Magnetic resonance metamaterial magnetic field enhancer optimization method based on NSGA-II genetic algorithm

Abstract

The application relates to a magnetic resonance metamaterial magnetic field intensifier optimization method based on an NSGA-II genetic algorithm, which comprises the following steps: initially constructing a metamaterial intensifier model structure; extracting an equivalent circuit model of the metamaterial intensifier; constructing a radio frequency coil, a metamaterial intensifier and a measured model system; extracting equivalent circuit models of the radio frequency coil and the metamaterial intensifier; calculating the equivalent resistance and the equivalent inductance of the metamaterial intensifier; calculating the radio frequency coil current and the metamaterial intensifier induced current; obtaining a calculation formula of the induced magnetic field in a target area; initializing the structure parameters of the metamaterial intensifier; setting optimization targets, wherein the first optimization target is to maximize the average magnetic field intensity in the magnetic resonance imaging target area, and the second optimization target is to minimize the volume of the metamaterial intensifier; adopting a non-dominated sorting genetic algorithm NSGA-II to optimize the structure of the metamaterial intensifier, so that the magnetic field intensification effect is best; and the structure parameters of the optimal metamaterial intensifier are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic resonance imaging, and in particular relates to a method for optimizing a magnetic resonance metamaterial magnetic field enhancer based on an NSGA-II genetic algorithm. Background Art

[0002] Magnetic resonance imaging (MRI) uses the phenomenon of nuclear magnetic resonance to obtain electromagnetic signals from the human body and reconstruct information about the body. It is a biomagnetic spin imaging technique that exploits the characteristics of atomic nuclear spin motion. In an external magnetic field, after the radiofrequency pulse ceases, the excited spin systems of the atomic nuclei cannot maintain this state and return to their original arrangement in the magnetic field, releasing weak energy as radio signals. These signals are detected by detectors and input into a computer, which processes and converts them into images displayed on a screen. MRI has been applied to diagnostic imaging of various body systems, with particular effectiveness in areas such as the brain and spinal cord, heart and major vessels, joints and bones, soft tissues, and the pelvis. For cardiovascular disease, it can not only visualize anatomical changes in various chambers, major vessels, and valves, but also perform ventricular analysis, enabling qualitative and semi-quantitative diagnosis. Multiple cross-sectional images can be generated with high spatial resolution, revealing the entire heart and lesions, as well as their relationship to surrounding structures. This is superior to other imaging methods such as X-ray imaging, two-dimensional ultrasound, radionuclide imaging, and CT. When diagnosing brain and spinal cord lesions, coronal, sagittal and transverse images can be taken.

[0003] Metamaterials refer to artificial composite structures or materials with extraordinary physical properties not possessed by natural materials. Through orderly structural design at the critical physical scale of the material, it is possible to break through the limitations of certain apparent natural laws, thereby obtaining extraordinary material functions that exceed the ordinary properties inherent in nature. The properties and functions of metamaterials mainly come from their internal structure rather than the materials that constitute them. Currently, the geometric shapes of existing metal artificial microstructures are open rings in the shape of "I" or "C" characters, but these structures cannot reduce the resonant frequency of the metamaterial or achieve isotropy. Only by designing metal artificial microstructures with special geometric shapes can the artificial electromagnetic material achieve a lower resonant frequency within a specific frequency band.

[0004] Currently, the most commonly used MRI machines in clinical practice are categorized by main magnetic field strength, including high-field models like 1.5T and 3.0T. However, some patients, such as those with implants like steel plates and heart stents, are not suitable for high-field MRI, posing safety risks. However, the low main magnetic field strength of 70mT ultra-low-field MRIs may potentially meet the imaging requirements of these patients. However, due to the low main magnetic field strength, the imaging signal is very weak, necessitating methods to enhance the RF field for clearer imaging. Summary of the Invention

[0005] The application aims to provide a magnetic resonance metamaterial magnetic field intensifier optimization method based on an NSGA-II genetic algorithm.

[0006] The technical solution of the application is as follows:

[0007] A magnetic resonance metamaterial magnetic field intensifier optimization method based on an NSGA-II genetic algorithm comprises the following steps:

[0008] 1) A metamaterial intensifier model structure is initially constructed, the metamaterial intensifier comprises a dielectric substrate, a spiral coil and an external capacitor, the spiral coil is arranged on the dielectric substrate, there is a gap between adjacent spiral coils, and the two ends of the spiral coil are connected through the external capacitor;

[0009] 2) An equivalent circuit model of the metamaterial intensifier is extracted;

[0010] 3) An RF coil, a metamaterial intensifier and a measured model system are constructed;

[0011] 4) An equivalent circuit model of the RF coil and the metamaterial intensifier is extracted;

[0012] 5) Circuit parameters are calculated according to circuit theory, and the equivalent resistance and the equivalent inductance of the metamaterial intensifier are calculated;

[0013] 6) RF coil current and metamaterial intensifier induced current are calculated according to the equivalent circuit model and circuit theory;

[0014] 7) The spiral coil is regarded as a square spiral loop, a square spiral loop of one metamaterial intensifier is regarded as a plurality of concentric square loops with different side lengths, the magnetic field calculation formula of a single-turn square loop is obtained by superimposing the induced magnetic fields of the four sides, and the calculation formula of the induced magnetic field in the target area is obtained;

[0015] 8) The structure parameters of the metamaterial intensifier are initialized;

[0016] 9) The optimization target is set, the first optimization target is to maximize the average magnetic field intensity in the magnetic resonance imaging target area, and the second optimization target is to minimize the volume of the metamaterial intensifier;

[0017] 10) The non-dominated sorting genetic algorithm NSGA-II is adopted to optimize the structure of the metamaterial intensifier, so that the magnetic field enhancement effect is best;

[0018] 11) The optimal structure parameters of the metamaterial intensifier are solved;

[0019] 12) Determine the tuning capacitance, add an external capacitance C MR Set the tuning capacitance, tune its resonant frequency to the target frequency.

[0020] Further, in step 1), let n be the number of turns of the spiral coil, g be the gap between adjacent wires MR , w be the width of the spiral coil MR , a be the inner length of the spiral coil MR-in , a be the outer length of the spiral coil MR-out , C be the external capacitance MR .

[0021] Further, in step 2), let R MF and L MF be the equivalent resistance and inductance, respectively, and C0 be the parasitic capacitance.

[0022] Further, in step 4), let R RF and L RF be the equivalent resistance and inductance of the RF coil, respectively, U be the excitation voltage of the RF coil, I RF be the current of the RF coil, and I MF be the induced current of the metamaterial enhancer.

[0023] Further, the method of step 5) is as follows:

[0024]

[0025] where, is the resistance caused by the skin effect, is the medium resistance, the spiral coil is made of copper wire, l MR is the path length of the copper wire, δ is the skin depth of copper, w MR is the width of the copper wire, σ is the electrical conductivity of copper, t is the thickness of copper, ω0 is the angular frequency, ε rair , ε rd and ε0 are the dielectric constants of air, dielectric plate and vacuum, respectively, μ is the magnetic permeability of copper, μ0 is the vacuum magnetic permeability, a MRavg is the average side length of the spiral coil, a MRavg = (a MR-in +a MR-out ) / 2, ρ is the filling ratio, ρ = (a MR-out -a MR-in ) / (a MR-in +a MR-out ).

[0026] Further, the method of step 6) is as follows:

[0027] R RF I RF +jωL RF IRF + jωM RF-MR I MR = U

[0028]

[0029] where ω is the angular frequency corresponding to the Larmor frequency, R RF and L RF are the equivalent resistance and inductance of the RF coil, respectively; M MR-RF is the mutual inductance between the metamaterial booster and the RF coil; when the metamaterial booster resonates, then the induced current is:

[0030]

[0031] Z RF-RF = R RF + jωL RF

[0032] Z RF-MR = Z MR-RF = jωM RF-MR

[0033] Z MR-MR = R MR

[0034] where Z is the impedance.

[0035] Further, in step 7), the method for calculating the induced magnetic field in the target region is:

[0036] According to the Biot-Savart law, the calculation formula of the induced magnetic field generated by a side length in the y direction is:

[0037]

[0038] In the formula, I is the current in the square loop, a is the side length of the square loop, x, y, z are the coordinates of the target point in space; the magnetic field of the metamaterial booster is equal to the sum of the magnetic fields of multiple concentric square loops with different side lengths; the magnetic field of the RF coil B RF is equal to the sum of the magnetic fields of five rectangular coils; the magnetic field size B ROI in the target region is the superposition of the magnetic fields of the RF coil and the metamaterial booster, that is:

[0039] B ROI = B RF + B MR

[0040] By calculating the impedance and mutual inductance of the metamaterial booster, the current I is obtained, and the magnetic field distribution in the target region is obtained according to the Biot-Savart law.

[0041] Further, the method of step 10) is: initializing a population P0, the population size is N, calculating the average magnetic field intensity and the volume of the metamaterial enhancer, performing fast non-dominated sorting on P0 and calculating the crowding degree, obtaining the evolution generation t = 1; performing selection-crossover-mutation operation on the population to generate the average magnetic field intensity and the volume Qt of the offspring population Pt; performing non-dominated sorting and crowding degree calculation on the parent population P0 and the offspring population Pt after merging, and generating a new parent population Rt by using the elite strategy to reserve excellent individuals; judging whether the genetic generation meets the set value, if not, repeating the selection-crossover-mutation operation, if yes, the evolution is completed. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 Structure diagram of the model of the metamaterial enhancer, wherein n is the number of spiral coils, g is the gap between adjacent wires MR w is the width of the spiral coil MR a is the inner edge length of the spiral coil MR-in a is the outer edge length of the spiral coil MR-out C is the external capacitor MR .

[0043] Figure 2 Equivalent circuit diagram of the metamaterial enhancer, R MF and L MF are the equivalent resistance and the equivalent inductance respectively, C0 is the parasitic capacitance, and C MR is the external capacitor.

[0044] Figure 3 System diagram of the radio frequency coil, the metamaterial enhancer and the cuboid model I.

[0045] Figure 4 Equivalent circuit diagram of the radio frequency coil and the metamaterial enhancer, wherein R RF and L RF are the equivalent resistance and the equivalent inductance respectively, U is the excitation voltage, I RF is the radio frequency coil current, I MF is the metamaterial enhancer induced current, R MF and L MF are the equivalent resistance and the equivalent inductance respectively, C0 is the parasitic capacitance, and C MR is the external capacitor.

[0046] Figure 5 Frequency spectrum characteristic diagram of the metamaterial enhancer.

[0047] Figure 6 (a) Model I transverse cross-sectional magnetic field diagram without the metamaterial enhancer; (b) Model I coronal plane magnetic field diagram without the metamaterial enhancer; (c) Model I transverse cross-sectional magnetic field diagram with the metamaterial enhancer; (d) Model I coronal plane magnetic field diagram with the metamaterial enhancer; (e) the magnetic field along the x direction arrow Enhancement factor curve; (f) along the y direction arrow Enhancement factor curve. The black rectangular dashed frame is the outline of the phantom I, and the outermost frame is the outline of the metamaterial enhancer. DETAILED DESCRIPTION

[0048] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Figure 1 The structure diagram of the metamaterial enhancer model, where the number of spiral coils is n and the gap between adjacent wires is g. MR , spiral coil width w MR , the inner side length of the spiral coil is a MR-in , the outer length of the spiral coil is a MR-out , external capacitor C MR . Figure 2 is the equivalent circuit diagram of the metamaterial enhancer, R MF and L MF are equivalent resistance and equivalent inductance respectively, C0 is parasitic capacitance, C MR For external capacitors. Figure 3 System diagram of RF coil, metamaterial enhancer and rectangular parallelepiped model I. Figure 4 is the equivalent circuit diagram of the RF coil and metamaterial enhancer, where R RF and L RF are the equivalent resistance and equivalent inductance respectively, U is the excitation voltage, I RF is the RF coil current, I MF is the induced current of the metamaterial enhancer, R MF and L MF are equivalent resistance and equivalent inductance respectively, C0 is parasitic capacitance, C MR For external capacitors. Figure 5 This is the spectrum characteristic diagram of the metamaterial enhancer. Figure 6 (a) is the cross-sectional magnetic field diagram of model I without metamaterial enhancer; (b) is the coronal magnetic field diagram of model I without metamaterial enhancer; (c) is the cross-sectional magnetic field diagram of model I with metamaterial enhancer; (d) is the coronal magnetic field diagram of model I with metamaterial enhancer; (e) is the magnetic field along the x-direction arrow Enhancement factor curve; (f) is the arrow along the y direction Enhancement factor curve. The black rectangular dashed frame is the outline of the phantom I, and the outermost frame is the outline of the metamaterial enhancer.

[0049] The specific process is as follows:

[0050] 1) Preliminary construction of metamaterial enhancer model structure, such as Figure 1 As shown, the metamaterial enhancer is composed of a spiral coil, a dielectric substrate (FR-4) and an external capacitor C MR In actual use, the external capacitor CMR The variable capacitor can be a variable capacitor, and its value should be determined according to the operating frequency (also called the target frequency) of different magnetic resonance systems. The spiral coil of this embodiment is a rectangular spiral copper wire. The method for making the rectangular spiral copper wire can be: using relevant technology to draw a spiral copper wire pattern on the copper-clad surface of the dielectric substrate. In the preliminary constructed model structure, the number of spiral coil turns n, the gap between adjacent wires g MR , spiral coil width w MR , the inner side length of the spiral coil is a MR-in , the outer length of the spiral coil is a MR-out , external capacitor C MR .

[0051] 2) Extract the equivalent circuit diagram of the metamaterial enhancer, such as Figure 2 As shown, where R MF and L MF are the equivalent resistance and equivalent inductance of the metamaterial enhancer, respectively, and C0 is the parasitic capacitance.

[0052] 3) Construct the RF coil, metamaterial enhancer and rectangular parallelepiped model I system, such as Figure 3 shown.

[0053] 4) Extract the equivalent circuit model of the RF coil and metamaterial enhancer, such as Figure 4 As shown, where R RF and L RF are the equivalent resistance and equivalent inductance of the RF coil, U is the excitation voltage, I RF is the RF coil current, I MF Inducing current for metamaterial enhancers.

[0054] 5) Calculate the circuit parameters according to circuit theory, and calculate the equivalent resistance and equivalent inductance of the metamaterial enhancer using formula (1-5).

[0055]

[0056] in, is the resistance caused by the skin effect, is the dielectric resistance, l MR is the copper wire path length, δ is the skin depth of copper, w MR is the width of the copper wire, σ is the conductivity of copper, t is the thickness of copper, ω0 is the angular frequency, ε rair , ε rd and ε0 are the dielectric constants of air, dielectric plate and vacuum respectively, μ is the magnetic permeability of copper, μ0 is the magnetic permeability of vacuum, a MRavg is the average side length of the spiral coil, a MRavg =(a MR-in +a MR-out ) / 2, ρ is the filling ratio, ρ=(aMR-out -a MR-in ) / (a MR-in +a MR-out ).

[0057] 6) Calculate the RF coil current I RF and the metamaterial booster induced current I MF ,

[0058] R RF I RF +jωL RF I RF +jωM RF-MR I MR = U (6)

[0059]

[0060] where ω is the angular frequency corresponding to the Larmor frequency, U is the excitation voltage of the RF coil, R RF and L RF are the equivalent resistance and inductance of the RF coil, respectively. C MR is the external capacitance of the metamaterial booster. M MR-RF is the mutual inductance between the metamaterial booster and the RF coil. When the metamaterial booster resonates, then the induced current is:

[0061]

[0062] Z RF-RF = R RF +jωL RF (10)

[0063] Z RF-MR = Z MR-RF = jωM RF-MR (11)

[0064] Z MR-MR = R MR (12)

[0065] where Z is the impedance.

[0066] 7) A square spiral loop of a metamaterial booster can be equivalent to multiple concentric square loops with different side lengths. The magnetic field of a single-turn square loop is calculated by superimposing the induced magnetic fields of four side lengths. According to the Biot-Savart law, the induced magnetic field generated by a side length in the y direction can be calculated as:

[0067]

[0068] where I is the current in the square loop, a is the side length of the square loop, and x, y, z are the coordinates of the target point in space. The magnetic field of the metamaterial booster (B MR ) is equal to the sum of the magnetic fields of multiple concentric square loops with different side lengths. The magnetic field of the radio frequency coil (B RF ) is equal to the sum of the magnetic fields of five rectangular coils. Finally, the magnetic field magnitude (B ROI ) in the target region is the superposition of the magnetic fields of the radio frequency coil and the metamaterial booster, i.e.

[0069] B ROI = B RF +B MR (14)

[0070] Therefore, the current I can be obtained by calculating the impedance and mutual inductance of the metamaterial booster, and then the magnetic field distribution in the target region can be obtained according to the Biot-Savart law. Since the impedance and mutual inductance are closely related to the geometric structure of the metamaterial booster, it is necessary to optimize the geometric structure before introducing the metamaterial booster in order to obtain the optimal magnetic field distribution.

[0071] 8) This embodiment takes the size of a human wrist as an example to initialize the structural parameters of the metamaterial booster,

[0072]

[0073] 9) Set the optimization goals, the first optimization goal is to maximize the average magnetic field strength in the wrist region, and the second optimization goal is to minimize the volume of the metamaterial booster.

[0074] 10) In order to improve the optimization efficiency, the non-dominant sorting genetic algorithm (Non-Dominant Sorting Genetic Algorithm II, NSGA-II) is used to optimize the structure of the metamaterial booster to achieve the best magnetic field enhancement effect.

[0075] 11) First, initialize the population P0, population size N = 100, calculate the average magnetic field strength and the volume of the metamaterial enhancer, fast non-dominated sorting of P0 and calculate the crowding, get the evolution of the number of t = 1; Then the population selection-crossover-mutation operation to generate offspring population Pt average magnetic field strength and the volume of the metamaterial enhancer Qt; Next, the parent population P0 and offspring population Pt combined after non-dominated sorting and crowding calculation, using the elite strategy to retain the excellent individual to generate a new parent population Rt; Finally, the genetic algebra whether to meet the set value, if not meet the repeat selection-crossover-mutation operation, if meet the evolution is completed. NSGA-II algorithm introduced the non-dominated sorting method to reduce the computational complexity of the algorithm, using the method of crowding to ensure the diversity of individuals in the population, and using the elite strategy to ensure that the excellent individual can have a greater probability of being retained. Select the individual with the smallest outer edge length, return the optimal structure parameters of the metamaterial enhancer.

[0076] 12) Solve the optimal structure parameters of the metamaterial enhancer, n = 5, g MR = 1 mm, w MR = 1 mm, a MR-in = 105 mm, h MR = 0.3 mm.

[0077] 13) Tune the capacitance to C MR = 0.4 nF, tune its resonance frequency to 2.98 MHz (the working frequency of the 70 mT MRI system), as Figure 5 shown.

[0078] 14) Finite element simulation analysis of model I with and without metamaterial enhancer.

[0079] 15) Analysis of the magnetic field enhancement factor distribution of the 70 mT MRI model I region with and without metamaterial enhancer, as shown, the black rectangular dashed line represents the outline of the model I, and the outer frame represents the outline of the metamaterial. By comparing Figure 6 (a, b) and (c, d), it is found that the metamaterial enhancer can significantly enhance the magnetic field. As Figure 6 shown in (e), in the area 10 mm away from the inner boundary of the metamaterial enhancer, Figure 6 it can be enhanced by 5.76 times. As shown in (f), the Figure 6 at the center point P of the metamaterial enhancer can be enhanced by 1.95 times. Therefore, the metamaterial enhancer can significantly enhance the magnetic field.

[0080] ​The above description of disclosed embodiments enables one of ordinary skill in the art to make and use the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended 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.

[0081] The above merely provides an example of the present application and is not intended to limit the present application. The present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application should be included in the scope of claims of the present application.

Claims

1. A method for optimizing a magnetic resonance metamaterial magnetic field enhancer based on the NSGA-II genetic algorithm, comprising the following steps: 1) Preliminary construction of the metamaterial enhancer model structure. The metamaterial enhancer includes a dielectric substrate, a spiral coil, and an external capacitor. The spiral coil is set on the dielectric substrate. There is a gap between adjacent spiral coils. The two ends of the spiral coil are connected by an external capacitor. The number of spiral coil turns is n, and the gap between adjacent wires is g. MR , the width of the spiral coil is w MR , the inner side length of the spiral coil is a MR-in The outer length of the spiral coil is a MR-out , the external capacitor is C MR ; 2) Extract the equivalent circuit model of the metamaterial enhancer; 3) Construct the RF coil, metamaterial enhancer, and the model system under test; 4) Extract the equivalent circuit model of the RF coil and metamaterial enhancer; 5) Calculate the circuit parameters based on circuit theory and the equivalent resistance and equivalent inductance of the metamaterial enhancer as follows: in, is the resistance caused by the skin effect, is the dielectric resistance, the spiral coil is made of copper wire, l MR is the copper wire path length, δ is the skin depth of copper, w MR is the width of the copper wire, σ is the conductivity of copper, t is the thickness of copper, ω0 is the angular frequency, ε rair , ε rd and ε0 are the dielectric constants of air, dielectric plate and vacuum respectively, μ is the magnetic permeability of copper, μ0 is the magnetic permeability of vacuum, a MRavg is the average side length of the spiral coil, a MRavg =(a MR-in +a MR-out ) / 2, ρ is the filling ratio, ρ=(a MR-out -a MR-in ) / (a MR-in +a MR-out ); 6) Calculate the RF coil current and metamaterial enhancer induced current based on the equivalent circuit model and circuit theory; 7) Assuming the spiral coil is a square spiral loop, a square spiral loop of a metamaterial enhancer can be considered as multiple concentric square loops with different side lengths. By superimposing the induced magnetic fields of the four sides, the magnetic field calculation formula of a single-turn square loop is obtained, and then the calculation formula of the induced magnetic field in the target area is obtained; 8) Initializing the structural parameters of the metamaterial enhancer; 9) setting optimization goals, wherein the first optimization goal is to maximize the average magnetic field intensity in the magnetic resonance imaging target area, and the second optimization goal is to minimize the volume of the metamaterial enhancer; 10) The non-dominated sorting genetic algorithm NSGA-II is used to optimize the metamaterial enhancer structure to achieve the best magnetic field enhancement effect; 11) Determine the optimal structural parameters of the metamaterial enhancer; 12) Determine the tuning capacitor and connect the external capacitor C MR Set as a tuning capacitor to tune its resonant frequency to the target frequency.

2. The method for optimizing a magnetic resonance metamaterial magnetic field enhancer according to claim 1, wherein: In step 2), let R MF and L MF are the equivalent resistance and equivalent inductance respectively, and C0 is the parasitic capacitance.

3. The method for optimizing a magnetic resonance metamaterial magnetic field enhancer according to claim 2, wherein: In step 4), let R RF and L RF are the equivalent resistance and equivalent inductance of the RF coil, U is the excitation voltage of the RF coil, I RF is the RF coil current, I MF Inducing current for metamaterial enhancers.

4. The method for optimizing a magnetic resonance metamaterial magnetic field enhancer according to claim 3, wherein: The method of step 6) is as follows: R RF I RF +jωL RF I RF +jωM RF-MR I MR =U Where ω is the angular frequency corresponding to the Larmor frequency, R RF and L RF are the equivalent resistance and equivalent inductance of the RF coil respectively; M MR-RF is the mutual inductance between the metamaterial enhancer and the RF coil; when the metamaterial enhancer resonates, Then the induced current is: Z RF-RF =R RF +jωL RF WITH RF-MR =Z MR-RF =jωM RF-MR Z MR-MR =R MR Where Z is the impedance.

5. The method for optimizing a magnetic resonance metamaterial magnetic field enhancer according to claim 4, wherein: In step 7), the method for calculating the induced magnetic field in the target area is: According to the Biot-Savart law, the calculation formula for the induced magnetic field generated by a side length along the y direction is: Where I is the current in the square loop, a is the side length of the square loop, x, y, z are the coordinates of the target point in space; the magnetic field of the metamaterial enhancer is equal to the sum of the magnetic fields of multiple concentric square loops with different side lengths; the RF coil B RF The magnetic field is equal to the sum of the magnetic fields of the five rectangular coils; the magnetic field size B in the target area ROI is the superposition of the magnetic field of the RF coil and the metamaterial enhancer, namely: B ROI =B RF +B MR The current I is obtained by calculating the impedance and mutual inductance of the metamaterial enhancer, and the magnetic field distribution in the target area is obtained according to the Biot-Savart law.

6. The method for optimizing a magnetic resonance metamaterial magnetic field enhancer according to claim 1, wherein: The method of step 10) is as follows: initialize a population P0 with a population size of N, calculate the average magnetic field strength and the volume of the metamaterial enhancer, perform a fast non-dominated sort on P0 and calculate the crowding degree, and obtain an evolutionary generation t=1; perform a selection-crossover-mutation operation on the population to generate the average magnetic field strength of the offspring population Pt and the volume Qt of the metamaterial enhancer; merge the parent population P0 and the offspring population Pt, perform a non-dominated sort and crowding degree calculation, and use an elite strategy to retain excellent individuals to generate a new parent population Rt; determine whether the genetic generation meets the set value. If not, repeat the selection-crossover-mutation operation. If so, the evolution is completed.

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