JPH0998962A - Measurement method of magnetic resonance and equipment therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable to extend a usable range of frequency and intensity of an oscillatory gradient magnetic field by generating an oscillatory gradient magnetic field toward at least two axial directions simultaneously with almost the same oscillatory corrugations. SOLUTION: At a space where a measurement object is laid, a magnet 21 to generate static magnetic field Ho and a set of coils 24, 25 and 26, to generate gradient magnetic field toward x axis direction, y axis direction and z axis direction respectively, and located. A computer 30 controls drive of coils 24, 25 and 26 to generate gradient magnetic field through equipments 27, 28 and 29 respectively to drive gradient magnetic field so that gradient magnetic field is generated toward x, y and z axes with specified timing and intensity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance measuring method and an apparatus therefor, and more particularly to a magnetic resonance measuring method and apparatus for obtaining a magnetic resonance signal by using a so-called oscillating gradient magnetic field as a gradient magnetic field applied to an object to be measured. It is about.

[0002]

2. Description of the Related Art A method of modulating a magnetic resonance signal from an object to be measured by using a so-called oscillating gradient magnetic field to measure a magnetic resonance image was devised by Mansfield (JP-A-53-81288), and an echo planer. A method called an imaging method (hereinafter referred to as EPI) is known. Here, the oscillating gradient magnetic field refers to a gradient magnetic field whose strength changes periodically with time.

Such a method operates according to a preset pulse sequence, and a schematic diagram of the pulse sequence is shown in FIG.

In the figure, an oscillating gradient magnetic field (Gx) 8 is applied in the x-axis direction of the space in which the object to be measured is placed, and a blip-shaped gradient magnetic field (Gy) 9 is applied in the y-axis direction. It has different behavior compared to other pulse sequences.

The magnetic resonance signals obtained in this case are sequentially collected on a so-called k-space by drawing a locus as shown in FIG. Here, the k-space is a space that represents the amount of modulation of the magnetic resonance signal, and is defined as a space whose coordinate axis is the time integration of each gradient magnetic field applied strength. It can be considered that the modulated magnetic resonance signal is data-collected in the k space, and an image such as a tomographic image can be obtained by performing Fourier transform on the data collected in this space.

Further, a method of modulating a magnetic resonance signal from a measurement object and measuring a chemical shift image by using the same oscillating gradient magnetic field is known, and this method is Mansfi.
eld (patent registration number 1686827) and Matsui (patent registration number 1873973) devised by the echo planar spectroscopic imaging method (hereinafter EP
It is referred to as SI).

Of these, a schematic diagram of the pulse sequence of the method by Matsui is shown in FIG. In the figure, an oscillating gradient magnetic field (Gx) 14 is applied in the x direction of the space where the measurement target is placed.
And a phase encode gradient magnetic field (G
y) Applying 15 has a different behavior compared to other pulse sequences.

The magnetic resonance signals obtained in this case are sequentially collected on the k-space by drawing a locus as shown in FIG. That is, kx, ky
The locus on the plane is the phase encoding gradient magnetic field Gy (15).
According to the change of, it is designed to proceed in the direction of the arrow in the figure. In addition, the phase encoding gradient magnetic field (Gy) 15
The locus of one-time data acquisition of the magnetic resonance signal obtained by each of the changes of (1) and (2) changes on the time axis (t) and the kx axis as shown in FIG.

Then, a chemical shift image to be measured can be obtained by Fourier-transforming the data in the k-space.

[0010]

However, in both the EPI and EPSI using the oscillating gradient magnetic field, there are maximum strength and maximum slew rate as characteristic parameters of the gradient magnetic field system. Since the frequency and strength of the gradient magnetic field are limited, the following problems have been pointed out.
Here, the slew rate means the time rate of change of the gradient magnetic field strength.

In the case of the EPI, the high-speed signal acquisition and the high spatial resolution in the EPI have a reciprocal relationship such that if one of them is attempted to be improved, the other cannot be sufficiently satisfied.

That is, in order to perform signal acquisition at high speed, the frequency of the oscillating gradient magnetic field must be increased.
At this time, in order to maintain the spatial resolution, it is necessary to increase the strength of the oscillating gradient magnetic field, but the upper limit is determined by the above two parameters, and the spatial resolution deteriorates when a higher value is required.

On the contrary, in order to realize high spatial resolution,
The product of the gradient magnetic field strength and the application time must be increased. At this time, in order to maintain the signal acquisition time, it is necessary to raise only the gradient magnetic field strength, but the upper limit is determined by the above two parameters, and if more than that is required, take a longer application time. Therefore, the signal acquisition time becomes long. Therefore, (1) artifacts due to static magnetic field inhomogeneity and body movements / flows increase, (2) the number of multi-slices decreases, (3) attenuation effect due to lateral relaxation time becomes strong, and signal-to-noise There arise problems such as a low ratio (SNR).

In the case of EPSI, in the wide spectrum observation band and the high spatial resolution in EPSI, they are in a mutually contradictory relationship such that if one is attempted to be improved, the other cannot be sufficiently satisfied.

That is, in order to expand the spectrum observation band, the frequency of the oscillating gradient magnetic field must be increased. At this time, in order to maintain the spatial resolution, the strength of the oscillating gradient magnetic field must be increased, but the upper limit is determined by the above two parameters, and if a higher value is required, the spatial resolution deteriorates.

On the contrary, in order to realize high spatial resolution, the product of the gradient magnetic field strength and the application time must be increased. At this time, in order to maintain the spectrum observation band, only the gradient magnetic field strength needs to be raised, but the upper limit is determined by the above two parameters, and if a higher value is required, the frequency of the oscillating gradient magnetic field is changed. As a result, the spectrum observation band is reduced.

The present invention has been made under such circumstances, and an object thereof is to provide a magnetic resonance measuring method and apparatus capable of expanding the usable range of the frequency and intensity of the oscillating gradient magnetic field. It is in.

For example, when the frequency of the oscillating gradient magnetic field is the same as the conventional one, the strength of the oscillating gradient magnetic field can be significantly improved. Further, when the strength of the oscillating gradient magnetic field is set to the conventional value, the frequency of the oscillating gradient magnetic field can be significantly improved. Another object of the present invention is to provide a magnetic resonance measuring method and apparatus capable of improving the frequency and strength of the oscillating gradient magnetic field more than ever before.

[0019]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

That is, a magnetic resonance signal is taken out from an object to be measured, an oscillating gradient magnetic field is generated to add position information of the measurement region to the magnetic resonance signal, and an image in the measurement region is reconstructed from the magnetic resonance signal. In the magnetic resonance method, the oscillating gradient magnetic field is simultaneously generated in at least two axis directions, and the vibration waveforms are substantially the same.

In the magnetic resonance measuring method thus constructed, when the magnetic resonance signals obtained thereby are collected in the so-called k space (spatial frequency domain), the gradient magnetic fields in the directions of the respective axes are combined in vector. It oscillates in a direction and moves as it moves in a direction perpendicular to the direction, and then it is collected.

When the oscillating frequency and strength of the oscillating gradient magnetic field in the directions of the respective axes are set as in the conventional case, this collection range is obtained by vector-synthesizing the gradient magnetic fields in the directions of the respective axes as compared with the conventional case. As a result, it increases correspondingly, and as a result, it extends to the high frequency region. As a result, the spatial resolution of the reconstructed image can be significantly improved.

On the contrary, in the above-mentioned structure, in the case of collecting the magnetic resonance signals in the k-space, if the spatial resolution is maintained in the same manner as in the conventional case and the spatial resolution is maintained, the directions of the respective axes can be changed. The vibration frequency of the vibration gradient magnetic field can be significantly increased.

In each of the above cases, when the vibration frequency and intensity of the oscillating gradient magnetic field in the direction of each axis are maintained as usual to improve the spatial resolution, and when the spatial resolution is maintained as usual, the oscillating gradient magnetic field in the direction of each axis is improved. The case of improving the oscillating frequency of the above is explained, but by setting them to appropriate values, both the spatial resolution and the oscillating frequency of the oscillating gradient magnetic field in the direction of each axis can be improved as compared with the conventional case. become able to.

That is, the usable range of the vibration frequency and the strength of the vibration gradient magnetic field can be expanded.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. FIG. 15 is a schematic configuration diagram showing an embodiment of a magnetic resonance apparatus to which the magnetic resonance measuring method according to the present invention is applied.

First, there is a measurement target 22, a static magnetic field magnet 21 for generating a static magnetic field H ₀ in a space where the measurement target 22 is arranged, and a gradient magnetic field generating coil 24 for generating a gradient magnetic field in the x-axis direction. A gradient magnetic field generating coil 25 that generates a gradient magnetic field in the y-axis direction and a gradient magnetic field generating coil 26 that generates a gradient magnetic field in the z-axis direction are arranged.

These gradient magnetic field generating coils 24, 25,
And 26 are gradient magnetic field drive devices 27, 28,
And 29, drive control is performed by the computer 30, and in the space, the x-axis direction, y
A gradient magnetic field is generated at a predetermined timing and strength in the axial direction and the z-axis direction, respectively.

Here, the gradient magnetic field generating coils and the gradient magnetic field driving devices are collectively referred to as a gradient magnetic field system.

Further, a high frequency coil 23 for inducing a magnetic resonance phenomenon in the measurement object 22 is provided in the space, and the high frequency coil 23 is instructed by the computer 30 to synthesizer 32 and modulator 33. A high frequency signal is output via the.

In that case, the gradient magnetic field generating coil 24,
Due to the gradient magnetic fields applied by 25 and 26, the magnetic resonance signal to which the position information and the like of the measurement target is added is obtained from the measurement target 22.

The high frequency coil 23 also serves as a receiving coil for receiving this magnetic resonance signal, and the magnetic resonance signal obtained thereby is passed through an amplifier 34, a detector 35, and an A / D converter. CPU via (not shown)
It is adapted to be input to the computer 30 which incorporates the above.

In the computer 30, the magnetic resonance signal is once collected in the k-space, and the reconstructed image is obtained by performing the arithmetic processing including the Fourier transform based on the collected data. There is. Then, after that, the image (tomographic image or the like) is displayed on the display 3 including a CRT or the like.
The image is displayed by outputting it to 1.

Here, the above-mentioned series of operations in the magnetic resonance apparatus is controlled by the computer 30 based on the information from the pulse sequence stored in the memory 20 in advance. An example of the sequence will be described below with reference to FIG.

In FIG. 1, first, an excitation radio frequency magnetic field pulse (RF) 1 is applied to induce a magnetic resonance phenomenon in the measurement object 22. At this time, the slice selection gradient magnetic field (Gz) 2 is applied in the z-axis direction at the same time as the application of the excitation high-frequency magnetic field pulse.
Is applied, and the cross section to be observed is selected from the measurement target 22.

After that, gradient magnetic fields (Gx) 3 and (G) for setting the starting point of data collection in the x-axis direction and the y-axis direction.
y) 4 is applied, and then the oscillating gradient magnetic fields (Gx) 5 and (Gy) 6 having substantially the same waveform are simultaneously formed in the respective directions of two axes of x and y.
Is applied.

That is, a magnetic field having a positive (+) gradient in the x-axis direction is given and a magnetic field having a positive (+) gradient is also given in the y-axis direction, and further in the x-axis direction. A magnetic field having a negative (-) gradient is applied and a magnetic field having a negative (-) gradient is also applied in the y-axis direction, and this procedure is repeated thereafter.

The magnetic resonance signal from the measurement object 22 is acquired (AD) 7 while being modulated by the application of the oscillating gradient magnetic field. Here, as indicated by the dotted line in the figure, the reversal times of the respective oscillating gradient magnetic fields are not completely the same but are set so as to be slightly deviated. This is because a waveform in which a blip-shaped gradient magnetic field is superimposed on each basic oscillating gradient magnetic field is used. The blip-shaped gradient magnetic field is in a direction (x−) orthogonal to the vectorally synthesized direction (x + y direction) of these fundamental oscillating gradient magnetic fields.
Since it is superimposed in the y direction), a negative blip-shaped gradient magnetic field is superimposed in the x-axis direction and a positive blip-shaped gradient magnetic field is superimposed in the y-axis direction. In this case, the positive and negative
The gradient magnetic fields 3 and 4 for setting the starting point are set to be opposite.

Magnetic resonance signals by such a pulse sequence are sequentially collected in the k-space as described above, and the locus of this collection is as shown in FIG.

In the k-space of the figure, the locus of data collection moves in the kx-ky direction while oscillating in the kx + ky direction. That is, when the gradient magnetic fields applied in the x-axis direction and the y-axis direction are applied with substantially the same intensity in a state of having positive (+) gradients, the directions in which the gradient magnetic fields are synthesized in vector Magnetic resonance signals are sequentially obtained (the direction corresponds to the kx + ky direction in FIG. 2). Then, after moving in the kx-ky direction in FIG. 2 by the action of the blip-shaped gradient magnetic field, each gradient magnetic field applied in the x-axis direction and the y-axis direction has a negative (−) gradient, respectively. Therefore, it is applied with almost the same intensity. Also in this case, magnetic resonance signals in the directions in which the respective gradient magnetic fields are combined in vector are sequentially obtained (the directions correspond to the −kx−ky direction in FIG. 2).

Here, in FIG. 2, the range surrounded by the dotted line shows the data collection range (corresponding to the range shown in FIG. 12) when measured by the conventional EPI. It can be seen that the data collection range obtained by this embodiment is expanded to a region beyond that of the conventional one, that is, to a high frequency region. As is clear from the figure, the range expansion is √2 times, and accordingly, the spatial resolution is also improved by about √2 times.

In this way, the data collected in the k-space is 2 with the kx + ky direction and the kx-ky direction as axes.
The image is reconstructed by applying the three-dimensional Fourier transform. In this case, the reconstructed image is centered on the origin and is 45
Since the image has been rotated by 45 degrees, it is possible to display an image in a normal orientation by performing an operation by coordinate conversion that rotates by -45 degrees.

According to the embodiment described above, the magnetic resonance signal obtained thereby oscillates in the direction in which the gradient magnetic fields in the directions of the respective axes are vector-synthesized in the k-space, and in the direction orthogonal to the direction. It will be collected as you move.

Then, the collection range is increased corresponding to the amount obtained by vector-wise combining the gradient magnetic fields in the directions of the respective axes, as compared with the conventional case, and as a result, reaches the high frequency region. Will be expanded to. As a result, the spatial resolution of the reconstructed image can be significantly improved.

In the above-mentioned embodiment, the strengths of the oscillating gradient magnetic fields are substantially equal to each other.
It goes without saying that the method is not necessarily limited to this. This is because the slope of the trajectory of data collection on the k-space is different, and the problem can be solved by performing coordinate conversion according to the slope.

Embodiment 2 FIG . In this embodiment, the pulse sequence is the same as that shown in FIG. 1, but unlike the first embodiment, its oscillating gradient magnetic fields (Gx) 5 and (Gx) are used.
y) doubling each frequency of 6 and multiplying the intensity by about 1 / √2.

The locus of data collection in the k space of the magnetic resonance signal obtained by such a pulse sequence is as shown in FIG. In this figure as well, the area surrounded by the dotted line shows the conventional data collection range.

As is clear from this figure, the spatial resolution of the reconstructed image is the same as the conventional one, but the frequency of the oscillating gradient magnetic field can be improved, and the data acquisition time is about 1 /
√ Has the effect of being able to be shortened by a factor of 2.

Further, since the data acquisition time can be shortened in this way, static magnetic field inhomogeneity, reduction of artifacts due to body movement / flow, increase of the number of multi-slices, improvement of SNR, etc. can be achieved.

Example 3. In this embodiment, as shown in FIG. 4A, in each of the oscillating gradient magnetic fields applied in the x-axis direction and the y-axis direction, when one is (+), the other is (-). That is different from the first embodiment.

In the case of such a configuration, the locus of data collection on the k-space is, as shown in FIG. 4 (b), the synthesizing direction of the oscillating gradient magnetic field is the xy direction, and the superimposed blip-like gradient is obtained. The synthetic direction of the magnetic field is the x + y direction. However, similarly to the first or second embodiment, the improvement of the spatial resolution or the shortening of the data acquisition time is ensured.

To obtain an image in a normal orientation after the Fourier transform calculation, it is only necessary to carry out coordinate conversion by a corresponding angle rotation.

Embodiment 4 FIG . In this embodiment, the oscillating gradient magnetic field in the x-axis direction is shifted to the (−) side, and the oscillating gradient magnetic field in the y-axis direction is shifted to the (+) side. A specific method of shifting can be achieved by superimposing a gradient magnetic field having a constant value on the underlying oscillating gradient magnetic field. The gradient magnetic field that takes this constant value is
It is indicated by a dotted line.

The synthesis direction of the gradient magnetic field having this constant value is a direction orthogonal to the synthesis direction of the oscillating gradient magnetic field,
As long as this is taken into consideration, it is not necessarily limited to shifting the oscillating gradient magnetic field in the x-axis direction to the (−) side and shifting the oscillating gradient magnetic field in the y-axis direction to the (+) side. Needless to say.

In this case, the data collection locus of the magnetic resonance signal in the k-space is zigzag as shown in FIG. 5B, but the spatial resolution is improved as in the first or second embodiment. Or, the reduction of data acquisition time will be ensured.

If an appropriate image is to be obtained as in the first embodiment, it can be easily solved by adding an appropriate correction process at the time of reconstruction.

Example 5. In this embodiment, as shown in FIG. 6, the frequency and intensity of the oscillating gradient magnetic fields (Gx) 5 and (Gy) 6 are temporally changed, and the acquisition locus of the magnetic resonance signal on the k space is shown in FIG. As shown, the measurement is performed so as to fill the circular area. That is, the vibration frequency of each oscillating gradient magnetic field is increased in the course of time ⇒
Small ⇒ large, strength is changed in order from small ⇒ large ⇒ small.

Also in this case, the spatial resolution is improved or the data acquisition time is shortened as in the first or second embodiment, and the reconstructed image has no direction dependency. , The effect of making truncation artifacts less noticeable.

In addition, the data acquisition time can be shortened by the amount of increase in the oscillating frequency of the oscillating gradient magnetic field.

Further, in this embodiment, the frequencies of the oscillating gradient magnetic fields (Gx) 5 and (Gy) 6 are temporally changed as described above, but the intensity of the oscillating gradient magnetic field is not changed. Even if is changed appropriately, the same data acquisition as shown in FIG. 7 can be performed.
Even in this case, it is possible to eliminate the harmful effects of truncation artifacts.

In this case, the effect of reducing the eddy current generated in the device is obtained by reducing the initial rise of the oscillating gradient magnetic field.

Example 6. This embodiment shows one embodiment of EPSI for measuring a chemical shift image using an oscillating gradient magnetic field, using the pulse sequence shown in FIG.

In the figure, the excitation high frequency magnetic field pulse (R
F) 1 is applied, and the magnetic resonance phenomenon is induced in the measurement target 22. At this time, the slice selection gradient magnetic field (Gz) 2 is applied in the z-axis direction at the same time as the excitation radio frequency magnetic field pulse is applied, and the cross section for observing the measurement target 22 is selected. Phase-encoding gradient magnetic fields (Gx) 10 and (Gy) 11 for setting the starting point of data acquisition in the x-axis direction and the y-axis direction are applied, and then the vibrations of the same waveform are simultaneously applied in each of the x-axis direction and the y-axis direction. Gradient magnetic fields (Gx) 12 and (Gy) 13 are applied. The oscillating gradient magnetic fields 12 and 13 at this time have the same waveform.

The magnetic resonance signal from the measuring object 22 is acquired (AD) 7 while being modulated by the application of these oscillating gradient magnetic fields.

Here, this series of pulse sequences is
This is repeated while changing the strength of the phase encode gradient magnetic fields 10 and 11, and in this case, the phase encode gradient magnetic field 1
The combined direction of 0 and 11 is changed so as to maintain the direction (xy direction) orthogonal to the combined direction of the oscillating gradient magnetic fields 12 and 13 (x + y direction).

The data acquisition locus in the k space of the magnetic resonance signal obtained by such a pulse sequence is shown in FIG.
As shown in (a) and (b). In the figure,
While oscillating zigzag in the (t, kx + ky) plane, the phase-encoding gradient magnetic field causes k for each repeated measurement.
It moves in the x-ky direction.

Here, in FIG. 9A, the area surrounded by the dotted line shows the data collection range (corresponding to the area shown in FIG. 14A) when measured by the conventional EPSI. . The data collection range obtained by this example is
It can be seen that the range beyond the conventional range, that is, the high frequency range has been expanded. As the expansion of the area,
As is clear from the figure, the effect is about √2 times, and with this, the improvement of the spatial resolution is also about √2 times.

The data thus collected are t,
The image is reconstructed and imaged by a three-dimensional Fourier transform with the kx + ky direction and the kx-ky direction as axes. At this time,
Appropriate correction processing may be added according to the zigzag data acquisition locus. The reconstructed image has (x,
y) Since it is rotated by 45 degrees on the plane, if an operation of rotating by -45 degrees is added, an image can be displayed in the same orientation as that when measured by the conventional EPSI.

Embodiment 7 FIG . In this embodiment, in the pulse sequence (FIG. 8) shown in the sixth embodiment, the frequency of the oscillating gradient magnetic fields 12 and 13 is multiplied by about √2 and the strength is set to about 1.
/ √2 times, and phase encoding gradient magnetic field 10, 1
The case where the intensity of 1 is increased by about 1 / √2 is shown.

In this case, the data collection loci of the magnetic resonance signals in the k space are shown in FIGS. 10 (a) and 10 (b). Also in this case, the range surrounded by the dotted line shown in FIG. 9A shows the data collection range when measured by the conventional EPSI.

From this, although the spatial resolution of the reconstructed image is the same as the conventional one, the data acquisition interval on the t-axis is about 1 /
Since it is √2 times, there is an effect that the spectrum observation band is about √2 times.

Example 8. In this embodiment, the chemical shift image is also based on the fact that various gradient magnetic field application methods are possible. For example, the gradient magnetic fields 12 and 13 shown in FIG. 8 do not have to be the same. Further, in the pulse sequence shown in FIG. 8, the intensity and frequency of the oscillating gradient magnetic field are changed in accordance with the intensity of the phase encoding gradient magnetic fields 12 and 13 in the synthesis direction (xy direction) to collect data. The locus is (kx, ky)
You can fill a circle with a plane. Also in this case, the reconstructed image has no direction dependence, and truncation artifacts in the spatial direction are inconspicuous. Further, when the spectrum observation band is expanded as shown in FIG. 10, if the application time of the oscillating gradient magnetic field and the data acquisition time are lengthened, the resolution in the spectrum direction can be improved.

Example 9. In the above description, all 2 of x and y
Although the case where the oscillating gradient magnetic field is applied to the axis is shown, the axis to be selected may be changed depending on the observation cross section. Further, the simultaneous application to the three axes makes it possible to increase the effect more than the case of applying to the two axes.

Example 10. In general, the two axes that correspond to the radial direction of the bore of the magnetic resonance apparatus have similar characteristics of the gradient magnetic field system. By selecting these two axes, it is possible to reduce the labor required for adjusting the rise time of the gradient magnetic field. Also, when axes with different characteristics are selected, the strength of each oscillating gradient magnetic field is
You may change according to the characteristic. For example, it goes without saying that the strength may be set in proportion to the maximum strength or the maximum slew rate of each gradient magnetic field system.

Other Embodiments In the above description, the two-dimensional case was described.
The same is possible for the dimensional case. For example, in the first to eighth embodiments, a phase encode gradient magnetic field may be added in the z-axis direction. In addition, in Examples 5 and 8,
Data may be collected to fill a sphere or hemisphere in (kx, ky, kz) space.

In each of the drawings, the trapezoidal wave is used as the oscillating gradient magnetic field, but a sine wave or the like may be used. For example, when a sine wave is used, it has an effect of reducing an eddy current generated in the device.

Further, in the above description, the data acquisition is continued during the application of the oscillating gradient magnetic field, but the data acquisition may be performed piecewise. This makes it possible to save the memory added to the computer 30 and speed up the data transfer. Also, this method may be used in combination with a technique for measuring about half on the k space (half measurement method), a technique for dividing the k space and performing a plurality of measurements (k space division, interleave), and the like. It goes without saying that it is good.

Further, in the above description, the improvement of the spatial resolution,
We have described a method that only takes either shortening the data acquisition time or expanding the spectral band. But,
The present invention does not select either one, but expands the range in which both are compatible.

Further, in the above description, a simplified pulse sequence is used for simplification of the description, but it goes without saying that the present method can be applied to all measurement methods using an oscillating gradient magnetic field.

[0080]

As is apparent from the above description,
According to the magnetic resonance measuring method and the apparatus therefor of the present invention, it becomes possible to expand the usable range of the frequency and the strength of the oscillating gradient magnetic field.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a pulse sequence applied to a magnetic resonance measurement method according to the present invention.

FIG. 2 is a schematic diagram showing an example of a trajectory in a k-space of data acquisition by the pulse sequence shown in FIG.

FIG. 3 is a schematic diagram showing another example of the trajectory in the k space of the data acquisition by the pulse sequence shown in FIG.

FIG. 4 is a diagram showing another embodiment of a pulse sequence applied to the magnetic resonance measurement method according to the present invention.

FIG. 5 is a diagram showing another embodiment of a pulse sequence applied to the magnetic resonance measurement method according to the present invention.

FIG. 6 is a diagram showing another embodiment of a pulse sequence applied to the magnetic resonance measurement method according to the present invention.

FIG. 7 is a schematic diagram showing an example of a trajectory in the k space of data acquisition by the pulse sequence shown in FIG.

FIG. 8 is a diagram showing another example of the pulse sequence applied to the magnetic resonance measurement method according to the present invention.

9 is a schematic diagram showing an example of trajectories in the t and k spaces of data collection by the pulse sequence shown in FIG.

FIG. 10 is a schematic diagram showing another example of trajectories in the t and k spaces of data collection by the pulse sequence shown in FIG.

FIG. 11 is a diagram showing an example of a conventional EPI pulse sequence in magnetic resonance image measurement.

FIG. 12 is a schematic diagram showing an example of a trajectory in the k space of data acquisition by the pulse sequence shown in FIG.

FIG. 13: Conventional EP in chemical shift image measurement method
It is a figure which shows an example of the pulse sequence of SI.

14 is a schematic diagram showing an example of trajectories in the t and k spaces of data acquisition by the pulse sequence shown in FIG.

FIG. 15 is a configuration diagram showing an embodiment of a magnetic resonance apparatus to which the present invention is applied.

[Explanation of symbols]

1 ... Excitation high frequency magnetic field pulse, 2 ... Slice selection gradient magnetic field, 3, 4 ... Gradient magnetic field, 5, 6, 8, 12, 13, 14
... oscillating gradient magnetic field, 7 ... data acquisition, 9 ... blip-shaped gradient magnetic field, 10, 11, 15 ... phase encoding gradient magnetic field,
21 ... Static magnetic field magnet, 22 ... Measuring object, 23 ... High frequency coil, 24, 25, 26 ... Gradient magnetic field generating coil, 27, 2
8, 29 ... Coil driver, 30 ... Calculator, 31 ... Display, 32 ... Synthesizer, 33 ... Modulator, 34
… Amplifier, 35… Detector.

Claims (23)

[Claims] 1. A magnetic resonance signal is extracted from an object to be measured,
In a magnetic resonance method of generating an oscillating gradient magnetic field to add position information of a measurement region to the magnetic resonance signal and reconstructing an image in the measurement region from the magnetic resonance signal, the oscillating gradient magnetic field has at least two axes. The magnetic resonance measuring method is characterized in that the waveforms of the vibrations are simultaneously generated in the directions of, and the waveforms of the vibrations are almost the same. 2. The magnetic resonance measuring method according to claim 1, wherein the oscillating gradient magnetic fields generated in at least two axis directions have substantially the same intensity. 3. An oscillating gradient magnetic field which is simultaneously generated in at least two axis directions, and when one of them has a positive gradient, the other also oscillates with a positive gradient. Magnetic resonance measurement method. 4. A magnetic field according to claim 1, wherein each of the oscillating gradient magnetic fields generated simultaneously in at least two axis directions vibrates with a positive gradient in one of them and a negative gradient in the other. Resonance measurement method. 5. Magnetic resonance signals obtained over time are sequentially collected in a k-space, and the data are collected in a constant angular direction in each of two mutually orthogonal axes showing the k-space.
The magnetic resonance measuring method according to claim 1, wherein the magnetic resonance signals are sequentially acquired in a meandering manner. 6. The magnetic resonance measurement method according to claim 1, wherein the image obtained is a chemical shift image. 7. The magnetic resonance measuring method according to claim 1, wherein the oscillating waveform of each oscillating gradient magnetic field has a trapezoidal shape. 8. The magnetic resonance measuring method according to claim 1, wherein the oscillating waveform of each oscillating gradient magnetic field has a sine wave shape. 9. A blip-shaped gradient magnetic field is superimposed on each oscillating gradient magnetic field applied at the same time in a direction orthogonal to the synthetic direction thereof. The magnetic resonance measurement method according to any one of claims. 10. The magnetic field according to claim 1, wherein a gradient magnetic field having a constant strength is superimposed on each of the simultaneously applied oscillating gradient magnetic fields in a direction orthogonal to their combined direction. Resonance measurement method. 11. The magnetic resonance measuring method according to claim 1, wherein a phase encode gradient magnetic field is applied to each of the simultaneously applied oscillating gradient magnetic fields in a direction orthogonal to a synthesis direction thereof. . 12. The oscillating gradient magnetic field has a gradient magnetic field system having substantially the same maximum slew rate or maximum strength.
The magnetic resonance measurement method according to claim 1, wherein the magnetic resonance measurement method is performed in the axial direction. 13. When the maximum slew rate or the maximum strength of the gradient magnetic field system differs depending on the axis to which the oscillating gradient magnetic field is applied, the applied strength of each oscillating gradient magnetic field is changed according to the maximum slew rate or the maximum strength. The magnetic resonance measuring method according to claim 1. 14. The data collected in k-space is Fourier-transformed in the constant angle direction and a direction orthogonal to the direction, and the image obtained thereby is coordinate-transformed into an angle obtained by inversely rotating the angle. The magnetic resonance measurement method according to claim 4, wherein 15. The magnetic resonance measuring apparatus according to claim 1, wherein each of the oscillating gradient magnetic fields is configured so that the frequency of its oscillation changes with time. 16. Magnetic resonance signals obtained with time are sequentially collected in a k-space, and meandering in a constant angular direction in each of two mutually orthogonal axes showing the k-space. The magnetic resonance signals are sequentially collected in
The magnetic resonance measurement method according to claim 4, wherein the collection region is substantially circular, semicircular, spherical, or hemispherical. 17. A magnetic resonance signal is extracted from a measurement target, an oscillating gradient magnetic field is generated to add position information of the measurement region to the magnetic resonance signal, and an image in the measurement region is reconstructed from the magnetic resonance signal. In the magnetic resonance apparatus, the oscillating gradient magnetic field is simultaneously generated in at least two axis directions, and the vibration waveforms are substantially the same, the magnetic resonance measuring apparatus. 18. An oscillating gradient magnetic field which is simultaneously generated in at least two axis directions is configured so that when one of them has a positive gradient, the other also oscillates with a positive gradient. Claim 16
The magnetic resonance measurement method described. 19. An oscillating gradient magnetic field which is simultaneously generated in at least two axis directions is configured to vibrate with a positive gradient on one side and a negative gradient on the other side. The magnetic resonance measuring method according to claim 16. 20. Magnetic resonance signals obtained with time are sequentially collected in a k-space, and meandering in a certain angular direction of two mutually orthogonal axes showing the k-space. 17. The magnetic resonance measuring apparatus according to claim 16, wherein the magnetic resonance signals are sequentially collected in the data. 21. The magnetic resonance measuring apparatus according to claim 16, wherein each oscillating gradient magnetic field is configured such that the frequency of each oscillating magnetic field changes with time. 22. The magnetic resonance measuring apparatus according to claim 16, wherein the oscillating waveform of each oscillating gradient magnetic field has a trapezoidal shape. 23. The oscillating waveform of each oscillating gradient magnetic field has a sine wave shape.
20. The magnetic resonance measurement apparatus according to any one of claims 19 to 19.