JPH0654820A - Magnetic resonance diagnostic device - Google Patents

Abstract

PURPOSE:To provide a magnetic resonance diagnostic device which can compensate satisfactorily the influence by an body current magnetic field which follows a gradient magnetic field extending over the whole exciting slice area. CONSTITUTION:The device is provided with an eddy current magnetic field memory 1 for storing the data of a time constant and the anti-gradient magnetic field intensity ratio of an eddy current magnetic field generated in connection with a slice gradient magnetic field, a driving waveform generating part 2 for generating a driving waveform modulated by the reverse response of a time response of the eddy current magnetic field in each slice area, from the data of the eddy current magnetic field corresponding to each slice area stored in this memory 1 and a driving waveform memory 3 for storing this driving waveform. Also, the magnetic resonance diagnostic device is provided with a D/A converter 4 for reading out the driving waveform of the slice area to be excited from the memory 3 and driving a slice gradient coil 6 in accordance with its driving waveform and a gradient coil power source 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance diagnostic apparatus, and more particularly to a method for correcting an eddy current magnetic field generated when a gradient magnetic field coil is driven.

[0002]

2. Description of the Related Art Magnetic resonance imaging is a technique in which a group of nuclei with unique magnetic moments is placed in a uniform static magnetic field.
It is a method of visualizing chemical and physical microscopic information of a substance by utilizing the phenomenon of resonantly absorbing the energy of a high frequency magnetic field rotating at a specific frequency. In this method, it is essential to use a gradient magnetic field in order to give spatial information (positional information) to the magnetic resonance signal. Since the gradient magnetic field is switched and applied, the switching induces an eddy current on the shield cylindrical conductor outside the gradient coil. A magnetic resonance signal is modulated by a magnetic field generated by this eddy current (hereinafter referred to as an eddy current magnetic field), which causes deterioration such as blurring on an image and deterioration such as distortion on a spectrum.

As a method for solving this problem, (a) a method of compensating the eddy current magnetic field by modulating the gradient coil drive waveform with an inverse response of the time response of the eddy current (b) a leakage magnetic field cutoff outside the gradient coil Has been proposed to install an active shield gradient coil (ASGC) for.

However, in the method (a) in which the compensation waveform of the drive waveform is determined at one point, the magnetic field formed by the eddy current and the magnetic field formed by the gradient coil current do not completely match, so that the magnetic fields of the two are not matched. Since there are different spatial non-linearities in, there remains an eddy current magnetic field that cannot be compensated (hereinafter referred to as residual eddy current magnetic field).

In the method (b), it is difficult to exactly match the center of the gradient coil and the center of the active shield gradient coil, and as a result, there is a problem of residual eddy current magnetic field.

[0006]

As described above, in the countermeasures against the eddy current magnetic field by the conventional technique, it is inevitable that the residual eddy current magnetic field is generated, and as a result, the deterioration such as the blur on the image and the distortion on the spectrum is caused. Was a factor of.

The present invention has been made in view of the above problems, and an object thereof is to provide a magnetic resonance diagnostic apparatus capable of favorably compensating for the influence of an eddy current magnetic field due to a gradient magnetic field over the entire excited slice region. And

[0008]

In order to solve the above problems, the present invention relates to a first storage means for storing data of an eddy current magnetic field generated along with a gradient magnetic field in association with a plurality of slice areas. Drive waveform means for generating a drive waveform modulated by the inverse response of the time response of the eddy current magnetic field in each slice area from the data of the eddy current magnetic field corresponding to each slice area stored by the second storage means; Second storage means for storing the drive waveform generated by the drive waveform generation means, and means for reading the drive waveform of the slice region to be excited from the second storage means and driving the gradient coil in accordance with the drive waveform. Is provided.

Further, according to the present invention, storage means for storing data of an eddy current magnetic field generated with a gradient magnetic field in association with a plurality of slice areas, and eddy current corresponding to each slice area stored by the storage means. Means for modulating the drive waveform of the gradient coil with the inverse response of the time response of the eddy current magnetic field in each slice area using the data of the magnetic field.

Here, the data of the eddy current magnetic field is specifically the time constant of the eddy current magnetic field and the ratio of the gradient magnetic field strength to the eddy current magnetic field,
These data are expanded to, for example, an orthogonal function and stored in the form of a distribution function, or the data for each point is stored, and all the data in the slice area is obtained by interpolation.

[0011]

As described above, according to the present invention, the gradient coil, particularly the slice gradient coil, is modulated by the inverse response of the time response of the eddy current magnetic field in the slice region, depending on the slice region to be excited. The effects of the eddy current fields produced by the gradient fields are well compensated over the slice area.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram showing an overall schematic configuration of a magnetic resonance diagnostic apparatus according to an embodiment of the present invention. In the figure, a static magnetic field magnet 21 and a gradient coil 22 and a shim coil 24 provided inside the static magnetic field magnet 21 form a uniform static magnetic field on a subject (not shown) and linear in three directions x, y, z orthogonal to each other in the same direction. A gradient magnetic field having a gradient magnetic field distribution is applied. The gradient coil 22 is driven by a gradient coil power supply 25, and the shim coil 24 is driven by a shim coil power supply 26. The probe 23 provided inside the gradient coil 22 applies a high-frequency magnetic field to the subject by being supplied with a high-frequency signal from the transmitter 27, and receives a magnetic resonance signal from the subject. The probe 23 may be provided for both transmission and reception, or may be separately provided for transmission and reception. The magnetic resonance signal received by the probe 23 is detected by the receiving unit 8, transferred to the data collecting unit 9, A / D converted by the data collecting unit 29, and then sent to the computer system 30 for data processing. Done.

The above gradient coil power supply 25, shim coil power supply 26, transmission unit 27, reception unit 28 and data collection unit 29 are all controlled by the sequence control unit 32, and the sequence control unit 32 is controlled by the computer system 30. To be done.

The computer system 30 is controlled by a command from the console 31. The magnetic resonance signal input from the data collection unit 29 to the computer system 30 is subjected to Fourier transform, phase calculation, etc., and based on that, image data such as the density distribution of desired nuclei in the subject and the eddy current magnetic field distribution are reconstructed. Composed. This image data is displayed on the image display 3
3 and is displayed as an image.

Next, the eddy current magnetic field compensating system by the gradient magnetic field for slicing in this embodiment will be explained. Figure 1
2 shows a portion related to the eddy current magnetic field compensation in the computer system 30 and the sequence control unit 32 in FIG. The eddy current magnetic field compensation system includes an eddy current magnetic field memory 1, a drive waveform generation unit 2, and a drive waveform memory 3. The eddy current magnetic field memory 1 stores, for example, the time constant of the eddy current magnetic field and the data of the gradient magnetic field strength ratio as the data of the eddy current magnetic field at each slice position. The drive waveform generation unit 2 generates drive waveform data corresponding to each slice plane for compensating the influence of the eddy current magnetic field based on the data of the eddy current magnetic field, and this is stored in the drive waveform memory 3 as digital data. To be done. This drive waveform memory 3
The data of the drive waveform corresponding to the slice plane to be excited is read from the device, converted into an analog signal by the D / A converter 4, and then input to the slice gradient coil power supply 5, whereby the slice gradient coil is supplied. 6 is driven. The eddy current magnetic field memory 1, the drive waveform generator 2, and the drive waveform memory 3 are realized by the computer system 30 shown in FIG. The D / A converter 4 is provided in the sequence controller 32 shown in FIG.

The procedure for compensating the eddy current magnetic field will be described below by taking the case of multi-slice chemical shift imaging, which is an example of a sequence using a gradient magnetic field for slicing, as an example. FIG. 4 shows a pulse sequence for multi-slice chemical shift imaging, and shows an example in which chemical shift imaging is performed on two slice planes S1 and S2 of a subject as shown in FIG. In FIG. 4, RF indicates a high frequency magnetic field, and Gz, Gx and Gy indicate gradient magnetic fields in the z, x and y axis directions. In this case, Gz is the slice gradient magnetic field.

The compensation of the eddy current magnetic field in this embodiment is as follows.
(1) Specify the slice position and calculate and generate the drive waveform of the slice gradient magnetic field at that slice position, (2) Drive the slice gradient coil according to the calculated drive waveform, and perform the nuclear spin at the slice position. Is performed in a two-step process of exciting.

FIG. 3 is a flow chart showing the procedure of (1) drive waveform generation. First, the slice planes S1 and S2 are designated, and the representative points Z1 and Z2 in these slice planes S1 and S2 are determined as slice positions (S1).
1). The representative points Z1 and Z2 are set at the center points on the z-axis within the slice planes S1 and S2, as shown in FIG. 5, for example.

Next, the modulation frequency f is set so as to excite the nuclear spins in each slice plane, that is, the following equation is satisfied.
s1, fs2 and slice gradient magnetic field strengths Gs1, Gs2 are determined (S12). γGs1 · Z1 = fs1 γGs2 · Z2 = fs2 (where γ is the gyromagnetic ratio)

Next, the time constants τzj (Z1) and τzj (Z2) of the eddy current magnetic field components at the slice positions Z1 and Z2 and the gradient magnetic field strength ratios Azj (Z1) and Azj (Z2) of the eddy current magnetic field components. )
(J = 1,2, ..., j is the number of each component of the eddy current magnetic field)
Is read from the eddy current magnetic field memory 1 of FIG. 1 (S13). The eddy current magnetic field is previously measured by detection with a pickup coil or by differentiating the phase of the magnetic resonance signal to obtain an eddy current magnetic field waveform, which is subjected to processing such as curve fitting by a method such as a nonlinear least square method. Give.
By this method, the z-axis direction distribution of the eddy current magnetic field generated when the slice gradient coil is driven can be obtained.

The data of the eddy current magnetic field stored in the eddy current magnetic field memory 1 may be the time constant and the gradient magnetic field strength ratio for each point, or the distribution of the time constant and the gradient magnetic field strength ratio may be expanded by an orthogonal function. It may be in the form of a function obtained by In the former case, the time constant and the gradient magnetic field strength ratio of the eddy current magnetic field at the slice positions Z1 and Z2 may be obtained by interpolation from the time constant and the gradient magnetic field strength ratio for each point.

Next, the time constants τzj (Z1) and τzj (Z2) of each component of the eddy current magnetic field read from the eddy current magnetic field memory 1 in S13.
And the data of the gradient magnetic field strength ratios Azj (Z1) and Azj (Z2), the time constants τczj (Z1) and τczj for eddy current magnetic field compensation are used.
(Z2) and gradient magnetic field strength ratio Aczj (Z1), Aczj (Z2)
Is calculated (S14). The calculation of the time constant and the gradient magnetic field strength ratio for the eddy current magnetic field reward is performed by, for example, IEEE TRANS
In ACTIONS OF MEDICAL IMAGING Vol.7,247 (1988)
The method of finding the inverse response of the time response of the eddy current magnetic field described by Michal A. Morch et al. Is used.

Next, the data τczj (Z calculated in S14
1), τczj (Z2) and Aczj (Z1), Aczj (Z2) are used to drive the slice gradient coil drive waveforms f1 (Z1, t) and f2 (Z2, t) corresponding to the slice planes S1 and S2. (S
15). These drive waveforms are represented by the equation (1) when f1 (Z1, t) is taken as an example. Further, the drive waveform f1 (Z1, t) thus obtained is shown in FIG. Other slice plane S
The drive waveforms f2 (Z2, t), ... Corresponding to 2, ...
It is required in the same way as t). Hereinafter, the slice planes S1, S2,
... is represented by SI, and drive waveforms f1 (Z1, t), f2 (Z2, t),
Is represented by fI (ZI, t).

[0024]

[Equation 1]

The drive waveform fI (ZI, t) calculated and generated in this manner is in a form modulated by the inverse response of the time response of the eddy current magnetic field. Therefore, if the slice gradient coil is driven using this drive waveform f1 (ZI, t), the slice surface SI
Since the time constant τzi (x, y, zi) and the gradient magnetic field strength ratio Azi (x, y, zi) in the observation region of are almost uniform, the eddy current magnetic field can be compensated.

The time constant and the gradient magnetic field strength ratio in S13 of FIG. 3 may be on-axis values or average values in each slice plane. The representative point ZI in the slice plane SI is shown in FIG.
It may be selected at the center of the slice plane SI as shown in (a), or as shown in FIG. 7 (b), the gradient magnetic field strength ratio as shown in equation (2) is weighted to give ZI. May be asked.

[0027]

[Equation 2]

Further, in S12 of FIG. 3, time constants and intensities are obtained for points in the slice plane, and then in S13, compensation time constants and intensities are obtained for each set, and the average value of these is used. A method of setting a drive waveform is also conceivable.

When the center of the gradient coil and the center of the eddy current magnetic field are slightly deviated from each other, the eddy current magnetic field also exists at the center of the gradient coil. Since the gradient magnetic field strength is zero at the center of the gradient coil, the time constant and strength may be obtained for points other than the center in the slice including the center position. The same applies when weighting is applied.

FIG. 8 is a diagram for explaining an eddy current magnetic field compensating system according to another embodiment of the present invention, and shows a portion related to the eddy current magnetic field compensation in the computer system 30 and the sequence control unit 32 in FIG. Shows. The eddy current magnetic field compensation system includes an eddy current magnetic field memory 1, a basic drive waveform generation unit 7, a D / A converter 8, a drive waveform control unit 9, and an eddy current magnetic field compensation circuit 10. The basic drive waveform generation unit 7 generates a basic drive waveform (normally a rectangular wave) of the slice gradient coil, and the D / A converter 8 converts this into an analog signal and sends it to the eddy current magnetic field magnetic field compensation circuit 10.

The drive waveform control unit 9 includes an eddy current magnetic field memory 1
By obtaining the inverse response of the time response of the eddy current magnetic field from the eddy current magnetic field data read from the eddy current magnetic field data, or in advance in the eddy current magnetic field memory 1, the variable resistance adjustment corresponding to the time constant and intensity ratio corresponding to the inverse response of the time response The amount or the variable capacitor capacitance adjustment amount is stored and read out to control the eddy current magnetic field compensation circuit 10. That is, in the eddy current magnetic field compensating circuit 10, the basic driving waveform from the D / A converter 8 is modulated by the driving waveform control unit 9 with an inverse response of the time response of the eddy current magnetic field. As a result, the eddy current magnetic field compensating circuit 10 outputs a gradient coil drive waveform having a predetermined time constant τcj and a gradient magnetic field strength ratio Acj corresponding to each slice plane, and passes through the gradient coil power supply 5 to the slice gradient coil 6
Is supplied to. The basic drive waveform generator 7 and the D / A
The converter 8 may be omitted, and the basic drive waveform may be directly input to the eddy current magnetic field compensation circuit 10.

FIG. 9 is a diagram showing a specific example of the eddy current magnetic field compensation circuit 10. The analog signal of the basic drive waveform input from the D / A converter 8 of FIG. 8 is passed through the variable resistor 101. It is input to the amplifier 102, and further output via a time constant circuit including a capacitor 103 and a resistor 104 connected between the output terminal of the amplifier 102 and the ground. In this case, by controlling the variable resistor 101 according to the control signal corresponding to the inverse response of the time response of the eddy current magnetic field from the drive waveform control unit 9 of FIG. 8, the ratio of the drive waveform to the gradient magnetic field strength Acj is changed. By changing the capacitor 103 or the resistor 104, the time constant τcj of the drive waveform changes.

In the above embodiment, the procedure for designating the slice plane, calculating the drive waveform of the slice gradient coil, and driving the slice gradient coil in accordance with this drive waveform has been described. If determined, the slice plane need not be specified. At that time, it is not necessary to store the time constant of the eddy current magnetic field and the gradient magnetic field strength ratio, and the drive waveform corresponding to each slice plane may be stored in advance in the memory in the computer.

Further, in the above embodiments, the case of multi-slice three-dimensional chemical shift imaging has been described, but the gist of the present invention is to compensate the eddy current magnetic field generated due to the switching of the slice gradient magnetic field. Therefore, the present invention can be applied to all other sequences using a gradient magnetic field for slicing, such as a local imaging sequence using stimulated echo.

Next, another embodiment of the present invention will be described. As a method for acquiring images at high speed in magnetic resonance imaging, so-called ultrafast imaging (hereinafter referred to as ultrafast MRI) methods such as the echo planar method by Mansfield and the ultrafast Fourier method by Hutchison et al. Are known. . In general, the data acquisition operation of ultra-high-speed MRI is equivalent to scanning over K space (Kx, Kz) in the case of two-dimensional imaging, for example, and an image is obtained by performing a two-dimensional Fourier transform on the obtained data.

Specifically, by first collecting data during the application of the readout gradient magnetic field, one line of data in the Kx direction is obtained, and then the same operation is performed after applying the phase encoding gradient magnetic field for a predetermined time. By doing so, data shifted by a predetermined amount in the Kz direction can be obtained. By repeating this series of operations a plurality of times, a data set on the K space necessary for image reconstruction can be obtained. This operation corresponds to the data collection operation of the ultra fast Fourier method, and the obtained data becomes the grid point data on the K space, so an image can be obtained by performing the two-dimensional Fourier transform. On the other hand, in the echo planar method, the gradient magnetic field for reading and the gradient for phase encoding are applied at the same time, so data obtained by obliquely scanning the K space can be obtained, and if this is directly Fourier-transformed, peculiar artifacts occur. .

When image reconstruction is performed in these ultra-high-speed MRI, a series of multi-echo signals written in the memory after A / D conversion are separated for each echo and rearranged to obtain a data set on the K space. . At this time, if the gradient magnetic field is an ideal rectangular wave, the number of data for one echo may be cut out at equal intervals from the beginning of the data.
Since the peak position of each echo shifts due to the characteristics of the rising edge, the influence of the eddy current magnetic field, the influence of the static magnetic field, etc., it is actually necessary to cut out the data based on the information of the peak position. At this time, the state with encoding (main scan)
However, since the waveform is deformed due to the phase dispersion in the encoding direction and the correct position of the echo peak cannot be obtained, it is necessary to obtain the echo peak in advance without encoding (prescan). In this case, if the uniformity of the static magnetic field does not change, the image can be reconstructed by one scan in the subsequent scans based on the data once collected. However, if the uniformity of the static magnetic field in the main scan differs from that in the pre-scan due to the influence of susceptibility due to the difference in size and structure of the target site, it is necessary to obtain pre-scan data for each site, and the inspection time Increase. At this time, if the static magnetic field has a large inhomogeneity, the relaxation time T of the transverse magnetization is
₂ ^* (Transverse magnetization phase relaxation time when there is static magnetic field inhomogeneity) is short, and the signal value decays rapidly with time.
There is a problem in that the static magnetic field inhomogeneity is affected such that the peak position of the multi-echo is not detected even if the prescan is performed.

In order to solve such a problem, the embodiment described below detects the waveform of the read gradient magnetic field using a pickup coil, integrates the detected read gradient magnetic field waveform, and zero-crosses the integrated waveform. By detecting points, the peak position of the multi-echo is obtained, scan data is reconstructed based on the peak position data, and then image distortion due to static magnetic field inhomogeneity is corrected if necessary. By obtaining the peak position data of the multi-echo by such a method, it is possible to reconstruct an image of ultra-high-speed MRI by one scan without performing prescan.

FIG. 10 shows an embodiment thereof, and in order to detect the read gradient magnetic field waveform generated by the read gradient coil 200, the pickup 20 as shown in FIG.
Two are provided. It is desirable that the lead wire from the pickup coil 202 is wound in a non-inductive manner.

The pickup coil 202 is set so that its axial direction coincides with that of the readout gradient coil 200. In this case, the pickup coil 202
12 may be arranged so as to be in contact with the inside of the gradient coil 200 as shown in A of FIG. 12, or set outside the probe bobbin 201 as shown in FIG. You may. Further, basically, if the gradient magnetic field generation system is not changed, the gradient magnetic field waveform need only be measured once, so that the pickup coil 202 may be temporarily set within a range that does not hinder imaging as shown in FIG. . However, in any case, it is necessary to set the gradient coil 200 at a position with good linearity. Further, when the direction of the read gradient magnetic field is, for example, the x direction, it is necessary to set the pickup coil 202 at a position other than at least x = 0 (position where the gradient magnetic field strength is 0).

The detection output of the pickup coil 202 is amplified by the amplifier 203 and then input to the integrator 204 or the A / D converter 205, and the output of the integrator 204 is input to the A / D converter 205. . A / D converter 205
Is output to the memory 206.

Next, the method for detecting the echo peak position will be described with reference to FIG.
This will be described with reference to the time chart shown in FIG. First, the readout gradient coil 200 is driven by the ultra-high-speed MRI sequence, and the readout gradient magnetic field waveform is detected by the pickup coil 202. At this time, the encoding gradient magnetic field and the high frequency magnetic field are not applied. Pickup coil 202
The signal from is input to the integrator 204 or the A / D converter 205 through the amplifier 203, and the A / D converter 205
Is stored in the memory 206 (S21).

FIG. 13A shows the pickup coil 202.
Is the output signal waveform of the read gradient magnetic field waveform. This pickup coil 202
When the integrator 204 integrates the output signal waveform of
A gradient magnetic field waveform as shown in (b) is obtained. Integrator 2
The output signal waveform of 04 is sampled by the A / D converter 205, converted into a digital signal, and stored in the memory 206.
Memorized in. At this time, if the sampling frequency and the number of bits of the A / D converter 206 are the same as those of the A / D converter for echo signals, it is convenient for processing the echo data. Here, it is not always necessary to use the integrator 204 for integration, and the output signal of the pickup coil 202 may be directly digitized by the A / D converter 205, stored in the memory 206, and then numerically integrated by a computer. .

In ultra-high-speed MRI, the gradient magnetic field for reading is inverted many times as shown in FIG. 13 (b) to generate many gradient echoes, but at the peak position, the integrated value of the gradient magnetic field waveform becomes zero. Occurs at time. Therefore, the echo peak position is obtained by integrating the gradient magnetic field waveform stored in the memory 206 as shown in FIG. 13 (c) and detecting the times t1, t2, ... Of zero crossing (S22). The data of the echo peak position is stored (S23).

Next, the data of the echo peak position thus obtained is used to reconstruct an image of the main scan data. The procedure of this image reconstruction will be described with reference to the flowchart shown in FIG. The signal (multi-echo data) obtained by the scanning (encoding) of the ultra-high speed MRI is digitized by the A / D converter and then stored in the memory (S31). This series of multi-echo data is cut out for each number of data points in the readout gradient magnetic field direction necessary for image reconstruction centering on each echo peak position obtained by the procedure of FIG. 14 (S32). In the thus obtained echo data, since the gradient magnetic field is reversed, the directions on the K space are opposite between the even number and the odd number. Therefore, by inverting either the even-numbered data or the odd-numbered data, a data set required for image reconstruction can be obtained.
Thereafter, processing such as offset processing, removal of image distortion due to static magnetic field inhomogeneity, and correction of probe characteristics as necessary is performed, and then normal ultra-high-speed MRI image reconstruction processing and display are performed ( S33). The image is displayed in absolute value.

Although the echo peak position detecting method and the image reconstructing method of the ultra high speed AMRI have been described above, the present invention can be applied to the precise control of the gradient magnetic field waveform. That is, by analyzing the gradient magnetic field waveform in the memory, for example, if the gradient magnetic field waveform during the period of data collection deviates from the ideal waveform due to the effect of rising, feedback to the input waveform of the gradient magnetic field power supply is performed. The gradient magnetic field waveform can be corrected by applying or performing an interpolation operation on the K space. The present invention can also be used for automatic adjustment of the echo peak position. For example, when the detected echo peak position is not in the center of each inversion period of the gradient magnetic field, the echo peak position can be adjusted by modifying the input waveform of the gradient magnetic field power supply.

As described above, according to this embodiment, it is possible to reconstruct an image of ultra-high speed MRI without prescanning. In addition, when the echo peak position is detected, the influence of the static magnetic field inhomogeneity is not exerted, and the influence of the static magnetic field inhomogeneity can be independently removed at the data processing stage, so that a good reconstructed image can be obtained. Further, based on the read gradient magnetic field waveform for which data is collected, the influence of the deviation from the ideal waveform can be removed by correcting the input waveform of the gradient magnetic field power source, etc., and the image quality can be improved.

[0048]

According to the present invention, the drive waveform of the gradient coil is set for each slice area to be excited, and the gradient coil is driven based on this, so that the eddy current generated along with the gradient magnetic field for slicing is generated. It is possible to provide a magnetic resonance diagnostic apparatus capable of compensating for the influence of a magnetic field over the entire slice region, without causing deterioration such as blurring on an image and causing deterioration such as distortion on a spectrum.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a configuration of an eddy current magnetic field compensation system according to an embodiment of the present invention.

FIG. 2 is a block diagram of a magnetic resonance diagnostic apparatus according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a procedure for generating a slice gradient coil drive waveform for compensating an eddy current magnetic field generated with a slice gradient magnetic field in the embodiment.

FIG. 4 is a diagram showing a sequence of multi-slice three-dimensional chemical shift imaging.

FIG. 5 is a diagram showing slices in the z direction.

FIG. 6 is a diagram showing a slice gradient coil drive waveform corresponding to a slice plane.

FIG. 7 is a diagram showing a method of selecting a distribution of a ratio of intensity of eddy current magnetic field to gradient magnetic field strength generated along with a gradient magnetic field for slicing and a position in a slice plane.

FIG. 8 is a structural explanatory view of an eddy current magnetic field compensation system according to another embodiment of the present invention.

9 is a diagram showing a specific example of an eddy current magnetic field compensation circuit in FIG.

FIG. 10 is a block diagram showing a configuration of a main part of still another embodiment of the present invention.

11 is a diagram showing the pickup coil in FIG.

FIG. 12 is a view for explaining various arrangement methods of the pickup coil.

FIG. 13 is a time chart for explaining a method for detecting a multi-echo peak position in the same embodiment.

FIG. 14 is a flowchart for explaining a procedure for detecting a multi-echo peak position in the same embodiment.

FIG. 15 is a flowchart for explaining an image reconstruction procedure in the embodiment.

[Explanation of symbols]

1 ... Eddy current magnetic field memory 2 ... Drive waveform generator 3 ... Drive waveform memory 4 ... D / A
Converter 5 ... Gradient coil power supply 6 ... Slice gradient coil 7 ... Basic drive waveform generator 8 ... D / A
Converter 9 ... Drive waveform control unit 10 ... Eddy current magnetic field compensation circuit

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[Procedure amendment]

[Submission date] September 1, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 4]

[Figure 5]

[Figure 6]

FIG. 11

[Figure 1]

[Fig. 2]

[Figure 7]

[Figure 9]

[Figure 3]

[Figure 8]

[Fig. 12]

[Figure 10]

[Fig. 13]

FIG. 14

FIG. 15

Claims (2)

[Claims] 1. A high frequency magnetic field and a gradient magnetic field generated by a gradient coil are applied to a subject arranged in a uniform static magnetic field in accordance with a predetermined pulse sequence to excite a desired slice area, and the excited slice In a magnetic resonance diagnostic apparatus for detecting and imaging a magnetic resonance signal from a region, first storage means for storing data of an eddy current magnetic field generated by applying the gradient magnetic field in association with a plurality of slice regions. And a drive waveform for generating a drive waveform modulated by the inverse response of the time response of the eddy current magnetic field in each slice area from the data of the eddy current magnetic field corresponding to each slice area stored by the first storage means. Means, a second storage means for storing the drive waveform generated by this means, a drive waveform of a slice region to be excited is read from the second storage means, and its drive A magnetic resonance diagnostic apparatus comprising: means for driving the gradient coil according to a waveform. 2. A desired slice area is excited by applying a high frequency magnetic field and a gradient magnetic field generated by a gradient coil to a subject arranged in a uniform static magnetic field in accordance with a predetermined pulse sequence, and the excited slices. In a magnetic resonance diagnostic apparatus that detects and visualizes a magnetic resonance signal from a region, a storage unit that stores data of an eddy current magnetic field generated by applying the gradient magnetic field, and slices stored by the storage unit A magnetic resonance diagnostic apparatus comprising: means for modulating the drive waveform of the gradient coil with an inverse response of the time response of the eddy current magnetic field in each slice area, using the data of the eddy current magnetic field corresponding to the area. .