JPH06114028A - Nuclear magnetic resonance inspection device - Google Patents

Abstract

PURPOSE:To realize a nuclear magnetic resonance inspection device using a superconductive magnet, automatically executing the accurate correction of the intensity of a magnetic field before measuring an object to be examined and capable of detecting a state exceeding a correctable range. CONSTITUTION:The data from a data taking-in part 7 is supplied to a Fourier transform part 86 through a data judging part 85 and a frequency spectrum is calculated. The frequency spectrum from the Fourier transform part 86 is supplied to a correction part 84 and magnetic field correction data is calculated. The calculated magnetic field correction data is supplied to a correction data judging part 83 and it is judged whether or not the correction data is within a tolerance range. In the case of exceeding the tolerance range, an error message is displayed on a display device 12 and, in the case of below the tolerance range, the magnetic field correction data is temporarily set and measurement is again executed in a corrected magnetic field. When the number of times of measurement reaches a prescribed number, final magnetic field correction data is set and actual measurement is started in the magnetic field corrected corresponding to said data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear magnetic resonance examination apparatus, and more particularly to a nuclear magnetic resonance examination apparatus in which a magnet for generating a uniform magnetic field space is a superconducting magnet.

[0002]

2. Description of the Related Art The magnetic field strength of a magnetic resonance inspection apparatus using a superconducting magnet is more stable than an apparatus using a normal conducting magnet or a permanent magnet. However, in the long term, the magnetic field strength fluctuates, and a significant difference occurs between the magnetic field strength stored in the control unit such as the high-frequency magnetic field and the actual magnetic field strength, and the slice position shift phenomenon must be considered. There are cases.

The higher the magnetic field strength, the more
The fluctuation amount between the actual magnetic field strength and the stored magnetic field strength becomes large. For example, the fluctuation amount of the magnetic field of the nuclear magnetic resonance inspection apparatus having the magnetic field strength of 1.5T is larger than that of the nuclear magnetic resonance inspection apparatus having the magnetic field strength of 0.5T. Is bigger. For this reason, in the nuclear magnetic resonance inspection apparatus using the superconducting magnet having a high magnetic field strength, the magnetic field strength fluctuation is manually corrected at the time of regular inspection performed once / year. However, in the above-mentioned regular inspection, the correction period of the magnetic field strength fluctuation is long,
In some cases, the amount of fluctuation increases and the accuracy of the tomographic image decreases.

Therefore, for example, Japanese Patent Laid-Open No. 61-23953
Some of them, such as the nuclear magnetic resonance apparatus described in Japanese Patent Publication, automatically correct the fluctuation of the magnetic field strength. That is, during measurement of the subject, the free decay signal of the nuclear magnetic resonance signal is Fourier transformed and the peak position in the obtained spectrum signal is compared with the peak position in the spectrum signal obtained in the previous measurement. To be done. Then, the frequency of the high-frequency magnetic field signal is changed according to the deviation of these peak positions, and the magnetic field strength fluctuation is automatically corrected.

[0005]

However, in the above-mentioned conventional nuclear magnetic resonance examination apparatus, during measurement of the subject,
Since it is configured to change the frequency of the high-frequency magnetic field signal, image flow (artifact) may occur in the obtained tomographic image. Further, in the conventional nuclear magnetic resonance examination apparatus, when the deviation exceeds the correctable range, it cannot be detected that it exceeds the above range, and appropriate treatment cannot be performed. Therefore, despite being unable to make an appropriate correction,
The measurement was carried out and ended, and there was a possibility that only low-accuracy tomographic images could be obtained.

An object of the present invention is to enable a nuclear magnetic resonance examination apparatus using a superconducting magnet to automatically perform highly accurate magnetic field strength correction before each measurement of a subject and to exceed the correctable range. If so, it is to realize a nuclear magnetic resonance inspection apparatus capable of detecting this.

[0007]

In order to achieve the above object, the present invention is configured as follows. A superconducting magnet that generates a static magnetic field in a region where a subject is placed, a gradient magnetic field generating means, a high frequency magnetic field signal generating means, a nuclear magnetic resonance signal receiving means, a high frequency magnetic field signal generating means and a nuclear magnetic resonance signal receiving means. In the nuclear magnetic resonance examination apparatus having a control unit that controls the operation of, and a control unit that calculates tomographic image information of the object to be examined based on the nuclear magnetic resonance signal from the receiving means
The control unit includes a Fourier transform unit that obtains a frequency spectrum by performing a fast Fourier transform from a nuclear magnetic resonance signal in a region where the subject is placed, a correction unit that calculates magnetic field correction data based on this frequency spectrum, and a calculated magnetic field correction. A correction data determination unit that determines whether or not the data is within an allowable range and determines whether or not the number of times of measurement of this magnetic field correction data has reached a specified number, and before the measurement of the subject, It is configured to correct the magnetic field strength of the region where the subject is placed a plurality of times.

Preferably, in the above-mentioned nuclear magnetic resonance examination apparatus, the control unit is configured to correct the magnetic field strength by correcting the reference frequency of the high frequency magnetic field signal.
Further, preferably, in the nuclear magnetic resonance examination apparatus,
When the calculated magnetic field correction data is outside the allowable range, the control unit is configured to display, by the display means, that the magnetic field correction data is outside the allowable range.

[0009]

[Operation] A nuclear magnetic resonance signal is supplied to the Fourier transform unit,
The frequency spectrum is determined. The frequency spectrum from the Fourier transform unit is supplied to the correction unit, and the magnetic field correction data is obtained. The calculated magnetic field correction data is supplied to the correction data determination unit, and it is determined whether the correction data is within the allowable range. If it exceeds the allowable range, an error message is displayed on the display means. If it is less than the allowable range, the magnetic field correction data is provisionally set, and the measurement is performed again with the corrected magnetic field. When the number of measurements reaches a prescribed number, final magnetic field correction data is set, and actual measurement is started with the magnetic field corrected accordingly.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a functional block diagram of essential parts of an embodiment of the present invention, and FIG.
FIG. 3 is an overall schematic configuration diagram of an embodiment of the present invention, FIG.
FIG. 4 is a diagram showing an acquisition sequence for detecting a nuclear magnetic resonance signal. First, in FIG. 3, reference numeral 1 is a superconducting magnet, and this superconducting magnet 1 generates a constant static magnetic field in a region where the subject 11 is arranged. Reference numeral 2 denotes a gradient magnetic field coil incorporated in the superconducting magnet 1, and the gradient magnetic field coil 2 has a function of generating a magnetic field different depending on the position. Reference numeral 3 denotes a bed of the subject, and the bed 3 transports the subject 11 to the center of the superconducting magnet 1. When the operator gives a command using the console 9, the control unit 8 controls the high-frequency magnetic field generator 5 and the gradient magnetic field power source 4 based on the capturing sequence according to the command. Then, the gradient magnetic field coil 2 generates a gradient magnetic field signal S3 as shown in FIG.
The high frequency magnetic field signals S1 and S2 as shown in FIG.

By the above operation, a nuclear magnetic resonance signal (echo signal S4 shown in FIG. 4C) is generated from the subject 11. This echo signal S4 is supplied to the high frequency transmitting / receiving coil 10
Is received by the data capturing unit 7 via the receiver 6.
Is supplied to. Then, the data capturing section 7 captures the signal S4 at the signal capturing timing Ts as shown in FIG. The echo signal S4 captured by the capturing unit 7 is supplied to the control unit 8, and the control unit 8 individually performs an appropriate number of integrations and Fourier transforms to form an image for each echo signal. The reconstructed image is displayed on the display unit 12.

In FIG. 1, reference numeral 81 is a patient registration / probe determination unit to which an operation signal from the console 9 is supplied, and reference numeral 82 is a command signal from the patient registration / probe determination unit 81. It is a magnetic field control unit that controls the operations of the gradient magnetic field power supply 4 and the high frequency magnetic field generator 5. Also, 85
Is a data judging unit, and this data judging unit 85 judges whether or not all the data from the data fetching unit 7 are zero. Reference numeral 86 is a Fourier transform unit for performing a Fourier transform on the data from the data judgment unit 85, and 87 is a Fourier transform unit 86.
Is a data processing unit that executes data processing necessary for image reconstruction and the like on the data from. Further, 84 is a correction unit that calculates correction data of the magnetic field strength based on the signal from the Fourier transform unit 86, and 83 is a correction that determines whether the correction data calculated by the correction unit 84 is within an allowable range. It is a data judgment unit. Further, 88 is a display drive unit, and this display drive unit 88 includes a data determination unit 85, a correction data determination unit 83, a patient registration and probe determination unit 81,
Display means 1 according to a command signal from the data processing unit 87
Drive 2

The operation of the embodiment configured as described above will be described below. In step 21 of FIG. 2, the patient registration / probe determination unit 81 determines whether or not a new patient registration is performed by the operator console 9, and if registration is performed, the process proceeds to step 22 and the number of times of measurement is counted. Initialization is performed by setting N to 0. Next, in step 23, the judgment unit 81
Determines whether the high frequency receiving coil 10 (probe) is set based on the signal from the magnetic field controller 82. If not, step 24
Then, the determination section 81 supplies a display command signal to the display means 12 via the display drive section 88 to display an error message. If the high frequency receiving coil 10 is set in step 23, the process proceeds to step 25. Then, the magnetic field controller 82 causes the gradient magnetic field power supply 4,
The high-frequency magnetic field generator 5 and the like are controlled, and data measurement is performed based on the acquisition sequence of FIG.

Next, at step 26, the data determining section 85 determines whether or not all the data of the echo signals captured by the data capturing section 7 are zero. Then, if all the data are 0, the process proceeds to step 24, and the data judging unit 85 causes the display driving unit 88 to display the display unit 1.
A display command signal is supplied to 2 to display an error message. If the data is not 0 in step 26,
Proceeding to step 27, the fetched data is processed by the Fourier transform unit 8
6 and performs a fast Fourier transform to obtain a frequency spectrum (signal S5 shown in FIG. 4E).

Next, in step 28, the Fourier transform unit 8
The frequency spectrum from 6 is supplied to the correction unit 84.
Then, the correction unit 84 obtains the deviation from the preset reference frequency, that is, the magnetic field correction data. continue,
In step 29, the magnetic field correction data calculated by the correction unit 84 is supplied to the correction data determination unit 83, and it is determined whether the correction data is within the allowable range. If the allowable range is exceeded, in step 24, the correction data determination unit 83 supplies a display command signal to the display means 12 via the display drive unit 88 to display an error message. If it is less than the allowable range in step 29, step 3
0, the number of measurements N is determined, and the specified number of times (here, 3
If not, the process proceeds to step 31 to temporarily set the magnetic field correction data. Then, in step 32,
The number of measurements N is incremented by +1 and the process returns to step 25. That is, the magnetic field control unit 82 executes the measurement again with the corrected magnetic field based on the magnetic field correction data from the determination unit 83.

If the number of times of measurement N reaches the specified number of times (3) in step 30, the process proceeds to step 33, and the final magnetic field correction data is set. Then, the process proceeds to step 34, and the actual measurement is started with the magnetic field corrected according to the final magnetic field correction data. In this case, the signal from the Fourier transform unit 86 is supplied to the data processing unit 87, and the data processing unit 87 executes the processing necessary for image reconstruction. Then, the data processed by the data processing section 87 is supplied to the display means 12 via the display drive section 88 and displayed.

In steps 25 to 32, the timing of taking in the measured data is determined based on the taking-in frequency band. For example, the correction range is ± 500 pp
m and the correction operation is measured three times, the first time is ± 750 ppm, and the second and third times are ± 200 pp.
If m, the first sampling rate is 10.5 μs and the sampling time Ts based on the sampling theorem.
Is 1.344 ms. Further, the sampling rates of the second and third times are 39.4 μs, and the sampling time Ts is 5.043 ms.

As described above, according to one embodiment of the present invention, in the nuclear magnetic resonance examination apparatus, the variation correction data of the magnetic field strength is calculated before the actual examination of the subject, and the calculated correction data is acceptable. It is judged whether or not it is within the range, and if it is outside the allowable range, it is detected and displayed by the display means, and if it is within the allowable range, the correction operation is repeatedly executed a predetermined number of times (three times). Therefore, in a nuclear magnetic resonance examination apparatus using a superconducting magnet, high-precision magnetic field strength correction can be automatically performed before each measurement of a subject, and if it exceeds the correctable range, It is possible to realize a nuclear magnetic resonance inspection apparatus capable of detecting

In the above example, the correction operation is repeated three times, but it may be repeated twice or four times or more instead of three times.

[0020]

As described above, according to the present invention, based on the superconducting magnet, the gradient magnetic field generating means, the high frequency magnetic field signal generating means, the nuclear magnetic resonance signal receiving means, and the nuclear magnetic resonance signal, In a nuclear magnetic resonance examination apparatus having a control unit that calculates tomographic image information of an inspection body, the control unit includes a Fourier transform unit that obtains a frequency spectrum from a nuclear magnetic resonance signal, and a correction that calculates magnetic field correction data based on the frequency spectrum. Unit and a correction data determination unit that determines whether or not the magnetic field correction data is within an allowable range and determines whether or not the number of times the magnetic field correction data has been measured reaches a specified number, and before measuring the subject. The magnetic field strength is corrected a plurality of times. Therefore, a highly accurate magnetic field strength correction can be automatically carried out before each measurement of the object, and a nuclear magnetic resonance examination apparatus capable of detecting this when the correctable range is exceeded. realizable.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a main part of an embodiment of the present invention.

FIG. 2 is an operation flowchart of one embodiment of the present invention.

FIG. 3 is an overall schematic configuration diagram of an embodiment of the present invention.

FIG. 4 is a diagram showing an acquisition sequence for detecting a nuclear magnetic resonance signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 superconducting magnet 2 gradient magnetic field coil 3 bed 4 gradient magnetic field power source 5 high frequency magnetic field generator 6 receiver 7 data acquisition section 8 calculator 9 operator's console 10 high frequency receiving coil 11 subject 12 display means 81 patient registration and probe determination section 82 magnetic field control Part 83 Correction data judgment part 84 Correction part 85 Data judgment part 86 Fourier transform part 87 Data processing part 88 Display drive part

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location 9219-2J G01N 24/06 H

Claims (3)

[Claims] 1. A superconducting magnet for generating a static magnetic field in a region where a subject is arranged, a gradient magnetic field generating means, a high frequency magnetic field signal generating means, a nuclear magnetic resonance signal receiving means, the high frequency magnetic field signal generating means, and In the nuclear magnetic resonance examination apparatus, which controls the operation of the nuclear magnetic resonance signal receiving means, and has a control section which calculates tomographic image information of the body to be inspected based on the nuclear magnetic resonance signal from the receiving means. The unit is a Fourier transform unit that obtains a frequency spectrum by performing a fast Fourier transform from the nuclear magnetic resonance signal in the region where the subject is placed, a correction unit that calculates magnetic field correction data based on this frequency spectrum, and the calculated magnetic field correction. A correction data determination unit that determines whether or not the data is within an allowable range, and also determines whether or not the number of times this magnetic field correction data has been measured reaches a specified number. The provided, before the measurement of the subject, the nuclear magnetic resonance examination apparatus and correcting multiple magnetic field strength in the region where the subject is disposed. 2. The nuclear magnetic resonance examination apparatus according to claim 1, wherein the controller corrects the magnetic field strength by correcting the reference frequency of the high frequency magnetic field signal. . 3. The nuclear magnetic resonance examination apparatus according to claim 1, further comprising a display means, wherein the controller, when the calculated magnetic field correction data is outside the allowable range, causes the display means to display outside the allowable range. A nuclear magnetic resonance examination apparatus characterized by displaying an indication.