A high-resolution magnetic particle three-dimensional imaging system

Abstract

The application relates to a high-resolution magnetic particle three-dimensional imaging system, which comprises a magnetic ring structure and a solenoid coil located at the center of the magnetic ring structure; the magnetic ring structure comprises a zero-pole and a dipole located at the outer ring of the zero-pole, the zero-pole comprises an outer zero-pole and an inner zero-pole, and the dipole comprises an outer dipole and an inner dipole; the solenoid coil comprises an excitation coil and a receiving coil, the excitation coil is nested at the periphery of the receiving coil, and the excitation coil and the receiving coil are both three-section solenoid coils; and the zero-pole and the dipole are both composed of multiple permanent magnets. The magnetic particle three-dimensional imaging system uses two zero-poles and two dipoles as gradient fields and uniform fields, uses a three-section two-end compensation solenoid coil as an excitation field, uses a gradient receiving coil to receive a magnetic particle response signal, can effectively realize a high gradient value and a large uniform field, thereby realizing three-dimensional imaging and increasing an imaging field of view.

Description

Technical Field

[0001] The invention belongs to the technical field of biomedical imaging, and in particular relates to a high-resolution magnetic particle three-dimensional imaging system. Background Art

[0002] Currently, magnetic particle imaging devices can be divided into two types: those based on electromagnetic coils and those based on permanent magnet arrays. The resolution of electromagnetic coil-based magnetic particle imaging devices is currently limited by the power consumption of the electromagnetic coils, making their clinical application difficult.

[0003] The magnetic field components of existing magnetic particle imaging devices primarily consist of a gradient selection field and a uniform drive field. The resolution of a magnetic particle imaging device is determined by the magnitude of the gradient field, while the imaging field of view (FOV) is determined by the uniform field. Therefore, achieving high resolution and a large field of view requires sufficiently large gradient and uniform field strengths. Typically, electromagnetic coil-based magnetic particle imaging devices use electromagnetic coils to generate gradient fields, forming zero magnetic field points (or zero magnetic field lines), and drive fields, driving the zero magnetic field points (or zero magnetic field lines) to rapidly move. To generate sufficiently large gradient and drive fields, a high-power power supply is required to power the electromagnetic coils. Furthermore, the power amplifier requires high output power, and the received signal must be filtered by a high-power passive filter to suppress the high harmonics directly generated by the power amplifier. This filtering operation is complex and can also filter out useful signals, reducing the available signal-to-noise ratio (SNR) in the receive chain. Consequently, existing electromagnetic coil-based magnetic particle imaging devices are limited by power consumption, making it difficult to achieve high resolution and a large field of view.

[0004] The above problems are more easily solved using permanent magnet arrays. However, magnetic particle imaging devices based on permanent magnet arrays also suffer from a fixed field of view and lack of flexibility. Furthermore, current permanent magnet array devices use a Halbach quadrupole permanent magnet array to generate a gradient field. This gradient field produces zero magnetic field lines in one dimension, resulting in a loss of axial resolution and inability to achieve three-dimensional imaging. Summary of the Invention

[0005] In order to solve the problems of resolution loss and poor imaging field of view in existing magnetic particle imaging devices, the present invention proposes a high-resolution magnetic particle three-dimensional imaging system, which uses a permanent magnet array to increase the magnetic field gradient value and uniform field strength, thereby improving the imaging resolution and imaging field of the device.

[0006] The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0007] A high-resolution magnetic particle three-dimensional imaging system includes a magnetic ring structure and a solenoid coil, wherein the solenoid coil is located at the center of the magnetic ring structure, the magnetic ring structure includes a null pole and a dipole located in the outer circle of the null pole, the null pole includes an outer null pole and an inner null pole, and the dipole includes an outer dipole and an inner dipole; the solenoid coil includes an excitation coil and a receiving coil, and the excitation coil is nested outside the receiving coil.

[0008] Furthermore, the excitation coil and the receiving coil are both three-section solenoid coils.

[0009] Furthermore, the excitation coil is a two-end compensated solenoid coil, the inner layer of the excitation coil is fully wound, and the outer layer of the excitation coil is only wound at both ends.

[0010] Furthermore, both ends of the receiving coil are compensation coils, and the middle section of the receiving coil is a receiving coil, and the compensation coils compensate for the baseband signal received by the receiving coil.

[0011] Furthermore, the above-mentioned zero poles and dipoles are both composed of multiple permanent magnets.

[0012] Furthermore, the null pole generates a gradient field, and the dipole generates a uniform field. The magnetic field distribution can be expressed as:

[0013]

[0014] In formula (a), B dr is the magnetic field strength of the uniform field, G qr is the gradient distribution of the gradient field.

[0015] Furthermore, the gradient distribution of the gradient field is fixed, and the magnetic field strength of the uniform field is adjusted by changing the rotation angle of the outer dipole and the inner dipole. The magnetic field strength B of the uniform field is dr As shown in the following formula:

[0016]

[0017] In formula (b), B dr represents the magnetic field strength of the outer dipole and inner dipole, θ d1 ,θ d2 Represent the rotation angles of the outer dipole and inner dipole respectively. When the rotation angle θ d1 =θ d2 = 0, the maximum uniform field strength B dr,max =2B dp ; When the rotation angle θ d1 +θ d2 =180°, the minimum uniform field strength is B dr,min= 0, that is, by rotating the outer dipole and the inner dipole, the driving field amplitude is between 0 and 2B dp Scope changes.

[0018] Furthermore, the outer dipole and inner dipole generate two layers of uniform fields, which rotate at different angular velocities. The outer layer rotates at an angular velocity ω1, and the inner layer rotates at an angular velocity ω2. At this time, the uniform field magnetic field strength is:

[0019]

[0020] In formula (c), ω1 represents the outer layer angular velocity, ω2 represents the inner layer angular velocity, and B dr is the magnetic field strength of the uniform field.

[0021] Beneficial effects of the present invention:

[0022] 1. This invention improves the imaging resolution and field of view of the device by using a permanent magnet array to increase the magnetic field gradient and uniform field strength. The invention proposes using a permanent magnet ring to provide the magnetic field required for magnetic particle imaging, which can more effectively achieve high gradient values ​​and a large uniform field.

[0023] 2. The present invention improves the resolution of magnetic particle imaging equipment by using zero poles as gradient fields, and can generate three-dimensional gradients, thereby achieving three-dimensional imaging;

[0024] 3. The present invention uses a dipole as a uniform field, which has good magnetic field uniformity and high magnetic field strength, thereby increasing the imaging field of view of the device;

[0025] 4. The present invention can realize two scanning modes by controlling the rotation speed of the two dipoles;

[0026] 5. The present invention improves the detection sensitivity of the equipment by adopting a three-section receiving coil. By improving the structure of the receiving coil, it is more convenient for actual debugging and can further improve the detection sensitivity.

[0027] 6. The present invention can achieve variable FOV scanning by controlling the rotation mode of the two layers of dipole rings in the driving field, thereby increasing the flexibility of the device and improving the imaging speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the structure of the three-dimensional imaging system of this embodiment;

[0029] Figure 2 This is a schematic diagram of the driving magnetic field change in this embodiment;

[0030] Figure 3 Schematic diagram of uniform magnetic field distribution when the rotation angle is 0 degrees;

[0031] Figure 4 Schematic diagram of uniform magnetic field distribution when the rotation angle is 90 degrees;

[0032] Figure 5 Schematic diagram of uniform magnetic field distribution when the rotation angle is 180 degrees;

[0033] Figure 6 This is the linear distribution diagram of the gradient field magnetic field of this embodiment;

[0034] Figure 7 This is the thermal map of the gradient magnetic field distribution in this embodiment;

[0035] Figure 8 Schematic diagram of the excitation coil structure;

[0036] Figure 9 Schematic diagram of the receiving coil structure;

[0037] Figure 10 The directions of ω1 and ω2 are opposite, and ω1 is slightly larger than ω2, forming a two-dimensional scanning trajectory;

[0038] Figure 11 The directions of ω1 and ω2 are the same, and ω1 ≥ 20ω2, imaging two-dimensional scanning trajectory;

[0039] Figure 12 Schematic diagram of the scanning method with fixed FOV;

[0040] Figure 13 Schematic diagram of scanning method with variable FOV;

[0041] Figure 14 Schematic diagram of variable FOV rotation method;

[0042] Figure 15 This is the schematic diagram of the Halbach ring construction.

[0043] In the figure, 1. External dipole; 2. Inner dipole; 3. External null pole; 4. Inner null pole; 5. Excitation coil; 6. Receiving coil. DETAILED DESCRIPTION

[0044] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose, the specific implementation methods, structural features and effects of the present invention are described in detail below with reference to the accompanying drawings and examples.

[0045] This embodiment provides a high-resolution magnetic particle three-dimensional imaging system. Figure 1The high-resolution magnetic particle three-dimensional imaging system includes a magnetic ring structure and a solenoid coil, and the solenoid coil is located at the center of the magnetic ring structure. The magnetic ring structure includes a zero pole and a dipole located in the outer ring of the zero pole, the zero pole includes an outer zero pole 3 and an inner zero pole 4, and the dipole includes an outer dipole 1 and an inner dipole 2. The solenoid coil includes an excitation coil 5 and a receiving coil 6, and the excitation coil 5 is nested on the periphery of the receiving coil 6. Specifically, from the outer ring to the inner ring, they are outer dipole 1, inner dipole 2, outer zero pole 3, inner zero pole 4, excitation coil 5 and receiving coil 6. The high-resolution magnetic particle three-dimensional imaging system improves the magnetic field gradient value and the driving field strength by using a permanent magnet array, thereby improving the imaging resolution and imaging field of the device.

[0046] This embodiment uses Halbach null poles and dipoles. Figure 15 , the angle of the magnetic block position is θ, the angle of the magnetization direction is α, α=(k+1)θ, k∈Z. The polarity p of the field can be corresponded by p=2|k|, where k is the modulus value. When the mode k=0, it is named as zero pole. When the mode k=1, it is named as dipole. The excitation coil and the receiving coil of this embodiment are both three-segment solenoid coils, which improves the detection sensitivity of the equipment. This implementation does not use traditional electromagnetic coils as the selection field and the driving field, and can achieve the effects of good gradient field linearity, large magnetic field gradient, strong driving field and high uniformity. Refer to the attached Figure 9 The excitation coil of this embodiment is a two-end compensation type solenoid coil. The inner layer of the excitation coil is fully wound, and the outer layer of the excitation coil is only wound at both ends. Compared with the commonly used solenoid coil, this coil generates a magnetic field with a larger uniform range and higher uniformity. Figure 8 The two ends of the receiving coil are compensation coils, and the middle section of the receiving coil is the receiving coil. The compensation coils compensate for the baseband signal received by the receiving coil. This embodiment improves the structure of the receiving coil, making it easier to debug and further improving detection sensitivity.

[0047] The excitation coil in this embodiment generates an excitation magnetic field, producing a high-frequency magnetic field that excites particles. A three-stage receiving and compensating coil receives the particle response signals. The main power consumption of this embodiment is comprised of the permanent magnet rotating motor and the excitation coil. This significantly reduces power consumption compared to magnetic particle imaging devices using electromagnetic coils of the same level.

[0048] The dipole of this embodiment includes two nested dipoles (outer dipole and inner dipole). The uniform magnetic field vectors generated by the outer dipole and the inner dipole are superimposed to form the driving field of the magnetic particle imaging scanner. The function of the driving field is to move the magnetic field free point on a specific trajectory to achieve the scanning requirements required for imaging. The magnetic field strength of the driving field can be adjusted by changing the rotation angle of the outer dipole and the inner dipole. The inner and outer layers have the same field strength, and the magnitude of the driving field strength is changed by rotating the inner and outer magnetic rings. The uniform field magnetic field distribution is as follows Figure 2-5 As shown, it can be seen from the depth of the color in the central area that the depth of the color corresponds to the magnitude of the magnetic field value. Figure 2 Schematic diagram of driving magnetic field change; Figure 3 Schematic diagram of uniform magnetic field distribution when the rotation angle is 0 degrees; Figure 4 Schematic diagram of uniform magnetic field distribution when the rotation angle is 90 degrees; Figure 5 Schematic diagram of uniform magnetic field distribution when the rotation angle is 180 degrees.

[0049] The zero poles include two nested zero poles (outer zero pole and inner zero pole). The zero poles generate zero magnetic field points, which can realize three-dimensional scanning imaging. The magnetic field distribution is as follows: Figure 6 and 7 As shown in Figure 2, the two layers of gradient fields are fixed in position, generating a magnetic field with high uniformity and high gradient field. Figure 6 is the linear distribution diagram of the gradient field magnetic field, Figure 7 is the gradient magnetic field distribution heat map.

[0050] The zero poles and dipoles of this embodiment are both composed of multiple permanent magnets. Three-dimensional imaging is achieved by using a permanent magnet array to generate a three-dimensional gradient field. Current permanent magnet arrays use a Halbach quadrupole permanent magnet array to generate gradient fields. This gradient field produces zero magnetic field lines in the axial dimension, resulting in a loss of resolution. The magnetic particle imaging device of this embodiment presents zero magnetic field points in all three dimensions, and the axial imaging field of view is unrestricted, thus enabling high-resolution three-dimensional imaging.

[0051] In this embodiment, the magnetic field strength of the driving field can be adjusted by rotating the two dipoles, and the zero magnetic field point can be driven to move by changing the magnetic field strength of the uniform field, thereby achieving scanning within the imaging field of view. The magnetic field distribution of the magnetic particle imaging device of this embodiment can be expressed as:

[0052]

[0053] In formula (a), B dr is the magnetic field strength of the uniform field, G qr is the gradient distribution of the gradient field.

[0054] The gradient distribution of the gradient field is fixed, and the magnetic field strength of the uniform field is adjusted by changing the rotation angle of the outer dipole and the inner dipole. The magnetic field strength B of the uniform field dr As shown in the following formula:

[0055]

[0056] In formula (b), B dr represents the magnetic field strength of the outer dipole and inner dipole, θ d1 ,θ d2 Represent the rotation angles of the outer dipole and inner dipole respectively. When the rotation angle θ d1 =θ d2 = 0, the maximum uniform field strength B dr,max =2B dp ; When the rotation angle θ d1 +θ d2 =180°, the minimum uniform field strength is B dr,min = 0, that is, by rotating the outer dipole and the inner dipole, the driving field amplitude is between 0 and 2B dp Scope changes.

[0057] The outer dipole and the inner dipole generate two layers of uniform fields. The two layers of uniform fields rotate at different angular velocities. The outer layer rotates at an angular velocity ω1, and the inner layer rotates at an angular velocity ω2. At this time, the uniform field magnetic field strength is:

[0058]

[0059] In formula (c), ω1 represents the outer layer angular velocity, ω2 represents the inner layer angular velocity, and B dr is the magnetic field strength of the uniform field.

[0060] This embodiment adopts two scanning modes. In this structure, the two layers of uniform field rotate at different angular velocities, the outer layer rotates at an angular velocity ω1, and the inner layer rotates at an angular velocity ω2. Figure 10 In the equation, ω1 and ω2 are in opposite directions, and ω1 is slightly larger than ω2; Figure 11 In the equation, ω1 and ω2 are in the same direction, and ω1 ≥ 20ω2.

[0061] At the same time, this embodiment can also achieve variable FOV by controlling the scanning mode to reduce the scanning time required for imaging. Figure 12-14 As shown, let the outer layer rotation offset angle be θ1, the inner layer rotation offset angle be θ2, and rotate in opposite directions at angular velocities ω1 and ω2 respectively. The rotation angle is expressed as:

[0062]

[0063] In formula (d), θ d1is the outer layer rotation angle, θ d2 is the inner layer rotation angle.

[0064] Rotate θ again d1 ,θ d2 , the arc length can be expressed as:

[0065]

[0066] In formula (e), L1(t) is the outer arc length and L2(t) is the inner arc length.

[0067] Then the amplitude of the driving field can be expressed as:

[0068]

[0069] In formula (f), r1 and r2 are the radii of the outer and inner magnetic rings respectively. Then the maximum field strength of the driving field is:

[0070]

[0071] Then rotate the outer layer rotation offset angle θ1 and the inner layer rotation offset angle θ2, θ1, θ2>0, then B dr,max '<2B dp , that is, B dr,max ' dr,max .

[0072] The magnetic particle imaging system structure proposed in this embodiment is composed of multiple permanent magnets, so the entire structure will be subjected to a magnetic field force of thousands of Newtons. The force between the magnets in this design is calculated based on the Maxwell surface stress tensor, as shown in formula (g).

[0073]

[0074] In formula (g), F represents the magnetic force; V represents the volume of the object receiving the force; and T represents the stress tensor.

[0075] According to Gaussian divergence law, the stress tensor can be expressed by the area of ​​the object under stress, as shown in formula (h).

[0076]

[0077] In formula (h), A represents the surface area of ​​the object subjected to the force, n represents the normal vector of A, dV represents the differentiation of V, and dA represents the differentiation of A.

[0078] In this structure, the stress tensor can also be expressed by formula (i):

[0079]

[0080] ​In formula (i), μ0 represents the vacuum magnetic permeability, and B represents the average magnetic field strength within the magnetic field range of the object being stressed. In actual design, formula (gi) is used to analyze the stress on the structure.

[0081] The high-resolution magnetic particle three-dimensional imaging system of this embodiment uses two zero poles and two dipoles as gradient fields and driving fields, a three-segment two-terminal compensation solenoid coil as an excitation field, and a gradient receiving coil to generate three-dimensional gradients, ultimately achieving three-dimensional imaging.

[0082] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A high-resolution magnetic particle three-dimensional imaging system comprising a magnetic ring structure and a solenoid coil, wherein the solenoid coil is located at the center of the magnetic ring structure, characterized in that: The magnetic ring structure includes a zero pole and a dipole located in the outer ring of the zero pole. The zero pole is composed of multiple permanent magnets and can generate a gradient field with a fixed gradient distribution, and a zero magnetic field point is generated in the central area. The null pole includes an outer null pole and an inner null pole, and the dipole includes an outer dipole and an inner dipole; The solenoid coil includes an excitation coil and a receiving coil, wherein the excitation coil is nested around the receiving coil.

2. The high-resolution magnetic particle three-dimensional imaging system according to claim 1, characterized in that: The excitation coil and the receiving coil are both three-section solenoid coils.

3. The high-resolution magnetic particle three-dimensional imaging system according to claim 2, characterized in that: The excitation coil is a two-end compensated solenoid coil, the inner layer of the excitation coil is fully wound, and the outer layer of the excitation coil is only wound at two ends.

4. The high-resolution magnetic particle three-dimensional imaging system according to claim 2, characterized in that: Both ends of the receiving coil are compensation coils, and the middle section of the receiving coil is a receiving coil. The compensation coils compensate for the baseband signal received by the receiving coil.

5. The high-resolution magnetic particle three-dimensional imaging system according to claim 1, characterized in that: The zero pole and the dipole are both composed of a plurality of permanent magnets.

6. The high-resolution magnetic particle three-dimensional imaging system according to claim 1, wherein: The null pole generates a gradient field, and the dipole generates a uniform field. The magnetic field distribution can be expressed as: (a) In formula (a), is the magnetic field strength of the uniform field, is the gradient distribution of the gradient field.

7. The high-resolution magnetic particle three-dimensional imaging system according to claim 6, characterized in that: The gradient distribution of the gradient field is fixed, and the magnetic field strength of the uniform field is adjusted by changing the rotation angle of the outer dipole and the inner dipole. As shown in the following formula: (b) In formula (b), represents the magnetic field strength of the outer dipole and inner dipole, 、 Represent the rotation angles of the outer dipole and inner dipole respectively. When the rotation angle When the uniform field has the maximum strength ; When the rotation angle When the uniform field strength is minimum , that is, by rotating the outer dipole and the inner dipole, the driving field amplitude is Scope changes.

8. The high-resolution magnetic particle three-dimensional imaging system according to claim 6, characterized in that: The outer dipole and the inner dipole generate two layers of uniform fields, which rotate at different angular velocities. The outer layer rotates at an angular velocity. Rotate, the inner layer with angular velocity Rotate, the uniform magnetic field strength is: (c) In formula (c), represents the outer angular velocity, represents the inner layer angular velocity, is the magnetic field strength of the uniform field.

Images