JPH04227232A - Magnetic resonance diagnosing device - Google Patents

Abstract

PURPOSE:To uniformalize the static magnetic field with high precision by fixing the electric current supplied to a shim coil for correcting the magnetic field when the line width of the magnetic resonance signal in a frequency region which is obtained by a conversion means is less than a prescribed value, and varying the electric current supplied into the shim coil for correcting the magnetic field when the line width is over the prescribed value. CONSTITUTION:The echo signal as MR signal is obtained from a receiver 26 by executing a pulse sequence, and this signal is converted to the MR signal in a frequency region by a Fourier converter 30, and this MR signal is introduced into a judging device 38 through a selector 32, and the line width (pi) at (epsilon)% from the peak of the MR signal in the frequency region is measured, and when the width (pi) is a predetermined value or less, the inclined magnetic field DC offset uniformalizes the static magnetic field with high precision, and fixed. When the width (pi) is not less than a prescribed value, the inclined magnetic field DC offset at this time does not uniformalize the static magnetic field with high precision, hence the DC offset which is varied by a DC offset changing device 40 is set.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to magnetic r
The present invention relates to a magnetic resonance diagnostic apparatus that obtains morphological information such as slice images of a subject (living body) and functional information such as spectroscopy using the MR (MR) phenomenon.

0002

2. Description of the Related Art Diagnostic information provided by a magnetic resonance diagnostic apparatus includes morphological information and functional information. The morphological information is a scano image, a slice image, or a three-dimensional image of a desired position of the subject. Functional information is spectroscopy or spectroscopic images. The former is information that reflects the density distribution of specific atomic nuclei such as protons. The latter is analysis information of multiple compounds containing specific atomic nuclei. Generally, the former is magnetic resonance i
magnetic resonance imaging (MRI), and the latter is called magnetic resonance imaging (MRI).
IC resonance spectroscopy (MRS)
), and in particular, obtaining spectroscopic images is called MRSI.

The information accuracy of MRI or MRS depends on the characteristics of the static magnetic field, which is the basic magnetic field condition that causes the MR phenomenon, and the MR
It is determined by the characteristics of the high-frequency pulse used to determine the position where the phenomenon occurs, the characteristics of the gradient magnetic field that adds position information to the MR signal, etc. Various techniques have been proposed to improve the above-mentioned individual characteristics. Some of the proposed techniques have been realized and are actually incorporated into devices and put into practical use. For example, a typical technique is to improve the uniformity of static magnetic fields. In this technique, a shim coil is provided along with a static magnetic field coil (main coil), and a correction current is passed through the shim coil to correct the magnetic field caused by the main coil.

0004

[Problem to be Solved by the Invention] However, various techniques, including the above-mentioned technique for improving the uniformity of the static magnetic field, are all correction techniques using computational methods, so there is a limit to their ability to improve accuracy. There is. Further, correction corresponding to changes over time or correction corresponding to each subject is impossible. Moreover, in systems such as MRS where even higher uniformity is desired, the operator has traditionally adjusted the current value flowing through the shim coil for each patient, but this is extremely time consuming and Since it is a manual operation, there is a problem in that sufficient effects cannot be obtained.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic resonance diagnostic apparatus capable of performing highly accurate MRI or MRS by achieving highly accurate homogenization of the static magnetic field.

[0006]

[Means for Solving the Problems] This object is achieved by the following magnetic resonance diagnostic apparatus.

That is, the present invention provides a magnet system including a static magnetic field generating means, a gradient magnetic field generating means, an excitation high frequency pulse generating means, a magnetic resonance signal detecting means, and a shim coil for magnetic field correction; a control means for controlling to obtain resonance diagnostic information; a conversion means for converting a magnetic resonance signal obtained from the magnetic resonance signal detection means from a time domain to a frequency domain signal; and a frequency domain magnetic resonance obtained by the conversion means. current control means that fixes the current supplied to the magnetic field correction shim coil when the line width of the signal is less than a predetermined value, and changes the current supplied to the magnetic field correction shim coil when the line width exceeds the predetermined value; It is a magnetic resonance diagnostic device including.

The present invention also provides a magnet system including a static magnetic field generating means, a gradient magnetic field generating means, an excitation high frequency pulse generating means, and a magnetic resonance signal detecting means, and a method for obtaining magnetic resonance diagnostic information by using each means of this magnet system. a control means for controlling the magnetic resonance signal obtained from the magnetic resonance signal detection means from a time domain to a frequency domain signal; an offset control means that fixes the offset current supplied to the gradient magnetic field generation means when the line width is less than a predetermined value, and changes the offset current supplied to the gradient magnetic field generation means when the line width exceeds a predetermined value. This is a magnetic resonance diagnostic device.

Furthermore, the present invention provides a magnet system including a static magnetic field generating means, a gradient magnetic field generating means, an excitation high frequency pulse generating means, a magnetic resonance signal detecting means, and a shim coil for magnetic field correction; a control means for controlling to obtain resonance diagnostic information; a conversion means for converting a magnetic resonance signal obtained from the magnetic resonance signal detection means from a time domain to a frequency domain signal; and a frequency domain magnetic resonance obtained by the conversion means. When the line width of the signal is less than or equal to a predetermined value, the current supplied to the gradient magnetic field generation means and the magnetic field correction shim coil is fixed, and when the line width exceeds the predetermined value, the current supplied to the gradient magnetic field generation means and the magnetic field correction shim coil is fixed. This is a magnetic resonance diagnostic apparatus including current control means for changing the current supplied to the shim coil.

0010

[Operation] This magnetic resonance diagnostic apparatus operates as follows. In other words, the uniformity of the static magnetic field is achieved not by controlling the static magnetic field but by controlling the DC offset of the gradient magnetic field, and the DC offset is obtained when the convergence condition is satisfied for the actual resonance signal. It is highly accurate and can be automated. In addition, the sequence for MRI or the sequence for MRS can be executed under the highly accurate uniform control of the static magnetic field achieved by executing the static magnetic field homogenization control mode.
I or MRS can be performed.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the magnetic resonance diagnostic apparatus according to the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a magnet assembly 10 capable of accommodating a subject 100 therein includes a static magnetic field magnet (or a permanent magnet) using a normal conduction or superconductivity method. Good.）12
, gradient magnetic field generating coils 14 on the X, Y, and Z axes as a gradient magnetic field generating system that generates a gradient magnetic field for providing positional information of the induced site of the magnetic resonance signal, and a radio frequency pulse for excitation (RF
pulse) and the induced magnetic resonance signal (M
R signal: Produced as a transmitting and receiving system consisting of a transmitting coil and a receiving coil to receive echo signals and FID signals.
16.

[0013] Also, the X, Y, Z axis gradient magnetic field generating coil 1
X as a gradient magnetic field generation system that performs excitation control for each of 4.
Axial gradient magnetic field power supply (GX) 18, Y-axis gradient magnetic field power supply (GY
) 20, a Z-axis gradient magnetic field power supply (GZ) 22, a transmitter (T) 24 as a transmission/reception system that controls the transmission of RF pulses,
A receiver (
R) 26, and these gradient magnetic field power supplies 18, 20, 2
2. It has a controller 28 that controls the transmitter 24 and receiver 26.

This controller 28 is a gradient magnetic field power supply 1
8, 20, 22, transmitter 24, and receiver 26 are activated and controlled according to a predetermined pulse sequence. With this control, based on methods such as the two-dimensional Fourier transform method,
Applying an RF pulse to the subject and applying a gradient magnetic field GX
, GY, GZ are added. In the case of the two-dimensional Fourier transform method, the gradient magnetic fields GX, GY, and GZ can be used in any combination as a gradient magnetic field (GS) for slicing, a gradient magnetic field (GE) for phase encoding, and a gradient magnetic field (GE) for reading. Gradient magnetic field (GR)
Add to the test sample as This causes excitation, and then the MR signal induced from the excitation site is transmitted to the probe 16.
Collect at.

Furthermore, it has a Fourier transformer (FFT) 30 for performing the two-dimensional Fourier transform method. This Fourier transformer 30 performs Fourier transform processing on a large amount of data (MR signals) obtained by the receiver 26. The output of the Fourier transformer 30 is given to a reconstruction device (REC) 34 via a switch 32 to reconstruct a slice image (two-dimensional image) or a three-dimensional image, which is then displayed on a display (
DIS) 36.

On the other hand, the output of the Fourier transformer 30 is given to a determiner 38 via a switch 32, where it is determined whether the line width value of the signal that has been Fourier transformed only once by the Fourier transformer 30 is less than or equal to a predetermined value. It is determined whether or not. The one-time Fourier transform transforms the MR signal from a time domain signal to a frequency domain signal.

The output of the determiner 38 is applied to a DC (direct current) offset changer 40. That is, when it is determined that the line width value of the MR signal in the frequency domain is not less than a predetermined value, the DC offset changer 40 changes the DC offset of the gradient magnetic field to the gradient magnetic field power supply via the controller 28. 18, 20, and 22 to issue a command to re-execute the gradient magnetic field generation system and the transmission/reception system.

Further, when it is determined that the value is equal to or less than the predetermined value, the DC offset of the gradient magnetic field is fixed, and the fixed DC offset is applied to the gradient magnetic field generating system, so that the transmitting/receiving system and the gradient magnetic field generating system It is designed to operate as a stop command.

Furthermore, the controller 28 includes a control system 44 that executes a pulse sequence FS for static magnetic field uniformity control (the pulse sequence shown in FIGS. 3 and 13, which will be described in detail later), and a control system 44 that executes a pulse sequence FS for static magnetic field uniformity control (the pulse sequence shown in FIGS. 3 and 13, which will be described in detail later), and a A control system that executes the sequence IS (the pulse sequence shown in FIGS. 7, 8, and 9, which will be described in detail later) or the MRS sequence SS (the pulse sequence shown in FIGS. 10 and 11, which will be described in detail later). 46 are connected via the switch 42. The switch 42 performs a switching operation in conjunction with the switch 32.

Next, the operation of this embodiment constructed as described above will be explained. That is, in this embodiment, as shown in FIG. 2, it is considered that the static magnetic field at the slice site SL of the subject 100 is made uniform. In order to obtain magnetic resonance signals from this slice site SL, the switchers 32 and 44 are set as shown in FIG. 1, and the so-called spin echo method (
A pulse sequence modified from the SE method is executed. This pulse sequence consists of a phase encoding gradient magnetic field (GE) and a read gradient magnetic field (GE) from the spin echo method (SE method).
GR) is deleted. In this state, it is assumed that the DC offset of the Z-axis gradient magnetic field GZ is GZ0, and the DC offset of the Y-axis gradient magnetic field GY is GY0,
It is assumed that the DC offset of the X gradient magnetic field GX is GX0.

By executing the pulse sequence shown in FIG.
A signal is obtained, and the MR signal in the frequency domain is introduced into the determiner 38 through the switch 32, and the line width π at ε% from the peak of the MR signal in the frequency domain is measured. When the value is less than or equal to the value, the gradient magnetic field DC offset at this time homogenizes the static magnetic field with high precision and is fixed. Here, it is desirable that ε is 50 to 80. Within this range, the static magnetic field can be made uniform with high precision.

On the other hand, when the width π is not less than the predetermined value, the gradient magnetic field DC offset at this time does not homogenize the static magnetic field with high precision, so the DC offset changed by the DC offset changer 40 is set, This is applied to the gradient magnetic field power supplies 18, 20, and 22 via the controller 28.

The above control for homogenizing the static magnetic field is executed in the sequence shown in FIG. That is, D of the Z-axis gradient magnetic field in the first stage ST1 to third stage ST3
The C offset is set as GZ0, and the DC of the Y-axis gradient magnetic field is set at the fourth stage ST4 to the sixth stage ST6.
The offset is set as GY0 and the seventh stage S
T7 ~ DC of X-axis gradient magnetic field at 10th stage ST10
The offset is set as GX0. For example, in DC offset control of the Z-axis gradient magnetic field, the pulse sequence shown in FIG. 3 is executed with the DC offset set to +GZ1 in the first stage ST1, and in this case, it is determined that the line width π is equal to or greater than the predetermined value. , DC in the second stage ST2
The pulse sequence of FIG. 3 is executed with the offset changed to -GZ1. In this case as well, it is determined that the line width π is greater than the expected value, and the DC offset is changed to +GZ2 (GZ2 = GZ1 /2 ), and the pulse sequence of FIG. 3 is executed. In this case, it is determined that the line width π is less than the expected value, and the DC
The offset is fixedly set as GZ0.

Similarly to the above, DC offset control of the Y-axis gradient magnetic field and DC offset control of the X-axis gradient magnetic field are performed.
The DC offsets of the gradient magnetic fields GX, GY, and GZ of each axis are fixedly set. After that, the switching devices 32 and 42 are
By setting the state opposite to the state shown in , the control system 46 that executes the MRI sequence IS or the MRS sequence is activated. This executes a series of procedures for MRI or MRS. Therefore, highly accurate MRI or MRS can be obtained for the slice site SL in FIG. 2.

[0025] In the above example, the DC offset change control is such that the value is initially varied greatly up and down, and then the intermediate value is adopted. This control method has the effect of reducing the number of stages. In addition to this method, as shown in FIG. 5, the value may be decreased each time the number of stages increases. Alternatively, as shown in FIG. 6, the value may be increased each time the number of stages increases. In any case, it is sufficient that these stages are sequentially executed so that the line width of the one-dimensional Fourier transformed signal of the echo signal converges.

Here, the MRI sequence IS is shown in FIGS. 7, 8, and 9. Figure 7 is a timing diagram showing the pulse sequence of the spin echo method, Figure 8 is a timing diagram showing the pulse sequence of the field echo method, which allows faster data collection than the spin echo method, and Figure 9 is a timing diagram showing the pulse sequence of the field echo method, which allows ultra-high speed data collection. FIG. 3 is a timing diagram showing an example of a pulse sequence of the planar method.

Next, the MRS sequence SS is shown in FIGS. 10 and 11. Figure 10 shows spectroscopy.
Figure 10 is a timing diagram showing an example of a pulse sequence to obtain a spectroscopic image (MRS).
FIG. 3 is a timing diagram showing an example of a pulse sequence for obtaining SI).

In the above example, the subject 10 as shown in FIG.
This is a description of a static magnetic field homogenization method for high-accuracy measurement in MRI or MRS with respect to the slice site SL of 0. In the case of MRS, it is customary to collect signals about a cubic local site Di. In this case, the sequence for collecting the offset signal adopts the so-called STE (stimulated echo) method shown in FIG.
It is assumed that the procedure shown in FIG. 4, FIG. 5, or FIG. 6 is executed for i.

Although the offset signal collection sequence in the above embodiment uses the SE method or the STE method, this is just an example and is not intended to be limiting.

The example shown in FIG. 1 described above is a technique for making the magnetic field uniform by correcting the gradient magnetic field in the region where data is to be collected, but as shown in FIG. In the case where one shim coil 48 is provided, in addition to the offset correction of the gradient magnetic field shown in FIG. 1, a signal is given from the controller 28 to the shim power supply (SS) 50 to directly correct the static magnetic field. You can do it like this. This achieves even more uniform control. Further, in the example shown in FIG. 1, the gradient magnetic field coil is used to generate a correction magnetic field for uniformizing the static magnetic field in addition to generating the original gradient magnetic field. Of course, the gradient magnetic field coils may be used only to generate the original gradient magnetic field, and the shim coil 48 may be used to generate a correction magnetic field for homogenizing the static magnetic field. This is because some devices are not equipped with shim coils.

The present invention is not limited to the above embodiments, but can be implemented with various modifications without departing from the gist of the present invention.

[0032]

As described above, according to the present invention, it is possible to provide a magnetic resonance diagnostic apparatus that achieves highly accurate homogenization of the static magnetic field. In addition, MRI is performed under a highly precisely homogenized static magnetic field.
Alternatively, a magnetic resonance diagnostic apparatus capable of performing MRS can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a preferred example of a magnetic resonance diagnostic apparatus according to the present invention.

FIG. 2 is a schematic diagram illustrating a slice portion to be homogenized in the static magnetic field.

FIG. 3 is a diagram showing an example of a pulse sequence for obtaining a DC offset signal in static magnetic field equalization control.

FIG. 4 is a diagram showing a first example of a series of pulse sequences for static magnetic field homogenization control.

FIG. 5 is a diagram showing a second example of a series of pulse sequences for static magnetic field homogenization control.

FIG. 6 is a diagram showing a third example of a series of pulse sequences for static magnetic field homogenization control.

FIG. 7 is a diagram showing a pulse sequence of a spin echo method for MRI performed after static magnetic field homogenization control.

FIG. 8 is a diagram showing a pulse sequence of a field echo method for MRI performed after static magnetic field homogenization control.

FIG. 9 is a diagram showing a pulse sequence of an example of an echo planar method for MRI performed after static magnetic field homogenization control.

FIG. 10: MRS (
FIG. 2 is a diagram showing an example of a pulse sequence for performing spectroscopy.

[Figure 11] MRSI executed after static magnetic field homogenization control
The figure which shows an example of the pulse sequence for performing.

FIG. 12 is a schematic diagram showing a small cubic region on the subject to be subjected to static magnetic field homogenization.

FIG. 13 is a diagram showing another example of a pulse sequence for obtaining a DC offset signal in static magnetic field equalization control.

FIG. 14 is a block diagram showing the configuration of another embodiment of the magnetic resonance diagnostic apparatus according to the present invention.

[Explanation of symbols]

10... Magnet assembly, 12... Static magnetic field magnet, 1
4...Gradient magnetic field generation coil, 16...Probe, 18...X-axis gradient magnetic field power supply (GX), 20...Y-axis gradient magnetic field power supply (GY)
), 22... Z-axis gradient magnetic field power supply (GZ), 24... transmitter (
T), 26... Receiver (R), 28... Controller, 30
... Fourier transformer (FFT), 32 ... switching device, 34 ... reconstruction device (REC), 36 ... display (DIS),
38... Determiner, 40... DC (direct current) offset changer,
42...Switcher, 44...Control system that executes pulse sequence FS for static magnetic field uniformity control, 46...Control system that executes MRI sequence IS or MRS sequence SS, 48...Shim coil , 50...Shim power supply (
SS).

Claims (3)

[Claims] [Claim 1] Static magnetic field generating means, gradient magnetic field generating means,
Excitation high frequency pulse generation means, magnetic resonance signal detection means,
a magnet system including a shim coil for magnetic field correction; a control means for controlling each means of the magnet system to obtain magnetic resonance diagnostic information; a converting means for converting into , and fixing the current supplied to the magnetic field correction shim coil when the line width of the frequency domain magnetic resonance signal obtained by the converting means is equal to or less than a predetermined value;
A magnetic resonance diagnostic apparatus comprising: current control means for changing a current supplied to the magnetic field correction shim coil when the line width exceeds a predetermined value. [Claim 2] Static magnetic field generating means, gradient magnetic field generating means,
a magnet system including an excitation high-frequency pulse generating means and a magnetic resonance signal detecting means; a control means for controlling each means of the magnet system to obtain magnetic resonance diagnostic information; and a magnetic resonance signal obtained from the magnetic resonance signal detecting means. converting means for converting from a time domain to a frequency domain signal, and fixing an offset current supplied to the gradient magnetic field generating means when a line width of a frequency domain magnetic resonance signal obtained by the converting means is equal to or less than a predetermined value; A magnetic resonance diagnostic apparatus comprising: offset control means for changing an offset current supplied to the gradient magnetic field generation means when the line width exceeds a predetermined value. [Claim 3] Static magnetic field generating means, gradient magnetic field generating means,
Excitation high frequency pulse generation means, magnetic resonance signal detection means,
a magnet system including a shim coil for magnetic field correction; a control means for controlling each means of the magnet system to obtain magnetic resonance diagnostic information; and fixing the current supplied to the gradient magnetic field generating means and the magnetic field correction shim coil when the line width of the frequency domain magnetic resonance signal obtained by the converting means is below a predetermined value, A magnetic resonance diagnostic apparatus comprising: current control means for changing the current supplied to the gradient magnetic field generation means and the magnetic field correction shim coil when the gradient magnetic field generation means and the magnetic field correction shim coil exceed a predetermined value.