JP2019118781A - Magnetic resonance imaging device - Google Patents

Abstract

To provide an MRI device capable of maintaining uniformity of a static magnetic field during imaging by effectively reducing induction current generated in a shim coil when driving a gradient magnetic field coil without having to grasp its magnitude.SOLUTION: An MRI device includes a static magnetic field generation device, a gradient magnetic field coil 30a for giving a magnetic field gradient to a static magnetic field generated by the static magnetic field generation device, and a shim coil 80a arranged close to the gradient magnetic field coil for correcting ununiformity of the static magnetic field. The MRI device further includes an additional circuit connected between the shim coil and a power source 81a in series for increasing a time constant of a circuit including the shim coil. The additional circuit is arranged so as to generate mutual inductance Mpositive to each other, and includes two additional coils 90 and 91, and these additional coils are arranged at a position where mutual inductance is not generated between the gradient magnetic field coil and the shim coil.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a technique for reducing an induced current generated between a plurality of coils in a magnetic resonance imaging apparatus, and more particularly to a technique for reducing an induced current generated in a shim coil for static magnetic field correction when a gradient coil is driven.

  A magnetic resonance imaging (hereinafter referred to as “MRI”) apparatus comprises a static magnetic field generator such as a superconducting magnet that generates a uniform magnetic field in an imaging space, and a pulsed gradient magnetic field in the imaging space to add positional information to an imaging section. A gradient magnetic field coil to be generated, an irradiation coil to generate a high frequency electromagnetic wave for causing magnetic resonance in atomic nuclei constituting a subject, a reception coil to detect an echo signal (magnetic resonance signal) generated by magnetic resonance, etc. , And the echo signal is used to reconstruct an image to obtain a tomographic image.

  In such an MRI apparatus, a magnetic field correction coil (shim coil) for correcting a magnetic field uniformly is disposed in the vicinity of the gradient magnetic field coil, and a steady current is generated in the shim coil to generate a correction magnetic field. (Shim current) is supplied. Essentially, the gradient magnetic field coil and the shim coil are not magnetically coupled, that is, designed so as not to generate mutual inductance, but if an error occurs in parts or assembly, a mutual inductance of about several μH occurs. Therefore, when a current is applied to the gradient magnetic field coil, a current is induced in the shim coil when the current rises or falls, and an incorrect current (induced current) flows separately from the shim current. This induced current makes it difficult to correct the magnetic field uniformly by the shim coils.

  In order to address this problem, in Patent Document 1, a cancellation coil is installed in series in both the gradient magnetic field coil and the shim coil, and an induction current is generated between the two cancellation coils to generate an induced voltage in the shim coil when the gradient magnetic field coil is driven. A method has been proposed to offset (current). Further, Patent Document 2 proposes a technique of detecting an output current of a gradient magnetic field power supply and adding a current to the shim power supply which cancels an induced current generated in the gradient magnetic field coil and the shim coil.

Unexamined-Japanese-Patent No. 1-284239 Unexamined-Japanese-Patent No. 5-212010

  Since both the method according to Patent Document 1 and the method according to Patent Document 2 aim to cancel the induced current generated in the gradient magnetic field coil and the shim coil, the induced current generated at the time of driving the gradient magnetic field coil can be accurately grasped It will be necessary. For example, in the method of Patent Document 1, in order to determine the constant of the cancellation coil, it is necessary to grasp the magnitude of the induced current. In the method of Patent Document 2, in order to determine the current to be added to the shim power supply, it is necessary to detect the output current at the time of driving the gradient magnetic field coil. And the circuit becomes complicated by adding means for that purpose.

  Therefore, in the present invention, it is an object to effectively reduce the induced current without the need to grasp the magnitude of the induced current generated.

The present invention solves the above-mentioned problem by adding a circuit for reducing the induced current to the shim coil itself. Specifically, the MRI apparatus of the present invention has the following configuration. A static magnetic field generator, a gradient magnetic field coil which gives a magnetic field gradient to a static magnetic field generated by the static magnetic field generator, and a shim coil which is disposed close to the gradient magnetic field coil and corrects inhomogeneity of the static magnetic field. . Furthermore, an additional circuit connected in series between the shim coil and a shim power supply for supplying current to the shim coil is provided to increase a time constant of a circuit including the shim coil and the shim power supply. The said additional circuit is arrange | positioned in the position which does not produce a mutual inductance between the said gradient magnetic field coil and the said shim coil.
Further, the additional circuit includes a first additional coil and a second additional coil, and the first additional coil and the second additional coil are arranged to generate mutual mutual inductances. Is preferred.

  According to the present invention, only the shim coil can be changed to effectively reduce the induced current without grasping the magnitude of the induced current.

The figure which shows the whole structure of the MRI apparatus to which this invention is applied. Diagram showing equivalent circuit of conventional gradient magnetic field coils and shim coils Diagram explaining induced current flowing in shim coil The figure which shows the equivalent circuit of the gradient magnetic field coil of 1st embodiment, and a shim coil. Diagram showing an example of additional circuit The figure which shows the equivalent circuit of the gradient magnetic field coil and shim coil of a reference example Graph showing induced current measured using actual MRI system A figure showing a modification of a first embodiment The figure which shows the equivalent circuit of the gradient magnetic field coil of 2nd embodiment, and a shim coil.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, referring to FIG. 1, the entire configuration of an MRI apparatus to which the present invention is applied will be described. The MRI apparatus 100 mainly includes a static magnetic field generator, a gradient magnetic field generating system (30, 31, 80), a sequencer 40, a transmitting system (50, 51), a receiving system (60, 61), and a computer 70. And consists of.

  The static magnetic field generator comprises a static magnetic field generating magnet 20 of a permanent magnet type, a normal conduction type or a superconducting type, and the static magnetic field generating magnet 20 generates a uniform static magnetic field in the space where the subject 10 is placed. Depending on the direction of the generated static magnetic field, there are a horizontal magnetic field method and a vertical magnetic field method, the former generates a uniform static magnetic field in the same direction as the body axis direction of the subject 1 and the latter is uniform in the direction perpendicular to the body axis direction Generates a static magnetic field. FIG. 1 shows a static magnetic field generator of a horizontal magnetic field type as an example.

  The gradient magnetic field generation system includes a plurality of gradient magnetic field coils 30 applying gradient magnetic fields in three axial directions of x, y and z, which are coordinate systems of the MRI apparatus, and gradient magnetic field power sources 31 driving respective gradient magnetic field coils 30. And a plurality of shim coils 80 for correcting magnetic field inhomogeneity in the imaging space, and a shim power supply 81 for driving the respective shim coils 80. The gradient magnetic field generating system applies gradient magnetic fields Gx, Gy, Gz in three axial directions of x, y, z by driving the gradient magnetic field power supply 31 in accordance with an instruction from the sequencer 40. Further, in order to equalize the magnetic field in the presence of the subject 10, the shim power supply 81 is driven according to the instruction from the sequencer 40 to generate a magnetic field from the shim coil 80.

  The gradient magnetic field generated by the gradient magnetic field coil 30 provides positional information to the nuclear magnetic resonance signal, and is applied as a pulse according to a predetermined pulse sequence. Specifically, slice direction gradient magnetic field pulses are applied in the direction orthogonal to the slice plane (the imaging section), and the slice plane for the subject 10 is set. Then, the phase encoding direction gradient magnetic field pulse and the frequency encoding direction gradient magnetic field pulse are applied in the remaining two directions orthogonal to the slice plane and orthogonal to each other, and position information of each direction is encoded in the echo signal. Ru.

  The magnetic field generated by the shim coil 80 is a magnetic field formed to keep the magnetic field uniform during imaging of the subject 10, and a predetermined current (shim current) is continuously supplied from the shim power supply 81.

  The sequencer 40 is controlled by the computer 70 and operates, and sends various commands necessary for collecting data of tomographic images of the subject 10 to the transmitting unit 51, the gradient magnetic field generating system, and the receiving unit 61. As a result, the radio frequency magnetic field pulse (RF pulse) and the gradient magnetic field pulse are controlled to be repeatedly applied in a predetermined pulse sequence.

  The transmission system includes a high frequency coil 50 disposed close to the subject 10 and a transmission unit 51. Although not shown, the transmission unit 51 includes a modulator, a high frequency oscillator, a high frequency amplifier, and the like, and sends a signal of a predetermined frequency to the high frequency coil 50. As a result, the subject 10 is irradiated with an RF pulse for causing nuclear magnetic resonance to occur in nuclear spins of atoms constituting the living tissue of the subject 10.

  The receiving system is disposed in proximity to the subject 10, and receives a high-frequency coil 60 that detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of nuclear spins constituting the living tissue of the subject 10; And a unit 61. Although not illustrated, the receiving unit 61 includes a signal amplifier, a quadrature phase detector, an A / D converter, and the like, and sends an echo signal converted into a digital signal to a computer (or signal processing circuit) 70.

  The computer 70 performs various data processing and displays and saves processing results. A display 71, a storage device 72 and an operating device 73 are connected to the computer 70.

  In FIG. 1, the elements enclosed by a dashed dotted line are elements placed in a shield room that shields electromagnetic waves, and the elements enclosed by a dotted line are elements placed outside the shield room, for example, in the operation room.

  Each of the gradient magnetic field coil 30 and the shim coil 80 is manufactured by cutting, bending or the like a conductive metal (for example, copper), and is fixed to a cylindrical or disk-shaped insulating support. In the gradient magnetic field coil 30, three sets of coils for generating gradient magnetic fields in three axial directions are formed on each support, and are integrated while maintaining insulation from each other. Although the direction of the gradient magnetic field generated by the shim coil 80 does not necessarily coincide with the direction of the gradient magnetic field generated by the gradient magnetic field coil 30, it is similar to the gradient magnetic field coil that the coil of the conductor is fixed on the support .

An equivalent circuit of such a gradient magnetic field coil 30 and shim coil 80 is shown in FIG. Here, the coils 30a and 80a of the plurality of gradient magnetic field coils and shim coils are respectively shown as a representative. In the equivalent circuit, the gradient magnetic field coil 30a can be represented by a resistance R _G and an inductance L _G , and the shim coil 80a can be represented by a resistance R _S and an inductance L _S.

The gradient magnetic field coil 30 and the shim coil 80 are designed so that mutual inductance is ideally zero, but if an error occurs in parts or assembly, mutual inductance M _GS [H] of about several μH occurs . As a result, when current flows in the gradient magnetic field coil 30, an induced current is generated in the shim coil 80.

That is, in the state where there is mutual inductance M _GS , for example, when a trapezoidal current as shown in FIG. 3A flows in the gradient magnetic field coil 30 a on the primary side (300), the current rises (the current changes ), An induced electromotive force is generated in the shim coil 80a on the secondary side (800), and an induced current flows as indicated by a dotted line in FIG. Although FIG. 3 shows a state in which no current is generated from the shim power supply 81a, in fact, the shim coil 80a is supplied with a predetermined current for correcting the nonuniformity of the static magnetic field from the shim power supply 81a. Therefore, when such an induced current flows, the static magnetic field can not be accurately corrected. In practice, it is difficult to detect and correct the induced current because each of the plurality of shim coils may have mutual inductance with the three gradient coils.

In the MRI apparatus of the present embodiment, instead of taking an approach of detecting and correcting the induced current, driving of the gradient magnetic field coil is performed by connecting an additional circuit that increases the time constant of the shim coil side circuit to the shim coil. Thus, the rising of the induced current flowing to the shim coil side (secondary side) is blunted, and the resulting induced current is suppressed low.
Hereinafter, an embodiment of the additional circuit connected to the shim coil will be described. Also in the following embodiments, one shim coil 80a will be described as a representative.

First Embodiment
In this embodiment, an induction current reduction coil configured of a pair of additional coils, a first additional coil, and a second additional coil is used as the additional circuit. Hereinafter, each additional coil is abbreviated as a first coil or a second coil. FIG. 4 shows an equivalent circuit of the gradient magnetic field coil 30a and the shim coil 80a including the additional circuit (induction current reduction coil) of the present embodiment.

As illustrated, the primary-side closed circuit 300 includes the gradient magnetic field coil 30 a and the gradient magnetic field power supply 31 a and is connected in series. The gradient magnetic field coil 30a has a resistance component R _G [Ω] and a self-inductance component L _G [H].

The secondary side closed circuit 810 includes a shim coil 80a, a shim power supply 81a, and an induced current reduction coil (additional circuit) 90, and is connected in series. The shim coil 80a has a resistance R _S [Ω] and a self-inductance L _S [H]. Induction current reduction coil 90 includes a first coil 91 of the self-inductance _L A [H], and a second coil 92 of the self-inductance _L B [H], the first coil 91 and the second coil 92, The mutual inductance M _AB [H] is set so as to be a distance and a polarity (winding direction) that occurs at a positive value. That is, as shown in FIG. 4, the direction of the magnetic flux generated by the current flowing through the first coil 91 and the direction of the magnetic flux generated by the current flowing through the second coil 92 are the same. By arranging the mutual inductance to have a positive value, it is possible to reduce the induced current flowing through the shim coil 80a as described later. Incidentally as for the state shown in FIG. 4 will be reversed polarity example, the mutual inductance M _AB is a negative value.

Mutual inductance M _AB is desirably as large as possible, thereby, a higher induced current reduction effect is obtained. To increase the mutual inductance M _AB, for example the first coil 91 or to be installed is brought closer to the second coil 92, is good wound on the same core (core). For example, if a common mode choke coil is used, mutual inductance can be ideally increased, and can be increased to about _MAB ² = L _A × L _B. In this case, the induction current reduction coil 91 can be realized by only one common mode choke coil.

Also, it is desirable that the self inductances of the coils 91 and 92 be equal (L _A = L _B ). In particular, when the shim power supply 81 is a power supply in which the neutral point of the power supply is grounded, stable operation within the withstand voltage can be ensured by arranging the two additional coils electrically symmetrical.

An example of a common mode choke coil that can be used in the present embodiment is shown in FIG. As illustrated, in the common mode choke coil, two coils 91 and 92 are wound around the same core 93, the number of turns of the coil 91 and the coil 92 is the same, and the winding direction is reverse. is there. The terminals A and B are connected to the shim coil 80a side, and the terminals C and D are connected to the shim power supply 81a side. As an example, the diameter of the core 93 is about 50 mm, and the wire diameter of the coil 91 and the coil 92 is about 1.5 mm. When current flows from the terminal A through the coil 91 in the direction of the terminal C in such a system, the current also flows from the terminal D through the coil 92 to the terminal B direction. Then, a magnetic flux generated in the iron core 93 by the coil 91, the magnetic flux generated in the iron core 93 by the coil 92 constructively in the same direction, the mutual inductance M _AB of the coil 91 and 92 is increased.

  The induction current reduction coil 90 having such a configuration is disposed at a distance from the gradient coil 30a and the shim coil 80a so that mutual inductance does not occur. Specifically, for example, as shown in FIG. 1, the superconducting magnet 20, the gradient magnetic field coil 30, and the shim coil 80 are installed near the center of the shield room. The induction current reduction coil 90 is preferably installed at a position as far as possible from near the center in the shield room, for example, at the wall of the shield room.

  Next, in the present embodiment, the reduction effect of the current induced in the shim coil 80a when the gradient magnetic field coil 30a is driven will be described again with reference to FIG.

As shown in FIG. 3A, when a trapezoidal current is supplied from the gradient power supply 31a to the gradient coil 30a and a current is generated from the primary side, induced current is generated on the secondary side due to the presence of the mutual inductance M _GS. Occurs. The induced current increases or decreases exponentially. The time constant of this change is equal to the inductance divided by the resistance (time constant = inductance / resistance). The larger the time constant, the smaller the proportion of induced current that increases or decreases within a given time.

In this embodiment, the inductance of the secondary side (810) may be regarded as the sum of the inductance L _S of the shim coil 80a, the self-inductance L _A and L _{B of} the first coil 91 and the second coil 92, and the mutual inductance 2M _AB Since it can be done, the time constant τ of the induced current on the secondary side is τ = (L _S + L _A + L _B +2 M _AB ) / R _S ,
It is.

On the other hand, as shown in FIG. 2, when the means such as the induction current reduction coil 90 is not used (comparative example),
τ = L _S / R _S
Thus, it can be seen that the maximum value of the induced current can be significantly reduced by the present embodiment.

As shown in FIG. 6 as a reference example, two additional coils 901 and 902 are inserted in the secondary side (820), and the arrangement is such that mutual inductance does not occur between the additional coils or mutual inductance The time constant τ is very small if
τ = (L _S + L _A + L _B ) / R _S
Thus, although the effect of reducing the induced current is obtained compared to the comparative example, the effect is smaller than the present embodiment. Therefore, the maximum value of the induced current increases in the order of this embodiment (with additional circuit)> reference example (without mutual inductance in additional circuit)> comparative example (without additional circuit), and the maximum value of induced current in this embodiment Can be suppressed most.

Fig. 7 shows the result of measurement of the induced current generated on the shim coil side (secondary side) when the gradient magnetic field coil is driven by the echo planar method (EPI) which is a general pulse sequence in an actual MRI apparatus. . No current is supplied to the shim coil. The circuit constants on the shim coil side at the time of measurement were: R _S 22Ω, Ls ≒ 1.5 mH, L _A = L _B 33 mH, M _AB AB3 mH. In the figure, the dotted line indicates the case where the induction current reduction coil is not inserted, and the solid line indicates the case where the induction current reduction coil of the present embodiment is inserted. From this result, it was confirmed that the induction current can be reduced by installing the induction current reduction coil also in the actual machine.

  According to the present embodiment, in the shim coil which inevitably causes mutual inductance with the gradient magnetic field coil, the shim coil side is provided with means for reducing the induced current at the time of driving the gradient magnetic field coil to detect the induced current. It is possible to maintain the stable operation of the shim coil with a simple configuration by eliminating the means of the above. Further, by using a coil as an additional circuit, it is possible to increase the time constant of the shim coil side circuit without affecting the shim current (steady current) originally supplied to the shim coil.

  In particular, by using a combination of two coils generating mutual inductance as induction current reduction means, the time constant can be further increased, and a high induction current reduction effect can be obtained. Furthermore, by using a common mode choke coil as a combination of two coils, simplification of circuit elements and cost reduction can be realized.

  2 and 4 show an example in which additional circuits are added symmetrically to the shim coil and the shim power supply from the viewpoint of withstand voltage, for example, only between one terminal of the shim coil and the shim power supply, It is also possible to insert additional circuits. In that case, for example, as shown in FIG. 8, two additional coils 911 and 912 connected in series are disposed to face each other (additional circuit 910), and the direction of the magnetic flux generated by them is the same. By winding, a positive mutual inductance can be generated between the two, and an induced current reduction effect can be obtained.

Second Embodiment
In the first embodiment, two additional coils that provide an induced current reduction effect are respectively connected in series between the shim coil and the shim power supply, but in the present embodiment, two additional coils connected in series are used as one set. , And in series between the shim coil and the shim power supply.

  Hereinafter, the additional circuit of the present embodiment will be described with reference to FIG. In FIG. 9, elements having the same functions as the elements shown in FIG. 4 are denoted by the same reference numerals, and redundant description will be omitted. Also in the following description, the gradient coil side is described as the primary side (300), and the shim coil side is described as the secondary side.

  As shown in FIG. 9, the secondary side closed circuit 840 includes a shim coil 80a, a shim power supply 81a, and induction current reduction coils 94 and 95, which are connected in series. The induction current reduction coils 94 and 95 are disposed at positions sandwiching the shim power supply 91a so as to be separated from each other and not to generate mutual inductance with the shim coil 80a and the gradient magnetic field coil 40a.

Induction current reduction coil 94 includes a first coil 941 of the self-inductance _L C [H], and a second coil 942 of the self-inductance _L D [H], a first coil 941 and the second coil 942, The mutual inductance M _CD [H] is set so as to be the distance and the polarity that occur to a positive value. Similarly, the induction current reduction coil 95 includes a first coil 951 of the self-inductance _L E [H], and a second coil 952 of the self-inductance _L F [H], the first coil 951 second coil 952 _Are set such that the mutual inductance M _EF [H] is the distance and the polarity that occur at positive values.

It is desirable that the self inductances of the four coils 941, 942, 951, 952 constituting the induction current reduction coils 94 and 95 be equal (L _C = L _D = L _E = L _F ). Moreover, the mutual inductance _{M CD} and _{M EF} is desirably as large as possible, the mutual inductance _{M CD} and _{M EF} is preferably equal _{(M CD =} M EF). A common mode choke coil can be used as the induction current reduction coil which satisfies such conditions as in the first embodiment. In the case of this embodiment, it can be realized at two places in total: two points between one terminal of the shim coil 80a and the shim power supply 81a and between the other terminal of the shim coil 80a and the shim power supply 81a.

In this case, the inductance L of the closed circuit 840 on the secondary side is as follows, assuming that the inductances of the induction current reduction coils 94 and 95 are L ₁ and L ₂ .
L = L _S + L ₁ + L ₂
L ₁ = L _C + L _D + 2M _CD
L ₂ = L _E + L _F + 2M _EF
Thus, the time constant of the shim coil is
Since τ = (L _S + L ₁ + L ₂ ) / R _S , the value can be made much higher than the value (τ = L _S / R _S ) when the induction current reduction coils 94 and 95 are not disposed. In addition, a large time constant can be realized as compared with the case where the induced current reduction coils 94 and 95 are replaced with one coil having the same self inductance as the first coil 941 (the reference example of FIG. 6).

  According to this embodiment, as in the first embodiment, a large induction current reduction effect can be obtained. Further, even if an induction current reduction coil having smaller self inductance and mutual inductance than the induction current reduction coil of the first embodiment shown in FIG. 5 is used, the induction current generated on the secondary side is equivalent to that of the first embodiment. It can be reduced to some extent.

  Although FIG. 9 shows an example in which the two induction current reduction coils 94 and 95 are electrically symmetrical with respect to the shim coil and the shim power supply, one induction current reduction coil may be omitted. It is.

  Further, although the above embodiment has been described by way of example of a combination of one gradient magnetic field coil and one shim coil among a plurality of gradient magnetic field coils and a plurality of shim coils, the present invention is not limited to one combination, An additional circuit may be provided for all of the plurality of shim coils, or one or more shim coils most affected by the mutual inductance with the gradient magnetic field coil may be selected to provide an additional circuit.

10: subject, 20: static magnetic field generator, 40: sequencer, 30: gradient magnetic field coil, 30a: gradient magnetic field coil, 50: high frequency coil, 51: transmission unit, 60: high frequency coil, 61: reception unit, 70 : Computer, 80: Shim coil, 80a: Shim coil, 81: Shim power supply, 90: Induction current reduction coil (additional circuit), 91: First addition coil, 92: Second addition coil, 94: Induction current reduction coil ( Additional circuit), 941: first additional coil, 942: second additional coil, 95: inductive current reduction coil (additional circuit), 951: first additional coil, 952: second additional coil, 910: induction Current reduction coil, 911: first additional coil, 912: second additional coil, 100: MRI apparatus, 300: primary side closed circuit, 800: secondary side closed circuit, 810: secondary side Circuit, 820: secondary closed circuit, 830: secondary closed circuit, 840: secondary closed circuit

Claims (10)

A static magnetic field generator, a gradient magnetic field coil for giving a magnetic field gradient to a static magnetic field generated by the static magnetic field generator, and a shim coil disposed close to the gradient magnetic field coil to correct nonuniformity of the static magnetic field ,
An additional circuit connected in series between the shim coil and a shim power supply for supplying current to the shim coil to increase a time constant of a circuit including the shim coil and the shim power supply, the additional circuit including the gradient magnetic field A magnetic resonance imaging apparatus characterized in that the magnetic resonance imaging apparatus is disposed at a position where mutual inductance does not occur between the coil and the shim coil. The magnetic resonance imaging apparatus according to claim 1,
The additional circuit includes a first additional coil and a second additional coil,
The magnetic resonance imaging apparatus according to claim 1, wherein the first additional coil and the second additional coil are disposed to generate a positive mutual inductance with each other. The magnetic resonance imaging apparatus according to claim 2,
The first additional coil is disposed between one terminal of the shim coil and the shim power supply, and the second additional coil is disposed between the other terminal of the shim coil and the shim power supply. Magnetic resonance imaging apparatus characterized by The magnetic resonance imaging apparatus according to claim 2,
The magnetic resonance imaging apparatus according to claim 1, wherein the additional circuit is a common mode choke coil in which the first additional coil and the second additional coil are wound around the same iron core. The magnetic resonance imaging apparatus according to claim 2,
The magnetic resonance imaging apparatus according to claim 1, wherein a self inductance of the first additional coil and a self inductance of the second additional coil are substantially equal. The magnetic resonance imaging apparatus according to claim 2,
The magnetic resonance imaging apparatus, wherein the first additional coil and the second additional coil are connected in parallel. The magnetic resonance imaging apparatus according to claim 2,
The magnetic resonance imaging apparatus, wherein the first additional coil and the second additional coil are connected in series. The magnetic resonance imaging apparatus according to claim 7,
An additional circuit comprising a pair of the first additional coil and a second additional coil connected in series is connected between one terminal of the shim coil and the shim power supply, and the other terminal of the shim coil and the shim power supply And a magnetic resonance imaging apparatus, which is disposed between them. The magnetic resonance imaging apparatus according to claim 8,
A magnetic resonance imaging apparatus, wherein the first additional coil and the second additional coil constituting each additional circuit have substantially the same self inductance. The magnetic resonance imaging apparatus according to claim 1,
A magnetic resonance imaging apparatus comprising: a plurality of shim coils, wherein the additional circuit is connected to at least one shim coil of the plurality of shim coils.

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