Permanent magnet gradient coil assembly

Abstract

The application provides a permanent magnet gradient coil assembly, and relates to the field of gradient coils.The application adopts the following scheme: a gradient coil body layer is arranged, and the direction pointing to the imaging center is upward;an RF transmitting layer is arranged on the upper part of the gradient coil body layer;an upper epoxy plate is arranged on the upper part of the RF transmitting layer;the first shielding layer is arranged between the gradient coil body layer and the RF transmitting layer;and a lower epoxy plate is arranged on the lower part of the gradient coil body layer.The application can reduce the distance between the two poles of the system magnet, reduce the energy consumption, and maintain the field uniformity.

Description

Technical Field

[0001] This invention relates to the field of gradient coils, and more particularly to a permanent magnet gradient coil assembly. Background Technology

[0002] Gradient coils are one of the main components of medical magnetic resonance imaging (MRI) systems. Their primary function is to generate gradient magnetic fields in three orthogonal directions to spatially locate, phase-encode, and frequency-encode MRI signals. Performance indicators mainly include gradient field strength, magnetic field linearity, effective volume, gradient field switching rate, and eddy current issues. Their performance directly affects the imaging speed and quality of MRI.

[0003] In existing technologies, permanent magnet MRI systems typically employ a modular layout that physically separates gradient coils and radio frequency (RF) transmit coils. The RF transmit coil (often used as a body coil) is fixed on the inside near the patient area, while the independent gradient coil module is installed on its periphery. By creating a physical barrier through spatial isolation, the magnetic and electrical coupling interference of the strong transient electromagnetic field generated during high-speed switching of the gradient coil on sensitive RF signals is minimized, thus fundamentally ensuring the signal-to-noise ratio of the image.

[0004] However, the above technical solutions significantly increase the physical size and weight of the nuclear magnetic resonance system. In particular, they force the distance between the magnet poles to increase, requiring more and heavier permanent magnet materials to maintain a specific field strength, which directly restricts the miniaturization, weight reduction and cost control of the system. Secondly, since the gradient coil is forced to move away from the imaging center, it requires a larger current to generate the target gradient field, which not only aggravates its own heating and energy consumption, but also amplifies the eddy current effect and thermal drift, bringing greater challenges to maintaining magnetic field uniformity. Summary of the Invention

[0005] To address the technical problems of increased system size, increased energy consumption, and difficulty in maintaining magnetic field uniformity caused by the physical separation of the gradient coil and the radio frequency transmitting coil in the prior art, the present invention provides a permanent magnet gradient coil assembly that can reduce the distance between the two poles of the system magnet, reduce energy consumption, and maintain field uniformity.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is: a permanent magnet gradient coil assembly, including a gradient coil body layer, with the direction pointing to the imaging center being upward, an radio frequency emission layer disposed on the upper part of the gradient coil body layer, an upper epoxy plate disposed on the upper part of the radio frequency emission layer, a first shielding layer disposed between the gradient coil body layer and the radio frequency emission layer, and a lower epoxy plate disposed on the lower part of the gradient coil body layer.

[0007] This invention integrates the radio frequency transmitting layer with the gradient coil body layer, greatly reducing the magnet gap and laying the physical foundation for the miniaturization, weight reduction and cost reduction of permanent magnet systems. At the same time, by setting a first shielding plate between the gradient coil and the radio frequency transmitting layer, a highly efficient near-field electromagnetic isolation barrier is constructed, which can actively suppress electromagnetic interference to sensitive radio frequency signals when the gradient coil body layer switches, fundamentally ensuring the image signal-to-noise ratio.

[0008] Furthermore, the first shielding layer includes a first shielding plate, on both ends of which are provided multiple electrically connected capacitors, and the first shielding plate is also connected to a grounding wire.

[0009] The present invention, by adding a capacitor to the shielding plate, forms an LC resonant structure that can more effectively reduce the electromagnetic interference of the gradient coil body layer to the radio frequency transmitting layer.

[0010] Furthermore, the capacitors are evenly distributed on the end face of the first shielding plate.

[0011] This invention arranges capacitors evenly so that each unit area of ​​the shielding plate surface has almost the same electromagnetic properties, so that no matter where the interfering electromagnetic field approaches the shielding plate, it will encounter a resonant reflection barrier of the same strength.

[0012] Furthermore, the first shielding plate has an insulating layer on both sides, a copper foil on the insulating layer, a circuit etched on the copper foil, a plurality of pads on the circuit, the pads being connected to the first shielding plate through corresponding metallized vias, and the capacitors being disposed on the corresponding pads.

[0013] This invention uses PCB technology to place the capacitor on the shielding plate first, which makes the first shielding plate have precise performance and compact structure, thereby improving the reliability of electromagnetic shielding.

[0014] Furthermore, the capacitor is a ceramic capacitor.

[0015] Furthermore, the gradient coil body layer, from bottom to top, includes a Y coil, an X coil, a Z coil, and a copper plate.

[0016] This invention employs a gradient coil body layer with an integrated copper plate, which enables the gradient coil body layer to have a self-shielding effect, further reducing electromagnetic interference to the radio frequency transmission layer.

[0017] Furthermore, it also includes a cooling layer disposed below the gradient coil body layer.

[0018] The present invention can dissipate the heat generated by the radio frequency transmitting layer and the gradient coil body layer by setting a cooling layer, thereby ensuring the reliable operation of the coil assembly.

[0019] Furthermore, the cooling layer includes an upper plate and a lower plate connected to each other. The upper plate and the lower plate have cooling channels with the same structure on their opposite end faces. The cooling channels have a serpentine structure and a semi-circular cross-section.

[0020] This invention achieves uniform and efficient heat dissipation by setting the cooling channels in a serpentine structure.

[0021] Furthermore, a second shielding plate is provided at the lower part of the cooling layer. The second shielding plate is located above the lower epoxy plate and is made of a high magnetic permeability material.

[0022] This invention uses the high permeability material of the second shielding plate to constrain the diffusion of the gradient magnetic field, suppress the external eddy current effect, and ensure the stability of the main magnetic field.

[0023] Furthermore, it also includes a shimming coil layer, which is located below the second shielding plate and is adjacent to the lower epoxy plate. The shimming coil layer is provided with an X-axis first-order linear compensation coil, a Y-axis first-order linear compensation coil and a Z-axis first-order linear compensation coil.

[0024] This invention enables precise correction of the linear non-uniformity of the main magnetic field in three orthogonal directions in space by setting first-order linear compensation coils in the X, Y and Z directions on the shimming coil layer.

[0025] As can be seen from the above technical solutions, the present invention has the following advantages: This invention provides a permanent magnet gradient coil assembly. By integrating the radio frequency (RF) emitting layer with the gradient coil body layer, the gap between magnets is significantly reduced, laying the physical foundation for the miniaturization, weight reduction, and cost reduction of permanent magnet systems. Simultaneously, by placing a first shielding plate between the gradient coil and the RF emitting layer, a highly efficient near-field electromagnetic isolation barrier is constructed, actively suppressing electromagnetic interference to sensitive RF signals during gradient coil body layer switching, fundamentally ensuring the image signal-to-noise ratio. The LC resonant structure formed by adding capacitors to the shielding plate further effectively reduces electromagnetic interference from the gradient coil body layer to the RF emitting layer. By uniformly arranging the capacitors, each unit area of ​​the shielding plate surface has almost identical electromagnetic characteristics, ensuring that interfering electromagnetic fields encounter the same intensity of resonance regardless of their approach to the shielding plate. The system incorporates several key features: a reflection barrier; a PCB-based design with capacitors mounted on the shielding plate, resulting in a precise and compact shielding system that enhances electromagnetic shielding reliability; a gradient coil body layer with integrated copper plates provides self-shielding, further reducing electromagnetic interference to the RF transmitter layer; a cooling layer dissipates heat generated by the RF transmitter layer and gradient coil body layer, ensuring reliable operation of the coil assembly; a serpentine cooling channel structure enables uniform and efficient heat dissipation; the high permeability of the second shielding plate constrains gradient magnetic field diffusion, suppressing external eddy current effects and ensuring main magnetic field stability; and first-order linear compensation coils in the X, Y, and Z directions on the shimming coil layer precisely correct the linear non-uniformity of the main magnetic field in three orthogonal spatial directions. Attached Figure Description

[0026] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention.

[0028] Figure 2 This is a schematic diagram of the structure of the first shielding layer in an embodiment of the present invention. Figure 1 .

[0029] Figure 3 This is a schematic diagram of the structure of the first shielding layer in an embodiment of the present invention. Figure 2 .

[0030] Figure 4 This is a schematic diagram of the assembly structure of the gradient coil body layer, cooling layer and shimming coil layer in an embodiment of the present invention.

[0031] Figure 5 This is a schematic diagram of the upper plate in an embodiment of the present invention.

[0032] Figure 6 This is a schematic diagram of the structure of the uniform coil layer in an embodiment of the present invention.

[0033] In the diagram, 1. Upper epoxy board; 2. RF transmitting layer; 3. First shielding layer; 301. Copper foil; 302. Insulating layer; 303. First shielding plate; 304. Capacitor; 305. Grounding wire; 306. Circuit; 307. Pad; 308. Metallized via; 4. Gradient coil body layer; 401. Copper plate; 402. Y coil; 403. Z coil; 404. X coil; 5. Cooling layer; 501. Upper plate; 502. Cooling channel; 6. Second shielding plate; 7. Shimming coil layer; 701. X-direction first-order linear compensation coil; 702. Y-direction first-order linear compensation coil; 703. Z-direction first-order linear compensation coil; 8. Lower epoxy board. Detailed Implementation

[0034] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the specific embodiments. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this patent, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this patent.

[0035] Gradient coils generate strong time-varying electromagnetic fields with rich frequency components during high-speed switching. These transient magnetic fields induce noise voltages in the conductors of the radio frequency (RF) transmit coils through near-field coupling mechanisms, severely interfering with the pure high-frequency signals required for the RF layer to operate. This leads to decreased transmission efficiency and introduces image noise, ultimately degrading the system's signal-to-noise ratio and imaging quality. Therefore, in existing technologies, gradient coils and RF transmit coils can only be arranged separately, with the RF transmit coil (often used as a body coil) fixed on the inner side near the patient area, while an independent gradient coil module is installed on its periphery. This reduces interference with sensitive RF signals, but significantly increases the size and weight of the permanent magnet MRI system. In one embodiment of this specific implementation, the applicant creatively integrates the gradient coils and RF transmit coils, while introducing a first shielding plate with corresponding shielding functions to avoid interference with sensitive RF signals.

[0036] like Figure 1 and Figure 2As shown, this specific embodiment provides a permanent magnet gradient coil assembly, including a gradient coil body layer 4, with the direction pointing towards the imaging center being upward. An RF emission layer 2 is disposed on the upper part of the gradient coil body layer 4, an upper epoxy plate 1 is disposed on the upper part of the RF emission layer 2, a first shielding layer 3 is disposed between the gradient coil body layer 4 and the RF emission layer 2, and a lower epoxy plate 8 is disposed on the lower part of the gradient coil body layer 4.

[0037] This embodiment integrates the radio frequency transmitting layer 2 with the gradient coil body layer 4, greatly reducing the magnet gap and laying a physical foundation for the miniaturization, weight reduction and cost reduction of the permanent magnet system. At the same time, by setting a first shielding plate 303 between the gradient coil and the radio frequency transmitting layer 2, a highly efficient near-field electromagnetic isolation barrier is constructed, which can actively suppress electromagnetic interference to sensitive radio frequency signals when the gradient coil body layer 4 switches, fundamentally ensuring the image signal-to-noise ratio.

[0038] In this embodiment, the first shielding layer 3 includes a first shielding plate 303. Multiple electrically connected capacitors 304 are disposed on both ends of the first shielding plate 303. The first shielding plate 303 is also connected to a grounding wire 305. The first shielding plate 303 is a copper plate 401. This arrangement further reduces electromagnetic interference from the gradient coil body layer 4 to the radio frequency transmitting layer 2. The copper plate 401, as a good conductor, primarily shields through reflection. Rapidly changing electromagnetic fields induce eddy currents on the copper plate 401, which generate a reverse magnetic field, thereby canceling and reflecting most of the incident high-frequency electromagnetic energy, resulting in a significant effect. Furthermore, the capacitors 304 and the inductance of the first shielding plate 303 form an LC resonant circuit, which has an inherent resonant frequency. , , L represents the inductance of the first shielding plate, measured in Henry, which can be determined using an impedance analyzer. C represents the capacitance, measured in Farads. By carefully selecting a suitable capacitor, this resonant frequency can be achieved. The frequency band is precisely adjusted to the low-frequency band where the gradient coil noise energy is most concentrated, generating extremely high impedance at a specific interference frequency point. This reflects most of the gradient switching energy back, preventing it from propagating to the RF layer at the source. The ground wire 305 provides a low-impedance path to the ground for this residual noise current, safely conducting it away and preventing it from accumulating on the shielding plate and being re-radiated, thus forming secondary interference.

[0039] like Figure 2 and Figure 4As shown, furthermore, to avoid forming shielding loopholes, the capacitors 304 are evenly arranged on the end face of the first shielding plate 303. By evenly arranging the capacitors 304, each unit area of ​​the shielding plate surface has almost the same electromagnetic characteristics, so that the interfering electromagnetic field will encounter the same intensity of resonant reflection barrier no matter where it approaches the first shielding plate 303. In this embodiment, multiple capacitors 304 are arranged radially on the end face of the first shielding plate 303, and multiple capacitors 304 are evenly distributed along four radii on the end face of the first shielding plate 303, with three capacitors 304 arranged on each radius.

[0040] like Figure 2 and Figure 3As shown, to ensure the manufacturing quality and reliability of the shielding function of the first shielding plate 303, capacitors 304 are installed using PCB manufacturing processes. Specifically, both sides of the first shielding plate 303 are provided with insulating layers 302, the insulating layer 302 being made of glass fiber. Copper foil 301 is provided on the insulating layer 302, and circuits 306 are etched on the copper foil 301. Multiple pads 307 are provided on the circuits 306, and the pads 307 are connected to the first shielding plate 303 through corresponding metallized vias 308. The capacitors 304 are mounted on the corresponding pads 307. The specific steps are as follows: Using a photochemical process, the designed circuit pattern 306 (including pads 307 and connecting lines) is transferred onto copper foil 301. Then, unwanted copper is etched away, leaving precise pads 307 and fine traces connecting them to vias on copper foil 301. These fine traces constitute circuit 306, which is a grid pattern covering the entire shielding area. It is composed of interwoven vertical and horizontal wires forming numerous small rhombuses or squares. The width of the grid lines needs to be calculated to be wide enough to carry the high-frequency current during resonance. Pads 307 are located at the grid nodes, where connections are needed. Tiny holes are drilled at the positions of disk 307 and copper plate 401. A layer of copper is plated onto the inner wall of these holes using chemical deposition and electroplating processes, forming a conductive channel—this channel is the metallized via 308. Capacitor 304 is a ceramic capacitor. This method of installing capacitor 304 eliminates the inductance introduced by traditional leads, ensuring precise and controllable LC resonant frequency. The solder joints can withstand the strong, long-term vibrations generated by the gradient coil body layer 4, preventing failure due to fatigue. Simultaneously, installing a large number of capacitors 304 within the limited area of ​​copper plate 401 achieves a uniform and dense distributed shielding network, making... The first shielding layer 3 has a reliable shielding effect, while the circuit 306 has extremely low loop inductance. Current can start from any capacitor 304 and flow to the first shielding plate through the shortest path (grid and via), forming the smallest loop area. The grid and via array ensure that the potential changes in different areas of the entire shielding plate are synchronized, avoiding the problem of "hot spots" and "cold spots" where some areas resonate strongly and others resonate weakly. This makes the overall shielding effectiveness uniform. The entire grid shares the current and can withstand large high-frequency currents during resonance without being damaged by local overheating during the manufacturing of the metallized vias 308.

[0041] like Figure 4 As shown, in this embodiment, in order to further enhance the electromagnetic shielding effect of the gradient coil body layer 4, the gradient coil body layer 4 adopts a self-shielded gradient coil. The gradient coil body layer 4, from bottom to top, includes a Y coil 402, an X coil 404, a Z coil 403, and a copper plate 401.

[0042] like Figure 4 and Figure 5As shown, after integrating the RF transmitting layer 2 into one unit, the heat generated by this coil assembly during operation is higher. To ensure the reliability of the coil assembly, this embodiment also includes a cooling layer 5. The cooling layer 5 is located below the gradient coil body layer. The cooling layer 5 can communicate with a cooling unit, which includes a water pump, a heat exchanger, a liquid storage tank, a filter, and a deionization column, forming a closed loop. The cooling unit is responsible for transferring the heat absorbed by the liquid cooling layer to the cooling water of the hospital or laboratory facilities, which then dissipates the heat into the atmosphere. To achieve efficient heat dissipation, the cooling layer 5 includes an upper plate 501 and a lower plate connected by brazing. The upper plate 501 and the lower plate have identical cooling channels 502 on their opposite end faces. The cooling channels 502 have a serpentine structure and a semi-circular cross-section. When the upper plate 501 and the lower plate are welded together, a circular cross-section cooling medium flow channel is formed inside the cooling layer 5. By setting the cooling channels 502 to a serpentine structure, uniform and efficient heat dissipation is achieved.

[0043] like Figure 4 As shown, in this embodiment, a second shielding plate 6 is also provided at the lower part of the cooling layer 5. The second shielding plate 6 is located above the lower epoxy plate 8. The second shielding plate 6 is made of a high magnetic permeability material, such as niobium-titanium alloy or permalloy. The second shielding plate 6 provides a low magnetic resistance shielding path for the rapidly changing magnetic field generated by the rapid switching of the gradient coil body layer 4, "binding" most of the magnetic lines of force inside the second shielding plate 6, effectively preventing them from leaking out to permanent magnets and other metal components, thereby fundamentally suppressing the eddy current effect and ensuring the stability of the main magnetic field and the fidelity of the gradient waveform.

[0044] It is impossible to achieve an absolutely uniform magnetic field within the imaging space using ideal permanent magnets or superconducting magnets. Material inhomogeneities during manufacturing, limitations in processing precision, and the physical design of the magnet structure all contribute to an inherent, initially non-uniform distribution of the static magnetic field. Furthermore, ferromagnetic objects surrounding the MRI equipment, such as building steel reinforcement, moving metal vehicles, or equipment, can disturb the distribution of magnetic field lines. This non-uniformity in the main magnetic field causes a shift in the MRI frequency, ultimately leading to image geometric distortion and signal loss. To address this issue, such as... Figure 4 and Figure 6As shown, this embodiment also includes a shimming coil layer 7, which is located below the second shielding plate 6 and adjacent to the lower epoxy plate 8. The shimming coil layer 7 is provided with an X-direction first-order linear compensation coil 701, a Y-direction first-order linear compensation coil 702, and a Z-direction first-order linear compensation coil 703. The first-order linear compensation coils are composed of specific planar conductor patterns etched on the flexible circuit 306 board. These patterns are precisely arranged according to the spherical harmonic function model. The X-direction and Y-direction first-order linear compensation coils 702 adopt a symmetrically distributed saddle-shaped or figure-eight-shaped wiring layout. In this embodiment, a figure-eight-shaped wiring layout is adopted. By controlling the directionality of the current in the conductors on both sides, a compensation magnetic field that varies linearly along the X-axis and Y-axis is generated in the imaging plane, respectively. The Z-direction first-order coil is composed of one or more pairs of parallel ring conductors. A linear gradient field along the principal axis is formed by excitation with current in the same direction. With this arrangement, the linear non-uniformity of the main magnetic field in three orthogonal directions in space can be accurately corrected.

[0045] In this embodiment, the upper epoxy plate 1, the radio frequency transmitting layer 2, the first shielding layer 3, the gradient coil body layer 4, the cooling layer 5, the second shielding plate 6, and the lower epoxy plate 8 are resin-cured integral structures.

[0046] As can be seen from the above specific embodiments, the present invention has the following beneficial effects: 1. By integrating the radio frequency transmitting layer 2 with the gradient coil body layer 4, the gap between magnets is greatly reduced, laying a physical foundation for the miniaturization, weight reduction and cost reduction of the permanent magnet system. At the same time, by setting the first shielding plate 303 between the gradient coil and the radio frequency transmitting layer 2, a highly efficient near-field electromagnetic isolation barrier is constructed, which can actively suppress the electromagnetic interference of the gradient coil body layer 4 to sensitive radio frequency signals when switching, fundamentally ensuring the image signal-to-noise ratio. 2. By adding capacitor 304 to the shielding plate, the LC resonant structure formed can more effectively reduce the electromagnetic interference of gradient coil body layer 4 to radio frequency transmission layer 2. 3. By uniformly arranging the 304 capacitors, the electromagnetic properties of each unit area on the surface of the shielding plate are almost the same, so that the interfering electromagnetic field will encounter the same intensity of resonant reflection barrier no matter where it approaches the shielding plate. 4. By using PCB technology to place capacitor 304 on the shielding plate first, the first shielding plate 303 has precise performance and compact structure, thus improving the reliability of electromagnetic shielding. 5. By adopting the gradient coil body layer 4 with its own copper plate 401, the gradient coil body layer 4 has a self-shielding effect, further reducing electromagnetic interference to the radio frequency transmission layer 2. 6. By setting the cooling layer 5, the heat generated by the radio frequency transmitting layer 2 and the gradient coil body layer 4 can be dissipated, ensuring the reliable operation of this coil assembly; 7. By setting the cooling channel 502 to a serpentine structure, uniform and efficient heat dissipation is achieved; 8. The diffusion of the gradient magnetic field is constrained by the high magnetic permeability material of the second shielding plate 6, which suppresses the external eddy current effect and ensures the stability of the main magnetic field; 9. By setting first-order linear compensation coils in the X, Y and Z directions on the shimming coil layer 7, the linear non-uniformity of the main magnetic field in the three orthogonal directions in space can be accurately corrected respectively.

[0047] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A permanent magnet gradient coil assembly, comprising a gradient coil body layer (4), characterized in that, The direction pointing to the imaging center is upward. A radio frequency emission layer (2) is provided on the upper part of the gradient coil body layer (4). An upper epoxy plate (1) is provided on the upper part of the radio frequency emission layer (2). A first shielding layer (3) is provided between the gradient coil body layer (4) and the radio frequency emission layer (2). A lower epoxy plate (8) is provided on the lower part of the gradient coil body layer (4). The first shielding layer (3) includes a first shielding plate (303), and multiple electrically connected capacitors (304) are provided on both ends of the first shielding plate (303). The first shielding plate (303) is also connected to a grounding wire (305). The capacitors (304) are evenly arranged on the end face of the first shielding plate (303); The first shielding plate (303) has an insulating layer (302) on both sides. A copper foil (301) is provided on the insulating layer (302). A circuit (306) is etched on the copper foil (301). A plurality of pads (307) are provided on the circuit (306). The pads (307) are connected to the first shielding plate (303) through corresponding metallized vias (308). The capacitor (304) is provided on the corresponding pad (307).

2. The permanent magnet gradient coil assembly as described in claim 1, characterized in that, The capacitor (304) is a ceramic capacitor (304).

3. The permanent magnet gradient coil assembly as described in any one of claims 1-2, characterized in that, The gradient coil body layer (4) includes, from bottom to top, a Y coil (402), an X coil (404), a Z coil (403), and a copper plate (401).

4. The permanent magnet gradient coil assembly as described in claim 3, characterized in that, It also includes a cooling layer (5), which is disposed below the gradient coil body layer (4).

5. The permanent magnet gradient coil assembly as described in claim 4, characterized in that, The cooling layer (5) includes an upper plate (501) and a lower plate connected to each other. The upper plate (501) and the lower plate have cooling channels (502) with the same structure on their opposite end faces. The cooling channels (502) have a serpentine structure and a semi-circular cross-section.

6. The permanent magnet gradient coil assembly as described in claim 5, characterized in that, A second shielding plate (6) is also provided at the lower part of the cooling layer (5), and the second shielding plate (6) is located above the lower epoxy plate (8).

7. The permanent magnet gradient coil assembly as described in claim 6, characterized in that, It also includes a shimming coil layer (7), which is located below the second shielding plate (6). The shimming coil layer (7) is adjacent to the lower epoxy plate (8). The shimming coil layer (7) is provided with an X-direction first-order linear compensation coil (701), a Y-direction first-order linear compensation coil (702) and a Z-direction first-order linear compensation coil (703).

Images