Shim ring and magnetic resonance magnet having the shim ring

Abstract

The present invention provides a shim ring and a magnetic resonance magnet having the shim ring. The shim ring has two symmetrical through-notches along the patient entry and exit direction. The present invention expands the effective patient space and reduces the weight of the magnet by changing the shim ring structure, while also ensuring the uniformity of the magnetic field. The shim ring of the present invention can be used for a variety of magnets, which can greatly expand the application field of magnetic resonance.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic resonance imaging, and in particular to a shim ring and a magnetic resonance magnet having the shim ring. Background Art

[0002] Magnetic resonance imaging (MRI) equipment is one of the greatest inventions of the last century. It can be used to scan almost every part of the human body, without any ionizing radiation damage to the human body, and can clearly display soft tissue structures, and can be used to diagnose diseases in all parts of the body. The magnet is a core component of the MRI equipment, which is used to generate the main magnetic field required for magnetic resonance imaging. There are currently three types of magnets used in clinical magnetic resonance imaging equipment: permanent magnets, normal conductive magnets, and superconducting magnets.

[0003] The magnetic field of the permanent magnet is generated by the electromagnetic coil. After the power is turned off, the magnetic field disappears. The electromagnetic coil needs to be powered on all the time to work properly. Since the coil resistance is not zero, the power consumption is very large during operation, and a lot of heat is generated, requiring the cooling device to keep running all the time. The stability of use is poor, and it is currently less used.

[0004] Superconducting magnets generate magnetic fields from superconducting coils, which need to be kept at low temperatures for a long time. Therefore, the coils are wrapped in a cryogenic dewar and a cold head is used to keep their low temperature from being destroyed. Superconducting coils are generally cooled by liquid helium, and their operating costs are relatively high.

[0005] Permanent magnets have low operating and maintenance costs, and relatively low manufacturing costs, and are currently the mainstream of application. Permanent magnets are usually designed as open structures, such as C-type, double-column type, four-column type, etc. Due to the limitations of magnetic material properties, the patient space of permanent magnets is smaller than that of superconducting magnets, usually around 400mm, and they are heavier.

[0006] In order to quickly obtain clear and realistic images for accurate diagnosis of patients, the magnetic resonance imaging system requires that the magnets therein can provide a very uniform spatial magnetic field over a large range. After the permanent magnet is assembled, the non-uniformity of the magnetic field in the sample area is often 1000-1500ppm, or even higher. Therefore, a uniform magnetic field is usually obtained by active shimming and passive shimming. Active shimming is to arrange a group of current coils at the appropriate part of the magnet. When powered on, the magnetic field generated by the coils will offset the non-uniform harmonic components in the basic field. This method is often used for conventional and superconducting magnets. For open permanent magnets, considering that the uniformity of the basic field is worse than that of conventional magnets, and in order not to destroy its openness, the passive shimming method is mainly used. The passive shimming method is to set a shimming ring on the surface of the permanent magnet pole. The shimming ring is generally annular. The non-uniform components in the main magnetic field are eliminated by the additional magnetic field of the shimming ring, so that the magnetic field in the sample area is evenly distributed.

[0007] The shim ring is relatively arranged on the inner surface of the permanent magnet pole. Although it improves the uniformity of the magnetic field, it has a certain height, which relatively reduces the limited patient space of the magnet, causing inconvenience in practical use. Summary of the invention

[0008] In view of this, the present invention proposes a shim ring and a magnetic resonance magnet having the shim ring, aiming to solve the existing problems.

[0009] The present invention provides a magnetic resonance shim ring, which has two symmetrical through-notches along the patient entry and exit direction, wherein the height of the notches is less than or equal to the height of the shim ring, and the thickness of the notches is equal to the thickness of the shim ring.

[0010] Furthermore, the gap of the shim ring is in a step shape.

[0011] Furthermore, the gap of the shim ring is a step.

[0012] Furthermore, the shim ring is also provided with arc-shaped compensation shim strips, which are attached to the notch and the inner wall of the shim ring on both sides of the notch.

[0013] Furthermore, the angle of the arc where the compensation shim strips of the shim ring are located is ≤ 90°.

[0014] Another aspect of the present invention provides a magnetic resonance magnet comprising any one of the above-mentioned shim rings.

[0015] Furthermore, the magnetic resonance magnet of the present invention also includes a yoke, a magnetic material, and a pole plate. The inner surface of the yoke is provided with a pair of upper and lower symmetrical magnetic materials, and the opposite inner surfaces of the magnetic materials are provided with pole plates. The shim rings are respectively fixed on the opposite inner surfaces of the pole plates. The opposite inner surfaces of the magnetic materials are provided with pole plates. The shim rings are respectively fixed on the opposite inner surfaces of the pole plates. The yoke corresponding to the gap in the shim ring also has a corresponding gap in the magnetic material.

[0016] Furthermore, concentric compensation rings and stretching rings are respectively provided on the relative inner surfaces of the electrode plates, and the compensation rings and stretching rings are both convex rings, wherein the compensation ring is located inside the stretching ring, in the middle position of the inner surface; the stretching ring is located at the edge of the inner surface, close to the shim ring; and a groove is also provided between the compensation ring and the stretching ring.

[0017] Furthermore, the height of the compensation ring is greater than the height of the stretching ring.

[0018] Furthermore, the compensation ring is an anti-eddy current compensation ring.

[0019] The shim ring provided by the present invention breaks the conventional design thinking pattern and boldly sets a gap on the shim ring, thereby expanding the effective patient space, reducing the weight of the magnet, and also ensuring the uniformity of the magnetic field. The shim ring of the present invention can be used for a variety of magnets, which can greatly expand the application field of magnetic resonance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0021] Figure 1 Schematic diagram of the existing magnetic resonance imaging magnet structure Figure 1 ;

[0022] Figure 2 Schematic diagram of the existing magnetic resonance imaging magnet structure Figure 2 ;

[0023] Figure 3 Schematic diagram of the existing magnetic resonance imaging magnet structure Figure 3 ;

[0024] Figure 4 A schematic diagram of a shim ring structure provided in an embodiment of the present invention;

[0025] Figure 5 A schematic diagram of the angle of compensation shim strips provided in an embodiment of the present invention;

[0026] Fig. 6A Schematic diagram of the magnetic resonance imaging magnet structure of the present invention Figure 1 ;

[0027] Figure 6B Schematic diagram of the magnetic resonance imaging magnet structure of the present invention Figure 2 ;

[0028] Figure 7 A schematic diagram of the magnet structure effect provided by an embodiment of the present invention;

[0029] Figure 8 Schematic diagram of the pole plate structure of the magnet provided in the embodiment of the present invention Figure 1 ;

[0030] Fig. 9 Schematic diagram of the magnet structure provided in the embodiment of the present invention Figure 3 ;

[0031] Fig.10 Schematic diagram of the pole plate structure of the magnet provided in the embodiment of the present invention Figure 2 . DETAILED DESCRIPTION

[0032] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to be able to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0033] refer to Figure 1-3 , which are the permanent magnet structures of several common nuclear magnetic imaging devices. Figure 3 It is a schematic diagram of the existing four-column magnet structure. The permanent magnet structure mainly includes a yoke 1', a magnetic material 2', a pole plate 3', and a shim ring 4'. The yoke 1' mainly functions to conduct the upper and lower parts of the magnetic material 2' to form a loop, and also plays a role in supporting the two magnetic poles. The magnetic material 2' is used to provide the basic magnetic field used for magnetic resonance, generally an alloy material such as neodymium iron boron and ferrite. The pole plate 3' mainly functions to support and fix the magnetic material, and to make the magnetic field in the imaging area more uniform, and the shape is generally a flat plate. The shim ring 4' is generally annular, and its main function is to expand the uniform area so that the magnetic field in the magnet imaging area does not gather in the center, but forms a space with a relatively uniform magnetic field.

[0034] The magnetic material 2', the pole plate 3', and the shim ring 4' are arranged symmetrically up and down. The spatial area between the two pole plates 3' where the magnetic field uniformity meets the imaging requirements is called the imaging area 8', which is generally spherical or ellipsoidal. The space between the two shim rings 4' is the available space for patients in magnetic resonance scanning, which can be called the patient space. However, the area far from the center of the magnetic field is of little value in actual use. The imaging scan must include the entire imaging part in the imaging area. Therefore, the cylindrical area or elliptical area that encompasses the imaging area can be called the available patient space 7'.

[0035] Based on existing design experience, Figure 1-2 The magnet is designed in the manner shown, with a magnetic field of 0.3T, a patient space of Φ440mm, an imaging area of ​​Φ420mm*Φ420mm*Φ380mm (X*Y*Z), and a magnet weight of about 16 tons. If the available patient space is increased to Φ710mm and the magnetic field remains unchanged, the magnet weight will reach more than 60 tons, which will bring great inconvenience to manufacturing and use.

[0036] refer to Figure 4, is a schematic diagram of a shim ring structure of the present invention. Specifically, the shim ring 4 has two symmetrical through gaps along the patient entry and exit direction, the height of the gaps is less than or equal to the height of the shim ring, and the thickness of the gaps is equal to the thickness of the shim ring.

[0037] There is no special requirement for the shape of the notch, which can be arc, rectangular, square, etc. In order to facilitate processing and implementation, it is preferably stepped. The steps can be made into one or more levels. The more levels there are, the less the uniform field ring is reduced, and the smaller the impact on the magnetic field is. Conversely, the greater the impact on the magnetic field. However, the more levels there are, the more complicated the processing of the matching parts is. Therefore, the number of steps needs to be determined based on actual conditions.

[0038] At the same time, the use of the notched shim ring 4 may affect the uniformity of the magnetic field, resulting in a reduction in the size of the magnet imaging area in the Y direction, and in inconsistency between the magnetic field imaging areas in the X direction and the Y direction. Therefore, further, an arc-shaped compensation shim strip 4-2 is provided on the inner side of the shim ring 4, which fits the notch and the inner wall of the shim ring 4 on both sides of the notch. The angle of the compensation shim strip 4-2 generally does not exceed 90 degrees. Figure 5 As shown, otherwise the compensation effect will be affected. Theoretically, if the compensation shim strip is wide enough, the inconsistency caused by the gap of the shim ring can be compensated. However, since the gradient coil for magnetic resonance imaging needs to be installed in the pit formed by the shim ring 4 and the pole plate 3, it is impossible to increase the width of the compensation shim strip 4-2 indefinitely. Therefore, the installation of the gradient coil needs to be guaranteed first, and the part that cannot be compensated is compensated by other designs.

[0039] Since the space between the upper and lower shim rings 4 is the available patient space, the shim ring of the present invention increases the available patient space of the magnet by setting a gap in the patient's entry and exit direction, and also avoids the increase of the magnet weight. Because usually in order to increase the available patient space, the upper and lower shim rings are usually pulled apart as a whole to expand the distance between the upper and lower shim rings, which has a greater impact on the magnetic field and requires the increase of the magnet weight. However, the present invention cleverly sets a gap in the shim ring along the patient's entry and exit direction, which reduces the impact on the magnetic field, and at the position outside the gap, the shim ring distance is relatively reduced, the magnetic field strength is stronger, and it is more conducive to imaging, thereby relatively reducing the magnet weight while ensuring imaging.

[0040] See also Fig. 6A 6B is a schematic diagram of the magnet structure provided by an embodiment of the present invention. The magnet of the present invention comprises a yoke 1, a pair of magnetic materials 2 symmetrically arranged on the inner surface of the yoke 1, pole plates 3 are arranged on the opposite inner surfaces of the magnetic materials, and shim rings 4 are fixed on the opposite inner surfaces of the pole plates 3. The shim ring 4 has two symmetrical through gaps along the patient entry and exit direction, the height of the gap is less than or equal to the height of the shim ring, and the thickness of the gap is equal to the thickness of the shim ring.

[0041] When the shim ring 4 with gaps of the present invention is applied to a magnet, there are two situations.

[0042] A situation such as Fig. 6A As shown, the yoke 1, the magnetic material 2, the pole plate 3, and the shim ring 4 are all flat plate structures, which are stacked layer by layer. The shim ring 4 is at the bottom layer, and there is no other component blocking it on the same plane. When the shim ring 4 has a gap along the patient entry and exit direction, the entire magnet has a gap in the patient entry and exit direction accordingly, which can ensure that the available patient space can be increased, thereby achieving the corresponding technical effect.

[0043] In another case, refer to Figure 6B The yoke 1, the magnetic material 2, and the pole plate 3 are not strictly flat plate structures. There are other components in other spaces on the same plane of the shim ring 4, such as the yoke 1 and the magnetic material 2. Therefore, when the shim ring 4 has a gap along the patient entry and exit direction, the yoke 1 and the magnetic material 2 corresponding to the gap position also need to be missing to form a gap, so as to ensure the increase of the available patient space.

[0044] In summary, in order to truly increase the available patient space, not only does the shim ring 4 need to have two symmetrical through gaps along the patient entry and exit direction, but the yoke 1 and the magnetic material 2 may also be missing at the positions corresponding to the gaps, and correspondingly have gaps, that is, to ensure that the gap effect of the magnet is finally obtained as shown in the figure Figure 7 As shown, the purpose can be achieved.

[0045] Furthermore, in order to ensure the imaging range of the magnet and meet the requirement that the magnetic field error in the imaging area is about 60PPM, the shape of the pole plate 3 can be improved. Usually, the imaging quality is improved by increasing the diameter of the magnetic material 2, but this will inevitably cause a significant increase in the weight of the magnet. The pole plates are located on both sides of the available patient space, closest to the imaging area, and have a great impact on the imaging area. They are usually designed as a flat structure. After analysis, it was found that changing the shape of the pole plate 3 has a great impact on the imaging area. Therefore, this feature can be used to expand the range of the magnet imaging area to meet the imaging requirements, thereby relatively reducing the weight of the magnet.

[0046] Therefore, further reference Figure 8 Concentric compensation rings 5 ​​and stretching rings 6 are respectively provided on the opposite inner surfaces of the electrode plate 3. Both the compensation ring 5 and the stretching ring 6 are convex rings, which are higher than the inner surface of the electrode plate 3. The compensation ring 5 is located inside the stretching ring 6, in the middle position of the inner surface; the stretching ring 6 is located at the edge of the inner surface, close to the shim ring 4; and a groove is also provided between the compensation ring 5 and the stretching ring 6.

[0047] The function of the compensation ring 5 is to pull out the magnetic field at the center of the magnet, reduce the magnetic field at the center of the magnet, and increase the magnetic field in the imaging area close to the compensation ring, which can expand the range of the magnet imaging area. The stretching ring 6 is used to compensate for the problem of low magnetic field in the central part of the imaging area caused by the stretching effect of the compensation ring 5. The groove between the stretching ring 6 and the compensation ring 5 is designed to eliminate the high points of the magnetic field caused by the superposition effect between the two rings. The three parts work together to expand the imaging area and keep the original magnetic field uniformity from being broken, further solving the problem of reduced magnetic field uniformity that may be caused by the lack of the shim ring.

[0048] The size of the compensation ring 5 and the stretching ring 6 and the position and size of the grooves need to be optimized and designed according to the specific magnet and needs. Generally, the height of the compensation ring 5 is greater than that of the stretching ring 6. The stretching ring 6 needs to be designed to prevent the generation of eddy currents, and silicon steel or amorphous laminated structures are used to prevent additional eddy currents generated by the stretching ring 6 from affecting the imaging quality of the magnetic resonance system.

[0049] The number of the compensation ring 5, the stretching ring 6 and the grooves therebetween can be one or more, which is specifically determined according to the size and processing requirements.

[0050] In another embodiment of the magnet of the present invention, the magnet structure is as follows: Figure 8-9 The magnet includes a yoke 1, a magnetic material 2, a pole plate 3, and a shim ring 4, wherein: the magnetic material 2 includes a first magnetic material 2-1, a second magnetic material 2-3, and a third magnetic material 2-4, wherein the second magnetic material 2-3 and the third magnetic material 2-4 are arranged in an arc shape to form a circle, and the first magnetic material 2-1 is laid flat in the middle of the circle; the pole plate 3 is located above the first magnetic material, in the middle of the circle formed by the second magnetic material 2-3 and the third magnetic material 2-4, and the fourth magnetic material 2-2 is located between the first magnetic material 2-1 and the pole plate 3, and is arranged in a circle around the inner side of the circle formed by the second magnetic material 2-3 and the third magnetic material 2-4, and the magnetic orientation is the same as that of the first magnetic material 2-1.

[0051] The yoke 1 includes a planar yoke 1-1 and a circumferential yoke 1-2. The planar yoke 1-1 is located on the bottom surface of the circle formed by the second magnetic material 2-3 and the third magnetic material 2-4, and the circumferential yoke 1-2 is wrapped around the outside of the circle. This is to better guide the magnetic field of the second magnetic material 2-3 and the third magnetic material 2-4 into the yoke 1, and play a better supporting role.

[0052] The shim ring 4 is located above the pole plate 3, lower than the circumference formed by the second magnetic material 2-3 and the third magnetic material 2-4, and has two symmetrical through gaps along the patient entry and exit direction. The height of the gap is less than or equal to the height of the shim ring, and the thickness of the gap is equal to the thickness of the shim ring. Accordingly, the magnetic material 2 and the yoke 1 are also installed downward at the corresponding gap position to form a gap, thereby ensuring that the patient space can be increased. The magnet gap adopts a one-step design, and the height is increased at the place that does not interfere with the available patient space.

[0053] Concentric compensation rings 5 ​​and stretching rings 6 are respectively provided on the opposite inner surfaces of the electrode plates 3. Both the compensation rings 5 ​​and stretching rings 6 are convex rings, which are higher than the inner surfaces of the electrode plates. The compensation ring 5 is located inside the stretching ring 6, in the middle of the inner surface; the stretching ring 6 is located at the edge of the inner surface, close to the shim ring 4; and a groove is also provided between the compensation ring 5 and the stretching ring 6. The compensation ring 5, the stretching ring 6 and the groove are all one.

[0054] In the above Figure 8 In a specific embodiment of a magnet of the structure, the designed magnetic strength is 0.3T, and the available patient space diameter is 710mm. A four-column structure is adopted, the opening angle is about 80%, the gap of the shim ring 4 adopts a one-step design, and the gap height is about 4 / 5 of the height of the shim ring, that is, the ratio of the remaining shim ring height at the gap to the height of the shim ring itself is about 1:4, the compensation ring 5 is 10mm thick and 50mm wide, the stretching ring 6 is 6mm thick and 100mm wide, and the material is silicon steel sheet lamination material. The groove between the compensation ring 5 and the stretching ring 6 is 10mm deep and 10mm wide, and is located at a position about 25mm away from the stretching ring 6. The distance from the magnetic field drop point in the final imaging area to the magnetic field center position is expanded from about 200mm to about 230mm. The final designed product has an imaging area range of 420mm*420mm*380mm (X*Y*Z), and the magnetic performance is equivalent to that of traditional magnets, and the overall weight is less than 17 tons.

[0055] The magnet design of the present invention has no requirements on the magnet type and can be adjusted to other structural forms such as double-column, C-shape, etc. according to different actual application scenarios. Only the change in mechanical strength needs to be considered, which has little effect on the magnetic field design result.

[0056] The above is an explanation of the shim ring structure of the present invention in combination with a permanent magnet, but the shim ring of the present invention is not limited to a permanent magnet, and can also be used for a normal or superconducting magnet. In a normal or superconducting magnet, a normal or superconducting coil is used to replace a permanent magnetic material to generate a magnetic field, and an image is formed by using the vertical magnetic field between the two coils. In order to make the magnetic field in the imaging area meet the imaging requirements, a shim ring, a pole plate, etc. are also provided. The use of the shim ring with a notch of the present invention can also increase the effective patient space, reduce the weight of the coil, and thus reduce the weight of the magnet.

[0057] When the notched shim ring of the present invention is used in a conventional conductive or superconducting magnet, the coil winding design can be utilized to make the coil generate a magnetic field with inconsistent attenuation speeds along the X and Y axes, which can be used to compensate for the magnetic field inconsistency caused by the notch on the shim ring, thereby achieving the purpose of expanding the imaging area.

[0058] At the same time, an open magnet that uses permanent magnetic materials and conventional or superconducting coils to provide a magnetic field can also use a shim ring with a gap to expand the patient space, and the coil design can be used to compensate for the inconsistency of the magnetic field in the X and Y directions caused by the gap in the shim ring.

[0059] The above describes the shim ring and the magnet of the present invention in combination with the preferred embodiments of the present invention. The technical solution of the present invention breaks the traditional thinking pattern and boldly sets a gap on the shim ring, thereby expanding the effective patient space, reducing the weight of the magnet, and also ensuring the uniformity of the magnetic field. The shim ring of the present invention can be used for a variety of magnets, which can greatly expand the application field of magnetic resonance.

[0060] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A magnetic resonance magnet, comprising a shim ring, a yoke, a magnetic material, and a pole plate, wherein the shim ring has two symmetrical through gaps along the patient entry and exit direction, the height of the gaps is less than or equal to the height of the shim ring, and the thickness of the gaps is equal to the thickness of the shim ring; the shim ring is also provided with arc-shaped compensation shim strips, which are attached to the gaps and the inner wall of the shim ring on both sides of the gaps; the angle of the arc where the compensation shim strips are located is ≤90°; the inner surface of the yoke is provided with a pair of upper and lower symmetrical magnetic materials, the opposite inner surfaces of the magnetic materials are respectively provided with pole plates, the shim rings are respectively fixed on the opposite inner surfaces of the pole plates, and the yoke and the magnetic material corresponding to the gaps of the shim ring are also vacant to form gaps; Concentric compensation rings and stretching rings are respectively provided on the opposite inner surfaces of the electrode plates, and both the compensation rings and stretching rings are convex rings, wherein the compensation ring is located inside the stretching ring, in the middle of the inner surface; the stretching ring is located at the edge of the inner surface, close to the shim ring; and a groove is also provided between the compensation ring and the stretching ring; in: The magnetic material comprises a first magnetic material, a second magnetic material and a third magnetic material, wherein the second magnetic material and the third magnetic material are arranged in an arc shape to form a circle, and the first magnetic material is spread in the middle of the circle; the pole plate is located above the first magnetic material, in the middle of the circle formed by the second magnetic material and the third magnetic material; the fourth magnetic material is located between the first magnetic material and the pole plate, and is arranged in a circle around the inner side of the circle formed by the second magnetic material and the third magnetic material, and the magnetic orientation is the same as that of the first magnetic material; the yoke comprises a planar yoke and a circumferential yoke, the planar yoke is located on the bottom surface of the circle formed by the second magnetic material and the third magnetic material, and the circumferential yoke is wrapped around the outside of the circle; the height of the shim ring is lower than the height of the circle formed by the second magnetic material and the third magnetic material.

2. The magnetic resonance magnet according to claim 1, characterized in that The compensation ring is higher than the stretching ring.

3. The magnetic resonance magnet according to claim 1, characterized in that The compensation ring is an anti-vortex compensation ring.

4. The magnetic resonance magnet according to claim 1, characterized in that: The cross section of the notch is step-shaped.

5. The magnetic resonance magnet according to claim 4, characterized in that: The notch is a step.

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