CN108182329A - A kind of radio frequency coil designs method and loop construction using particle cluster algorithm - Google Patents

Abstract

The invention belongs to the technical field of magnetic resonance imaging, and relates to a radio frequency coil design method and a coil structure using a particle swarm algorithm. It is mainly used in magnetic resonance imaging of the human brain. Form a hemispherical cavity for wrapping the brain, the coils below it form a magnetic field component unit, and establish the main part of the radio frequency magnetic field, and the coils above it are used to compensate the magnetic field, so that in a specific area inside the hemispherical cavity The magnetic field tends to be uniform; the performance of the coil is adjusted by adjusting the number N of coils and the height of the coil, and the optimal coil structure is searched in a wide range through the particle swarm algorithm, and the traditional blind multiple tests are replaced by algorithm design, improving The design efficiency is improved, the complexity of the design is reduced, and the design quality of the coil structure is improved.

Description

A Design Method and Coil Structure of Radio Frequency Coil Using Particle Swarm Algorithm

technical field

The invention belongs to the technical field of magnetic resonance imaging, and relates to a radio frequency coil design method and a coil structure using a particle swarm algorithm.

Background technique

Magnetic resonance imaging technology is widely used in the field of medical diagnosis. Due to the limitation of its use conditions, high-field magnetic resonance medical imaging system cannot be equipped in general departments. Magnetic resonance imaging equipment with low-field permanent magnet structure is relatively high-field ultra-low-field magnetic The resonance imaging system has the characteristics of light weight, low cost, and convenient maintenance, and can be used as a special detection instrument in various departments. However, the corresponding low-field magnetic resonance and high-field magnetic resonance have low signal-to-noise ratio and poor image quality, and various aspects are required to ensure the image quality of the equipment.

The radio frequency coil is an important component of the magnetic resonance system. It is mainly used to transmit radio frequency signals to excite hydrogen protons to generate resonance, and to receive magnetic resonance signals generated by protons. The uniformity of the radio frequency magnetic field and the strength of the radio frequency magnetic field of the coil are an important parameter to measure the radio frequency coil, which affects the signal-to-noise ratio of the received signal and the image quality.

Therefore, in order to improve the image quality of the head-specific low-field vertical magnetic resonance medical imaging equipment, it is necessary to propose a radio frequency coil structure for head imaging, and propose a design method for the optimal design of the structure.

Contents of the invention

In view of this, the object of the present invention is to provide a radio frequency coil design method and coil structure using particle swarm optimization algorithm.

To achieve the above object, the present invention provides the following technical solutions:

A method for designing a radio frequency coil using a particle swarm algorithm, comprising the following steps:

S1: Set the range of coil turns, the number of coil turns n∈[a,b], go to step S2

S2: Initialize the coil model parameter population, Pi, proceed to step S3

S3: Detect whether the number of coil turns n is in the interval [a,b], if n∈[a,b], go to step S4; if The optimal coil structure is obtained;

S4: Calculate the magnetic field uniformity and magnetic field strength in the area according to the coil model, calculate the fitness Fi corresponding to each particle, and proceed to step S5;

S5: Calculate the fitness of the optimal particle, if it meets the requirements of the optimization objective function or reaches the maximum iteration step, proceed to S6; if it does not meet the requirements of the optimization objective function, proceed to step S7;

S6: Record the parameters of the optimal particle, replace the number of coil turns n with (n+1), and return to step S3;

S7: update each particle information, return to step S4;

Wherein, a<b, and both a and b are positive integers.

Optionally, the optimization objective function described in step S5 is in Indicates the uniformity of the magnetic field in the target area, B _zAVG is the magnetic field strength value in the target area, and γ is the weight coefficient.

Optionally, the particle update function described in step S7 is:

v _i (t+1)＝w×v _i (t)+c ₁ ×rand _i (P _{i -xi} (t))+c ₂ ×rand _i (Q _{i -xi} (t)),

A radio frequency coil structure applying particle swarm optimization algorithm, comprising n coils, the coaxial arrangement of the several coils, assuming that the intersection point of the plane where the first coil is located and the axis is O, then along the direction away from point O, the coil The radius of is gradually reduced to form a uniform magnetic field in the inner space of the radio frequency coil structure, n is a positive integer and n≥2.

Optionally, the radius of the first coil is r ₀ , the radius of the i-th coil is r _i , and the distance between the geometric center of the i-th coil and point O is h _i , then the radius of the i-th coil i is a positive integer.

Optionally, adjacent coils are fixed by connecting strips.

Optionally, the orthographic projections of the connecting strips on the first coil are all on a straight line.

Optionally, the internal space of the radio frequency coil structure matches the size of the human head.

Optionally, the coils include adjacent magnetic field composition units and magnetic field compensation units, the first coil to the xth coil form a magnetic field composition unit for establishing a radio frequency magnetic field; the remaining coils form a magnetic field compensation unit for compensating all The radio frequency magnetic field is used to form a uniform magnetic field, x<n, where x is a positive integer.

Optionally, the inner space of the radio frequency coil structure is hemispherical.

The beneficial effects of the present invention are:

1. A radio frequency coil structure using particle swarm algorithm involved in the present invention is mainly used in magnetic resonance imaging of the human brain. The radio frequency coil wiring area is selected on a hemispherical surface, and the inner part is formed to wrap the brain. In the hemispherical cavity, the coils below it form a magnetic field component unit, which establishes the main part of the radio frequency magnetic field, and the coils above it are used to compensate the magnetic field, so that the magnetic field in a specific area inside the hemispherical cavity tends to be uniform.

2. A radio frequency coil design method using particle swarm algorithm involved in the present invention adjusts the performance of the coil by adjusting the number N of coils and the height of the coil, and searches for the optimal coil in a wide range by particle swarm algorithm The structure is replaced by the traditional blind multiple tests through algorithm design, which improves the design efficiency, reduces the complexity of the design, and improves the design quality of the coil structure.

Other advantages, objects and features of the present invention will be set forth in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the investigation and research below, or can be obtained from It is taught in the practice of the present invention. The objects and other advantages of the invention may be realized and attained by the following specification.

Description of drawings

In order to make the purpose of the present invention, technical solutions and advantages clearer, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

Fig. 1 is the coil calculation optimization model figure of a kind of application particle swarm algorithm involved in the present invention radio frequency coil structure;

Fig. 2 is the actual coil connection structure diagram of a kind of radio frequency coil structure of application particle swarm algorithm involved in the present invention;

Fig. 3 is the computational model of the spatial magnetic field produced by a single coil;

Fig. 4 is the flow chart of a kind of radio frequency coil design method using particle swarm algorithm involved in the present invention;

Fig. 5 is the simulation result of the magnetic field strength before the coil optimization structure;

FIG. 6 is a simulation result of the magnetic field strength after the coil structure is optimized by using a radio frequency coil design method involving particle swarm optimization algorithm involved in the present invention.

Detailed ways

Embodiments of the present invention are described below through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation modes, and various modifications or changes can be made to the details in this specification based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the diagrams provided in the following embodiments are only schematically illustrating the basic concept of the present invention, and the following embodiments and the features in the embodiments can be combined with each other in the case of no conflict.

Please refer to Fig. 1-Fig. 6, the component numbers in the accompanying drawings represent respectively: magnetic field compensating unit 1, magnetic field forming unit 2, first coil 3, internal space 4 of the radio frequency coil structure, and connecting strip 5.

The present invention relates to a radio frequency coil design method using particle swarm optimization algorithm and a coil structure. The flow chart of the radio frequency coil design method using particle swarm optimization algorithm is shown in Figure 4, and its main steps are as follows.

S1: Set the range of coil turns, the number of coil turns n∈[a,b], go to step S2

S2: Initialize the coil model parameter population, Pi, proceed to step S3

S3: Detect whether the number of coil turns n is in the interval [a,b], if n∈[a,b], go to step S4; if The optimal coil structure is obtained;

S4: Calculate the magnetic field uniformity and magnetic field strength in the area according to the coil model, calculate the fitness Fi corresponding to each particle, and proceed to step S5;

S5: Calculate the fitness of the optimal particle, if it meets the requirements of the optimization objective function or reaches the maximum iteration step, proceed to S6; if it does not meet the requirements of the optimization objective function, proceed to step S7;

S6: Record the parameters of the optimal particle, replace the number of coil turns n with (n+1), and return to step S3;

S7: update each particle information, return to step S4;

Wherein, a<b, and both a and b are positive integers.

Preferably, the optimization objective function described in step S5 is in Represents the homogeneity of the magnetic field in the target area, B _zAVG is the magnetic field strength value in the target area, and γ is a weight coefficient; the particle update function described in step S7 is: v _i (t+1)=w×v _i (t)+ c ₁ ×rand _i (P _i -x _i (t))+c ₂ ×rand _i (Q _i -x _i (t)),

The spatial magnetic field generated by the RF coil can be regarded as the superposition of the magnetic fields generated by multiple single-loop coils, and the magnetic field generated by a single circular-loop coil in space can be calculated by the following formula.

Among them, r ² =x ² +y ² +z ² , ρ ² =x ² +y ² , α ² =a ² +r ² -2aρ, k ² =1-α ² /β ² , E(k ² ) , K(k ² ) is an elliptic integral. The optimal design parameters of the radio frequency coil structure are the number of turns n of the toroidal coil and the radius r _i of each toroidal coil, which are mainly used to balance the uniformity and magnetic field strength. The simulation result before coil structure optimization is shown in FIG. 5 , and the coil optimization result using the design method in the present invention is shown in FIG. 6 . The simulation results in Fig. 6 are obviously better than the simulation results in Fig. 5 in field intensity uniformity.

The coil structure designed by a radio frequency coil design method using the particle swarm algorithm involved in the present invention is as follows, including n coils, the coaxial arrangement of the several coils, assuming that the plane where the first coil 3 is located is the same as the plane of the coil. If the intersection point of the axes is O, the radius of the coil gradually decreases along the direction away from point O, and a uniform magnetic field is formed in the internal space 4 of the radio frequency coil structure, n is a positive integer and n≥2.

Preferably, the radius of the first coil 3 is r ₀ , the radius of the i-th coil is r _i , and the distance between the geometric center of the i-th coil and point O is h _i , then the radius of the i-th coil i is a positive integer.

In this embodiment, the adjacent coils are fixed by connecting strips 5; the orthographic projections of the connecting strips 5 on the first coil 3 are all on a straight line; the inner space 4 of the radio frequency coil structure and The size of the human head matches; the coils include adjacent magnetic field composition units 2 and magnetic field compensation units 1, and the first coil 3 to the xth coil form the magnetic field composition unit 2 for establishing a radio frequency magnetic field; the remaining coils form The magnetic field compensation unit 1 is used to compensate the radio frequency magnetic field to form a uniform magnetic field, x<n, where x is a positive integer; the internal space 4 of the radio frequency coil structure is hemispherical.

A radio frequency coil structure using the particle swarm algorithm involved in the present invention is mainly used in magnetic resonance imaging of the human brain. The radio frequency coil wiring area is selected on a hemispherical surface, and its interior forms a hemispherical shape for wrapping the brain. In the cavity, the coils below it form the magnetic field composition unit 2, which establishes the main part of the radio frequency magnetic field, and the coils above it are used to compensate the magnetic field, so that the magnetic field in a specific area inside the hemispherical cavity tends to be uniform. And a kind of radio frequency coil design method using particle swarm algorithm involved in the present invention adjusts the performance of the coil by adjusting the number N of coils and the height of the coil, and searches for the optimal coil structure in a large scale through the particle swarm algorithm , the traditional blind multiple tests are replaced by algorithm design, which improves the design efficiency, reduces the complexity of the design, and improves the design quality of the coil structure

Finally, it is noted that the above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be carried out Modifications or equivalent replacements, without departing from the spirit and scope of the technical solution, should be included in the scope of the claims of the present invention.

Claims (10)

1. a radio frequency coil design method using particle swarm algorithm, is characterized in that, comprises the following steps: S1: Set the range of coil turns, the number of coil turns n∈[a,b], go to step S2 S2: Initialize the coil model parameter population, Pi, proceed to step S3 S3: Detect whether the number of coil turns n is in the interval [a,b], if n∈[a,b], go to step S4; if The optimal coil structure is obtained; S4: Calculate the magnetic field uniformity and magnetic field strength in the area according to the coil model, calculate the fitness Fi corresponding to each particle, and proceed to step S5; S5: Calculate the fitness of the optimal particle, if it meets the requirements of the optimization objective function or reaches the maximum iteration step, proceed to S6; if it does not meet the requirements of the optimization objective function, proceed to step S7; S6: Record the parameters of the optimal particle, replace the number of coil turns n with (n+1), and return to step S3; S7: update each particle information, return to step S4; Wherein, a<b, and both a and b are positive integers. 2. the radio frequency coil design method of application particle swarm algorithm as described in claim 1 is characterized in that, the optimization objective function described in step S5 is in Indicates the uniformity of the magnetic field in the target area, B _zAVG is the magnetic field strength value in the target area, and γ is the weight coefficient. 3. the radio frequency coil design method of application particle swarm algorithm as described in claim 1 is characterized in that, the particle update function described in step S7 is: 4. A radio frequency coil structure using particle swarm algorithm, is characterized in that, comprises n coils, the coaxial arrangement of described several coils, if the intersection point of the plane where the first coil is located and this axis is 0, then along the distance In the direction of point O, the radius of the coil decreases gradually, forming a uniform magnetic field in the inner space of the radio frequency coil structure, n is a positive integer and n≥2. 5. the radio frequency coil structure of application particle swarm algorithm as described in claim 4, it is characterized in that, the radius of described first coil is r ₀ , the radius of ith coil is r _i , the radius of ith coil The distance between the geometric center and point O is h _i , then the radius of the i-th coil 1≤i≤n, i is a positive integer. 6. The radio frequency coil structure applying particle swarm optimization algorithm as claimed in claim 4, characterized in that adjacent coils are fixed by connecting strips. 7. The radio frequency coil structure applying particle swarm optimization algorithm as claimed in claim 5, characterized in that, the orthographic projections of the connecting strips on the first coil are all on a straight line. 8. The radio frequency coil structure applying particle swarm optimization algorithm as claimed in claim 4, characterized in that the internal space of the radio frequency coil structure matches the size of the human head. 9. the radio frequency coil structure of application particle swarm algorithm as described in claim 4, it is characterized in that, described coil comprises adjacent magnetic field composition unit and magnetic field compensating unit, and first coil forms magnetic field composition to the xth coil The unit is used to establish a radio frequency magnetic field; the remaining coils form a magnetic field compensation unit, which is used to compensate the radio frequency magnetic field to form a uniform magnetic field, x<n, where x is a positive integer. 10. The radio frequency coil structure applying particle swarm optimization algorithm as claimed in claim 4, characterized in that, the internal space of the radio frequency coil structure is hemispherical.