JPH10248822A - Magnetic resonance measuring device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the effect of the unevenness of a magnetic field caused by a gradient magnetic field to be applied and highly accurately measure a diffusion coefficient and an intensified diffusion image by generating an offset magnet field by a gradient magnetic field generating means according to diffusion gradient magnetic fields. SOLUTION: A high frequency magnetic field for exciting two unclear spins of an object generates high frequency generated by a synthesizer 12 by shaping the waveform, amplifying the power of by a modulator 13, and supplying the current to a coil 3. Gradient magnetic field generation coils 4, 5, 6 supplied with the current from a shim coil drive device 7 generate a gradient magnetic field so as to modulate the magnetic resonance signal from the object 2. After the modulated signal is received by the coil 3, amplified by an amplifier 14, and detected by a detector 15, it is inputted in a computer 10 and the computed results are displayed on a display 11. The current supplied to the gradient magnetic field coils 4, 5, 6 and the shim coil 8 is changed here according to diffusion gradient magnetic fields to be applied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance apparatus, and more particularly, to a magnetic resonance apparatus characterized by suppressing magnetic field inhomogeneity based on a gradient magnetic field generated for diffusion measurement, and a method thereof.

[0002]

2. Description of the Related Art Diffusion measurement is to measure a random motion such as a Brownian motion of a molecule. Under the spatial resolution conditions normally observed by magnetic resonance equipment, the random motion of molecules in a living body is not only due to molecular diffusion, but also due to the motion of molecules generated by blood flow in capillary blood vessels and the flow of extracellular fluid. You. For this reason, the random movement of molecules in a living body is also called apparent diffusion.

[0003] The diffusion measurement method currently widely used is the pulse sequence of Stejskal-Tanner (Journal of Chemical Physics, 42).
No., pp. 288-292, published in 1965). In this method, in order to measure the influence of diffusion, after excitation of nuclear spins by a high-frequency magnetic field, a gradient magnetic field that compensates each other is applied twice to obtain a signal. Here, the meaning of “compensate with each other” means that if molecules do not move, the phase rotation of nuclear spin generated by the first gradient magnetic field application is canceled by the next gradient magnetic field application. If there is diffusion, even if gradient magnetic fields that compensate each other are applied, phase rotation cannot be completely canceled out, and the signal intensity attenuates at a rate corresponding to the applied intensity and time of the gradient magnetic field. These two gradient magnetic fields are called diffusion gradient magnetic fields. In the ideal case, the attenuation of the signal strength is represented by an exponential function with the diffusion coefficient as an index. When such a signal is represented by a graph, the horizontal axis quantifies the effect of the gradient magnetic field on the decay rate of the signal intensity, and is called a gradient magnetic field factor. The diffusion-weighted image is an image obtained when a certain gradient magnetic field factor is set, and a portion where a diffusion coefficient is high is emphasized darkly. Further, it is possible to perform the measurement a plurality of times while changing the gradient magnetic field factor, and obtain the diffusion coefficient from the attenuation rate of the signal intensity. This method is reported in Radiology, 168, pp. 497-505, 1988. In the diffusion measurement, there is a problem that body movements such as respiration and pulsation of a living body cause extreme degradation of image quality because the measurement of minute movement of a molecule called diffusion is measured. Further, in order to measure the diffusion coefficient, it is necessary to measure a plurality of images while changing the gradient magnetic field factor, and there is a problem that the measurement time is long. In order to solve these problems, a method combined with a high-speed imaging method has been proposed (Radiology, 177, pp. 407-414, published in 1990). This method uses the Echo Planar Ima
ging), it is possible to extremely shorten the measurement time and to reduce the deterioration of the image quality due to body movement. In this method, data is acquired at high speed by using an oscillating readout gradient magnetic field that switches a strong gradient magnetic field at high speed.

However, this method has a problem that an eddy current is generated due to a synergistic action of a high-intensity diffusion gradient magnetic field and a high-intensity vibration readout gradient magnetic field, and the magnetic field uniformity is reduced. The term “magnetic field uniformity” as used herein refers to a magnetic field uniformity obtained by adding a static magnetic field generated by a static magnetic field generating magnet and a magnetic field generated by an eddy current generated by applying a gradient magnetic field. Normally, the uniformity of the static magnetic field depends on the characteristics of the device, the temperature of the device, the magnetic susceptibility of the target object, and the like. On the other hand, the uniformity of the magnetic field due to the eddy current varies depending on the measurement method and the like. A decrease in the magnetic field uniformity causes a decrease in the signal strength, and lowers the measurement accuracy of the diffusion weighted image and the diffusion coefficient. As a method for reducing the eddy current, a method using an active shield gradient magnetic field device, a method using a waveform of an oscillating gradient magnetic field as a sine wave, and a method using a waveform of a diffusion gradient magnetic field as a sine wave (Magnetic resonance in medicine) (Magneti
c Resonance in Medicine), No. 20, pp. 89-99, published in 1991), etc., but these have not yet been sufficiently effective.

[0005] Diffusion spectroscopic imaging has been proposed as a method for measuring the diffusion coefficient of each metabolite contained in a living body. In this method, the measurement time is longer than that of the normal diffusion measurement, and a method combined with the echo planar method has been proposed to shorten the measurement time (Japanese Patent Laid-Open No. Hei 7-84875). Also in this case, there is a problem that the magnetic field uniformity is reduced due to the influence of the eddy current. In the diffusion spectroscopic imaging, since the spatial resolution is lower than that of the normal imaging, the uniformity of the magnetic field in the voxel is more likely to be reduced. with this,
This causes a decrease in signal intensity and a decrease in the separation accuracy of each metabolite due to an increase in the line width of the spectral peak. For this reason, the measurement accuracy of the diffusion-weighted image and the diffusion coefficient is more likely to be lower than in a normal imaging method.

The method of correcting the non-uniformity of the static magnetic field inherent in the apparatus and the insertion of the target object is described in, for example, Magnetic resonance in Medicine, No. 18, pp. 335-347, 1991.
Reported in the year issuance. A method for locally improving the uniformity of the static magnetic field with respect to the measurement target region is reported, for example, in JP-A-8-595. In this method, the current value supplied to the offset magnetic field of the gradient magnetic field and the shim coil for correcting the static magnetic field uniformity with respect to the measurement area is changed. These are methods for reducing the non-uniformity of the static magnetic field, and do not reduce the non-uniformity of the magnetic field due to the application of the diffusion gradient magnetic field or the like as described above.

[0007]

In the above prior art, the signal strength is reduced due to the non-uniform magnetic field caused by the applied gradient magnetic field, and it is difficult to measure the diffusion coefficient and the diffusion weighted image with high accuracy. It is.

It is an object of the present invention to provide a measuring apparatus and a measuring method capable of reducing the influence of magnetic field inhomogeneity caused by an applied gradient magnetic field and enabling highly accurate measurement of a diffusion coefficient and a diffusion-weighted image. .

[0009]

In order to solve the above-mentioned problems, the present invention comprises a magnetic field generating means for generating a static magnetic field, a gradient magnetic field and a high-frequency magnetic field, and a control means for controlling the application of each magnetic field. In the measuring apparatus for applying a diffusion gradient magnetic field for causing signal attenuation by diffusion in order to observe the diffusion of molecules in an object, the control means includes an offset magnetic field corresponding to the diffusion gradient magnetic field and the gradient magnetic field generation means. It is characterized by being generated by

Further, the present invention has a magnetic field generating means for generating a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, and a control means for controlling the application of each magnetic field. In a measuring apparatus for applying a diffusion gradient magnetic field for causing a signal attenuation by diffusion and a gradient magnetic field for obtaining a spatial distribution of the signal attenuation, the control unit may adjust the offset magnetic field according to the diffusion gradient magnetic field. It is characterized by being generated by magnetic field generating means.

Usually, an eddy current is generated in the housing of the apparatus due to the influence of each gradient magnetic field, especially the diffusion gradient magnetic field, and the magnetic field uniformity is reduced. However, by generating the offset magnetic field as in the present invention, the diffusion gradient is generated. An eddy current due to a magnetic field or the like can be suppressed, and a decrease in magnetic field uniformity can be avoided.

In the present invention, it is preferable that an offset magnetic field is generated by the gradient magnetic field generating means in accordance with at least one of an application intensity, an application time, and an application timing of the diffusion gradient magnetic field.

Further, in the present invention, it is preferable that the gradient magnetic field generating means generates an offset magnetic field in the same application direction according to the application direction of the diffusion gradient magnetic field.

Further, in the present invention, the gradient magnetic field generating means may add an offset magnetic field only to a signal acquisition time.

Further, in the present invention, a relationship between at least one of the application intensity, application time and application timing of the diffusion gradient magnetic field and an offset magnetic field generated by the gradient magnetic field generation means is stored in the control means, and the relation is stored in the control means. Preferably, the offset magnetic field is used to set the offset magnetic field.

The present invention also provides a magnetic field generating means for generating a static magnetic field, a gradient magnetic field and a high-frequency magnetic field, a shim coil for correcting magnetic field uniformity, a driving means for the shim coil, and a control means for controlling the application of each magnetic field. In a measuring apparatus having a diffusion gradient magnetic field for causing a signal to be attenuated by diffusion in order to observe diffusion of molecules in a target object, the control unit is set for static magnetic field inhomogeneity correction. The current value is reset by adding a current value determined according to at least one of the application intensity, application time, and application timing of the diffusion gradient magnetic field, and a current is supplied to the shim coil by the shim coil driving unit. The present invention further provides a magnetic field generating means for generating a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, a shim coil for correcting magnetic field uniformity, and the shim coil. A driving device for controlling the application of each magnetic field, and a measuring device for applying a diffusion gradient magnetic field for causing a signal attenuation by diffusion in order to observe the diffusion of molecules in the target object. The control unit generates an offset magnetic field by the gradient magnetic field generation unit in response to the application of the diffusion gradient magnetic field,
The current value supplied for the shim coil set for the static magnetic field non-uniformity correction is reset by adding a current value determined according to at least one of the application intensity, application time, and application timing of the diffusion gradient magnetic field. Further, a current is supplied to the shim coil by the shim coil driving means.

That is, in order to obtain the offset magnetic field generated by the gradient magnetic field generating means and the current value flowing through the shim coil, parameters such as the applied intensity, application time, and application timing of each gradient magnetic field and the offset magnetic field and the shim coil to be set are set in advance. The relationship with the flowing current value is measured and stored in a computer. At the time of the main measurement, there is provided a means for calculating a set value of an offset magnetic field and a current value passed through the shim coil from the set value of the gradient magnetic field and the stored relationship.

The present invention also provides a radio frequency magnetic field, a gradient magnetic field for manipulating a molecular signal in the target object, and a diffusion for observing the diffusion of the molecule in the target object by causing the signal to be attenuated by the diffusion. In a magnetic resonance measurement method using a pulse sequence for applying a gradient magnetic field, an offset magnetic field is added to the pulse sequence in accordance with at least one of an application intensity, an application time, and an application timing of the diffusion gradient magnetic field.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic configuration diagram of a magnetic resonance apparatus according to the present invention. In FIG. 2, 1 is a magnet for generating a static magnetic field H0, 2 is a target object, 3 is a coil for generating a high-frequency magnetic field and detecting a magnetic resonance signal generated from the target object 2, 4,
Reference numerals 5 and 6 denote gradient magnetic field generating coils for generating gradient magnetic fields in the X, Y and Z directions, respectively. Reference numeral 7 denotes a shim coil driving device for supplying a current to each of the gradient magnetic field generating coils 4, 5, and 6. 8 is a shim coil for correcting static magnetic field uniformity, and 9 is a shim coil driving device for supplying a current to the shim coil. Reference numeral 10 denotes a computer for controlling the generation timing and intensity of each magnetic field and calculating the measured data. Reference numeral 11 denotes a display for displaying the calculation result of the computer 10.

Next, an outline of the operation of the present apparatus will be described. The high-frequency magnetic field H1 that excites the nuclear spin of the target object 2 is generated by applying a current to the coil 3 by shaping the waveform of the high-frequency generated by the synthesizer 12 with the modulator 13, amplifying the power, and supplying the current to the coil 3. The gradient magnetic field generating coils 4, 5, 6 supplied with current from the shim coil driving device 7 generate gradient magnetic fields and modulate magnetic resonance signals from the target object 2. The modulated signal is received by the coil 3, amplified by the amplifier 14, detected by the detector 15, and then input to the computer 10.
After the calculation, the computer 10 displays the calculation result on the display 11. The computer 10 controls each device to operate at a timing and intensity programmed in advance. Among these programs, those describing the high-frequency magnetic field, the gradient magnetic field, and the timing and intensity of signal reception are called sequences. The static magnetic field H0 slightly changes under the influence of the target object 2. In order to correct this, a current is supplied from the shim coil driving device 9 to the shim coil 8. The current value to be supplied is calculated and controlled by the computer 10 so as to improve the uniformity of the static magnetic field. The gradient magnetic field generating coils 4, 5,
By supplying a constant current to 6, it is used for correcting a non-uniform magnetic field having a first-order gradient.

Next, FIG. 3 shows an example of a sequence of diffusion measurement according to the present invention. An excitation high-frequency magnetic field pulse 21 is applied to induce a magnetic resonance phenomenon in the target object. The slice gradient magnetic field 24 is applied simultaneously with the application of the high-frequency magnetic field pulse, and Z
Select a slice in the direction. Inverted high frequency magnetic field pulse 22
Is applied, the magnetization is inverted, and an echo 23 is generated. The generated echo 23 is sampled by the AD converter and stored as data. In addition, simultaneously with the sampling by the AD converter, the readout gradient magnetic field 2 in the X direction is set.
5 is applied, and the position information in the X direction is added to the data. Further, a phase encoding gradient magnetic field 26 is applied to give position information in the Y direction to the data, and the intensity is changed each time measurement is repeated. Two diffusion gradient magnetic fields 27 that compensate each other are applied between the excitation high-frequency magnetic field pulse 21 and the inverted high-frequency magnetic field pulse 22 and between the inverted high-frequency magnetic field pulse 22 and the echo 23 in order to provide diffusion information. The diffusion gradient magnetic field is a combination of a gradient magnetic field in the X direction generated from the gradient magnetic field generating coil 4, a gradient magnetic field in the Y direction generated from the gradient magnetic field generating coil 5, and a gradient magnetic field in the Z direction generated from the gradient magnetic field generating coil 6. Or given alone. The two diffusion gradient magnetic fields are adjusted so that the time integral of the intensity becomes equal. At this time, if there is no diffusion motion, the phase of the magnetization dephased by the first diffusion gradient magnetic field is completely rephased by the second diffusion gradient magnetic field and compared with the case where no diffusion gradient magnetic field is applied. The signal strength does not attenuate. However, if the spread occurs, the phase cannot be completely rephased, so that the signal intensity is attenuated at a rate corresponding to the intensity. In an ideal situation, this decay is represented by the following exponential function:

[0023]

(Equation 1)

Here, D is the diffusion coefficient, S0 is the signal intensity when the gradient magnetic field factor is 0, and S (b) is the signal intensity when the gradient magnetic field factor is b. The gradient magnetic field factor b [s / m2] is a value determined by the applied intensity and application time of the diffusion gradient magnetic field, and is calculated by the following equation.

[0025]

(Equation 2)

Here, Te is the echo time [s], γ is the gyromagnetic ratio [Hz / T], and G (τ) is the gradient magnetic field applied strength [T /
m]. When measuring a diffusion-weighted image, an image is captured with a specific gradient magnetic field factor b set. When the diffusion coefficient is measured, measurement is performed at least twice while changing the gradient magnetic field factor b, and fitting is performed using (Equation 1).

A method has been proposed which is combined with an echo planar method in order to shorten the measurement time and reduce the influence of body movements such as pulsation and respiration of a living body. FIG. 4 shows a schematic diagram of the sequence. The readout gradient magnetic field 24 becomes an oscillating gradient magnetic field, and the phase encoding gradient magnetic field 25 is applied together with the switching of the oscillating gradient magnetic field. Thus, an image can be created by one or several repeated measurements.
A diffusion gradient magnetic field 27 for giving diffusion information is applied in the same manner as described above.

At this time, an eddy current is generated in the casing of the apparatus due to the influence of the applied gradient magnetic field, and the magnetic field uniformity is reduced. In particular, the diffusion gradient magnetic field 27 and the readout gradient magnetic field 24
Has a strong effect because it is applied at a high intensity. Also,
When the diffusion coefficient is measured, the effect changes because the intensity of the diffusion gradient magnetic field 27 is changed. For example, when the applied intensity of the diffusion gradient magnetic field 27 is increased, the magnetic field uniformity is significantly reduced, and the signal intensity is reduced. For this reason, a strong diffusion-weighted image shows a lower value than it should be. Further, the obtained diffusion coefficient shows a higher value than the original value.

In the present invention, in order to suppress a decrease in magnetic field uniformity due to the application of a gradient magnetic field, the gradient magnetic field coils 4, 5, 6
The current supplied to the shim coil 8 is changed according to the applied gradient magnetic field. In particular, the current supplied is changed according to the diffusion gradient magnetic field 27 to improve the measurement accuracy of the diffusion weighted image and the diffusion coefficient. FIG. 1 shows an example of a sequence according to the present invention. The operation is the same as the above-described sequence, but schematically shows how the offset magnetic field of the gradient magnetic field is changed according to the applied intensity of the diffusion gradient magnetic field.
This offset magnetic field is calculated and controlled so as to maximize the magnetic field uniformity. In addition, for the method of calculation and control, a known technique for reducing static magnetic field inhomogeneity that occurs when the device is inserted into the magnetic field and the target object is inserted can be used. This technique is reported, for example, in JP-A-8-595. In this method, the relationship between the current supplied to the gradient coils 4, 5, 6 and the shim coil 8 and the magnetic field distribution is measured in advance, and the relationship is stored in the computer 10. Then, at the time of the main measurement, the magnetic field non-uniformity is obtained from the phase difference of the image and the like, and the current value to be supplied to each coil is obtained so as to minimize the magnetic field non-uniformity using the relationship stored in advance. .

The following operation may be performed to reduce both the non-uniformity of the static magnetic field and the non-uniformity of the magnetic field caused by the application of the gradient magnetic field. First, an offset magnetic field that minimizes static magnetic field inhomogeneity is calculated without applying a diffusion gradient magnetic field. Next, an offset magnetic field corresponding to the applied diffusion gradient magnetic field is calculated. The two offset magnetic fields are added, and the sum is set and generated as an offset magnetic field.

In FIG. 1, the offset magnetic field of the gradient magnetic field is changed by changing the current supplied to the gradient coils 4, 5 and 6. Magnetic field inhomogeneity components equal to or higher than the second order can also be corrected, and the magnetic field uniformity can be further improved. However, since the shim coil and the shim coil driving device are designed for the purpose of correcting the non-uniformity of the static magnetic field, a long time is required until the shim coil and the shim coil driving device are stabilized against a sudden change. Therefore, when a sudden change is required, a stable result can be obtained by changing only the offset magnetic field of the gradient magnetic field or shortening the integration time constant of the low-pass filter for smoothing the output current of the shim coil driving device. Becomes possible.

In some cases, a stable result can be obtained. Since the direction in which the magnetic field uniformity decreases is mainly the direction of the diffusion gradient magnetic field 27 and the readout gradient magnetic field 24, only the offset magnetic field in that direction (X direction in FIG. 1) may be adjusted. Further, in FIG. 1, the adjustment is performed with the steady offset magnetic field, but the offset magnetic field may be adjusted only during the signal acquisition time as shown in FIG.

The eddy current which causes a reduction in the magnetic field uniformity is mainly generated in the apparatus housing, and has little dependence on the target object 2. For this reason, the relationship between the diffusion gradient magnetic field intensity and the offset magnetic field may be obtained in advance and stored in the computer 10, and the main magnetic field may be used to set the offset magnetic field during the main measurement. That is, it is possible to eliminate the trouble of measuring the magnetic field distribution and adjusting the offset magnetic field at the time of the main measurement. In addition, the offset magnetic field is not only the applied intensity of the diffusion gradient magnetic field, but also its application time, application timing, waveform, readout gradient magnetic field applied intensity, application time, application timing, oscillation period, waveform, slice gradient magnetic field, and phase. Encoding gradient magnetic field applied strength, applied time,
It depends on many parameters such as application timing.
The offset magnetic field may be calculated using all or some of them.

Although FIGS. 1 and 5 show schematic diagrams in which the offset is adjusted based on the sequence to which the echo planar method is applied, the original sequence is not limited to this method. For example, the sequence shown in FIG.

FIG. 6 shows an example of the measurement result. In order to confirm the effect of the present invention, the echo 23 was measured without applying the phase encoding gradient magnetic field 26 using the sequence shown in FIG. 5, and compared with the case where no offset adjustment was performed. (1)
Shows the case where the offset is not adjusted, and (2) shows the case where the offset is adjusted according to the present invention. Each image was created as follows. A series of echoes 23 was divided into individual echoes, which were Fourier-transformed to create a projection image in the X direction, and then the phase was calculated. The horizontal axis represents the X direction, and the vertical axis represents the echo number. Black and white fringes are represented by binarizing the phase of the signal, with white representing 0 to 180 degrees and black representing 0 to -180 degrees. The striped pattern at the center is a region where the target object is located, and the periphery is a noise region. From (1), it can be seen that the interval between the stripe patterns becomes narrower as the echo number increases, that is, the phase rotation increases. This indicates that the magnetic field homogeneity is low, and the peak is shifted toward the later echo due to the influence, and the phase is rotated. On the other hand, in the case of (2), almost no phase rotation is observed in the latter echo as compared with the case of (1), and it can be seen that the magnetic field uniformity is high.

Next, FIG. 7 shows a sequence in which the present invention is applied to diffusion spectroscopic imaging. An excitation high-frequency magnetic field pulse 21 is applied to induce a magnetic resonance phenomenon in the target object 2. The slice gradient magnetic field 24 is applied simultaneously with the application of the high-frequency magnetic field pulse, and a slice in the Z direction is selected. The application of the inverted high-frequency magnetic field pulse 22 inverts the magnetization and generates an echo 23. Generated echo 23
Is stored as data by sampling by the AD converter. At the same time as sampling by the AD converter, a readout gradient magnetic field 25 is applied in the X direction, and chemical shift information and position information in the X direction are added to the data. Further, a phase encoding gradient magnetic field 26 is applied to give position information in the Y direction to the data, and the intensity is changed each time measurement is repeated. Two diffusion gradient magnetic fields 27 that compensate each other are applied between the excitation high-frequency magnetic field pulse 21 and the inverted high-frequency magnetic field pulse 22 and between the inverted high-frequency magnetic field pulse 22 and the echo 23 in order to provide diffusion information. The gradient magnetic field offset is adjusted according to the applied intensity and application time of the diffusion gradient magnetic field 27. This suppresses the non-uniformity of the magnetic field due to the application of the gradient magnetic field.

For the adjustment of the gradient magnetic field offset and the use of the shim coil, the above method can be used as it is. Further, in FIG. 7, the sequence is described based on the diffusion spectroscopic imaging to which the echo planar method is applied, but the sequence based on this is not limited to this.

FIG. 8 shows an example of the measurement results. In order to confirm the effect of the present invention, a comparison was made with the case where no offset adjustment was performed. (1) shows a case where the offset adjustment is not performed, and (2) shows a case where the offset adjustment is performed. The horizontal axis represents the chemical shift, the vertical axis represents the signal intensity, and the three graphs represent the spectra of water and N-acetylalanine at three typical pixels. It can be seen that the peaks of the graph were aligned by the offset adjustment, that is, the magnetic field uniformity was improved. Especially in spectroscopic imaging, the magnetic field uniformity is important. For example, since the spatial resolution is lower than that of normal imaging, the magnetic field in one pixel becomes more uneven and the signal intensity is easily attenuated, and the line width of the peak becomes wider, making it difficult to separate metabolites. The significance of the magnetic field uniformity is significant. ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to suppress the fall of the signal intensity and the fall of a spectrum resolving power by a magnetic field inhomogeneity, and can measure a diffusion weighted image and a diffusion coefficient with high precision.

[0039]

As is apparent from the above description, according to the present invention, it is possible to suppress the influence of the non-uniform magnetic field caused by the applied gradient magnetic field, and to improve the measurement accuracy of the diffusion weighted image and the diffusion coefficient. It is.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a basic sequence according to the present invention.

FIG. 2 is a diagram showing a device configuration of a magnetic resonance apparatus which is an example of an application apparatus of the present invention.

FIG. 3 is a diagram showing an example of a basic sequence used for diffusion measurement.

FIG. 4 is a diagram showing an example of a sequence to which an echo planar method used for diffusion measurement is applied.

FIG. 5 is a diagram showing another example of the basic sequence according to the present invention.

FIG. 6 is a diagram showing an example of a measurement result according to the present invention.

FIG. 7 is a diagram showing an example of a sequence of spread spectroscopic imaging according to the present invention.

FIG. 8 is a diagram showing an example of a measurement result by diffusion spectroscopic imaging according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnet for static magnetic field generation 2 Target object 3 Coil for high frequency magnetic field generation and signal detection 4, 5, 6 Coil for gradient magnetic field generation 7 Coil drive device 8 Shim coil 9 Shim coil drive device 10 Computer 11 Display 12 Synthesizer 13 Modulator 14 Amplifier 15 Amplifier 15 Detector 21 Excitation high-frequency magnetic field pulse 22 Inverting high-frequency magnetic field pulse 23 Echo 24 Slice gradient magnetic field 25 Readout gradient magnetic field 26 Phase encoding gradient magnetic field 27 Diffusion gradient magnetic field

Claims (9)

[Claims] 1. An apparatus comprising: a magnetic field generating means for generating a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field; and a control means for controlling the application of each magnetic field. In a measuring apparatus for applying a diffusion gradient magnetic field for generating the magnetic field, the control means generates an offset magnetic field by the gradient magnetic field generation means according to the diffusion gradient magnetic field. 2. A system comprising: a magnetic field generating means for generating a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field; and a control means for controlling the application of each magnetic field. In order to observe the diffusion of molecules in a target object, the signal is attenuated by diffusion. In a measuring device that applies a diffusion gradient magnetic field for causing the gradient and a gradient magnetic field for obtaining the spatial distribution of the signal attenuation, the control unit controls the offset magnetic field according to the diffusion gradient magnetic field by the gradient magnetic field generation unit. A magnetic resonance measuring apparatus characterized in that the magnetic resonance is generated. 3. The gradient magnetic field generator according to claim 1, wherein the controller generates an offset magnetic field in accordance with at least one of an applied intensity, an application time, and an application timing of the diffusion gradient magnetic field. 3. The magnetic resonance measurement apparatus according to 2. 4. The gradient magnetic field generating means according to claim 1, wherein the control means generates an offset magnetic field in the same application direction according to the application direction of the diffusion gradient magnetic field. 7. The magnetic resonance measurement apparatus according to item 1. 5. The magnetic resonance measurement apparatus according to claim 1, wherein said gradient magnetic field generation means generates an offset magnetic field only during a signal acquisition time. 6. A relationship between at least one of an applied intensity, an application time, and an application timing of the diffusion gradient magnetic field and an offset magnetic field generated by the gradient magnetic field generation means is stored in the control means, and the offset magnetic field is stored using the relationship. 3. The magnetic resonance measurement apparatus according to claim 1, wherein 7. An object comprising a magnetic field generating means for generating a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, a shim coil for correcting magnetic field uniformity, a driving means for the shim coil, and a control means for controlling application of each magnetic field. In order to observe the diffusion of molecules in the object, in a measuring device that applies a diffusion gradient magnetic field for causing signal attenuation by diffusion, the control means, the current value set for static magnetic field non-uniformity correction, Applying a current value determined according to at least one of the application intensity, application time, and application timing of the diffusion gradient magnetic field, resets the current value, and supplies a current to the shim coil by the driving means of the shim coil. Magnetic resonance measurement device. 8. An object comprising: magnetic field generating means for generating a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field; a shim coil for correcting magnetic field uniformity; driving means for the shim coil; and control means for controlling application of each magnetic field. In order to observe the diffusion of molecules in an object, in a measuring device that applies a diffusion gradient magnetic field for causing signal attenuation by diffusion, the control unit includes: an application intensity, an application time, and an application timing of the diffusion gradient magnetic field. According to at least one, an offset magnetic field is generated by the gradient magnetic field generating means, and a current value supplied to the shim coil set for static magnetic field non-uniformity correction is determined in accordance with the application of the diffusion gradient magnetic field. A magnetic resonance measuring apparatus characterized in that a current value is added and reset, and a current is supplied to the shim coil by the shim coil driving means. 9. A high-frequency magnetic field, a gradient magnetic field for manipulating a molecular signal in the target object, and a diffusion gradient magnetic field for causing a signal to be attenuated by the diffusion in order to observe diffusion of the molecule in the target object. A magnetic resonance measurement method using a pulse sequence, wherein an offset magnetic field is added to the pulse sequence in accordance with at least one of the application intensity, application time, and application timing of the diffusion gradient magnetic field.