JPS62281934A - Static magnetic field magnet - 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 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to nuclear magnetic resonance computed tomography (NM
The present invention relates to a magnet for generating a static magnetic field used in a magnetic field (abbreviated as R-C, T), and more specifically to a static magnetic field magnet in which a magnetic circuit is constructed by combining a magnetic field generating means with a magnetic material having low magnetic resistance.

(Prior Art) NMR-CT is an inspection device that utilizes NMR phenomena to determine the distribution of specific atomic nuclei in a subject from outside the subject. In such NMR-CT, in order to generate an NMR signal, it is necessary to apply a relatively large uniform static magnetic field of about 0.04 to 1.5 Tesla to the subject.

Conventionally, normal conductive electromagnets, superconducting electromagnets, permanent magnets, and the like have been used as magnetic field generating means for generating such a uniform static magnetic field. In addition, these magnetic field generating means include materials such as iron for the purposes of (a) reducing the leakage magnetic field and reducing the influence on the surroundings, and (b) increasing the central magnetic field strength by the magnetic field enhancement effect. Magnetic shielding using a magnetic material is being applied.

This magnetic shield has traditionally been designed with a cylindrical shape, etc. to minimize disturbances in the magnetic field homogeneity within the imaging area.
Its shape was determined with symmetry in mind.

(Problem to be solved by the invention) However, the shape of the magnetic shield currently in practical use is not necessarily satisfactory in terms of reducing the leakage magnetic field and increasing the magnetic field enhancement effect of the magnetic material. .

The present invention has been made in view of the above circumstances, and its purpose is to realize a static magnetic field magnet that can enhance the shielding effect and the magnetic field enhancement effect.

(Means for Solving the Problems) A static magnetic field magnet of the present invention that solves the above-mentioned problems includes a magnetic field generating means and a flange installed to cover the magnetic field generating means from the outside and forming a magnetic circuit at both ends. The present invention is characterized in that it comprises a magnetic shield cylindrical part having a section, and a magnetic flux concentrating part of a magnetic material provided on the flange part and positioned so that its tip end enters inside the magnetic field generating means.

(Function) The magnetic flux concentrator whose tip is installed so as to enter inside the magnetic field generating means has the function of efficiently concentrating magnetic flux in the magnetic shield cylinder forming the magnetic circuit, reducing leakage magnetic flux, and increasing the central magnetic field. It works to increase strength.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, and FIG. 2 is a perspective view thereof. Here, an example is shown in which an electromagnet consisting of four normally conductive coils is used as the magnetic field generating means, and a cylindrical magnetic body is used to form a magnetic circuit with these and provide magnetic shielding.

In these figures, 1 is an annular coil made of, for example, copper wire bonded and solidified with epoxy resin, and is held by a holding frame (not shown) or the like. 2
is a cylindrical magnetic shield part that forms a magnetic circuit and is installed so as to cover each coil 1 from the outside. This cylindrical magnetic shield section 2 is made of a magnetic material such as iron, and is provided to reduce leakage magnetic field and enhance magnetic field strength as described above.

3 is a magnetic flange part provided at both ends of this cylindrical magnetic shield part 2; 4 is a magnetic flux concentrating part, which is a feature of the present invention; The tip thereof is placed inside by a distance Δa. The magnetic flux concentrator 4 is made of a magnetic material such as iron, and has an annular shape here.

The operation of the static magnetic field magnet configured as described above will be explained as follows.

First, FIG. 3 shows a magnetic flux line diagram of the magnetic field created by the four normally conducting coils 1. Here, only the 1/4 quadrant of the coil cross section is shown, but the other quadrants are above and below.

This can be easily understood from the fact that it is bilaterally symmetrical.

If there is no shielding member, normal conduction 4 as shown in Figure 3.
Coil 1 makes it! ! The field flux lines are widely distributed in the outward direction of the coil.

Next, FIG. 4 shows a magnetic flux line diagram in an apparatus of the present invention provided with a magnetic shield section 2 having a magnetic flux concentrating section 4. Here, the magnetic flux concentrator 4. The flange portion 3 and the magnetic shield portion 2 are both made of magnetic material made of iron. It is recognized that almost none of the magnetic flux lines coming out of each coil 1 exits from the magnetic shield part 2 to the outside area, and the magnetic flux lines inside the coil 1 gather in the magnetic flux concentrating part 4.

A comparison between FIG. 3 and FIG. 4 shows the general effect of arranging the magnetic shield section 2.

Next, FIG. 5 shows how the value of the central magnetic field of the coil 1 changes when the length Δl of the tip of the magnetic flux concentrator 4 in the device of the present invention that enters the inside of the coil 1 from the flange 3 is varied. FIG. 4 is a diagram showing whether the image is enhanced. Here, the length Δ that allows the magnetic flux concentrator 4 to enter inside the coil 1!
As shown in FIG. 6, the central radius of the magnetic shielding portion 2 is Ra, and this Ra is normalized to set the Z wheel direction scale from the center IjI10 to 2, which is expressed as Z/Ra.

In FIG. 5, Z/Ra-1,0 is a state without the magnetic flux concentrator 4, and the degree of enhancement at this time is about 25%, whereas the magnetic flux concentrator 4 is provided and its tip is By entering the inside of the coil 1, the degree of enhancement gradually increases, and the degree of enhancement is gradually increased to around Z/Ra = 0.4, that is, the tip of the magnetic flux concentrating part 4 is moved from the flange part 3 to Δl-0.6Ra.
When it goes inward to the vicinity, the enhancement degree is 52%
The effect is most noticeable when it comes to a certain degree.

In addition, the enhancement degree is the center of the coil when there is no magnetic material!
The i field value is Bo,! When the coil center magnetic field with magnetic material is BIll, enhancement degree -1oox (Bit -Bo) /B
.

(%) Let it be expressed as .

The seventh is a diagram showing leakage EfiPil (here, 5 Gauss line) when the coil center magnetic field is set to 0.3 Tesla. (A) is the case where the magnetic shield part 2 is not provided, (B) is the case where the magnetic shield part 2 and the flange part 3 are provided, and (C) is the case of the device of the present invention, where the magnetic shield part 2 and the flange part 3 are provided. This is a case in which a magnetic flux concentrator 4 whose tip end enters inside the coil 1 is provided.

It is clearly seen that the leakage magnetic flux is reduced by providing the magnetic flux concentrator 4 whose tip end enters inside the coil 1.

In addition, although the above-mentioned embodiment used a normal conducting coil as a magnetic field generating means, a superconducting coil or a permanent magnet may be used. Moreover, although the magnetic shield part 2 is of a cylindrical shape, it is not limited to this and may be of a rectangular cylinder shape.

(Effects of the Invention) As explained above, according to the present invention, the magnetic flux concentrating portion whose tip portion is installed so as to enter inside the magnetic field generating means generates a magnetic flux through the flange portion forming the magnetic circuit. It works to efficiently collect magnetic flux in the shield cylinder.
The magnetic shielding effect can be enhanced, and the magnetic field enhancement effect can also be enhanced. This means that in order to obtain a central magnetic field of the required magnitude, if an electromagnet is used as the magnetic field generating means, power consumption can be reduced, and if a permanent magnet is used, the magnetic poles can be superimposed. This has the practical effect of making it smaller.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing an embodiment of the present invention, Fig. 2 is a perspective view thereof, Fig. 3 is a magnetic flux line diagram of the magnetic field generated by four normally conducting coils, and Fig. 4 is a magnetic flux line diagram in the device of the present invention. Figure 5 is a diagram showing the relationship between the position of the tip of the magnetic flux concentrator and the degree of enhancement in the R position of the present invention, and Figure 6 is an explanatory diagram of the position of the tip of the magnetic flux concentrator in Fig. Figure 7 is a diagram showing the leakage limit in each case when the coil center magnetic field is 0°3 Tesla. 1... Magnetic flux generating coil 2... Magnetic shield section 3
...Flange part 4...Magnetic flux focusing part Patent applicant Yokogawa Medical System Co., Ltd.

Claims (2)

[Claims] (1) a magnetic field generating means; a magnetic shield cylinder having a flange portion installed to cover the magnetic field generating means from the outside and forming a magnetic circuit at both ends; A static magnetic field magnet consisting of a magnetic flux converging part of a magnetic material positioned so as to penetrate inside the magnet. (2) The magnetic shield cylindrical part is cylindrical, and the tip of the magnetic flux converging part is inserted into the magnetic flux generating part from the flange part to around 0.6 Ra with respect to the center radius Ra of the magnetic shield cylindrical part. A static magnetic field magnet according to claim 1.