JPS62183752A - Uniform magnetic field magnet for nuclear magnetic resonancediagnostic apparatus - 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 [Technical field to which the invention pertains] The present invention relates to a uniform magnetic field magnet for a nuclear magnetic resonance diagnostic apparatus (hereinafter abbreviated as NMR-CT), and particularly to a structural arrangement of a uniform magnetic field correction coil.

[Prior art and its problems]

FIG. 1 is a side cross-sectional view of a permanent magnet-type uniform magnetic field magnet showing an example of the prior art, in which a pair of disk-shaped permanent magnets 2A and 2B with diameters are arranged in a yoke 5 formed into a rectangular cylindrical shape. It is fixed parallel and concentrically to the inner wall surface, and has a permanent magnet of 2A.
, 2B are closely arranged with disk-shaped correction poles 6A and 3B whose diameter is equal to that of the permanent magnet, and furthermore, the peripheral edges of the correction poles 3A and 3B each have a triangular cross section protruding toward the side opposite to the permanent magnet. Annular protrusions 4A and 4B are provided to form a pair of magnetic poles iA and 1B, and a pair of magnetic poles 1A and 1B are formed.
It is configured to generate a uniform magnetic field 10 with a magnetic field strength of 0.05 to 0.3 T and a uniformity of the magnetic field strength of several QPPM or less in an area with a diameter of about 400 m + n at the center of the gap between the iBs. ing.

In the uniform magnetic field magnet configured as described above, disturbances in the uniform magnetic field caused by locally different magnetization strengths of the permanent magnets 2A and 2B are equalized by the correction pole made of ferromagnetic material, and the magnetic pole The leakage magnetic field leaking to the sides of 1A and 1B is suppressed by the annular protrusions 4A and 4B, and the uniformity of the uniform magnetic field 10 can be greatly improved. However, in order to increase the uniformity of the magnetic field to about 110 PPM, the diameter of the magnetic poles 1A and iB becomes very large.
A pair of correction coils 6A and 6B for fine adjustment of the uniform magnetic field are installed between them.
A structure is known in which the uniformity of the magnetic field is increased while suppressing an increase in diameter by providing a magnetic field. However, in the conventional device, since the pair of correction coils 6 are disposed in a protruding position in the gap between the annular protrusions 4A and 4B, the gap length required to bring the human body into the uniform magnetic field 10 is corrected. This is restricted by the coils 6A and 6B, and as a result, the distance H between the pair of magnets 2A and 2B inevitably increases. In order to maintain the uniformity of the uniform magnetic field 10 at a high level of about 110PP, it is necessary to make the diameter of each magnetic pole 1B more than twice the distance H between the magnets, and by providing the correction coil 6. As the distance H between the magnets increases, the magnetic pole diameter increases, resulting in an increase in the total amount of magnetic flux generated by the permanent magnets 2A and 2B, an increase in the amount of expensive permanent magnet material, and an increase in the magnetic path length of the yoke 5. , an increase in the total amount of generated magnetic flux causes a vicious cycle such as an increase in the cross-sectional area of the yoke 5, and as a result, there is a drawback that the magnetic field magnet becomes larger and heavier, and there is a need to improve this problem. .

[Purpose of the invention]

The present invention has been made in view of the above-mentioned situation, and eliminates the increase in the distance between the magnets due to the arrangement of correction coils, and therefore has a high degree of uniformity of the magnetic field, and is suitable for use in small, small, and inexpensive nuclear magnetic resonance diagnostic equipment. The purpose is to provide a uniform magnetic field magnet.

[Key points of the invention]

The object of the present invention has been achieved by forming a correction coil to a size that allows it to be placed in a recess of a correction pole surrounded by an annular projection, and using the recess as an installation space for the correction coil. It is something.

[Embodiments of the invention]

The present invention will be explained below based on examples.

FIG. 1 is a schematic side sectional view showing an embodiment of the present invention, and FIG. 2 is a horizontal sectional view taken along the line A--A in FIG. In the figure, a pair of magnetic poles 1A and 1B consisting of disk-shaped permanent magnets 2A and 2B and correction poles 3A and 3B are fixed concentrically and parallel to the inner wall surface of a rectangular yoke 5. , disk-shaped correction coils 16A, 16B are disposed in the recesses 7 of the correction poles 3A, 3A, 4B surrounded by annular protrusions 4A, 4B each having a triangular cross section. By forming the outer diameter smaller than the diameter of the magnetic poles IA and 1B, the recess 7 is
A, 16B can be used as the installation space, and the correction coils 16A, 16B can be used as the installation space for the annular projections 4A, 4.
It is possible to avoid protruding into the gap between B. therefore,
Since the gap between the annular protrusions can be set to a length necessary for carrying in a human body, an increase in the distance H between the magnets due to the provision of the correction coil can be completely eliminated.

In the uniform magnetic field magnet configured as described above, the uniformity of the uniform magnetic field 10 can be finely adjusted by controlling the current flowing through the correction coil, thereby increasing the uniformity of the magnetic field and increasing the distance between the magnets. H as magnetic pole 1A, 1B
As the distance H between the magnets increases, the magnetic pole area and the amount of permanent magnet material used can be set to the optimum size determined by the following.

It is possible to eliminate all increasing factors such as the total amount of magnetic flux generated, the cross-sectional area of the iron section, and the magnetic path length of the iron section.

FIG. 3 is an explanatory diagram of the arrangement of a correction coil showing a different embodiment of the present invention, and shows a portion corresponding to FIG. 2. In the figure, the correction coil is composed of four divided coils 26, 27, 28, and 29 in an oblong shape, and the four coils are arranged in a parallel cross shape in the recess of the magnetic pole 1B as described above. In contrast to the embodiment, four correction coils 2 are used.
6, 27, 28, and 29, it is possible to control the uniformity of the magnetic field of the uniform magnetic field 10 more precisely, but it is also possible to control the shape of the correction coil. It goes without saying that the dimensions, number, etc. should be selected in consideration of the non-uniformity of the magnetic field generated by the magnetic poles 1A and iB, and conditions suitable for correction thereof should be selected.

In addition, in each of the above-mentioned embodiments, the force ζ electromagnet type uniformity magnet described with respect to an example of application to a permanent magnet type uniform magnetic field magnet.
Application to magnetic field magnets can also be easily implemented based on the above explanation.

〔Effect of the invention〕

As described above, the present invention is configured such that the correction coil is formed in a size that can be accommodated in the recess of the correction pole surrounded by the annular protrusion, and the recess is used as the installation space for the correction coil. As a result, the problem of increasing the distance between the magnets due to the correction coil protruding into the gap between the annular protrusions in the prior art is avoided, and the magnetic pole area and total magnetic flux that occur with the increase in the distance between the magnets can be avoided. This prevents an increase in the amount of permanent magnet material used, making it possible to form a pair of magnetic poles in a small, lightweight, and inexpensive manner.In addition, an increase in the distance between the magnets reduces the cross-sectional area of the yoke and the length of the magnetic path. The influence on the increase in the magnetic field is also eliminated, so that it is possible to provide a uniform magnetic field magnet for a nuclear magnetic resonance diagnostic apparatus that is smaller and lighter in weight. In addition, the correction coil improves the uniformity of the magnetic field strength, and its small size and weight make it easier to transport and bring in to the installation site, as well as save space at the installation site. I can make a contribution.

[Brief explanation of drawings]

FIG. 1 is a schematic side sectional view showing an embodiment of the present invention, FIG. 2 is a horizontal sectional view taken along the line A-A in FIG. FIG. 4 is a schematic side sectional view of a conventional permanent magnet type uniform magnetic field magnet. iA, 1B...Magnetic pole, 2A, 2B...Permanent magnet, 6
A, 5B... Correction pole, 4A, 4B... Annular projection, 5
...Yoke, 6.6A, 6B...Correction coil, 7.
...Recess, 16.16A, 16B...Correction coil, 1
0... Uniform magnetic field, 26, 27, 28, 29... Correction coil (minute j... ・-l...,
Figure 2 Figure 3 A +-1 Figure 4

Claims (1)

[Claims] 1) A pair of disc-shaped magnets supported by a yoke in parallel and concentrically with each other across a uniform magnetic field space, and a counter-magnet side arranged closely on the surface of each magnet and on the peripheral edge of the disc-shaped part. and a correction pole for a uniform magnetic field having an annular protrusion projecting therein, characterized in that a correction coil for adjusting the uniform magnetic field is disposed in each recess of the correction pole surrounded by the annular protrusion. Uniform magnetic field magnet for nuclear magnetic resonance diagnostic equipment.