CN111933380A - Dipolar permanent magnet for magnetic resonance - Google Patents

Abstract

The utility model relates to a two-pole permanent magnet magnet for magnetic resonance. The shape is a polygonal prism or a cylinder. The permanent magnet material is distributed on the sides of the prism or the cylinder to form a hollow prism or a hollow cylinder. The magnetization direction of the permanent magnet material is the same, which is along the edge direction of the prism or the axial direction of the cylinder. Magnetically conductive steel yokes are respectively located on the upper and lower end faces of the prism or cylinder, and cover the end faces of the hollow cylinder made of permanent magnet material. The area enclosed by the permanent magnet material on the side of the cylinder or prism and the two yokes at the end is the magnet air gap. The side walls of the cylinder or prism may have one or more openings to the magnet air gap. There are prismatic or cylindrical bosses on the side of the end two yokes facing the air gap of the magnet. There is an annular protrusion on the end face of the boss facing the air gap of the magnet, the outer side of the annular protrusion coincides with the outer side of the prismatic or cylindrical boss, and the side of the magnet has an opening. The present invention has a lighter weight under the same imaging space requirement. It can meet the requirements of light weight and mobility for specialized magnetic resonance imaging applications.

Description

A two-pole permanent magnet for magnetic resonance

technical field

The present invention relates to a permanent magnet.

Background technique

Magnetic resonance imaging equipment can be used to scan various parts of the human body, without ionizing radiation damage to the human body, and the soft tissue structure is clearly displayed. The magnet is a core component of magnetic resonance imaging equipment. Magnets are used to generate the main magnetic field necessary for magnetic resonance imaging. Permanent magnets are widely used in nuclear magnetic resonance systems and nuclear magnetic resonance imaging systems due to their advantages of energy saving, small stray field and low cost. With the improvement of medical level, professional, lightweight and movable requirements are put forward for the MRI system.

A general conventional permanent magnet is shown in Figures 1 and 2. After the permanent magnet material 4a is attached to the parallel and symmetrical pole plates 2, it is connected to the yoke 1 of a frame or C-shaped structure that provides a closed peripheral magnetic circuit. The space between the two pole plates 2 is the working air gap 3, the arrow in the permanent magnet material 4a represents the magnetization direction of the magnet, and the arrow in the air gap represents the generated magnetic field direction in the working area. In addition, in the prior art, there are four-column structure, two-column structure and the like according to different structural forms of the yoke. For the above-mentioned magnet device for MRI, refer to IEEE TRANSACTIONS OF APPLIEDSUPERCONDUCTIVITY, VOL.14, NO.2, JUNE 2004, or the contents of Chapter 1, Section 1.3.1 of MAGNETICRESONANCEIMAGING, 2nd Edition, written by M.T.Vlaardingerbroek and J.A.Den Boer. CN2404130Y discloses a magnet device for magnetic resonance imaging system; CN2430698Y discloses a C-type magnetic resonance imaging permanent magnet without plugging magnetic poles; CN1371000A discloses a fully open magnetic resonance imaging apparatus; CN1400473A discloses a A permanent magnet device for a magnetic resonance imaging system; CN2542225Y discloses a two-column open C-type permanent magnet magnetic resonance magnet; CN1491613A discloses a magnetic component assembly method for a magnetic field generating device for magnetic resonance imaging: CN1588582A Disclosed is a main magnet of a sheet-shaped magnetic field fully open magnetic resonance imaging device; CN1877757A discloses a permanent magnet, an MRI magnet device including the magnet, and a manufacturing method thereof.

The above-mentioned magnet has the advantages of simple structure, convenient assembly and high magnetic steel efficiency. The disadvantage is that a large number of soft magnetic yokes are used to close the entire magnetic circuit, and the design of the soft magnetic material pole head makes the weight of the entire magnet remain high, which cannot meet the requirements of lightweight and movable.

SUMMARY OF THE INVENTION

The object of the present invention is to propose a dipole permanent magnet for magnetic resonance imaging equipment. Compared with conventional magnetic resonance equipment or nuclear magnetic resonance imaging equipment, the present invention has a lighter weight with the same imaging space requirement. Especially suitable for specialist mobile MRI device. The permanent magnet of the present invention can be applied to, but not limited to, magnetic fields for nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) applications.

The shape of the two-pole permanent magnet of the present invention is a polygonal prism or a cylinder, and the permanent magnet material is distributed on the sides of the prism or the cylinder to form a hollow prism or a hollow cylinder. The magnetization direction of the permanent magnet material is the same, which is along the edge direction of the prism or the axial direction of the cylinder. The yoke made of magnetically permeable low carbon steel material is located on the upper and lower bottoms of the prism or cylinder, and covers the end face of the hollow prism or hollow cylinder made of permanent magnet material. The area enclosed by the permanent magnet material distributed on the side of the prism or cylinder and the upper and lower yokes distributed on the end of the prism or cylinder is the magnet air gap. The side walls of the cylinder or prism have one or more openings leading to the air gap. There are prismatic or cylindrical bosses on the sides of the two yokes on the upper and lower ends of the permanent magnet facing the air gap of the magnets. There is an annular protrusion along the outer edge of the end face of the prismatic or circular boss.

The permanent magnet material on the side of the two-pole permanent magnet can be partially removed to form an opening. One of the functions of the opening is to form a passage to the imaging space; the second function of the opening is to adjust the intensity of the magnetic field. Either the entire permanent magnet material from the upper yoke to the lower yoke can be removed at the selected place, or the permanent magnet material can be partially removed symmetrically at the selected place with the central cross section of the magnet as the symmetry plane.

The manufacturing method of the two-pole permanent magnet of the present invention is as follows: firstly, the two yokes and the prismatic or circular bosses and annular projections on the yokes are processed and formed by a general machining method; the two yokes are placed facing each other. , connect the upper and lower yokes with non-magnetic material columns to ensure the placement space of the permanent magnetic strips. The permanent magnet raw materials are bonded and each permanent magnet strip is cut into shape. Then, the processed permanent magnetic strips are inserted into the space between the upper and lower yokes at intervals, and fixed by mechanical methods. Remove the non-magnetic material column connecting the upper and lower yokes, insert the remaining permanent magnetic strips in the remaining space, and fix them mechanically.

The dipole permanent magnet of the present invention has a lighter weight when the imaging space requirements are the same. The weight of the magnet of the present invention is greatly reduced because part of the yoke structure is omitted. Similarly, a 0.2 Tesla magnetic resonance magnet with a DSV of 200 mm, a conventional C-shaped or frame structure magnet weighs 800 kg, and the magnet of the present invention weighs only 600 kg, which can reduce the weight by 25%.

The magnet of the present invention can meet the requirements of light weight and mobility for professional magnetic resonance imaging applications.

Description of drawings

Figure 1 and Figure 2 show the structure of a traditional NMR magnet, in the figure, 1 yoke, 2 pole plates, 3 air gaps, 4a permanent magnet materials;

Figure 3a, Figure 3b, Figure 3c, Figure 3d are schematic diagrams of the opening mode of the magnet structure; wherein, Figure 3a is a polygonal prism structure, and the permanent magnet material at the opening position is all removed; Figure 3b is a cylindrical structure, and the permanent magnet material at the opening position is all removed. Figure 3c is a polygonal prism structure, and the permanent magnet material at the opening position is partially removed; Figure 3d is a cylindrical structure, and the permanent magnet material at the opening position is partially removed;

Figure 4a, Figure 4b, Figure 4c, Figure 4d are schematic diagrams of the installation of the two-pole permanent magnet of the present invention, Figure 4a is a non-magnetic material column connecting the upper and lower yokes; Figure 4b is a permanent magnetic strip inserted between the upper and lower yokes at intervals Figure 4c is to remove the non-magnetic material column connecting the upper and lower yokes; Figure 4d is to insert the remaining permanent magnetic strips in the remaining space; in the figure, 8 non-magnetic material columns, 9 permanent magnetic strips.

Fig. 5, Fig. 6 are the longitudinal cross-sectional views of the bipolar permanent magnet of the present invention, wherein, Fig. 5 is the bipolar permanent magnet that the shape is polygonal cylinder; Fig. 6 is the bipolar permanent magnet that the shape is polygonal prism; Fig. Among them, 4 permanent magnet materials, 5 lower yokes, 5' upper yokes, 6 prismatic or cylindrical bosses, and 7 annular projections.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

The shape of the two-pole permanent magnet of the present invention is a polygonal prism or a cylinder. As shown in FIGS. 5 and 6 , the permanent magnet material 4 is distributed on the side of the prism or cylinder to form a hollow prism or hollow cylinder. The magnetization direction of the permanent magnet material is the same, which is along the edge direction of the prism or along the axial direction of the cylinder. The two yokes 5' and 5 made of magnetically permeable low carbon steel material are located at the upper and lower bottoms of the prism or cylinder respectively, and cover the end face of the hollow prism or hollow cylinder formed by the permanent magnet material. The area enclosed by the permanent magnet material distributed on the side of the prism or cylinder and the two yokes 5' and 5 distributed on the end of the prism or cylinder is the magnet air gap. The side walls of the cylinder or prism have one or more openings leading to the air gap. There are prismatic or cylindrical bosses 6 on the side of the two yokes 5' and 5 at the upper and lower ends of the permanent magnet facing the air gap of the magnet. An annular protrusion 7 is distributed along the outer edge on the end face of the prismatic or cylindrical boss 6 . The outer surface of the annular protrusion 7 coincides with the outer surface of the prismatic or cylindrical protrusion 6, and the inner surface of the annular protrusion 7 is cylindrical.

The permanent magnet material on the sides of the permanent magnet can be partially removed, ie openings are made in the magnet, to form access to the imaging volume. It is possible to remove all the permanent magnet material from the upper yoke to the lower yoke, as shown in Figure 3a and Figure 3b, or to remove part of the permanent magnet material symmetrically at the center of the magnet, as shown in Figure 3c and Figure 3d shown.

The manufacturing method of the embodiment of the present invention is as follows: first, two yokes 5 and 5 ′, and the prismatic or cylindrical bosses 6 on the yokes 5 and the annular bosses 7 on the periphery of the bosses are processed and formed by a general machining method. , the yoke material is Q235. The two yokes 5' and 5 are placed facing each other, and the upper and lower two yokes 5' and 5 are connected with a non-magnetic material column 8 to ensure the distance between the upper and lower two yokes 5' and 5. The non-magnetic material can be SUS304 austenitic stainless steel. Each permanent magnetic strip 9 is processed and formed. In this embodiment, NdFeB material is used, and the magnetization direction is the height direction of the prism. Insert the manufactured permanent magnetic strips 9 into corresponding positions at intervals to ensure consistent magnetization directions, and fix them mechanically. After that, the non-magnetic material column 8 connecting the upper and lower yokes 5' and 5 is removed. Then insert the remaining permanent magnetic strips 9 in the remaining spaced positions, leaving open positions, and fix them mechanically. That is, the production of the magnet is completed.

Claims (3)

1. A dipolar permanent magnet for magnetic resonance is characterized in that: the permanent magnet body is in the shape of a polygonal prism or a cylinder, and the permanent magnet materials (4) are distributed on the side surface of the prism or the cylinder to form a hollow prism or a hollow cylinder; the magnetization directions of the permanent magnetic materials (4) are the same and are along the edge direction of the prism or the axial direction of the cylinder; two yokes (5) made of magnetic conductive low-carbon steel materials are respectively positioned at the upper bottom and the lower bottom of the prism or the cylinder and cover the end surfaces of the hollow prism or the hollow cylinder formed by the permanent magnet materials (4); a region surrounded by the permanent magnet material (4) distributed on the side surface of the prism or the cylinder and the two yokes (5, 5') distributed at the end parts of the prism or the cylinder is a magnet air gap; the side wall of the cylinder or prism has one or more openings to the air gap of the magnet.

2. The permanent magnet of claim 1, wherein: prismatic or cylindrical bosses (6) are arranged on one sides, facing the air gap of the permanent magnet, of the two yokes (5) at the upper end part and the lower end part of the permanent magnet; the upper edge of the end face of the prismatic or cylindrical boss (6) is provided with an annular bulge (7); the outer side surface of the annular bulge (7) is superposed with the outer side surface of the prismatic or cylindrical bulge (6), and the inner side surface of the annular bulge (7) is cylindrical.

3. The permanent magnet according to claim 1 or 2, wherein: firstly, processing and molding two yokes (5, 5') and prismatic or cylindrical bosses (6) and annular bulges (7) at the peripheries of the bosses by a general machining method; the two yokes (5, 5 ') are oppositely arranged, and the non-magnetic material upright post (8) is used for connecting the upper yoke (5) and the lower yoke (5, 5 ') so as to ensure the distance between the upper yoke (5) and the lower yoke (5, 5 '); processing and molding the permanent magnetic stripe (9); the permanent magnetic stripes (9) are inserted into corresponding positions at intervals to ensure that the magnetization directions are consistent and are fixed by a mechanical method; and then removing the non-magnetic material upright posts (8) connecting the upper yoke iron and the lower yoke iron (5), inserting the residual permanent magnetic strips (9) into the rest spacing positions, reserving the opening positions, and fixing by a mechanical method.

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