JPS61114148A - Magnetic field generating device - Google Patents

Abstract

PURPOSE:To obtain a tomographic image of a necessary object of diagnosis through a relatively small-sized gap by detecting relative positions of a target in the three-axial coordinate system of the object of diagnosis and the three-axial coordinate system of a moving means in a magnetostatic field, and making a uniform magnetic field coincident. CONSTITUTION:A magnetic circuit 1 has a couple of plate type magnetic pole pieces 3 whose main surface face each other at a constant interval, columnar permanent magnets 2 are connected between both end facing parts of the magnetic pole pieces 3 to form the gap 4 between the magnetic pole pieces 4, and pieces of magnetic flux produced by the magnets 2 are equalized in direction and form magnetic fields through the magnetic pole pieces 3, thereby forming a uniform magnetostatic field part 5 which is intense within a sphere having a radius (r) and has extremely high uniformity in the gap 4 as center. The whole of the circuit 1 is moved by a linear motor 6 in three axial directions. The object of diagnosis mounted on a rack which is movable in the three axial directions is sent in the three-axial coordinate system of this moving device and the magnetostatic field part 6 is moved to the necessary target; and the position of the magnetostatic field part 5 is measured 7 by arithmetic on the basis of input electric power to the motor 6, which is controlled 8 according to the measurement result to make the object coincident with target coordinates.

Description

Detailed Description of the Invention [Industrial Field] The present invention relates to a permanent magnet used in a medical nuclear magnetic resonance tomography system (hereinafter referred to as NMR-CT) that can obtain a cross-sectional image of an object and depict it using a tissue property method. The present invention relates to a magnetic field generating device using a magnetic field generating device, and particularly to a magnetic field generating device that is small and generates a strong, highly accurate, and uniform static magnetic field within a required air gap without using many permanent magnets.

BACKGROUND TECHNOLOGY NMR-CT can detect part or all of the human body at 1 to 10 KG.
In order to obtain the desired tomographic image by inserting the NMR-C into a gap that forms a strong magnetic field, this magnetic field must be strong, uniform, and stable with an accuracy of 10-4 or less.
As magnetic field generators for T, there are known normal conducting magnets made of conductive wires made of copper or aluminum wrapped around them in a cylindrical shape, and superconducting magnets that use special conductive wires cooled to a temperature close to absolute zero. ing.

The former is structurally inexpensive, but it requires a huge amount of electricity and cooling water to generate a sufficiently strong magnetic field, resulting in high running costs, and the leakage magnetic field created by the coil can be a factor in adverse effects depending on the application. On the other hand, the latter type of superconducting magnet has the advantage of consuming less power, being compact, and generating a strong magnetic field, but it requires the use of expensive liquid helium as a coolant, and the so-called There is a problem that the running cost is extremely high as well as the initial cost.

The present applicant previously developed a permanent magnet circuit that has a magnetic field strength equal to or higher than that of the above-mentioned normal conduction magnet, consumes less power, and has less leakage magnetic field. A magnetic field generating device is proposed in which a magnet is magnetically coupled with a yoke to generate a magnetic field in the air gap, and the magnetic field generating device is characterized in that annular protrusions are provided on each of the opposing surfaces of the magnetic pole pieces. No. 58-196785).

The above-mentioned magnetic field generating device made it possible to significantly improve the uniformity of the magnetic field generated in the air gap.

Its structure consists of a pair of permanent magnets (10
) are fixed to one end of each of the magnetic pole pieces (11) so as to face each other, and the other ends are connected with a yoke (12) to generate a static magnetic field in the gap (13) between the magnetic pole pieces (11). In this configuration, the pair of magnetic pole pieces (11) have an annular protrusion with a substantially trapezoidal cross section having a predetermined inner diameter and height protruding from the periphery of the opposing surfaces. Since the magnetic field strength tends to be higher as the magnetic field is closer, in order to obtain the required high uniform magnetic field in a normally used magnetic field space, for example, a spherical space with a radius of 200 mm or more, it is necessary to increase the size of the permanent magnet, the distance between the magnetic poles, and the magnetic pole area. 10 of the magnetic field space used, such as increasing the
This required more than twice as much air space, making it difficult to miniaturize the magnetic circuit.

Purpose of the Invention In view of the current situation, the present invention provides a highly accurate, uniform, and stable method for obtaining a tomographic image of a desired object to be diagnosed in the air gap of a magnetic field generator using a permanent magnet capable of generating a strong magnetic field. The purpose of the present invention is to create a magnetic field generating device that can achieve this with a relatively small air gap without having to expand the magnetic field, allowing for miniaturization of the device.

Structure and Effects of the Invention The present invention provides a magnetic circuit for a nuclear magnetic resonance tomography apparatus that generates a static magnetic field in a permanent magnet forming an air gap or a magnetic pole piece connected to the permanent magnet, and the magnetic circuit. 3
A moving means for moving in the axial direction, and a target in a three-axis coordinate system of the object to be diagnosed.

A measuring means for detecting a relative position with a three-axis coordinate system centered on a uniform magnetic field area in a static magnetic field, and a control for aligning the uniform magnetic field with the target by operating the moving means in accordance with the detection by the measuring means. A magnetic field generating device is characterized in that it consists of means.

With this invention, targeting the required part of the object to be diagnosed,
Since the highly accurate uniform magnetic field area within the magnetic circuit gap is moved to the above target, it is possible to obtain a tomographic image of the entire or necessary part of the object to be diagnosed, even with a relatively small static magnetic field gap. It is not necessary to make the magnetic circuit large enough to accommodate most of the object to be diagnosed within the uniform magnetic field (as shown in the example, a magnetic circuit of about 1 ton is sufficient, compared to conventional methods using ferrite magnets). The size can be reduced to less than 1/100 compared to other devices.

The magnetic circuit includes a circuit shown in the example, a static magnetic field generating gap formed by a permanent magnet, and a vA connected to a permanent magnet.
Any magnetic circuit may be used as long as it has a static magnetic field generating gap, such as a static magnetic field generating gap formed by a magnetic pole piece,
It may be selected as appropriate depending on the magnitude of the uniform magnetic field required in the required gap, the configuration of the drive device for moving the magnetic circuit in three axial directions, etc.

The means for moving the magnetic circuit in the three-axis directions may be configured to move the magnetic circuit in the three-axis directions of the X-axis, Y-axis, and Z-axis, with the high-precision uniform magnetic field area in the air gap of the magnetic circuit as the center of movement. Any configuration may be used; for example, a voice coil type linear motor that is easy to detect and control the moving position can be used.

In addition, the measuring means for detecting the relative positional relationship between the target of the object to be diagnosed and the center of the three-axis direction of the magnetic circuit is configured to incorporate the placed object to be diagnosed into a certain three-axis coordinate axis system, or Various settings can be made, such as making the pedestal on which the object is placed movable in three axes directions and incorporating it into the three-axis coordinate system. It measures and detects the relative positional relationship in the system or another coordinate system, and the magnetic circuit moving means is adopted to move the high-precision uniform magnetic field of the magnetic circuit to the location where you want to obtain a tomographic image of the object to be diagnosed. Depending on the situation, measuring means and control means that can handle this can be appropriately selected.

Permanent magnet used in the invention The permanent magnet used in the magnetic field generator of the invention can be a ferrite magnet, an alnico magnet, or a rare earth cobalt magnet. As a performance permanent magnet, a permanent magnet of the Fe-B-R system (where R is at least iF among rare earth elements including Y) not only has a large maximum energy product but also a residual magnetic flux density ( Br)
Since this permanent magnet has a temperature coefficient of 0.07%/°C to 0.15%/°C, it can be used in the above NMR-C
By applying it to T, the device can be made smaller and excellent performance can be obtained.Furthermore, the magnetic properties of this permanent magnet have a significantly high maximum energy, especially when used after being cooled to below O'C. The property of being able to obtain products can be effectively used.

The above Fe-B-R permanent magnet is composed of R (where R is at least one kind of rare earth elements including Y, and 8 atomic % to 30
atomic%, B2 atomic% to 28 atomic%, Fe42 atomic% to 9
It is a permanent magnet whose main component is 0 atomic % and whose main phase is a tetragonal phase, and uses resource-rich light rare earths such as +4 and metal as R, and 25MG with El and Fe as its main components.
It is an excellent permanent magnet that exhibits an extremely high energy product of Oa or more.

Disclosure of the Invention Based on the Drawings FIG. 1 is a perspective view showing a magnetic field generating device according to the present invention.

The magnetic circuit (1) has a pair of plate-shaped magnetic pole pieces (3) facing each other at a constant interval on their main surfaces, and a pair of columnar Fe-[3- R-based permanent magnet (21
are connected to form a gap (4) between the plate-shaped magnetic pole pieces (3), and the magnetic fluxes of the Fe BR permanent magnets (2) are in the same direction, and the magnetic flux generated by these is connected to the magnetic pole pieces (3). ), the magnetic field is formed through the air gap (4), and the radius r
The inside of the sphere is strong and has an extremely high degree of uniformity.
A static magnetic field section (5) is obtained.

! The moving device of the 1-air circuit (1) is equipped with a voice coil type linear motor (6
), and the entire magnetic circuit (1) is connected to a linear motor (6
), it is suspended movably in three axes.

The object to be diagnosed, which is placed on a stand movable in three axes, is incorporated into the three-axis coordinate system of the above-mentioned moving device, and the uniform static magnetic field section (5) is moved to a desired target. , operate the linear motor (6). At this time, a measuring device (7) is installed that detects the amount of movement of the mover based on the amount of electrical input to each linear motor (6), and calculates and measures the position of the uniform static magnetic field section (5) based on this detection. and a control device (8) that controls the operation of each linear motor (6) to match the target coordinates according to the signal from the measuring device (sword).
) is provided.

In order to obtain a certain tomographic image, the uniform static magnetic field section is sequentially moved to multiple locations depending on the size of the target location of the object to be diagnosed, and tomographic data at each location is obtained, and For example, in a computer, the measurement data at the plurality of locations is reorganized to form one tomographic image based on the amount of movement in the coordinate system of the magnetic circuit and the data on the target coordinates of the object to be diagnosed.

Incidentally, in the NMR-CT having the configuration shown in Fig. 1, Fe-B-R having a characteristic of a maximum energy product of 35 MGOe
Using permanent magnets, external dimensions: height 500mm x width 138mm
When a magnetic circuit of 0 mm x 350 mm length is assembled, the magnetic field strength at the center of the air gap is 1.5 kQ, and the uniform magnetic field range in the 3-axis directions (300 ppIIILJ, bottom) is a radius of 2.
A uniform static magnetic field section of 5 mm was obtained. The weight of the magnetic circuit is approximately 1 ton.
is on, and a tomographic image of any part of the human body can be easily obtained.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a magnetic field generating device according to the present invention. FIG. 2 is a longitudinal cross-sectional explanatory diagram of a magnetic circuit for another magnetic field generator. 1...Magnetic circuit, 2...Fs-BR system permanent magnet,
3... Magnetic pole piece, 4... Air gap, 5... Uniform static magnetic field part, 6... Linear motor, 1... Measuring device, 8...
·Control device.

Claims (1)

[Claims] 1. A magnetic circuit for a nuclear magnetic resonance tomography apparatus that generates a static magnetic field in the gap using a permanent magnet that forms a gap or a magnetic pole piece connected to the permanent magnet, and a moving means that moves the magnetic circuit in three axial directions. a measuring means for detecting a relative position between a target in a three-axis coordinate system of the object to be diagnosed and a three-axis coordinate system of a moving means whose movement center is a uniform magnetic field area within a static magnetic field;
A magnetic field generating device comprising: a control means that operates the moving means in response to detection by the measuring means to bring a uniform magnetic field to the target.