JPS6088407A - Magnetic field generating device - Google Patents

Abstract

PURPOSE:To obtain uniform, stable and high-accuracy magnetic field by providing annular projections for each of opposite planes of a pole piece. CONSTITUTION:Each of opposite planes of a pole pieces 2 is provided with annular projections 5. For example, a magnetic circuit used for an NMR-CT device is constituted as follows. The pole pieces 2 are fixed to one end of each of a pair of Fe-B-R group permanent magnets 1 and these face each other. Other ends are connected by a joint iron 3. In an air gap 4 between the pole pieces 2, a strong magnetic field of 1-10kG is generated and a part of a human body or the whole body is inserted in that air gap for making a diagnosis. Then, a pair of pole pieces 2 have outer diameters of D1, annular projections 5 having inner diameters of D2 and height of H are arranged on circumferential edges of the opposite planes and these projections face in the air gap 4. If the inner diameter planes of these annular projections are inclined planes, a good and uniform magnetic field can be obtained stably.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for detecting a cross-sectional image of a target object in a large cavity used in a medical nuclear magnetic resonance tomography system (hereinafter referred to as NMR-CT), which can depict the properties of tissues. This invention relates to a magnetic field generator that generates a strong, highly accurate, and uniform magnetic field.

NMR-CT tests part or all of the human body at 1 to 10
In order to obtain the required tomographic image by inserting it into the air gap that forms the strong magnetic field of KG, this magnetic field is strong and 10-4
It is required to be uniform and stable with the following accuracy, NM
Magnetic field generators for R-CT include normal conducting magnets made of conductive wire made of copper or aluminum wrapped around them in a cylindrical shape, and superconducting magnets that use special conducting wire and are cooled to a temperature close to absolute zero. Are known.

The former is structurally inexpensive, but in order to generate a sufficiently strong magnetic field, it requires a huge amount of electricity and cooling water, resulting in high running costs, and the leakage magnetic field created by the coil can be a negative factor depending on the application. On the other hand, the latter type of superconducting magnet has the advantage of consuming less power and being small and generating a strong magnetic field, but it requires the use of expensive liquid helium or the like as a coolant. , there is a problem that the running cost is extremely high as well as the so-called initial cost.
It has not yet become widely used.

In addition, if the magnetic field strength of a permanent magnet circuit can be equal to that of the above-mentioned solenoids and electromagnets, it can be said that it consumes no power and has a weak leakage magnetic field, making it ideal for practical use in the above applications. However, the currently used magnetic circuits have various problems when put into practical use, and their applications are extremely limited.

In view of the current situation, the present invention aims to provide a magnetic field generator having a magnetic circuit that can obtain a uniform and stable magnetic field with high precision in the air gap of a magnetic field generator using permanent magnets that can obtain a strong magnetic field. There is.

That is, the present invention provides a magnetic field generating device in which magnetic pole pieces facing each other with an air gap are magnetically coupled to at least one permanent magnet using a yoke to generate a magnetic field in the air gap. ! This magnetic field generating device is characterized in that an annular projection is provided on each of the opposing surfaces of the magnetic pole pieces.

The permanent magnet used in the magnetic field generator of the present invention can be a ferrite magnet, an alnico magnet, or a rare earth Kobal 1-based magnet. Fe-8'-R as a magnet
The system (R is at least one rare earth element including Y) permanent magnet (Japanese Patent Application No. 57-145012) not only has a large maximum energy product, but also has a residual magnetic flux density of 11 (Br
> has a temperature coefficient of 0.07%/℃ to 0.15%/℃, so this permanent magnet can be
By applying it to CT, the device can be made smaller.
Excellent performance can be obtained, and furthermore, the magnetic properties of this permanent magnet, especially when used after being cooled to 0° C. or below, can be effectively utilized to obtain a significantly high maximum energy product.

The above-mentioned Fe-B-R permanent magnet has a composition of 8% to 30% (where R is at least one rare earth element including Y)
atomic%, B 2 atomic% to 28 atomic%, Fe42 atomic% to
It is a permanent magnet whose main component is 90 atomic % and whose main phase is a tetragonal phase.R is a light rare earth that is abundant in resources, mainly ceramics and Pr, and 25M is made with El and Fe as the main components.
It is an excellent permanent magnet that exhibits an extremely high energy product exceeding GOe.

Hereinafter, this invention will be explained in detail based on the drawings.

FIG. 1 is an explanatory diagram of a magnetic circuit used in the NMR-CT device, in which a pair of Fe'E3R permanent magnets (1) are each fixed with a magnetic pole piece (2) at one end and faced to each other. , the other end is connected with a yoke (3), and the air gap (4) between the pole pieces (2) is
A strong magnetic field of 1 to 10 KG is generated within the cavity, and a part or all of the human body is inserted into this cavity for diagnosis.

The pair of magnetic pole pieces (2) have an outer diameter of Dl, and an annular protrusion (5) with an inner diameter of Dz + height of 1'' is protruded from the periphery of the opposing surface, and the two magnetic pole pieces (2) face each other in the gap (4). A highly accurate, uniform and stable magnetic field can be obtained. If the annular protrusion (5) has an inclined inner surface that expands upward, a good uniform magnetic field can be stably obtained.

Figure 2 shows a vertical cross-sectional view of the magnetic pole piece (2); Figure A shows a case where the cross section is triangular, Figure 2 shows a case where the cross section is trapezoidal, and Figure C
The figure shows the same d when the inner slope of the triangular cross section is curved.
The figure shows, for example, a case where the corners of a trapezoidal cross section are chamfered to create a curved surface structure.

In the magnetic circuit for NMR-CT shown in FIG. 3, a pair of yokes (3) with a magnetic pole piece (2) fixed to one end are arranged facing each other to form a gap (4), and the other end is made of Fe-B- R-based permanent magnet (1)
It is a circuit in which an annular protrusion (5) with a triangular cross section is provided on the periphery of the opposing surface of the magnetic pole piece (2).

Furthermore, the magnetic circuit is not limited to the above example, and can be applied to any magnetic circuit as long as the annular protrusion is configured to have a stepped G-node magnetic pole piece on the opposing surface, and the shape and dimensions of the annular protrusion are It may be appropriately selected depending on the dimensions of the permanent magnet, magnetic properties, and size of the air gap, but it is particularly effective within the following range.

D2≧1/2・Dl, H≦1/4・LQ However, DI
; External diameter of magnetic pole piece, D2: Inner diameter of annular protrusion, LQ: Air gap, H
; Height of the annular process.

By the way, in the magnetic circuit having the configuration shown in FIG.
<Using permanent magnet, DI=500mm, D2=
400 mm, H = 30 mm with a magnetic pole piece with an annular protrusion and an outer diameter of 50 mm without an annular protrusion.
In both cases when 0mm pole piece is placed, LG is 35
When we measured the magnetic field distribution in the air gap maintained at 0 mm, we found that in the case of this invention having an annular protrusion, compared to the comparative example,
The volume of the 10-3 region of uniform magnetic field was expanded three times.

Further, in the case of the magnetic pole piece according to the structure of the present invention, when compared at the same magnetic field strength, the magnetic pole piece and magnet may have a much smaller diameter than those of the above-mentioned comparative example, which is advantageous in reducing the size and weight.

[Brief explanation of the drawing]

FIG. 1 and FIG. 3 show the longitudinal direction of the magnetic field generating device according to the present invention.
17i is an explanatory diagram, and FIG. 2 is an explanatory diagram of the vertical Vji of the magnetic pole piece. 1...Fe-B I< system permanent magnet, 2... Magnetic pole piece,
3...Yoke, 4...Gap, 5...Annular protrusion. Applicant Sumitomo Special Metals Co., Ltd. Representative Ryo Hisakeichi] II Figure 1 Figure 2 (Q) (b) (c) (d) Figure 3

Claims (1)

[Claims] 1. In a magnetic field generating device that magnetically couples magnetic pole pieces facing each other with an air gap and at least one permanent magnet using a yoke to avoid generating a magnetic field in the air gap, an annular projection is provided on each of the opposing surfaces of the magnetic pole pieces. A magnetic field generating device characterized in that: