CN106772162B - Non-winding form gradient coil for magnetic resonance imaging system and design method thereof - Google Patents

Non-winding form gradient coil for magnetic resonance imaging system and design method thereof Download PDF

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CN106772162B
CN106772162B CN201611215604.3A CN201611215604A CN106772162B CN 106772162 B CN106772162 B CN 106772162B CN 201611215604 A CN201611215604 A CN 201611215604A CN 106772162 B CN106772162 B CN 106772162B
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coil
gradient coil
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magnetic resonance
manufacturing
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CN106772162A (en
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刘震宇
潘辉
王强龙
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Changchun Institute of Optics Fine Mechanics and Physics of CAS
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/385—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/385—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils
    • G01R33/3858—Manufacture and installation of gradient coils, means for providing mechanical support to parts of the gradient-coil assembly

Abstract

The invention relates to a non-winding type gradient coil for a magnetic resonance imaging system and a design method thereof, belonging to the field of design and manufacture of coils of the magnetic resonance system. Aiming at the defects of the existing winding type gradient coil, the invention provides a non-winding type gradient coil to replace the existing winding type gradient coil. The invention is beneficial to expanding the imaging space, shortening the imaging time, reducing the power consumption, reducing the eddy current effect, reducing the equipment volume and the like, and simultaneously improves the MRI imaging quality and saves the cost. On the other hand, the invention provides a new coil configuration, which can effectively reduce the influence of self-inductance and is beneficial to the rapid switching of a magnetic field; the number of the coils is reduced, and the high consistency of coil excitation signals is ensured. The design method provided by the invention provides the manufacturing modes of 3D printing, etching and the like, effectively improves the manufacturing precision of the coil and solves the manufacturing problem of the coil with a complex shape. The problems that the existing winding manufacturing method is low in manufacturing precision and difficult to manufacture in complex shapes are solved.

Description

Non-winding form gradient coil for magnetic resonance imaging system and design method thereof
Technical Field
The invention relates to the field of design and manufacture of gradient coils of a magnetic resonance system, in particular to a non-winding type gradient coil for a magnetic resonance imaging system and a design method thereof.
Background
The gradient coil is used as a core functional component of the magnetic resonance system, and performance parameters such as linearity and inductance of the gradient coil directly influence the imaging quality and response time of the magnetic resonance imaging system. Currently, the gradient coils are all in a wound form to generate the target magnetic field. In order to achieve the winding form, a winding portion of the coil needs to be additionally added. On one hand, the length of the coil is increased, the space required by the coil is increased, and the space utilization rate of the magnetic resonance system is reduced; on the other hand, due to the increase of the length of the coil and the winding form, the inductance and the resistance of the gradient coil are increased, so that the energy consumption, the heat generation amount and the system response time are increased.
Disclosure of Invention
The invention provides a novel non-winding type gradient coil for a magnetic resonance imaging system and a design method thereof, aiming at the technical problems of the existing winding type gradient coil.
In order to solve the technical problems, the technical scheme of the invention is as follows:
a non-winding form gradient coil for a magnetic resonance imaging system is formed by connecting two or more wires, and the connection mode of the wires in the non-winding form gradient coil comprises parallel connection, series connection or other feasible topologies.
In the above technical solution, the non-winding form gradient coil is driven by current or voltage.
In the above technical solution, the non-winding type gradient coil is of a single-input type or a multi-input type, and a rated voltage is applied to one or more pairs of nodes to generate a required gradient magnetic field.
In the above technical solution, the gradient coil in the non-winding form is used for designing an electromagnetic coil used in a magnetic resonance imaging system, such as a gradient magnetic field coil, a shim coil, or a shield coil.
In the above technical solution, the non-winding form gradient coil configuration realizes its function on a plane, a cylindrical surface, or any smooth single-communication or multi-communication curved surface.
In the above technical solution, the non-winding type gradient coil may be processed by, but not limited to, numerical control processing of conductor lines, conductor strips, a flexible PCB board in combination with a 3D printing technology, or in combination with an etching technology.
A method of designing a gradient coil of a non-wound form for use in a magnetic resonance imaging system, comprising the steps of:
designing a non-winding gradient coil with a parallel or serial connection mode by adopting a parameter optimization method; and designing the non-winding gradient coil with a connection mode of a topological structure by adopting a topological optimization method.
In the technical scheme, the specific steps of designing the non-winding gradient coil with the parallel or serial connection mode by adopting a parameter optimization method are as follows:
the method comprises the following steps: parametric modeling: introducing design variables, establishing a non-winding gradient coil analysis model by an objective function, and establishing a linear f (r)0θ, z) is expressed as:
wherein (r)0Theta, z) corresponds to the linear coordinate r in a cylindrical coordinate system0Is the radius of the cylindrical design surface and g (theta) is the characteristic parameter equation for the selected line type.
According to Biot-Savart law
Wherein the content of the first and second substances,
Figure BDA0001191702440000023
is the coordinates of the point of the field,
Figure BDA0001191702440000024
is the source point coordinate; i is the current through the wire, μ0Is the vacuum permeability; the component B of the magnetic field intensity in the Z direction can be obtainedzComprises the following steps:
Figure BDA0001191702440000031
an objective equation can be established according to the requirements:
Figure BDA0001191702440000032
step two: solving the model: introducing a proper optimization algorithm solution model, and calculating the magnetic field intensity;
step three: and (5) forward verification of a calculation result, and processing and experimental measurement if the design requirement is met.
In the above technical solution, the specific steps of designing the non-winding gradient coil with the connection mode of the topological structure by using the topological optimization method are as follows:
the method comprises the following steps: optimizing the distribution of the conductive material by adopting continuum topology optimization and taking the physical quantity of the electromagnetic coil as a design variable; the design variable expression is:
σ(ρ)＝σAir+ρp(σCu-σAir)
wherein σAirIs the electrical conductivity of air, σCuIs the conductivity of the copper conductive material used, p is a penalty term; ρ is the design variable:
Figure BDA0001191702440000033
the design variables satisfy the continuity equation:
wherein V is an electric potential;
then according to Biot-Savart law
Figure BDA0001191702440000035
To obtain BzExpression (c):
wherein Jx,JyThe component of the current density in the x and y directions in the expansion plane;
RC＝rcosθ-ricosθi，RS＝rsinθ-risinθi；
step two: establishing a geometric model in software according to the formula deduced in the step one, and solving B by using a semi-analytic or numerical methodzSolving the sensitivity by using an adjoint equation method;
step three: performing result post-processing, extracting a calculation result and selecting different processing methods according to the shape of the result; if the coil is not a single connected coil, a layout can be made;
step four: processing and manufacturing are carried out, and the magnetic field intensity is detected.
The invention has the following beneficial effects:
the non-winding type gradient coil for the magnetic resonance imaging system has the advantages of low inductance, high electromagnetic conversion rate and the like. The structure of the flexible printed circuit board can be designed through parameter optimization or structural topology optimization, and can be manufactured and processed by adopting numerical control processing or combining 3D printing, flexible PCB (printed circuit board) and other technical methods.
The non-winding type gradient coil for the magnetic resonance imaging system can effectively reduce the influence of self-inductance and is beneficial to the quick switching of a magnetic field; and the single input coil can be realized, the required gradient magnetic field is generated by applying rated voltage to a pair of nodes, the influence of current passing through the coils respectively is reduced, and the high consistency of coil excitation signals can be ensured.
The non-winding type gradient coil for the magnetic resonance imaging system is designed in a wire configuration mode on the basis of meeting the magnetic field intensity distribution, and an invalid rewinding part in the traditional coil is removed; and simultaneously optimizing parameters such as inductance energy consumption of the coil. On the basis, the invention can effectively reduce the space volume occupied by the magnetic resonance system; the inductance is reduced to realize rapid imaging; and the coil resistance is reduced, and the system energy consumption is reduced.
The non-winding type gradient coil for the magnetic resonance imaging system adopts a parallel gradient coil with optimized parameter design, and the longitudinal length of the parallel gradient coil can be reduced to 1.6 times of that of a target area; the longitudinal length of the gradient coil is reduced by more than 50% compared with the traditional winding type gradient coil; the space utilization rate of the magnetic resonance system is effectively improved. On the other hand, due to the high symmetry, the inductance value is reduced, the influence of self-inductance can be effectively reduced, parameters such as resistance and inductance are obviously reduced, and the energy consumption and the response time of the coil are reduced.
According to the design method of the non-winding type gradient coil for the magnetic resonance imaging system, in the manufacturing process, due to the fact that the lead is possibly irregular due to the design method, the traditional winding method is difficult to achieve; and the method further provides the manufacturing method which combines the modes of numerical control processing, 3D printing, etching and the like through parameter optimization or structural topology optimization, so that the manufacturing precision of the coil is effectively improved, and the manufacturing problem of the coil with a complex shape is effectively solved. The problems that the existing winding manufacturing method is low in manufacturing precision and difficult to manufacture in complex shapes are solved.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
FIG. 1 is a schematic diagram of a parameterized design model of a cylindrical gradient coil.
FIGS. 2a-2c are schematic diagrams of three different wire configurations for which transverse gradient magnetic fields are the design objective; wherein:
FIG. 2a is a schematic diagram of a series coil configuration calculated based on a flow function method, wherein the closed coil is required to be opened and the concentric coils are connected in series in actual manufacturing;
FIGS. 2b and 2c are schematic diagrams of parallel coil configurations designed by a parameter method respectively; FIG. 2c can be driven by a single pair of node voltages (black dots being the voltage input locations).
FIG. 3a is a schematic diagram of a continuum topology optimization model of a cylindrical gradient coil.
FIG. 3b is a schematic diagram of one possible optimization result form (1/4) design area;
the protective results of the invention are not limited to those presented in the figures, but also include other coils in a non-wound form to change the coil topology.
Detailed Description
The invention idea of the invention is as follows: aiming at the defects of the existing gradient coil form, the invention provides a non-winding gradient coil. The non-winding gradient coil includes various connection modes such as series connection, parallel connection, topological structure and other mixed connection modes of wires, is not limited to the structural mode shown in the drawing, and also includes a mode of performing parameter optimization and topological optimization by taking the non-winding coil configuration as a target. The linear distribution structure form can be designed by a parameter optimization or topology optimization method. However, the design method is not limited to this method, and other methods aiming at obtaining the parallel connection form of the coils, such as shape optimization and size optimization, can be included; the method avoids the need of adding an additional winding part, thereby effectively improving the space utilization rate and the response time of the magnetic resonance system. The method can reduce the longitudinal size of the gradient coil by at least 50 percent, and the length of the lead and the resistance value are obviously reduced. On the other hand, the invention provides a novel parallel coil configuration, which can effectively reduce the influence of self-inductance and is beneficial to the rapid switching of a magnetic field; and the single input coil can be realized, and the high consistency of coil excitation signals is ensured.
The method aims at the problems that the traditional gradient coil is low in manufacturing precision in a winding manufacturing method and difficult to manufacture in complex shapes, and the manufacturing method combines the modes of numerical control processing, 3D printing, etching and the like, so that the manufacturing precision of the coil is effectively improved, and the manufacturing problem of the coil in the complex shape is solved.
The present invention will be described in detail with reference to the accompanying drawings.
Example one
The non-wound form gradient coil for a magnetic resonance imaging system and the design method thereof of the present invention are explained in a parametric configuration optimization manner.
The method comprises the following steps: parametric modeling: introducing design variables, and establishing a non-winding gradient coil analysis model by using an objective function, wherein the objective function is a physical model of a cylindrical gradient coil as shown in figure 1; wherein
Establishing a Linear form f (r)0θ, z) can be expressed as:
Figure BDA0001191702440000061
wherein (r)0Theta, z) corresponds to the linear coordinate r in a cylindrical coordinate system0Is the radius of the cylindrical design surface, and g (θ) is the characteristic parameter equation of the selected line type (selected in this example)
Figure BDA0001191702440000062
n 2,4,6, the equation for the parameters of this patent is not limited to this form);
according to Biot-Savart law
Figure BDA0001191702440000071
Wherein the content of the first and second substances,
Figure BDA0001191702440000072
is the coordinates of the point of the field,
Figure BDA0001191702440000073
is the source point coordinate, I is the current through the wire, μ0Is the vacuum permeability; the component B of the magnetic field intensity in the Z direction can be obtainedzIs composed of
Figure BDA0001191702440000074
An objective equation can be established according to the requirements:
Figure BDA0001191702440000075
step two: solving the model: introducing a proper optimization algorithm solution model, and calculating the magnetic field intensity;
for the implementation case, the least square method is adopted for solving, but the method is not limited to;
step three: and (5) forward verification of a calculation result, and processing and experimental measurement if the design requirement is met. According to the optimized line type, the manufacturing method can select wiring or plate making and etching modes to manufacture.
As shown in fig. 2b and 2c, the parallel non-wound gradient coils, which are designed in a parametric manner, have a significantly reduced longitudinal length, which is 1.6 times the target area; the longitudinal length of the gradient coil is reduced by more than 50% compared with the traditional winding type gradient coil; the space utilization rate of the magnetic resonance system is effectively improved. On the other hand, parameters such as resistance, inductance and the like are obviously reduced, and the energy consumption and the response time of the coil are reduced.
Example two
The non-wound form gradient coil for a magnetic resonance imaging system and the design method thereof of the present invention are explained in a topology optimization manner.
The method comprises the following steps: as shown in fig. 3a and 3b, continuum topology optimization is employed to optimize the distribution of the conductive material with the physical quantity of the electromagnetic coil (e.g., conductivity σ (ρ)) as a design variable; the design variables may be expressed as:
σ(ρ)＝σAir+ρp(σCu-σAir)
wherein sigmaAirIs the electrical conductivity of air, σCuIs the conductivity of the conductive material used, copper is used in the model, and p is a penalty term; ρ is the design variable:
Figure BDA0001191702440000081
the design variables satisfy the continuity equation:
Figure BDA0001191702440000082
wherein V is an electric potential;
and then according to the Biot-Savart law:
Figure BDA0001191702440000083
can obtain BzExpression (c):
Figure BDA0001191702440000084
wherein Jx,JyThe component of the current density in the x and y directions in the expansion plane;
RC＝rcosθ-ricosθi，RS＝rsinθ-risinθi；
step two: establishing a geometric model in software according to the formula derived in the step one, and solving B by using a semi-analytic or numerical method (FEM, BEM and the like)zSolving the sensitivity by using an adjoint equation method; the solving method is not limited to the method;
step three: performing result post-processing, extracting a calculation result and selecting different processing methods according to the shape of the result; if the coil is not a single connected coil, a layout can be made;
step four: and processing and manufacturing by adopting processing technical modes such as photoetching technology, 3D printing, numerical control processing and the like, and detecting the magnetic field intensity.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.

Claims (1)

1. A design method of a non-winding type gradient coil used for a magnetic resonance imaging system is characterized in that a parameter optimization method is adopted to design the non-winding type gradient coil with the connection mode of parallel connection or serial connection, and the specific steps are as follows:
the method comprises the following steps: parametric modeling: introducing design variables, establishing a non-winding gradient coil analysis model by an objective function, and establishing a linear f (r)0θ, z) is expressed as:
Figure FDA0002274142410000011
wherein (r)0Theta, z) corresponds to the linear coordinate r in a cylindrical coordinate system0Is the radius of the cylinder design surface, g (theta) is the characteristic parameter equation of the selected line type;
according to Biot-Savart law
Figure FDA0002274142410000012
Wherein the content of the first and second substances,is the coordinates of the point of the field,
Figure FDA0002274142410000014
is the source point coordinate, I is the current through the wire, μ0Is the vacuum permeability, L is the wire profile,
Figure FDA0002274142410000015
is the differential of the vector function L of the conductor profile, L being the vector function of the conductor profile L; the component B of the magnetic field intensity in the Z direction can be obtainedzComprises the following steps:
Figure FDA0002274142410000016
an objective equation can be established according to the requirements:
Figure FDA0002274142410000017
wherein, BzobjIs the component of the target magnetic field strength in the Z direction;
step two: solving the model: introducing a proper optimization algorithm solution model, and calculating the magnetic field intensity;
step three: and (5) forward verification of a calculation result, and processing and experimental measurement if the design requirement is met.
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