JPH05269101A - Nuclear magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To obviate disorder of an inclined magnetic field caused by a vibration magnetic field waveform, and to generate a desired inclined magnetic field by providing a means for superposing a vibration magnetic field compensation current to a driving current in an inclined magnetic field power source system. CONSTITUTION:An inclined magnetic field power source system is constructed by providing compensating circuits 11-13 and inclined magnetic field power sources 14-16 between a sequencer 2 and an inclined magnetic field coil 7. Also, in the compensating circuits 11-13, an eddy current compensating circuit and a vibration waveform compensating circuit are provided, and their output waveforms are synthesized by a waveform synthesizer and added to the inclined magnetic field power sources 14-16. Accordingly, a synthesized current obtained by superposing an eddy current compensation current and a vibration magnetic field compensation current to a driving current of a desired waveform set by the sequencer 2 from the inclined magnetic field power sources 14-16 is supplied to an incline magnetic field coil 7. In such a way, disorder of an inclined magnetic field caused by a vibration magnetic field waveform generated in the case a synthesized current obtained by only superposing the eddy current compensation current to the driving current is supplied to the inclined magnetic field coil can be obviated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a nuclear magnetic resonance signal (NMR signal) based on a nuclear magnetic resonance signal (NMR signal) collected by applying an excitation magnetic field (RF pulse) and a gradient magnetic field to an object placed in a static magnetic field space. The present invention relates to an MRI apparatus capable of obtaining a magnetic resonance imaging (MRI) image, and more particularly to an MRI apparatus adopting a configuration capable of supplying a drive current in which a current for eddy current compensation is superimposed on a gradient magnetic field coil as a gradient magnetic field power supply system.

[0002]

2. Description of the Related Art An MRI apparatus can excite an NMR signal by applying an RF pulse to a subject placed in a static magnetic field space formed in an air core by a main magnet having an air core structure. .. At this time, in order to obtain the position information of the NMR signal, it is customary to apply a gradient magnetic field to the subject so as to change the magnetic field strength by inclining in the directions of three orthogonal axes with respect to the subject. Then, the gradient magnetic field coil used to generate the gradient magnetic field functions by being supplied with a drive current from the gradient magnetic field power supply system.

However, when a driving current is supplied to the gradient magnetic field coil to generate a gradient magnetic field, an eddy current is generated in a conductor which is a constituent material of the main magnet, and due to the eddy current, the gradient magnetic field has a desired waveform. Deviate from. In this case, deterioration of the MRI image occurs.

Therefore, conventionally, an active gradient coil having a structure in which a gradient magnetic field is generated only in the imaging region as the gradient magnetic field coil and the gradient magnetic field does not reach the main magnet side, or a gradient magnetic field coil is used. An eddy current compensating method was applied in which a drive current in which an eddy current compensating current was superimposed was supplied.

[0005]

However, since the active gradient coil has a complicated coil structure and requires high precision in manufacturing, the cost is extremely high, which is practically disadvantageous.

On the other hand, when the eddy current compensation method is applied, the eddy current generating portions of the gradient magnetic field coil and the main magnet are completely fixed, and there is no LCR circuit or the like for coupling with the gradient magnetic field in the main magnet. In this case, the disturbance of the gradient magnetic field due to the eddy current can be avoided. However, in reality, such a portion exists or a portion where an eddy current is generated vibrates, so that a magnetic field waveform with a damped oscillation is generated, which causes disturbance in the gradient magnetic field, resulting in an MRI image. The image quality may deteriorate. Furthermore, when an object that generates an eddy current magnetic field, for example, a metal cylinder (for heat shield) in the main magnet is arranged asymmetrically with respect to the gradient magnetic field coil, a problem arises. Is an even-order component of. For example, when a metal cylinder is arranged asymmetrically with respect to a gradient magnetic field coil in the vertical direction, Japanese Patent Laid-Open No. 63-
As disclosed in Japanese Patent No. 82638, even-order components of the eddy current magnetic field are generated in the vertical direction, and the gradient magnetic field is disturbed. To correct this, the technique disclosed in Japanese Patent Laid-Open No. 63-82638 uses a correction coil.
No. 144440 employs a technique of dividing the gradient magnetic field coil into two systems and independently determining the correction gain. However, in order to divide the gradient magnetic field coil into two systems, two large constant current sources that generate the main magnetic field are required, which increases the cost, and it is necessary to correct a specific number of different eddy current magnetic fields in the vertical direction. There was a problem that could not be done.

The present invention has been made by paying attention to the above-mentioned circumstances, and the first object thereof is to eliminate the disturbance of the gradient magnetic field due to the oscillating magnetic field waveform and generate a desired gradient magnetic field. M with a gradient magnetic field power supply system capable of
It is to provide an RI device.

A second object is to provide an MRI apparatus equipped with a gradient magnetic field power supply system capable of eliminating the disturbance of the gradient magnetic field due to the asymmetry of the eddy current magnetic field with a simple system configuration. is there.

[0009]

In order to achieve the above first object, in the first invention of the present invention, a vortex is applied to a gradient magnetic field coil for applying a gradient magnetic field to an object arranged in a static magnetic field space. An MRI apparatus having a gradient magnetic field power supply system capable of supplying a drive current in which a current for compensating current is superimposed is characterized by comprising means for superimposing an oscillating magnetic field compensating current in the drive current.

In order to achieve the above-mentioned second object, according to the second invention of the present invention, an eddy current compensating current is applied to a gradient magnetic field coil for applying a gradient magnetic field to a subject arranged in a static magnetic field space. In the MRI apparatus provided with a gradient magnetic field power supply system capable of supplying a drive current in which the magnetic field is superimposed, the gradient magnetic field power supply system targets, for example, between the selected segments of the gradient magnetic field coil, the eddy current magnetic field of, for example, asymmetry in the drive current. And a means for superimposing a current for compensating for the sex.

[0011]

According to the structure of the first aspect of the present invention, in MRI imaging, the eddy current compensating current is superposed on the driving current of a desired waveform, and at the same time, the oscillating magnetic field compensating current is superposed to generate a combined current of these. Since the gradient magnetic field coil is supplied to the gradient magnetic field coil, the disturbance of the gradient magnetic field caused by the oscillating magnetic field waveform generated when the composite current, which is obtained by superimposing the eddy current compensation current on the drive current, is supplied to the gradient magnetic field coil. It can be resolved.

With the configuration of the second aspect of the present invention, the MRI
At the time of imaging, a synthetic current in which the eddy current compensating current is superimposed on the drive current of the desired waveform is supplied to the gradient magnetic field coil, and at the same time, the asymmetry of the eddy current magnetic field is asymmetrical between the selected segments of the gradient magnetic field coil. Therefore, the turbulence of the gradient magnetic field due to the non-uniformity of the eddy current magnetic field can be eliminated. Also,
In order to eliminate the disturbance of the gradient magnetic field in this way, since only one large constant power source can be used, the gradient magnetic field power source system can have a simple system configuration and, for example, can be specified in the vertical direction. It becomes possible to correct different numbers of eddy current magnetic fields.

[0013]

1 is a system configuration diagram showing an outline of an MRI apparatus to which the present invention is applied.

The MRI apparatus includes a computer system 1 as a control center of the entire system, and under the control of the computer system 1, a gradient magnetic field power supply system 3 and a transmitter 4 are operated according to a pulse sequence of a sequencer 2. As a result, an RF pulse is applied by the RF coil 6 to the subject P arranged in the static magnetic field space formed in the air core of the main magnet 5, and a gradient magnetic field is applied by the gradient magnetic field coil 7, The NMR signal excited in the sample P can be received and detected by the receiver 9 via the reception probe 8 and collected by the computer system 1. The computer system 1 can reconstruct an MRI image based on the collected NMR signal and display it on the monitor 10.

In such an MRI apparatus, when the first invention is applied, the gradient magnetic field power supply system 3 includes a sequencer 2 and a gradient magnetic field coil (X, Y, Z in the directions of three orthogonal axes as shown in FIG. 2). The compensation circuits 11 to 13 and the gradient magnetic field power supplies 14 to 16 are provided between each of the G coils 7 and the G coils 7 provided for generating the magnetic field. Of these, the compensating circuits 11 to 13 are provided with an eddy current compensating circuit 17 and an oscillating waveform compensating circuit 18, as shown in FIG. By adding to the power supplies 14 to 16, the gradient magnetic field power supply 1
From 4 to 16, a composite current in which the eddy current compensation current is superimposed on the drive current having the desired waveform set by the sequencer 2 and the oscillating magnetic field compensation current is superimposed is supplied to the gradient magnetic field coil 7.

In the first embodiment to which the first invention is applied, the eddy current compensating circuit 17 has a circuit configuration of a combination of a differentiator 20 and an adder 21 using operational amplifiers as shown in FIG. An original waveform having a desired waveform shape suitable for a gradient magnetic field waveform as shown in FIG. 5 and an overshoot current waveform obtained by adding a differential waveform of the original waveform to the gradient magnetic field coil 7 from the gradient magnetic field power supplies 14 to 16 shown in FIG. It is intended to supply and cancel the magnetic field waveform due to the eddy current to obtain the gradient magnetic field waveform corresponding to the original waveform. It should be noted that the differentiator 20 should have an optimal number of circuits in parallel according to how many time constants the eddy current generated in the main magnet 51 of FIG. 1 has, and G _{1 in} FIG. Etc., the gain of the differential waveform is adjusted, and the time constant is adjusted by R ₁ etc., so that the gradient magnetic field waveform becomes the original waveform.

On the other hand, the vibration waveform compensating circuit 18 has a circuit configuration of an LCR circuit using an operational amplifier as shown in FIG. 6 and generates a damped vibration waveform triggered by the original waveform. Create a vibration waveform according to it. It should be noted that the circuit 18a in FIG. 6 may have an optimal number of circuits in parallel according to the period of damping vibration and the time constant, and the gain of the circuit 18b in the circuit 18a may be changed from positive (+) to negative. It can be changed to (-). However, the time constant, 2L / R oscillation _{frequency, {(1 / L c)} - (R 2 / 4L 2)}
It is ^1/2 .

The output waveform of the oscillating waveform compensating circuit 18 is superposed with the output waveform of the eddy current compensating circuit 17 as shown in FIG. 7 to obtain the overshoot current waveform including the oscillating magnetic field waveform from the gradient magnetic field power supplies 14 to 16 shown in FIG. To gradient coil 7
It is possible to cancel the eddy wave waveform and the oscillating magnetic field waveform to obtain the gradient magnetic field waveform corresponding to the original waveform.

However, the inductance (L) may be several henries (H) or more depending on the time constant of vibration damping, and in this case, the circuit configuration of FIG. 6 cannot compensate the vibration waveform. Therefore, in the second embodiment when the first invention is applied, the circuit 18a portion of FIG.
The circuit configuration is as follows. Besides this, a circuit such as a NIC (Negative Immittance Converter) can be applied. In the circuit configuration of FIG. 8, the portion of the circuit 18c operates as L.

Further, the circuit of FIG. 8 can generate only a cosine waveform synchronized with the gradient magnetic field waveform. Therefore, in order to deal with the case where a sine waveform is required, in the third embodiment of the first invention, as shown in FIG. 9, an eddy current compensation differentiating circuit 22 is provided.
A combination circuit may be provided in which the cosine vibration circuit 23, the sine vibration circuit 24, and other integration circuits and the like are provided in parallel by the number necessary to compensate the gradient magnetic field waveform. When the compensation can be performed only with the cosine waveform, the present embodiment need not be applied.

Next, an embodiment of the second invention will be described. However, for simplification of explanation, the gradient magnetic field power supply system 3 in the MRI apparatus of FIG. 1 will be described as a representative of the Y-axis gradient magnetic field system for generating a gradient magnetic field in the Y direction.
The gradient magnetic field system of the A-axis and the Z-axis can be considered similarly to that of the Y-axis.

FIG. 10 shows a Y-axis gradient magnetic field system in the first embodiment of the second invention. As shown, a main eddy current correction arbitrary function generator 31 and a constant current source 32 for main magnetic field generation are inserted in series between the terminals of the gradient magnetic field coil 7,
Only by compensating the eddy current magnetic field by supplying the drive current in which the eddy current compensating current is superimposed to the gradient magnetic field coil 7, the problem of the eddy current asymmetry arises as described above. In view of this, in the present embodiment, between the winding A1, the winding A2, the winding B1, and the winding B1 of the gradient magnetic field coil 7, both terminals of the winding portion formed by the winding A1 and the winding A2 are connected in series. The asymmetric correction arbitrary function generator 33 and the asymmetric correction constant current source 34 are inserted in series to eliminate the asymmetry of the eddy current.

In the gradient magnetic field coil 7 shown in FIG. 10, the winding A1, the winding A2, the winding B1, and the winding B2 are, for example, as shown in FIG.
Each winding A1, A2, B1, B of saddle coil such as 1
Represented by 2. In this case, if the metal cylinder 35 that is eccentric in the Y direction is arranged outside the gradient magnetic field coil 7 as shown in FIG. 12, as described in JP-A-63-82638, the gradient magnetic field center And the eddy current magnetic field center do not coincide (solid line in FIG. 12). Therefore, a spatial asymmetry of the eddy current magnetic field is formed with respect to the magnetic field center of the gradient coil 7.

By the way, the solid line in FIG. 13 indicates the eddy current magnetic field (a) from the lower side of Y and the eddy current magnetic field (b) from the upper side thereof.
It is formed by overlapping with. In the case of this example, since the eddy current magnetic field in the metal cylinder 35 is eccentric to the upper side with respect to the gradient magnetic field coil 7, the eddy current magnetic field from the lower side strongly influences and the center of the eddy current magnetic field shifts upward.

On the other hand, the asymmetry between (a) and (b) of the eddy current magnetic field can be considered as shown in FIG. 14 by the difference. That is, due to the eccentricity of the metal cylinder 35, as shown in FIG.
It can be considered that the asymmetry of the eddy current magnetic field as described above occurs.

In order to correct this, first, the main eddy current correction arbitrary function generator 31 and the main constant current source 32 are combined to compensate in accordance with the side (b) in FIG.
The asymmetric component is revealed by the difference between the (a) side and the (b) side in the figure.

Therefore, the asymmetric correction arbitrary function generator 33
By using a combination of the asymmetric correction constant current source 34 and a current for compensating the asymmetric component, the asymmetry is corrected. In this case, as shown in FIG. 10, a current is further applied to I ₀ (t) in the direction of applying I _1A (t). Of course, in this case, the main eddy current correction arbitrary function generator 31 and the main constant current source 32 are used to perform compensation in accordance with the (a) side in FIG. 13, and the asymmetry is compensated in the B system shown in FIG. The current may be applied in the connection configuration as shown in FIG. At this time, a current is applied to the B system in the direction of decreasing the current.

FIG. 16 shows these relationships. In FIG. 16, (i) is the compensation current from the combination of the main eddy current correction arbitrary function generator 31 and the main constant current source 32, and (ii). Is a compensation current generated by a combination of the auxiliary eddy current correction arbitrary function generator 33 and the auxiliary constant current source 34 when flowing into the B system, and (iii) is the auxiliary eddy current correction arbitrary function generation when flowing into the A system. It is the compensation current by the combination of the device 33 and the auxiliary constant current source 34.

Further, depending on the asymmetric property, only one segment, for example, A1 as shown in FIG. 17 or 18,
Alternatively, the two segments A1 and A2 may be separately used, and as an analogy thereof, a combination including B1 and B2, for example, as shown in FIG. 19 may be adopted.

Further, in order to obtain the structure shown in FIG. 10, the result of the gradient magnetic field coil should be that the A system and the B system are in series, but for example, asymmetric correction currents are applied to A1 and B2. When it is desired to flow with the same gain with the same time constant, the connection as shown in FIG. 20 does not need to be divided into two. Note that if the connection in FIG. 10 is left as it is, two circuits for asymmetry correction are required as shown in FIG.

It is efficient to make connections so that the same circuit can be used for correction, following the example of FIG. For other asymmetries, an asymmetric correction arbitrary function generator 33 and an asymmetric correction constant current source 34 may be provided for each segment.

Further, each of the arbitrary waveform generators described above includes not only the differential waveform of the CR circuit normally used but also a CR differential waveform having a plurality of time constants and gains, that is, a configuration as shown in FIG. The CR differentiating circuit can be applied. The output waveform may be a waveform for correcting the oscillating magnetic field generated by the vibration of the gradient magnetic field coil, the vibration of the metal cylinder in which the eddy current is induced, or the like (see FIG. 23). That is, as shown in FIG.
A circuit for adding another correction waveform to the differentiating circuit group may be added in parallel.

When the time constant of the eddy current magnetic field is asymmetric in the main magnet, for example, in the above-mentioned eccentricity in the Y direction, even if the eccentricity is concentric, the upper half and the lower half are made of different materials. When the metal cylinder is manufactured in, the time constant of the upper vortex and the time constant of the lower vortex are naturally different. This is because the resistivity is different between the upper side and the lower side. Even when correcting the difference in the time constants, the main arbitrary waveform generator and the main constant current source are used to correct one of the shorter time constants, and the remaining unbalanced components are corrected by the method described with reference to FIG. Can be corrected. In this case, as shown in FIG.
In the main constant current source 32, the compensation current may not be superposed at all, and at this time, A1, A2, B1, and B2 may be circuits having different time constants and gains independently of each other.
The difference in the time constant is caused by the imbalance in the spatial distribution of the specific resistance and the original property of the eddy current.
If the gain is the same, the gain control is 1
You can leave it alone.

Further, in each of the above-mentioned examples of the asymmetry correction, the waveform generator and the constant current source for the asymmetry correction are connected between the selected segments of the gradient magnetic field coil.
As shown in FIG. 6, separately excited electromagnetic coupling may be performed to superimpose the asymmetric compensation current. In FIG. 26, the same symbols as those in FIG. 10 indicate corresponding parts.

In the above-described embodiments of each invention, the signal processing for compensation is performed by the analog circuit, but the signal processing can be performed by the digital circuit as described below.

FIG. 27 shows an example of a digital type vibration waveform compensation circuit. This is the vibration waveform compensation circuit 18 of FIG.
And is provided in each of the X, Y, and Z axes.

The digital vibration waveform compensating circuit 50 includes an arbitrary function generator 521 ... 52n, a variable gain up 541 ...
54n, and n circuit elements connected in parallel, each having a resistor 551 ... 55n, and an adder 56 for adding the outputs of these elements. The arbitrary function generators 521 ... 52n are respectively provided with trigger signals TR1.
The operation timing is determined by the input of TRn. The variable gain amplifiers 541 ... 54n are supplied with arbitrary function generators 521 ... 5 by inputting level signals LV1 ... LVn, respectively.
Determine the magnitude of the 2n output.

Required arbitrary function generators 521 ... 52
The number of n is determined as follows. In the MRI apparatus, the maximum density of the gradient magnetic field pulse (the number of pulse rises / falls per unit time) is determined by the pulse sequence. If the connection time of the oscillations to be compensated is known in advance, the arbitrary function generator will generate a rising edge of the gradient magnetic field pulse generated at least within the connection time of the oscillations.
The same number of falling times is required.

For example, in the example shown in FIG. 28, the number of rises / falls within the oscillation duration of the pulse current is eight. In this case, at least 8 arbitrary function generators are required. The rising and the falling of the eight gradient magnetic field pulses are sequentially compensated by using the outputs of the arbitrary function generators 521 ... 52n. Since the output of the arbitrary function generator becomes 0 after the oscillation duration of the pulse current has elapsed, the same arbitrary function generator can be used repeatedly.

Further, the MRI apparatus generates a gradient magnetic field of arbitrary strength by the pulse sequence. When a force is applied to the vibrating body due to the interaction between the eddy current flowing in the vibrating body and the static magnetic field to generate vibration, the gradient magnetic field is activated in a fixed time.
It is considered that the amplitude of the vibration is proportional to the rate of change of the gradient magnetic field strength with time during the fall. Therefore, depending on the direction and magnitude of the gradient magnetic field to be applied, gain increase 541 ... 54
Adjust each gain of n so that optimum correction can be performed.

FIG. 29 shows another example of the digital type vibration waveform compensation circuit. The vibration waveform to be compensated is detected by the pickup coil 61. The detected vibration waveform is integrated by the integrator 62 and converted into a digital signal by the A / D converter 63. The vibration data thus obtained is temporarily stored in the ROM 64 under the control of the CPU 65.
Written in. Subsequently, under the control of the CPU 65, the vibration data is read out in the reverse phase and held in the RAMs 661 ... 66n.

Thereafter, the vibration data is stored in the RAM 661 ... 66.
.. are read out from n at appropriate timings and converted into analog signals by D / A converters 671 ... 67n to obtain vibration signals. Then, this vibration signal is supplied to variable gain-ups 681 ... 68n, amplified to an appropriate intensity, and the respective signals are added to generate a desired compensation vibration signal. Here, it is not necessary to frequently collect the vibration data, but it may be performed at the time of adjustment when installing the MRI apparatus, for example. By writing the detected vibration data in the ROM and transferring the data from the ROM to the RAM when the power is turned on, correct compensation can be performed unless the vibration component to be compensated changes.

Further, by performing the following operation under the control of the CPU 65, a higher degree of compensation can be performed. As shown in FIG. 30A, the vibration waveform to be compensated is sampled and compensation is performed once. Next, as shown in FIG. 30 (b), the vibration waveform is sampled again in the state of performing the compensation once, and the compensation data is added to the compensation data of the first time to be the compensation output. Further, by repeating this operation, more accurate compensation can be performed. This method is particularly effective in a system having a transfer function in which a compensating magnetic field is superposed and a new fluctuation component is generated by the component.

By the way, the fluctuating magnetic field component may be due to the vibration of the mechanical system, and in this case, it may have a certain degree of non-linearity with respect to the magnetic field strength or the repetition period. At this time, as shown in FIG. 31, a varying magnetic field component that cannot be compensated due to the non-linearity remains in the magnetic field component. In the MRI apparatus, the fluctuating magnetic field component at the read timing for sampling the MR signal affects the image quality such as blurring. For example, in the spin-echo method, if the gradient magnetic field strengths at the time of applying the 90 ° pulse and the 180 ° pulse are different, the S / N ratio is lowered. In such a case, the timing when the fluctuating magnetic field component affects the image is limited to the read timing. Therefore, by compensating the compensation data obtained by sampling with an adaptive filter such as the method of least squares, it is possible to reduce the fluctuating magnetic field within a limited time and remove or reduce the influence on the image quality. is there.

Further, as shown in FIG. 32, a non-linear component due to the difference in the rising / falling characteristics of the gradient magnetic field pulse can be considered as a kind of non-linear composition caused by the vibration of the mechanical system. In this case, for example, if rising / falling compensation is performed using data sampled at the rising edge, even if good compensation is performed at the rising edge, compensation at the falling edge cannot be performed correctly. In order to accurately compensate for this, it is sufficient to use two systems for ROM and RAM, one for rising compensation data and the other for falling compensation data.

[0046]

As described above, according to the first aspect of the present invention, the eddy current compensating current and the oscillating magnetic field compensating current are superposed on the drive current set to obtain a desired gradient magnetic field waveform. The magnetic field coil can generate a desired gradient magnetic field waveform, which is convenient for avoiding deterioration of the MRI image.

Further, according to the second aspect of the invention, it is possible to remove the eddy current asymmetric component which could not be removed even if the eddy current compensating current is superposed on the drive current set to obtain the desired gradient magnetic field waveform. Since it can be performed by superimposing an asymmetry compensating current between the selected segments of the gradient magnetic field coil, the gradient magnetic field coil can generate a desired gradient magnetic field waveform, thereby degrading the MRI image. This is convenient for avoiding, and since only one large constant current source is required, the system configuration is simplified and economically advantageous.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing an outline of an MRI apparatus to which the present invention is applied.

FIG. 2 is a block diagram showing a general configuration of a gradient magnetic field power supply system.

FIG. 3 is a block diagram showing an outline of a compensation circuit used in the first embodiment of the first invention of the present invention.

FIG. 4 is a circuit diagram showing an example of an eddy current compensation circuit in a first embodiment of the first aspect of the present invention.

FIG. 5 is a waveform transition diagram showing the principle of eddy current compensation.

FIG. 6 is a circuit diagram showing an example of a vibration waveform compensation circuit in a first embodiment of the first aspect of the present invention.

FIG. 7 is a diagram showing waveform transitions when the vibration waveform compensation is performed according to the first aspect of the present invention.

FIG. 8 is a circuit diagram showing a main part of a vibration waveform compensation circuit according to a second embodiment of the first aspect of the present invention.

FIG. 9 is a circuit diagram showing a main part of a vibration waveform compensation circuit in a third embodiment of the first aspect of the present invention.

FIG. 10 is a diagram showing an example of the circuit configuration of the gradient magnetic field power supply system in the first embodiment of the second invention of the present invention.

FIG. 11 is a structural explanatory view of a gradient magnetic field coil.

FIG. 12 is a view showing a state where a metal cylinder is eccentric with respect to a gradient magnetic field coil.

FIG. 13 is a characteristic curve diagram showing an asymmetric state of an eddy current magnetic field.

FIG. 14 is a characteristic curve diagram showing an asymmetric component of an eddy current magnetic field.

FIG. 15 is a diagram showing another example of the circuit configuration of the gradient magnetic field power supply system in the first embodiment of the second invention of the present invention.

FIG. 16 is a timing chart used for explaining a compensation current waveform in the first embodiment of the second aspect of the invention.

FIG. 17 is a diagram showing an example of a circuit configuration of a gradient magnetic field power supply system according to another embodiment of the second aspect of the present invention.

FIG. 18 is a diagram showing another first example of the circuit configuration of the gradient magnetic field power supply system in another embodiment of the second invention of the present invention.

FIG. 19 is a diagram showing another second example of the circuit configuration of the gradient magnetic field power supply system in another example of the second invention of the present invention.

FIG. 20 is a diagram showing another third example of the circuit configuration of the gradient magnetic field power supply system in another example of the second invention of the present invention.

FIG. 21 is a diagram used for explaining FIG. 20.

FIG. 22 is a diagram showing an example of an arbitrary function generator using a CR differentiating circuit.

FIG. 23 is a diagram showing an example of a waveform for correcting an oscillating magnetic field.

FIG. 24 is a diagram showing an example of an arbitrary function generator using a CR differentiating circuit and an arbitrary waveform generating circuit.

FIG. 25 is a diagram showing another fourth example of the circuit configuration of the gradient magnetic field power supply system in another example of the second aspect of the present invention.

FIG. 26 is a diagram showing another fifth example of the circuit configuration of the gradient magnetic field power supply system in another example of the second aspect of the present invention.

FIG. 27 is a diagram showing an example in which the vibration waveform compensation circuit of the present invention is configured by a digital circuit.

28 is a diagram for explaining the operation of the arbitrary function generator in FIG.

FIG. 29 is a diagram showing another example in which the vibration waveform compensation circuit of the present invention is configured by a digital circuit.

FIG. 30 is a diagram illustrating a compensation operation by a digital circuit.

FIG. 31 is a diagram illustrating an oscillating magnetic field that cannot be completely compensated due to nonlinearity.

[Fig. 32] Fig. 32 is a diagram for describing compensation in the case where characteristics are different between rising and falling.

[Explanation of symbols]

 1 computer system 2 sequencer 3 gradient magnetic field power supply system 4 transmitter 5 receiver 6 RF coil 7 gradient magnetic field coil 8 receiving coil 9 receiver 10 monitor 11-13 compensation circuit 14-16 gradient magnetic field power supply

Claims (2)

[Claims] 1. A nucleus equipped with a gradient magnetic field power supply system capable of supplying a drive current in which an eddy current compensating current is superposed to a gradient magnetic field coil for applying a gradient magnetic field to a subject arranged in a static magnetic field space. In the magnetic resonance imaging apparatus, the gradient magnetic field power supply system includes means for superposing an oscillating magnetic field compensating current on the drive current. 2. A nucleus equipped with a gradient magnetic field power supply system capable of supplying a driving current in which an eddy current compensating current is superposed to a gradient magnetic field coil for applying a gradient magnetic field to a subject arranged in a static magnetic field space. In the magnetic resonance imaging apparatus, the gradient magnetic field power supply system includes means for superimposing an eddy current magnetic field compensating current on the drive current for a space between selected segments of the gradient magnetic field coil. Resonance imaging device.