A permanent magnet for magnetic resonance imaging

Abstract

The present invention relates to a medical magnetic resonance imaging system, specifically a magnetic resonance imaging permanent magnet, including a magnetic steel array and a magnet frame made of non-magnetic conductive material, wherein the magnet frame is provided with two corresponding upper and lower magnetic steel array groups, each group of the magnetic steel array group has a plurality of circles of magnetic steel arrays, and each circle of the magnetic steel array is evenly provided with a plurality of magnetic steels along the circumferential direction, and the magnetization direction of all the magnetic steels in each circle of the magnetic steel array is the same. The present invention abandons the pole head structure of the traditional permanent magnet, abandons the eddy current disk device and the magnetic conductive magnet frame, so that the permanent magnet truly realizes zero eddy current, greatly simplifies the permanent magnet structure, greatly reduces the volume of the permanent magnet, greatly reduces the weight, and effectively reduces the influence range of the escape field, and improves the uniformity of the permanent magnet.

Description

Technical Field

[0001] The invention relates to a medical magnetic resonance imaging system, in particular to a permanent magnet for magnetic resonance imaging. Background Art

[0002] Magnetic resonance imaging (MRI) system is a high-tech product that combines a variety of scientific technologies. It is the most advanced clinical diagnostic equipment for the detection and diagnosis of early cancer and many other diseases. Permanent magnets have a series of advantages such as simple structure, easy maintenance, safe and reliable operation, and are an important direction for the development of magnetic resonance imaging systems.

[0003] The MRI system consists of four parts: magnet system, gradient system, radio frequency system and spectrometer system. The magnet is a key core component of the magnetic resonance imaging system, which provides a stable main magnetic field for the magnetic resonance system. The main indicators for measuring the magnetic field are field strength, uniformity, escape field, weight, etc.

[0004] For traditional permanent magnets, the general design and manufacturing method is as follows: permanent magnetic material is used as the magnetic field source, and the two poles are connected by a magnetic yoke to form a closed loop, thereby improving the utilization rate of magnetic energy, reducing the stray field, and increasing the field strength, but the yoke contributes to most of the weight of the magnet. On the FOV (patient examination area) side, the magnetic poles will be connected to a pair of high-purity pure iron with high magnetic permeability to improve the uniformity of the magnet, but this pair of pure iron magnetic poles will be excited by the gradient alternating magnetic field to generate eddy currents, so it is necessary to add a de-eddy current device to isolate the gradient coil and the pure iron pole head. In addition, the pure iron pole head will also increase the stray field.

[0005] In short, traditional permanent magnets are large and heavy for various reasons, and use more expensive rare earth materials, which leads to high costs and restricted use environments. In addition, due to the special structure of traditional magnets, eddy currents are an important technical difficulty that cannot be avoided. Magnet eddy currents will reduce image quality and even cause some advanced sequences to fail to operate normally in permanent magnet MRI systems. Summary of the invention

[0006] In order to overcome the above-mentioned shortcomings of the existing magnets, the purpose of the present invention is to provide a permanent magnet for magnetic resonance imaging, which significantly reduces the weight and volume of the magnet, significantly reduces the manufacturing cost, achieves "zero eddy current", and can also reduce the stray magnetic field.

[0007] The objective of the present invention is achieved through the following technical solutions:

[0008] A permanent magnet of a structure of the present invention comprises a magnetic steel array and a magnetic frame made of non-magnetic conductive material, wherein the magnetic steel array frame is provided with two corresponding upper and lower groups, each group of the magnetic steel array group has multiple circles of magnetic steel arrays, and each circle of the magnetic steel array has multiple magnetic steels evenly arranged along the circumferential direction, and the magnetization direction of all the magnetic steels in each circle of the magnetic steel array is the same.

[0009] Wherein: the magnetization direction of all the magnetic steels in each circle of the magnetic steel array is axially upward or axially downward.

[0010] The height of the magnetic steels in each circle of the magnetic steel array gradually decreases from the outermost circle to the innermost circle, that is, the height of the magnetic steels in the magnetic steel array in the outermost circle is the highest, and the height of the magnetic steels in the magnetic steel array in the innermost circle is the lowest.

[0011] Each circle of the magnetic steel array is concentrically arranged, and the shape and size of each magnetic steel in each circle of the magnetic steel array are the same.

[0012] Another structure of a permanent magnet of the present invention includes a magnetic steel array and a magnetic frame made of non-magnetic conductive material, wherein two corresponding magnetic steel array groups are arranged on the magnetic frame, each of which has multiple circles of magnetic steel arrays, and multiple magnetic steels are evenly arranged on each circle of the magnetic steel array along the circumferential direction. In each circle of the magnetic steel array, the magnetization direction of the magnetic steel of one circle of the magnetic steel array is radial, and the magnetization direction of the magnetic steel of the remaining magnetic steel arrays is axial; in each circle of the magnetic steel array, including the outermost circle of the magnetic steel array, at least two circles of the magnetic steel array have the magnetization direction opposite to that of the magnetic steel of the remaining magnetic steel arrays, and the radially magnetized magnetic steel array is located between the outermost circle of the magnetic steel array and the other reversely magnetized magnetic steel array.

[0013] Among them: the height of the magnetic steels in each circle of the magnetic steel array gradually decreases from the outermost circle to the innermost circle, that is, the height of the magnetic steels in the magnetic steel array in the outermost circle is the highest, and the height of the magnetic steels in the magnetic steel array in the innermost circle is the lowest.

[0014] Each circle of the magnetic steel array is concentrically arranged, and the shape and size of each magnetic steel in each circle of the magnetic steel array are the same.

[0015] The magnet frame includes a connecting column, an upper frame body and a lower frame body, the upper frame body is connected to the lower frame body through the connecting column, or the upper frame body, the connecting column and the lower frame body are an integral structure; the lower surface of the upper frame body is provided with a plurality of circles of hole grooves, each circle of the hole grooves is a plurality of holes and is evenly arranged along the circumferential direction, and each of the hole grooves is installed with a magnetic steel; the upper surface of the lower frame body is provided with a plurality of circles of hole grooves, each circle of the hole grooves is a plurality of holes and is evenly arranged along the circumferential direction, and each of the hole grooves is installed with a magnetic steel.

[0016] The connecting column is a single column or a double column, the number of circles of holes and slots opened on the upper frame body and the lower frame body and the number of holes and slots in each circle are the same, and the upper frame body and the magnetic steel on the upper frame body are arranged in a mirror image with the lower frame body and the magnetic steel on the lower frame body.

[0017] The advantages and positive effects of the present invention are:

[0018] 1. The present invention abandons the pole head structure of the traditional permanent magnet, abandons the eddy current disk device and the magnetic magnet frame, so that the permanent magnet truly achieves zero eddy current.

[0019] 2. The present invention abandons the pole head structure in the traditional permanent magnet, abandons the eddy current disk device and the magnetic magnet frame, greatly simplifies the permanent magnet structure, greatly reduces the volume of the permanent magnet, and greatly reduces the weight.

[0020] 3. The present invention adopts a regularly arranged magnetic steel array as a magnetic field source, which greatly improves the utilization rate of magnetic energy and reduces the amount of rare earth materials used.

[0021] 4. The present invention adopts a brand-new magnetic circuit structure and magnetic steel arrangement method, and sets at least two circles of magnetic steel arrays for reverse magnetization in each circle of magnetic steel array, which effectively reduces the influence range of the escape field.

[0022] 5. The present invention adopts a new array-type magnetic steel assembly, which makes the permanent magnet manufacturing process simpler and the permanent magnet structure more stable.

[0023] 6. The present invention adopts a new magnet frame design to limit the magnetic steel, thereby increasing the stability of the permanent magnet and reducing the difficulty of assembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the three-dimensional structure of the first embodiment of the present invention;

[0025] Figure 2 Schematic diagram of the three-dimensional structure of the magnet frame in the first embodiment of the present invention;

[0026] Figure 3A It is a top view of the structure of the frame body with the magnetic steel array installed in the first embodiment of the present invention;

[0027] Figure 3B for Figure 3A A-A sectional view (the arrow is the magnetization direction of the magnet);

[0028] Figure 4A It is a schematic diagram of the three-dimensional structure of the second embodiment of the present invention;

[0029] Figure 4B This is a top view of the structure of the second embodiment of the present invention without the upper frame body;

[0030] Figure 5AThis is a structural front view of the magnet frame in the second embodiment of the present invention;

[0031] Figure 5B It is a structural side view of the magnet frame in the second embodiment of the present invention;

[0032] Fig. 6A It is a structural top view of a frame body with a magnetic steel array installed in the second embodiment of the present invention;

[0033] Figure 6B for Fig. 6A The B-B cross-sectional view in FIG. 1 (the arrow indicates the magnetization direction of the magnet);

[0034] Figure 7 This is a stray magnetic field distribution diagram of the first embodiment of the present invention;

[0035] Figure 8 This is a stray magnetic field distribution diagram of the second embodiment of the present invention;

[0036] Among them: 1 is a magnetic steel array, 2 is a magnetic frame, 201 is a connecting column, 202 is an upper frame body, 203 is a lower frame body, 3 is a magnetic steel, and 4 is a hole groove. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the accompanying drawings.

[0038] Embodiment 1

[0039] like Figure 1 , Figure 2 , Figure 3A and Figure 3B As shown, the magnetic resonance imaging permanent magnet of this embodiment includes a magnetic steel array 1 and a magnet frame 2 made of non-magnetic conductive material, wherein the magnet frame 2 is provided with two corresponding upper and lower magnetic steel array groups, each magnetic steel array group has multiple circles of magnetic steel arrays 1, and each circle of magnetic steel array 1 is evenly provided with multiple magnetic steels 3 along the circumferential direction, and the magnetization direction of all the magnetic steels 3 in each circle of magnetic steel array 1 is the same.

[0040] The magnet frame 2 of the present embodiment is made of non-magnetic conductive material, which can be epoxy resin, carbon fiber, nylon, engineering plastic, PVC or organic glass; since the magnet frame 2 does not need to be magnetic conductive, the appearance and shape can be adjusted according to the needs. The magnet frame 2 of the present embodiment includes a connecting column 201, an upper frame body 202 and a lower frame body 203, and the upper frame body 202 is connected to the lower frame body 203 through the connecting column 201, or the upper frame body 202, the connecting column 201 and the lower frame body 203 are an integral structure; the lower surface of the upper frame body 202 is provided with a plurality of circles of holes 4, each circle of holes 4 is a plurality of holes, and is evenly opened along the circumferential direction, and each hole 4 is installed with a magnetic steel 3; the upper surface of the lower frame body 203 is provided with a plurality of circles of holes 4, each circle of holes 4 is a plurality of holes, and is evenly opened along the circumferential direction, and each hole 4 is installed with a magnetic steel 3; the magnetic steel 3 of the present embodiment is bonded in the hole 4 by non-conductive epoxy resin glue, which is convenient for installation and also conducive to the stability of the magnetic steel 3. The connecting column 201 of the present embodiment is a single column (i.e., one connecting column 201), the number of circles of holes 4 and the number of holes 4 in each circle are the same on the upper frame body 202 and the lower frame body 203, and the upper frame body 202 and the magnets 3 on the upper frame body 202 are mirror-arranged with the lower frame body 203 and the magnets 3 on the lower frame body 203.

[0041] The more turns of the magnetic steel array 1 in each magnetic steel array group, the better the initial uniformity of the permanent magnet; in this embodiment, seven turns of the magnetic steel array 1 are respectively arranged on the upper frame body 202 and the lower frame body 203.

[0042] In this embodiment, the magnetization direction of all the magnetic steels 3 in each circle of magnetic steel arrays 1 is axially upward or axially downward (axially upward in this embodiment). Each circle of magnetic steel arrays 1 is concentrically arranged, and the shape and size of each magnetic steel 3 in each circle of magnetic steel arrays 1 are the same. The height of the magnetic steel 3 in each circle of magnetic steel arrays 1 gradually decreases from the outermost circle to the innermost circle, that is, the height of the magnetic steel 3 in the outermost circle of the magnetic steel array 1 is the highest, and the height of the magnetic steel 3 in the innermost circle of the magnetic steel array 1 is the lowest.

[0043] Experimental Example 1

[0044] The field strength of the permanent magnet is 700GS, the GAP (working gap between the upper and lower magnet array groups) is 290mm, the total weight is 145KG, and the outer diameter is 505mm. The height of the outermost magnet 3 is 85mm, and the height of the innermost magnet 3 is 50-64mm.

[0045] Experimental Example 2

[0046] The field strength of the permanent magnet is 715GS, the GAP is 340mm, the total weight is 240KG, and the outer diameter is 590mm. The height of the outermost circle of magnetic steel 3 is 100mm, and the height of the innermost circle of magnetic steel 3 is 70-80mm.

[0047] Experimental Example 3

[0048] The field strength of the permanent magnet is 1550GS, the GAP is 260mm, the total weight is 360KG, and the outer diameter is 430mm.

[0049] The permanent magnet of the present embodiment does not have a high-density magnetic conductive frame and a high-density pole head structure, so the permanent magnet of the present embodiment is light in weight; the permanent magnet of the present embodiment does not have a high-magnetic permeability magnetic conductive frame and a high-magnetic permeability pole head structure, so the permanent magnet of the present embodiment achieves "zero" eddy current; the permanent magnet of the present embodiment divides the annular magnet into a magnet array of a set size, making magnet processing and magnet assembly simpler and more convenient.

[0050] Embodiment 2

[0051] like Figure 4A , Figure 4B , Figure 5A , Figure 5B , Fig. 6A and Figure 6B As shown, the magnetic resonance imaging permanent magnet of this embodiment includes a magnetic steel array 1 and a magnetic frame 2 made of non-magnetic conductive material, wherein the magnet frame 2 is provided with two corresponding magnetic steel array groups, each of which has multiple circles of magnetic steel arrays 1, and multiple magnetic steels 3 are evenly arranged on each circle of magnetic steel array 1 along the circumferential direction. In each circle of magnetic steel array 1, the magnetization direction of the magnetic steel 3 of one circle of magnetic steel array 1 is radial, and the magnetization direction of the magnetic steel 3 of the remaining magnetic steel arrays 1 is axial; in each circle of magnetic steel array 1, including the outermost circle of magnetic steel array 1, at least two circles of magnetic steel array 1 have magnetization directions opposite to the magnetization directions of the magnetic steel 3 of the remaining magnetic steel arrays 1, and the radially magnetized magnetic steel array 1 is located between the outermost circle of magnetic steel array 1 and another reversely magnetized magnetic steel array 1.

[0052] The difference between the magnet frame 2 of this embodiment and the magnet frame 2 of the first embodiment is that the connection column 201 of the magnet frame 2 of this embodiment is a double column, that is, the upper frame body 202 and the lower frame body 203 are connected by two connection columns 201, or the upper frame body 202, the lower frame body 203 and the two connection columns 201 are an integrated structure. The rest is the same as the magnet frame 2 of the first embodiment.

[0053] In this embodiment, eight circles of magnetic steel arrays 1 are respectively arranged on the upper frame body 202 and the lower frame body 203. The circles of magnetic steel arrays 1 are arranged concentrically, and the shapes and sizes of the magnetic steels 3 in each circle of magnetic steel arrays 1 are the same. The height of the magnetic steels 3 in each circle of magnetic steel arrays 1 gradually decreases from the outermost circle to the innermost circle, that is, the height of the magnetic steels 3 in the outermost circle of the magnetic steel array 1 is the highest, and the height of the magnetic steels 3 in the innermost circle of the magnetic steel array 1 is the lowest.

[0054] In this embodiment, there are two circles of magnetic steel arrays 1, and the magnetization direction of the magnetic steel 3 is axially downward, which are the outermost circle of magnetic steel array 1 and the fourth circle of magnetic steel array 1 from the outside to the inside. The outermost circle of magnetic steel array 1 is used to reduce the stray magnetic field, and the fourth circle of magnetic steel array 1 is used to improve the uniformity of the permanent magnet; the radially magnetized magnetic steel array 1 is located in the second circle from the outside to the inside, and the magnetization direction of the magnetic steel 3 of the remaining circles of magnetic steel arrays 1 is axially upward.

[0055] Experimental Example 4

[0056] The field strength of the permanent magnet is 720GS, the GAP is 340mm, and the total weight is 290KG.

[0057] The permanent magnet of this embodiment does not have a high-density magnetic frame and a high-density pole head structure, so the permanent magnet of this embodiment is light in weight; the permanent magnet of this embodiment does not have a high-permeability magnetic frame and a high-permeability pole head structure, so the permanent magnet of this embodiment achieves "zero" eddy current; the permanent magnet of this embodiment divides the annular magnetic steel into magnetic steel arrays of set sizes, making magnetic steel processing and magnetic steel assembly simpler and more convenient. In this embodiment, two circles of magnetic steel arrays are set with opposite magnetization directions to other magnetic steel arrays. The reverse magnetization of the magnetic steel of the outermost circle of the magnetic steel array reduces the stray magnetic field in the XY plane, and the reverse magnetization of the magnetic steel of the fourth circle of the magnetic steel array expands the uniform area and improves the uniformity of the imaging area. The radial magnetization of the second circle of magnetic steel arrays from the outside to the inside of this embodiment has two functions, the first is to reduce the stray magnetic field in the Z reverse direction, and the second is to increase the field strength in the imaging area.

[0058] like Figure 7 As shown in FIG. 1 , it is the stray magnetic field distribution diagram of the experimental example 2; Figure 8 As shown, it is the stray magnetic field distribution diagram of Experimental Example 4. Under the premise that the field strength, GAP and uniformity are basically the same, the distance between the center of the 5 Gaussian lines in the magnetic field direction of Experimental Example 4 is 0.8 meters, and the distance between the center of the 5 Gaussian lines in the magnetic field direction of Experimental Example 2 is 2 meters. The distance between the center of the 5 Gaussian lines in the horizontal direction of Experimental Example 4 is 1.15 meters, and the distance between the center of the 5 Gaussian lines in the magnetic field direction of Experimental Example 2 is 1.8 meters. Embodiment 2 of the present invention increases the weight of the permanent magnet to a certain extent, but effectively shrinks the stray magnetic field.

Claims

1. A permanent magnet for magnetic resonance imaging, characterized in that: The invention comprises a magnetic steel array (1) and a magnetic frame (2) made of a non-magnetic conductive material, wherein the magnetic frame (2) is provided with two corresponding magnetic steel array groups, one above the other, each of which has a plurality of magnetic steel arrays (1), and each of which has a plurality of magnetic steel arrays (1) uniformly arranged along the circumferential direction. In each of the magnetic steel arrays (1), the magnetization direction of the magnetic steel (3) of one magnetic steel array (1) is radial, and the magnetization direction of the magnetic steel (3) of the remaining magnetic steel arrays (1) is axial; in each of the magnetic steel arrays (1), including the outermost magnetic steel array (1), at least two magnetic steel arrays (1) have the magnetization direction of the magnetic steel (3) opposite to that of the magnetic steel (3) of the remaining magnetic steel arrays (1), and the radially magnetized magnetic steel array (1) is located between the outermost magnetic steel array (1) and the other reversely magnetized magnetic steel array (1).

2. The magnetic resonance imaging permanent magnet according to claim 1, characterized in that: The height of the magnetic steel (3) in each circle of the magnetic steel array (1) gradually decreases from the outermost circle to the innermost circle, that is, the height of the magnetic steel (3) in the magnetic steel array (1) in the outermost circle is the highest, and the height of the magnetic steel (3) in the magnetic steel array (1) in the innermost circle is the lowest.

3. The magnetic resonance imaging permanent magnet according to claim 1, characterized in that: Each circle of the magnetic steel array (1) is concentrically arranged, and each magnetic steel (3) in each circle of the magnetic steel array (1) has the same shape and size.

4. The permanent magnet for magnetic resonance imaging according to any one of claims 1 to 3, characterized in that: The magnet frame (2) comprises a connecting column (201), an upper frame body (202) and a lower frame body (203), wherein the upper frame body (202) is connected to the lower frame body (203) via the connecting column (201); a plurality of circles of hole grooves (4) are provided on the lower surface of the upper frame body (202), wherein each circle of the hole grooves (4) is a plurality of holes and is evenly provided in the circumferential direction, and a magnetic steel (3) is installed in each of the hole grooves (4); a plurality of circles of hole grooves (4) are provided on the upper surface of the lower frame body (203), wherein each circle of the hole grooves (4) is a plurality of holes and is evenly provided in the circumferential direction, and a magnetic steel (3) is installed in each of the hole grooves (4).

5. The magnetic resonance imaging permanent magnet according to claim 4, characterized in that: The connecting column (201) is a single column or a double column, the number of circles of holes (4) provided on the upper frame body (202) and the number of holes (4) in each circle are the same, and the upper frame body (202) and the magnetic steel (3) on the upper frame body (202) and the magnetic steel (3) on the lower frame body (203) and the lower frame body (203) are arranged in a mirror image.

6. The permanent magnet for magnetic resonance imaging according to any one of claims 1 to 3, characterized in that: The magnet frame (2) comprises a connecting column (201), an upper frame body (202) and a lower frame body (203), wherein the upper frame body (202), the connecting column (201) and the lower frame body (203) are an integral structure; a plurality of circles of hole grooves (4) are provided on the lower surface of the upper frame body (202), each circle of the hole grooves (4) are multiple and are evenly provided in the circumferential direction, and a magnetic steel (3) is installed in each of the hole grooves (4); a plurality of circles of hole grooves (4) are provided on the upper surface of the lower frame body (203), each circle of the hole grooves (4) are multiple and are evenly provided in the circumferential direction, and a magnetic steel (3) is installed in each of the hole grooves (4).

7. The permanent magnet for magnetic resonance imaging according to claim 6, characterized in that: The connecting column (201) is a single column or a double column, the number of circles of holes (4) provided on the upper frame body (202) and the number of holes (4) in each circle are the same, and the upper frame body (202) and the magnetic steel (3) on the upper frame body (202) and the magnetic steel (3) on the lower frame body (203) and the lower frame body (203) are arranged in a mirror image.

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