CN117148241B - Intelligent metamaterial structure - Google Patents
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
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- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
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- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
- G01R33/3628—Tuning/matching of the transmit/receive coil
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- H01Q15/0013—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective
- H01Q15/002—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective said selective devices being reconfigurable or tunable, e.g. using switches or diodes
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- H—ELECTRICITY
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- H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
- H01Q15/0013—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective
- H01Q15/0026—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective said selective devices having a stacked geometry or having multiple layers
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- H01Q15/0086—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices having materials with a synthesized negative refractive index, e.g. metamaterials or left-handed materials
Abstract
The invention discloses an intelligent metamaterial structure, which relates to the field of metamaterial structures, and comprises a dielectric substrate, a conductor structure, an adjustable capacitor and a dynamic tuning device; the conductor structure is a conductor of a circular cylinder; the side surface of the conductor structure is provided with radial symmetrical notches; the adjustable capacitor is arranged in the notch; the conductor structure and the adjustable capacitor are arranged on the dielectric substrate; the dynamic tuning device is connected with the adjustable capacitor; the dynamic tuning device is used for controlling the capacitance value of the adjustable capacitor in the imaging scanning process of the magnetic resonance equipment. The invention is suitable for important body organs, has stable structure, is convenient to tune and has better gain, and nonlinear and real-time dynamic tuning can be realized.
Description
Technical Field
The invention relates to the field of metamaterial structures, in particular to an intelligent metamaterial structure.
Background
Magnetic Resonance Imaging (MRI) is a commonly used medical imaging technique, and the basic principle thereof is that a transmitting coil generates a resonant electromagnetic induction field inside a human body by transmitting a pulse sequence, so that atomic nuclei inside the human body spontaneously emit signals, the signals are detected and received by a receiving coil, and a magnetic resonance imaging device acquires fourier space data of a measured object and reconstructs according to the acquired data, thereby obtaining an internal structure image of a specific region of the human body. Compared with Computed Tomography (CT), MRI has the advantages of high tissue resolution, multi-sequence imaging, three-dimensional imaging, no influence of ionizing radiation and the like, and the technology is widely applied to the fields of clinical medicine, biomedical research, material science and the like.
Metamaterials are artificially created structures with sub-wavelengths, which are arranged in a specific manner and resonate with electromagnetic waves. By means of different unit shapes, structures and arrangement modes, absorption or reflection of specific wave bands is achieved, and meanwhile signal intensity can be adjusted according to selection of materials and structures. The study of metamaterials has attracted considerable attention and has many applications such as in the microwave, terahertz and optical fields.
In the field of magnetic resonance imaging, the application of metamaterials is still in a starting stage. Some studies have shown that better imaging results can be achieved by using metamaterials. In 2001 Wiltshire et al used metamaterial based on swiss coil structural units for magnetic resonance echo signal enhancement, which demonstrated the potential of metamaterial in magnetic resonance imaging signal enhancement. In 2008 Freire et al, a signal lens is realized by using a metamaterial with a negative refractive index, and the signal-to-noise ratio of a received signal is improved by about 60% by focusing an RF echo signal.
2016 Slobozhanyuk et al designed a metamaterial with a high dielectric constant medium as a substrate, and the metamaterial periodically arranged metal wires in a high dielectric constant solution, and experiments showed that the magnetic field of the imaging area on the surface of the metamaterial was improved by 2.5 times. However, the disadvantage of such metamaterials is the high Specific Absorption Rate (SAR) values in the region close to the wire edge, which makes the security during magnetic resonance impossible to guarantee and the poor magnetic field homogeneity in the region close to the resonator boundary, which is detrimental for clear imaging.
In 2019 Zhao X et al, a metamaterial based on a spiral structural unit is proposed, and the result is that a resonant ring is introduced into a solenoid metamaterial to achieve a nonlinear effect of the metamaterial, the gain of the metamaterial to a radio frequency magnetic field is restrained in a transmitting stage of a radio frequency signal, and the gain of the metamaterial to the radio frequency magnetic field is recovered in a receiving stage, so that the SNR of the surface area of the metamaterial is changed to be 10-15 times that of the former. The local increase of the transmitting power not only disturbs the uniformity of the transmitting field, but also has the potential threat of tissue heating and high SAR, and the metamaterial is not used for enhancing the radio frequency transmitting magnetic field, so that the safety of using the metamaterial is ensured. Solenoid-type metamaterials remain planar structures and still present problems in terms of magnetic field uniformity and magnetic field enhancement effects for specific structures or organs. And designing a solenoid-like metamaterial for a specific organ is challenging, in order to meet the fabry-perot resonance condition, the wire length of the solenoid should not exceed half the wavelength, which means that for solenoid coils with the same height and diameter, the number of turns that can be used is limited, which limits the amplitude and uniformity of the magnetic field generated.
Alena Shchelokova et al in 2020 propose a concept of targeted clinical magnetic resonance imaging that involves spatial redistribution and passive focusing of radio frequency magnetic flux using metamaterials to maximize the efficiency of a conventional MR system of a region of interest, which offers the prospect of targeted MRI. They designed a ceramic ring resonator dedicated to breast magnetic resonance imaging, and experiments show that using the metamaterial under the body coil for magnetic resonance imaging of the breast is close to using only breast surface coil imaging in terms of signal-to-noise ratio (SNR), while the average input power is reduced by 49 times, and the rf safe gain is increased by 7 times on average over the whole breast. However, such structures made of high dielectric constant ceramics are very fragile and challenging to manufacture, since the materials should have high temperature stability and low electromagnetic losses.
2021 Zhonghai Chi et al designed A Cylindrical Wireless Metamaterial (ACWM) with uniform field enhancement and adaptive resonant modes. The metamaterial is applied to the wrist, and the ACWM automatically switches the resonance mode between the radio frequency signal transmitting period and the receiving period through the capacitor and the pair of oppositely placed diodes, so that interference in a radio frequency transmitting field can be eliminated, and the signal to noise ratio can be improved. This adaptation also allows the ACWM to be used for all common clinical sequences without any modification of the scan parameters. The signal-to-noise ratio of human wrist MRI images acquired with ACWM is 2 to 4 times that of conventional coils. This provides a new way to avoid the interference of the meta-surface in the RF transmit field, but wrist magnetic resonance imaging is relatively weak in medical value compared to organs like breast, brain etc., whereas such metamaterials cannot migrate for use in other organs due to too small pore size.
2021 Viktor Puchnin et al devised a metamaterial for breast consisting of periodically arranged inductively coupled split ring resonators (SLR) made of telescopic copper tubes, the capacitors being realized in the form of copper strips on two Printed Circuit Boards (PCBs). Compared to conventional body coils used alone, the proposed metamaterial focuses the RF magnetic field within a region of interest (ROI), under a birdcage coil the average SNR of the breast phantom center plane is increased by 6.4 times and the maximum local SAR value is reduced by 18 times. However, the tuning of the metamaterial is to manually adjust the length of the copper bar, so that the tuning is inconvenient, meanwhile, the resonance mode conversion between the transmitting period and the receiving period is not considered, the copper bar is thinner and is only welded by two ends, the support is lacking, the structure is fragile, and the metamaterial is difficult to apply to actual medical treatment.
Luo Liuchun et al invent a magnetic signal enhancement device [ CN104459585A ] for magnetic resonance imaging, which employs a metamaterial having a plurality of artificial microstructures arranged in a periodic array, to enhance signals received by an antenna of a magnetic resonance imaging apparatus. Liu Repeng et al invent a metamaterial [ CN102723608A ], wherein a structural unit is an open ring formed by a wiring of a conductive material, a patch inductor is connected in series with the wiring of the open ring, the structural unit is periodically attached to a nonmetallic substrate, and when the metamaterial has negative magnetic permeability, the response electromagnetic wave frequency is smaller, so that the requirement of a magnetic resonance imaging system on low frequency can be met, the receiving radio frequency magnetic field generated by magnetic resonance imaging is enhanced, and the signal-to-noise ratio of the magnetic resonance imaging is improved. But these inventions are inconvenient or impossible to tune.
In summary, the current scientific research results still have many problems, and in practical application, the complex medical scene will change the resonance frequency of the metamaterial, so that the metamaterial cannot work in the highest gain state in the theoretical design, the radio frequency signal cannot have the best enhancement effect, and the image quality cannot be improved best, so that the metamaterial without dynamic tuning potential is still insufficient in practical application. Therefore, an intelligent metamaterial structure which is suitable for important body organs, stable in structure, convenient to tune, good in gain uniformity, nonlinear in realization and capable of achieving real-time dynamic tuning needs to be designed.
Disclosure of Invention
The invention aims to provide an intelligent metamaterial structure which is applicable to important body organs, stable in structure, convenient to tune, good in gain and capable of achieving nonlinear and real-time dynamic tuning.
In order to achieve the above object, the present invention provides the following solutions:
an intelligent metamaterial structure comprising: the dielectric substrate, the conductor structure, the adjustable capacitor and the dynamic tuning device;
the conductor structure is a conductor of a circular cylinder; the side surface of the conductor structure is provided with radial symmetrical notches; the adjustable capacitor is arranged in the notch; the conductor structure and the adjustable capacitor are arranged on the dielectric substrate; the dynamic tuning device is connected with the adjustable capacitor; the dynamic tuning device is used for controlling the capacitance value of the adjustable capacitor in the imaging scanning process of the magnetic resonance equipment.
Optionally, the conductor structure comprises a plurality of split conductor rings and a plurality of conductor posts;
the split conductor rings are stacked; radial symmetrical notches are arranged on the side surfaces of each layer of split conductor ring; the notch positions of the split conductor rings of each layer are the same; the adjustable capacitor is arranged in a space formed by the notch of each layer of split conductor ring; and a plurality of conductor columns are fixed on the side surface of each split conductor ring at intervals.
Optionally, the intervals between two adjacent conductor columns are the same; the conductor post is parallel to the axial direction of the split conductor ring.
Optionally, the conductor structure is a conductor sheet of a circular cylinder.
Optionally, the dynamic tuning device comprises a controller and a vector network analyzer connected with the controller; the controller is connected with the adjustable capacitor.
Optionally, the split conductor ring has an inner diameter in the range of 150mm-180mm; the split conductor ring has an outer diameter in the range of 154mm-192mm.
Optionally, the number of layers of the split conductor ring ranges from 8 to 14.
Optionally, the radius of the conductor post ranges from 1mm to 3mm.
Optionally, the adjustable capacitance is a digital adjustable capacitance.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention provides an intelligent metamaterial structure, which comprises the following components: the dielectric substrate, the conductor structure, the adjustable capacitor and the dynamic tuning device; the conductor structure is a conductor of a circular cylinder; the side surface of the conductor structure is provided with radial symmetrical notches; the adjustable capacitor is arranged in the notch; the conductor structure and the adjustable capacitor are arranged on the dielectric substrate; the dynamic tuning device is connected with the adjustable capacitor; the dynamic tuning device is used for controlling the capacitance value of the adjustable capacitor in the imaging scanning process of the magnetic resonance equipment, and can be suitable for important body organs, stable in structure, convenient to tune, good in gain and capable of achieving nonlinear and real-time dynamic tuning.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a front view of a smart metamaterial structure;
FIG. 2 is a top view of a smart metamaterial structure;
FIG. 3 is a right side view of the smart metamaterial structure;
FIG. 4 is a perspective view of a smart metamaterial structure;
FIG. 5 is a graph of magnetic field strength versus frequency for adjusting the resonant frequency of a metamaterial to 63.8 MHz;
FIG. 6 is a graph of magnetic field strength versus frequency for a tunable capacitance having a capacitance of 5 pF;
FIG. 7 is a graph of magnetic field strength versus frequency for a tunable capacitance having a capacitance of 7.7 pF;
FIG. 8 is a graph of magnetic field strength versus frequency for a capacitance value of 10pF for the tunable capacitance;
FIG. 9 is a graph showing the relationship between magnetic field strength and frequency when the metamaterial direction is changed to be orthogonal to the previous direction, namely, the central axis coincides with the y axis and is adjusted to be small caliber;
FIG. 10 is a graph showing the magnetic field distribution when plane wave excitation is linearly polarized, and the resonant frequency of the metamaterial is adjusted to 63.8 MHz;
FIG. 11 is a graph showing the magnetic field distribution when plane wave excitation is circularly polarized, and the resonant frequency of the metamaterial is adjusted to 63.8 MHz;
FIG. 12 is a graph showing the magnetic field distribution when plane wave excitation is circularly polarized and the capacitance value of the tunable capacitor is 5 pF;
FIG. 13 is a graph showing the magnetic field distribution when plane wave excitation is circularly polarized and the capacitance value of the tunable capacitor is 10 pF;
FIG. 14 is a magnetic field pattern of a single birdcage coil;
FIG. 15 is a graph of magnetic field profile for excitation using a birdcage coil to adjust the metamaterial resonant frequency to 63.8 MHz;
FIG. 16 is a graph of magnetic field profile for an excitation using a birdcage coil with an adjustable capacitance having a capacitance value of 5 pF;
FIG. 17 is a graph of magnetic field profile for a tuning capacitor having a capacitance of 10pF when excited with a birdcage coil;
FIG. 18 is a graph showing the magnetic field distribution when the metamaterial is changed to be in the direction orthogonal to the previous direction, namely, the central axis is coincident with the y axis and is adjusted to be small caliber, and circularly polarized plane waves are excited;
FIG. 19 is a magnetic field distribution diagram along a central cross-section of a voxel model when the voxel model is placed in a birdcage coil;
FIG. 20 is a graph of magnetic field distribution along a central cross-section of a voxel model with metamaterials placed in a birdcage coil;
FIG. 21 is a schematic diagram of an intelligent metamaterial structure implementation.
Symbol description:
dielectric substrate-1, split conductor ring-2, conductor column-3, tunable capacitance-4.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention aims to provide an intelligent metamaterial structure which is applicable to important body organs, stable in structure, convenient to tune, good in gain and capable of achieving nonlinear and real-time dynamic tuning.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
As shown in fig. 1 to 4, the present invention provides an intelligent metamaterial structure, which includes: a dielectric substrate 1, a conductor structure, an adjustable capacitor 4 and a dynamic tuning device.
The conductor structure is a conductor of a circular cylinder; the side surface of the conductor structure is provided with radial symmetrical notches; the adjustable capacitor 4 is arranged in the notch; the conductor structure and the adjustable capacitor 4 are arranged on the dielectric substrate 1; the dynamic tuning device is connected with the adjustable capacitor 4; the dynamic tuning device is used for controlling the capacitance value of the adjustable capacitor 4 in the imaging scanning process of the magnetic resonance equipment.
The dynamic tuning device comprises a controller and a vector network analyzer connected with the controller; the controller is connected with the adjustable capacitor 4. The output end of the controller is connected with the digital adjustable capacitor 4 and is used for receiving the S parameter of the vector network analyzer in the scanning process of the magnetic resonance equipment imaging, and outputting a control signal to the digital adjustable capacitor 4 according to a difference value between the resonance frequency and the Larmor frequency during imaging when the difference value exists, so as to control the capacitance value of the digital adjustable capacitor 4.
And the output end of the vector network analyzer is connected with the controller, and the measurement result is transmitted to the controller in the dynamic tuning device in real time.
The adjustable capacitor 4 is a digital adjustable capacitor. The adjustable capacitor 4 is connected with the controller.
The material of the dielectric substrate 1 may be a PCB board, a 3D printing material, a high dielectric coefficient material such as barium titanium oxide, etc., and the thickness of the dielectric substrate 1 is preferably between 1mm and 5mm.
As an alternative embodiment, the conductor structure comprises a plurality of split conductor loops 2 and a plurality of conductor posts 3; the split conductor rings 2 are stacked; radial symmetrical notches are arranged on the side face of each split conductor ring 2; the notch positions of each layer of split conductor ring 2 are the same; the adjustable capacitor 4 is arranged in a space formed by the notch of each layer of split conductor ring 2; the conductor columns 3 are fixed on the side face of each split conductor ring at intervals; the interval between two adjacent conductor columns 3 is the same; the conductor post 3 is parallel to the axial direction of the split conductor ring 2.
Specifically, the split conductor ring 2 structure is composed of a plurality of layers, each layer comprises the split conductor ring 2 welded on the dielectric substrate 1, and the split conductor ring is provided with radial symmetrical notches, and an adjustable capacitor 4 is respectively placed in each notch to form a loop; a plurality of conductor columns 3 are welded on the split conductor rings 2 at the periphery to form a new loop, each conductor column 3 is welded on each split conductor ring 2 in a penetrating way, and the adjacent conductor columns 3 have the same interval. The split conductor loop 2 and the tunable capacitor 4 are soldered to the dielectric substrate 1.
The inner diameter of the split conductor ring 2 ranges from 150mm to 180mm; the split conductor ring 2 has an outer diameter in the range of 154mm-192mm. The number of layers of the split conductor loop 2 is in the range of 8-14. The radius of the conductor post 3 is in the range of 1mm-3mm. The radially symmetrical notch length is preferably between 5mm and 15 mm. The distance between each layer of split conductor loops 2 and its adjacent layer of split conductor loops 2 is preferably between 8mm and 13 mm. The number of layers of the split conductor loop 2 and the capacitive loop is preferably between 8 and 14. The length of the conductor posts 3 is preferably between 80mm and 140mm, and the number of the conductor posts 3 may be more than 2. The conductor may be copper.
A specific way of implementing the conductor structure in practical applications is also provided. The inner diameter of the circle formed by each layer of split conductor rings 2 is 160mm, the radius of the section of the conductor rings is 1.5mm, and the length of the radial symmetrical notch is 10mm. The distance between each layer of split conductor loops 2 and its adjacent layer of split conductor loops 2 is 10mm. The number of layers of the split conductor loop 2 and the capacitor loop is 10. The conductor posts 3 have a length of 103mm, a radius of 1.5mm and a number of 6. The material of the medium substrate 1 can be a Rogowski board, the model can be RO4003C, and the thickness of the medium substrate 1 is 3mm. In one embodiment, the material of the dielectric substrate 1 may be polyimide.
As an alternative embodiment, the conductor structure is a conductor sheet of a circular cylinder. The split conductor ring 2 and the conductor column 3 in the metamaterial structure can be replaced by conductor plates, the width and the capacitance value of the conductor plates are adjusted to enable the metamaterial to reach the larmor frequency of 1.5T magnetic resonance of 63.8MHz, the radio frequency magnetic field can be enhanced, and the enhancement amplitude and uniformity of the magnetic field can achieve the same effect as those of the scheme.
All electromagnetic simulations were performed in a CST Studio Suite 2022 using a frequency domain solver.
1. The specific parameters of the metamaterial structure are as follows: the conductor adopts copper, and the internal diameter of the circle that every layer splits the copper ring and constitutes is 160mm, and the radius of copper ring cross-section is 1.5mm, and radial symmetry's breach length is 10mm, and every capacitance value is set to 7.7pF, and the distance between every layer splits copper ring and the split copper ring of its adjacent layer is 10mm, totally 10 layers, and the material of substrate is the PCB board, selects Rogers RO4003C, and the external diameter is 160mm, and the internal diameter is 154mm. The length of the copper column is 103mm, the radius is 1.5mm, and the number of the copper columns is 6. The size of the whole metamaterial structure is 166 multiplied by 103mm 3 . The output end of the controller is connected with the digital adjustable capacitor 4 in the realization of the intelligent metamaterial structure, and the digital adjustable capacitor is used for receiving the vector network analyzer in the scanning process of the magnetic resonance equipment imagingAnd when there is a difference between the resonance frequency and the larmor frequency at the time of imaging, a control signal for the digital tunable capacitor 4 is output according to the difference, and the capacitance value of the digital tunable capacitor 4 is controlled. The output end of the vector network analyzer is connected with the controller, and the measurement result is transmitted to the controller in the dynamic tuning device in real time. The intelligent metamaterial structure is shown in figures 1 to 4. An implementation diagram of the intelligent metamaterial is shown in fig. 21.
2. Electromagnetic simulation is carried out on the intelligent metamaterial structure, linear polarized plane waves are adopted for excitation, the propagation direction of the waves is the z-axis direction (pointing to the direction of the metamaterial), and a magnetic field probe positioned in the center of the intelligent metamaterial structure is used for observing the resonant frequency and observing the magnetic field distribution in and around the metamaterial cavity. The magnetic field distribution is shown in fig. 10.
3. Electromagnetic simulation is carried out on the intelligent metamaterial structure, circularly polarized plane waves are adopted for excitation, the propagation direction of the waves is the z-axis direction (pointing to the direction of the metamaterial), and a magnetic field probe positioned in the center of the intelligent metamaterial structure is used for observing the resonant frequency and observing the magnetic field distribution in and around the metamaterial cavity. The relationship between the magnetic field strength and the frequency is shown in fig. 5, and the magnetic field distribution is shown in fig. 11.
4. A human birdcage coil for a 1.5T magnetic resonance system was simulated, which was a high pass cylindrical quadrature coil with 16 legs, tuned and matched at 63.8MHz (larmor frequency of 1.5T magnetic resonance). The circularly polarized RF magnetic field (B1) is generated by the phase difference of the two 90 ° feed ports. Electromagnetic simulations observe the magnetic field distribution within a single birdcage coil. The magnetic field distribution of a single birdcage coil is shown in figure 14.
5. Electromagnetic simulation is carried out on the intelligent metamaterial structure, the birdcage coil is adopted for excitation, and magnetic field distribution in the metamaterial cavity and between the birdcage coil and the intelligent metamaterial structure is observed. The magnetic field distribution is shown in fig. 15.
6. And selecting the actual effective imaging area of the intelligent metamaterial structure and the same area of the magnetic field of the birdcage coil in the step 4, and calculating to obtain that the magnetic field uniformity of the actual effective imaging area of the intelligent metamaterial structure is 12.09%, and the ratio of the magnetic field intensity average value of the imaging area to the magnetic field intensity average value of the same area of the magnetic field of the birdcage coil in the step 4 is 7.3.
7. And changing the capacitance value, carrying out electromagnetic simulation on the intelligent metamaterial structure, exciting by adopting circularly polarized plane waves, wherein the propagation direction of the waves is the z-axis direction (pointing to the direction of the metamaterial), and observing the resonance frequency by using a magnetic field probe positioned in the center of the intelligent metamaterial structure. Fig. 6 to 8 show the relationship between the magnetic field strength and the frequency, wherein fig. 6 is a graph of the magnetic field strength and the frequency when the capacitance value of the adjustable capacitor is 5pF, fig. 7 is a graph of the magnetic field strength and the frequency when the capacitance value of the adjustable capacitor is 7.7pF, and fig. 8 is a graph of the magnetic field strength and the frequency when the capacitance value of the adjustable capacitor is 10pF, and the magnetic field distribution is shown in fig. 11 to 13.
8. And changing the capacitance value, performing electromagnetic simulation on the intelligent metamaterial structure, exciting by using the birdcage coil, and observing the magnetic field distribution changes in the cavity of the intelligent metamaterial structure and between the birdcage coil and the intelligent metamaterial structure. The magnetic field distribution is shown in fig. 15 to 17.
9. From the results of fig. 7 and 8, the smart metamaterial structure can change the resonant frequency and change the magnetic field enhancement effect by adjusting the capacitance value, so that the smart metamaterial structure has the capability of real-time dynamic tuning in the actual magnetic resonance imaging process.
10. Changing the metamaterial direction to be orthogonal to the previous direction, namely, overlapping the central axis with the y axis, and adjusting the inner diameter to be 48.5mm.
11. The radius of copper is adjusted to be 1mm, electromagnetic simulation is carried out on the intelligent metamaterial structure, circularly polarized plane waves are adopted, the propagation direction of the waves is the y-axis direction (pointing to the direction of the metamaterial), and a magnetic field probe positioned in the center of the intelligent metamaterial structure is used for observing the resonance frequency. And observing the resonant frequency and the distribution of the magnetic field in and around the metamaterial cavity. The relationship between the magnetic field strength and the frequency is shown in fig. 9, and the magnetic field distribution is shown in fig. 18.
12. The female voxel model of the CST Studio Suite 2022 manikin library was imported and the magnetic field distribution along the central cross section of the voxel model was observed using birdcage coil excitation. The magnetic field distribution is shown in fig. 19. Within the box is the actual effective imaging area.
13. A female voxel model of the CST Studio Suite 2022 manikin library was imported, and when the metamaterial was placed at the breast position of the voxel model using birdcage coil excitation, the magnetic field distribution along the center cross section of the voxel model was observed. The magnetic field distribution is shown in fig. 20. Within the box is the actual effective imaging area.
14. And selecting the same areas in the actual effective imaging area and the actual effective imaging area in the area 12 in the area 13, and calculating to obtain that the magnetic field uniformity of the actual effective imaging area of the intelligent metamaterial structure is 13.39%, wherein the ratio of the magnetic field intensity average value of the effective imaging area in the area 13 to the magnetic field intensity average value of the same area in the area 12 is 5.
The result shows that the intelligent metamaterial structure has high feasibility and effectiveness for enhancing the 1.5T magnetic resonance imaging radio frequency magnetic field.
The intelligent metamaterial structure provided by the invention is oriented to 1.5T high-field magnetic resonance imaging radio frequency magnetic field enhancement, and has the advantages and beneficial effects that for the prior art:
because the invention is a cylindrical three-dimensional structure, the invention can cover a target area in a large range and symmetrically in practical magnetic resonance imaging application, and the enhancement effect and uniformity of a radio frequency magnetic field in the target area are better, thereby realizing targeted magnetic resonance imaging of specific structures or organs of the target, such as organs of breast, brain, knee and the like. Compared with the existing majority of planar structures, the structural form of the invention is more suitable for the actual requirements of the medical imaging field.
The metamaterial is an intelligent metamaterial, specifically an adjustable capacitor 4 in a metamaterial structure is connected with a controller by using a digital adjustable capacitor 4 to form a dynamic tuning device, S parameters of a system are transmitted to the controller in the dynamic tuning device in real time through a vector network analyzer, a control signal of the digital adjustable capacitor 4 is output to control the capacitance value of the digital adjustable capacitor 4 so as to adjust the resonance frequency of the metamaterial, the metamaterial is always kept in an optimal resonance mode in the use process, namely the resonance frequency is consistent with the larmor frequency, the real-time dynamic tuning capability in the actual magnetic resonance imaging process is achieved, the highest imaging signal-to-noise ratio gain is achieved, the image quality is improved best, and the metamaterial is beneficial to actual medical diagnosis. Meanwhile, the existence of the adjustable capacitor 4 means that the metamaterial can realize nonlinearity, the metamaterial can be detuned in a radio frequency transmitting stage through the adjustment of the capacitor, unnecessary induced current is prevented from being generated, and the metamaterial resonates in a radio frequency receiving stage, so that a resonant system can maintain a uniform transmitting field, image artifacts and signal loss are reduced, and meanwhile, higher receiving sensitivity is maintained.
The invention consists of a conductor, a capacitor and a conductor structure, wherein the conductor structure is a PCB or a 3D printing material or a material with high temperature stability and low electromagnetic loss, such as barium-titanium oxide and the like, and the materials have good mechanical properties and are easy to process, so that the metamaterial structure is convenient to process and produce, has a certain strength, and is more suitable for practical medical environments. In addition, the conductor structure of the invention adopts a cylindrical shape and is matched with the metamaterial structure, so that the stability and the reliability of the metamaterial structure can be enhanced.
The metamaterial structure can be used for other organs and specific structures by adjusting the pore diameter, the distribution of conductors and the capacitance, the mobility means that the metamaterial structure has higher research value, and the properties of the metamaterial such as the enhancement effect and uniformity of a radio frequency magnetic field under different target areas can be explored by researching and adjusting the basic structure.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the above examples being provided only to assist in understanding the structure of the present invention and its core ideas; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (8)
1. An intelligent metamaterial structure, which is characterized by comprising: the dielectric substrate, the conductor structure, the adjustable capacitor and the dynamic tuning device;
the conductor structure is a conductor of a circular cylinder; the side surface of the conductor structure is provided with radial symmetrical notches; the adjustable capacitor is arranged in the notch; the conductor structure and the adjustable capacitor are arranged on the dielectric substrate; the dynamic tuning device is connected with the adjustable capacitor; the dynamic tuning device is used for controlling the capacitance value of the adjustable capacitor in the imaging scanning process of the magnetic resonance equipment;
the conductor structure comprises a plurality of split conductor rings and a plurality of conductor posts;
the split conductor rings are stacked; radial symmetrical notches are arranged on the side surfaces of each layer of split conductor ring; the notch positions of the split conductor rings of each layer are the same; the adjustable capacitor is arranged in a space formed by the notch of each layer of split conductor ring; the split conductor ring and the adjustable capacitor are welded on the dielectric substrate; and a plurality of conductor columns are fixed on the side surface of each split conductor ring at intervals.
2. The smart metamaterial structure according to claim 1, wherein the spacing between two adjacent ones of the conductor posts is the same; the conductor post is parallel to the axial direction of the split conductor ring.
3. The smart metamaterial structure according to claim 1, wherein the conductor structure is a conductor sheet of a circular cylinder.
4. The smart metamaterial structure according to claim 1, wherein the dynamic tuning device comprises a controller and a vector network analyzer connected to the controller; the controller is connected with the adjustable capacitor.
5. The smart metamaterial structure according to claim 1, wherein the split conductor ring has an inner diameter in the range of 150mm-180mm; the split conductor ring has an outer diameter in the range of 154mm-192mm.
6. The smart metamaterial structure according to claim 1, wherein the number of layers of split conductor rings is in the range of 8-14.
7. The smart metamaterial structure according to claim 1, wherein the radius of the conductor posts is in the range of 1mm-3mm.
8. The smart metamaterial structure of claim 1, wherein the adjustable capacitance is a digital adjustable capacitance.
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