WO2013166810A1

WO2013166810A1 - Magnetic resonance imaging superconducting magnet system and method and device for acquiring structural parameter thereof

Info

Publication number: WO2013166810A1
Application number: PCT/CN2012/083287
Authority: WO
Inventors: 倪志鹏; 王秋良; 严陆光
Original assignee: 中国科学院电工研究所
Priority date: 2012-05-11
Filing date: 2012-10-22
Publication date: 2013-11-14
Also published as: CN102707250B; CN102707250A

Abstract

A magnetic resonance imaging superconducting magnet system and a method and device for acquiring structural parameters thereof. The method includes: performing continuous grid division on a spatial range where a coil system is to be disposed, regarding each grid obtained by the division as a current circle, and uniformly dividing a DSV surface of a superconducting magnet system and an ellipsoidal surface of a 5 Gauss stray field into a plurality of target points; by means of a linear programming algorithm, calculating the current distribution at the site of each grid, which makes the volume of the coil system minimum, so as to obtain a current distribution pattern; and taking the number and spatial positions of non-zero current values in the current distribution pattern as the number and initial positions of solenoid coils in the coil system respectively, and by means of a nonlinear optimization algorithm, calculating the size and position parameter of each solenoid coil when the coil system volume is minimum, so as to acquire the final structural parameters of the coil system. The method and device can improve the acquisition efficiency of the structural parameters of an MRI superconducting magnet system, and make a coil structure in the MRI superconducting magnet system relatively small.

Description

Magnetic resonance imaging superconducting magnet system and method and device for acquiring structural parameters thereof

The magnetic resonance imaging technology of the present invention especially relates to a magnetic resonance imaging superconducting magnet system and a method and a device for acquiring the structural parameters thereof. Background technique

Magnetic Resonance Imaging (MRI) is a high-tech image based on the magnetic properties of biological magnetic nuclei, such as hydrogen atoms, in magnetic fields. It has no electromagnetic radiation, high image contrast, and can be imaged in any direction. The advantages make it the first in medical imaging equipment.

In 1946, Flelix Bloch of Stanford University and Edward Purcell of Harvard University independently discovered nuclear magnetic resonance. A spin-having nucleus in a constant magnetic field is irradiated with radio frequency radiation, and a resonance absorption phenomenon occurs when the radio frequency is equal to the precession frequency of the atomic nucleus in a constant magnetic field. American Raymond Damadian filed a patent application on March 17, 1972, and obtained US Patent No. 3,788,732 on February 5, 1974, using NMR for medical clinical testing. A magnetic resonance imaging technique was invented. It uses nuclear magnetic resonance to excite the selected human tissue nucleus in a high-energy state. When the high-frequency electromagnetic field is removed, it will generate a radio frequency pulse signal when it returns to the equilibrium state. These signals are detected by the detector and input into the computer for processing. , the reconstructed image is displayed on the screen. His great contribution has laid the foundation for the rapid development of magnetic resonance imaging today.

The core components of the RI system mainly include magnet systems (also known as: superconducting magnet systems), spectrometer systems, computer systems, and image display systems. The magnet system (also known as the MRI superconducting magnet system) is the most important and costly component of an MRI system. The function of the magnet system is to produce a high field strength, high uniformity, and high stability spatial magnetic field distribution in a generally spherical imaging region, so that the hydrogen atoms inside the human body are magnetized in the magnetic field, and the RF is generated by the RF line. The signal causes the hydrogen atom to resonate and attract the RF excitation, so that the energy absorbed by the hydrogen atom is released to be captured by the signal receiving device. Capture, finally through the image processing after the image processing, the resulting image resolution is proportional to the magnetic field strength.

After more than 30 years of development of MRI technology, the design technology of MRI superconducting magnet system has been greatly developed. From the early passive shielding, low magnetic field, poor uniformity and long length of magnet system, it has developed into today's active shielding and magnetic field. High, uniformity and short magnet system length, thanks to the rapid development of superconducting technology and low temperature technology. The development trend of MRI superconducting magnet system development is toward short cavity, high magnetic field and self-shielding.

MRI magnet designers have sought to generate high field strength and high uniformity magnetic field distribution over a large Diameter of Spherical Volume (DSV) through a shorter length magnet system. The peak-to-peak homogeneity (Hpp) is generally characterized by the performance of a high-uniformity magnet system, defined as the difference between the highest and lowest values of the magnetic field strength and the average of the magnetic field strength within the DSV. The ratio, ie: Hpp = (B _max - B _min ) / mean (B) xl0 ⁶ , in parts per million, ppm, where B _max represents the highest value of the magnetic field strength within the DSV, 8 „^ indicates the lowest value of the magnetic field strength in the DSV, mean(B) represents the average value of the magnetic field strength in the DSV, and the smaller the value of the peak-to-peak uniformity of the magnetic field, the better the peak-to-peak uniformity of the magnetic field. For the MRI system, The DSV requires a high uniformity magnetic field distribution with a peak-to-peak uniformity of the magnetic field better than lOppni in an imaging spherical region with a diameter of 40 to 50 cm. In the early MRI system, the magnet system was more than two meters long, and the patient performed magnetic resonance detection. Out of tension and worry, this phenomenon is called claustrophoscopic clinically. In order to reduce the phenomenon of claustrophobia, MRI superconducting magnet system design has been moving toward how to reduce the length of the magnet system without reducing the size and magnetic of the imaging area. In the direction of uniformity, for example, in a 1.5T MRI system in 1989, the magnet system was up to 2.4m in length and weighed 13t. In 2009, the same 1.5T MRI system, the length of the magnet system was reduced to 1.37m, and the weight was 3.2t. However, if the magnet system is too short, it will bring other problems, such as difficulty in achieving uniformity, large electromagnetic stress, and difficult construction due to compact structure. Therefore, the MRI superconducting magnet system is designed. The process of balancing multiple parameters.

The design parameters of the MRI superconducting magnet system mainly include: 1 the spatial size of the line pattern to be arranged; 2 the size, shape, central magnetic field strength and peak-to-peak uniformity of the magnetic field; 3 screens Masking technique and 5 Gaussian stray field range; the highest value of magnetic field strength and current safety margin in 4-line graph. These parameters become the main indicators determining the performance of MRI superconducting magnets. among them:

1 Space size to be laid out: Generally, it is a hollow core solenoid space with a rectangular cross section. The size of the hollow core solenoid space is mainly determined by the inner diameter _mi „, outer diameter and length of the hollow core solenoid. The inner diameter of the space determines the minimum inner diameter of the magnet system, determines the room temperature aperture of the final magnet system and the comfort level during the patient's diagnosis; the outer diameter of the space determines the outer diameter of the magnet system, outside the magnet system. The size of the path determines the overall system cost and floor space; and the length of the space determines the final length of the magnet system, which is the decisive factor in reducing the phenomenon of claustrophobia.

2 Imaging area size, shape, central magnetic field strength and peak-to-peak value of the magnetic field: The imaging area is generally a spherical body with a diameter of 40cm~50cm, which can meet the needs of whole body imaging; the central magnetic field strength determines the resolution of imaging, 1.5T and 3T is the mainstream product in the current market. The peak-to-peak uniformity of the magnetic field is generally better than lOppm to meet the imaging needs.

3 Shielding technology and 5 Gaussian stray field range: Shielding technology is generally divided into passive shielding and active shielding technology. Magnetic shielding is used to shield the influence of the magnetic field generated by MRI on the surrounding environment. For example, the magnetic field coupling of ferromagnetic substances around the magnetization affects the MRI magnetic field uniformity. Degree, influence on surrounding electronic products and interference from the human heart pacemaker. Passive shielding technology is to form a magnetic field loop around the MR1 through a ferromagnetic material, and to control the magnetic field outside the ferromagnetic material within a certain range. This technology makes the MRI large-area, inconvenient to install and susceptible to environmental factors such as temperature. Disadvantages, but the structure of the magnet is relatively simple and the cost of the magnet is greatly reduced. Many early products shield the magnetic field in this way. With the continuous development of magnet design technology, one or more pairs of reverse current coils can be added to the outer layer of the magnet system by active shielding technology to shield the stray field. This design makes the magnet system footprint greatly reduced. However, the turns structure is more complicated than the passive shield magnet system. At present, most of the commercial products on the market adopt active shielding technology. Stray fields generally require a magnetic field strength of less than 5 Gauss in an ellipsoid.

The highest value of the magnetic field strength and the current safety margin in the 4-wire :: When the coil is energized, a magnetic field distribution is generated in the space, and the energized coil generates an electromagnetic force in the magnetic field. The larger the magnetic field is the electromagnetic force received by the coil. The greater the force, the greater the electromagnetic force will weaken the superconducting wire Performance, even destroying superconducting magnets. Therefore, in order to avoid excessive electromagnetic force on the coil, the maximum value of the magnetic field strength in the coil is usually limited to less than 8T. The working point of the coil, including the running current (lop) of the coil and the highest value of the magnetic field strength (B _max ) in the coil, combined with the critical characteristics of the selected superconducting wire, calculates the critical point corresponding to the working point (Ic, Bc), calculate the current safety margin of the magnet system by the ratio of the operating current (lop) at the operating point to the operating current (Ic) at the critical point. Normally, the current safety margin should be set to less than 80%.

The difficulty in designing an MRI superconducting magnet system is to design a magnetic field distribution that produces a high magnetic field and high uniformity in a small space. The design parameters of the MRI superconducting magnet system are contradictory to each other. The shorter the length of the magnet, the more difficult it is to achieve the image area and the more complex the magnet structure. Therefore, for the magnet system designer to balance the advantages and disadvantages, select the appropriate design parameters, and design the MRI superconducting magnet system to meet the requirements. The design of the magnet system is essentially a solution to the electromagnetic field problem. The solution of the electromagnetic field problem can be divided into two categories, one is the positive problem of the electromagnetic field, that is: the electromagnetic field distribution of the space is calculated according to the current source distribution in the space; the other is the inverse problem of the electromagnetic field, ie: according to the space The required electromagnetic field distribution is used to solve the current source position of the space.

In the early days, magnet system designers used the method of solving the positive problem of electromagnetic field, and through the distribution characteristics of the magnetic field generated by the solenoid coil, patching multiple turns in space to improve the uniformity of the magnetic field generated by the magnet system, the workload is large. It is difficult to meet the requirements. With the rapid improvement of the computing power of computer technology, designers continue to solve the electromagnetic field inverse problem through a variety of numerical optimization algorithms, such as Monte Carlo, simulated annealing algorithm, genetic algorithm, etc. The numerical optimization algorithm can be divided into global Optimization algorithm and local optimization algorithm. The global optimization algorithm can solve the global optimal solution in the whole space, but due to the slow calculation speed, it is difficult for the magnet designer to modify the program effectively and effectively, so that the magnet design efficiency is low. The local optimization algorithm can optimize the parameters of the coil according to the initial values of the parameters. However, the selection of the initial values determines whether the global optimal solution can be solved. For many years, magnet system designers have been trying to solve a reasonable initial value and combine a local optimization algorithm to design a more reasonable magnet system, so that the entire design process of the magnet system has higher computational efficiency and can achieve a global optimal solution.

In 2001, Dr. Huawei Zhao proposed a multilayer current density design method for designing a compact MI magnet system. He proposed dividing the space in the line to be divided into multiple layers. Structure, each source layer is divided into several source points, each source point represents an ideal current ring, and the current distribution curve at all source point positions satisfying the requirements of the magnet system is solved by the regularization numerical method, and the current distribution is obtained. The peak position of the curve is used as the initial position of the spiral pipeline, and combined with the nonlinear optimization algorithm, the magnet system that meets the system design requirements is finally solved. The design method can obtain the initial value of the position of the coil by a layered method, and then design a magnetic system that meets the requirements by a local optimization algorithm. However, the design of the multilayer current density has at least the following problems: The stratified position selection has blindness, making it difficult to ensure that the line graph structure is a global optimal solution; a magnet system design scheme needs to run for 4 to 10 hours, and the design efficiency is relatively high. low.

In 2009, Dr. Quang M. Tien proposed a global optimal design method based on the minimum energy storage of magnet systems. First, in the space where the space is to be arranged, each grid represents a spiral line 圏, and the current distribution map in all the grids is calculated under the condition that the magnet system requirements are met and the magnet system has the minimum energy storage; also in the current distribution At the peak position, the initial position of the solenoid coil is reasonably arranged, and the sequence quadratic programming algorithm is combined to solve the magnet system that meets the requirements. The design method is that the global optimum initial value is obtained in the entire layout space, and the coil structure is more reasonable. However, the global optimal design method based on the minimum energy storage of the magnet system has at least the following problems: In the current distribution map calculated by the minimum energy storage method, the grid current is a continuously changing curved surface, and it is difficult to define each spiral pipeline. In the initial position, it is difficult to achieve an optimal design. Summary of the invention

One of the technical problems to be solved by the embodiments of the present invention is to provide a magnetic resonance imaging superconducting magnet system and a method and device for acquiring the structural parameters thereof, so as to improve the acquisition efficiency of the structural parameters of the MRI superconducting magnet system, and The coil structure in the MRI superconducting magnet system manufactured by the structural parameters is small, so that the MRI superconducting magnet system manufactured based on the structural parameters has higher performance.

In order to solve the above technical problem, a method for acquiring structural parameters of a magnetic resonance imaging superconducting magnet system according to an embodiment of the present invention includes:

Continuously meshing the spatial extent of the system to be arranged, each grid obtained by the division is regarded as a current ring, and the current value of each current ring includes a positive value, a negative value or zero; And uniformly dividing the surface of the spherical imaging region of the superconducting magnet system and the surface of the ellipsoid of the 5 Gaussian stray field into a plurality of target points according to a preset standard;

The magnetic field + value uniformity at each target point on the surface of the spherical imaging region is not greater than the first predetermined magnetic field peak-to-peak uniformity, and the limiting condition of the magnetic field strength value at each target point on the surface of the ellipsoid of the 5 Gaussian stray field is a constrained component, calculating a current distribution at each of the meshes that minimizes the volume of the coil system under a given operating current density condition by a linear programming algorithm, and obtaining a current distribution map; the first predetermined magnetic field value uniformity is greater than or Equal to the second preset magnetic field value uniformity in the design requirements of the superconducting magnet system;

The number and spatial position of the non-zero current values in the current distribution diagram are respectively taken as the number and initial position of the spiral pipeline diagram in the coil system;

The second preset magnetic field peak-to-peak uniformity limit condition in the design requirements of the superconducting magnet system, and the magnetic field strength value at each target point on the surface of the ellipsoid of the 5 Gaussian stray field limit the maximum magnetic field strength value in the coil system The limiting condition and the current safety margin limit of the operation of the coil system are the second constraint condition. The nonlinear optimization algorithm is used to calculate the size and position parameters of each solenoid coil when the volume of the coil system is the smallest, and the final structural parameters of the coil system are obtained. Wherein, the size and positional parameters of each solenoid coil include an inner radius, an outer radius, and an axial position of each end of each spiral line.

According to an embodiment, the spatial extent of the coil system to be arranged is specifically a solenoid-shaped region having a rectangular cross-section, the extent of the region being determined by parameters of a rectangular cross-section, the parameters of the rectangular cross-section including the inner diameter of the rectangular cross-section , outer diameter and length;

Continuous meshing of the spatial extent of the coil system to be arranged includes: successively meshing the radial cross sections in the radial and axial directions, respectively.

According to an embodiment, the continuous meshing of the rectangular cross section in the radial direction and the axial direction respectively comprises: performing a two-dimensional continuous mesh division on the rectangular cross section in the radial direction and the axial direction, respectively The radial and axial directions are divided into several equal parts to form a two-dimensional continuous space grid.

According to one embodiment, the current profile gives the magnitude and direction of the current at each grid, and non-zero current values at the grid are brought together to form a clear boundary non-zero current cluster.

According to an embodiment, according to the distribution of non-zero current clusters in the spatial range, respectively A forward current spiral pipeline map is placed at each positive position of the non-zero current cluster, and a reverse current spiral pipeline map is respectively placed at each negative position of the non-zero current cluster.

According to one embodiment, the limiting conditions of the magnetic field strength values at the respective target points on the surface of the ellipsoid of the 5 Gaussian stray field include: 5 The magnetic field strength value at each target point on the surface of the ellipsoid of the Gaussian stray field is not more than 5 Gauss.

According to an embodiment, the second constraint comprises:

The peak-to-peak uniformity of the magnetic field of the axial magnetic field at each target point on the surface of the spherical imaging region is not greater than the peak-to-peak uniformity of the second predetermined magnetic field;

5 The superimposed magnetic field strength of the axial magnetic field and the radial magnetic field at each target point on the surface of the ellipsoid of the Gaussian stray field is not greater than the preset magnetic field strength;

The current safety margin of the coil system operation is not greater than a preset current safety margin calculated from a highest magnetic field strength value in the coil system and a critical characteristic of the superconducting wire selected by the coil system;

The spacing between adjacent solenoid coils in the turns system is greater than the preset spacing;

The size and positional parameters of each of the solenoid lines 使 cause the line drawing system to be within the spatial extent of the line system to be placed.

According to one embodiment, the superimposed magnetic field strength of the axial magnetic field and the radial magnetic field at each target point on the surface of the ellipsoid of the 5 Gaussian stray field is not greater than the preset magnetic field strength including:

5 The superimposed magnetic field strength of the axial magnetic field and the radial magnetic field at each target point on the surface of the ellipsoid of the Gaussian stray field is not more than 5 Gauss.

According to an embodiment, the method further includes:

The current safety margin of the coil system operation is obtained by the maximum magnetic field strength value in the preset coil system and the critical characteristics of the superconducting wire selected by the coil system.

An apparatus for acquiring structural parameters of a magnetic resonance imaging superconducting magnet system according to an embodiment of the present invention includes:

a receiving unit, configured to receive spatial range information of the coil system to be arranged, a first predetermined magnetic field peak-to-peak uniformity, a limit condition of a magnetic field strength value at each target point on an ellipsoid surface of a 5 Gaussian stray field, and a running current density condition , the second preset magnetic field peak-to-peak uniformity limit condition in the design requirements of the superconducting magnet system, and the target points on the surface of the ellipsoid of the 5 Gaussian stray field The magnetic field strength value limitation condition at the position, the highest magnetic field strength value limit in the coil system, and the current safety margin limit condition of the operation of the coil system; the first predetermined magnetic field peak-to-peak uniformity is greater than or equal to the first Two preset magnetic field peak-to-peak uniformity;

a dividing unit, configured to perform continuous meshing on a spatial range of the line graph system to be arranged, each divided grid is regarded as a current ring, and the current value of each current ring includes a positive value, a negative value or zero; And uniformly dividing the surface of the spherical imaging region of the superconducting magnet system and the surface of the ellipsoid of the 5 Gaussian stray field into a plurality of target points according to a preset standard;

a first calculating unit, configured to: the magnetic field peak-to-peak uniformity at each target point on the surface of the spherical imaging region is not greater than the first predetermined magnetic field peak-to-peak uniformity, and the magnetic field at each target point on the surface of the ellipsoid of the 5 Gaussian stray field The limiting condition of the intensity value is a first constraint component, and a current distribution map is obtained by a linear programming algorithm for calculating a current distribution at each grid at a given operating current density condition to minimize the volume of the coil system;

a second calculating unit, configured to respectively use the number and spatial position of the non-zero current values in the current distribution map as the number and initial position of the solenoid line 圏 in the coil system; and the second predetermined magnetic field peak-to-peak uniformity Restricted condition, magnetic field strength value limit at each target point on the surface of the ellipsoid of the 5 Gaussian stray field, maximum magnetic field strength value limit condition in the coil system, current safety margin limit of the operation of the coil system is the second constraint In the piece, the size and position parameters of each solenoid coil are calculated by a nonlinear optimization algorithm to obtain the final structural parameters of the coil system; wherein the size and position parameters of each spiral line include each spiral The inner radius, outer radius, and axial position of the two ends of the line.

According to an embodiment, the spatial extent of the coil system to be arranged is specifically a solenoid-shaped region having a rectangular cross section, the range of the region being determined by parameters of a rectangular cross section, and the parameters of the rectangular cross section include a rectangular cross section. Inner diameter, outer diameter and length;

When the dividing unit performs continuous meshing on the spatial extent of the coil system to be arranged, specifically, the rectangular cross section is divided into two dimensions in the radial direction and the axial direction, respectively, and the rectangular cross section is along the radial direction. The axial directions are divided into several equal parts to form a two-dimensional continuous space grid.

According to an embodiment, the current distribution diagram gives the magnitude and direction of the current at each grid, and the non-zero current values at the grid are gathered together to form a clear-cut non-zero current cluster; Each positive position of the non-zero current cluster is used to arrange a forward current solenoid line 分别, and each negative value position is used to arrange a reverse current solenoid line 分别, respectively.

According to an embodiment, the second constraint comprises:

The peak-to-peak uniformity of the magnetic field of the axial magnetic field at each target point on the surface of the spherical imaging region is not greater than the uniformity of the second predetermined magnetic field value;

The current safety margin of the coil system operation is not greater than a preset current safety margin calculated from the highest magnetic field strength value in the line surrounding system and the critical characteristic of the superconducting wire selected by the coil system. ;

The spacing between adjacent spiral conduits in the coil system is greater than a predetermined spacing;

The size and positional parameters of each solenoid line 使 cause the coil system to be within the spatial extent of the coil system to be placed.

According to an embodiment, the limitation of the magnetic field strength value at each target point on the surface of the ellipsoid of the 5 Gaussian stray field comprises: 5 The magnetic field strength value at each target point on the surface of the ellipsoid of the Gaussian stray field is not more than 5 Gauss;

5 The superimposed magnetic field strength of the axial magnetic field and the radial magnetic field at each target point on the surface of the ellipsoid of the Gaussian stray field is not greater than the preset magnetic field strength including: 5 The axial magnetic field at each target point on the surface of the ellipsoid of the Gaussian stray field The superimposed magnetic field strength with the radial magnetic field is not more than 5 Gauss.

According to an embodiment, the second calculating unit is further configured to obtain a current safety margin of the coil system operation according to a highest magnetic field strength value in the preset coil system and a critical characteristic of the superconducting wire selected by the coil system.

A magnetic resonance imaging superconducting magnet system provided by an embodiment of the present invention is obtained by acquiring a structural parameter of the magnetic resonance system.

The method and device for acquiring structural parameters of the MRI superconducting magnet system according to the embodiment of the present invention, wherein the peak-to-peak uniformity of the magnetic field at each target point on the surface of the DSV is not greater than the first predetermined magnetic field peak-to-peak uniformity, and the ellipsoid of the 5 Gaussian stray field The constraint condition of the magnetic field strength value at each target point on the surface is the first constraint condition, and the condition of the given operating current density is calculated by the linear programming algorithm. The current distribution at each grid that minimizes the volume of the coil system is obtained, and the current distribution map is obtained, and then the number and spatial position of the non-zero current values in the current distribution map are respectively taken as the number of spiral pipeline turns in the coil system. The initial position is the second constraint condition in the design requirements of the superconducting magnet system. The nonlinear structure optimization parameter is used to calculate the size and position parameters of each spiral pipeline diagram when the volume of the coil system is the smallest, and the final structural parameters of the coil system are obtained.

Because the hybrid design method combining the linear programming algorithm and the nonlinear optimization algorithm is adopted in the embodiment of the present invention, the number and initial position of the spiral pipeline 线圈 in the coil system are obtained by the linear programming algorithm with higher efficiency, and the nonlinear optimization algorithm is combined. Obtaining the final structural parameters of the coil system, such as the number of coils included in the coil system, the position and size parameters of each spiral line, thereby improving the acquisition efficiency of the structural parameters of the MRI superconducting magnet system; The MRI superconducting magnet system with the structural parameters obtained in the above embodiment has a smaller wire loop structure, requires the least amount of superconducting wire, has the advantages of simple and compact wire loop structure, low cost, and is easy to construct and install, thereby making it based on The MRI superconducting magnet system manufactured by the structural parameters has high performance, and overcomes the problem that the existing MRI superconducting magnet system is inefficient in electromagnetic design and difficult to realize optimal design. In addition, the current safety margin limit provides a robust guarantee for the stable operation of the entire MRI superconducting magnet system.

Further features of the present invention and its advantages will become apparent from the Detailed Description of the Drawing. DRAWINGS

The drawings which form a part of the specification are intended to illustrate the embodiments of the invention

The invention can be more clearly understood from the following detailed description, in which:

1 is a schematic flow chart of a method for obtaining structural parameters of an MRI superconducting magnet system according to an embodiment of the present invention;

2 is a schematic flow chart of a method for acquiring structural parameters of an MRI superconducting magnet system according to another embodiment of the present invention;

3 is a structural parameter of an MRI superconducting magnet system according to an application embodiment of the present invention. Schematic flow chart of the acquisition method;

4 is a schematic diagram of a spatial extent, a DSV region, and a 5 Gaussian stray field region in which the turns are arranged in the application embodiment shown in FIG. 3;

FIG. 5 is a current distribution diagram obtained by a linear programming algorithm in the application embodiment shown in FIG. 3;

6 is a magnetic field «value uniformity distribution diagram of an axial magnetic field at a target point on the surface of the DSV obtained in the application example shown in FIG. 3;

7 is a magnetic field intensity distribution map at each target point on the surface of an ellipsoid of a 5 Gaussian stray field obtained in the application example shown in FIG. 3;

8 is a schematic diagram of initial position and size parameters of a non-zero current cluster discrete into a spiral line 圏 in the application embodiment shown in FIG. 3;

9 is a schematic diagram of final structural parameters of a line 圏 system optimized by a nonlinear optimization algorithm in the application embodiment shown in FIG. 3;

10 is a magnetic field uniformity distribution diagram of a DSV surface optimized by a nonlinear optimization algorithm in the application embodiment shown in FIG. 3;

11 is a magnetic field intensity distribution diagram at each target point on the surface of an ellipsoid of a 5 Gaussian stray field obtained by a nonlinear optimization algorithm in the application embodiment shown in FIG. 3;

Figure 12 is a current safety margin diagram of the MRI superconducting magnet system in the application embodiment shown in Figure 3;

Figure 13 is a diagram showing the distribution of magnetic field strength generated by the coil system in space in the application embodiment shown in Figure 3;

Figure 14 is a magnetic field intensity distribution diagram of a solenoid enthalpy in one end of the inner layer in the coil system of the application embodiment shown in Figure 3;

Figure 15 is a schematic block diagram of an apparatus for acquiring structural parameters of an MRI superconducting magnet system according to an embodiment of the present invention. detailed description

Various exemplary embodiments of the present invention will now be described in detail with reference to the drawings. It should be noted that the relative components and steps set forth in these embodiments are unless otherwise specifically stated. The arrangement, numerical expressions and numerical values do not limit the scope of the invention.

In the meantime, it should be understood that the dimensions of the various parts shown in the drawings are not drawn in the actual scale relationship for the convenience of the description.

The following description of the at least one exemplary embodiment is merely illustrative and is in no way

Techniques, methods and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the techniques, methods and apparatus should be considered as part of the specification.

In all of the examples shown and discussed herein, any specific values are to be construed as illustrative only and not as a limitation. Thus, other examples of the exemplary embodiments may have different values.

It should be noted that similar reference numerals and letters indicate similar items in the following figures, and therefore, once an item is defined in a drawing, it is not necessary to further discuss it in the subsequent drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic flow chart showing a method of obtaining structural parameters of an MRI superconducting magnet system according to an embodiment of the present invention. As shown in FIG. 1, the method for obtaining the structural parameters of the MRI superconducting magnet system of this embodiment includes:

101. Perform continuous meshing on the spatial extent of the system to be arranged, and each divided grid is regarded as a current ring, and the current value of each current ring may be positive, negative or zero; The preset standard evenly divides the DSV surface of the superconducting magnet system and the ellipsoidal surface of the 5 Gaussian stray field into several target points.

Among them, the space range in which the coil system is to be arranged is preset according to the production requirements of the MRI superconducting magnet system.

102, wherein the uniformity of the magnetic field intensity at each target point on the surface of the DSV is not greater than the first predetermined magnetic field peak-to-peak uniformity, and the magnetic field strength value at each target point on the surface of the ellipsoid of the 5 Gaussian stray field is The first constraint condition is obtained by calculating a current distribution at each grid at a given operating current density to minimize the volume of the coil system by a linear programming algorithm.

Wherein, the first predetermined magnetic field peak-to-peak degree is greater than or equal to the design of the superconducting magnet system Finding the second preset magnetic field value uniformity.

Illustratively, the limitation of the magnetic field strength value at each target point on the surface of the ellipsoid of the 5 Gaussian stray field may include: 5 The magnetic field intensity value at each target point on the surface of the ellipsoid of the Gaussian stray field is not more than 5 Gauss.

103, respectively, the number and spatial position of the non-zero current values in the current distribution diagram, as the number and initial position of the solenoid line 圏 in the coil system, and the second preset magnetic field peak in the design requirements of the superconducting magnet system Peak uniformity limit condition, magnetic field strength value limit at each target point on the surface of the ellipsoid of the 5 Gaussian stray field, maximum magnetic field strength value limit in the coil system, current safety margin limit for the operation of the coil system For the second constraint element, the nonlinear structure optimization parameter is used to calculate the size and position parameters of each spiral line 圏 when the volume of the coil system is the smallest, and the final structural parameters of the coil system are obtained.

Wherein, the size and position parameters of each spiral line include the inner radius, the outer radius of each solenoid coil, and the axial position of the two ends.

In the embodiment of the present invention, a hybrid design method combining a linear programming algorithm and a nonlinear optimization algorithm is adopted, and the number and initial position of the spiral pipelines in the coil system are obtained by a linear programming algorithm with high efficiency, and then combined with a nonlinear optimization algorithm. Obtaining the final structural parameters of the coil system, such as the number of turns included in the coil system, the position and size parameters of each spiral line, thereby improving the acquisition efficiency of the structural parameters of the MRI superconducting magnet system, based on the implementation of the present invention In one application of the example, the acquisition of the entire structural parameter takes only about 20 minutes; and the coil structure of the MRI superconducting magnet system using the structural parameters obtained by the above embodiment of the present invention is small, and the required amount of superconducting wire is minimum. The utility model has the advantages of simple compactness and low cost, and is easy to construct and install, so that the MRI superconducting magnet system manufactured based on the structural parameter has high performance and overcomes the existing MRI superconducting magnet system in electromagnetic field. Designed to be less efficient and difficult to achieve optimal design issues. In addition, the current safety margin limits provide a robust guarantee for the stable operation of the entire MRI superconducting magnet system.

According to a specific example of the method for obtaining the structural parameters of the MRI superconducting magnet system according to the present invention, the second constraint may specifically include:

The peak-to-peak uniformity of the magnetic field of the axial magnetic field at each target point on the surface of the spherical imaging region is not greater than the peak-to-peak uniformity of the second predetermined magnetic field; 5 The superimposed magnetic field strength of the axial magnetic field and the radial magnetic field at each target point on the surface of the ellipsoid of the Gaussian stray field is not greater than the preset magnetic field strength, for example, the axial direction at each target point on the surface of the ellipsoid of the 5 Gaussian stray field The superimposed magnetic field strength of the magnetic field and the radial magnetic field is not more than 5 Gauss; the current safety margin of the coil system operation is not greater than the preset current safety margin, and the preset current safety margin is the highest magnetic field strength value and coil in the coil system The critical characteristics of the superconducting wire selected by the system are calculated;

The size and positional parameters of each solenoid line 使 place the coil system within the space within which the coil system is to be placed.

Illustratively, the spatial extent of the wire loop system to be disposed in the embodiment of the present invention may specifically be a solenoid-shaped region having a rectangular cross section, the range of the region being determined by parameters of the rectangular cross section, wherein the parameters of the rectangular cross section include The inner diameter, outer diameter, and length of the rectangular section. Correspondingly, according to a specific example of the method for acquiring the structural parameters of the MRI superconducting magnet system according to the present invention, and not limiting, in the embodiment shown in FIG. 1, the continuous meshing of the spatial extent of the system to be arranged may be : Continuous meshing of the rectangular section in the radial direction and the axial direction respectively. For example, continuous meshing of the rectangular section in the radial direction and the axial direction respectively includes: two-dimensional continuous radial and axial directions respectively for the rectangular section Meshing divides the rectangular section into several equal parts along the radial and axial directions to form a two-dimensional continuous space grid. Thus, by the method for obtaining the structural parameters of the MRI superconducting magnet system of the embodiment of the present invention, the coil structure in the MRI superconducting magnet system can be obtained in the region of the solenoid shape having a rectangular cross section, and the performance is relatively small. The spatial position of the high enthalpy system, wherein the line drawing system includes an inner layer 圏 and an outer shield 圏.

According to a specific example of the embodiment of the method for acquiring structural parameters of the MRI superconducting magnet system according to the present invention, the current distribution diagram gives the magnitude and direction of the current at each grid, and the current values at the grid are not zero. Together form a clear, non-zero current cluster.

Specifically, according to the distribution of the non-zero current clusters in the spatial range, a forward current spiral line 圏 is respectively arranged at each positive value position of the non-zero current cluster, and a reverse current spiral line 圏 is respectively arranged on the Each negative position of a non-zero current cluster.

Another embodiment of a method for acquiring structural parameters of an MRI superconducting magnet system of the present invention The preset current safety margin can be calculated according to the highest magnetic field strength value in the preset coil system and the critical characteristic of the superconducting wire selected by the coil system.

In another embodiment of the method for acquiring structural parameters of the MRI superconducting magnet system of the present invention, the spatial range of the coil system to be arranged is preset according to the manufacturing requirements of the MRI superconducting magnet system, and the spatial range is specifically a rectangular cross section. The area of the solenoid shape, the range of which is determined by the parameters of the rectangular section, wherein the parameters of the rectangular section include the inner diameter, the outer diameter and the length of the rectangular section. 2 is a schematic flow chart of a method for acquiring structural parameters of an MRI superconducting magnet system according to another embodiment of the present invention. As shown in FIG. 2, the method for acquiring structural parameters of the MRI superconducting magnet system of the embodiment includes:

201. Perform a two-dimensional continuous mesh division on the rectangular section of the coil system to be arranged in the radial direction and the axial direction respectively, and divide the rectangular section into a plurality of equal parts along the radial direction and the axial direction to form a two-dimensional continuous space grid. Each grid is regarded as a current ring, and the current value of each current ring can be positive, negative or zero; and the DSV surface of the superconducting magnet system and the ellipsoid of the 5 Gaussian stray field according to preset criteria The surface is evenly divided into several target points.

202. The current value of the current ring at each mesh obtained by dividing the rectangular section is used as a variable to be optimized, so that the peak-to-peak uniformity of the magnetic field at each target point on the DSV surface is not greater than the first predetermined magnetic field peak-to-peak uniformity, 5 The height of the magnetic field at each target point on the surface of the ellipsoid of the Gaussian stray field is not more than 5 Gauss is the first constraint. The linear programming algorithm is used to calculate the meshes that minimize the volume of the coil system under the given operating current density. At the current distribution, a current distribution diagram is obtained. The current distribution diagram shows the magnitude and direction of the current at each grid. The current value at most of the grid is zero, and only a few current values are not zero, not Zero current values are grouped together to form a clear, non-zero current cluster. The first predetermined magnetic field peak-to-peak uniformity is greater than or equal to the second predetermined magnetic field value uniformity in the superconducting magnet system design requirements.

According to the distribution of non-zero current clusters in the spatial range, a forward current spiral line 圏 is respectively arranged at each positive value position of the non-zero current cluster, and a reverse current solenoid coil is respectively arranged in the non-zero current coil. Each negative position of the zero current cluster, the arrangement of the spiral line 符合 conforms to the requirement that the actual magnet system consists of a plurality of separate spiral line diagrams of the same current magnitude; and, by the position and total current of the non-zero current cluster The size can be used to construct the initial position and size parameters of each spiral line. Initial position and size parameters of the solenoid line As the initial value of the spiral pipeline 圏 structural parameters in the subsequent nonlinear optimization algorithm, it compensates for the blindness of the local optimization algorithm in the initial value selection of the solenoid coil structure parameters.

203. Obtain a current safety margin of the operation of the coil system according to the highest magnetic field strength value in the preset coil system and the critical characteristic of the superconducting wire selected by the coil system.

204, the number and the spatial position of the non-zero current values in the current distribution diagram respectively, as the number and initial position of the solenoid coils in the coil system, and the following conditions in the design requirements of the superconducting magnet system as the second constraint Condition, through the nonlinear optimization algorithm to calculate the size and position parameters of each spiral pipeline diagram when the volume of the coil system is the smallest ( r _inner (i), r. _uter (i), _Z|ef , (i), _Zright (i) , i=l, 2,...,N) , including the inner radius, the outer radius of each spiral line, and the axial position of the two ends, to obtain the final structural parameters of the line graph system: spherical imaging area surface The peak-to-peak uniformity of the magnetic field of the axial magnetic field at each of the target points is not greater than the uniformity of the second predetermined magnetic field value;

5 The superimposed magnetic field strength of the axial magnetic field and the radial magnetic field at each target point on the surface of the ellipsoid of the Gaussian stray field is not more than 5 Gauss;

The current safety margin of the coil system operation is not greater than the preset current safety margin to ensure the safety of the MRI superconducting magnet system;

The spacing between adjacent solenoid coils in the coil system is greater than the preset spacing, and the axial dimension of each solenoid coil may be constrained so that the spacing of adjacent spiral pipelines is greater than a preset spacing, thereby avoiding Each of the solenoid coils overlap each other to facilitate the construction of the solenoid line ;;

Where N is the number of solenoids included in the coil system, ie: the number of solenoid coils required for the MRI superconducting magnet system, r _inner is the ith spiral line of the N solenoid coils The inner radius of 圏, r. For the outer radius of the i-th spiral line, z _lert is the axial position of one end of the i-th solenoid coil; z _right is the axial position of the other end of the i-th solenoid line.

Through the above operation 204, the optimal line graph system structure can be obtained, and the coil system is now The smallest volume.

The embodiment shown in FIG. 2 of the present invention greatly improves the acquisition efficiency of the structural parameters of the MRI superconducting magnet system. According to an application of the embodiment shown in FIG. 2, the acquisition of the entire structural parameter takes only about 20 minutes, wherein operation 201 - 202 takes about 5 minutes, and operation 203 - 203 takes about 15 minutes. The MRI superconducting magnet system using the structural parameters obtained by the embodiment shown in Fig. 2 above requires the least amount of superconducting wire, which reduces the i-price of the entire MRI superconducting magnet system; meanwhile, the wire loop system has a simple structure and is easy to construct. And installation, the limitation of current safety margin provides an effective guarantee for the stable operation of the entire MRI superconducting magnet system.

The specific application of the method for obtaining the structural parameters of the short cavity and self-shielding MRI superconducting magnet system is taken as an example to further illustrate the embodiment of the method for obtaining the structural parameters of the MRI superconducting magnet system of the present invention.

As shown in FIG. 3, it is a schematic flow chart of a method for acquiring structural parameters of an MRI superconducting magnet system according to an application embodiment of the present invention. In this application example, the MRI superconducting magnet system is required to generate a magnetic field distribution with a central magnetic field strength of 1.5T in a DSV having a diameter of 50 cm, and the peak-to-peak uniformity of the magnetic field needs to be better than 10 ppm; 5 Gaussian stray field is constrained to an ellipsoid In the region, the long semi-axis length of the ellipsoid is 5m, and the short semi-axis is 4m; the inner radius of the coil system is not less than 0,40m, the outer radius is not more than 0.80m, and the length is shorter than 1.15m, namely: the coil system The minimum inner radius is 0.40m, the maximum outer radius of the coil system is 0.80m, and the maximum length of the coil system is 1.15m; the highest magnetic field strength in the coil system is less than 8T, and the current safety margin needs to be less than 80%.

First, in operation 301, the spatial extent of the coil system to be arranged is set according to the production requirements of the MRI superconducting magnet system.

Specifically, from the minimum inner radius, the maximum outer radius, and the maximum length of the coil system, the spatial range in which the coil system is to be arranged is determined to be: 0.40 m <= r < = 0.80 m, - 1.15 / 2 = 0.575 m <= z < =1.15/2=0.575m, ie: -0.575m<=z<=0.575m, where r is the radial position range of the spatial extent in which the coil system is to be arranged, and z is the axis of the spatial extent in which the coil system is to be arranged To the position range, the space range is a solenoid-shaped area having a rectangular cross section.

In operation 302, for the solenoid-shaped region of the rectangular section where the coil system is to be arranged, Do not perform two-dimensional continuous meshing in the axial and radial directions, and uniformly divide the DSV surface of the superconducting magnet system and the ellipsoidal surface of the 5 Gaussian stray field into several target points according to preset criteria. There are no restrictions on the execution order of several operations included in the 302. Several operations can be performed simultaneously, or any one or several of them can be executed first.

The two-dimensional continuous mesh division of the rectangular cross-section of the coil system to be arranged is respectively performed in the axial direction and the radial direction, and the rectangular cross-section is respectively divided into 80 and 40 in the axial direction and the radial direction. A total of 80*40=3200 grids are formed to form a two-dimensional continuous space grid. Each grid is regarded as an ideal current ring, and the current value of each current ring can be positive, negative or zero. .

Since the superconducting magnet system is an axisymmetric structure, in the present application embodiment, only the 1/4 boundary line of the surface of the ellipsoid of the DSV surface and the 5 Gaussian stray field is evenly divided into 50 equal parts, and 51 target points are obtained. As shown in FIG. 4, it is a schematic diagram of a spatial range, a DSV surface area, and a 5 Gaussian stray field area in which the turns are to be arranged in the application embodiment of the present invention. In Fig. 4, the upper part is a schematic diagram of a two-dimensional continuous space grid; the lower part is a schematic diagram of a coil system of a spiral line arranged in a subsequent operation, and the outermost rectangle represents a section of the coil system, each of which is small The rectangle represents the cross section of a spiral line. The outer ellipse represents the cross section of the ellipsoidal surface of the 5 Gaussian stray field, and the inner circle represents the section of the DSV surface. Gap represents the spacing between adjacent solenoid coils, specifically the inter-turn spacing.

In operation 303, the current value of the current ring at each grid obtained by dividing the rectangular section is used as a variable to be optimized, and the current distribution of each grid at the smallest volume of the line graph system is calculated by a linear programming algorithm to obtain a current distribution map. .

Calculate the magnetic field contribution matrix A _zd generated by loading each unit current at each target point on the DSV surface with each ideal current ring, and calculate the axial magnetic field at each target point on the surface of the ellipsoid of the 5 Gaussian stray field. The matrix of the contribution matrix A _zs and the radial magnetic field contribution matrix A _rs , the magnetic field contribution matrix A _zd , the magnetic field contribution matrix A _zs and the magnetic field contribution matrix ^ are both 51x3200; the variable to be optimized is the current value I at all the grids,

.

Assuming that the current densities are the same at all grids, the ideal current loop can be represented by a spiral line 具有 with a certain cross section, establishing a mathematical model of the linear programming algorithm, since the mesh with the smallest volume of the coil system is obtained. Current distribution at all grids The total volume of 圏 is used as the objective function, and the minimum value of the objective function takes the smallest volume of the line 圏 system. Based on the design requirements of the MRI superconducting magnet system according to the embodiment of the present application, the minimum value of the peak-to-peak uniformity of the axial magnetic field at each target point on the DSV surface is set to each target point on the surface of the ellipsoid of 20 ppm, 5 Gaussian stray field. The maximum values of the axial magnetic field and the radial magnetic field strength are set to 5 Gauss; assuming that the cross-sectional area of the superconducting wire used in the spiral line is 4.5312 _m ² , the critical current of the superconducting wire at 9 T background magnetic field strength is 950 A, Set the operating current density of the solenoid line 为 to 148ΜΑ/η

To arrange the spiral line 圏 at the i-th grid in the space, the radial position of the i-th grid is _ri , and the cross-sectional area of the spiral line 代表 represented by the ί grid is Ai, Then the volume ^ at the i-th grid is 2π ><Α·, assuming the same operating current density, the total volume of the coil system is:

. 40x80

Therefore, the mathematical model for building a linear programming algorithm is as follows: The objective function is:

Max« x/)— min( x/) / B ₀ < 20 ppm

A _rs x I≤ 5Gauss

The first constraint includes: A... xl ≤ 5 Gauss

1.48 x10 ^s ί_ _{Α In the} above first constraint, max(A _zd xI) represents the maximum value of the magnetic field strength of the target point on the DSV surface, and min(A _zd xI) represents the minimum value of the magnetic field strength of the target point on the DSV surface. B. The value of the center magnetic field strength is 1.5T; J is the operating current density of the spiral line ;; A _mesh is the area occupied by each grid. In the above first constraint, [max( — _rf x/)- min(4 _rf x )]/ ) ≤ 20/y7w represents that the peak-to-peak uniformity of the magnetic field at each target point on the DSV surface is not more than 20 ppm, „x/ ≤5Gm^ and 4></≤5(3⁄4^5 respectively represent the magnetic field of the radial magnetic field and the axial magnetic field at each target point on the surface of the ellipsoid of the 5 Gaussian stray field The field strength is not more than 5Gauss, |/|≤1.48χ 10 ⁸ χ Λ^, indicating that the current at each grid is no more than 1.48 xl 0 ⁸ x A _{mesh e}

40x80

Calculate the current distribution at each grid by the linear programming optimization algorithm = ² % ^ |/,| at the minimum value, and form the current distribution map, and obtain the ellipsoid surface on the DSV surface and the 5 Gaussian stray field at this time. The magnetic field distribution at each target point. As shown in FIG. 5, it is a current distribution diagram obtained by a linear programming algorithm, and the current distribution diagram includes a plurality of non-zero current clusters with alternating positive and negative values. In Figure 5, a positive value indicates that a spiral line 通 with a forward current is required at the corresponding grid, and a negative value indicates that a solenoid coil with a reverse current is required at the corresponding grid, and zero corresponds to There is no need to arrange a spiral line around the grid. From the position of the non-zero current cluster of the current profile, it can be clearly seen that the spatial position of the six pairs of solenoids and the arrangement of the solenoid coils needs to be arranged.

As shown in Fig. 6, the magnetic field peak-to-peak uniformity distribution map of the axial magnetic field at each target point on the surface of the DSV obtained corresponding to the current profile shown in Fig. 5 is shown. It can be seen from Fig. 6 that the magnetic field peak-to-peak uniformity of the axial magnetic field at each target point on the surface of the DSV satisfies 20 ppm.

As shown in FIG. 7, the magnetic field intensity distribution map at each target point on the surface of the ellipsoid corresponding to the 5 Gaussian stray field obtained in the current distribution diagram shown in FIG. 5, wherein the radial magnetic field and the axial magnetic field are combined with the p magnetic field The intensity values are not greater than 5 Gauss.

Referring to Figure 3, according to the current distribution diagram obtained by the linear programming algorithm, the boundaries of the six non-zero current clusters are clearly identifiable and the current values at each grid point are the same, which is consistent with the same current in the actual solenoid coil. . Distributing the non-zero current cluster into an energized spiral line 具有 having a rectangular cross section, and calculating the total current of each non-zero current cluster as the initial total current of each spiral line ,, according to the operating current density of the spiral line 圏The initial area of each solenoid coil is set. According to the ratio of the initial thickness to the width of each spiral line diagram set, for example, the ratio of the initial thickness to the width of each solenoid coil can be exemplarily set to 0.8. The initial position and size parameters of each spiral line 可 can be obtained and used as the initial values of the spiral line group structure parameters in the subsequent nonlinear optimization algorithm. As shown in FIG. 8, the initial position and size parameters of the non-zero current clusters in the current distribution diagram obtained by the linear programming algorithm in this application embodiment are separated into spiral pipelines.

In operation 304, the solenoid line obtained in operation 303 is performed by a nonlinear optimization algorithm The initial values of the structural parameters of the circle are optimized, and the size and position parameters of each spiral line 圏 are calculated when the volume of the coil system is the smallest, and the final structural parameters of the coil system are obtained.

The variables to be optimized in the nonlinear optimization algorithm are the structural parameters of each spiral line, including the following dimensions and spatial position parameters of each solenoid coil: r _inner (i), r _outer (i), z _left ( i), z _right (i), where 1,2 ..,6, r _inner (i) is the inner radius of the ith spiral line ,, r. _Uter (i) is the outer radius of the ith spiral line _,, z, _eft (i) is the end axial position of the ith spiral line _,, z _right (i) is the ith solenoid The other end of the coil is axially positioned.

Taking the total volume of the six pairs of spiral pipelines as the objective function, the minimum value of the objective function takes the minimum volume of the system. Setting the magnetic field peak-to-peak uniformity of the axial magnetic field at the target point on the DSV surface to 10 ppm, the magnetic field strength of the axial magnetic field and the radial magnetic field of the target point on the surface of the ellipsoid of the 5 Gaussian stray field is set to be no more than 5 Gauss; The highest magnetic field strength in the coil system is less than 8T, and the current safety is less than 80% according to the highest magnetic field strength in the coil system and the performance of the selected superconducting wire; the same layer of spiral pipelines are convenient for construction and It is avoided that the solenoid coils overlap each other, exemplarily preset that the inter-turn spacing of the spiral line turns is greater than 1 cm, and the radial different interlayer spacing is greater than 1 cm.

The mathematical model of the nonlinear optimization algorithm is as follows:

6

The objective function is: ∑ ^{2 x} [_ ^r ou, er ( ² - r _imer {if" x [z _right (i) - ζ ₁ (0)

=1

The second constraint includes:

In the above second constraint, 8 _{3⁄4 (} ^ is the magnetic field strength of the axial magnetic field generated by the solenoid coil at each target point on the DSV surface, 8^^ is the ellipse of the spiral line 圏 in the 5 Gaussian stray field The magnetic field strength of the axial magnetic field generated at each target point on the surface of the sphere, B _rstray is the magnetic field strength of the radial magnetic field generated at each target point on the surface of the 5 Gaussian stray field ellipsoid, max(B _zdsv ) Indicates the maximum value of the magnetic field strength at all target points, max(B _zdsv ) represents the minimum of the magnetic field strength at all target points, mean(B _zdsv ) represents the average of the magnetic field strength at all target points; lop is the superconducting magnet The operating current of the system at the operating point, Ic(B _max ), is the corresponding critical current value Ic in the superconducting wire calculated from the operating current lop of the superconducting magnet system at the operating point and the highest value of the magnetic field strength in the coil system. among them,

Min^jj/^^CS^^lO/^w indicates that the peak-to-peak uniformity of the magnetic field at each target point on the DSV surface is not more than 10 ppm, B _r ² _s , _ray ≤ 50

5 The superimposed magnetic field strength of the axial magnetic field and the radial magnetic field of each target point on the surface of the Gaussian stray field ellipsoid is not more than 5 _g auss

O.SO indicates that the current safety margin is not more than 0.8 3⁄4('+l)-3⁄4, ( >=lcm, = 1,2... 4 and ^ (6) >=1^ = 1 2,,.., 4,5 respectively indicate that the inter-turn spacing and inter-layer spacing between the solenoid coils are not less than 1 cm >=

0.575 and z _/e< (6):>=0 _1⁄4/w (6)<=0.575 indicates that the spiral line group needs to be within the space of the system to be laid.

As shown in FIG. 9, it is a schematic diagram of the final structural parameters of the coil system obtained by the nonlinear optimization algorithm in the application embodiment shown in FIG. Among them, the black area indicates the solenoid coil in which the energization direction is forward, and the white area indicates the negative solenoid line 通电 in the energization direction. The line drawing system has two layers of six pairs of spiral lines, wherein the inner layer has five pairs of spiral lines and the outer layer has a pair of shielded spiral lines. Fig. 10 is a view showing the distribution of the peak-to-peak uniformity of the magnetic field of the axial magnetic field at each target point on the DSV surface optimized by the nonlinear optimization algorithm in the application embodiment. 11 is a magnetic field intensity distribution diagram at each target point on the surface of an ellipsoid of a 5 Gaussian stray field obtained by a nonlinear optimization algorithm in the application embodiment shown in FIG. 3.

12 is a current safety margin diagram of the MRI superconducting magnet system in the application embodiment shown in FIG. 3, wherein the thick curve (Ic, Be) represents the critical current characteristic Ic-Bc curve of the selected superconducting wire, and the thin line (B) _Max lop) represents the relationship between the operating current lop of the coil system at the operating point and the highest magnetic field strength value B _max in the coil system. The intersection of the two curves is the critical point corresponding to the operating point of the coil system. Current safety margin for this application example when Ic=953.3A Degree is 70.35%,

13 is a magnetic field intensity distribution diagram of a coil system generated in a space in the application embodiment shown in FIG. 3, wherein the magnetic field distribution in the coil system has symmetry, and FIG. 14 is an inner layer in the coil system of the application embodiment shown in FIG. The distribution of the spatial magnetic field strength in the solenoid coil closest to the end. It can be seen from Fig. 13 and Fig. 14 that the highest magnetic field in the coil system (i.e., the magnetic field with the highest magnetic field strength) is located in the spiral line 端 at the end of the inner layer, and the maximum magnetic field strength is 4.9127T. Table 1 shows the structural parameters of each solenoid coil in the MRI superconducting magnet system corresponding to the application embodiment shown in Fig. 3. Table 2 shows the structural parameters of the MRI superconducting magnet system finally obtained in the application example:

Table 1 Structural parameters of the spiral line

Structural parameters of MRI superconducting magnet system

The outer diameter of the magnet is 1.60m

Magnet length 1.15m

Imaging sphere diameter / uniformity 500mm/10ppm

Stray field strength / ellipsoid range 5Gauss/4mx5m

Operating current 670.62A

Operating current density 148MA/m ²

The highest magnetic field in the coil 4.9I27T

Current safety desire 70.35%

Super wire usage 1.2871t

OST:

Super wire specification

2.56 mm * 1.77 mm 950A @ 7T It will be understood by one of ordinary skill in the art that the methods of the various embodiments of the present invention may be implemented in a number of ways. For example, the method of an embodiment of the present invention can be implemented by software, hardware, firmware, or any combination of software, hardware, and firmware. The above-described order of operation in the method is for illustrative purposes only, and the order of operation of the method of the embodiments of the present invention is not limited to the order specifically described above unless otherwise specifically stated. In addition, in some embodiments, all or part of the operations of implementing the above method embodiments may be performed by hardware associated with the program instructions, the foregoing program including machine readable instructions for implementing the method according to the present invention, which may be stored in a The computer readable storage medium, the program, when executed, performs the steps comprising the above-described method embodiments; the invention may also be embodied as a program recorded in a recording medium, the program comprising means for implementing the method according to the invention. Machine readable instructions. Thus, the invention also covers a storage medium storing a program for performing the method according to the invention. Previous storage media include: ROM, RAM, disk or optical disk, and other media that can store program code.

For example, when the method for acquiring the structural parameters of the MRI superconducting magnet system of the present invention is implemented by software, hardware, firmware or any combination of software, hardware, and firmware, the method can be specifically implemented by:

First, enter the production requirements parameters of the MRI superconducting magnet system, for example, including but not Limited to central magnetic field strength, DSV size, magnetic field value uniformity requirement, 5 Gaussian stray field requirements, spatial extent of the coil system, operating current density of a given coil system, current safety margin;

Secondly, according to the production demand parameters of the MRI superconducting magnet system, the loop iterative calculation is performed by the linear programming algorithm and the nonlinear optimization algorithm, and the structural parameters of the coil system satisfying the production requirements of the MRI superconducting magnet system are obtained. The process is divided into linear programming. Process and nonlinear optimization process two steps.

In the first step, the operation of 101 - 102 or 201 ~ 202 is performed, and the variable to be optimized in the linear programming algorithm is the current value at each mesh in the spatial range of the system to be arranged, and the objective function is the snail at all the grids. The total volume of the line pipeline , is cyclically iteratively calculated by a linear programming algorithm. If the magnetic field at the target point does not satisfy the first constraint condition, the linear programming algorithm automatically adjusts all variables to be optimized (ie, the current values at each grid) and Perform the next iteration calculation until the magnetic field at all target points satisfies the first constraint and the total volume of the spiral line 代表 represented by all the grids is the smallest, stop the iterative calculation, and obtain the optimal solution of the variable to be optimized. The optimal solution of the optimization variables forms a current distribution map at each grid.

When the linear iterative algorithm is used for loop iterative calculation, the iterative calculation of the preset number of times can be performed based on the convergence characteristic of the total volume of the solenoid coil. For example, iterative calculation is performed 150 times, and the first constraint is satisfied and all the networks are selected. The current value of the smallest volume of the solenoid coil represented by the grid forms a current profile.

In the second step, according to the current distribution map at each grid obtained in the first step, the non-zero current cluster is converted into a spiral pipeline 圏, and the total current and spatial position of each non-zero current cluster are respectively corresponding. The initial total current and initial position of the solenoid coil, performing 103 or 203 ~ 204 operation, the variables to be optimized in the nonlinear optimization algorithm are the inner and outer radii of each solenoid coil and the axial directions of the two ends Position, the objective function is the total volume of the spiral line 所有 at all grids.

The loop iterative calculation is performed by the nonlinear optimization algorithm. If the second constraint is not satisfied, the nonlinear optimization algorithm automatically adjusts the size and position parameters of each spiral pipeline within the spatial range of the system to be arranged for the next iterative calculation. , until the conditions in the second constraint are satisfied and the total volume of all the solenoid coils is the smallest, outputting the inside and outside of each solenoid coil The radius and the axial position of the two ends provide the final structural parameters of the coil system.

When the loop optimization calculation is performed by the nonlinear optimization algorithm, the iterative calculation of the preset number of times can be performed based on the convergence characteristic of the total volume of the spiral pipeline circle, for example, iterative calculation

300 times, from which the inner and outer radii of the respective spiral line diagrams and the axial positions of the two end portions satisfying the second constraint and having the smallest total volume of the solenoid line 代表 represented by all the grids are selected.

Based on the final structural parameters of the coil system, an MRI superconducting magnet system can be constructed to meet the production requirements.

Figure 15 is a schematic block diagram of an apparatus for acquiring structural parameters of an MRI superconducting magnet system according to an embodiment of the present invention. The obtaining device of this embodiment can be used to implement the flow of the embodiment of the method for acquiring structural parameters of each of the above MRI superconducting magnet systems of the present invention. As shown in FIG. 15, it includes a receiving unit 301, a dividing unit 302, a first calculating unit 303, and a second calculating unit 304.

The receiving unit 301 is configured to receive spatial range information of the coil system to be arranged, a first predetermined magnetic field peak-to-peak uniformity, a limitation condition of a magnetic field strength value at each target point on an ellipsoid surface of a 5 Gaussian stray field, and an operating current density The second preset magnetic field peak-to-peak uniformity limit condition in the design requirements of the nano-superconducting magnet system, the magnetic field strength value limit condition at each target point on the surface of the ellipsoid of the 5 Gaussian stray field, and the highest magnetic field in the coil system Strength value limits, current safety margin limits for line system operation. The first predetermined magnetic field peak-to-peak value uniformity is greater than or equal to the second preset magnetic field value uniformity.

The dividing unit 302 is configured to perform continuous meshing on the spatial extent of the coil system to be arranged, and each divided grid is regarded as a current ring, and the current value of each current ring includes a positive value, a negative value or zero; And according to the preset standard, the DSV surface of the superconducting magnet system and the ellipsoid surface of the 5 Gaussian stray field are evenly divided into thousands of target points.

The first calculating unit 303 is configured to: the magnetic field peak-to-peak uniformity at each target point on the surface of the DSV is not greater than the first predetermined magnetic field peak-to-peak uniformity, and the magnetic field strength at each target point on the surface of the ellipsoid of the 5 Gaussian stray field The value constraint is the first constraint. The current distribution map is obtained by linear programming algorithm to calculate the current distribution at each grid which minimizes the volume of the coil system under a given operating current density.

a second calculating unit 304, configured to respectively use the number of current values that are not zero in the current distribution map Head and space position, as the number and initial position of the solenoid coil in the coil system; limit of the magnetic field strength at each target point on the surface of the ellipsoid with 5 Gaussian stray field with the second preset magnetic field peak-to-peak uniformity limit condition The condition of the highest magnetic field strength in the line graph system limits the current safety margin limit of the coil system operation as the second constraint condition. The size of each solenoid coil is calculated by the nonlinear optimization algorithm when the volume of the coil system is the smallest. The positional parameter, the final structural parameters of the coil system are obtained. Wherein, the size and position parameters of each solenoid coil include an inner radius, an outer radius, and an axial position of the two end portions of each solenoid coil.

According to a specific example of the apparatus for obtaining structural parameters of the MRI superconducting magnet system according to the present invention, and not by limitation, the spatial extent of the coil system to be arranged is specifically a solenoid-shaped region having a rectangular cross section, the range of which is rectangular The parameters of the rectangular section determine the inner diameter, outer diameter and length of the rectangular section. Correspondingly, when the dividing unit 302 performs continuous meshing on the spatial extent of the line graph system to be arranged, the two-dimensional continuous meshing may be performed on the rectangular cross-section in the radial direction and the axial direction, respectively, and the rectangular cross-section is along the radial direction. The axial directions are divided into several equal parts to form a two-dimensional continuous space grid.

Another specific example of the apparatus for obtaining structural parameters of the MRI superconducting magnet system according to the present invention, without limitation, the current distribution diagram gives the magnitude and direction of the current at each grid, and the non-zero current values at the grid are gathered together. Form a clear, non-zero current cluster. Wherein, each positive position of the non-zero current cluster is used to arrange a forward current solenoid line 圏, and each negative value position is used to arrange a reverse current solenoid line 分别, respectively.

According to another specific example of the apparatus for acquiring structural parameters of the MRI superconducting magnet system according to the present invention, the second constraint includes:

The peak-to-peak uniformity of the magnetic field of the axial magnetic field at each target point on the surface of the DSV is not greater than the uniformity of the second predetermined magnetic field value;

The current safety margin of the coil system operation is not greater than the preset current safety margin, and the preset current safety margin is calculated from the highest magnetic field strength value in the coil system and the critical characteristic of the superconducting wire selected by the coil system;

The spacing between adjacent spiral lines in the turns system is greater than the preset spacing; The size and positional parameters of each solenoid line 使 place the coil system within the spatial extent of the system in which the coil is to be placed.

Illustratively, the limiting value of the magnetic field strength value at each target point on the surface of the ellipsoid of the 5 Gaussian stray field may be: 5 The magnetic field strength value at each target point on the surface of the ellipsoid of the Gaussian stray field is not more than 5 Gauss;

5 The superimposed magnetic field strength of the axial magnetic field and the radial magnetic field at each target point on the surface of the ellipsoid of the Gaussian stray field is not greater than the preset magnetic field strength, which may be: 5 The axial direction at each target point on the surface of the ellipsoid of the Gaussian stray field The superposed magnetic field strength of the magnetic field and the radial magnetic field is not more than 5 Gauss.

Exemplarily, the second calculating unit 304 can also be used to calculate the current safety margin of the coil system operation according to the highest magnetic field strength value in the preset coil system and the critical characteristic of the superconducting wire selected by the coil system. degree.

The embodiment of the present invention further provides an MRI superconducting magnet system, and the structural parameters of the MRI superconducting magnet system can be obtained by the method for acquiring structural parameters of any of the MRI superconducting magnet systems of the present invention.

The various embodiments in the specification are described in a progressive manner, and each embodiment is focused on differences from the other embodiments, and the same or similar parts between the various embodiments may be referred to each other. For the MRI superconducting magnet system structural parameter acquisition device and the MRI superconducting magnet system embodiment, since it basically corresponds to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the description of the method embodiment.

The description of the present invention has been presented for purposes of illustration and description. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention and the embodiments of the invention.

Claims

Rights request

A method for acquiring structural parameters of a magnetic resonance imaging superconducting magnet system, characterized in that:

Continuously meshing the spatial extent of the system to be arranged, each grid obtained by the division is regarded as a current ring, and the current value of each current ring includes positive value, negative value or zero; and according to preset standards The surface of the spherical imaging region of the superconducting magnet system and the surface of the ellipsoid of the 5 Gaussian stray field are evenly divided into a plurality of target points;

The limitation of the magnetic field value at each target point on the surface of the spherical imaging region is not greater than the first predetermined magnetic field peak-to-peak uniformity, and the magnetic field strength value at each target point on the surface of the ellipsoid of the 5 Gaussian stray field is a constraint condition, wherein a current distribution map is obtained by calculating a current distribution at each grid that minimizes the volume of the coil system under a given operating current density condition; and the first predetermined magnetic field value uniformity is greater than or equal to The second predetermined magnetic field value uniformity in the design requirements of the superconducting magnet system;

The number and spatial position of the non-zero current values in the current distribution diagram are respectively taken as the number and initial position of the solenoid coils in the coil system;

In the superconducting magnet system design requirements, the second preset magnetic field peak-to-peak uniformity limit is limited to the magnetic field strength value at each target point on the surface of the ellipsoid of the 5 Gaussian stray field, and the highest magnetic field in the coil system The limit value of the strength value and the current safety margin limit of the operation of the coil system are the second constraint conditions. The size and position parameters of each spiral line 时 are calculated by the nonlinear optimization algorithm when the volume of the coil system is minimum, and the loop system is obtained. The final structural parameters; wherein the size and positional parameters of each solenoid coil include the inner radius, the outer radius of each solenoid coil, and the axial position of the two ends.

2. The method according to claim 1, wherein the spatial extent of the coil system to be arranged is specifically a solenoid-shaped region having a rectangular cross section, and the extent of the region is determined by parameters of the rectangular cross section. The parameters of the rectangular cross section include an inner diameter, an outer diameter, and a length of a rectangular cross section;

Continuous meshing of the spatial extent of the system in which the coil is to be arranged includes: performing continuous meshing of the rectangular sections in the radial and axial directions, respectively.

3. The method of claim 2, wherein continuously dividing the rectangular cross section in the radial direction and the axial direction comprises: performing two-dimensionally on the rectangular cross section in the radial direction and the axial direction, respectively With continuous meshing, the rectangular cross section is divided into several equal parts along the radial and axial directions to form a two-dimensional continuous space mesh.

4. The method according to claim 1, wherein the current distribution map gives the magnitude and direction of the current at each grid, and the non-zero current values at the grid are gathered together to form a clear boundary. Zero current cluster.

5. The method according to claim 4, wherein a forward current spiral line 圏 is arranged at each positive position of the non-zero current cluster according to a distribution of the non-zero current clusters in a spatial range. , respectively, a reverse current solenoid coil is placed at each negative position of the non-zero current cluster.

6. A method according to any one of claims 1 to 4, characterized in that the limiting conditions of the magnetic field strength values at the respective target points on the surface of the ellipsoid of the 5 Gaussian stray field include: 5 ellipsoidal surface of the Gaussian stray field The value of the magnetic field strength at each of the upper target points is not more than 5 Gauss.

The method according to any one of claims 1 to 4, wherein the second constraint comprises:

The current safety margin of the coil system operation is not greater than a preset current safety margin calculated from the highest magnetic field strength value in the coil system and the critical characteristic of the superconducting wire selected by the coil system. ;

The spacing between adjacent spiral lines in the turns system is greater than the preset spacing;

The size and positional parameters of each of the solenoid lines 使 cause the coil system to be within the spatial extent of the line system to be placed.

8. The method according to claim 7, wherein the superimposed magnetic field strength of the axial magnetic field and the radial magnetic field at each target point on the surface of the ellipsoid of the 5 Gaussian stray field is not greater than the preset magnetic field strength, including: 5 The superimposed magnetic field strength of the axial magnetic field and the radial magnetic field at each target point on the surface of the ellipsoid of the Gaussian stray field is not more than 5 Gauss.

9. The method according to claim 7, further comprising:

The current safety margin of the coil system operation is obtained based on the highest magnetic field strength value in the preset coil system and the critical characteristics of the superconducting wire selected by the coil system.

10. A device for acquiring structural parameters of a magnetic resonance imaging superconducting magnet system, characterized in that:

a receiving unit, configured to receive spatial range information of the coil system to be arranged, a first predetermined magnetic field peak-to-peak uniformity, a limit condition of a magnetic field strength value at each target point on an ellipsoid surface of a 5 Gaussian stray field, and an operating current density The second preset magnetic field peak-to-peak uniformity limit condition in the design requirements of the superconducting magnet system, the magnetic field strength value at each target point on the surface of the ellipsoid of the 5 Gaussian stray field, and the highest magnetic field strength in the coil system a value limit condition, a current safety margin limit condition of the coil system operation; the first preset magnetic field peak-to-peak uniformity is greater than or equal to the second preset magnetic field ¹ ^ value uniformity;

a dividing unit, configured to perform continuous meshing on a spatial range of the coil system to be arranged, each divided grid is regarded as a current ring, and the current value of each current ring includes a positive value, a negative value or zero; According to a preset standard, the surface of the spherical imaging region of the superconducting magnet system and the surface of the ellipsoid of the 5 Gaussian stray field are evenly divided into a plurality of target points;

a first calculating unit, configured to: the magnetic field peak-to-peak uniformity at each target point on the surface of the spherical imaging region is not greater than the first predetermined magnetic field peak-to-peak uniformity, and the magnetic field at each target point on the surface of the ellipsoid of the 5 Gaussian stray field The constraint condition of the intensity value is a first constraint condition, and a current distribution map is obtained by a linear programming algorithm for calculating a current distribution at each grid which minimizes the volume of the coil system under a given operating current density condition;

a second calculating unit, configured to respectively use the number and spatial position of the non-zero current values in the current distribution map as the number and initial position of the solenoid line 圏 in the coil system; and the second predetermined magnetic field peak-to-peak uniformity Limiting the magnetic field strength value at each target point on the surface of the ellipsoid of the 5 gaussian stray field, limiting the maximum magnetic field strength value in the line and the 圏 system, and limiting the current safety margin of the coil system operation. The second constraint condition is obtained by calculating the size and position parameters of each spiral line 时 when the volume of the coil system is minimum by a nonlinear optimization algorithm. The final structural parameters of the system; wherein the size and positional parameters of each spiral line include the inner radius, the outer radius, and the axial positions of the two end portions of each spiral line diagram.

The device according to claim 10, wherein the spatial extent of the coil system to be arranged is specifically a solenoid-shaped region having a rectangular cross section, and the range of the region is determined by parameters of the rectangular cross section. The parameters of the rectangular section include the inner diameter, the outer diameter and the length of the rectangular section;

When the dividing unit performs continuous meshing on the spatial extent of the wire loop system to be arranged, the rectangular cross section is respectively subjected to two-dimensional continuous mesh division in the radial direction and the axial direction, and the rectangular cross section is along the radial direction. And the axial direction is divided into several equal parts to form a two-dimensional continuous space grid.

12. The device according to claim 10, wherein the current distribution map gives the magnitude and direction of the current at each grid, and the non-zero current values at the grid are gathered together to form a clear boundary. Zero current cluster

Each positive position of the non-zero current cluster is used to arrange a forward current solenoid line 分别, and each negative position is used to arrange a reverse current solenoid coil, respectively.

13. Apparatus according to any one of claims 10 to 12 wherein the second constraint comprises:

The current safety margin of the coil system operation is not greater than a preset current safety margin calculated from the highest magnetic field strength value in the coil system and the critical characteristic of the superconducting wire selected by the coil system;

The size and positional parameters of each solenoid coil are such that the coil system is within the spatial extent of the coil system to be placed.

14. The apparatus according to claim 13, wherein the limiting condition of the magnetic field strength value at each target point on the surface of the ellipsoid of the 5 Gaussian stray field comprises: 5 Gaussian stray field The value of the magnetic field strength at each target point on the surface of the ellipsoid is not more than 5 Gauss;

15. The apparatus according to claim 13, wherein the second calculating unit is further configured to obtain the coil according to a maximum magnetic field strength value in a preset coil system and a critical characteristic of the superconducting wire selected by the coil system. The current safety margin of the system operation.

16. A magnetic resonance imaging superconducting magnet system, characterized in that the structural parameters of the magnetic resonance imaging superconducting magnet system are obtained by the structural parameters of the magnetic resonance imaging superconducting magnet system according to any one of claims 1 to 9. Method to get.