System function calibration method and device for non-magnetic field line magnetic particle imaging

Abstract

The invention belongs to the field of magnetic particle imaging, particularly relates to a system function calibration method and device for magnetic particle imaging without magnetic field lines, and aims to solve the problem of poor system function effect during magnetic particle image reconstruction in the prior art. The method comprises the following steps: acquiring an empty background signal, and fixing a calibration phantom at a central position without a magnetic field line; according to the normal direction of the non-magnetic-field line, moving the non-magnetic-field line or calibrating the phantom and synchronously acquiring an original signal; according to the empty background signal and the original signal, determining an effective signal and extracting a target signal; constructing a mapping array according to the relative distance between the non-magnetic field line and the calibration phantom, performing up-sampling, and mapping to a calibration space of a system function; and calculating the relative distance of each point in the system function and pairing and filling the calibration data to obtain a calibrated system function. According to the method, the measurement and calibration of the system function can be completed only by gradually scanning the non-magnetic field line along the normal single direction, the interference is small, and the efficiency and the accuracy are higher.

Description

Technical Field

[0001] The present invention belongs to the field of magnetic particle imaging, and particularly relates to a method and device for calibrating a system function of magnetic particle imaging without magnetic field lines. Background Art

[0002] Magnetic Particle Imaging (MPI) is a new generation of multifunctional tomographic imaging equipment. By utilizing the non-linear magnetization response characteristics of ferromagnetic contrast agents - superparamagnetic iron oxide nanoparticles (SPIO), it realizes the imaging of the spatial distribution of magnetic particles. The MPI system has characteristics such as no imaging depth limitation, high spatial resolution, and high sensitivity, and has been proven suitable for applications such as vascular imaging, cell tracing, and cancer detection.

[0003] In the process of magnetic particle image reconstruction, the system function imaging algorithm is one of the most widely used imaging algorithms currently. The accurate and high-quality acquisition of the system function is an important prerequisite for this imaging algorithm. At present, the system function is mainly obtained by directly measuring the vertical and horizontal movement of a point-like phantom in the field of view. This measurement method is simple, but it also faces many problems, resulting in poor effects, specifically manifested as: ① long measurement time and low efficiency; after long-term operation, the coil temperature rises, resulting in large measurement errors of the system function; ② the point-like phantom is small, the signal is weak, and the signal-to-noise ratio is low, resulting in low quality of the system function; ③ it is necessary to use a displacement platform to repeatedly move and calibrate the phantom to each sampling point in the entire field of view, resulting in an increase in position cumulative error and a large deviation of the measured system function (especially for the system function of high-resolution and large field of view). Summary of the Invention

[0004] To solve the above problems in the prior art, that is, the technical problem of poor system function effect in magnetic particle image reconstruction in the prior art, the present invention proposes a method for calibrating the system function of magnetic particle imaging without magnetic field lines, which is applied to a magnetic particle imaging system. There are no magnetic field lines inside the magnetic particle imaging system. The method includes: Obtaining the empty background signal of the calibration sample outside the magnetic particle imaging system; Fixing the calibration phantom at the central position of the magnetic field-free line, making the calibration phantom parallel to the magnetic field-free line. The calibration phantom is a single-dimensional multi-voxel long-strip calibration phantom; Moving the magnetic field-free line or the calibration phantom in the normal direction of the magnetic field-free line to change the relative distance between the magnetic field-free line and the calibration phantom, and synchronously collecting the original signals between the magnetic field-free line and the calibration phantom at different relative distances; Determine the effective signal based on the empty background signal and the original signal, and perform Fourier analysis on the effective signal to extract the target signal that meets the preset frequency domain; Construct a mapping array according to the relative distance between the field-free line and the calibration phantom, and perform upsampling on the target signal according to the mapping array and map it to the calibration space of the system function; Calculate the relative distance between the field-free line and the calibration phantom corresponding to each point in the system function and pair and fill the calibration data to obtain the calibrated system function.

[0005] In some preferred embodiments, the effective signal satisfies: ; wherein, is the effective signal, is the original signal at different relative distances between the field-free line and the calibration phantom, is the empty background signal.

[0006] In some preferred embodiments, the method further includes: Solve for the magnetic particle concentration distribution information according to the preset linear equation based on the system function matrix to complete magnetic particle image reconstruction, and the linear equation is: ; wherein, A is the system function, X is the magnetic particle concentration distribution information, is the target signal.

[0007] In some preferred embodiments, the moving of the field-free line or the calibration phantom specifically includes: Gradually move the field-free line in the target direction, the target direction is perpendicular to the field-free line, and the calibration phantom remains fixed during the movement of the field-free line; During the movement of the field-free line, the corresponding number of measurement times is , wherein, is the polar coordinate distance of the sample points in the calibration space, is the number of rotation angles of the field-free line and the polar coordinate angle of the sample points in the calibration space, is the number of translation layers.

[0008] In some preferred embodiments, the relative distance between the field-free line and the calibration phantom is specifically: ; wherein, is the relative distance between the field-free line and the calibration phantom, For calibrating the radial distance between the sample and the origin of the coordinate system, For the current polar angle without magnetic field lines (FFL), For the initial polar angle of the calibration sample, For the polar angle difference between the magnetic field line-free and the calibration sample.

[0009] The present invention also proposes a system function calibration device for implementing the above method, and the device includes: A calibration phantom configured to be parallel to the direction of the magnetic field line-free; A phantom holder for fixing the calibration phantom so that the one-dimensional multi-voxel strip-shaped calibration phantom is at the center position of the magnetic field line-free; A movement control unit for driving the magnetic field line-free to translate step by step along its normal direction to change the relative distance between the magnetic field line-free and the one-dimensional multi-voxel strip-shaped calibration phantom; A data acquisition unit for acquiring the original signals of the magnetic field line-free and the one-dimensional multi-voxel strip-shaped calibration phantom at different relative distances and performing background elimination on the original signals; A system function construction unit for generating a complete system function matrix according to the relative distance and combining the original signals after background filtering.

[0010] In some preferred embodiments, the device further includes: An image reconstruction unit for reconstructing the magnetic particle concentration distribution according to the system function matrix and the solution algorithm.

[0011] In some preferred embodiments, the calibration phantom is a one-dimensional multi-voxel strip-shaped calibration phantom, and the one-dimensional multi-voxel strip-shaped calibration phantom is filled with superparamagnetic iron oxide nanoparticle phantoms uniformly distributed therein.

[0012] In some preferred embodiments, the movement control unit drives the magnetic field line-free by an electric drive method, and the calibration phantom remains fixed during the process of the movement control unit driving the magnetic field line-free.

[0013] In some preferred embodiments, the length of the one-dimensional multi-voxel strip-shaped calibration phantom matches the aperture of the magnetic particle imaging device.

[0014] Advantages of the present invention: (1) The present invention solves the problem of low signal-to-noise ratio of the dot-like phantom by using a single-dimensional multi-voxel calibration sample (the traditional method needs to measure all positions in space, so only dot-like samples can be used for measurement); simplifies the measurement steps through relative position mapping, enabling the measurement of the system matrix to obtain the system matrix data of the full field of view only by changing the relative distance between the field-free line and the calibration sample, solving the problems of long acquisition time, low efficiency, and large error in obtaining the traditional system function; and solves the problem of large cumulative position error caused by a large number of sampling points by moving the field-free line or the calibration sample separately in one direction and combining sparse measurement. Therefore, the method proposed by the present invention has the advantages of simplicity, high efficiency, and high signal quality, and is of great significance for systems using the system function reconstruction method.

[0015] (2) Compared with the existing system function calibration method that requires point-by-point calibration of all positions, all FFL rotation angles, and scanning layers in the calibration space, resulting in a large number of measurements, low efficiency, and since the FFL needs to be rotated, only dot-like samples can be used for calibration instead of long bar-shaped samples, leading to low signal-to-noise ratio, the method of the present invention only needs to gradually scan the FFL along the normal direction to complete the measurement of the system function, greatly shortening the measurement time and having high efficiency. In addition, since the FFL does not need to be rotated and long bar-shaped samples are used for calibration, the signal-to-noise ratio is high and the quality of the system function is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Other features, objects, and advantages of the present application will become more apparent by reading the detailed description of the non-limiting embodiments with reference to the following drawings: Figure 1 is a schematic flow chart of a method and device for calibrating the system function of a field-free line magnetic particle imaging proposed in an embodiment of the present invention; Figure 2 is a schematic illustration of a traditional calibration method proposed in an embodiment of the present invention; Figure 3 is a schematic diagram of the position distribution of the calibration sample and the field-free line during the system function calibration of the invention; Figure 4 is a schematic diagram of the process of constructing the system function in the system function calibration method of the present invention; Figure 5 is a schematic structural diagram of the calibration sample and its supporting device adopted by the present invention; Figure 6 is a schematic structural diagram of the computer system of the server for implementing the method and system embodiments of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] The present application will be further described in detail below with reference to the accompanying 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. In addition, it should be noted that for the convenience of description, only the parts related to the invention are shown in the drawings.

[0018] 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.

[0019] Referring to Figure 1 , as Figure 1 shown, the present invention provides a method and device for calibrating the system function of magnetic particle imaging without magnetic field lines, including: Step S10, obtaining an empty background signal when the calibration sample is outside the magnetic particle imaging system; Step S20, fixing the calibration phantom at the central position of the magnetic field line-free region, making the calibration phantom parallel to the magnetic field line-free region, and the calibration phantom is a single-dimensional multi-voxel long-strip calibration phantom; Step S30, moving the magnetic field line-free region or the calibration phantom in the normal direction of the magnetic field line-free region to change the relative distance between the magnetic field line-free region and the calibration phantom, and synchronously collecting the original signals between the magnetic field line-free region and the calibration phantom at different relative distances; Step S40, determining the effective signal according to the empty background signal and the original signal, and performing Fourier analysis on the effective signal to extract the target signal that meets the preset frequency domain; Step S50, constructing a mapping array according to the relative distance between the magnetic field line-free region and the calibration phantom, and performing upsampling on the target signal according to the mapping array and mapping it to the calibration space of the system function; Step S60, calculating the relative distance between the magnetic field line-free region and the calibration phantom corresponding to each point in the system function and filling the calibration data in pairs to obtain the calibrated system function.

[0020] It should be noted that, in order to achieve the purpose of the present invention, a single-dimensional multi-voxel sample is used in this embodiment, and the single-dimensional multi-voxel sample corresponds to a supporting phantom bracket.

[0021] The calibration method of this embodiment uses the relative position relationship between the calibration sample and the FFL (i.e., the magnetic field line-free region) to quickly reconstruct the system function. By controlling the FFL to move along the normal direction of the FFL, all relative distance data between the sample and the FFL are obtained to achieve the function of inertial-free measurement, further reducing the cumulative error and noise interference caused by mechanical displacement.

[0022] Specifically, let be the number of grids in the cylindrical calibration space, As the polar coordinate distance of the sample points within the calibration space, As the number of FFL rotation angles and the polar coordinate angles of the sample points within the calibration space, As the number of translation layers. The traditional system function calibration method requires calibration at each grid position of each layer separately. At the same time, at each position, FFL rotation and layer movement are required, and sequential measurements are needed for each point. Therefore, the traditional three-dimensional system function calibration requires measurements.

[0023] Those skilled in the art can understand that, regarding the rotational movement characteristics of the scanner, through the analysis of the cylindrical calibration space, there are many repetitions in the displacement between the FFL and the dot-like sample. Utilizing this redundancy, in this embodiment, relative distance mapping is used within the calibration space to calibrate the system matrix.

[0024] More specifically, please refer to Figure 2 , as Figure 2 shown in the schematic diagram for the description of the traditional calibration method in the present invention. As shown in the figure, in the left part of Figure 2 , by rotating or moving the FFL, as long as the relative position between the calibration sample and the FFL remains unchanged, the calibration signals generated are the same; Figure 2 In the right part of , the calibration space is divided into a grid. The entire two-dimensional plane is divided into grid points, and the relative position relationship between the FFL and is illustrated. The relative distance is recorded as:

[0025] Based on such understanding, the dot-like calibration sample only needs to be gradually moved along the direction perpendicular to the FFL. That is, by controlling the FFL to gradually move along the direction perpendicular to the FFL and keeping the calibration sample stationary, all the relative distance data between the sample and the FFL can be obtained. Further, through the mapping relationship, the system function can be reconstructed. By this method, the number of measurements can be reduced to measurements.

[0026] In addition, considering the gradient magnetic field, excitation magnetic field, and the uniformity of the sensitivity along the direction of the magnetic field free line, in this embodiment, a long strip-shaped calibration sample parallel to the magnetic field free line (i.e., the above-mentioned single-dimensional multi-voxel long strip-shaped calibration phantom) is used to replace the dot-like sample in the traditional method to obtain a higher signal-to-noise ratio, thereby obtaining a higher-quality system function.

[0027] In a more optimal implementation, since only the electric drive FFL needs to be moved and the calibration sample does not need to be moved, the long bar-shaped calibration sample can be set to the longest within the limited aperture space without being restricted by the limit problem of vertical movement, thereby maximizing the signal-to-noise ratio.

[0028] Further, please refer to Figure 3 , Figure 3 which is a schematic diagram of the position distribution of the calibration sample and the magnetic field-free lines during the calibration of the system function in the invention. Among them, the calibration sample is placed at the center of the device aperture, and the FFL or the calibration sample is gradually translated (the most efficient solution is to gradually scan the FFL) to change the relative distance between the calibration sample and the FFL. After completing the grid division, all measurements (a more optimal solution is to use the sparse sampling method for measurement and perform upsampling recovery during the construction of the system function) can be completed, and the information measurement of all sample points required for the system function can be completed; Figure 3 is a calibration schematic diagram between the FFL and the sample at different layers in three-dimensional space. Similarly, after fixing the calibration sample on a certain layer (the optimal solution is the central layer), the FFL is gradually moved to scan at different layers to complete the information measurement of the distance between the calibration sample and the FFL at different layers.

[0029] Figure 4 is the process of constructing the system function in the system function calibration method of the present invention. First, the above sparse sampling data is upsampled according to all the relative distance quantities after grid division to complete the calibration construction of the initial function, and then it is mapped to the column vector model of the system function rule, and according to the calculation of the relative distance , it is mapped back to the complete system function A.

[0030] Based on the system function, the magnetic particle concentration distribution information is solved according to a preset linear equation to complete the magnetic particle image reconstruction. The linear equation is: ; In the formula, A is the system function, x is the magnetic particle concentration distribution information, is the target signal.

[0031] More specifically, in the above embodiment, the effective signal satisfies: ; In the formula, is the effective signal, is the original signal between the magnetic field-free line and the calibration phantom at different relative distances, is the empty background signal.

[0032] More specifically, in the above embodiments, moving the field-free line or the calibration phantom specifically includes: Gradually move the field-free line in the target direction, where the target direction is perpendicular to the field-free line, and the calibration phantom remains fixed during the movement of the field-free line; During the movement of the field-free line, the number of measurement times corresponds to , where is the polar coordinate distance of the sample point in the calibration space, is the number of rotations of the field-free line and the polar coordinate angle of the sample point in the calibration space, is the number of translation layers.

[0033] More specifically, in the above embodiments, the relative distance between the field-free line and the calibration phantom is specifically: ; In the formula, is the relative distance between the field-free line and the calibration phantom, is the radial distance between the calibration sample and the origin of the coordinate system, is the current polar angle of the field-free line (FFL), is the initial polar angle of the calibration sample, is the polar angle difference between the field-free line and the calibration sample.

[0034] Among them, the origin of the above coordinate system is the origin in the reference coordinate system constructed after grid division of the calibration space.

[0035] The present invention proposes a system function calibration device for implementing the above method, specifically including: A calibration phantom configured to be parallel to the direction of the field-free line; A phantom support for fixing the calibration phantom so that the single-dimensional multi-voxel long strip calibration phantom is at the center position of the field-free line; A movement control unit for driving the field-free line to gradually translate along its normal direction to change the relative distance between the field-free line and the single-dimensional multi-voxel long strip calibration phantom; A data acquisition unit for collecting the original signals of the field-free line and the single-dimensional multi-voxel long strip calibration phantom at different relative distances and eliminating the background of the original signals; A system function construction unit for upsampling and mapping the sparse sampling data according to the relative distance to generate a complete system function matrix; the specific process can refer to the above method.

[0036] More specifically, the device further includes: An image reconstruction unit for reconstructing the magnetic particle concentration distribution according to the system function matrix and the solution algorithm.

[0037] More specifically, the calibration phantom is a single-dimensional multi-voxel strip-shaped calibration phantom, and the interior of the single-dimensional multi-voxel strip-shaped calibration phantom is filled with superparamagnetic iron oxide nanoparticle (SPIO) phantoms with a uniform distribution.

[0038] More specifically, the movement control unit drives the field-free line by an electric drive method, and the calibration phantom remains fixed during the process of the movement control unit driving the field-free line.

[0039] More specifically, the length of the single-dimensional multi-voxel strip-shaped calibration phantom matches the aperture of the magnetic particle imaging device.

[0040] Please refer to Figure 5 , Figure 5 which is a structural diagram of the calibration sample and its supporting device belonging to the present invention. First, magnetic particles are injected into the phantom 3, and the calibration sample 2 is installed in the calibration sample holder 1. The system is run, and background sampling without a sample is performed outside the magnetic particle imaging device 4 and recorded. Then, the calibration sample 2 is sent into the magnetic particle imaging device 4 and is in the center position of the FFL, and the FFL is controlled to be in a position parallel to the sample.

[0041] Next, refer to Figure 6 , which shows a schematic structural diagram of a computer system of a server suitable for implementing the method and system embodiments of the present application. Figure 6 The server shown is only an example and should not impose any limitations on the functions and usage scope of the embodiments of the present application.

[0042] As Figure 6 shown, the computer system includes a central processing unit (CPU, Central Processing Unit) 301, which can perform various appropriate actions and processes according to the program stored in the read-only memory (ROM, Read Only Memory) 302 or the program loaded from the storage section 308 into the random access memory (RAM, Random Access Memory) 303. In the RAM 303, various programs and data required for system operation are also stored. The CPU 301, ROM 302, and RAM 303 are connected to each other through a bus 304. The input / output (I / O, Input / Output) interface 305 is also connected to the bus 304.

[0043] The following components are connected to the I / O interface 305: an input section 306 including a keyboard, a mouse, etc.; an output section 307 including a cathode ray tube (CRT), a liquid crystal display (LCD), etc. and a speaker, etc.; a storage section 303 including a hard disk, etc.; and a communication section 309 including a network interface card such as a LAN (Local Area Network) card, a modem, etc. The communication section 309 performs communication processing via a network such as the Internet. A drive 310 is also connected to the I / O interface 305 as required. A removable medium 311, such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, etc., is mounted on the drive 310 as required so that a computer program read therefrom is installed into the storage section 308 as required.

[0044] Specifically, according to an embodiment of the present invention, the processes described above with reference to the flowchart can be implemented as a computer software program. For example, an embodiment of the present invention includes a computer program product that includes a computer program carried on a computer-readable medium, and the computer program includes program code for performing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from a network via the communication section 309, and / or installed from the removable medium 311. When the computer program is executed by a central processing unit (CPU) 301, the above functions defined in the method of the present application are executed. It should be noted that the above computer-readable medium in the present application can be a computer-readable signal medium or a computer-readable storage medium or any combination of the two. The computer-readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination of the above.

[0045] More specific examples of computer-readable storage media may include, but are not limited to: electrical connections with one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing. In the present application, a computer-readable storage medium may be any tangible medium that contains or stores a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. In the present application, a computer-readable signal medium may include a data signal propagated in a baseband or as part of a carrier wave, which carries computer-readable program code. Such a propagated data signal may take many forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the foregoing. A computer-readable signal medium may also be any computer-readable medium other than a computer-readable storage medium, which can send, propagate, or transmit a program for use by or in conjunction with an instruction execution system, apparatus, or device. The program code contained on a computer-readable medium may be transmitted using any appropriate medium, including but not limited to: wireless, wire, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

[0046] Computer program code for performing the operations of the present application may be written in one or more programming languages or combinations thereof. The foregoing programming languages include object-oriented programming languages such as Java, Smalltalk, C++, and also include conventional procedural programming languages such as the "C" language or similar programming languages. The program code may execute entirely on the user's computer, partially on the user's computer, as a stand-alone software package, partially on the user's computer and partially on a remote computer, or entirely on the remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., through the Internet using an Internet service provider).

[0047] The flowcharts and block diagrams in the accompanying drawings illustrate the possible architectures, functions, and operations of systems, methods, and computer program products according to various embodiments of the present application. In this regard, each block in the flowchart or block diagram may represent a module, a segment of a program, or a portion of code that contains one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions noted in the blocks may occur in a different order than that noted in the accompanying drawings. For example, two consecutive blocks shown may actually be executed substantially in parallel, and they may sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that each block in the block diagram and / or flowchart, and combinations of blocks in the block diagram and / or flowchart, may be implemented by a dedicated hardware-based system that performs the specified functions or operations, or may be implemented by a combination of dedicated hardware and computer instructions.

[0048] The terms "first", "second", etc. are used to distinguish similar objects and not to describe or indicate a particular order or sequence.

[0049] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or also includes elements inherent in such process, method, article, or apparatus / device.

[0050] Thus far, the technical solution of the present invention has been described in conjunction with the preferred embodiments shown in the accompanying drawings.

[0051] The above are only embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the scope of the claims of the present application.

Claims

1. A method for calibrating the system function of magnetic particle imaging without magnetic field lines, characterized in that Applied to a magnetic particle imaging system based on magnetic field line-free scanning, the method includes: Obtaining an empty background signal when the calibration sample is outside the magnetic particle imaging system; Fixing the calibration phantom at the central position of the magnetic field line-free, making the calibration phantom parallel to the magnetic field line-free, and the calibration phantom is a single-dimensional multi-voxel strip-shaped calibration phantom; Moving the magnetic field line-free or the calibration phantom in the normal direction of the magnetic field line-free to change the relative distance between the magnetic field line-free and the calibration phantom, and synchronously collecting the raw signals between the magnetic field line-free and the calibration phantom at different relative distances; Determining the effective signal based on the empty background signal and the raw signal, and performing Fourier analysis on the effective signal to extract the target signal that meets the preset frequency domain; Constructing a mapping array according to the relative distance between the magnetic field line-free and the calibration phantom, and performing upsampling on the target signal according to the mapping array and mapping it to the calibration space of the system function; Calculating the relative distance between the magnetic field line-free and the calibration phantom corresponding to each point in the system function and pairing and filling the calibration data to obtain the calibrated system function.

2. The system function calibration method for magnetic particle imaging without magnetic field lines according to claim 1, wherein The effective signal satisfies: ； wherein, is the effective signal, is the original signal between the magnetic field-free line and the calibration phantom at different relative distances, is the empty background signal.

3. The system function calibration method for magnetic particle imaging without magnetic field lines according to claim 1, wherein The method further includes: Based on the system function, solving for the magnetic particle concentration distribution information according to a preset linear equation to complete the magnetic particle image reconstruction, and the linear equation is: ； Wherein, A is the system function, and X is the magnetic particle concentration distribution information, which is the target signal.

4. The system function calibration method for magnetic particle imaging without magnetic field lines according to claim 1, wherein The moving the magnetic field line-free or the calibration phantom specifically includes: Gradually moving the magnetic field line-free in the target direction, the target direction is perpendicular to the magnetic field line-free, and the calibration phantom remains fixed during the movement of the magnetic field line-free; During the process of moving without magnetic field lines, the corresponding number of measurement times is , where is the polar coordinate distance of the sample point in the calibration space, is the number of rotation angles of the magnetic field-free line and the polar coordinate angle of the sample point in the calibration space, is the number of translation layers.

5. The method for calibrating the system function of magnetic particle imaging without magnetic field lines according to claim 4, characterized in that, The relative distance between the magnetic field line-free and the calibration phantom is: ； Wherein, is the relative distance between the magnetic field-free line and the calibration phantom, is the radial distance between the calibration sample and the origin of the coordinate system, is the current polar angle of the magnetic field-free line (FFL), is the initial polar angle of the calibration sample, is the polar angle difference between the magnetic field-free line and the calibration sample.

6. A system function calibration device for implementing the method according to any one of claims 1-5, characterized in that, The device includes: A calibration phantom configured to be parallel to the direction of the magnetic field line-free; A phantom support for fixing the calibration phantom so that the calibration phantom is at the exact center position of the magnetic field line-free; A movement control unit for driving the magnetic field line-free to translate step by step along its normal direction to change the relative distance between the magnetic field line-free and the calibration phantom; A data acquisition unit for collecting the raw signals between the magnetic field line-free and the calibration phantom at different relative distances and performing background elimination on the raw signals; A system function construction unit for generating a complete system function matrix according to the relative distance and the raw signal after background filtering; 7. The system function calibration device according to claim 6, characterized in that, The device further includes: An image reconstruction unit for reconstructing the magnetic particle concentration distribution according to the system function matrix and the solution algorithm.

8. The system function calibration device according to claim 6, characterized in that, The calibration phantom is a single-dimensional multi-voxel strip-shaped calibration phantom, and the single-dimensional multi-voxel strip-shaped calibration phantom is filled with superparamagnetic iron oxide nanoparticle phantoms with uniform distribution inside.

9. The system function calibration device according to claim 7, wherein The movement control unit drives the magnetic field line-free in an electric drive mode, and the calibration phantom remains fixed during the process of the movement control unit driving the magnetic field line-free.

10. The system function calibration device according to claim 7, characterized in that, The length of the single-dimensional multi-voxel strip-shaped calibration phantom matches the aperture of the magnetic particle imaging device.

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