A magnetic particle imaging system and method based on a flexible receiving coil array

Abstract

The present invention belongs to the field of magnetic particle imaging technology, and specifically relates to a magnetic particle imaging system and method based on a flexible receiving coil array, which aims to solve the problems of poor adaptability of current rigid receiving coils to biological surfaces and low signal-to-noise ratio for imaging tiny geometric textures. The present invention: Structurally, the receiving coil array is adhered to the surface of the object to be measured, and the compensation coil array is distributed on both sides of the flexible substrate. The receiving coil array is used to receive magnetic nanoparticle signals, and the block-type small compensation coil array is used to compensate for feedthrough interference and electromagnetic interference of the receiving coil; in terms of reconstruction method, the collected receiving signal is Fourier transformed in sequence, the in-phase third harmonic is extracted and superimposed to obtain the processed signal, interpolation is used to construct a sinusoidal diagram for the Cartesian coordinate distribution, and the filtered back projection method is used to reconstruct the three-dimensional particle concentration distribution of the object to be measured. The present invention adopts a flexible receiving coil array strategy and provides an adaptive reconstruction method, thereby improving the imaging signal-to-noise ratio.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomedical imaging, and in particular relates to a magnetic particle imaging system and method based on a flexible receiving coil array. Background Art

[0002] Magnetic particle imaging technology has experienced rapid development and has passed pre-clinical verification in fields such as stem cell tracking, cancer imaging, and magnetic hyperthermia, demonstrating good clinical application potential.

[0003] Magnetic particle imaging uses magnetic nanoparticles with strong magnetic moments as tracers and has the technical advantage of high sensitivity. However, in the existing magnetic particle imaging system architecture, the receiving coil is usually rigid, with a fixed shape and size. The sensitivity map covers the entire imaging field of view, providing global field of view imaging capabilities. For small-sized or specially shaped objects, the electromagnetic conversion efficiency is limited due to the certain distance between the receiving coil and the object, so that the current receiving coil has a low signal-to-noise ratio for imaging tiny geometric textures. In contrast, flexible receiving coils have good shape adaptability and can be wrapped around the surface of the imaging object, with a high fill factor, which helps to reduce signal noise and improve image quality.

[0004] However, global receiving coils and rigid coils are currently commonly used in the field of magnetic particle imaging technology, and there is a lack of related technologies for flexible receiving coils.

[0005] This invention patent aims to propose a magnetic field free line magnetic particle imaging system and method based on a flexible receiving coil array, providing a solution for high-quality magnetic particle imaging. Summary of the Invention

[0006] In order to solve the above-mentioned problems in the prior art, namely, the existing receiving coils are rigid and have a certain distance from the object being measured, which limits the electromagnetic conversion efficiency. As a result, the current receiving coils have a low signal-to-noise ratio for imaging tiny geometric textures, which in turn leads to low reconstructed image quality. In a first aspect, the present invention proposes a magnetic particle imaging system based on a flexible receiving coil array, the system comprising:

[0007] a fourth coil configured to excite the magnetic nanoparticles to generate a magnetization response;

[0008] a driving coil pair configured to generate a uniform alternating magnetic field to drive the magnetic field free line to move; the driving coil pair includes two pairs of electromagnetic coils, serving as a second coil pair and a third coil pair; the two electromagnetic coils in the second coil pair are symmetrically arranged on the upper and lower sides outside the fourth coil; and the two electromagnetic coils in the third coil pair are symmetrically arranged on the left and right sides outside the fourth coil;

[0009] a first magnet group configured to generate a magnetic field free line at the center of the imaging field of view; the first magnet group includes four magnet units, the four magnet units are arranged in groups of two, and are symmetrically arranged on the upper and lower sides of the driving coil pair; the two magnet units in each group are placed side by side;

[0010] A flexible receiving coil array is configured to receive magnetization response signals of magnetic nanoparticles; the flexible receiving coil array includes a receiving coil array layer, a supporting base layer and a compensation coil array layer; the receiving coil array layer is a uniform planar array for receiving magnetization response signals, wherein M receiving coils are included in the uniform planar array, one side of each receiving coil is adhered to the inner side of the supporting base layer, and the other side is adhered to the surface of the object to be measured; the compensation coil array layer is a block uniform planar array for compensating for feedthrough interference and electromagnetic interference of the receiving coil, the block uniform planar array is N compensation coils arranged within the coverage range of each receiving coil, one side of each compensation coil is adhered to the outer side of the supporting base layer, and the other side is away from the object to be measured, and the compensation coil array has a total of M×N coils.

[0011] In some preferred embodiments, the system further comprises a data acquisition and processing circuit configured to receive the magnetization response signal, filter, amplify, perform digital-to-analog conversion, and process the signal to generate a magnetic particle image;

[0012] It also includes a mechanical structure and a mechanical controller; the mechanical structure includes a magnet support structure for supporting and fixing the first magnet group, the drive coil pair and the fourth coil;

[0013] The mechanical controller is used to drive the first magnet group to rotate, including the rotation angle and speed of the rotation.

[0014] In some preferred embodiments, the fourth coil comprises a solenoid coil or a Helmholtz coil;

[0015] The two pairs of electromagnetic coils in the driving coil pair are both Helmholtz coils.

[0016] In some preferred embodiments, the magnet units in the first magnet group include permanent magnets, electromagnetic coils, and superconducting magnets.

[0017] In some preferred embodiments, the N compensation coils are connected in series in phase and then in antiphase series with the corresponding receiving coils. The sum of the inductances of the N compensation coils is equal to the inductance of the receiving coil, and the diameter of the compensation coil is smaller than that of the receiving coil.

[0018] In some preferred embodiments, the supporting substrate layer (800) has a supporting substrate with a preset thickness, and the supporting substrate thickness is h, wherein 2 mm <h<4mm。

[0019] In a second aspect, the present invention provides a magnetic particle imaging method based on a flexible receiving coil array. Based on the magnetic particle imaging system based on a flexible receiving coil array, the method comprises the following steps:

[0020] S1, using the first magnet group to generate a magnetic field free line, the gradient of the magnetic field free line is ; The imaging field of view radius is ;

[0021] Applying current to the second coil pair and the third coil pair respectively to generate a uniform alternating magnetic field to drive the magnetic field free line to move along a predetermined trajectory, wherein the predetermined trajectory motion is a discrete Cartesian motion;

[0022] Passing current through the fourth coil to generate a magnetic field to excite the magnetic nanoparticles;

[0023] S2, attaching the flexible receiving coil array to the object to be measured to receive the magnetization response signals of the magnetic nanoparticles, wherein the flexible receiving coil array specifically uses M receiving coils arranged in an array to receive the magnetization response signals of the M magnetic nanoparticles;

[0024] S3, performing Fourier transform on each of the magnetization response signals to convert them into frequency domain signals, and distinguishing in-phase and anti-phase signals;

[0025] Extracting and superimposing in-phase third harmonics from all frequency domain signals to obtain processed signals;

[0026] interpolating the spatial distribution of the processed signal from the polar coordinate mode to the Cartesian coordinate distribution to form a sinusoidal diagram;

[0027] S4, the mechanical controller drives the first magnet group to rotate, and obtains a corresponding sinusoidal graph at each angle according to the method of S1-S3;

[0028] The rotation angle sequence is: ;

[0029] S5, based on all acquired sinusoidal graphs, a filtered back projection method is used to reconstruct the three-dimensional particle concentration distribution of the measured object, thereby obtaining a reconstructed magnetic particle image.

[0030] In some preferred embodiments, the current flowing through the second coil pair is: ;

[0031] The current flowing through the third coil pair is: ;

[0032] Among them, the current sequence is: , the phase sequence is: ;

[0033] The current flowing through the fourth coil is .

[0034] In some preferred embodiments, the filtered back projection method includes a filtered back projection method using Cosine as a filter kernel.

[0035] Beneficial effects of the present invention:

[0036] 1) A flexible receiving coil array is used to wrap the object to be measured to receive the magnetization response signal of the magnetic nanoparticles. A compensation coil is set on the outside of the flexible substrate to achieve the effect of compensating the receiving coil. Every four compensation coils in the compensation coil array layer correspond to the receiving coils in the receiving coil array layer. They are connected in series with each other in phase and in series with the corresponding receiving coil in anti-phase. The coils are constructed in an asymmetric manner to further avoid direct feedthrough interference of the receiving coil and improve the compensation effect.

[0037] 2) The received signal is Fourier transformed to extract the in-phase third harmonic superposition to obtain the processed signal, which is then interpolated into a Cartesian coordinate distribution to form a sinusoidal diagram. Finally, the filtered back projection method is used to reconstruct the three-dimensional particle concentration distribution of the measured object, further reducing interference and improving the imaging signal-to-noise ratio;

[0038] In summary, the problem that the existing receiving coils are rigid, have a certain distance from the measured object, and have limited electromagnetic conversion efficiency, resulting in a low signal-to-noise ratio for imaging tiny geometric textures, has been solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Other features, objects and advantages of the present application will become more apparent upon reading the detailed description of non-limiting embodiments made with reference to the following drawings:

[0040] Figure 1 This is a component diagram of a magnetic particle imaging system based on a flexible receiving coil array according to the present invention.

[0041] Figure 2 This is a magnetic field distribution diagram of a component of a magnetic particle imaging system based on a flexible receiving coil array of the present invention. 。

[0042] Figure 3 This is a distribution diagram of magnetic induction lines of the first magnet group of a magnetic particle imaging system based on a flexible receiving coil array according to the present invention.

[0043] Figure 4 The present invention is a structural schematic diagram of a flexible receiving coil array layer and a compensation coil array layer of a magnetic particle imaging system based on a flexible receiving coil array.

[0044] Figure 5 The present invention is a schematic diagram of a three-layer arrangement structure of a flexible receiving coil array of a magnetic particle imaging system based on a flexible receiving coil array.

[0045] Figure 6 This is a diagram of the movement trajectory of the magnetic field free line of a magnetic particle imaging method based on a flexible receiving coil array of the present invention.

[0046] Figure 7 This is a flow chart of the steps of a magnetic particle imaging method based on a flexible receiving coil array of the present invention.

[0047] In the accompanying drawings, 101-104: four magnet units of the first magnet group 1; 201-202: two electromagnetic coils of the second coil pair of the driving coil; 301-302: two electromagnetic coils of the third coil pair of the driving coil; 401: the fourth coil; 500: the imaging field of view; 600: the receiving coil layer in the flexible receiving coil array; 601: a coil unit in the receiving coil array; 700: the compensation coil layer in the flexible receiving coil array; 701: a coil unit in the compensation coil array; 800: the flexible supporting substrate in the flexible receiving coil array; 901-904: the four moving positions and scanning trajectories of the free line of the magnetic field driven by the second coil pair 201-202 and the third coil pair 301-302. DETAILED DESCRIPTION

[0048] The present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are intended only to illustrate the relevant invention and are not intended to limit the invention. It should also be noted that, for ease of description, only portions relevant to the relevant invention are shown in the accompanying drawings.

[0049] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0050] In order to more clearly explain the magnetic particle imaging system based on the flexible receiving coil array of the present invention, the following Figures 1 to 6 Each step in the embodiment of the present invention is described in detail.

[0051] A magnetic particle imaging system based on a flexible receiving coil array according to the first embodiment of the present invention is described in detail. Figure 1 , the system comprises:

[0052] a first magnet group 1 configured to generate a magnetic field free line at the center 5 of the imaging field of view; the first magnet group 1 includes four magnet units, which are arranged in groups of two and symmetrically disposed on the upper and lower sides of the driving coil pair; the two magnet units in each group are placed side by side;

[0053] In this embodiment, the four magnet units (or coil units) 101-104 of the first magnet group 1 include permanent magnets, electromagnetic coils, and superconducting magnets, and are specifically configured as follows: four magnet units, two of which are placed side by side on the upper and lower sides, wherein the magnet units 101 and 103 are a group and are arranged in parallel on the upper side of the driving coil pair (on the same plane above the second coil pair 2, the third coil pair 3, and the fourth coil 4, and are parallel to the coils on the corresponding sides of the second coil pair 2, i.e., 201-202), and the magnet units 102 and 104 are a group and are placed in parallel on the lower side of the driving coil pair (on the same plane below the second coil pair 2, the third coil pair 3, and the fourth coil 4, and are parallel to the coils on the corresponding sides of the second coil pair 2, i.e., 201-202), and are configured to generate a magnetic field free line at the center 500 of the imaging field of view, with the energization direction as shown in the attached figure. Figure 3 As shown, a magnetic field free line with a gradient of G = 1.5 T / m is generated at the center of the imaging field of view 500, and the imaging field of view is set to ;

[0054] a driving coil pair configured to generate a uniform alternating magnetic field to drive the magnetic field free line to move; the driving coil pair includes two pairs of electromagnetic coils, serving as a second coil pair 2 and a third coil pair 3; the two electromagnetic coils in the second coil pair 2 are symmetrically arranged on the upper and lower sides outside the fourth coil 4; and the two electromagnetic coils in the third coil pair 3 are symmetrically arranged on the left and right sides outside the fourth coil 4;

[0055] In this embodiment, the two pairs of electromagnetic coils are the second coil pair 2 and the third coil pair 3, including Helmholtz coils and electromagnetic coils, respectively including two electromagnetic coils 201-202 and 301-302, wherein the electromagnetic coils 201-202 are symmetrically arranged on the upper and lower sides outside the fourth coil 4, and a sinusoidal alternating current is passed through to generate a uniform alternating magnetic field to drive the free line of the magnetic field to move in the vertical direction. The current sequence passed through is , , , in which a typical magnetic field is generated such as Figure 2 As shown in the left figure, the electromagnetic coil 201 is placed on the upper side of the imaging field of view center 5, the electromagnetic coil 202 is placed on the lower side of the imaging field of view center 5, and the two electromagnetic coils of the third coil pair 3 are symmetrically arranged on the left and right sides outside the fourth coil 4. A sinusoidal alternating current is passed through to generate a uniform alternating magnetic field to drive the magnetic field free line to move in the horizontal direction. The current sequence passed through is , , , in which a typical magnetic field is generated as Figure 2As shown in the middle figure, the peak value of the magnetic field intensity is 30 mT and the frequency is 100 Hz. Specifically, the electromagnetic coil 301 is set to the left of the imaging field center 5, and the electromagnetic coil 302 is set to the right of the imaging field center 5;

[0056] The fourth coil 4 includes an electromagnetic coil 401 (which may be a solenoid coil or a Helmholtz coil) configured to excite the magnetic nanoparticles to generate a magnetization response, specifically by passing an alternating current. , can be set, , generating a 5mT uniform alternating magnetic field to stimulate the magnetic nanoparticles to produce a magnetization response, wherein a typical magnetic field generated is as follows Figure 2 As shown in the right figure, the frequency is 100Hz;

[0057] See also Figure 4 、 Figure 5, the flexible receiving coil array 6 is configured to receive the magnetization response signal of the magnetic nanoparticles; the flexible receiving coil array 6 includes a receiving coil array layer 600, a supporting base layer 800 and a compensation coil array layer 700; the receiving coil array layer 600 is a uniform planar array for receiving the magnetization response signal, and there are M (9 in the figure) receiving coils in the uniform planar array, and the sub-field range covered by each receiving coil is a block, and one side of the receiving coil is adhered to the inner side of the supporting base layer 800, and the other side is adhered to the surface of the object to be measured, and the compensation coil array layer 700 is a block uniform planar array for compensating for the feedthrough interference and electrical Magnetic interference, the block uniform planar array is N (4 in the figure) compensation coils arranged within the coverage range of each receiving coil, that is, within the block, and the compensation coil array has a total of M×N coils (36 in the figure). One side of the compensation coil is adhered to the outside of the supporting base layer 800, and the other side is away from the object to be measured and faces the center of the imaging field of view; wherein, the supporting base layer 800 is arranged between the coil array layer 600 and the compensation coil array layer 700, and is used to isolate and support the position of the coil, wherein the receiving coil and the compensation coil can be circular coils, and the supporting base layer can be a polyurethane (PU) base, PU The substrate has good flexibility, which makes the entire array receiving device flexible. This flexible receiving strategy enables the device to better fit surfaces of different shapes, and has better adaptability and stability in scenarios such as energy reception or signal acquisition on wearable devices and surfaces of special-shaped objects. It is explained here that the number M of receiving coils, the number N of compensation coils, and the distance between each receiving coil and the compensation coils can be adaptively adjusted according to the actual needs of the object being measured. Taking the small animal imaging device with an imaging field of view of 10 cm as an example, the PU substrate layer thickness is set to 1 mm, the receiving coil size is a 2 cm ring coil, a 5×5 array with a spacing of 1 mm is set, the block sub-field of view is 2 cm×2 cm, the compensation coil is a 1 cm ring coil, a 2×2 compensation coil array is set in each block, and the compensation coil spacing is 0.5 mm. The receiving coil inductance is equal to the sum of the compensation coil inductances of the corresponding block.

[0058] In this embodiment, the N compensating coils are connected in series in phase, and then connected in series in anti-phase with the receiving coil. The sum of the inductances of the N compensating coils is equal to the inductance of the receiving coil. The compensating coils have a smaller diameter than the receiving coil, are arranged more densely, and are evenly arranged within the corresponding block.

[0059] The supporting base layer 800 has a supporting base with a preset thickness, and the thickness of the supporting base is h, wherein 2 mm <h<4mm;

[0060] In this embodiment, the device further comprises a data acquisition and processing circuit configured to receive the magnetization response signal, filter, amplify, perform digital-to-analog conversion, and process the signal to generate a magnetic particle image;

[0061] It also includes a mechanical structure and a mechanical controller, wherein the mechanical structure includes a magnet support structure for supporting and fixing the first magnet group 1, the driving coil pair and the fourth coil 4;

[0062] The mechanical controller is used to drive the first magnet group 1 to rotate, including the rotation angle and speed of the rotation, around the z-axis Angle sequence rotation.

[0063] It should be noted that the above-described embodiment provides a magnetic particle imaging system based on a flexible receiving coil array, and the division of the above-described functional modules is merely an example. In actual applications, the above-described functions can be assigned to different functional modules as needed, 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-described embodiments can be combined into a single module or further divided into multiple sub-modules to complete all or part of the functions described above. The names of the modules and steps involved in the embodiments of the present invention are merely for the purpose of distinguishing the modules or steps and are not to be construed as undue limitations on the present invention.

[0064] In a second aspect, the present invention provides a magnetic particle imaging method based on a flexible receiving coil array. Based on the magnetic particle imaging system based on a flexible receiving coil array, the method comprises the following steps:

[0065] S1, using the first magnet group to generate a magnetic field free line, the gradient of the magnetic field free line is ; The imaging field of view radius is ;

[0066] Current is applied to the second coil pair 2 and the third coil pair 3 respectively to generate a uniform alternating magnetic field to drive the magnetic field free line to move along a predetermined trajectory. The predetermined trajectory motion is a discrete Cartesian motion, that is, a discrete Cartesian motion along the plane formed by the second and third coil pairs; as shown in the attached figure Figure 6 As shown, the sports mode is: Figure 3 The coordinate system is used as the reference, and the magnetic field free line is scanned along 901; adjust and in The sequence can rotate the scanning line of the magnetic field free line Angle, typical positions are 902, 903 and 904, Determines the trajectory density of the magnetic field free line scan;

[0067] Passing current through the fourth coil 4 to generate a magnetic field to excite the magnetic nanoparticles;

[0068] In this embodiment, the ;

[0069] The current flowing through the second coil pair 2 is , which can be set to ;

[0070] The current flowing through the third coil pair 3 is , which can be set to ;

[0071] Among them, the current sequence is: , the phase sequence is:

[0072] ;

[0073] The current flowing into the fourth coil 4 is , which can be set to , generating a 5mT uniform alternating magnetic field with a frequency of 100Hz;

[0074] S2, attach the flexible receiving coil array 6 to the object to be measured to receive the magnetization response signal of the magnetic nanoparticles , the flexible receiving coil array specifically uses M receiving coils arranged in an array to receive the magnetization response signals of M magnetic nanoparticles;

[0075] In this embodiment, since the magnetization of magnetic nanoparticles is vectorial, the receiving coils symmetrically located on either side of the particles will receive signals with the same amplitude but opposite phases. Directly superimposing these two signals will cancel each other out. Therefore, during implementation, the in-phase signals in the receiving coil array are extracted. Due to the movable nature of the receiving coils, it is difficult to avoid a reduction in compensation effect, resulting in severe direct feedthrough interference. The compensation coils are arranged in an asymmetric pattern, closely adjacent to the compensation coils while reducing the impact on sensitivity, achieving a better compensation effect and suppressing direct feedthrough.

[0076] S3, due to the magnetization response signal Since time domain signals are easily interfered with, each magnetization response signal Perform Fourier transform and convert it into frequency domain signal. Indicates that the mth receiving coil in the flexible receiving coil array 6 rotates to At this angle, the free lines of the magnetic field move to The signal collected when the position is

[0077] Extract all the frequency domain signals The in-phase third harmonics in the signal are superimposed to obtain the processed signal ;

[0078] Since the signal after superposition processing The spatial distribution of Figure 6 As shown, it presents a polar coordinate mode, which needs to be interpolated into a Cartesian coordinate distribution for subsequent processing. The spatial distribution of is interpolated from the polar coordinate mode to the Cartesian coordinate distribution to form a sinusoidal diagram, which can be used as the sinusoidal diagram of the magnetic field free line scan;

[0079] S4, the mechanical controller drives the first magnet group to rotate, and obtains the corresponding sinusoidal diagram according to steps 1-3 at each angle; the rotation angle sequence is:

[0080] The rotation angle sequence is: ;

[0081] S5, based on all acquired sinograms, a filtered back-projection method is used to reconstruct the three-dimensional particle concentration distribution of the measured object, thereby obtaining a reconstructed magnetic particle image;

[0082] In this embodiment, the filtering back projection method includes a filtering back projection method using Cosine as the filtering kernel, but other filtering kernels and other filtering back projection parameters can generally be used for image reconstruction, which can meet the technical method requirements involved in this patent.

[0083] Although the various steps in the above embodiment are described in the above-mentioned order, those skilled in the art will understand that in order to achieve the effect 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 reverse order. These simple changes are within the scope of protection of the present invention.

[0084] Those skilled in the art should be able to appreciate that the modules and method steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two, and the programs corresponding to the software modules and method steps can be placed in random access memory (RAM), internal memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disks, removable disks, CD-ROMs, or any other form of storage medium known in the art. In order to clearly illustrate the interchangeability of electronic hardware and software, the above description has generally described the components and steps of each example according to their functions. Whether these functions are performed in electronic hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0085] The terms "first", "second", etc. are used to distinguish similar objects, rather than to describe or indicate a particular order or sequence.

[0086] The term "comprise" or any other similar term is intended to cover non-exclusive inclusion such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0087] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A magnetic particle imaging system based on a flexible receiving coil array, characterized in that: The system comprises: a fourth coil configured to excite the magnetic nanoparticles to generate a magnetization response; a driving coil pair configured to generate a uniform alternating magnetic field to drive the magnetic field free line to move; the driving coil pair includes two pairs of electromagnetic coils, serving as a second coil pair and a third coil pair; the two electromagnetic coils in the second coil pair are symmetrically arranged on the upper and lower sides outside the fourth coil; and the two electromagnetic coils in the third coil pair are symmetrically arranged on the left and right sides outside the fourth coil; a first magnet group configured to generate a magnetic field free line at the center of the imaging field of view; the first magnet group includes four magnet units, the four magnet units are arranged in groups of two, and are symmetrically arranged on the upper and lower sides of the driving coil pair; the two magnet units in each group are placed side by side; A flexible receiving coil array configured to receive magnetization response signals of magnetic nanoparticles; the flexible receiving coil array comprises a receiving coil array layer, a supporting substrate layer, and a compensation coil array layer; the receiving coil array layer is a uniform planar array for receiving magnetization response signals, wherein M receiving coils are included in the uniform planar array, one side of each receiving coil being adhered to the inner side of the supporting substrate layer and the other side being adhered to the surface of the object being measured; the compensation coil array layer is a block uniform planar array for compensating for feedthrough interference and electromagnetic interference of the receiving coils, wherein the block uniform planar array comprises N compensation coils arranged within the coverage range of each receiving coil, one side of each compensation coil being adhered to the outer side of the supporting substrate layer and the other side being away from the object being measured, and the compensation coil array comprises a total of M×N coils; The N compensation coils are connected in series in phase and then in antiphase series with the corresponding receiving coils. The sum of the inductances of the N compensation coils is equal to the inductance of the receiving coil and the diameter of the compensation coil is smaller than that of the receiving coil.

2. A magnetic particle imaging system based on a flexible receiving coil array according to claim 1, characterized in that: The system further includes a data acquisition and processing circuit configured to receive the magnetization response signal, filter, amplify, perform digital-to-analog conversion, and process the signal to generate a magnetic particle image; It also includes a mechanical structure and a mechanical controller; the mechanical structure includes a magnet support structure for supporting and fixing the first magnet group, the drive coil pair and the fourth coil; The mechanical controller is used to drive the first magnet group to rotate, including the rotation angle and speed of the rotation.

3. The magnetic particle imaging system based on a flexible receiving coil array according to claim 1, characterized in that: The fourth coil includes a solenoid coil and a Helmholtz coil; The two pairs of electromagnetic coils in the driving coil pair are both Helmholtz coils.

4. The magnetic particle imaging system based on a flexible receiving coil array according to claim 1, characterized in that: The magnet units in the first magnet group include permanent magnets, electromagnetic coils, and superconducting magnets.

5. The magnetic particle imaging system based on a flexible receiving coil array according to claim 1, characterized in that: The supporting base layer has a supporting base with a preset thickness, and the thickness of the supporting base is h, wherein 2mm <h<4mm。 6. A magnetic particle imaging method based on a flexible receiving coil array, based on a magnetic particle imaging system based on a flexible receiving coil array according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: S1, using the first magnet group to generate a magnetic field free line, the gradient of the magnetic field free line is ; The imaging field of view radius is ; applying current to the second coil pair and the third coil pair respectively to generate a uniform alternating magnetic field to drive the magnetic field free line to move along a predetermined trajectory, wherein the predetermined trajectory motion is a discrete Cartesian motion; Passing current through the fourth coil to generate a magnetic field to excite the magnetic nanoparticles; S2, attaching the flexible receiving coil array to the object to be measured to receive the magnetization response signal of the magnetic nanoparticles, wherein the flexible receiving coil array uses M receiving coils arranged in an array to receive the magnetization response signals of the M magnetic nanoparticles; S3, performing Fourier transform on each magnetization response signal, converting it into a frequency domain signal, and distinguishing between in-phase and anti-phase; Extracting and superimposing in-phase third harmonics from all frequency domain signals to obtain processed signals; interpolating the spatial distribution of the processed signal from the polar coordinate mode to the Cartesian coordinate distribution to form a sinusoidal diagram; S4, the mechanical controller drives the first magnet group to rotate, and obtains a corresponding sinusoidal graph at each angle according to the method of S1-S3; The rotation angle sequence is: ; S5, based on all acquired sinusoidal graphs, a filtered back projection method is used to reconstruct the three-dimensional particle concentration distribution of the measured object, and then a reconstructed magnetic particle image is obtained.

7. The magnetic particle imaging method based on a flexible receiving coil array according to claim 6, characterized in that: The current flowing through the second coil pair is: ; The current flowing through the third coil pair is: ; Among them, the current sequence is: , the phase sequence is: ; The current flowing through the fourth coil is .

8. The magnetic particle imaging method based on a flexible receiving coil array according to claim 6, characterized in that: The filtering back projection method includes a filtering back projection method using Cosine as a filtering kernel.

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