JPH02297337A - Magnetic field measuring device for magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To measure the uniformity of a magnetic field by utilizing the measurement technique which is essential for MRI by only introducing the simple measurement machinery by installing a small-sized high frequency coil having a phantom for generating MR signal built in and a positioning device for positioning the small-sized high frequency coil at each position for measuring uniformity. CONSTITUTION:A positioning device for positioning a phantom 16 at each measurement point in a static magnetic field measurement space and a means for applying the static magnetic field and high frequency signals which are essential for a magnetic resonance imaging device onto the phantom 16 are installed. Further, a high frequency coil 20A for detecting the pseudoresonance signal obtained from the phantom 16 by the application of the high frequency signal and a means which allows a magnetic resonance imaging device to take in the received resonance signal in the high frequency coil 20A and calculates the uniformity of the static magnetic field are installed. Thus, the MR signal is received from the coil owing to the measurement function which is essential for the MRI device is received at each installation position of the small-sized high frequency coil 20A which is detected by a positioning device, and the uniformity of the static magnetic field is obtained from the received MR signal. Therefore, the measurement of the uniformity of the magnetic field is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic resonance imaging apparatus, and particularly to a magnetic field measuring apparatus for a magnetic resonance imaging apparatus used for measuring static magnetic field uniformity.

[Conventional technology]

The magnetic resonance imaging device applies a static magnetic field,
A high-frequency signal is applied to this to detect the movement of protons in the living body as a resonance signal, including their position, to obtain a tomographic image of the inside of the living body, which is displayed on a screen. The static magnetic field must be uniform over the measurement space. However, since a static magnetic field is generated over a wide space using permanent magnets, electromagnets, etc., it is essential to check whether the static magnetic field is generated uniformly.

In the conventional measurement of static magnetic field uniformity, a static magnetic field strength measuring device is prepared, and this is used at XY7. It was fixed to a movable table, the xyz movable table was given each measurement position, the table was moved, and each measurement position was measured using a static magnetic field strength measuring device.

Regarding general conventional examples of magnetic resonance imaging devices (MRI devices), please refer to "rNMR Medicine (Basic and Clinical)" (Complete Nuclear Magnetic Resonance Medical Research, published by Maruzen Co., Ltd. in 1987).

[Problem to be solved by the invention]

In measurements using an XYz moving table, the static magnetic field is directly measured. Therefore, a device for measuring static magnetic field uniformity is definitely required. These include a static magnetic field strength measuring device and an xyz moving table.

However, the need for special equipment for static magnetic field homogeneity measurement for the MHI device is costly.

This is not a good thing from both aspects of the equipment.

An object of the present invention is to provide a magnetic field measuring device for an MRI apparatus that can measure the uniformity of a static magnetic field without requiring a special large-sized device for measuring the uniformity of the static magnetic field.

[Means to solve the problem]

The present invention has built-in fans 1 to 1 for generating MR signals.

A small high-frequency coil and a positioning device for positioning the small high-frequency coil at each location for uniformity measurement are provided, and the MR multiplied signal from the small high-frequency coil is received by the original function of the MRI device, and the uniformity measurement is then performed. Closed.

[Effect]

According to the present invention, for each position where a small high-frequency coil is installed by the positioning device, an MR multiplied signal is received from the coil using the measurement function inherent in the MRI apparatus, and the uniformity of the static magnetic field is determined from the received MR multiplied signal.

〔Example〕

FIG. 1 is an embodiment of the entire MRI apparatus of the present invention. This MHI device consists of a static magnetic field generating magnet 2°CPU3. Sequencer 4. Transmission system 5. Receiving system 8° display 9. Remote control console 17. It consists of a gradient magnetic field power supply 6.

The static magnetic field generating magnet 2 is a gradient magnetic field coil 7A.

7B, and generates a static magnetic field in each of the X, Y, and Z directions.

The transmission system 5 includes a high frequency oscillator 10. Amplitude modulator 11, high frequency amplifier 12. Consists of high frequency coil 2OA. This transmission system 5 applies a high frequency signal for MR signal detection to the subject.

The sequencer 4 performs time sequence control according to the measurement mode (for example, spin-E-two method, etc.), and specifically controls the magnetic fields GX, G according to the time sequence.
Generates y, Gz generation commands and high frequency generation commands (modulation commands).

The receiving system 8 includes an amplifier 13. In addition to having a quadrature phase detector 14 and an AD converter 15, a phantom 16 for uniformity measurement is newly installed. It has a small coil 2o. The phantom 16 and the small coil 20 may be integrated to form a small coil section.

The phantom 16 is a pseudo-test object, and was made for measuring static magnetic field uniformity. The phantom 16 is made of, for example, a plastic outer part and an aqueous nickel chloride solution forced into an internal cavity.

The high-frequency coil 20B may also be used as an original receiving coil for MRI, but in the embodiment, it is a special coil for uniformity measurement.

The remote control console 17 has an indicator light 18. It consists of a switch 17, and when the switch 17 is turned on during measurement, it is used as a measurement command.

The indicator light 18 lights up during the measurement.

The display 9 displays an MRI tomographic image.

The CPU 3 controls the sequencer 4 and the MR from the receiving system 8.
Double signal acquisition and calculation of tomographic data.

Display control on the display 9 is performed. In addition, the operation console 17
Import measurement commands.

In the MRI apparatus shown in FIG. 1, when measuring a regular subject, the phantom 16 may be removed and the subject may be inserted into the static magnetic field space.

FIG. 2 shows a static magnetic field uniformity measurement space 20. As shown in FIG. This space is a sphere, and the measurement point is at the center position Aoo of the sphere 20.
, and the Z direction (height direction) of the sphere is divided equally, and the circumferential line no, Ω1°Q2. . . . Evenly divided points on the top (for example, on the circumference line Q1, as shown in Fig. 3, points All to A1 divided at 45° intervals from the center)
8). Therefore, if there are i circumferential lines and j dividing points on the circumference, the number of measurement points is (iXj+1).

Note that equal division in two directions means d5. For f14, d4 means that the distances in the Z direction between all other adjacent circumferential lines are equal to (d5-da). Normally, it is preferable to divide it into 7 parts in the Z direction and 12 points in the circumferential direction (divided at 30 degrees).

In order to measure at each point in FIG.
Use a positioning device as shown in the figure.

The positioning device shown in FIG. and a shaft portion 22 fixed to this rotation mechanism portion 26. It consists of a positioning part 24 fixed to the shaft part 22.

The rotation mechanism section 26 includes a fixed section 26A and a rotating section 26B, and only the rotating section 26B rotates while being supported by the fixed section 26Δ. The fixing portion 26A has markings on its circumference at intervals of 45°, thereby positioning is performed at intervals of 45° in the circumferential direction.

The rotating portion 26B, the shaft portion 22, and the positioning portion 24 are integrally fixed. Therefore, by positioning the rotating part 26B in the circumferential direction, the positioning part 24 can also be positioned as it is.

An attachment section 24 is provided on the outer peripheral side 24A of the positioning section 24 to which the small high-frequency coil section 21 is attached. There are eight mounting parts 24 in the Z direction as shown in ■ to ■, and the positions of these eight parts are 8 in two directions as shown in FIG.
corresponding to circumferential lines. Therefore, ■ to ■ are positions on each divided circumference of the sphere in the Z direction.

An example of the configuration of the small high-frequency coil section 21 is shown in FIG. A small high-frequency coil 20B was wound around the phantom 16, a tuning circuit 20C was connected to the coil 20B, and these were inserted into a plastic container.

Such small high-frequency coil portions 21 are sequentially installed at each of the positions ① to ②. Specifically, a starting rotation angle of 0° is set by the rotation mechanism section 26, and then the small high-frequency coil section 21 is attached to position (2) (center position).

Then, a static magnetic field is applied to the signal and the signal is received by the MR multiplier signal coil 20B from the phantom 16. Next, remove the small high-frequency coil section 21 from position 2 and attach it to position 3. Applying a static magnetic field again, the MR multiplier signal coil 20 from the phantom 16
Receive at B. Hereinafter, similar measurements will be made at each of the points ① to ②.

Next, set the rotation angle to 45°, and measure again at each point (■) to (■).

Similarly, measurements are made at 8 points (■) to (■) for all rotation angles such as 900°, 135°, and so on.

Through the above series of measurements, it is possible to obtain measurement values from the phantom at the center of the sphere and at necessary measurement points on its circumference. In addition, the rotation angle pitch was set to 45°, but it was set to 30°.
If so, it is possible to obtain even more detailed measurement data for each position.

Next, the measurement procedure will be explained.

Normally, a gradient magnetic field is applied to the open side of the subject, but in magnetic field measurement, no gradient magnetic field is applied. While this gradient magnetic field is not applied, the frequency of the high-frequency oscillator 10 is sequentially changed and applied to the phantom 6. On the other hand, the position of the phantom 16 changes in various ways as described in FIG. Therefore, measurements are performed while changing various frequencies for each position.

At each measurement point, data is collected by changing the frequency sequentially (CPU 3 collects data via 20B → 13 → 14 → 15)6 However, it is proportional to the static magnetic field strength at the location where the phantom 16 is placed. When the resonance frequency and the frequency of the high-frequency oscillator 10 match, data of the maximum value is obtained. The CPU 3 performs Fourier transform processing using this maximum value data as collected data, and can measure the resonance frequency and static magnetic field strength at the location where the phantom 16 is placed from the frequency component having the maximum amplitude.

In addition, changing the high frequency frequency for each measurement point and collecting maximum value data are the same in actual measurements with the object under test.
Nothing will change. That is, in this embodiment, by simply providing the high-frequency coil section 21 and the positioning device, the measurement procedure used in the original MRI apparatus can be used, thereby making it possible to measure the static magnetic field uniformity.

Note that the remote control console 17 has one of the following remote control functions.

(i) Generate a positioning command for the rotating section 26B of the rotating mechanism section 26. This positioning command is O in the above embodiment.
The position commands are o, 45°, 90°, etc.

(ii) In addition to positioning commands for rotational positions, position ■～■
A command to automatically set the coil section 21 to each position is generated. In this case, since one switch 19 provides two commands, the two commands are given in chronological order. Naturally, in the case of (1), the coil section 21 is moved manually to each of the positions (1) to (2).

In the case of (ii), FIG. 4 does not disclose an automatic setting mechanism to positions (1) to (2). This is because it can be easily realized using normal technology.

(iii) Only the automatic setting command to the coil section 21 is generated. In this case, the positioning of the rotating part 26B is performed manually.

(iv) Although (i) to (1i) are examples of remote control of the positioning device, the object of remote control may be the CPU 3. That is, all operations of the positioning device are performed manually, and a command to start MHI measurement is given remotely from the console 19.

Which of the above (i) to (iv) should be adopted?
This is due to the mechanism of the positioning device and rough wear on the CPU 3.

Note that in FIG. 4, member 27 indicates the current rotational position.

On the other hand, the rotating portion 26A has a label portion 2 corresponding to the rotational position.
8 is provided, and a rotation position number (for example, 0 for Oo, 1 for 30 degrees, 2 for 60 degrees, etc.) is attached in this label portion 28.

Thereby, by looking at the label of the member 28 at the position facing the member 27, the current rotational position can be known. An example of the label section 28 is shown in FIG.

FIG. 7 is a flowchart for measuring static magnetic field uniformity by remote control as described in (iv) above. First, the receiving coil section 21 is manually set to position (Fl). Check whether magnetic field strength can be measured (F2). This is to check whether the MRI apparatus is ready for measurement. Next, a display indicating that the remote controller 17 is ready is displayed on the indicator light 18 (F3).

Turn on the switch 19 and give a measurement start command (F4
)a Change the high frequency to obtain an MR multiplied signal (F5).

This is the maximum value of this MR multiplied signal. Next, check whether the next magnetic field strength measurement is possible (F6), and if OK, move the coil section 21 to the next measurement position (F1). and,
Under the condition that the switch 19 is ON (F8), the magnetic field strength at position ■ is measured (F9). Check whether measurement is possible again (FIO), and if OK, rotate by 30 degrees (FIL). Turn on switch 19 and press F 12
), measure the magnetic field strength (F 13). Further rotation is 30
Measurement is carried out over a range of 360 degrees at each point (F14), and measurement is continued up to position ■ (F15).

Finally, the magnetic field uniformity is calculated (F16) and the result is displayed on the display 19 (F17).

FIG. 8 shows an example of measuring magnetic field strength. This is a time chart for obtaining an MR multiplied signal by irradiating high frequency RF. This M
Fourier transform the signal with the maximum value (intensity) in the R signal (
In the figure, the frequency f at which the maximum value is obtained is set to fo). This fo
Magnetic field strength Ff o at the position where fans 1 to 16 are placed
is calculated using the following formula.

O Ho = - 2πγ Here, γ indicates the proton gyromagnetic ratio.

Note that G Cs, G CE, and G CR represent magnetic fields.

FIG. 9 shows an external view for measurement. MRI body 30
A positioning device is inserted into the measurement space, and measurements are performed by changing each measurement point.

〔Effect of the invention〕

According to the present invention, MHI can be achieved by simply introducing a simple measuring machine.
It becomes possible to measure the uniformity of the magnetic field by making use of the original measurement technology.

[Brief Description of the Drawings] Fig. 1 is an embodiment of the present invention, Figs. 2 and 3 are explanatory diagrams of uniformity measurement points of the present invention, and Fig. 4 is an embodiment of the positioning device of the present invention. , FIG. 5 is an embodiment diagram of the receiving coil section of the present invention, FIG. 6 is an embodiment diagram of the label section, FIG. 7 is a processing flow diagram of the present invention, FIG. 8 is a side view of measuring magnetic field strength, and FIG. Figure 9 is an external view of the measurement system. 5... Transmission system, 8... Receiving system, 16... Phantom, 17... Remote control console (device), 20B... Receiving coil. No. 40 30 n Ha15 6s Whispering figure

Claims (1)

[Claims] 1. A magnetic resonance imaging apparatus that obtains a tomographic image inside a subject from a resonance signal obtained by applying a static magnetic field and a high-frequency signal, including a phantom and the phantom placed at each measurement point in a static magnetic field measurement space. a positioning device for positioning; a means for applying a static magnetic field and a high frequency signal inherent in a magnetic resonance imaging device to the phantom at each of the measurement points; and a high frequency coil for detecting a pseudo resonance signal obtained from the phantom by applying the high frequency signal. A magnetic measurement device for a magnetic imaging device, comprising: means for inputting a received resonance signal from the high-frequency coil into a magnetic resonance imaging device to calculate static magnetic field homogeneity.