Open-close type radio frequency coil structure for neck and limb joint magnetic resonance imaging and design method

Abstract

The invention relates to an open-close type radio frequency coil structure for neck and limb joint magnetic resonance imaging and a design method, and belongs to the technical field of nuclear magnetic resonance. The coil structure adopts a separated design, and comprises a first radio frequency coil part and a second radio frequency coil part which can move relatively, and a connecting mechanism for connecting the two parts. According to the structural design, the coil can be conveniently opened and closed, so that a patient can conveniently put parts such as necks or joints of four limbs which are inconvenient to move into the coil for magnetic resonance imaging. In addition, the invention further provides a design method of the open-close type radio frequency coil, according to the method, a boundary element and stream function combined method is adopted, optimization design can be carried out according to the special shape of a to-be-detected part, and therefore the filling factor and the signal-to-noise ratio of the coil are improved, and then a magnetic resonance image with higher quality is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear magnetic resonance, and relates to an open-and-closed radio frequency coil structure and a design method for magnetic resonance imaging of the neck and limb joints. Background Art

[0002] In low-field mobile MRI systems, MRI imaging diagnosis of joints such as the limbs and cervical spine has broad application prospects.

[0003] However, for patients with cervical spine and limb joint injuries, it is inconvenient to move their joints. When using conventional coil structures (such as rings or other closed coil structures) for magnetic resonance imaging, there are the following problems:

[0004] The part to be examined is difficult to place inside the coil: Since the coil structure has a fixed size and the injured part is usually difficult to move, it is difficult for the patient to place the injured part inside the coil, which increases the difficulty of the operation and may also cause secondary damage to the injured part.

[0005] The coil filling factor is low and the signal-to-noise ratio decreases: The conventional coil size is large, resulting in a small ratio of the volume of the sample to be tested to the volume of the RF coil (filling factor), which reduces the signal-to-noise ratio of the coil and affects the image quality.

[0006] In order to solve the above problems, it is necessary to develop a new type of RF coil structure that can facilitate patients to place the injured part inside the coil, while ensuring that the coil size fits the imaging part to improve image quality. Summary of the invention

[0007] In view of this, the purpose of the present invention is to provide an open-and-closed radio frequency coil structure and design method for magnetic resonance imaging of the neck and limb joints. In the existing mobile low-field magnetic resonance imaging system, the radio frequency coil structure is integrated, which is not conducive to the diagnosis of injured parts, such as the cervical spine and limb joints. Since the cervical spine and limb joints are relatively small, if a large-sized radio frequency coil is used, the signal-to-noise ratio of the coil is reduced due to its small filling factor (the ratio of the volume of the sample to be measured to the volume of the radio frequency coil), which affects the image quality. In order to improve the image quality, it is hoped that the coil size fits the imaging part. In this way, the commonly used integrated radio frequency coil structure has shortcomings. For example, to measure the neck, the entire head needs to be placed in, and the coil size must be larger than the head size. For example, to measure the knee joint, the limb needs to be fixed and then slowly inserted into the coil, which increases the difficulty of operation and brings disadvantages to the patient. In view of these situations, the present invention proposes to adopt an open-and-closed radio frequency coil structure scheme. Because of the special shape of the part to be measured, in order to optimize the performance of the radio frequency coil, the present invention proposes to use the boundary element combined with the stream function method to realize the structural design of the radio frequency coil.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] Split RF coil for MRI of the neck and limb joints, including:

[0010] A first radio frequency coil part and a second radio frequency coil part, wherein the first radio frequency coil part and the second radio frequency coil part can move relative to each other to realize an opening and closing structure;

[0011] The connecting mechanism is used to connect the first RF coil part and the second RF coil part and allow the first RF coil part and the second RF coil part to move relative to each other.

[0012] Furthermore, the connection mechanism includes a straight-insert pin header, a flexible PCB cable, or a multi-row pin-type aviation connector.

[0013] Furthermore, the first RF coil part and the second RF coil part each include a coil body and a connecting part, and the connecting part is used to connect the first RF coil part and the second RF coil part.

[0014] Furthermore, the coil body is designed using a boundary element combined with a stream function method.

[0015] A design method for a split radio frequency coil comprises the following steps:

[0016] Step 1: Assume the current density distribution on the coil surface and perform linear interpolation;

[0017] Step 2: Discretize the coil surface into triangular boundary elements;

[0018] Step 3: Define the vector basis function associated with the global node;

[0019] Step 4: Based on the results of steps 1 to 3, approximate the current density on the coil surface;

[0020] Step 5: Calculate the magnetic vector potential and magnetic flux density;

[0021] Step 6: According to the target magnetic field distribution, reversely solve the stream function value;

[0022] Step 7: Generate the wire path of the coil based on the stream function value.

[0023] Furthermore, in step six, the stream function value is obtained by solving a set of linear algebraic equations.

[0024] Furthermore, in step seven, a continuous stream function field is constructed through interpolation and discretization, and the trajectory path of the coil is drawn according to the target stream function value.

[0025] A magnetic resonance imaging system comprises the split-type radio frequency coil.

[0026] A magnetic resonance imaging method comprises the following steps:

[0027] Placing the part to be tested in the open-close radio frequency coil;

[0028] Magnetic resonance imaging of the area to be tested is performed.

[0029] The beneficial effects of the present invention are:

[0030] (1) Coil structure: A separate coil structure is used to achieve close fit of the detection site, which helps protect patients with severe joint injuries (preventing secondary injuries due to excessive movement).

[0031] (2) The boundary element combined with stream function method is used to realize the RF coil structure design of arbitrary wiring surface. The coil structure design is not restricted by the target to be measured and has high flexibility.

[0032] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0034] Figure 1 Schematic diagram of a single triangular boundary element; (a) is a schematic diagram of a linear triangular boundary element divided in real physical space (plane); (b) is a schematic diagram of a boundary element after a linear triangular boundary element is mapped to a local coordinate system (ξ,η); (c) is a schematic diagram of a quadratic triangular boundary element divided in real physical space (surface); (d) is a schematic diagram of a quadratic triangular boundary element after it is mapped to a local coordinate system (ξ,η);

[0035] Figure 2 It is a schematic diagram of the triangular subdivision unit structure;

[0036] Figure 3 is the global node x in the physical space m Adjacent boundary elements Γ n The collection C m and the corresponding vector v n,i(m,n) Schematic diagram of nodes and their associated vectors;

[0037] Figure 4 is a schematic diagram of a triangle associated with node m;

[0038] Figure 5 The designed 5-turn coil and magnetic field distribution diagram;

[0039] Figure 6 The designed 10-turn coil and magnetic field distribution diagram;

[0040] Figure 7 It is a winding track and an open and close three-dimensional structure therein (including the skeleton of the winding coil and its supporting structure). DETAILED DESCRIPTION

[0041] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0042] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order 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 actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0043] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0044] Since the cervical spine and limb joints are relatively small, if a large-sized RF coil is used, the signal-to-noise ratio of the coil will decrease due to its small filling factor (the ratio of the volume of the sample to be measured to the volume of the RF coil), affecting the image quality. In order to improve the image quality, it is hoped that the coil size fits the imaging part. As a result, the commonly used integrated RF coil structure has shortcomings. For example, to measure the neck, the entire head needs to be placed in, and the coil size must be larger than the head size. For example, to measure the knee joint, the limb needs to be fixed and then slowly inserted into the coil, which increases the difficulty of operation and brings disadvantages to the patient. In response to these situations, the present invention proposes to adopt an open-and-closed RF coil structure. Because of the special shape of the part to be measured, in order to optimize the performance of the RF coil, the present invention proposes to use a boundary element combined with a stream function method to achieve the structural design of the RF coil.

[0045] Regarding the coil with a separate structure, the connections between its various parts use straight-plug pin headers, flexible PCB cables, multi-row pin aviation connectors, etc.

[0046] The separate structure can be divided into a two-part separate coil structure, a three-part separate structure and other multi-part separate structures. It can be appropriately selected depending on the specific detection site and the severity of the disease, so as to ensure both the imaging effect and the safety of the patient's injured site.

[0047] Design method details:

[0048] First, assume that the coil surface Γ coil The current density distribution J coil , satisfying the divergence-free condition and flows in a plane Γ that is tangent to the coil surface coil , that is, satisfying the formula J coil (x)·v(x)=0

[0049] The formula is:

[0050]

[0051] In the above formula, v(x) represents the angle perpendicular to the coil surface Γ coil The outward unit length vector of .

[0052] Introduce the vector formula A=(A x ,A y ,A z ) T , and is defined as:

[0053]

[0054] The vector potential A satisfies Poisson's equation:

[0055]

[0056] The vector potential A can be determined from Poisson's equation (5) by its integral expression, namely

[0057]

[0058] u * (x,x') is the Green matrix of the three-dimensional Laplace, that is,

[0059]

[0060] Combining formula (4) and formula (6), the magnetic induction field can be rewritten as

[0061]

[0062] For current density J coil Linear interpolation is performed. Linear interpolation allows the current density to transition smoothly between adjacent finite elements, avoiding sudden increases or decreases, thereby keeping the divergence of the current density zero overall, that is, satisfying In addition, linear interpolation can also ensure that the current density J coil In Γ coil In the tangent plane of the surface, J also satisfies coil (x)·v(x)=0.

[0063] The unit triangle is a reference unit defined in the finite element discretization, usually a standardized triangle, expressed in the local coordinate system (ξ,η). Its size and shape are fixed, providing a simplified analysis model when performing numerical integration and interpolation. The physical triangle is based on the partitioning result of the actual geometric model and is defined in the global coordinate system (x,y). During the calculation process of the finite element method, each physical triangle can be mapped to the unit triangle through the Jacobian matrix, thereby converting the complex geometric shape of the physical space into a standardized reference unit. This mapping relationship not only simplifies the numerical calculation, but also ensures the continuity and accuracy between different units, so it becomes a core step in finite element analysis. Through this mapping, a unified numerical solution process can also be performed on the standard reference unit, and then the solution results can be mapped back to the physical space, thereby greatly improving the solution efficiency and accuracy.

[0064] Assume that the coil surface Γ coil It can be approximated as where Γ n ,1≤n≤N, is a triangular boundary element. In the subsequent analysis, the following representation is used, such as Figure 1 shown.

[0065] 1.n is the number of triangular elements in the mesh;

[0066] 2. Gamma n :Δx n1 x n2 x n3 ,1≤n≤N,triangular boundary element;

[0067] 3.x nj ,1≤j≤N e , corresponds to the triangular boundary element Γ n The local vertices of the linear triangle unit N e =3, for the quadratic triangular element N e =6;

[0068] 4. Γ nj is the boundary element of the triangle directly opposite to the vertex x nj The edge of , 1≤j≤3;

[0069] 5.v nj is perpendicular to the edge Γ nj The outward unit vector, 1≤j≤3, is located at the boundary element Γ of the triangle n On a tangent plane;

[0070] 6.v n is the outward unit vector, perpendicular to the triangle boundary element Γ n ;

[0071] 7.x m , 1≤m≤M, is the coil surface Γ n The global node corresponds to the triangular boundary element Γ n The generated boundary element mesh;

[0072] 8.N is the number of triangular boundary elements;

[0073] 9.M is the coil surface Γ n The number of global nodes;

[0074] 10.N e is the boundary element Γ corresponding to each triangle n The number of local nodes;

[0075] The mapping relationship between the unit triangle (b) and the points in the physical space triangle (a) is, and the parameterization of the triangle boundary element is expressed as:

[0076]

[0077] Among them, Γ n (ξ,η)={(ξ,η)ξ≥0,η≥0,ξ+η≤1}, N j (ξ,η),1≤j≤N eis a geometric shape function. For linear triangular boundary elements, that is, N e =3, its shape function is:

[0078] N1(ξ,η)=ξ,N2(ξ,η)=η,N3(ξ,η)=1-ξ-η (8)

[0079] Substituting the above formula into (8), we can obtain the parameterized expression of a point in the linear triangular boundary element, that is, by mapping x(ξ,η), we can transform the calculation result on the reference element into the actual physical space:

[0080]

[0081] Therefore, the directional derivatives of any point in the physical space in the ξ and η directions, that is, on the coordinate axes of the unit triangle, can be derived:

[0082]

[0083] It can be seen from the above formula that under the linear triangle boundary element, the inverse of the direction of the point in the physical space with respect to the unit triangle coordinate axis is obtained, and the result is still a global coordinate expression, which is independent of the unit triangle coordinate point and only related to the triangle edge obtained by the decomposition. When the decomposition structure is obtained, its value is also a constant. By calculating these partial derivatives, the deformation relationship of the physical unit in the reference coordinate system can be determined, thereby accurately describing the geometric structure of the physical unit.

[0084]

[0085] Vector v nj (ξ,η) satisfies the identity:

[0086]

[0087] Define the association function i to determine the connection relationship between vertices or nodes, as follows:

[0088] i(·,·):{1,2,...,M}×{1,2,...,N}→{0,1,2,3}

[0089]

[0090] The above definition indicates that each mesh unit is a triangle, and the triangle has three vertices, which are marked as x nj , j = 1, 2, 3. The entire mesh has n triangles, and each vertex in the mesh also has a global number x m. i(m,n) is a function used to identify the association between node m and unit n. When i(m,n)=0, it means that node m does not belong to triangle unit n, that is, node m is not among the three vertices of this triangle unit. When i(m,n)=j, it means that node m is exactly the jth vertex of unit n. For example, if i(m,n)=2, it means that the node m is located at the second vertex of unit n, which is like finding this node at a specific corner of a triangle. For linear triangle units, each unit contains only 3 vertices, so its nodes are all located at vertices. In this way, each node m will only belong to a vertex of a unit, so in this case, i(m,n) will not be equal to 0. For quadratic triangle units, its units usually contain 6 nodes, 3 of which are located at vertices and the other 3 are on edges. Quadratic units can introduce more nodes, which may span multiple units or be in non-vertex positions. Therefore, if a node m we are looking at is not a vertex in a unit n or is not directly associated with this unit, i(m,n) will be equal to 0.

[0091] For every global node x m , 1≤m≤M, defined as x m The associated triangle boundary element Γ n The collection C m , 1≤n≤N, C m Contains all and nodes x m Directly adjacent triangular boundary elements, such as Figure 3 As shown, that is:

[0092]

[0093] Physical Space and the global node x m Adjacent boundary elements Γ n The collection C m and the corresponding vector v n,i(m,n)

[0094] Definition and global node x m The associated vector basis function f m Defined as

[0095]

[0096] For the global node m, the schematic diagram is as follows Figure 4 As shown, the basis functions associated with the nodes are defined as:

[0097]

[0098] Among them, m is the vertex obtained by segmentation, Δ miis the i-th triangle associated with node m, N n is the number of triangles associated with the current node m, for example Figure 3 In the same node x m There are 6 associated triangles, so N n =6. Figure 3 In the example, node x m The associated triangular area, that is, the set C m Contains all unit triangles adjacent to the global node (shown in the shaded area), the basis function f m (x) is defined in this set C m For any position in C m For a point x inside, we need to determine the specific unit triangle Γ to which it belongs. n Once the cell Γ where the point x is located is determined n , then the local basis function v of the unit is used n,i(m,n) (x) to represent f m (x). Therefore, the basis function f m (x) in set C m It has the characteristics of piecewise definition, switching to the corresponding local basis function v as the point x changes between different units n,i(m,n) (x), thus achieving a continuous distribution representation of the current density on the entire surface.

[0099] Coil surface Γ coil The current density J coil Approximately:

[0100]

[0101] In the above formula, is the unknown coefficient corresponding to each global node x m The stream function strength at 1≤m≤M. Among them, i(m,n)≠0 means that node m is only involved in the summation when it is associated with triangle unit n, that is, node m belongs to unit n. This means that only the unit n related to node m is summed, avoiding the accumulation of irrelevant items. n,i(m,n) is the triangular unit Γ n The local basis function defined on the node x m This basis function will be multiplied by the current coefficient I m To obtain the contribution of the local current density at the position x. Finally, the current density J formed on the entire surface coil It is formed by the superposition of local current gradients on each unit.

[0102] Surface current density J coil The order of the approximate expression is higher than that of the triangular boundary element Γ nThe order of is one less, because v nj (ξ,η) and geometric shape function N j (ξ,η),1≤j≤N e The derivative of .

[0103] Because v nj (ξ,η) is defined by the derivative of the geometric shape function, while the current density J coil The approximate expression of is given by the vector v nj (ξ,η), thus giving a spatial distribution of current density compared to the triangular boundary unit Γ n The geometric shape function N used j (ξ,η),1≤j≤N e More precisely, the linear and quadratic triangular boundary elements provide constant and linear approximations for the surface current density, respectively. n When meshing, the selected global nodes are always located at the vertices of the triangular boundary elements. Therefore, when the interpolation order increases, the change of current density is only described more precisely, but no new global nodes are added or the scale of the system is changed, so the complexity of solving the system of equations will not increase. This makes it possible to more accurately describe the distribution of current density by increasing the interpolation order while keeping the dimension of the system equation unchanged. For each triangular boundary element Γ n , vector v nj (ξ,η) and the unit normal vector v pointing outward n (ξ,η) are orthogonal.

[0104] For linear triangle elements, the basis vectors are constant vectors on each triangle element, so they must satisfy the divergence condition. The same conclusion can be drawn from the mathematical formula, as follows:

[0105] If F(x,y,z)=F x (x,y,z)i+F y (x,y,z)j+F z (x,y,z)k, where i,j,k are unit vectors in the x,y,z directions, then the divergence of the vector field F is:

[0106]

[0107] e in the formula mi It is a unit vector along the length of the side of the subdivided triangle. It can be regarded as a vector field F, focusing on a specific point x. The divergence of the basis function related to this point is:

[0108]

[0109] When the model subdivision structure is determined, the shape of the boundary linear triangle is also determined. Therefore, the unit vector at this time is equivalent to a constant vector, and the components along all directions are constants. Therefore, the rate of change in the x, y, and z directions is zero, that is:

[0110]

[0111] Therefore, the interpolation given by equation (18) is divergence-free at each point, and the approximate expression for the surface current density is given by:

[0112]

[0113] Unknown coefficient I m ,1≤m≤M can be found in every triangle boundary element Γ n ,1≤n≤N is locally defined, that is:

[0114] I nj =I mj , where m j ∈{1,2,...,M}:i(m j ,n)=j (22)

[0115] i(m j ,n) is to obtain the global node m and the triangle unit Γ n For example, for the triangular boundary element Γ n , each of its three local nodes corresponds to a global node m j , j = 1, 2, 3, if its local node 1 can correspond to the global node 7, that is, i(m1, n) = 1, where m1 = 7. This is equivalent to the local node j in unit Γ n The current density coefficient on the node m is directly used. j The coefficient of .

[0116] Therefore, each triangular boundary element Γ is obtained n ,1≤n≤N Current density J coil A local approximation of :

[0117]

[0118] It can be seen from the above formula that if the mesh structure of the coil surface is fixed, then for a triangle Γ n For example, the basis function corresponding to each vertex is also a constant vector. Then after multiplying by the corresponding coefficient, the current density of each triangle is actually a constant value, which is a constant vector approximation.

[0119] To derive the discrete conditions for the stream functions associated with the global nodes belonging to the boundary curves of the coil surface, such as: j is the number of boundaries on the coil surface, represents the jth boundary of the coil. Consider a triangular boundary element And suppose, The schematic diagram can be seen Figure 1 .v n1 is perpendicular to the local node x n1 The opposite side Γ n1 and is located at the triangle boundary element Γ n Outward unit vector on the tangent plane, see also Figure 1 , v n1 (x)+v n2 (x)+v n3 (x) = 0 and it is easy to get v by definition n1 (x)·v n1 (x) = 0, so we can get:

[0120]

[0121] where v n3 (x)·v n1 (x)≠0, so we can get the result:

[0122] I n2 =I n3 (25)

[0123] By extending this conclusion to the curve All triangular boundary elements that share two nodes obtain the discretization conditions for the stream function associated with the global node on the boundary curve of the coil surface:

[0124]

[0125] According to the previous derivation, the magnetic vector potential A is approximately:

[0126]

[0127] The magnetic flux density B is approximated as follows:

[0128]

[0129] It can be simplified as

[0130]

[0131] In the above formula,

[0132]

[0133] If the coil shape and the split structure are determined, then the h corresponding to the fixed split structure of each coil shape is m If it is known and can be calculated, then the exact target field distribution can be determined in combination with the requirements, and the stream function value I at each node can be reversed. m .

[0134] If the z-component of the magnetic flux density B is known at point L in the target region Ω, the BEM discretization of the inverse problem yields the following set of linear algebraic equations:

[0135]

[0136] In the above formula, H∈R L×M , used to convert the stream function I at the global node to the component of the magnetic induction intensity Associated, including the BEM vector h m The z component of is calculated at L target points in the target area Ω. In addition, the vector Contains the z-component of the magnetic induction intensity at L target points within Ω. Vector is a vector containing all stream functions I m , 1≤m≤M unknown value. Then, at the global node:

[0137]

[0138] It should be noted that the components H of the BEM matrix H lm The integral involved is non-singular, meaning that the calculation can be performed without encountering a situation where the denominator goes to zero, thus avoiding infinite results. This is because, That is, the integration point x' is not on the coil surface Γ coil Instead, they are in other regions, so these integrals can be evaluated numerically by using Gaussian quadrature on the triangle.

[0139] In order to approximate the current density distribution to the form of a continuous wire, the stream function needs to be processed to generate the wire path for coil design. First, the scale of the average current density of the entire coil wiring surface is calculated to approximate the current density distribution to a continuous wire flow, and I c It can also be called "equivalent current density". Its calculation formula is as follows:

[0140]

[0141] In the above formula, I represents the stream function value at each global node, N loops is the number of coil turns set.

[0142] Determine each equipotential line s n ,n=1,...,Nloops The value of , that is:

[0143] s n =min(I m )+(n-1)I c ,1≤m≤M (34)

[0144] The stream function value of each global node has been inferred by the boundary element method. Based on these known data, a continuous stream function field is constructed by interpolation and discretization on the triangular mesh. The target stream function value s for each equipotential line has been calculated according to the required number of coil turns. n Therefore, in each triangular unit, use the discretized stream function value to find the stream function value equal to s n points, and thus draw a continuous path of current distribution, that is, the trajectory path of the coil.

[0145] In this case, the least squares solution I of the inverse problem can be obtained by solving the following equation:

[0146]

[0147] First item ||BB target || 2 represents the error between the magnetic field distribution generated by the calculated stream function and the ideal target magnetic field distribution. The second term ||Γ(I-I0)|| 2 is the introduced regularization term, which represents the deviation of the stream function to be solved from the reference value I0. Adjusting λ can find a balance between the smoothness of the solution and error control. Its value is generally determined by experiments. Usually, part of the magnetic field accuracy is sacrificed in exchange for a smooth solution of the stream function, that is, the deviation of the calculated magnetic field distribution and the smoothness of the stream function solution cannot be achieved at the same time, and the deviation of the magnetic field is essentially determined by the accuracy of the stream function solution. During the calculation, I is a column vector as the array of stream functions to be solved, and the reference value I0 needs to be obtained based on empirical values. When there is no empirical value, if there is no empirical value, select a suitable initial setting to ensure the rationality of the result. It can be set to zero in advance. After several iterative calculations, the approximate range of the empirical value can be determined, and I0 is very small compared to I.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. An open and close radio frequency coil for magnetic resonance imaging of the neck and limb joints, characterized in that: include: A first radio frequency coil part and a second radio frequency coil part, wherein the first radio frequency coil part and the second radio frequency coil part can move relative to each other to realize an opening and closing structure; The connecting mechanism is used to connect the first RF coil part and the second RF coil part and allow the first RF coil part and the second RF coil part to move relative to each other.

2. The split-type radio frequency coil according to claim 1, characterized in that: The connection mechanism includes a straight-insertion pin header, a flexible PCB cable or a multi-row pin-type aviation connector.

3. The split type radio frequency coil according to claim 1, characterized in that: The first RF coil part and the second RF coil part each include a coil body and a connection part, and the connection part is used to connect the first RF coil part and the second RF coil part.

4. The split-type radio frequency coil according to claim 1, characterized in that: The coil body is designed by using a boundary element combined with a stream function method.

5. A design method for a split-type radio frequency coil, characterized in that: The following steps are involved: Step 1: Assume the current density distribution on the coil surface and perform linear interpolation on it; Step 2: Discretize the coil surface into triangular boundary elements; Step 3: Define the vector basis function associated with the global node; Step 4: Based on the results of steps 1 to 3, approximate the current density on the coil surface; Step 5: Calculate the magnetic vector potential and magnetic flux density; Step 6: According to the target magnetic field distribution, reversely solve the stream function value; Step 7: Generate the wire path of the coil based on the stream function value.

6. The design method according to claim 5, characterized in that: In step six, the stream function value is obtained by solving a set of linear algebraic equations.

7. The design method according to claim 5, characterized in that: In the step seven, a continuous stream function field is constructed through interpolation and discretization, and the trajectory path of the coil is drawn according to the target stream function value.

8. A magnetic resonance imaging system, characterized in that: The invention comprises the split-type radio frequency coil according to any one of claims 1 to 7.

9. A magnetic resonance imaging method, characterized in that: The following steps are involved: Placing the part to be tested in the split-type radio frequency coil as claimed in any one of claims 1 to 7; Magnetic resonance imaging of the area to be tested is performed.

Images