阅读说明：本技术 基于逆向表面边界单元法的磁共振头部射频线圈设计方法 (Magnetic resonance head radio frequency coil design method based on reverse surface boundary cell method ) 是由 徐征 何为 王凡 贺玉成 吴嘉敏 于 2020-06-28 设计创作，主要内容包括：本发明涉及一种基于逆向表面边界单元法的磁共振头部射频线圈设计方法,属于核磁共振技术领域,包括以下步骤：S1：在需要布线的线圈表面进行规则三角形单元剖分,使得模型由一定目标数量的平面直角三角形单元构成；S2：在三维坐标系中,根据所建立线圈模型的三角形单元顶点坐标值,对空间顶点和三角形单元进行编号；S3：将处于模型边界的空间顶点全部整合提取,存放在顶点数组的顶部,与边界内部的顶点区分开；S4：计算三角形单元的流函数基函数；S5：设定射频线圈成像区域与目标点；S6：设定线圈计算参数,并计算流函数值；S7：计算布线路径,并对结果进行优化处理。(The invention relates to a magnetic resonance head radio frequency coil design method based on a reverse surface boundary unit method, which belongs to the technical field of nuclear magnetic resonance and comprises the following steps: s1: the method comprises the following steps of (1) performing regular triangle unit subdivision on the surface of a coil needing wiring, so that a model is formed by a certain target number of plane right-angle triangle units; s2: in a three-dimensional coordinate system, numbering the space vertexes and the triangular units according to the vertex coordinate values of the triangular units of the established coil model; s3: integrating and extracting all the space vertexes at the boundary of the model, storing the space vertexes at the top of the vertex array, and distinguishing the space vertexes from vertexes inside the boundary; s4: calculating a flow function basis function of the triangle unit; s5: setting an imaging area and a target point of a radio frequency coil; s6: setting coil calculation parameters and calculating a flow function value; s7: and calculating a wiring path and optimizing the result.)

1. A magnetic resonance head radio frequency coil design method based on an inverse surface boundary unit method is characterized in that: the method comprises the following steps:

s1: the method comprises the following steps of (1) performing regular triangle unit subdivision on the surface of a coil needing wiring, so that a model is formed by a certain target number of plane right-angle triangle units;

s2: in a three-dimensional coordinate system, numbering the space vertexes and the triangular units according to the vertex coordinate values of the triangular units of the established coil model;

s3: integrating and extracting all the space vertexes at the boundary of the model, storing the space vertexes at the top of the vertex array, and distinguishing the space vertexes from vertexes inside the boundary;

s4: calculating a flow function basis function of the triangle unit;

s5: setting an imaging area and a target point of a radio frequency coil;

s6: setting coil calculation parameters and calculating a flow function value;

s7: calculating a wiring path, and optimizing the result: and discretizing the final flow function calculation result, namely discretizing the current flowing region between the adjacent contour lines of the flow function, namely the actual wiring region of the coil, discretizing the flow function calculation result to obtain a final wiring result, comparing the actual wiring result again, and restarting from S6 until the final result meets the requirement if the result is not satisfactory.

2. The method for designing a radio frequency coil of a magnetic resonance head based on an inverse surface boundary cell method as claimed in claim 1, wherein: in step S1, the curved surface needing to be arranged with the radio frequency coil is divided into triangles, the whole wiring curved surface is gradually filled with triangular plane small patches with similar sizes, and the top point of each triangular unit and each triangular unit surface are numbered; the triangle subdivision on the surface of the coil is a regular subdivision, the subdivision shape is a right triangle, and for the coil model with symmetry, the number and the shape of the triangle subdivision on the two symmetrical parts are also symmetrical; the vertices of the triangle units on the surface of the coil are sequenced and numbered according to the descending order of Z-axis coordinate values in a three-dimensional coordinate system and are stored in a vertex coordinate array, namely, from the top to the bottom of the coil model, the vertices with the same longitudinal coordinate values are sequenced on the plane where the vertices are positioned according to the anticlockwise order, so that the vertex sequencing serial numbers with similar spatial positions are also similar; integrating the triangle vertexes on the boundary, and in a vertex coordinate array storing vertex coordinates, placing the vertexes at the boundary at the top end of the array and distinguishing the vertexes from the vertexes in the boundary; recording numbers on the triangle unit surfaces, calculating the centroid coordinates of each triangle, and representing the triangle by the centroid of each triangle; and simultaneously recording three vertex numbers of each triangle unit, and storing the three space vertex numbers together with the triangle unit surface numbers.

3. The method for designing a radio frequency coil of a magnetic resonance head based on an inverse surface boundary cell method as claimed in claim 1, wherein: in step S3, the boundary vertices are determined by: the common vertex of the two space vertexes is only one, namely the vertex connected with the two space vertexes is only one, namely one side of the triangle unit only belongs to the triangle unit, and other triangle units are not formed, the side belongs to the boundary of the coil model, and the two vertexes of the side are called boundary vertexes; and calculating the area size and the space coordinate of the centroid of each triangle through the three-dimensional coordinates of the vertexes of the triangle units.

4. The method for designing a radio frequency coil of a magnetic resonance head based on an inverse surface boundary cell method as claimed in claim 1, wherein: in step S4, the direction of the basis function is parallel to the opposite side of the vertex of the triangle, and the size is the reciprocal of the length of the triangle height corresponding to the opposite side; the flow function basis vector at each vertex consists of the basis functions of all triangle element flow functions associated with that vertex; discretizing the flow function psi to the vertices of the triangular elements of the coil surface, expressed as

5. The method for designing a radio frequency coil of a magnetic resonance head based on an inverse surface boundary cell method as claimed in claim 1, wherein: in step S5, the imaging region is defined as the interior of a spherical surface inside the radio frequency coil, a certain number of points are taken on the spherical surface as the target points of the imaging region, the magnetic field at the target points represents the magnetic field of the imaging region, i.e. the magnetic field at the target points should reach the desired magnetic field, the number of the target points on the spherical surface of the imaging region is changed by setting the number of longitudinal and transverse points of the target points of the imaging region, and the size of the spherical surface of the imaging region is changed to change the spatial position of the target points; setting the magnetic field direction of a target point in an imaging area.

6. The method for designing a radio frequency coil of a magnetic resonance head based on an inverse surface boundary cell method as claimed in claim 1, wherein: in step S6, the calculation parameters of the coil include: the minimum number of turns of the expected radio frequency coil, the distance between two adjacent radio frequency coils, a regularization coefficient lambda and the number of target points in an imaging region are set; establishing a target magnetic field matrix according to the magnetic field requirement of a target point, wherein the established target magnetic field matrix is a mapping relation between a flow function of the coil surface subdivision unit and the magnetic field of the target point in an imaging areaEstablishing a relation between a target magnetic field and a current density function on the surface of the coil, B_z(r₀) Is the magnetic field component in the Z-axis direction of the target magnetic field, j_xIs the component of the triangular cell current density on the X axis, j_yIs the component of the current density on the Y axis; since j (r) ═ cur (ψ (r) n (r)), j (r) current density, ψ (r) is a flow function, n (r) is a normal vector of the current density, cur is a convolution operator, thereby establishing a relationship between the flow function and the current density; discretizing the flow function to each coil subdivision unit, havings_nWeights that are discretized in units; the current density is expressed by a flow function and is brought into a magnetic field B_z(r₀) A relation with the current density to obtain

Establishing a relation matrix C of the magnetic field of the target area and the surface flow function of the coil_ztThe matrix is a sparse matrix, and the sparse matrix needs to be converted into a full storage matrix; adding flow function vector at node, setting flow function at boundary node to the same value, setting an initial value of flow function weighting coefficient s, calculating solution of s and solving by regularization method according to the initial valueAnd (3) slipping processing, namely calculating an actual magnetic field B generated by a flow function according to the mapping relation between the target point magnetic field of the imaging area and the flow function, wherein the calculation method comprises the following steps: setting B as the calculated magnetic field matrix, B_targetIs a target magnetic field matrix, λ is a regularization coefficient to control the error magnitude of the solution, Г is a regularization matrix which is substantially a unit operator to control the smoothness of the solution, and | B-B_target‖²+λ²‖Гs‖²The formula result is the minimum premise, an initial value of a flow function weighting coefficient s is set, iterative calculation is carried out on s, a magnetic field B actually generated is calculated according to the flow function obtained each time, a regularization matrix Г is used as a punishment item of the flow function weighting coefficient s, the accuracy of the solution is controlled, the smoothness of the flow function solution is changed by manually adjusting the regularization coefficient lambda, for the selection of the regularization coefficient lambda, the larger the lambda is, the larger the weight of the regularization matrix is, the accuracy of the flow function solution is lost, the formula calculation cannot be converged if the lambda is too small, oscillation occurs, the physical significance is lost, and the most appropriate value is found in the test.

Technical Field

The invention belongs to the technical field of nuclear magnetic resonance, and relates to a magnetic resonance head radio-frequency coil design method based on a reverse surface boundary unit method.

Background

The radio frequency coil is an important factor for determining the quality of nuclear magnetic resonance imaging, and the existing head coil surrounds the whole head, blocks eyes, a nose and a mouth, and is not beneficial to a doctor to observe the conditions of facial expression, eye spirit change and the like of a cerebral apoplexy patient. The accurate design of parameters such as the shape, the size and the winding mode of the head radio-frequency coil not only has obvious influence on the detection imaging quality of nuclear magnetic resonance, but also can facilitate doctors to observe diseases through reasonable design, and the diagnosis effect is improved.

The current radio frequency coil design methods are mostly the following: (1) a regular winding method: the shape of the coil is predetermined, then the winding position on the coil frame is continuously adjusted, and the optimal winding structure is selected through numerical optimization; (2) flow function method: calculating a current density function required for generating the magnetic field according to an expected target magnetic field through the Biao-Saval law so as to obtain a flow function value, connecting places with the same flow function size into a line so as to obtain a flow function equipotential line, wherein the flow function equipotential line can not only represent the trend of a winding, but also the area between adjacent equipotential lines is an actual wiring area; (3) dipole equivalent method: the surface of a coil with current flowing is divided into a plurality of small units, each small unit is equivalent to a small current loop, magnetic fields generated by the small current loops are synthesized into an expected magnetic field, namely, equivalent magnetic dipoles are used for replacing current distribution on a plane, magnetic field calculation is carried out through surface integration, and the equivalent magnetic dipoles can also be used by being combined with a current function method; the regular winding method is used more in earlier stages and is used less at present due to too large limitation. The dipole equivalent method has great limitation when in use, is not suitable for coils with irregular surface change, and has poor effect when being applied to open-type coils or coils with special design requirements.

Disclosure of Invention

In view of the above, an object of the present invention is to provide a method for designing a radio frequency coil for a nuclear magnetic resonance head based on a reverse surface boundary element method, which is a wearable helmet with a radio frequency coil exposed on the face below the eyes for the convenience of observation by a doctor. The problems that an existing radio frequency coil is single in design method and not wide in application range are solved, and coils with irregular shapes can be designed through an algorithm.

In order to achieve the purpose, the invention provides the following technical scheme:

a magnetic resonance head radio frequency coil design method based on an inverse surface boundary element method comprises the following steps:

s1: the method comprises the following steps of (1) performing regular triangle unit subdivision on the surface of a coil needing wiring, so that a model is formed by a certain target number of plane right-angle triangle units;

s2: in a three-dimensional coordinate system, numbering the space vertexes and the triangular units according to the vertex coordinate values of the triangular units of the established coil model;

s3: integrating and extracting all space vertexes at the boundary of the model, storing the space vertexes at the top of the vertex array, distinguishing the space vertexes from vertexes inside the boundary, and preparing for inserting stream function vectors at subsequent vertexes and setting the same value for the vectors at the boundary;

s4: calculating a flow function basis function of the triangle unit;

s5: setting an imaging area and a target point of a radio frequency coil;

s6: setting coil calculation parameters and calculating a flow function value;

s7: calculating a wiring path, and optimizing the result: and discretizing the final flow function calculation result, namely discretizing the current flowing region between the adjacent contour lines of the flow function, namely the actual wiring region of the coil, discretizing the flow function calculation result to obtain a final wiring result, comparing the actual wiring result again, and restarting from S6 until the final result meets the requirement if the result is not satisfactory.

Further, in step S1, performing triangle segmentation on the curved surface on which the radio frequency coil needs to be arranged, gradually filling the entire wiring curved surface with triangular planar facets of similar sizes, and numbering the vertices of each triangular unit and each triangular unit facet; the triangle subdivision on the surface of the coil is a regular subdivision, the subdivision shape is a right triangle, and for the coil model with symmetry, the number and the shape of the triangle subdivision on the two symmetrical parts are also symmetrical; the vertices of the triangle units on the surface of the coil are sequenced and numbered in a three-dimensional coordinate system from big to small according to the Z-axis coordinate values and are stored in a vertex coordinate array, namely, the vertices with the same longitudinal coordinate values are sequenced on the plane where the vertices are positioned according to a counterclockwise sequence from the top to the bottom of the coil model, so that vertex sequencing serial numbers with similar spatial positions are also similar, the subsequent wiring path is more smooth, and the coil is easy to manufacture; integrating the triangle vertexes on the boundary, and in a vertex coordinate array storing vertex coordinates, placing the vertexes at the boundary at the top end of the array and distinguishing the vertexes from the vertexes in the boundary; recording numbers on the triangle unit surfaces, calculating the centroid coordinate of each triangle, representing the triangle by the centroid of each triangle, and adopting the sequence of the centroid longitudinal coordinate values from large to small in the numbers; and simultaneously recording three vertex numbers of each triangle unit, and storing the three space vertex numbers together with the triangle unit surface numbers.

Further, in step S3, the boundary vertices are determined by: the common vertex of the two space vertexes is only one, namely the vertex connected with the two space vertexes is only one, namely one side of the triangle unit only belongs to the triangle unit, and other triangle units are not formed, the side belongs to the boundary of the coil model, and the two vertexes of the side are called boundary vertexes; and calculating the area size and the space coordinate of the centroid of each triangle through the three-dimensional coordinates of the vertexes of the triangle units.

Further, in step S4, the direction of the basis function is parallel to the opposite side of the vertex of the triangle, and the size is the reciprocal of the length of the triangle corresponding to the opposite side; the flow function basis vector at each vertex consists of the basis functions of all triangle element flow functions associated with that vertex. Discretizing the flow function psi to the vertices of the triangular elements of the coil surface, expressed ass is the weighting coefficient of the flow function at each vertex; and setting all the flow functions of the boundary vertexes in the vertex coordinate array to be the same value, ensuring that no current flows into the boundary and flows out of the boundary, and ensuring that all the current flows in the boundary.

Further, in step S5, the imaging region is defined as an interior of a spherical surface of the rf coil, a certain number of points are taken on the spherical surface as target points of the imaging region, the magnetic field at the target point represents the magnetic field of the imaging region, i.e. the magnetic field at the target point should reach a desired magnetic field, the number of the target points on the spherical surface of the imaging region is changed by setting the number of longitudinal and transverse points of the target points of the imaging region, and the size of the spherical surface of the imaging region is changed to change the spatial position of the target points; setting the magnetic field direction of a target point in an imaging area.

Further, in step S6, the calculation parameters of the coil include: the minimum number of turns of the expected radio frequency coil, the distance between two adjacent radio frequency coils, the regularization coefficient lambda and the number of target points in an imaging area are set. Establishing a target magnetic field matrix according to the magnetic field requirement of a target point, wherein the established target magnetic field matrix is a mapping relation between a flow function of the coil surface subdivision unit and the magnetic field of the target point in an imaging areaEstablishing a relation between a target magnetic field and a current density function on the surface of the coil, B_z(r₀) Is the magnetic field component in the Z-axis direction of the target magnetic field, j_xIs the component of the triangular cell current density on the X axis, j_yIs the component of the current density on the Y axis; since j (r) ═ cur (ψ (r) n (r)), j (r) current density, ψ (r) is a flow function, n (r) is a normal vector of the current density, cur is a convolution operator, thereby establishing a relationship between the flow function and the current density; discretizing the flow function to each coil subdivision unit, havings_nWeights that are discretized in units; by applying a current to the current densityFunctional representation of the incoming magnetic field B_z(r₀) A relation with the current density to obtain

Establishing a relation matrix C of the magnetic field of the target area and the surface flow function of the coil_ztThe matrix is a sparse matrix, and the sparse matrix needs to be converted into a full storage matrix. Adding a flow function vector at a node, setting the flow function at a boundary node to be the same value, setting an initial value of a flow function weighting coefficient s, calculating a solution of s and smoothing solution by using a regularization method according to the initial value, and calculating an actual magnetic field B generated by the flow function according to a mapping relation between a target point magnetic field of an imaging area and the flow function, wherein the calculation method comprises the following steps: setting B as the calculated magnetic field matrix, B_targetIs a target magnetic field matrix, λ is a regularization coefficient to control the error magnitude of the solution, Г is a regularization matrix which is substantially a unit operator to control the smoothness of the solution, and | B-B_target‖²+λ²‖Гs‖²The formula result is the minimum premise, an initial value of a flow function weighting coefficient s is set, iterative calculation is carried out on s, a magnetic field B actually generated is calculated according to the flow function obtained each time, a regularization matrix Г is used as a punishment item of the flow function weighting coefficient s, the accuracy of the solution is controlled, the smoothness of the flow function solution is changed by manually adjusting the regularization coefficient lambda, for the selection of the regularization coefficient lambda, the larger the lambda is, the larger the weight of the regularization matrix is, the accuracy of the flow function solution is lost, the formula calculation cannot be converged if the lambda is too small, oscillation occurs, the physical significance is lost, and the most appropriate value is found in the test.

The invention has the beneficial effects that: 1. the invention can realize the design of the coil with any curved surface shape, and can calculate the wiring result by the algorithm when the triangular unit subdivision is carried out on the area needing wiring on the surface of the coil with any shape.

2. The invention starts from the inverse problem, namely, the coil required by generating the target magnetic field is calculated according to the required target magnetic field, so that the design efficiency of the coil is greatly improved.

3. The invention can continuously change the coil structure by adjusting the regularization coefficient, the minimum turn number of the radio frequency coil, the minimum distance between the two radio frequency coils, the size of an imaging area and the number of target points on the imaging area until a proper coil structure is found.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the means of the instrumentalities and combinations particularly pointed out hereinafter.

Drawings

For the purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made to the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic view of a regular triangle subdivision;

FIG. 2 is a schematic view of triangle numbering;

FIG. 3 is a subdivision of a coil drawn in accordance with the present invention;

figure 4 is a coil winding result calculated for a drawn coil model according to the present invention,

FIG. 5(a) is a diagram of the magnitude of the magnetic field of the designed coil, and FIG. 5(b) is a diagram of the vector of the magnetic field of the designed coil;

fig. 6(a) is the result of the simulated magnetic field distribution of the coil calculated by the method, and fig. 6(b) is the result of the magnetic field distribution of the coil wound according to experience;

fig. 7(a) shows the magnetic field distribution of the central region of the simulated magnetic field of the coil calculated by the method, and fig. 7(b) shows the magnetic field distribution of the central region of the simulated magnetic field of the coil wound according to experience.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention in a schematic way, and the features in the following embodiments and examples may be combined with each other without conflict.

Wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same, and in which there is shown by way of illustration only and not in the drawings in which there is no intention to limit the invention thereto; to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.

The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there is an orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", etc., based on the orientation or positional relationship shown in the drawings, it is only for convenience of description and simplification of description, but it is not an indication or suggestion that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes, and are not to be construed as limiting the present invention, and the specific meaning of the terms may be understood by those skilled in the art according to specific situations.

A magnetic resonance head radio frequency coil design method based on a reverse surface boundary unit method includes firstly, dividing an irregular curved surface by using a plane triangle, numbering and processing vertexes of the triangle, distinguishing the vertex of the triangle at the boundary from the vertex of the triangle inside the boundary, independently storing the vertex of the boundary, establishing and calculating a flow function basis function of each triangle small unit, establishing a mapping relation matrix of a target point magnetic field of an imaging area and a flow function of a coil model wiring area, after a flow function initial value is set artificially, bringing the flow function initial value into a regularization method to calculate a flow function value and carry out smoothing processing on a flow function solution, and finally smoothing wiring tracks of a coil; and calculating the actual magnetic field of the imaging area according to the calculated flow function, and continuously adjusting coil parameters until the requirement of the expected magnetic field is met.

The method comprises the following steps:

s1: the method comprises the following steps of (1) performing regular triangle unit subdivision on the surface of a coil needing wiring, so that a model is formed by a certain target number of plane right-angle triangle units, as shown in figure 1;

s2: in the three-dimensional coordinate system (x, y, z), the spatial vertices and the triangle elements are numbered according to the triangle element vertex coordinate values of the established coil model. The space vertexes are sequenced and numbered according to the descending order of the Z-axis ordinate and are stored in the vertex coordinate array, the vertexes with the same ordinate are arranged on the plane where the vertexes are located according to the anticlockwise order, so that the vertexes with the similar space positions are also similar in the numbering in the vertex array, the subsequent wiring route is more smooth, and coils are easy to manufacture, and the numbering is as shown in figure 2. And recording numbers on the triangle unit surfaces, calculating the centroid coordinate of each triangle, representing the triangle by the centroid of each triangle, and adopting the sequence of the centroid longitudinal coordinate values from large to small for the numbers. Simultaneously recording three vertex numbers of each triangle unit, and storing the three space vertex numbers and the triangle unit surface numbers together; the method comprises the steps of performing triangular segmentation on a curved surface needing to be provided with a radio frequency coil, gradually filling the whole wiring curved surface with triangular plane small surface patches with similar sizes, and numbering the top point of each triangular unit and each triangular unit surface. The method is characterized in that: the triangle subdivision on the surface of the coil is a regular subdivision, the subdivision shape is a right triangle, and for the coil model with symmetry, the number and the shape of the triangle subdivision on the two symmetrical parts are also symmetrical. In the three-dimensional coordinate system, the vertices of the triangle units on the coil surface are sorted according to the Z-axis coordinate values, the order is from large to small, namely from the top to the bottom of the coil model, the vertices with the same longitudinal coordinate values are sorted on the plane where the vertices are located according to the counterclockwise order, so that vertex sorting orders with similar spatial positions are also similar. The vertices of the triangles on the boundary are integrated and, in the vertex coordinate array storing the coordinates of the vertices, the vertices at the boundary are placed at the top of the array and are distinguished from the vertices within the boundary.

S3: and integrating and extracting all the space vertexes at the boundary of the model, storing the space vertexes at the top of the vertex array, distinguishing the space vertexes from vertexes inside the boundary, and preparing for inserting stream function vectors at the subsequent vertexes and setting the same value for the vectors at the boundary. The method for judging the boundary vertex comprises the following steps: the common vertex of the two space vertices is only one, that is, the vertex connected to the two space vertices is only one, and it can also be understood that one side of the triangle unit only belongs to the triangle unit, and does not form other triangle units, and the side belongs to the boundary of the coil model, and the two vertices of the side are called boundary vertices. Calculating the area size and the space coordinate of the centroid of each triangle through the three-dimensional coordinates of the vertexes of the triangle units;

s4: and calculating the flow function basis function of the triangle unit, wherein the direction of the basis function is parallel to the vertex opposite side of the triangle, and the size of the basis function is the reciprocal of the length of the triangle corresponding to the opposite side. The flow function basis vector at each vertex consists of the basis functions of all triangle element flow functions associated with that vertex. Discretizing the flow function psi to the vertices of the triangular elements of the coil surface, expressed ass is the weighting factor of the flow function at each vertex.

S5: setting an imaging area and a target point of the radio frequency coil. The imaging area is determined to be inside a spherical surface inside the radio frequency coil, a certain number of points are taken on the spherical surface as target points of the imaging area, the magnetic field at the target point represents the magnetic field of the imaging area, namely the magnetic field at the target point is required to reach the expected magnetic field, the number of the target points on the spherical surface of the imaging area can be changed by setting the number of longitudinal and transverse points of the target points of the imaging area, and the size of the spherical surface of the imaging area can be changed to change the spatial position of the target points. Setting the magnetic field direction of a target point in an imaging area.

S6: and setting coil calculation parameters and calculating a flow function value. The calculated parameters of the coil include: the minimum number of turns of the expected radio frequency coil, the distance between two adjacent radio frequency coils, the regularization coefficient lambda and the number of target points in an imaging area are set. Establishing a target magnetic field matrix according to the magnetic field requirement of a target point, wherein the established target magnetic field matrix is a mapping relation between a flow function of the coil surface subdivision unit and the magnetic field of the target point in an imaging area

Establishing a relation between a target magnetic field and a current density function on the surface of the coil, B_z(r₀) Is the magnetic field component in the Z-axis direction of the target magnetic field, j_xIs the component of the triangular cell current density on the X axis, j_yIs the component of the current density on the Y axis; since j (r) ═ cur (ψ (r) n (r)), j (r) current density, ψ (r) is a flow function, n (r) is a normal vector of the current density, cur is a convolution operator, thereby establishing a relationship between the flow function and the current density; discretizing the flow function to each coil subdivision unit, havings_nAre weights scattered at each cell. For the boundary vertices in the vertex coordinate array, the flow functions of the boundary vertices are all set to the same value, so that no current flows into the boundary and flows out of the boundary, and the current flows inside the boundary.

The current density is expressed by a flow function and is brought into a magnetic field B_z(r₀) A relation with the current density to obtain

Establishing a relation matrix C of the magnetic field of the target area and the surface flow function of the coil_ztThe matrix is a sparse matrix, and the sparse matrix needs to be converted into a full storage matrix. Adding flow function vector at node, and adding boundary nodeThe flow functions at the points are set to be the same value, an initial value of a flow function weighting coefficient s is set, a regularization method is used for calculating the solution of s and smoothing the solution according to the initial value, the actual magnetic field B generated by the flow functions is calculated according to the mapping relation between the target point magnetic field and the flow functions in the imaging area, and the calculation method comprises the following steps: setting B as the calculated magnetic field matrix, B_targetControlling the error magnitude of the solution for the target magnetic field matrix, λ being the regularization coefficient, Г being the regularization matrix, essentially a unit operator, which controls the smoothness of the solution_target‖²+λ²‖Гs‖²The formula result is the minimum premise, an initial value of a flow function weighting coefficient s is set, iterative calculation is carried out on s, a magnetic field B actually generated is calculated according to the flow function obtained each time, a regularization matrix Г is used as a punishment item of the flow function weighting coefficient s, the accuracy of the solution can be controlled, the regularization coefficient lambda can be manually adjusted to change the smoothness of the flow function solution, the bigger the lambda is, the bigger the weight of the regularization matrix is, the accuracy of the flow function solution is lost, the formula calculation cannot be converged when the lambda is too small, oscillation occurs, the physical significance is lost, and the most appropriate value can be found in the test.

The regularization method can enable the coil wiring result to be more smooth, and is characterized in that: the regularization method is used for solving a stable approximate solution of an inverse problem, the solution precision is controlled by changing a penalty term added to a flow function weighting coefficient solution, iterative calculation is carried out on the flow function, and the smoothness of the solution is controlled by adjusting regularization parameters. Assume the desired imaging region magnetic field is B_targetAnd s is a column vector, each row is a weighting coefficient of the flow function at each vertex, the calculated magnetic field is B, and lambda is a regularization coefficient, the error of the solution is adjusted to be a regularization matrix, namely a penalty term of the flow function weighting coefficient s, and an identity matrix is selected as the regularization matrix and used for controlling the precision and the smoothness of the solution. Adding regularization coefficient lambda and regularization matrix to II B-B_target‖²+λ²‖Гs‖²Is used as a target, and an initial value of a flow function weighting coefficient s is artificially set through a magnetic field and a flowThe magnetic field B can be calculated through the mapping relation of the functions, iterative calculation is carried out on the weighting coefficient s of the flow function, wiring can be smooth, and the magnetic field of an imaging area can better accord with an expected value. For the selection of the regularization coefficient lambda, the bigger lambda is, the larger the weight of the regularization matrix is, and the too small lambda can cause the above formula not to be converged, so that the oscillation occurs and the physical significance is lost.

S7: calculating a wiring path, and optimizing the result: discretizing the final flow function calculation result, namely discretizing the current flowing region between the adjacent contour lines of the flow function, namely the actual wiring region of the coil, obtaining the final wiring result, comparing the actual wiring result again, and restarting from S6 until the final result meets the requirement if the result is not satisfactory.

One preferred embodiment is: firstly, drawing a nuclear magnetic resonance head radio-frequency coil model shown in the figure 3 in drawing software, manufacturing the size according to actual engineering requirements, carrying out triangle unit subdivision on the surface of the coil, and completely storing required space vertex and triangle data after storing the triangle unit subdivision into an obj format file.

And (4) introducing the model into an algorithm, calculating the space coordinates of the triangle units and the barycentric coordinates of each triangle, and storing the space vertex coordinates and the triangle information associated with the vertexes. The nodes at the coil boundaries are extracted and reordered, and the numbers of triangles associated therewith are reordered. Then, the meshes of the coil model are processed, barycentric coordinates of the triangles are calculated to represent the triangular units, a unidirectional magnetic field along the Z-axis direction is established in the target area according to the requirements of the radio frequency coil to be designed, a target magnetic field matrix is established according to the requirements, a wiring path required by generating the target magnetic field is calculated by applying an inverse surface boundary unit method, and the calculation result is shown in fig. 4. Then, the actual magnetic field generated by the designed coil is calculated to compare the requirement in the initial design, and fig. 5(a) is a magnetic field vector diagram and fig. 5(b) is a magnetic field size distribution diagram. Comparing the existing empirically wound rf head coil, fig. 6(a) shows the simulated magnetic field distribution of the coil calculated by the present method, and fig. 6(b) shows the magnetic field distribution of the empirically wound coil, it can be found by comparing the two figures that the magnetic field uniformity of the coil calculated by the present method is much better than the magnetic field of the empirically wound coil, (a) the maximum value of the magnetic field of the figure is about 10 times the minimum value, and (b) the maximum value of the magnetic field of the figure is about 1000 times the minimum value; fig. 7(a) shows the magnetic field distribution of the central region of the simulated magnetic field of the coil calculated by the method, and fig. 7(b) shows the magnetic field distribution of the central region of the simulated magnetic field of the coil wound according to experience.

Finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.