Opm-based superparamagnetic nanoparticle relaxation signal detection system and method

Abstract

The application discloses an OPM-based superparamagnetic nanoparticle relaxation signal detection system and method. The detection system comprises a magnetic nanoparticle module, an OPM array and a magnetic field generation module in a magnetic shielding environment, and a magnetic field control module and a data acquisition module connected therewith outside the magnetic shielding environment. The magnetic nanoparticle module is placed in a controllable magnetic field region of the magnetic field generation module to wait for magnetization, the OPM array receives the relaxation signal generated after the particle magnetization, and the magnetic field generation module is used for generating a particle magnetization field and a background field inside; the magnetic field control module receives a magnetic field module instruction of a host computer, and supplies power to the magnetic field generation module through a constant-voltage power supply; the data acquisition module is connected with the OPM array to collect the relaxation signal, simultaneously receives a magnetic field mode signal generated by the magnetic field control module, and transmits data back to the host computer. The application improves the particle magnetization device, and suppresses the magnetization background noise from the hardware.

Description

Technical Field

[0001] The present invention belongs to the field of biomedical engineering, and in particular relates to a superparamagnetic nanoparticle relaxation signal detection system and method based on OPM. Background Art

[0002] In recent years, various bioimaging methods have been proposed for superparamagnetic nanoparticles. In particular, superparamagnetic nanoparticles (Fe3O4 or FeO4) are widely used as contrast agents with excellent magnetic properties and good biocompatibility for cell and tissue imaging. Currently, enhanced magnetic resonance imaging (MRI) and magnetic particle imaging (MPI) are commonly used methods for studying the spatial distribution of superparamagnetic nanoparticles and are also research hotspots in nanomedicine. Their commonality lies in obtaining spatial imaging information by magnetizing particles with a high-frequency alternating magnetic field. This approach has important applications in the detection of lesions such as tumors and in magnetic hyperthermia.

[0003] With the development and maturity of superconducting quantum interference devices (SQUIDs) and optical pumping magnetometers (OPMs), the detection of extremely weak biological magnetic fields has garnered widespread attention and research. OPMs offer advantages such as flexible layout, multi-axis measurement, high sensitivity, and low cost, leading to rapid development in the fields of brain and heart magnetometry.

[0004] Ordinary tumor tissues and other cellular tissues are unable to spontaneously generate potentials and displacements in a directional manner. Current ultra-sensitive magnetometers, such as SQUIDs and OPMs, cannot reach the detection limits of cellular magnetic fields. Therefore, superparamagnetic nanoparticles are required as a medium for tumor cell detection. The superparamagnetic nanoparticle relaxation detection method based on OPMs leverages the magnetic properties of superparamagnetic nanoparticles with the advantages of OPM layout and sensitivity, offering significant advantages in small-cell, low-dose imaging.

[0005] Superparamagnetic nanoparticles themselves are macroscopically non-magnetic and require magnetization by an external magnetic field to generate specific characterization signals. Due to the bandwidth limitations and time resolution characteristics of ultra-high-sensitivity magnetic sensors, DC field magnetization detection of particles can be used to detect relaxation attenuation signals. However, the current magnetic relaxation detection for superparamagnetic nanoparticles detected by OPM has the following problems: (1) Particle magnetization and relaxation detection are performed under the same conditions. The particle magnetization process will affect the magnetic shielding environment of the relaxation detection device, interfering with the detection of the relaxation field. The coil inductance effect and the recovery time of the magnetic sensor are not conducive to signal recovery. (2) There is a lack of a spatial magnetic particle source and quantitative detection system for OPM. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention proposes a superparamagnetic nanoparticle relaxation signal detection system and method based on OPM to realize spatial magnetic particle detection in extremely weak magnetic environment.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] On the one hand, the present invention provides a superparamagnetic nanoparticle relaxation signal detection system based on OPM, comprising a particle magnetization module and a relaxation signal synchronization detection module, wherein:

[0009] The particle magnetization module includes a magnetic nanoparticle module, a magnetic field generation module and a magnetic field control module, and the relaxation signal synchronization detection module includes an OPM array and a data acquisition module;

[0010] The magnetic nanoparticle module includes fixed ferroferric oxide or iron oxide superparamagnetic nanoparticles, which are placed in the controllable magnetic field area generated by the magnetic field generation module;

[0011] The magnetic field generating module includes a background field generating module composed of a coil without magnetic moment and a magnetizing field generating module composed of a one-dimensional Helmholtz coil. The coil without magnetic moment and the one-dimensional Helmholtz coil use a non-magnetic frame to generate a magnetic field in the area where the magnetic nanoparticle module is placed. The magnetic field generating module is connected to a constant voltage power supply to power the background field generating module and the magnetizing field generating module.

[0012] The magnetic field control module includes a circuit control panel capable of setting a magnetization mode. The circuit control panel is detachably arranged between the no-magnetic-moment coil and the constant-voltage power supply. The upper computer controls the magnetization field generation module to generate a pulsed magnetic field, and simultaneously controls the background field generation module to generate a constant magnetic field.

[0013] The OPM array is used to receive the magnetic field generated by the magnetic field generation module and act on the magnetic nanoparticle module to generate a relaxation signal, and the OPM array outputs multiple sets of analog data of over-range magnetization field and particle Neel relaxation signal;

[0014] The data acquisition module includes an analog-digital conversion data acquisition card connected to the OPM array and the circuit control board, which synchronously acquires analog data output by the OPM array and pulse electrical signals representing the magnetic field mode and transmits them to the upper computer.

[0015] Further, the one-dimensional Helmholtz coil is a set of symmetrical single-plane coils, the set of symmetrical single-plane coils includes two mutually symmetrical annular coils having the same number of turns, the same coil winding mode and a coil radius equal to a coil spacing, and the non-magnetic moment coil includes at least one set of double-plane coils, the set of double-plane coils being a one-dimensional Helmholtz coil structure with two mutually parallel double-plane coils having a symmetrical center coinciding and opposite winding directions.

[0016] Further, the background field generation module uses at least one set of double-plane coils to generate a controllable near-zero magnetic field, and the magnetization field generation module uses a set of one-dimensional Helmholtz coils with the same winding direction to generate a controllable uniform pulsed square wave excitation magnetic field, and the magnetization field generation module is placed in the near-zero magnetic field region of the background field generation module.

[0017] Further, the circuit control board includes a mode setting module and a mode acquisition module, the mode setting module includes a mode control circuit connected to the constant voltage power supply to provide a controllable direct current for the background field generation module, and connected to the electromagnetic relay to provide a pulse current with adjustable duty cycle for the magnetization field generation module; the mode acquisition module outputs a pulse electrical signal representing the opening of the electromagnetic relay.

[0018] Further, the near-zero magnetic field generated by the background field generation module is a fixed uniform constant magnetic field with an order of magnitude of nT to pT, which covers the magnetization field generation module and the OPM array region.

[0019] Further, the OPM array is arranged on an OPM array platform, the OPM array platform includes square or ring arranged card slot planes, the OPM magnetic sensitive axes on all card slot planes are parallel to the direction of the uniform magnetic field center of the magnetization field generation module, the OPM array platform is a horizontally and vertically movable flat plate with a measurable scale, and the OPM array, the OPM array platform, the one-dimensional Helmholtz coil of the magnetization field generation module and the non-magnetic moment coil of the background field generation module are all parallel to the plane.

[0020] Further, the upper computer is connected to the magnetic field control module to output control instructions, and is connected to the data acquisition module to receive analog data output by the OPM array and pulse electrical signal data representing the magnetic field mode, and process and analyze the received data.

[0021] Furthermore, the magnetic nanoparticle module, magnetic field generation module and OPM array are all placed in a magnetic shielding barrel or a magnetic shielding room, and the host computer, constant voltage power supply, magnetic field control module and data acquisition module are all placed outside the magnetic shielding barrel or the magnetic shielding room. The inner and outer parts are connected by a coaxial cable or twisted pair cable with a shielding effect for coil power supply and information transmission.

[0022] On the other hand, the present invention also provides an OPM-based superparamagnetic nanoparticle relaxation signal detection method, which is applied to the aforementioned OPM-based superparamagnetic nanoparticle relaxation signal detection system, comprising the following steps:

[0023] Step 1: placing the superparamagnetic nanoparticles to be tested at a position to be tested in the magnetic field generating module, wherein the position to be tested is the center of the internal uniform magnetic field generated by the magnetization field generating module;

[0024] Step 2: Turn on the constant voltage power supply and set the circuit control module connected to the magnetizing field generation module to a pulse output mode with a high level time in the range of (1s, 2s) and a low level time in the range of (5s, 20s) through the host computer.

[0025] Step 3: Connect the background field generation module to a fixed DC output mode through the constant voltage power supply and the circuit control panel and start it, so that the background field generation module generates an adjustable fixed uniform magnetic field;

[0026] Step 4: Turn on the OPM array, perform gas chamber heating, magnetic compensation, and calibration, and start measurement and data acquisition.

[0027] Step 5: Start the circuit control module to output voltage to the magnetizing field generation module, so that a uniform pulsed DC field sequence is generated at the center of the magnetizing field generation module to magnetize the sample. The OPM array always remains in the open and data acquisition state, and synchronously acquires the switch control signal in the pulse output mode of the circuit control module;

[0028] Step 6: Turn off the circuit control board and the OPM array, stop data acquisition, and transmit the measured data to the host computer as the original particle signal;

[0029] Step 7: Remove or replace the superparamagnetic nanoparticles to be tested in step 1 with pure water, repeat steps 2 to 5, and collect the data measured by the OPM array as the background attenuation signal;

[0030] Step 8: Filter and cancel the original particle signal data collected in step 6 and the background attenuation signal data collected in step 7 to obtain the spatial detection signal of the particle.

[0031] The beneficial effects of the present invention are:

[0032] The present invention provides a relaxation signal detection device and measurement method for superparamagnetic nanoparticles that can be used under OPM atomic magnetometer measurement conditions. The device can effectively suppress the influence of background decay generated by the magnetization process on the OPM working state and particle relaxation detection, and can effectively restore the relaxation signal generated by the particles, thereby obtaining a more accurate quantitative estimation of the particle source in space. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the superparamagnetic nanoparticle relaxation signal detection system based on OPM of the present invention;

[0034] Figure 2 Schematic diagram of coil arrangement in a magnetic field generating module according to an embodiment of the present invention;

[0035] Figure 3 Schematic diagram of the OPM array and detection platform layout according to an embodiment of the present invention.

[0036] Reference numerals:

[0037] 1. Background field generation module, 11. First group of planar coils without magnetic moment, 12. Second group of planar coils without magnetic moment; 2. Magnetization field generation module; 3. Measurement platform, 31. OPM array platform, 32. Particle placement platform, 33. Slide platform, 34. Longitudinal slide, 35. OPM atomic magnetometer. DETAILED DESCRIPTION

[0038] The present invention is described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0039] The working principle of the superparamagnetic nanoparticle relaxation signal detection system based on OPM of the present invention is as follows: superparamagnetic nanoparticles with magnetization and relaxation times in the millisecond and second range, such as ferroferric oxide or iron oxide nanoparticles with a core diameter of about 23-27nm, are selected; a multi-plane magnetic moment-free coil is used instead of a single-plane Helmholtz coil as a magnetic field generation module, and an adjustable near-zero background magnetic field in the order of nT to pT is generated internally, as well as a uniform directional pulsed magnetic field in the order of mT, which decays rapidly externally; a relay is used to control the output of a pulsed square wave current, so that the particles are rapidly magnetized and then relax, and the entire signal is collected. In addition, a background attenuation signal is collected under the same magnetization conditions without particles or pure water. The above two signals are synchronously collected by a data acquisition module and transmitted back to a host computer for subsequent analysis and processing.

[0040] In a first aspect, the present invention provides an OPM-based superparamagnetic particle magnetization module, comprising a magnetic nanoparticle module, a magnetic field generation module, and a magnetic field control module.

[0041] Specifically, the particles used in the magnetic nanoparticle module are spherical or quasi-spherical nanoparticles of ferroferric oxide or ferric oxide with a biocompatible coating material, with a diameter of about 23-27 nm and a narrow particle size distribution. When the particles are in a fixed state, including targeted binding, particle aggregation, freeze drying, etc., the particles will undergo a relaxation process mainly based on Neel relaxation during the relaxation process, and its relaxation time is ,in, is the particle core volume, is the characteristic damping time constant, usually 10 -9 s, k B =1.38×10 -23 JK -1 is the Boltzmann constant, K[J / m 3 ] is magnetic anisotropy, T[K] represents temperature. The Brownian relaxation process that enables the particles to physically rotate will be suppressed, and its relaxation time , is the viscosity of the local environment, is the hydrodynamic volume of the particle. Therefore, the effective relaxation time of the particle is Under the above conditions, the effective relaxation time of particles is in the range of milliseconds to seconds and can be effectively detected by OPM.

[0042] Particles require external magnetic field magnetization before relaxation occurs. Multi-plane coils with no magnetic moment can generate a uniform magnetic field in a large range in the center, allowing most particles to be magnetized within a few hundred milliseconds to a few seconds. The magnetization process of particles can be described by the Langevin function:

[0043] ,

[0044] ,

[0045] in, represents the net magnetization intensity after the particle is magnetized, represents the saturation magnetization, is the applied magnetizing field strength, µ0=4π×10 -7 N / A 2 is the permeability of free space, is the Langevin function that characterizes the magnetization process, and the intermediate parameter , Coth(·) represents the hyperbolic cotangent function. The ratio of magnetization can be expressed as According to simulation calculations, the magnetic field required to complete magnetization is on the order of mT (millitesla), or tens of G (gauss).

[0046] The magnetic field generation module is a coil group composed of two or more parallel plane winding groups, which are respectively used for the background field generation module 1 and the magnetization field generation module 2. One group of non-magnetic moment plane coils includes four center-symmetric winding planes. On one side of the center, two winding planes have different radii, and the total magnetic moment is zero. Assuming that there are m groups of non-magnetic moment coils, all the plane coil groups should satisfy:

[0047]

[0048] The number of turns of the two planes on one side is represented by N and N', and the winding radius of the two planes on one side is represented by R and R'. For the non-magnetic moment coil used for the background field generation module 1, the winding direction of the adjacent planes on one side is opposite, and the winding direction of the two symmetrically opposite planes is the same. For the Helmholtz coil used for the magnetization field generation module 2, the winding direction of the two symmetrically opposite planes is the same. The current direction of the coil is consistent with the winding direction. The position of each group of coil planes from the center point is adjusted according to the optimization method to satisfy the OPM array generated inside the background field generation module 1 and the nT to pT order magnetic field in the range of the magnetization field generation module. The magnetization field generation module 2 can generate a magnetic field of mT order in the range of cm level in the center. The magnetic field outside the background field generation module 1 decays rapidly, meeting the magnetic shielding requirement.

[0049] The magnetic field control module includes a circuit control board composed of a mode setting module and a mode acquisition module, and is connected to a constant voltage power supply for power supply of the circuit control board. At the same time, the constant voltage power supply is connected to the host computer to output voltage to the magnetic field generation module. In addition, it is connected to the data acquisition module to output pulse electrical signals. The constant voltage power supply provides the required power supply for the circuit control board and powers the magnetic field generation module, outputs low-noise constant voltage, and provides one branch for power supply of the circuit control board and another branch connected with the direct access of the magnetic field generation module, and is opened and closed by the mode setting module. The mode setting module is a pulse control circuit integrated on the circuit control board. The host computer accesses the circuit control board and interacts with the MCU through the communication interface, and controls the pulse control circuit. The main devices of the pulse control circuit are electromagnetic relays. By setting the host computer, the opening and closing time can be controlled to make the circuit board output pulse voltage sequence. The mode acquisition module is a potential measurement circuit integrated on the circuit control board. It collects the opening and closing signals of the electromagnetic relay and outputs pulse electrical signals with a maximum value of 3.3V. The interface of the signal output is set on the circuit board and connected to the data acquisition module.

[0050] ​​​​​In the second aspect, the present invention provides a particle relaxation detection and acquisition scheme. First, the center of the OPM array plane is placed on the central axis of each coil, about 5 cm or less from the center of the magnetizing field, and the OPM measurement axis is set to align with the direction of the magnetizing field. The number of OPMs is M. Then, the background decay signal is collected under the magnetic field excitation conditions of no particles or pure water. The pulse high level is recorded as the excitation time. , the low level section of the pulse, i.e. the disconnection time, is recorded as , use multiple groups of pulse square waves to excite the Helmholtz coil of the magnetizing field generation module, the number of pulses is recorded as N, the OPM output signal and the switch control signal of the relay are collected synchronously, and the sampling rate is set to , then the collected background attenuation signal is recorded as , is a set of size While collecting the OPM signal, the relay disconnection signal is collected synchronously, which is recorded as , the sampling rate is consistent with the OPM signal, and the matrix is ​​of the same size. Next, the excitation and magnetization signals of the magnetic nanoparticles are collected under the same conditions, and the method is consistent with the above. The obtained particle original signal and the synchronous relay disconnection signal are recorded as and .

[0051] Through the signal processing module, using the synchronous breaking signal and The background attenuation signal and the original particle signal collected are respectively and The background attenuation signal after segmented processing is filtered and canceled with the original particle signal to finally obtain the spatial detection signal of the particle.

[0052] The superparamagnetic particle magnetization module based on OPM provided in the first aspect is applied to the present invention, such as Figure 1 As shown, the superparamagnetic nanoparticle relaxation signal detection system based on OPM of the present invention includes: a particle magnetization module and a relaxation signal synchronization detection module. The particle magnetization module includes a magnetic nanoparticle module, a magnetic field generation module, and a magnetic field control module.

[0053] The magnetic nanoparticle module is a selected fixed state of ferroferric oxide or iron oxide superparamagnetic nanoparticles, which mainly undergo Neel relaxation after magnetization;

[0054] The magnetic field generating module is a non-magnetic moment coil and a Helmholtz coil with a non-magnetic frame and a low-inductance multi-turn winding. The coil is connected to a constant voltage power supply, which is used to power the magnetizing coil to generate a uniform background field and a pulsed magnetizing field in the central area to magnetize the magnetic nanoparticle module.

[0055] The magnetic field control module is a circuit control board with settable magnetization mode, which is detachably arranged between the non-magnetic moment coil and the constant voltage power supply, and is turned off to make the magnetization field generating module 2 generate a pulsed magnetic field, so that the magnetic nano-particle module has a suitable magnetization process and sufficient relaxation process.

[0056] The relaxation signal synchronous detection module includes an OPM array and a data acquisition module. The magnetic sensitive axis of the OPM array is parallel to the direction of the uniform magnetic field of the center of the Helmholtz coil of the magnetization field generating module. The data acquisition module includes an analog-digital conversion data acquisition card connected to the OPM array and the circuit control board, which can realize the synchronous acquisition of the particle signal detected by the magnetometer and the pulsed electric signal representing the magnetic field mode. The OPM array outputs analog data of multiple groups of super-range magnetization field and particle NMR relaxation signal, and the circuit control board outputs a 3.3V TTL conversion square wave signal data. The analog-digital conversion data acquisition card synchronously acquires and saves the two signals at the same sampling rate. The magnetic nano-particle module, the magnetic field generating module and the OPM array are all placed in a magnetic shielding environment to enable the OPM array to detect extremely weak magnetism. The constant voltage power supply, the magnetic field control module and the data acquisition module are placed outside the magnetic shielding environment. The connection between the modules in the magnetic shielding environment and the non-magnetic shielding environment adopts coaxial cable or twisted pair cable to reduce electromagnetic interference.

[0057] As shown in Figure 2 , the arrangement of the non-magnetic moment coil of a background field generating module and the Helmholtz coil of the magnetization field generating module in the magnetic field generating module of the present application. The background field generating module 1 in the figure includes two groups of interconnected non-magnetic moment plane coil groups: the first group of non-magnetic moment plane coil 11 and the second group of non-magnetic moment plane coil 12. One group of plane coil groups is four plane windings symmetrical about the measurement platform 3. The radius and winding turns of the first group of non-magnetic moment plane coil 11 from left to right are respectively represented as 、 、 、 , and the radius and winding turns of the second group of non-magnetic moment plane coil 12 from left to right are respectively represented as 、 、 、 . Among them, the winding direction of the adjacent plane on one side is opposite, the winding direction of the two sides symmetrical to each other is the same, and the entrances and exits of all planes are connected in series. The non-magnetic moment coil group satisfies the following conditions:

[0058] ,

[0059] The magnetization field generating module 2 is a group of Helmholtz coils on the nearest two sides of the measurement platform, and the number of turns is . The distance between the two coils is equal to the coil radius , the uniform magnetization field area in the center covers the entire measurement platform. Assume that the current is I, and the magnetic field generated in the center is Size:

[0060] ,

[0061] Where, µ0=4π×10 -7 N / A 2 is the permeability of free space, The background magnetic field is generated by the background field generation module 1 in the measurement platform area.

[0062] The distance between each coil in the magnetic field generation module is determined by an optimization method so that it can generate a uniform pulsed magnetic field of the order of mT in the measurement platform 3 area and a controllable uniform extremely weak background magnetic field of the order of nT to pT. The magnetic field decays rapidly outside the range of the magnetic field generation module 2. The number of planar coil groups in the background field generation module 1 can be increased or decreased according to the optimization results.

[0063] like Figure 3 As shown, a design mode of the OPM array measurement platform of the present invention. From top to bottom, there are three platforms, namely, OPM array platform 31, particle placement platform 32 and slide platform 33. OPM array platform 31 and slide platform 33 are interconnected by longitudinal slide rail 34, and particle placement platform 32 is connected with slide platform 33 by transverse slide rail. Particle placement platform 32 can be moved in plane to change the particle position in space by slide platform 33, and longitudinal slide rail 34 can be disassembled. When particle placement platform 32 moves in plane, two longitudinal slide rails 34 on one side of the moving direction can be removed, and two longitudinal slide rails 34 on the other side are locked and fixed, and then moved by transverse slide rail. When it is necessary to change the longitudinal movement, the transverse slide rail between particle placement platform 32 and slide platform 33 is locked, and particle placement platform 32 and slide platform 33 are kept relatively still and moved by longitudinal slide rail 34. Slide rails are all marked with scales, and the position of particles in space is all controllable. During the measurement process, the OPM array platform 31 and the magnetization field generation module 2 are kept relatively stationary, and the information content of the spatial measurement is increased by moving the particles. The OPM array platform 31 is used to accommodate multiple OPM atomic magnetometers 35, which can be arranged in a variety of ways, including annular and rectangular arrays. The particle placement platform 32 can be configured with a multi-porous structure, which can be placed in different wells to increase the spatial information content and also allow for multi-particle source measurement.

[0064] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A superparamagnetic nanoparticle relaxation signal detection system based on OPM, characterized in that: It includes a particle magnetization module and a relaxation signal synchronous detection module, wherein: The particle magnetization module includes a magnetic nanoparticle module, a magnetic field generation module and a magnetic field control module, and the relaxation signal synchronization detection module includes an OPM array and a data acquisition module; The magnetic nanoparticle module includes fixed ferroferric oxide or iron oxide superparamagnetic nanoparticles, which are placed in the controllable magnetic field area generated by the magnetic field generation module; The magnetic field generation module includes a background field generation module composed of a coil with no magnetic moment and a magnetization field generation module composed of a one-dimensional Helmholtz coil. The coil with no magnetic moment and the one-dimensional Helmholtz coil use a non-magnetic frame to generate a magnetic field in the area where the magnetic nanoparticle module is placed. The coil with no magnetic moment includes at least one set of dual-plane coils, each set of dual-plane coils being a structure of two mutually parallel one-dimensional Helmholtz coils with overlapping symmetry centers and opposite winding directions. The magnetic field generation module is connected to a constant voltage power supply to power the background field generation module and the magnetization field generation module. The background field generation module uses at least one set of dual-plane coils to generate a controllable near-zero magnetic field. The magnetization field generation module uses a set of one-dimensional Helmholtz coils with the same winding direction to generate a controllable uniform pulse square wave excitation magnetic field. The magnetization field generation module is placed in the near-zero magnetic field area of ​​the background field generation module, wherein the near-zero magnetic field is a fixed uniform constant magnetic field of the order of nT to pT, and the magnetic field range covers the magnetization field generation module and the OPM array area; The magnetic field control module includes a circuit control panel capable of setting a magnetization mode. The circuit control panel is detachably arranged between the no-magnetic-moment coil and the constant-voltage power supply. The upper computer controls the magnetization field generation module to generate a pulsed magnetic field, and simultaneously controls the background field generation module to generate a constant magnetic field. The OPM array is used to receive the magnetic field generated by the magnetic field generation module and act on the magnetic nanoparticle module to generate a relaxation signal, and the OPM array outputs multiple sets of analog data of over-range magnetization field and particle Neel relaxation signal; The data acquisition module includes an analog-to-digital conversion data acquisition card connected to the OPM array and the circuit control panel, which synchronously collects the analog data output by the OPM array and the pulse electrical signal representing the magnetic field pattern and transmits them to the host computer.

2. The superparamagnetic nanoparticle relaxation signal detection system based on OPM according to claim 1, characterized in that: The one-dimensional Helmholtz coil is a group of symmetrical single-plane coils, which includes two mutually symmetrical annular coils. The two mutually symmetrical annular coils have the same number of turns, the same coil winding method, and the coil radius is equal to the coil spacing.

3. The superparamagnetic nanoparticle relaxation signal detection system based on OPM according to claim 1, characterized in that: The circuit control module includes a mode setting module and a mode acquisition module. The mode setting module includes a mode control circuit, which is connected to the constant voltage power supply to provide a controllable DC current to the background field generation module, and is connected to the electromagnetic relay to provide a pulse current with an adjustable duty cycle to the magnetization field generation module; The pattern acquisition module outputs a pulse electrical signal representing the switching of the electromagnetic relay.

4. The superparamagnetic nanoparticle relaxation signal detection system based on OPM according to claim 1, characterized in that: The OPM array is arranged on an OPM array platform, which includes a card slot plane arranged in a square or a ring. The OPM magnetic sensitive axis on all card slot planes is parallel to the center direction of the uniform magnetic field of the magnetization field generation module. The OPM array platform is a flat plate that can move horizontally and vertically and has a measurable scale. The OPM array and the OPM array platform are parallel to the one-dimensional Helmholtz coil of the magnetization field generation module and the magnetic moment-free coil plane of the background field generation module.

5. The superparamagnetic nanoparticle relaxation signal detection system based on OPM according to claim 1, characterized in that: The host computer is connected to the magnetic field control module to output control instructions, and is also connected to the data acquisition module to receive the analog data output by the OPM array and the pulse electrical signal data representing the magnetic field pattern, and process and analyze the received data.

6. The superparamagnetic nanoparticle relaxation signal detection system based on OPM according to any one of claims 1 to 5, characterized in that: The magnetic nanoparticle module, magnetic field generation module and OPM array are all placed in a magnetically shielded room, and the host computer, constant voltage power supply, magnetic field control module and data acquisition module are all placed outside the magnetically shielded room. The inner and outer parts are connected by a coaxial cable or twisted pair cable with a shielding effect for coil power supply and information transmission.

7. A superparamagnetic nanoparticle relaxation signal detection method based on OPM, applied to the superparamagnetic nanoparticle relaxation signal detection system based on OPM according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: placing the superparamagnetic nanoparticles to be tested at a position to be tested in the magnetic field generating module, wherein the position to be tested is the center of the internal uniform magnetic field generated by the magnetization field generating module; Step 2: Turn on the constant voltage power supply and set the circuit control module connected to the magnetizing field generation module to a pulse output mode with a high level time in the range of (1s, 2s) and a low level time in the range of (5s, 20s) through the host computer. Step 3: Connect the background field generation module to a fixed DC output mode through the constant voltage power supply and the circuit control panel and start it, so that the background field generation module generates an adjustable fixed uniform magnetic field; Step 4: Turn on the OPM array, perform gas chamber heating, magnetic compensation, and calibration, and start measurement and data acquisition. Step 5: Start the circuit control module to output voltage to the magnetizing field generation module, so that a uniform pulsed DC field sequence is generated at the center of the magnetizing field generation module to magnetize the sample. The OPM array always remains in the open and data acquisition state, and synchronously acquires the switch control signal in the pulse output mode of the circuit control module; Step 6: Turn off the circuit control board and the OPM array, stop data acquisition, and transmit the measured data to the host computer as the original particle signal; Step 7: Remove or replace the superparamagnetic nanoparticles to be tested in step 1 with pure water, repeat steps 2 to 5, and collect the data measured by the OPM array as the background attenuation signal; Step 8: Filter and cancel the original particle signal data collected in step 6 and the background attenuation signal data collected in step 7 to obtain the spatial detection signal of the particle.

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