Passive large-aperture magnetic resonance metamaterial with stable gain

Abstract

The invention discloses a passive large-aperture magnetic resonance metamaterial with stable gain, and relates to the technical field of magnetic resonance imaging, the passive large-aperture magnetic resonance metamaterial comprises a body, the body comprises a plurality of coil assemblies distributed at intervals in the circumferential direction, the plurality of coil assemblies are in central symmetry about the central point of the body, and the adjacent coil assemblies are connected through metal wires; each coil assembly comprises two spiral coils with opposite spiral directions, and the two spiral coils are distributed at intervals in the circumferential direction and the outer ends of the two spiral coils are connected. The passive large-aperture magnetic resonance metamaterial with stable gain, provided by the invention, can be effectively applied to an MRI (Magnetic Resonance Imaging) system required by a large-aperture imaging target, keeps the gain stable when being multiplexed with a radio frequency coil, effectively focuses a magnetic field in a region of interest, and improves the signal-to-noise ratio of magnetic resonance imaging.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear magnetic resonance imaging, and particularly to a passive large-aperture magnetic resonance metamaterial with stable gain. Background Art

[0002] Magnetic Resonance Imaging (MRI) is a high-resolution non-ionizing imaging technology widely used in the field of clinical medical imaging; the distribution of the radiofrequency field is directly related to the signal-to-noise ratio and is a key indicator for evaluating the performance of MRI. The optimization of the radiofrequency field mainly focuses on the generation and propagation of the radiofrequency field. In addition to optimizing the coil performance and improving the transmission and reception efficiency, in the process of receiving magnetic resonance signals, using metamaterials to improve the distribution of the radiofrequency field to increase the signal-to-noise ratio is a more effective method; metamaterials are artificial synthetic materials composed of sub-wavelength units. By utilizing their ability to adjust and redistribute incident electromagnetic waves in the near-field region, the focusing and enhancement of MRI signals can be achieved, the imaging quality can be improved, and the imaging efficiency can be increased.

[0003] Currently, there are already related studies on using metamaterials to improve the signal-to-noise ratio of MRI. The application scenarios are all for body coil excitation to transmit and receive radiofrequency fields. The gain distance of the metamaterials is limited, so they need to be close to the imaging target. As a result, due to coupling problems, they cannot be used jointly with surface coil arrays, and the sensitivity of the metamaterials is limited compared with advanced surface receiving coil arrays, which hinders the clinical application of metamaterials. Most existing metamaterials are based on two-dimensional planar or volumetric designs. The effective gain distance of planar metamaterials is limited to the shallow surface area of the imaging target, and the gain effect rapidly weakens as the penetration depth increases. Although volumetric metamaterials have more advantages in terms of gain distance, their apertures are limited and still cannot meet the imaging requirements of large apertures, such as head detection. As the aperture of the metamaterials increases, the coupling with the coil is significantly enhanced, and the magnetic field focusing effect of the metamaterials is interfered, making it difficult to ensure an effective gain depth. Especially in ultra-low field MRI systems, the magnet aperture limits the imaging space, and the space utilization rate and detection range of conventional metamaterials in ultra-low field MRI systems are more restricted. Therefore, there is a need to provide a passive large-aperture metamaterial that maintains stable gain when coupled and reused with coils. Summary of the Invention

[0004] The purpose of the present invention is to provide a passive large-aperture magnetic resonance metamaterial with stable gain to solve the problems existing in the above-mentioned prior art, which can be effectively applied to MRI systems with large-aperture imaging target requirements, maintain stable gain when reused with radiofrequency coils, effectively focus the magnetic field in the region of interest, and improve the signal-to-noise ratio of magnetic resonance imaging.

[0005] To achieve the above purpose, the present invention provides the following solutions:

[0006] The present invention provides a passive large-aperture magnetic resonance metamaterial with stable gain, including a body, the body includes multiple groups of coil components distributed at intervals in the circumferential direction, the multiple groups of coil components are centrosymmetric about the center point of the body, and adjacent coil components are connected by metal wires; each group of coil components includes two spiral coils with opposite spiral directions, and the two spiral coils are distributed at intervals in the circumferential direction and their outer ends are connected.

[0007] Preferably, the body is arranged in a cylindrical shape, and the curvature of the cross-section of the body is consistent with the curvature of the part to be detected.

[0008] Preferably, the body includes two groups of the coil components, and the curvature of the metal wire is consistent with the curvature of the coil components.

[0009] Preferably, the cross-sectional shapes of each of the spiral coils and the metal wires are regular shapes.

[0010] Preferably, the materials of the spiral coils and the metal wires are copper materials.

[0011] Preferably, the number of turns of each of the spiral coils is the same.

[0012] Preferably, the axial ends between adjacent coil components are all connected by the metal wires.

[0013] Preferably, the inner diameter of the body is not less than 250 mm, and the axial dimension of the body is not less than 150 mm.

[0014] Preferably, variable tuning capacitors for connecting the two spiral coils are arranged between the inner ends of the two spiral coils of each group of coil components and at one end of the interval between the two spiral coils of each group of coil components.

[0015] Preferably, the number of turns of each of the spiral coils is 5 turns, the cross-sectional width of each of the spiral coils is 5 mm, and the turn pitch of each of the spiral coils is 5 mm.

[0016] The present invention has achieved the following technical effects compared with the prior art:

[0017] The passive large-aperture magnetic resonance metamaterial with stable gain provided by the present invention is formed by bending around a component to be detected with multiple coil assemblies circumferentially distributed and centrosymmetrically arranged. Adjacent coil assemblies are connected by metal wires, and each coil assembly includes spiral coils with opposite winding directions. The spiral coils with opposite winding directions are complementarily arranged, further concentrating the magnetic field energy inside the radio-frequency coil, i.e., the Helmholtz coil. The multiple coil assemblies placed on the side can integrate and concentrate the interfering magnetic field energy caused by the edge effect into the required magnetic field, and can achieve the gain of the magnetic field in the axial plane or transverse plane of the coil according to the excitation direction of the receiving coil, significantly improving the signal-to-noise ratio and resolution of the image, thereby providing clearer and more accurate diagnostic information. Moreover, the use of the spiral-wound structure metamaterial has higher frequency stability, and can achieve a stable signal-to-noise ratio gain effect under the coupling interference of the receiving coil such as the Helmholtz coil, effectively avoiding the gain failure problem caused by frequency shift coupling when the Helmholtz coil and the metamaterial are closely shared, having the potential to be shared with the Helmholtz coil array, greatly improving the space utilization rate. Especially for ultra-low field MRI systems with limited magnet apertures, it can meet the design of large apertures to be applicable to various detection target requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0019] Figure 1 Schematic diagram of the structure of the passive large-aperture magnetic resonance metamaterial with stable gain provided for Embodiment 1;

[0020] Figure 2 Schematic diagram of the structure of the passive large-aperture magnetic resonance metamaterial with stable gain provided for Embodiment 1 closely shared with a 70 mT ultra-low field MRI Helmholtz coil;

[0021] Figure 3 Comparison of the curves of the magnetic field strength and frequency when the passive large-aperture magnetic resonance metamaterial with stable gain provided for Embodiment 1 is applied to a 70 mT ultra-low field MRI system;

[0022] Figure 4 For the B1 with and without the passive large-aperture magnetic resonance metamaterial with stable gain provided for Embodiment 1 - FIELD DISTRIBUTION MAP;

[0023] Figure 5 Signal-to-noise ratio gain curve along the central transverse axis with and without the passive large-aperture magnetic resonance metamaterial with stable gain provided for Embodiment 1.

[0024] In the figure: 1 - body; 10 - coil assembly; 11 - metal wire; 12 - helical coil; 13 - variable tuning capacitor; 2 - Helmholtz coil. Specific embodiments

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] The object of the present invention is to provide a passive large - aperture magnetic resonance metamaterial with stable gain to solve the problems existing in the above - mentioned prior art, which can be effectively applied to an MRI system for large - aperture imaging target requirements, maintain stable gain when multiplexed with a radio - frequency coil, effectively focus the magnetic field in the region of interest, and improve the signal - to - noise ratio of magnetic resonance imaging.

[0027] To make the above - mentioned objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Embodiment 1

[0029] This embodiment provides a passive large - aperture magnetic resonance metamaterial with stable gain. Please refer to Figure 1 , which includes a body 1. The body 1 includes multiple groups of coil assemblies 10 that are circumferentially spaced apart. The multiple groups of coil assemblies 10 are centrosymmetric about the center point of the body 1, and adjacent coil assemblies 10 are connected by a metal wire 11. Each group of coil assemblies 10 includes two helical coils 12 with opposite helical directions. The two helical coils 12 are circumferentially spaced apart and connected at their outer ends.

[0030] Multiple sets of coil assemblies 10 are circumferentially distributed and centrosymmetrically arranged, bent and formed around the component to be detected. Adjacent coil assemblies 10 are connected by metal wires 11, and each coil assembly 10 includes helical coils 12 with opposite helical directions. The helical coils 12 with opposite helical directions are complementarily arranged, further concentrating the magnetic field energy inside the radiofrequency coil, i.e., the Helmholtz coil 2. The multiple sets of coil assemblies placed on the side can integrate and concentrate the interfering magnetic field energy caused by the edge effect into the required magnetic field, can achieve the gain of the magnetic field in the axial plane or the transverse plane of the coil according to the excitation direction of the receiving coil, can significantly improve the signal-to-noise ratio and resolution of the image, thereby providing clearer and more accurate diagnostic information, and the use of the spiral-wound structure metamaterial has higher frequency stability, can achieve a stable signal-to-noise ratio gain effect under the coupling interference of the receiving coil such as the Helmholtz coil 2, effectively avoiding the gain failure problem when the Helmholtz coil 2 and the metamaterial are closely adjacent and shared, has the potential to be shared with the Helmholtz coil 2 array, greatly improving the space utilization rate, especially for ultra-low field MRI systems with limited magnet apertures, can meet the design of large apertures so as to be applicable to various detection target requirements.

[0031] In an alternative embodiment of the present invention, preferably, the body 1 is arranged in a cylindrical shape, and the cross-sectional curvature of the body 1 is consistent with the curvature of the part to be detected. Specifically, it can be conformal with the bent head to be detected and maintain the same curvature to meet the imaging requirements of large apertures.

[0032] In an alternative embodiment of the present invention, preferably, the body 1 includes two sets of coil assemblies 10, and the curvature of the metal wire 11 is consistent with the curvature of the coil assembly 10; the specific number of coil assemblies 10 can be specifically determined according to the actual part to be detected.

[0033] In an alternative embodiment of the present invention, preferably, the cross-sectional shapes of the helical coils 12 and the metal wires 11 are regular shapes, and the regular shapes can be square or circular, which are determined according to specific requirements.

[0034] In an alternative embodiment of the present invention, preferably, the helical coils 12 and the metal wires 11 are made of copper material, which can meet the requirements of electrical conductivity and thermal stability.

[0035] In an alternative embodiment of the present invention, preferably, the number of turns of each helical coil 12 is the same, and the same number of turns of adjacent coils can significantly improve the signal-to-noise ratio.

[0036] In an alternative embodiment of the present invention, preferably, both axial ends between adjacent coil assemblies 10 are connected by metal wires 11, enabling the multiple sets of coil assemblies 10 to be conductively connected in the circumferential direction, and can achieve the gain of the magnetic field of the Helmholtz coil 2 in the axial direction.

[0037] In an alternative embodiment of the present example, preferably, a variable tuning capacitor 13 for connecting the two spiral coils 12 is provided between the inner ends of the two spiral coils 12 of each coil assembly 10 and at one end of the gap between the two spiral coils 12 of each coil assembly 10. By providing the variable tuning capacitor 13, the metamaterial resonance frequency can be adjusted. The variable tuning capacitor 13 can be applied to different field strength MRI systems, including ultra-low field, low field, and high field MRI.

[0038] In an alternative embodiment of the present example, preferably, the inner diameter of the body 1 is not less than 250 mm, and the axial dimension of the body 1 is not less than 150 mm to meet the imaging requirements of a large aperture. The specific dimensions are determined according to actual needs.

[0039] In an alternative embodiment of the present example, preferably, the number of turns of each spiral coil 12 is 5, the cross-sectional width of each spiral coil 12 is 5 mm, and the turn spacing of each spiral coil 12 is 5 mm. With the inner diameter of the body 1 set to 250 mm and the axial dimension of the body 1 set to 150 mm, the signal-to-noise ratio is in the best state.

[0040] Specifically, in order to fully demonstrate the effect of the gain-stable passive large-aperture magnetic resonance metamaterial provided in this embodiment, the inner diameter of the body 1 is set to 250 mm, the axial dimension is 150 mm, the number of turns of a single spiral coil 12 is 5, the wire width is 5 mm, the turn spacing is 5 mm, and the capacitance value of the variable tuning capacitor 13 is 180 pF, so that the metamaterial resonates at a frequency of 2.98 MHz, corresponding to the Larmor frequency of a 70 mT ultra-low field MRI system;

[0041] As Figure 2 shown, it is a schematic diagram of the adjacent shared structure of the gain-stable passive large-aperture magnetic resonance metamaterial provided in this embodiment and a 70 mT ultra-low field MRI Helmholtz coil. The inner diameter of the Helmholtz coil 2 is 255 mm, the width is 200 mm, and the distance from the metamaterial is only 2.5 mm, realizing the model setting of the adjacent sharing of the metamaterial and the radio frequency coil. The resonance frequency of the Helmholtz coil 2 is 2.98 MHz, and the 50-ohm impedance matching of the radio frequency coil is set well, enabling it to effectively operate in a 70 mT ultra-low field MRI system.

[0042] As Figure 3As shown, it is a comparison of the relationship curves between magnetic field intensity and frequency when the gain-stable passive large-aperture magnetic resonance metamaterial provided by this embodiment is applied to a 70 mT ultra-low field MRI system. The magnetic field probe is set at the center inside the metamaterial. It can be seen from the figure that both the Helmholtz coil 2 and the metamaterial resonate at a frequency of 2.98 MHz. After adding the metamaterial, the magnetic field focusing enhancement effect is achieved. The magnetic field intensity measured by the magnetic field probe in the deepest region is 5.13 A / m. Compared with simply setting the Helmholtz coil 2, the magnetic field enhancement effect in the deepest region reaches 1.9 times, which can significantly improve the imaging quality.

[0043] As Figure 4 shown, it is the magnetic field distribution map when there is or without the gain-stable passive large-aperture magnetic resonance metamaterial provided by this embodiment. The results are normalized to the 1 W input power of the radiofrequency coil. A cylindrical simulation phantom is added to simulate human head imaging. The inner diameter of the phantom is 230 mm, the width is 200 mm, the relative permittivity of the phantom material is 68.5, and the conductivity of the phantom material is 0.4 S / m. It can be seen from the figure that after adding the metamaterial, the magnetic field intensity inside the coil is significantly increased (the darker the color, the higher the field strength), especially the enhancement amplitude in the region covered by the metamaterial is further improved. After being excited by the Helmholtz coil 2, the metamaterial effectively focuses the magnetic field in the inner region of the metamaterial and can ensure sufficient gain distance. The radiofrequency field of the Helmholtz coil 2 does not destructively interfere with the magnetic field focusing effect of the metamaterial. The metamaterial can be used adjacent to the radiofrequency coil, improving the imaging quality and signal-to-noise ratio of ultra-low field MRI while increasing the space utilization rate. magnetic field, and can ensure sufficient gain distance; the radiofrequency field of the Helmholtz coil 2 does not destructively interfere with the magnetic field focusing effect of the metamaterial. The metamaterial can be used adjacent to the radiofrequency coil, improving the imaging quality and signal-to-noise ratio of ultra-low field MRI while increasing the space utilization rate.

[0044] As Figure 5 shown, it is the signal-to-noise ratio gain curve along the central transverse axis of the gain-stable passive large-aperture magnetic resonance metamaterial provided by this embodiment, that is, the signal-to-noise ratio gain along the Figure 4 white dotted line in

[0045] Since the introduction of the metamaterial, a signal-to-noise ratio gain of more than 3.5 times that of the Helmholtz coil 2 has been achieved inside the phantom to be measured. The metamaterial can maintain a stable signal-to-noise ratio gain at large apertures and high penetration depths, effectively improving the imaging quality. Compared with traditional metamaterials, the metamaterial overcomes the gain failure phenomenon when adjacent to the coil, has the potential to be used jointly with the surface coil array, has more application flexibility, effectively improves the space utilization rate, and promotes the large-scale clinical application of the metamaterial. Among them, in the MRI system, the calculation formula of the signal-to-noise ratio is as follows:

[0046]

[0047] Among them, is the radiofrequency field excited by the system, P coilis the loss power of the RF coil, P meta is the loss power of the metamaterial, P vhantom is the loss power of the imaging target to-be-measured object.

[0048] The calculation formula for the signal-to-noise ratio gain is:

[0049]

[0050] wherein, SNR1 is the signal-to-noise ratio after loading the metamaterial, and SNR2 is the signal-to-noise ratio when the RF coil is not loaded with the metamaterial.

[0051] In the present invention, specific examples are used to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A passive large-aperture magnetic resonance metamaterial with stable gain, characterized in that: It includes a body (1), and the body (1) includes multiple groups of coil components (10) that are circumferentially spaced apart. The multiple groups of coil components (10) are centrosymmetric about the center point of the body (1), and adjacent coil components (10) are connected by a metal wire (11); each group of coil components (10) includes two helical coils (12) with opposite helical directions, and the two helical coils (12) are circumferentially spaced apart and their outer ends are connected.

2. The gain-stable passive large-aperture magnetic resonance metamaterial according to claim 1, characterized in that: The body (1) is arranged in a cylindrical shape, and the cross-sectional curvature of the body (1) is consistent with the curvature of the part to be detected.

3. The gain-stabilized passive large-aperture magnetic resonance metamaterial according to claim 2, wherein: The body (1) includes two groups of coil components (10), and the curvature of the metal wire (11) is consistent with the curvature of the coil components (10).

4. The gain-stable passive large-aperture magnetic resonance metamaterial according to claim 1, wherein: The cross-sectional shapes of each helical coil (12) and the metal wire (11) are regular shapes.

5. The gain-stable passive large-aperture magnetic resonance metamaterial according to claim 1, wherein: The materials of the helical coils (12) and the metal wire (11) are copper materials.

6. The gain-stable passive large-aperture magnetic resonance metamaterial according to claim 1, wherein: The number of turns of each helical coil (12) is the same.

7. The gain-stable passive large-aperture magnetic resonance metamaterial according to claim 1, wherein: Both ends between the axial ends of adjacent coil components (10) are connected by the metal wire (11).

8. The gain-stable passive large-aperture magnetic resonance metamaterial according to claim 2, wherein: The inner diameter of the body (1) is not less than 250 mm, and the axial dimension of the body (1) is not less than 150 mm.

9. The gain-stable passive large-aperture magnetic resonance metamaterial according to claim 1, characterized in that: Variable tuning capacitors (13) for connecting the two helical coils (12) are provided between the inner ends of the two helical coils (12) of each group of coil components (10) and at one end of the interval between the two helical coils (12) of each group of coil components (10).

10. The gain-stable passive large-aperture magnetic resonance metamaterial according to claim 8, characterized in that: The number of turns of each helical coil (12) is 5 turns, the cross-sectional width of each helical coil (12) is 5 mm, and the turn pitch of each helical coil (12) is 5 mm.

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