmitting an RF pulse or receiving a magnetic resonance signal, and the first coil. A first inter-coil connecting capacitor that is included in a coil loop of the first coil and generates a voltage that cancels a voltage generated by a mutual inductance between the first coil and the second coil; and the second coil And a second inter-coil connection capacitor that generates a voltage that cancels a voltage generated by a mutual inductance between the first coil and the second coil, and the first inter-coil connection. A first neutralizing capacitor for connecting the two coils at one end of the capacitor and one end of the second inter-coil connecting capacitor; and the first coil indirect An RF coil including a connection line connecting the two coils at the other end of the capacitor and the other end of the second inter-coil connection capacitor or a second neutralization capacitor; and the first coil and the By changing the capacitance of the first neutralization capacitor and / or the second neutralization capacitor in response to a change in the mutual distance or angle of the second coil, the first coil and the second coil The magnetic coupling due to the mutual inductance between the second coils is removed.

  As described above, according to the present invention, the distance and angle between two coils used for transmission of RF pulses and reception of magnetic resonance signals can be changed, and a capacitive coupling is generated using a capacitor. Thus, it is possible to provide an RF coil that can sufficiently remove the magnetic coupling and an MRI apparatus using the RF coil.

FIG. 1 is a diagram showing an MRI apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the MRI apparatus 10 according to the present embodiment includes a magnet system 11, a cradle 12, a gradient magnetic field drive unit 13, an RF transmission coil drive unit 14, and a data (Data) collection unit. 15, a control unit 16, and an operator console (Operator Console) 17.

  As shown in FIG. 1, the magnet system 11 has a generally cylindrical inner space (Bore) 111, and a cradle 12 on which the subject 20 is placed via a cushion is placed in the bore 111. It is carried in by a transport unit (not shown).

  In the magnet system 11, as shown in FIG. 1, an RF coil 40, a static magnetic field generation unit 112, a gradient magnetic field coil unit 113, and a magnet center (Magnet Center, center position for scanning) around the bore 111 are provided. An RF transmission coil unit 114 is disposed.

  As will be described later, the RF coil 40 includes two coils that receive a magnetic resonance signal. When changing the distance or angle between these coils, the RF coil 40 is magnetically generated by a method of generating capacitive coupling using a capacitor. It is possible to sufficiently cancel the mechanical bond.

  The static magnetic field generator 112 generates a static magnetic field in the bore 111. The direction of the static magnetic field is, for example, parallel to the body axis direction of the subject 20. However, the direction of the static magnetic field may be perpendicular to the body axis direction of the subject 20.

  The gradient magnetic field coil unit 113 generates a gradient magnetic field that gives a gradient to the strength of the static magnetic field formed by the static magnetic field generation unit 112 so that the magnetic resonance signal received by the RF coil 40 has three-dimensional position information. There are three types of gradient magnetic fields generated by the gradient magnetic field coil unit 113: a slice selection gradient magnetic field, a frequency encoding (Encode) gradient magnetic field, and a phase encoding gradient magnetic field. The coil unit 113 has three types of gradient magnetic field coils.

  The RF transmission coil unit 114 transmits an RF pulse, and generates a magnetic resonance signal by exciting a proton spin in the subject 20 in the static magnetic field space formed by the static magnetic field generation unit 112. Let

  The gradient magnetic field drive unit 13 gives a drive signal DR1 to the gradient magnetic field coil unit 113 based on an instruction from the control unit 16 to generate a gradient magnetic field. The gradient magnetic field drive unit 13 has three systems of drive circuits (not shown) corresponding to the three systems of gradient magnetic field coils of the gradient magnetic field coil unit 113.

  The RF transmission coil drive unit 14 has an RF pulse frequency synthesizer, and generates a drive signal DR2 using the RF pulse frequency synthesizer. The drive signal DR2 is given to the RF transmission coil unit 114, and RF pulses are transmitted from the RF transmission coil unit 114.

  The data collection unit 15 takes in the magnetic resonance signal received by the RF coil 40, converts it into a digital signal, and outputs it to the data processing unit 171 of the operator console 17.

  The control unit 16 controls the gradient magnetic field drive unit 13 and the RF transmission coil drive unit 14 according to a predetermined pulse sequence (Pulse Sequence), and generates the drive signal DR1 and the drive signal DR2. Further, the control unit 16 controls the data collection unit 15.

As shown in FIG. 1, the operator console 17 includes a data processing unit 171, an image database (Data Base) 172, an operation unit 173, and a display unit 174.
The data processing unit 171 performs overall control of the MRI apparatus 10, image reconstruction processing, and the like. A control unit 16 is connected to the data processing unit 171, and the data processing unit 171 controls the control unit 16.
In addition, an image database 172, an operation unit 173, and a display unit 174 are connected to the data processing unit 171. The image database 172 includes, for example, a hard disk (Hard Disk) device that can be recorded and reproduced, and records the reconstructed reconstructed image data and the like. The operation unit 173 includes a keyboard, a mouse, and the like, and the display unit 174 includes a graphic display.

  FIG. 2 is a diagram showing a parallel plate capacitor. The parallel plate capacitor 30 includes a flat plate 31 and a flat plate 32, and the flat plate 31 and the flat plate 32 are arranged to face each other. The areas of the flat plate 31 and the flat plate 32 are both S, and the distance between the flat plate 31 and the flat plate 32 is d. The capacitance C of the parallel plate capacitor 30 is expressed by the following equation.

  Here, ε is a dielectric constant.

FIG. 3 is a diagram illustrating an example of a parallel plate capacitor in which the capacitance is changed by changing the area of the overlapping portion by moving the plate in parallel.
From the above equation (1), it is understood that the capacitance C of the parallel plate capacitor 30 changes in proportion to the area of the overlapping portion by changing the area of the overlapping portion of the flat plate 31 and the flat plate 32. For example, as shown in FIG. 3A, when the overlapping area S1 is small, the capacitance C becomes small. Conversely, as shown in FIG. 3B, when the overlapping area S2 is large, the capacitance C increases.

  Further, from the above formula (1), it can be seen that the capacitance C of the parallel plate capacitor 30 changes in inverse proportion to the distance d between the flat plate 31 and the flat plate 32.

FIG. 4 is an equivalent circuit diagram of an RF coil having two coils and a magnetic coupling neutralization circuit.
The RF coil 40 includes a coil 41, a coil 42, and a neutralization circuit 43. The neutralization circuit 43 includes an inter-coil connection capacitor 44, an inter-coil connection capacitor 45, a neutralization capacitor 46, and a neutralization capacitor 47. The RF coil 40 is used for either transmission of RF pulses or reception of magnetic resonance signals, or both transmission of RF pulses and reception of magnetic resonance signals.
The inter-coil connection capacitor 44 is included in a coil loop of the coil 41. Similarly, the inter-coil connection capacitor 45 is included in the coil loop of the coil 42. One end of the inter-coil connecting capacitor 44 is connected to one end of the inter-coil connecting capacitor 45 via the neutralizing capacitor 46. Similarly, the other end of the inter-coil connection capacitor 44 is connected to the other end of the inter-coil connection capacitor 45 via a neutralizing capacitor 47.

L1 and R1 are the inductance and resistance of the coil 41. Similarly, L2 and R2 are the inductance and resistance of the coil 42. M is a mutual inductance between the coil 41 and the coil 42.
Further, v1 and i1 are an electromotive force generated in the coil 41 and a current flowing through the coil 41. Similarly, v2 and i2 are an electromotive force generated in the coil 42 and a current flowing through the coil 42. The electromotive force v1 and the electromotive force v2 are generated by a drive signal applied to receive a magnetic resonance signal or transmit an RF pulse.
im is a current flowing through the inter-coil connection capacitor 44, the neutralization capacitor 46, the inter-coil connection capacitor 45, and the neutralization capacitor 47.
C1 and C2 are capacities of the inter-coil connection capacitor 44 and the inter-coil connection capacitor 45, respectively.

  Cm is a variable capacity of the neutralizing capacitor 46 and the neutralizing capacitor 47. The variable capacitor Cm can be changed according to the change of the mutual inductance M. Although the variable capacitances of the neutralizing capacitor 46 and the neutralizing capacitor 47 may be different, they are the same for convenience in order to simplify the derivation of an expression to be described later. Further, either the neutralizing capacitor 46 or the neutralizing capacitor 47 may be a fixed capacitor having a constant capacity. Further, only one of the neutralizing capacitor 46 and the neutralizing capacitor 47 may exist, and the coil 41 and the coil 42 may be directly connected by a connection line on the other side.

  When the center frequency of the magnetic resonance signal or the center frequency of the RF pulse is ω, the following equation is established.

  From the above equations (2), (3), and (4), the following equation is obtained.

  From the above formulas (5) and (6), the magnetic coupling due to the mutual inductance M can be eliminated when the following formula is established.

  When the above equation (7) is solved, the following equation is obtained.

When the mutual inductance M of the coil 41 and the coil 42 changes, the magnetic coupling by the mutual inductance M is achieved by changing the variable capacitance Cm of the neutralizing capacitor 46 and the neutralizing capacitor 47 so that the above equation (8) is satisfied. Can be removed.
For example, when the mutual inductance M increases, the numerator of equation (8) increases and the denominator decreases. Therefore, it can be seen that the magnetic coupling due to the mutual inductance M can be eliminated by increasing the variable capacitance Cm. On the other hand, when the mutual inductance M decreases, the numerator of the equation (8) becomes smaller and the denominator becomes larger. For this reason, it is understood that the magnetic coupling due to the mutual inductance M can be eliminated by reducing the variable capacitance Cm.

  The frequency of the magnetic resonance signal or RF pulse has a bandwidth corresponding to the slice width, but the bandwidth is extremely narrow compared to the size of the center frequency ω of the magnetic resonance signal or RF pulse. When the above equation (8) is established, artifacts due to the influence of the mutual inductance M do not appear in the reconstructed image, and good image quality can be obtained.

  Further, in the above equations (2) and (4), when v1 = 0 and i1 = 0, the following equation is obtained.

Solving the above equations (9) and (10) yields the above equation (8). Here, as described above, when the above equation (8) is established, the magnetic coupling due to the mutual inductance M between the coil 41 and the coil 42 is removed. Further, the left side of the equation (9) is a voltage generated in the coil 41 by the mutual inductance M by the current i2 flowing through the coil 42. On the other hand, the right side of the equation (9) is a voltage generated at both ends of the inter-coil connection capacitor 44 by the current im flowing through the neutralization circuit 43.
This is because when the voltage generated in the coil 41 by the current i2 flowing through the coil 42 and the voltage generated at both ends of the inter-coil connection capacitor 44 by the current im flowing through the neutralization circuit 43 are equal, This means that the influence of the inductance M is eliminated.

  Further, in the above equations (3) and (4), if v2 = 0 and i2 = 0, the following equation is obtained.

  Solving the above equations (11) and (12) yields the above equation (8). In the same way as the equation (9), the equation (11) is applied to both ends of the inter-coil connection capacitor 45 by the voltage generated in the coil 42 by the mutual inductance M and the current im flowing through the neutralization circuit 43. When the generated voltages are equal, it means that the influence of the mutual inductance M is canceled out in the coil 42.

  The coil 41 is an example of the first coil of the present invention, the coil 42 is an example of the second coil of the present invention, and the inter-coil connection capacitor 44 is an example of the first inter-coil connection capacitor of the present invention. The inter-coil connecting capacitor 45 is an example of the second inter-coil connecting capacitor of the present invention, the neutralizing capacitor 46 is an example of the first neutralizing capacitor of the present invention, and the neutralizing capacitor 47 is the first of the present invention. It is an example of the neutralization capacitor | condenser of 2. FIG.

FIG. 5 is a diagram showing an RF coil according to the first embodiment of the present invention.
The RF coil 50A includes a coil 51A, a coil 52A, and a neutralization circuit 53. The neutralization circuit 53 includes an inter-coil connection capacitor 54, an inter-coil connection capacitor 55, a neutralization capacitor 56, and a neutralization capacitor 57. The inter-coil connection capacitor 54 is included in the coil loop of the coil 51A. Similarly, the inter-coil connection capacitor 55 is included in the coil loop of the coil 52A. One end of the inter-coil connection capacitor 54 is connected to one end of the inter-coil connection capacitor 55 via the neutralization capacitor 56. Similarly, the other end of the inter-coil connection capacitor 54 is connected to the other end of the inter-coil connection capacitor 55 via a neutralization capacitor 57.

The coil 51A and the coil 52A are arranged on the same plane, can translate in the same plane, and can change the mutual distance on the same plane.
The neutralization circuit 53 removes the magnetic coupling due to the mutual inductance M between the coil 51A and the coil 52A on the same principle as the neutralization circuit 43 shown in FIG.
The neutralizing capacitor 56 and the neutralizing capacitor 57 include at least two chargeable flat plates arranged in parallel, and the areas of overlapping portions of the flat plates can be changed by moving these flat plates in parallel. The flat plate is made of copper foil, for example. Adjustment of the amount of increase in capacity and the direction of increase / decrease is optimized by the shape of the copper foil and how it is superimposed.
As the coil 51A and the coil 52A approach each other and the mutual inductance M increases, the area of the overlapping portion of the copper foils of the neutralizing capacitor 56 and the neutralizing capacitor 57 is increased, so that the variable capacitance Cm By increasing the value, the magnetic coupling due to the mutual inductance M can be eliminated.

  An insulating material such as ceramics having a high dielectric constant may be attached to the surfaces of the copper foils of the neutralizing capacitor 56 and the neutralizing capacitor 57. When the area of the overlapping portion of the copper foils of the neutralizing capacitor 56 and the neutralizing capacitor 57 is changed by adhering the insulating material, an effect of preventing the copper foil from contacting is also produced.

  The RF coil 50A is used, for example, to image the abdomen and chest of the subject 20.

  The coil 51A is an example of the first coil of the present invention, the coil 52A is an example of the second coil of the present invention, and the inter-coil connection capacitor 54 is an example of the first inter-coil connection capacitor of the present invention. The inter-coil connecting capacitor 55 is an example of the second inter-coil connecting capacitor of the present invention, the neutralizing capacitor 56 is an example of the first neutralizing capacitor of the present invention, and the neutralizing capacitor 57 is the present invention. This is an example of the second neutralizing capacitor.

FIG. 6 is a diagram showing an RF coil according to the second embodiment of the present invention.
The RF coil 50B includes a coil 51B, a coil 52B, and a neutralization circuit 53. The neutralization circuit 53 includes an inter-coil connection capacitor 54, an inter-coil connection capacitor 55, a neutralization capacitor 56, and a neutralization capacitor 57. 5 and 6 indicate the same components.
In the first embodiment, the coil 51A and the coil 52A are arranged on the same plane, can translate on the same plane, and can change the mutual distance on the same plane. In the embodiment, the coil 51B and the coil 52B are arranged to face each other, and are different in that the distance to face each other can be changed. The structure of the neutralization circuit 53 is the same between the first embodiment and the second embodiment.

  The RF coil 50B is used, for example, to image the shoulder of the subject 20.

  The coil 51B is an example of the first coil of the present invention, and the coil 52B is an example of the second coil of the present invention.

  In the first embodiment and the second embodiment, the neutralizing capacitor 56 and the neutralizing capacitor 57 change the variable capacitance Cm by translating the chargeable flat plate on the same plane. The variable capacitor Cm may be changed by changing the interval between the flat plates.

FIG. 7 is a diagram showing an RF coil according to the third embodiment of the present invention.
The RF coil 60 includes a coil 61, a coil 62, and a neutralization circuit 63. The neutralization circuit 63 includes an inter-coil connection capacitor 64, an inter-coil connection capacitor 65, a neutralization capacitor 66, and a neutralization capacitor 67. The inter-coil connection capacitor 64 is included in the coil loop of the coil 61. Similarly, the inter-coil connection capacitor 65 is included in the coil loop of the coil 62. One end of the inter-coil connecting capacitor 64 is connected to one end of the inter-coil connecting capacitor 65 through the neutralizing capacitor 66. Similarly, the other end of the inter-coil connection capacitor 64 is connected to the other end of the inter-coil connection capacitor 65 via a neutralization capacitor 67.

The angle between the coil surfaces of the coil 61 and the coil 62 can be changed by rotating the coil 61 and the coil 62 about the rotation axis.
When the angle of the coil surfaces of the coils 61 and 62 is 180 degrees, the mutual inductance M between the coils 61 and 62 is the largest. As the angle of the coil surfaces of the coils 61 and 62 becomes narrower, the mutual inductance M between them decreases. When the angle of the coil surfaces of the coils 61 and 62 reaches 90 degrees, the coils 61 and 62 form a quadrature coil. For this reason, the mutual inductance M between them becomes zero.

The neutralization circuit 63 removes the magnetic coupling due to the mutual inductance M between the coil 61 and the coil 62 based on the same principle as the neutralization circuit 43 shown in FIG.
However, the neutralizing capacitor 66 and the neutralizing capacitor 67 include two curved plates arranged around the rotation axis, and the area of the overlapping portion of the curved plates is changed by rotating these curved plates. Can be made. When the angle of the coil surfaces of the coil 61 and the coil 62 changes and the mutual inductance M between them changes, the curved plate is rotated to change the variable capacitance Cm so that the above equation (8) is satisfied. The influence of magnetic coupling due to the mutual inductance M can be eliminated.
As the angle of the coil surfaces of the coils 61 and 62 increases and approaches 180 degrees, the area of the overlapping portion of the two curved plates increases, and the capacitances of the neutralizing capacitors 66 and 67 increase.
On the other hand, the angle of the coil surfaces of the coils 61 and 62 decreases, and as the angle approaches 90 degrees, the area of the overlapping portion of the two curved plates decreases, and the capacitance of the neutralizing capacitors 66 and 67 decreases. To do.
The curved plate is made of, for example, copper foil. Adjustment of the amount of increase in capacity and the direction of increase / decrease is optimized by the shape of the copper foil and how it is superimposed.

FIG. 8 is a diagram illustrating an example of a neutralizing capacitor that changes the electrostatic capacitance by rotating the curved plate to change the area of the overlapping portion.
The neutralizing capacitor 66 and the neutralizing capacitor 67 have the same structure, and include a rotating shaft 681, a curved plate 682, and a curved plate 683. The curved plate 682 and the curved plate 683 rotate around the rotation axis 681.
As the angle of the coil surfaces of the coils 61 and 62 increases and approaches 180 degrees, the mutual inductance M between them increases. Therefore, the magnetic coupling between the coil 61 and the coil 62 is eliminated by increasing the area of the overlapping portion of the curved plate 682 and the curved plate 683 and increasing the capacitance of the neutralizing capacitor 66 and the neutralizing capacitor 67. .
On the other hand, as the angle of the coil surfaces of the coils 61 and 62 decreases and approaches 90 degrees, the mutual inductance M between them decreases. Therefore, the magnetic coupling between the coil 61 and the coil 62 is eliminated by reducing the area of the overlapping portion of the curved plate 682 and the curved plate 683 and reducing the capacitance of the neutralizing capacitor 66 and the neutralizing capacitor 67. .

FIG. 9 is a diagram illustrating an example of a carotid artery coil.
The carotid coil may change the relative position of the two coils in accordance with the shape of the neck. Even in this case, the magnetic coupling due to the mutual inductance between the coil 61 and the coil 62 can be eliminated by using the RF coil 60 as a carotid artery coil.

  The coil 61 is an example of the first coil of the present invention, the coil 62 is an example of the second coil of the present invention, and the inter-coil connection capacitor 64 is an example of the first inter-coil connection capacitor of the present invention. The inter-coil connecting capacitor 65 is an example of the second inter-coil connecting capacitor of the present invention, the neutralizing capacitor 66 is an example of the first neutralizing capacitor of the present invention, and the neutralizing capacitor 67 is the present invention. This is an example of the second neutralizing capacitor.

  As described above, according to the RF coil of the present invention, magnetic coupling due to mutual inductance is removed by a method of generating capacitive coupling using a capacitor. Therefore, the RF coil is used for transmission of RF pulses and reception of magnetic resonance signals. Even when the distance or angle between the two coils is changed, the magnetic coupling due to the mutual inductance can be sufficiently removed.

  Although the embodiments of the present invention have been described above, various modifications and combinations necessary for design reasons and other factors are described in the inventions described in the claims and the specific embodiments described in the embodiments of the invention. It should be understood that it falls within the scope of the invention corresponding to the examples.

It is a figure which shows the MRI apparatus which concerns on one Embodiment of this invention. It is a figure which shows a parallel plate capacitor. It is a figure which shows the example of the parallel plate capacitor which changes an electrostatic capacitance by moving a flat plate and changing the area of an overlapping part. FIG. 5 is an equivalent circuit diagram of an RF coil having two coils and a magnetic coupling neutralization circuit. It is a figure which shows the RF coil which is the 1st Embodiment of this invention. It is a figure which shows the RF coil which is the 2nd Embodiment of this invention. It is a figure which shows the RF coil which is the 3rd Embodiment of this invention. It is a figure which shows the example of the neutralizing capacitor which changes an electrostatic capacitance by rotating a curved board and changing the area of an overlap part. It is a figure which shows the example of a carotid artery coil.

Explanation of symbols

30 ... Parallel plate capacitor, 31, 32 ... Flat plate, 40, 50A, 50B, 60 ... RF coil, 41, 42, 51A, 52A, 51B, 52B, 61, 62 ... Coil, 44, 45, 54, 55, 64 , 65 ... Coil connection capacitor, 46, 47, 56, 57, 66, 67 ... Neutralization capacitor, 681 ... Rotating shaft, 682, 683 ... Curved plate

Claims (8)

A first coil used to transmit RF pulses or receive magnetic resonance signals;
A second coil used to transmit RF pulses or receive magnetic resonance signals;
A first inter-coil connection capacitor that is included in a coil loop of the first coil and generates a voltage that cancels a voltage generated by a mutual inductance between the first coil and the second coil;
A second inter-coil connecting capacitor that is included in a coil loop of the second coil and generates a voltage that cancels a voltage generated by a mutual inductance between the first coil and the second coil;
A first neutralizing capacitor that connects the two coils at one end of the first inter-coil connecting capacitor and one end of the second inter-coil connecting capacitor;
A connection line connecting the two coils at the other end of the first inter-coil connecting capacitor and the other end of the second inter-coil connecting capacitor, or a second neutralizing capacitor;
By changing the capacitance of the first neutralization capacitor and / or the second neutralization capacitor in response to a change in the distance or angle between the first coil and the second coil, An RF coil for removing magnetic coupling due to mutual inductance between the first coil and the second coil. The RF coil according to claim 1, wherein the first coil and the second coil are arranged on the same plane, and a mutual distance can be changed on the same plane. The RF coil according to claim 1, wherein the first coil and the second coil are disposed so as to face each other and a distance between the first coil and the second coil can be changed. The first neutralization capacitor and / or the second neutralization capacitor includes at least two chargeable flat plates arranged in parallel, and an area of an overlapping portion of the flat plates by translating the flat plates The RF coil according to claim 2, wherein the capacitance is changed. The RF coil according to claim 4, wherein an insulating material having a high dielectric constant is attached to a surface of the flat plate. The first coil and the second coil can change the angle formed by the coil surfaces of the first coil and the second coil by rotating around the rotation axis,
The first neutralization capacitor and / or the second neutralization capacitor includes at least two chargeable curved plates arranged to rotate about the rotation axis; and The RF coil according to claim 1, wherein the capacitance is changed by changing an area of an overlapping portion of the curved plates by rotating the curved plates according to an angle formed by a coil surface of the second coil. . The RF coil according to claim 6, wherein an insulating material having a high dielectric constant is attached to a surface of the curved plate. A first coil used to transmit RF pulses or receive magnetic resonance signals;
A second coil used to transmit RF pulses or receive magnetic resonance signals;
A first inter-coil connection capacitor that is included in a coil loop of the first coil and generates a voltage that cancels a voltage generated by a mutual inductance between the first coil and the second coil;
A second inter-coil connecting capacitor that is included in a coil loop of the second coil and generates a voltage that cancels a voltage generated by a mutual inductance between the first coil and the second coil;
A first neutralizing capacitor that connects the two coils at one end of the first inter-coil connecting capacitor and one end of the second inter-coil connecting capacitor;
An RF coil including a connection line connecting the two coils at the other end of the first inter-coil connection capacitor and the other end of the second inter-coil connection capacitor or a second neutralization capacitor;
By changing the capacitance of the first neutralization capacitor and / or the second neutralization capacitor in response to a change in the distance or angle between the first coil and the second coil, An MRI apparatus that removes magnetic coupling due to mutual inductance between the first coil and the second coil.

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