Dumbbell-shaped magnet structure and magnetic resonance imaging system

Abstract

The invention discloses a dumbbell-shaped magnet structure and a magnetic resonance imaging system, and relates to the technical field of magnets, a first end magnet comprises at least one first magnet assembly, and the first magnet assembly comprises at least two layers of first annular magnets which are sleeved in sequence; the middle magnet comprises at least one second magnet assembly, each second magnet assembly comprises at least one layer of second annular magnet, and the multiple layers of second annular magnets of the second magnet assemblies are sequentially arranged in a sleeving mode; the second end magnet comprises at least one third magnet assembly, and each third magnet assembly comprises at least two layers of third annular magnets which are sequentially arranged in a sleeved mode. The number of layers of the first annular magnets of the first magnet assemblies is larger than that of the second annular magnets of the second magnet assemblies, and the number of layers of the third annular magnets of the third magnet assemblies is larger than that of the second annular magnets of the second magnet assemblies. And the magnet structure is dumbbell-shaped. According to the invention, the uniformity of magnetic field distribution can be improved, and the imaging space requirement of a magnetic resonance imaging system can be better met.

Description

Technical Field

[0001] The invention relates to the technical field of magnets, in particular to a dumbbell-shaped magnet structure and a magnetic resonance imaging system. Background Art

[0002] Magnetic resonance imaging (MRI) has the advantages of zero radiation exposure and good soft tissue imaging contrast, and is widely used in the observation of the nervous system, musculoskeletal system, and tumors. As the most basic component of the MRI system, the performance of the main magnet will directly affect the quality of the MRI image.

[0003] The existing main magnets are mainly divided into two types: superconducting electromagnetic type and permanent magnet type. Superconducting electromagnetic type main magnets are easier to achieve high field strength, thereby improving imaging quality, but superconducting electromagnetic type main magnets are expensive and need to be regularly replenished with scarce liquid helium, which has high maintenance costs, seriously restricting the popularization of magnetic resonance. In comparison, permanent magnet type main magnets are generally made of rare earth permanent magnet materials, which are low in cost and easy to popularize. In addition, permanent magnet type main magnets also have the advantages of low energy consumption and low maintenance costs; but the magnetic field uniformity of permanent magnet type main magnets is poor, and magnetic resonance imaging systems based on permanent magnet type main magnets usually have poor imaging quality. Therefore, research on high-uniformity permanent magnet type main magnets can reduce the cost of magnetic resonance imaging systems, increase the total number of magnetic resonance deployments in society, thereby increasing the overall throughput of magnetic resonance detection and facilitating the popularization of magnetic resonance.

[0004] Among them, the Halbach Array magnet structure is generally composed of multiple magnetic blocks made of permanent magnetic materials according to a specially designed spatial distribution. It can use the arrangement of special magnetic units to enhance the field strength in a unit direction. The traditional dumbbell-shaped magnet structure is cylindrical. At the openings at both ends of the cylindrical dumbbell-shaped magnet structure, there is a lack of adjacent magnets to support the concentration of the magnetic field. The magnetic field cannot be completely guided and concentrated like in the middle of the dumbbell-shaped magnet structure, resulting in the dispersion of the magnetic field at the open end and the interruption of the magnetic flux path, which in turn causes part of the magnetic field to be unable to be effectively shielded, and the magnetic field lines will escape at the ends, forming leakage magnetic field. Summary of the invention

[0005] The purpose of the present invention is to provide a dumbbell-shaped magnet structure and a magnetic resonance imaging system to solve the problems existing in the prior art, reduce magnetic leakage, improve the uniformity of magnetic field distribution, and better meet the spatial requirements of magnetic resonance imaging systems.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] The present invention provides a dumbbell-shaped magnet structure, comprising a magnet structure, wherein the magnet structure comprises a first end magnet, a middle magnet and a second end magnet arranged in sequence, wherein:

[0008] The first end magnet includes at least one first magnet assembly, and each of the first magnet assemblies includes at least two layers of first annular magnets that are sequentially arranged;

[0009] The middle magnet includes at least one second magnet assembly, each of the second magnet assemblies includes at least one layer of second annular magnets, and the multiple layers of the second annular magnets of each of the second magnet assemblies are sequentially nested;

[0010] The second end magnet includes at least one third magnet assembly, and each of the third magnet assemblies includes at least two layers of third annular magnets which are arranged in sequence; the first annular magnet, the second annular magnet and the third annular magnet are all annular Halbach array magnets; the number of layers of the first annular magnets of each of the first magnet assemblies is more than the number of layers of the second annular magnets of each of the second magnet assemblies, the plane perpendicular to the center line of the first magnet assembly is the first plane, and the projection of the outer ring edge of each of the first magnet assemblies on the first plane is located outside the projection of the outer ring edge of each of the second magnet assemblies on the first plane; the number of layers of the third annular magnets of each of the third magnet assemblies is more than the number of layers of the second annular magnets of each of the second magnet assemblies, and the projection of the outer ring edge of each of the third magnet assemblies on the first plane is located outside the projection of the outer ring edge of each of the second magnet assemblies on the first plane.

[0011] Preferably, center lines of all the first annular magnets, all the second annular magnets and all the third annular magnets are collinear.

[0012] Preferably, the plane perpendicular to the center line of the first magnet assembly is the first plane, and the projection of the first annular magnets of the outermost circle of each of the first magnet assemblies on the first plane is located outside the projection of each of the second magnet assemblies on the first plane; the projection of the third annular magnets of the outermost circle of each of the third magnet assemblies on the first plane is located outside the projection of each of the second magnet assemblies on the first plane.

[0013] Preferably, the projection of the first annular magnet of the innermost circle of each of the first magnet assemblies on the first plane is located on the inner side of the projection of each of the second magnet assemblies on the first plane; the projection of the third annular magnet of the innermost circle of each of the third magnet assemblies on the first plane is located on the inner side of the projection of each of the second magnet assemblies on the first plane.

[0014] Preferably, there are multiple second magnet assemblies.

[0015] Preferably, all the first annular magnets of each first magnet assembly have the same length along the center line of the first magnet assembly, all the second annular magnets of each second magnet assembly have the same length along the center line of the second magnet assembly, and all the third annular magnets of each third magnet assembly have the same length along the center line of the third magnet assembly.

[0016] Preferably, the magnet structure is a symmetrical part which is symmetrical in the length direction of the magnet structure.

[0017] Preferably, the spacing between the first end magnet and the middle magnet along the center line of the first end magnet is a first spacing, the spacing between the second end magnet and the middle magnet along the center line of the first end magnet is a second spacing, the spacing between two adjacent first magnet assemblies along the center line of the first end magnet is a third spacing, the spacing between two adjacent second magnet assemblies along the center line of the first end magnet is a fourth spacing, the spacing between two adjacent third magnet assemblies along the center line of the first end magnet is a fifth spacing, and the first spacing, the second spacing, the third spacing, the fourth spacing and the fifth spacing are the same.

[0018] Preferably, the first annular magnets of each of the first magnet assemblies are four layers, the second annular magnets of each of the second magnet assemblies are two layers, and the third annular magnets of each of the third magnet assemblies are four layers.

[0019] The present invention provides a magnetic resonance imaging system, comprising a main magnet, wherein the main magnet is the dumbbell-shaped magnet structure.

[0020] Compared with the prior art, the present invention has achieved the following technical effects:

[0021] The present invention provides a dumbbell-shaped magnet structure and a magnetic resonance imaging system. The first end magnet comprises at least one first magnet assembly, each of which comprises at least two layers of first annular magnets which are sequentially sleeved; the middle magnet comprises at least one second magnet assembly, each of which comprises at least one layer of second annular magnets, and the multiple layers of second annular magnets of each second magnet assembly are sequentially sleeved; the second end magnet comprises at least one third magnet assembly, each of which comprises at least two layers of third annular magnets which are sequentially sleeved; the first annular magnet, the second annular magnet and the third annular magnet are all annular Haier Baker array magnet; the number of layers of the first annular magnets of each first magnet assembly is greater than the number of layers of the second annular magnets of each second magnet assembly, the plane perpendicular to the center line of the first magnet assembly is the first plane, and the projection of the outer ring edge of each first magnet assembly on the first plane is located outside the projection of the outer ring edge of each second magnet assembly on the first plane; the number of layers of the third annular magnets of each third magnet assembly is greater than the number of layers of the second annular magnets of each second magnet assembly, and the projection of the outer ring edge of each third magnet assembly on the first plane is located outside the projection of the outer ring edge of each second magnet assembly on the first plane.

[0022] Among them, the middle magnet is used to generate a high-intensity magnetic field; the first end magnet and the second end magnet are used to reduce leakage magnetic field and improve the uniformity of the magnetic field. The principle is: since the number of layers of the first annular magnet of each first magnet assembly is more than the number of layers of the second annular magnet of each second magnet assembly, and the number of layers of the third annular magnet of each third magnet assembly is more than the number of layers of the second annular magnet of each second magnet assembly, it is equivalent to adding at least one layer of the first annular magnet and at least one layer of the third annular magnet at both ends of the cylindrical Halbach array magnet. The annular magnets added at both ends can help guide the magnetic flux, so that a closed magnetic flux path is formed at the openings at both ends of the dumbbell-shaped magnet structure, thereby reducing the leakage of the magnetic field lines and helping to keep the magnetic field concentrated inside the coil or magnet; the annular magnets added at both ends can compensate for the end effect and reduce the weakening of the magnetic field strength due to the openings at both ends of the dumbbell-shaped magnet structure. By applying an additional magnetic field at both ends of the dumbbell-shaped magnet structure, the leakage magnetic field can be offset, so that the inside of the dumbbell-shaped magnet structure and the working area maintain a more uniform magnetic field distribution. At the same time, the magnet structure is dumbbell-shaped, that is, a compensating magnet is added to the outside of the outer end of the magnet structure. A compensating magnet of greater thickness can be added to the outside as needed to reduce the addition of too many compensating magnets in the inner cavity of the magnet structure, or to avoid setting compensating magnets in the inner cavity of the magnet structure. When the size of the middle magnet is constant, the inner cavity size of the dumbbell-shaped magnet structure is larger, which can better perform magnetic resonance imaging system imaging through the magnetic field in the inner cavity of the magnet structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A front view of the dumbbell-shaped magnet structure provided in Example 1;

[0025] Figure 2 for Figure 1 Sectional view of AA in the middle;

[0026] Figure 3 for Figure 1 Cross-sectional view of the middle BB;

[0027] Figure 4 A left side view of the first end magnet provided in Example 1;

[0028] Figure 5 A left side view of the middle magnet provided in Example 1;

[0029] Figure 6 A left side view of the second end magnet provided in Example 1;

[0030] In the figure: 100, dumbbell-shaped magnet structure; 1, first magnet assembly; 101, first annular magnet; 2, second magnet assembly; 201, second annular magnet; 3, third magnet assembly; 301, third annular magnet; 4, magnetic block. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The purpose of the present invention is to provide a dumbbell-shaped magnet structure and a magnetic resonance imaging system to solve the problems existing in the prior art, reduce magnetic leakage, improve the uniformity of magnetic field distribution, and better meet the spatial requirements of magnetic resonance imaging systems.

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] Example 1

[0035] like Figures 1 to 6As shown, this embodiment provides a dumbbell-shaped magnet structure 100, including a magnet structure, the magnet structure includes a first end magnet, a middle magnet and a second end magnet arranged in sequence, wherein: the first end magnet includes at least one first magnet assembly 1, each first magnet assembly 1 includes at least two layers of first annular magnets 101 arranged in sequence; the middle magnet includes at least one second magnet assembly 2, each second magnet assembly 2 includes at least one layer of second annular magnet 201, and the multiple layers of second annular magnets 201 of each second magnet assembly 2 are arranged in sequence; the second end magnet includes at least one third magnet assembly 3, each third magnet assembly 3 includes at least two layers of third annular magnets 301 arranged in sequence; the first annular magnet 101, the second annular magnet 201 and the third end magnet 101 are arranged in sequence. The three annular magnets 301 are all annular Halbach array magnets; the number of layers of the first annular magnets 101 of each first magnet assembly 1 is greater than the number of layers of the second annular magnets 201 of each second magnet assembly 2, the plane perpendicular to the center line of the first magnet assembly 1 is the first plane, and the projection of the outer ring edge of each first magnet assembly 1 on the first plane is located outside the projection of the outer ring edge of each second magnet assembly 2 on the first plane; the number of layers of the third annular magnets 301 of each third magnet assembly 3 is greater than the number of layers of the second annular magnets 201 of each second magnet assembly 2, and the projection of the outer ring edge of each third magnet assembly 3 on the first plane is located outside the projection of the outer ring edge of each second magnet assembly 2 on the first plane, that is, the magnet structure is in a dumbbell shape with a small middle and large ends. Among them, the middle magnet is used to generate a high-intensity magnetic field; the first end magnet and the second end magnet are used to reduce leakage magnetic field and improve the uniformity of the magnetic field. The principle is: since the number of layers of the first annular magnet 101 of each first magnet assembly 1 is more than the number of layers of the second annular magnet 201 of each second magnet assembly 2, and the number of layers of the third annular magnet 301 of each third magnet assembly 3 is more than the number of layers of the second annular magnet 201 of each second magnet assembly 2, it is equivalent to adding at least one layer of the first annular magnet 101 and at least one layer of the third annular magnet 301 at both ends of the cylindrical Halbach array magnet, respectively. The annular magnets added at both ends can help guide the magnetic flux, so that a closed magnetic flux path is formed at the openings at both ends of the magnet structure, thereby reducing the leakage of the magnetic field lines and helping to keep the magnetic field concentrated inside the coil or magnet; the annular magnets added at both ends can compensate for the end effect and reduce the weakening of the magnetic field strength due to the openings at both ends of the magnet structure. By applying an additional magnetic field at both ends of the magnet structure, the leakage magnetic field can be offset, so that the magnetic field distribution inside the magnet structure and the working area can be more uniform.At the same time, the magnet structure is dumbbell-shaped, that is, a compensating magnet is added to the outside of the outer end of the magnet structure, and a compensating magnet of greater thickness can be added to the outside as needed to reduce the addition of too many compensating magnets in the inner cavity of the magnet structure, or avoid setting compensating magnets in the inner cavity of the magnet structure. When the size of the middle magnet is constant, the inner cavity size of the dumbbell-shaped magnet structure 100 is larger, which can better perform magnetic resonance imaging system imaging through the magnetic field in the inner cavity of the magnet structure.

[0036] In this embodiment, the center lines of all the first annular magnets 101 , all the second annular magnets 201 , and all the third annular magnets 301 are collinear.

[0037] In this embodiment, the plane perpendicular to the center line of the first magnet assembly 1 is the first plane, and the projection of the first annular magnet 101 of the outermost circle of each first magnet assembly 1 on the first plane is located outside the projection of each second magnet assembly 2 on the first plane; the projection of the third annular magnet 301 of the outermost circle of each third magnet assembly 3 on the first plane is located outside the projection of each second magnet assembly 2 on the first plane.

[0038] In this embodiment, the projection of the first annular magnet 101 of the innermost circle of each first magnet assembly 1 on the first plane is located inside the projection of each second magnet assembly 2 on the first plane; the projection of the third annular magnet 301 of the innermost circle of each third magnet assembly 3 on the first plane is located inside the projection of each second magnet assembly 2 on the first plane. It should be noted that in order to ensure the size of the inner cavity of the magnet structure, it is not easy to add too many compensating magnets to the inner cavity of the magnet structure. As a feasible implementation method, the first annular magnet 101 and the third annular magnet 301 protruding from the inner wall of the middle magnet are both one layer.

[0039] In this embodiment, there are multiple second magnet assemblies 2.

[0040] In this embodiment, all the first annular magnets 101 of each first magnet assembly 1 have the same length along the center line of the first magnet assembly 1, all the second annular magnets 201 of each second magnet assembly 2 have the same length along the center line of the second magnet assembly 2, and all the third annular magnets 301 of each third magnet assembly 3 have the same length along the center line of the third magnet assembly 3.

[0041] In this embodiment, the magnet structure is a symmetrical part that is symmetrical in the length direction of the magnet structure, that is, the cross section located in the middle of the length direction of the magnet structure is the symmetry plane of the magnet structure, which can ensure the uniformity of the magnetic field.

[0042] As a feasible implementation manner, the spacing between the first end magnet and the middle magnet along the center line of the first end magnet is a first spacing, the spacing between the second end magnet and the middle magnet along the center line of the first end magnet is a second spacing, the spacing between two adjacent first magnet assemblies 1 along the center line of the first end magnet is a third spacing, the spacing between two adjacent second magnet assemblies 2 along the center line of the first end magnet is a fourth spacing, the spacing between two adjacent third magnet assemblies 3 along the center line of the first end magnet is a fifth spacing, and the first spacing, the second spacing, the third spacing, the fourth spacing and the fifth spacing are the same.

[0043] In this embodiment, the first annular magnet 101 of each first magnet assembly 1 is four layers, the second annular magnet 201 of each second magnet assembly 2 is two layers, and the third annular magnet 301 of each third magnet assembly 3 is four layers. As a preferred embodiment, there are two first magnet assemblies 1 and three third magnet assemblies 3, and four second magnet assemblies 2.

[0044] In this embodiment, each first annular magnet 101, each second annular magnet 201 and each third annular magnet 301 are formed by combining multiple magnetic blocks 4 of the same shape but different magnetization directions. The first annular magnet 101, the second annular magnet 201 and the third annular magnet 301 are all multi-layered, which is beneficial to reducing the volume of a single magnetic block 4 and facilitating processing and manufacturing; and when the annular magnet is formed by combining smaller magnetic blocks 4, the space utilization rate can be increased. Specifically, Figures 2 to 6 As shown, the cross section of the magnetic block 4 is rectangular, and the number of the magnetic blocks 4 of the annular magnet gradually increases from the inner circle to the outer circle, thereby increasing the space utilization.

[0045] Example 2

[0046] This embodiment provides a magnetic resonance imaging system, including a main magnet, wherein the main magnet is the dumbbell-shaped magnet structure 100 in Embodiment 1.

[0047] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A dumbbell-shaped magnet structure, comprising a magnet structure, characterized in that: The magnet structure comprises a first end magnet, a middle magnet and a second end magnet arranged in sequence, wherein: The first end magnet includes at least one first magnet assembly, and each of the first magnet assemblies includes at least two layers of first annular magnets that are sequentially arranged; The middle magnet includes at least one second magnet assembly, each of the second magnet assemblies includes at least one layer of second annular magnets, and the multiple layers of the second annular magnets of each of the second magnet assemblies are sequentially nested; The second end magnet includes at least one third magnet assembly, and each of the third magnet assemblies includes at least two layers of third annular magnets which are arranged in sequence; the first annular magnet, the second annular magnet and the third annular magnet are all annular Halbach array magnets; the number of layers of the first annular magnets of each of the first magnet assemblies is more than the number of layers of the second annular magnets of each of the second magnet assemblies, the plane perpendicular to the center line of the first magnet assembly is the first plane, and the projection of the outer ring edge of each of the first magnet assemblies on the first plane is located outside the projection of the outer ring edge of each of the second magnet assemblies on the first plane; the number of layers of the third annular magnets of each of the third magnet assemblies is more than the number of layers of the second annular magnets of each of the second magnet assemblies, and the projection of the outer ring edge of each of the third magnet assemblies on the first plane is located outside the projection of the outer ring edge of each of the second magnet assemblies on the first plane.

2. The dumbbell-shaped magnet structure according to claim 1, characterized in that: Center lines of all of the first ring magnets, all of the second ring magnets, and all of the third ring magnets are collinear.

3. The dumbbell-shaped magnet structure according to claim 1, characterized in that: The projection of the first annular magnets of the outermost circle of each of the first magnet assemblies on the first plane is located outside the projection of each of the second magnet assemblies on the first plane; the projection of the third annular magnets of the outermost circle of each of the third magnet assemblies on the first plane is located outside the projection of each of the second magnet assemblies on the first plane.

4. The dumbbell-shaped magnet structure according to claim 3, characterized in that: The projection of the first annular magnet of the innermost circle of each of the first magnet assemblies on the first plane is located on the inner side of the projection of each of the second magnet assemblies on the first plane; the projection of the third annular magnet of the innermost circle of each of the third magnet assemblies on the first plane is located on the inner side of the projection of each of the second magnet assemblies on the first plane.

5. The dumbbell-shaped magnet structure according to claim 1, characterized in that: The number of the second magnet assemblies is plural.

6. The dumbbell-shaped magnet structure according to claim 1, characterized in that: All of the first annular magnets of each of the first magnet assemblies have the same length along the center line of the first magnet assembly, all of the second annular magnets of each of the second magnet assemblies have the same length along the center line of the second magnet assembly, and all of the third annular magnets of each of the third magnet assemblies have the same length along the center line of the third magnet assembly.

7. The dumbbell-shaped magnet structure according to claim 1, characterized in that: The magnet structure is a symmetrical piece that is symmetrical in the length direction of the magnet structure.

8. The dumbbell-shaped magnet structure according to claim 7, characterized in that: The distance between the first end magnet and the middle magnet along the center line of the first end magnet is a first distance, the distance between the second end magnet and the middle magnet along the center line of the first end magnet is a second distance, the distance between two adjacent first magnet assemblies along the center line of the first end magnet is a third distance, the distance between two adjacent second magnet assemblies along the center line of the first end magnet is a fourth distance, the distance between two adjacent third magnet assemblies along the center line of the first end magnet is a fifth distance, and the first distance, the second distance, the third distance, the fourth distance and the fifth distance are the same.

9. The dumbbell-shaped magnet structure according to claim 1, characterized in that: The first annular magnets of each of the first magnet assemblies are formed into four layers, the second annular magnets of each of the second magnet assemblies are formed into two layers, and the third annular magnets of each of the third magnet assemblies are formed into four layers.

10. A magnetic resonance imaging system, characterized in that: It comprises a main magnet, wherein the main magnet is a dumbbell-shaped magnet structure as described in any one of claims 1 to 9.

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