JPS6365849A - Nuclear magnetic resonance imaging apparatus - Google Patents

Abstract

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

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to a nuclear magnetic resonance imaging apparatus.

In particular, the present invention relates to a nuclear magnetic resonance imaging apparatus having a gradient magnetic field coil suitable for reducing pressure on a subject and obtaining high-quality images.

[Background of the invention]

As gradient magnetic field coils, rectangular coils/I/10a, 10'a, 10b, and 10'b as shown in FIG. 6 are available. As a condition for gradient magnetic field coils to obtain high quality images in nuclear magnetic resonance imaging equipment.

Two things that can be mentioned are that the gradient of the magnetic field created by the coil is highly uniform, and the gradient of the magnetic field is large.

Rectangular coils 10a, 10'a, 10b,
In the case of 10'b, the size of the coil must be large to satisfy the above conditions (Nuclear Magnetic Resonance Medical Research Society 11iNM
R Medicine (Basic and Clinical), P82).

On the other hand, two conditions for the static magnetic field to obtain high-quality images are high uniformity of the magnetic field and high magnetic field strength. To satisfy the former, pole pieces are used, especially in the center. To improve uniformity, a pole piece with a concave structure is used.

To satisfy the latter requirement, the distance between the pole pieces is kept short.

Due to the above, when a pole piece and a rectangular coil are combined, the coil will be located further inside the pole piece, and the gap between the pole pieces will become narrower.
In order to obtain high quality images.

Gives a feeling of pressure to the subject. Alternatively, if the distance between the pole pieces is increased to eliminate the feeling of pressure, the strength of the static magnetic field will weaken and the signal-to-noise ratio will deteriorate. Conventionally, no consideration has been given to the shape of the coil to reduce the feeling of pressure on the person.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a gradient A4 coil that reduces pressure on a subject and provides images with excellent image quality in a nuclear magnetic resonance imaging apparatus.

[Summary of the invention]

Nuclear magnetic resonance image puffer fish equipment uses gradient magnetic fields for slicing and positioning of images. #i The way to create an oblique m field is basically that the static magnetic field is divided into two directions: vertical (Z axis) direction and horizontal (X, Y axis) direction.
The principles for each are briefly described below. In the former case, the fourth
As shown in FIG. 4(a), by arranging two circular coils facing each other and passing currents in opposite directions, a gradient magnetic field in the Z-axis direction as shown in FIG. 4('b) is generated. In the latter case, if the two Helmholtz coils 8a and 8b are arranged as shown in Fig. 3, and the directions of the currents a and b are opposite to each other, as shown in Fig. 3, Alternatively, a gradient magnetic field in the Y-axis direction is generated. We have just discussed the Helmholtz coil, but in general, even if it is not a circular ring, if it is a closed loop, a gradient magnetic field will be generated.

A rectangular closed loop of the horizontal gradient magnetic field coil is the coil 10 shown in FIG. 6, and a fan-shaped coil that is a combination of straight lines and circular arcs is the coil 6 according to the present invention shown in FIG. In Figures 5 and 6, 2D=
Table 1 specifically shows the shapes when the performance (uniformity of gradient, size) of each coil as a gradient magnetic field coil is the same when the diameter is 450 mm. According to this table, coil 6 is inserted into the concave inner surface of the pole piece.

Table 1 Difference in size between the conventional coil and the coil of the present invention (if the performance is the same) Minimum diameter of the circle in which the entire reference tatami coil can fit (bone diagram) [Example of the invention] The following is an implementation of the present invention An example will be explained with reference to FIGS. 1 and 2. The yokes 1 and 1' are arranged vertically symmetrically, and each yoke 1,
Attach yoke 2 to the four corners of 1'.

Inside each of the yokes 1 and 1', a permanent magnet 3.3' and a pole piece 4.4' are arranged in this order in a vertically symmetrical manner, and supported by support frames 5 and 5'.

Install. The pole pieces 4, 4' are formed in a concave shape to increase the uniformity of the static magnetic field. Ball Piece 4s 4,
Support plates 7 and 7' each having a gradient magnetic field coil 6°6' attached to the inside of the pole piece 4' are attached to the support frame so that the coils are on the pole piece side.

Attaching the coils 6, 6' to the support plates 7, 7'.

All you have to do is make a groove in the support plate that has the same shape as the coil, fit the copper wire into it, and fix it with adhesive. The relationship between the shape parameter of the coil 6,6' and the diameter D2 of the concave edge of the pole pieces 4,4' is Ds<Ih. The distance between the support plates 7 and 7' is .

In a nuclear magnetic resonance imaging system, a subject is placed in a G& field space created by a permanent magnet 3°3' and a gradient magnetic field coil 6.6'. 7′
A coil that generates radio waves is installed in between, and the subject is irradiated with electromagnetic waves in pulses, and a tomographic image is then formed using nuclear magnetic resonance signals measured from the subject.

〔Effect of the invention〕

According to the present invention, it is possible to eliminate the feeling of pressure on the subject and improve the quality of the image.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a permanent magnet type magnetic field generator of a nuclear magnetic resonance imaging apparatus showing an embodiment of the present invention. FIG. 2(a) is a top plan view of the above device. 42
Figure (b) is a sectional view taken along the line A--person' in Figure 2a. FIG. 3 is a perspective view of a horizontal gradient coil. Figure 4 (
a) is a perspective view of a vertical gradient coil; Fourth
FIG. 4(b) is a diagram showing the relationship between the two components (Bz) of the magnetic field generated by the coil shown in FIG. 4(a) and Z. FIG. 45 is a perspective view of a gradient coil according to the present invention. FIG. 6 is a perspective view of a conventional gradient magnetic field coil. 1.1'...Yoke, 2. 2'...Yoke, 3,3
'...Permanent magnet, 4,4'...Pole piece, 5.
5'...Support frame, 6...6'...Gradient magnetic field coil of the present invention (6a. 6/a...X direction gradient magnetic field coil, 6b,
6'b...X-direction gradient magnetic field coil), 7.7'...
Support plate, 8a. 8b... Helmholtz coil, 9... Vertical force M gradient magnetic field coil + 10 a * 10' b... Conventional X-direction gradient magnetic field coil, 10b, 10'b... Conventional y-direction gradient magnetic field coil Figure j 2nd (a) 3rd

Claims (1)

[Claims] 1. In a nuclear magnetic resonance imaging apparatus having a static magnetic field generating means and a gradient magnetic field coil that constitute a magnetic circuit by a magnet, a pole piece, and a yoke, the pole piece has a concave shape, and further the gradient magnetic field coil has a concave shape. A nuclear magnetic resonance imaging device characterized in that it is disposed within a space created by a concave surface of a pole piece.