JPH02224643A - Nuclear magnetic resonance tomography device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application This invention relates to a nuclear magnetic resonance tomography (MRI) apparatus that obtains tomographic images by exciting target nuclides in a subject. related to technology to suppress vibrations in coils for use.

B. Prior Art FIG. 8 is a longitudinal sectional view of a gantry section of a nuclear magnetic resonance tomography apparatus according to a conventional example.

MR [The gantry part of the device includes a main coil 1 that forms a main static magnetic field space that is uniform in the body axis direction of the subject M, and a main coil 1 that is arranged within this main static magnetic field space and that is arranged in the direction of the X, YZ orthogonal coordinate axes. A saddle-shaped 1ψ gradient magnetic field generating coil (C;

First, the subject M lying supine on the top plate 9 is inserted into the main static magnetic field in the Z-axis direction formed by the main coil l. If an excitation pulse is applied to an excitation coil (not shown) in this state, an MRI signal can be detected. At this time, in order to distinguish which part of the subject M the signal is coming from, each gradient magnetic field is used to linearly change the magnetic field strength in the Z-axis direction along three orthogonal axes (X, Y, and Z-axis directions). A pulsed electric coolant is supplied to the generating coil 2.

C9 Problems to be Solved by the Invention However, the above-mentioned conventional device has the following problems.

That is, when a pulsed current is passed through the gradient magnetic field generating coil 2 placed in the main static magnetic field, a corresponding Lorentz force acts on the gradient magnetic field generating coil 2. This force acts in the radial direction of the gradient coil bobbin 5, that is, as if the gradient magnetic field generating coil 2 strikes the gradient coil bobbin 5. becomes large due to the echo of the gradient coil bobbin 5.

For this reason, in the past, a vibration isolating material 13 was inserted between the gradient magnetic field generating coil 2 and the gradient coil bobbin 5 to reduce the hammering sound, or earplugs were placed on the subject M to avoid hammering. It alleviated Subject M's mental pain caused by the sound.

Furthermore, since the gradient magnetic field generating coil 2 provides positional information for distinguishing from which part of the subject M the MRi signal originates, a force acts on the gradient magnetic field generating coil. When the gradient magnetic field generating coil vibrates, reliable position information cannot be obtained, which may lead to a decrease in resolution and S/N ratio, that is, a decrease in image quality.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a nuclear magnetic resonance tomography apparatus that can suppress as much as possible the vibration of the gradient magnetic field generating coil and the generation of tapping sounds due to this vibration. The purpose is

Means for Solving the Problems The present invention has the following configuration to achieve the above object.

That is, the nuclear magnetic resonance tomography apparatus according to the present invention is a nuclear magnetic resonance tomography apparatus in which a gradient magnetic field generating coil is installed in a main static magnetic field formed by a main static magnetic field generating means. The device is characterized in that it is provided with local static magnetic field generating means for generating a static magnetic field for canceling the main static magnetic field in the local space where the is installed.

E0 effect According to the present invention, the local static magnetic field generation means generates a static magnetic field in a local space where the gradient coil is placed in a direction opposite to the direction of the main static magnetic field, thereby improving the position of the gradient coil. The main static magnetic field in the local space is canceled out.

F. Example Embodiments of the present invention will be described below based on the drawings.

Figures 1 to 3 relate to the first embodiment, where Figure 1 is a longitudinal sectional view of the gantry, Figure 2 is a partially cutaway perspective view of the gantry, and Figure 3 is an inclined view. It is an explanatory diagram of the action of the coil sound removal coil.

In these figures, the parts indicated by the same reference numerals as those shown in FIG. 8 according to the conventional example are the same constituent parts as in the conventional example, so the explanation here will be omitted. This also applies to other embodiments to be described later.

A top plate 9 on which a subject M is placed in the internal space of the main coil l is removably installed in the gantry, and the main coil l and the top plate 9
A gradient magnetic field generating coil 2 that generates a gradient magnetic field is provided between the two. The gradient magnetic field generation coil 2 is located in a local space A sandwiched between a cylindrical gradient coil bobbin (inner bobbin) 5 and a cylindrical gradient coil sound removal coil outer bobbin 6 provided concentrically therewith. placed on the inner bobbin 5
It is attached along the outer circumferential surface of the

Gradient coil sound removal coil 3 as local static magnetic field generating means
After going around the outer circumferential surface of the outer bobbin 6 approximately once, it passes through the outer bobbin 6 and the inner bobbin 5 and is drawn out into the inner space of the inner bobbin 5 . Then, it goes around the inner circumferential surface of the inner bobbin 5 in a direction opposite to the outer circumferential winding direction of the outer bobbin 6, passes through the inner bobbin 5 and the outer bobbin 6, and returns to the outer bobbin 6. 6 and is wound on the outer corner surface of the outer bobbin 6 in the same direction as the outer circumferential winding direction.

In this way, over almost the entire area in the axial direction of the two coil bobbins 5 and 6 provided concentrically, the gradient coil sound eliminating coil 3 is applied on the outer circumferential surface of the outer bobbin 6 and on the inner circumferential surface of the inner bobbin 5. It is wrapped around.

Next, the operation of the above-described embodiment device will be explained.

The main coil 1 forms a uniform main static magnetic field B in the internal space of the main coil 1. In this embodiment, a pulse current is supplied to the gradient magnetic field generating coil 2 in order to generate a zero-order gradient magnetic field in which the direction of the main static magnetic field B is to the left in FIG. At this time, in order to prevent the Lorentz force from acting on the gradient magnetic field generating coil 2, current is supplied to the gradient coil removal coil 3.

As shown in FIG. 3, when a current is supplied to the gradient coil removal coil 3, a static magnetic field B' in the right direction in the figure is generated in the local space A sandwiched between the inner bobbin 5 and the outer bobbin 6.
occurs. Since the static magnetic field B' is in the opposite direction to the main static magnetic field B formed by the main coil l, the main static magnetic field B in the local space A is canceled by this static magnetic field B'. Therefore, even if a pulse current is supplied to the IIJt gradient magnetic field generating coil 2 arranged in the local space A, no force acts on the gradient magnetic field generating coil 2, suppressing the vibration of the gradient magnetic field generating coil 2. be able to.

Furthermore, in a region outside the local space A, the lines of magnetic force of the gradient coil combination removal coil 3 are in opposite directions, so that the static C11 field B' in this region is hardly generated.

Therefore, in the imaging region at the center of the gantry, a tomographic image of the subject M can be captured without the main static magnetic field B being disturbed by the static magnetic field 13'.

1.2Jul FIG. 4 shows a side view of the gantry section according to the second embodiment.

Reference numeral 4 denotes a main magnet as a main static magnetic field generating means for forming a main static magnetic field. The main magnets 4 are a pair of permanent magnets with north poles and south poles facing each other, and are supported by support legs 8 at C1.

A gradient coil sound eliminating magnet 7 serving as a local magnetic field generating means is arranged outside the pair of main magnets 4. (The oblique coil sound eliminating magnets 7 are a pair of permanent magnets with N poles and S poles facing each other, and are supported by the support legs 10. The N pole of the main magnet 4 and the oblique coil sound eliminating magnets 7 A gradient magnetic field generating coil 2 wound around a gradient coil bobbin 5 is provided in a local space A sandwiched between the N pole of the main magnet 4 and the S pole of the main magnet 4. A gradient magnetic field generating coil 2 wound around another gradient coil bobbin 5 is provided in a local space Δ2 sandwiched between the S pole of the magnet 7 and the S pole of the main magnet 4 in the local space AI. The direction of the magnetic field lines coming out from the N pole and the N pole of the gradient coil sound removal magnet 7 is as follows:
Since the directions are opposite to each other, almost no main static magnetic field is generated in this local space A1, and similarly, the local space Δ sandwiched between the S pole of the main magnet 4 and the S pole of the gradient coil sound removal magnet 7
Since the main static magnetic field is not generated within the gradient magnetic field generating coil 2, even if a pulse current is supplied to the gradient magnetic field generating coil 2, the gradient magnetic field generating coil 2 does not vibrate.

On the other hand, in the space sandwiched between the N and S poles of the main magnet 4, the static magnetic fields of the magnets 4 and 7 are generated in the same direction. By inserting the subject M, imaging becomes possible.

Further, this second embodiment can be modified as shown in FIG.

FIG. 5 is a side view of this modified example device.

In this modification, the main magnet 4 of the second embodiment is used as the main coil 11, and the gradient coil sound removal magnet 7 is used as the gradient coil removal coil 1.
This will be implemented in place of 2.

With respect to the direction of the current ■' flowing back through the main coil 11, the direction of the current ■ flowing through the gradient coil sound removal coil 12 is ``ζ''.
It is in the opposite direction. Therefore, in the local spaces A, , A, the direction of the main static magnetic field generated by the current 1' flowing back through the main coil li and the direction of the static magnetic field generated by the current 2 flowing back through the gradient coil removal coil 12 are mutually mutual. Since the directions are opposite, the static magnetic field in the local spaces A, , A is canceled out, and even if a pulse current is supplied to the gradient magnetic field generating coil 2, the gradient magnetic field generating coil 2 does not vibrate.

On the other hand, in the space sandwiched by the main coil 11, the lines of magnetic force are oriented to strengthen each other, so that a static magnetic field is generated in this space. When capturing a tomographic image of the subject M, the subject M can be inserted into this space.

Figs. 6 and 7 of the JJ11 section relate to the third embodiment, in which Fig. 6 is a longitudinal sectional view of the gantry section, and Fig. 7 is a partially cutaway perspective view of the gantry section.

Reference numeral 7 denotes a gradient coil sound eliminating magnet that forms a static magnetic field B'. The gradient coil sound eliminating magnet 7 is constituted by an annular permanent magnet in which an N pole and an S pole are arranged to face each other. Static magnetic field B formed in the space sandwiched between this Ni and the S pole
The N and S poles of the gradient coil sound eliminating magnet 7 are connected to the cylindrical inner bobbin 5 so that the direction of the gradient coil 1 is opposite to the direction of the main static magnetic field B formed by the main coil 1. They are installed facing each other on both end faces.

As a result, in the local space A outside the gradient coil bobbin 5 where the gradient magnetic field generating coil 2 is installed, a static magnetic field B' is always acting in the right direction in FIG. 6, so that the main coil l
As a result, the main static magnetic field B (to the left in the figure) generated in this local space A is canceled out, so that even if a pulse current is supplied to the gradient magnetic field generating coil 2, the gradient magnetic field generating coil 2
vibration can be suppressed.

Note that since the gradient coil sound removal magnet 7 is annular, the influence of the static magnetic field B' on the main static magnetic field B in the imaging area corresponding to the center thereof is slight, and does not interfere with the imaging of the tomographic image of the subject M. It will not cause

G1 Effect of the Invention As is clear from the above explanation, in the nuclear magnetic resonance tomography apparatus according to the present invention, the local static magnetic field generating means generates the main static magnetic field in the local space in which the gradient magnetic field generating coil is installed. Therefore, even if a pulse current is supplied to the gradient magnetic field generating coil, no force is applied to the coil, and it is possible to prevent the generation of hammering noise.

Therefore, it is possible to eliminate the mental pain of the subject,
This is convenient for performing imaging work because the operator can clearly hear the voice of the subject.

In addition, since there is no displacement of the gradient magnetic field generating coil due to vibration, accurate position information can be provided.
Image quality can be improved.

[Brief explanation of the drawing]

1 to 7 relate to one embodiment of the present invention, in which FIG. 1 is a longitudinal sectional view of the gantry section according to the first embodiment, FIG. 2 is a partially cutaway perspective view of the gantry section, and FIG. 4 is a side view of the gantry section according to the second embodiment, FIG. 5 is a side view of the gantry section according to a modification thereof, and FIG. 6 is a side view of the gantry section according to the third embodiment. FIG. 7 is a longitudinal sectional view of the gantry part according to the example, and FIG. 7 is a perspective view of the gantry part. FIG. 8 is a longitudinal sectional view of a gantry section according to a conventional example. 1.11... Main coil 2... Gradient magnetic field generation coil 2 3.12... Gradient coil sound removal coil 34... Main magnet 7... Gradient coil sound removal magnet Fig. 4 Fig. 5 Figure Figure

Claims (1)

[Claims] (1) In a nuclear magnetic resonance tomography apparatus in which a gradient magnetic field generating coil is installed in the main static magnetic field formed by the main static magnetic field generating means, the main static magnetic field in the local space where the gradient magnetic field generating coil is installed. 1. A nuclear magnetic resonance tomography apparatus characterized by comprising local static magnetic field generating means for generating a static magnetic field for canceling a magnetic field.