Multi-resolution magnetic particle imaging method and system based on parallel excitation of magnetic field free lines

Abstract

The present invention belongs to the field of magnetic particle imaging, and particularly relates to a multi-resolution magnetic particle imaging method and system based on parallel excitation of magnetic field free lines, aiming to solve the problem that high-resolution and high-sensitivity image reconstruction cannot be achieved simultaneously. The present invention includes: generating magnetic field free lines; moving the magnetic field free lines to the target position; turning on the alternating current of the excitation coil to generate an excitation field with a single frequency, and collecting the voltage signals induced by the receiving coil; extracting the amplitudes of different order harmonics as single pixel values; mapping the single pixel values corresponding to different order harmonics to the spatial positions of the magnetic field free lines until all spatial positions are scanned to obtain a multi-resolution image. The present invention can obtain multi-resolution images simultaneously through a single scan, without the need for repeated scans of multiple parameters and additional registration and fusion, greatly improving the measurement efficiency. At the same time, the multi-resolution images can provide complementary information on structural localization and concentration quantification, which helps to guide clinical diagnosis.

Description

Background Art

[0002] Magnetic particle imaging (MPI) is a promising molecular imaging technique that enables highly sensitive quantitative visualization of superparamagnetic iron oxide nanoparticles (SPIONs) in the body. Generally, high-resolution MPI images provide fine structural information for accurate localization of tracer positions; highly sensitive MPI images have a high detection limit and can quantify tracer doses in low-concentration regions. However, the resolution and sensitivity metrics are mutually restrictive and difficult to achieve simultaneously. One is the classical MPI system, which usually selects certain scanning parameters during image reconstruction and can only obtain images of a single resolution. The other is multi-resolution images obtained by multiple scans with different parameters. It faces a repeated scanning process, and different scanning parameters lead to image offsets, and additional registration is required. This method is very time-consuming and laborious.

[0003] Based on this, the present invention proposes a multi-resolution magnetic particle imaging method and system based on parallel excitation of magnetic field free lines. Summary of the Invention

[0004] To solve the above problems in the prior art, that is, the problem that existing magnetic particle imaging technologies are difficult to simultaneously achieve high-resolution and high-sensitivity image reconstruction due to the use of fixed scanning parameters, the present invention provides a multi-resolution magnetic particle imaging method and system based on parallel excitation of magnetic field free lines.

[0005] In the first aspect of the present invention, a multi-resolution magnetic particle imaging method based on parallel excitation of magnetic field free lines is proposed. The method includes the following steps:

[0006] Step S1, construct a magnetic field environment through an excitation coil, a receiving coil, and selection and focusing coils arranged orthogonally to generate magnetic field free lines parallel to the direction of the excitation field;

[0007] Step S2, plan the scanning path of the magnetic field free lines through a control platform, and drive the input current of the selection and focusing coils to move the magnetic field free lines to the target position;

[0008] Step S3, after the magnetic field free lines move to the target position, turn on the alternating current of the excitation coil to generate an excitation field of a single frequency, and simultaneously collect the voltage signals induced by the receiving coil;

[0009] Step S4, process the collected voltage signals through a multi-channel digital lock-in amplifier, and based on the multi-harmonic signal mapping strategy of the non-linear response of magnetic particles, extract the amplitudes of different order harmonics as single pixel values;

[0010] Step S5, map the single pixel values corresponding to different order harmonics to the spatial positions of the magnetic field free lines to generate multi-resolution images;

[0011] Step S6, check whether the scanning of all spatial positions is completed. If completed, directly output the multi-resolution image; otherwise, jump to Steps S2 to S5 until the scanning of all spatial positions is completed.

[0012] Furthermore, the direction of the alternating excitation field generated by the excitation coil is parallel to the direction of the magnetic field free line, and the selection and focusing coils are used to dynamically adjust the spatial position of the magnetic field free line.

[0013] Furthermore, the scanning path of the magnetic field free line is planned through the control platform, specifically:

[0014] The imaging area is planned as discrete spatial points through the control platform, and the input current of the selection and focusing coils is driven to move the magnetic field free line to cover the entire field of view in a point-by-point scanning manner, where the target position of the magnetic field free line for each scan is the area where the corresponding spatial point is located.

[0015] Furthermore, based on the multi-harmonic signal mapping strategy of the non-linear response of magnetic particles, the amplitudes of different orders of harmonics are extracted as single pixel values, specifically:

[0016] A set of sine wave reference signals are respectively input to each digital lock-in amplifier, and their reference frequencies are respectively , n where is an integer and n ≥1;

[0017] The original voltage signals induced by the receiving coil are respectively synchronously demodulated with the reference frequency signals to separate the harmonic components of the corresponding orders;

[0018] The amplitudes of the harmonic components are measured through the digital lock-in amplifier, and the amplitudes are used as the single pixel values of the corresponding spatial positions.

[0019] On the other hand, the present invention proposes a multi-resolution magnetic particle imaging system based on parallel excitation of the magnetic field free line, based on a multi-resolution magnetic particle imaging method based on parallel excitation of the magnetic field free line. The system includes a magnetic field coil subsystem, a control platform subsystem, and a matching circuit subsystem;

[0020] The magnetic field coil subsystem includes at least one set of excitation coils for generating an alternating excitation field parallel to the magnetic field free line, at least one set of receiving coils for sensing the non-linear response signals of magnetic particles, and multiple sets of selection and focusing coils for generating and dynamically adjusting the spatial position of the magnetic field free line; wherein, the receiving coil and the excitation coil are coaxially arranged, and the opening directions of the receiving coil and the excitation coil coaxial are orthogonal to the opening direction of the selection and focusing coils;

[0021] The control platform subsystem includes a computer for planning the magnetic field free line scanning path, sending control instructions, and parsing received signals, a signal generator for generating drive excitation coil analog signals according to the computer instructions, and a data acquisition card for converting the analog signals of the receiving coil into digital signals;

[0022] The matching circuit subsystem includes multiple power amplifiers and signal conditioning circuits for amplifying the excitation signal and enhancing the detection ability of the magnetic particle response signal.

[0023] Further, the selection and focusing coils are 2 groups of Maxwell coil pairs for simultaneously generating and moving the position of the magnetic field free line.

[0024] Further, an alternating current is passed through the excitation coil to generate an alternating excitation field.

[0025] Further, the signal generator and the data acquisition card are synchronously managed through a unified clock signal to ensure the timing consistency of the excitation field output and the received signal acquisition.

[0026] Further, among multiple groups of selection and focusing coils, the axial directions of every two adjacent selection and focusing coils are perpendicular.

[0027] Further, the signal conditioning circuit includes: an impedance matching circuit, a band-pass circuit, a low-pass filter circuit, and a low-noise amplifier;

[0028] Each power amplifier is used to receive the analog excitation signal from the signal generator, directly send it to each selection and focusing coil, and send it to the excitation coil through the impedance matching circuit and the band-pass circuit;

[0029] The analog signal generated by the receiving coil is sent to the data acquisition card through the low-pass filter circuit and the low-noise amplifier.

[0030] Advantages of the present invention:

[0031] Multi-resolution image synchronous acquisition: By extracting the amplitudes of different order harmonics (such as high-order harmonics corresponding to high-resolution images and low-order harmonics corresponding to high-sensitivity images), a series of combined requirements for resolution and sensitivity are simultaneously obtained in a single scan, breaking through the limitation of the single imaging mode caused by fixed parameters in traditional MPI.

[0032] Significantly improved imaging efficiency: The parallel excitation of the magnetic field free line combined with the dynamic scanning path planning avoids the multiple repeated scans required to obtain different resolution images in the traditional method, greatly reducing the operation complexity and time cost, and is especially suitable for the real-time monitoring of dynamic biological processes.

[0033] Natural alignment of multi-modal data: The generated multi-resolution images are decoupled from the signals of the same scanning process, with completely consistent spatial positions, and can be directly fused without additional registration, providing complementary information for structural localization and concentration quantification.

[0034] Optimization of system stability and compatibility: The orthogonal coil layout and the magnetic field free line generation mechanism reduce the interference of magnetic field distortion. Combined with the multi-channel parallel signal processing design, it avoids the influence of electromagnetic noise when traditional systems switch parameters, improving the imaging reliability. Description of the Drawings

[0035] Other features, objects, and advantages of the present application will become more apparent by reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0036] Figure 1 is a schematic flow chart of a multi-resolution magnetic particle imaging method based on parallel excitation of magnetic field free lines of the present invention;

[0037] Figure 2 is a schematic diagram of multi-resolution image simulation in the multi-resolution magnetic particle imaging method based on parallel excitation of magnetic field free lines of the present invention;

[0038] Figure 3 is a schematic diagram of the connection relationship of a multi-resolution magnetic particle imaging system based on parallel excitation of magnetic field free lines of the present invention;

[0039] Figure 4 is a schematic structural diagram of a magnetic field coil subsystem in the multi-resolution magnetic particle imaging system based on parallel excitation of magnetic field free lines of the present invention. Detailed Description of the Invention

[0040] The present application will be further described in detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related invention, rather than limiting the invention. Additionally, it should be noted that for the convenience of description, only parts related to the relevant invention are shown in the drawings.

[0041] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present application will be described in detail below with reference to the drawings and embodiments.

[0042] The present invention provides a multi-resolution magnetic particle imaging method based on parallel excitation of magnetic field free lines, and the method includes the following steps:

[0043] Step S1, constructing a magnetic field environment through an excitation coil, a receiving coil, and a selection and focusing coil arranged orthogonally to generate magnetic field free lines parallel to the direction of the excitation field;

[0044] Step S2, plan the scanning path of the magnetic free line through the control platform, and drive the input current of the selection and focusing coils to move the magnetic free line to the target position;

[0045] Step S3, after the magnetic free line moves to the target position, turn on the alternating current of the excitation coil to generate an excitation field with a single frequency, and simultaneously collect the voltage signal induced by the receiving coil;

[0046] Step S4, process the collected voltage signal through a multi-channel digital lock-in amplifier, and based on the multi-harmonic signal mapping strategy of the non-linear response of magnetic particles, extract the amplitudes of different orders of harmonics as single pixel values;

[0047] Step S5, map the single pixel values corresponding to different orders of harmonics to the spatial position of the magnetic free line to generate a multi-resolution image;

[0048] Step S6, check whether all spatial positions have been scanned. If completed, directly output the multi-resolution image; otherwise, jump to Step S2 to Step S5 until all spatial positions have been scanned.

[0049] For a clearer description of a multi-resolution magnetic particle imaging method based on parallel excitation of magnetic free lines according to the present invention, the following will be combined with Figure 1 Expand and detail each step in the embodiments of the present invention.

[0050] A multi-resolution magnetic particle imaging method based on parallel excitation of magnetic free lines according to the first embodiment of the present invention includes Step S1 - Step S5, and each step is described in detail as follows:

[0051] Step S1, construct a magnetic field environment through an excitation coil, a receiving coil, and selection and focusing coils arranged orthogonally to generate a magnetic free line parallel to the direction of the excitation field;

[0052] Among them, the alternating excitation field generated by the excitation coil in this embodiment is parallel to the direction of the magnetic free line. The selection and focusing coils are used to dynamically adjust the spatial position of the magnetic free line. More specifically, the receiving coil and the excitation coil are coaxially arranged, and the opening directions of the receiving coil and the excitation coil coaxial are orthogonal to the opening directions of the selection and focusing coils.

[0053] Step S2, plan the scanning path of the magnetic free line through the control platform, and drive the input current of the selection and focusing coils to move the magnetic free line to the target position;

[0054] In this embodiment, the imaging area is planned as discrete spatial points by the control platform, and the currents of the selection and focusing coils are driven to move the field-free line to cover the entire field of view in a point-by-point scanning manner. Among them, each discrete point corresponds to the target position of the field-free line, and the current control of the selection and focusing coils satisfies the following relationship:

[0055] ;

[0056] Among them, y and z represent the distances of the FFL in the corresponding directions from the center of the field of view, which are controlled by the focusing field parameters and in two directions. and are gradient field parameters. By adjusting and the field-free line is moved to any target position within the field of view;

[0057] Step S3: After the field-free line moves to the target position, turn on the alternating current of the excitation coil to generate an excitation field with a single frequency, and simultaneously collect the voltage signal induced by the receiving coil;

[0058] Step S4: Process the collected voltage signal through a multi-channel digital lock-in amplifier, and based on the multi-harmonic signal mapping strategy of the magnetic particle non-linear response, extract the amplitudes of different orders of harmonics as single-pixel values;

[0059] Specifically, input a set of sine wave reference signals into each digital lock-in amplifier respectively, and their reference frequencies are , n where n is an integer and n ≥1;

[0060] Synchronously demodulate the original voltage signal induced by the receiving coil with each reference frequency signal to separate the harmonic components of the corresponding orders;

[0061] Measure the amplitudes of each harmonic component through a digital lock-in amplifier, and use the amplitudes as the single-pixel values of the corresponding spatial positions.

[0062] Among them, the harmonic component model is represented by the following formula:

[0063] ;

[0064] Among them, is the frequency component (regarded as the PSF distribution here), T is the excitation period, is the magnetization combination of excitation and reception in the x direction, is the excitation amplitude, is the local magnetic field of the excitation region is the second kind of Chebyshev polynomial.

[0065] The system function reflects the relationship between the spatial position of the SPIONs tracer and the frequency response. However, for MPI imaging a single harmonic, the distribution of the point spread function (PSF) is equivalent to the spatial dependence of the frequency components in the system function. Mathematically, the spatial dependence of the frequency components can be modeled as the convolution of the magnetization combination and the one-dimensional Chebyshev in the direction of the driving field.

[0066] The frequency response model of the harmonic component is defined by the following formula:

[0067] ;

[0068] O x is the static bias field, n is the harmonic order, is the saturation magnetization of the magnetic particles.

[0069] Step S5, map the single-pixel values corresponding to different order harmonics to the spatial positions of the field-free lines to generate a multi-resolution image;

[0070] The field-free lines satisfy the requirement that the absolute values of the orthogonal direction gradients are equal, i.e.: .

[0071] The point spread function model of the image reconstruction module can be described by the following formula:

[0072] ;

[0073] where, , represents the sensitivity calibration coefficient constant, which is jointly determined by factors such as the reception sensitivity, gradient, and particle characteristics.

[0074] As Figure 2 shows, it is a multi-resolution image simulation, showing the 1D simulation results of the 3rd, 4th, 5th, 6th, and 11th order harmonics. Among them, a certain bias field needs to be applied along the excitation direction during the MPI scans of the even harmonics of the 4th and 6th orders.

[0075] The PSF in the ideal case is simulated according to the mathematical model. Among them, the magnetization component is convolved with the one-dimensional Chebyshev polynomial to obtain the 2D system function. Taking the center of the image as the reference point, the vertical direction represents the magnitude of the bias field applied along the field-free line, and the horizontal direction represents the position. It can be observed that as the harmonic order increases, the PSF shrinks towards the center. This may be because the magnetization component has a more blurred convolution kernel at a far distance from the center, making the fine structure of the higher-order Chebyshev polynomial averaged close to 0.

[0076] In summary, the resolutions of different harmonic orders in MPI are different. Moreover, as the harmonic order increases, the resolution of the single-harmonic MPI image increases.

[0077] Step S6: Check whether all spatial positions have been scanned. If so, directly output the multi-resolution image; otherwise, jump to Steps S2 to S5 until all spatial positions have been scanned.

[0078] After jumping to Step S2, switch to a new scanning position and start a new round of scanning from the selection of the spatial position.

[0079] Although the various steps have been described in the above sequential order in the above embodiments, those skilled in the art can understand that, in order to achieve the effects of this embodiment, different steps do not have to be executed in such an order. They can be executed simultaneously (in parallel) or in a reversed order, and these simple changes are all within the protection scope of the present invention.

[0080] A multi-resolution magnetic particle imaging system based on parallel excitation of magnetic field free lines according to the second embodiment of the present invention is based on the multi-resolution magnetic particle imaging method based on parallel excitation of magnetic field free lines described in the first embodiment. The system includes a magnetic field coil subsystem, a control platform subsystem, and a matching circuit subsystem;

[0081] The magnetic field coil subsystem includes at least one set of excitation coils for generating an alternating excitation field parallel to the magnetic field free line, at least one set of receiving coils for sensing the non-linear response signal of the magnetic particles, and multiple sets of selection and focusing coils for generating and dynamically adjusting the spatial position of the magnetic field free line; wherein, the opening direction of the selection and focusing coils is orthogonal to that of the excitation coils and the receiving coils; among the multiple sets of selection and focusing coils, the axial directions of every two adjacent selection and focusing coils are perpendicular.

[0082] The control platform subsystem includes a computer for planning the scanning path of the magnetic field free line, sending control instructions, and analyzing the received signals, a signal generator for generating a driving analog signal for the excitation coils according to the computer instructions, and a data acquisition card for converting the analog signal of the receiving coils into a digital signal;

[0083] The matching circuit subsystem includes multiple power amplifiers and signal conditioning circuits for amplifying the excitation signal and enhancing the detection ability of the magnetic particle response signal.

[0084] Next, in combination with Figure 3 and Figure 4 further explanation will be given for this system. Specifically:

[0085] In this embodiment, one set of receiving coil and one set of exciting coil are provided. The selection and focusing coils are provided in four sets and are arranged around the exciting coil. The axial directions of the receiving coil and the exciting coil are in the x-axis direction. Among the selection and focusing coils, the axial directions of two of them are in the y-axis, and the axial directions of the other two selection and focusing coils are in the z-axis. In other words, the receiving coil and the exciting coil are coaxially arranged, and the opening directions of the receiving coil and the exciting coil that are coaxial are orthogonal to the opening directions of the selection and focusing coils.

[0086] The selection and focusing coils are 2 sets of Maxwell coil pairs, which are used to simultaneously generate and move the position of the magnetic field free line.

[0087] Among them, the method for generating the alternating excitation field is: passing an alternating current through the exciting coil to generate an alternating excitation field.

[0088] The receiving coil and the exciting coil are coaxially arranged from the inside to the outside, and the imaging field of view is set inside the receiving coil.

[0089] Among them, in this embodiment, the signal generator and the data acquisition card are synchronously managed through a unified clock signal to ensure the timing consistency of the excitation field output and the received signal acquisition.

[0090] The signal conditioning circuit includes: an impedance matching circuit, a band-pass circuit, a low-pass filter circuit, and a low-noise amplifier;

[0091] Each power amplifier is used to receive the analog excitation signal from the signal generator, directly send it to each selection and focusing coil, and send it to the exciting coil through the impedance matching circuit and the band-pass circuit;

[0092] The analog signal generated by the receiving coil is sent to the data acquisition card through the low-pass filter circuit and the low-noise amplifier.

[0093] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working process and related descriptions of the above-described system can refer to the corresponding process in the foregoing method embodiment, and will not be repeated here.

[0094] It should be noted that the multi-resolution magnetic particle imaging system based on parallel excitation of magnetic field free lines provided in the above embodiments is only illustrated by dividing the above functional modules. In practical applications, the above functions can be allocated to different functional modules according to needs, that is, the modules or steps in the embodiments of the present invention can be further decomposed or combined. For example, the modules in the above embodiments can be combined into one module, or further split into multiple sub-modules to complete all or part of the functions described above. For the names of the modules and steps involved in the embodiments of the present invention, they are only used to distinguish each module or step, and are not regarded as an improper limitation of the present invention.

[0095] An electronic device according to a third embodiment of the present invention includes:

[0096] At least one processor; and

[0097] A memory communicatively connected to at least one of the processors; wherein,

[0098] The memory stores instructions executable by the processor, and the instructions are used to be executed by the processor to implement the above-mentioned multi-resolution magnetic particle imaging method based on parallel excitation of magnetic field free lines.

[0099] A computer-readable storage medium according to a fourth embodiment of the present invention stores computer instructions, and the computer instructions are used to be executed by the computer to implement the above-mentioned multi-resolution magnetic particle imaging method based on parallel excitation of magnetic field free lines.

[0100] Those skilled in the art can clearly understand that for the convenience and conciseness of description, the specific working processes and related descriptions of the above-mentioned storage device and processing device can refer to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0101] Those skilled in the art should be able to realize that the modules and method steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of the two. The programs corresponding to the software modules and method steps can be placed in a random access memory (RAM), internal memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium well-known in the technical field. To clearly illustrate the interchangeability of electronic hardware and software, the composition and steps of each example have been generally described according to functions in the above description. Whether these functions are executed in the form of electronic hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0102] The terms "first", "second", etc. are used to distinguish similar objects, rather than to describe or represent a specific order or sequence.

[0103] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, so that a process, method, article, or device / apparatus comprising a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent in these process, method, article, or device / apparatus.

[0104] So far, the technical solution of the present invention has been described in combination with the preferred embodiments shown in the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present invention.

Claims

1. A multi - resolution magnetic particle imaging method based on parallel excitation of magnetic field free lines, characterized in that The method includes the following steps: Step S1: Construct a magnetic field environment through an excitation coil, a receiving coil, and selection and focusing coils arranged orthogonally, and generate magnetic field free lines parallel to the direction of the excitation field. Step S2: Plan the scanning path of the magnetic field free lines through a control platform, and drive the input current of the selection and focusing coils to move the magnetic field free lines to the target position. Step S3: After the magnetic field free lines move to the target position, turn on the alternating current of the excitation coil to generate an excitation field with a single frequency, and simultaneously collect the voltage signals induced by the receiving coil. Step S4: Process the collected voltage signals through a multi-channel digital lock-in amplifier, and based on the multi-harmonic signal mapping strategy of the non-linear response of magnetic particles, extract the amplitudes of different-order harmonics as single pixel values. Step S5: Map the single pixel values corresponding to different-order harmonics to the spatial positions of the magnetic field free lines to generate a multi-resolution image. Step S6: Check whether all spatial positions have been scanned. If completed, directly output the multi-resolution image; otherwise, jump to Step S2 to Step S5 until all spatial positions have been scanned.

2. The multi - resolution magnetic particle imaging method based on parallel excitation of magnetic field free lines according to claim 1, wherein The alternating excitation field generated by the excitation coil is parallel to the direction of the magnetic field free lines, and the selection and focusing coils are used to dynamically adjust the spatial position of the magnetic field free lines.

3. A multi-resolution magnetic particle imaging method based on parallel excitation of magnetic field free lines according to claim 1, characterized in that, Planning the scanning path of the magnetic field free lines through the control platform specifically includes: The control platform plans the imaging area as discrete spatial points, and drives the input current of the selection and focusing coils to move the magnetic field free lines to cover the entire field of view in a point-by-point scanning manner. Among them, the target position of the magnetic field free lines for each scan is the area where the corresponding spatial point is located.

4. A multi-resolution magnetic particle imaging method based on parallel excitation of magnetic field free lines according to claim 1, characterized in that, Based on the multi-harmonic signal mapping strategy of the non-linear response of magnetic particles, extracting the amplitudes of different-order harmonics as single pixel values specifically includes: A set of sine wave reference signals are respectively input into each digital lock-in amplifier, and their reference frequencies are respectively , n where m is an integer and n ≥ 1; Synchronously demodulate the original voltage signals induced by the receiving coil with each reference frequency signal to separate the harmonic components of the corresponding order. Measure the amplitudes of each harmonic component through a digital lock-in amplifier, and use the amplitudes as the single pixel values of the corresponding spatial positions.

5. A multi-resolution magnetic particle imaging system based on parallel excitation of magnetic field free lines, based on the method for multi-resolution magnetic particle imaging based on parallel excitation of magnetic field free lines according to any one of claims 1-4, characterized in that, The system includes a magnetic field coil subsystem, a control platform subsystem, and a matching circuit subsystem. The magnetic field coil subsystem includes at least one group of excitation coils for generating an alternating excitation field parallel to the magnetic field free lines, at least one group of receiving coils for sensing the non-linear response signals of magnetic particles, and multiple groups of selection and focusing coils for generating and dynamically adjusting the spatial position of the magnetic field free lines. Among them, the receiving coil and the excitation coil are coaxially arranged, and the opening directions of the receiving coil and the excitation coil coaxial are orthogonal to the opening direction of the selection and focusing coils. The control platform subsystem includes a computer for planning the scanning path of the magnetic field free lines, sending control instructions, and parsing received signals, a signal generator for generating a driving analog signal for the excitation coil according to the computer instructions, and a data acquisition card for converting the analog signal of the receiving coil into a digital signal. The matching circuit subsystem includes multiple power amplifiers and signal conditioning circuits for amplifying the excitation signal and enhancing the detection ability of the magnetic particle response signal.

6. A multi-resolution magnetic particle imaging system based on parallel excitation of magnetic field free lines according to claim 5, characterized in that, The selection and focusing coils are 2 groups of Maxwell coil pairs, which are used to simultaneously generate and move the position of the magnetic field free lines.

7. A multi-resolution magnetic particle imaging system based on parallel excitation of magnetic field free lines according to claim 5, characterized in that, An alternating current is applied to the excitation coil to generate an alternating excitation field.

8. A multi-resolution magnetic particle imaging system based on parallel excitation of magnetic field free lines according to claim 5, characterized in that, The signal generator and the data acquisition card are synchronously managed through a unified clock signal to ensure the timing consistency between the excitation field output and the received signal acquisition.

9. A multi-resolution magnetic particle imaging system based on parallel excitation of magnetic field free lines according to claim 5, characterized in that, Among the multiple sets of selection and focusing coils, the axial directions of every two adjacent selection and focusing coils are perpendicular to each other.

10. A multi-resolution magnetic particle imaging system based on parallel excitation of magnetic field free lines according to claim 5, characterized in that, The signal conditioning circuit includes: an impedance matching circuit, a band-pass circuit, a low-pass filter circuit, and a low-noise amplifier; Each power amplifier is used to receive the analog excitation signal from the signal generator, directly send it to each selection and focusing coil, and send it to the excitation coil through the impedance matching circuit and the band-pass circuit; The analog signal generated by the receiving coil is sent to the data acquisition card through the low-pass filter circuit and the low-noise amplifier.

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