Open three-dimensional magnetic particle imaging device and method based on free lines of magnetic field

Abstract

The present specification relates to the field of MPI imaging technology, and discloses an open three-dimensional magnetic particle imaging device and method based on a magnetic field free line. The device comprises: a signal detection module configured to provide an open scanning environment by installing a magnetic field free line generating unit composed of two circular permanent magnets arranged in a cross direction of the magnetic poles and a signal receiving unit in two coaxial cylindrical scanning devices symmetrically arranged above and below, emit an initial scanning signal and receive a magnetic particle response signal; an electric control module for controlling the position, intensity and motion trail of the initial scanning signal emitted by the signal detection module; an external signal compensation module for measuring a direct feedthrough signal; and a signal processing and image reconstruction module for processing the magnetic particle response signal and the direct feedthrough signal to obtain a reconstructed image. The present application does not need to consider a high-power power supply module, eliminates the filtering operation on the input current, does not need to consider the heating problem possibly caused by long-time power-on, and simplifies the system.

Description

Technical Field

[0001] This document relates to the field of MPI imaging technology, and in particular to an open three-dimensional magnetic particle imaging device and method based on magnetic field free lines. Background Technology

[0002] Superparamagnetic iron oxide nanoparticles (SPIONs) have great potential for application in clinical diagnosis and treatment. Magnetic particle imaging (MPI) can image spatially distributed SPIONs. MPI utilizes the movement of field-free regions (FFRs) in space to excite SPIONs and generate nonlinear response signals. The spatial distribution of SPIONs can be obtained by reconstructing the response signals. Currently, the two main types of FFRs used are field-free points and field-free lines (FFLs).

[0003] Compared to FFP, MPI instruments using FFL have higher sensitivity and can scan larger target areas, showing great potential for future clinical applications. Currently, MPI instruments using FFL mainly include three types: closed-aperture, single-sided, and open-aperture. For traditional closed-aperture MPI instruments, to meet the needs of future human applications, the aperture will need to be significantly increased, which will introduce more noise that is difficult to eliminate, interfering with the particle signal. While single-sided MPI devices are not limited by the size of the object being measured, their imaging depth is limited, only meeting the needs of surface imaging. Open-aperture MPI, developed from single-sided MPI, achieves three-dimensional imaging by electrically driving the rotation and translation of the FFL. However, this method places more complex circuitry on the electromagnetic coils, requires higher power, and the inclusion of receiving and compensation coils in the device reduces the field of view. Therefore, a superior large-field-of-view MPI system solution is currently lacking. Based on this, this invention proposes a large-field-of-view, open-aperture three-dimensional magnetic particle imaging device, system, and method based on magnetic field free lines. Summary of the Invention

[0004] This specification provides an open three-dimensional magnetic particle imaging device based on free lines of magnetic fields, which solves the problems of complex circuit system requirements, high power requirements, and small field of view of the receiving coil and compensation coil in the existing imaging methods. The device includes: a signal detection module, an electronic control module, an external signal compensation module, and a signal processing and image reconstruction module.

[0005] The signal detection module is configured to provide an open scanning environment by installing a magnetic field-free line generation unit 8, composed of circular permanent magnets arranged in two intersecting directions, and a signal receiving unit 10 in two coaxial cylindrical scanning devices that are symmetrically arranged vertically, thereby emitting an initial scanning signal and receiving magnetic particle response signals.

[0006] The electronic control module is used to control the position, intensity, and trajectory of the initial scanning signal emitted by the signal detection module;

[0007] The external signal compensation module is used to measure the direct feedthrough signal;

[0008] The signal processing and image reconstruction module is used to process the magnetic particle response signal and the direct feedthrough signal to obtain a reconstructed image.

[0009] In some preferred embodiments, the signal detection module specifically includes:

[0010] The system includes a stage 15, a magnetic field line generation unit 8, a magnetic field line inertial drive unit 7, a magnetic field line inertial drive unit 16, a current excitation unit 9, and a signal receiving unit 10.

[0011] Let the center point of two coaxial cylindrical scanning devices that are symmetrical about each other be the origin. Let the first direction 1 represent the vertical direction, and the second direction 2 and the third direction 3 represent two mutually perpendicular directions on the horizontal plane.

[0012] The stage 15 is a displacement bed;

[0013] In the cylindrical scanning device located below:

[0014] The magnetic field-free line generation unit 8 is a pair of circular permanent magnets horizontally arranged in the middle of the cylindrical scanning device;

[0015] Each of the circular permanent magnets is composed of two semi-circular permanent magnets with opposite magnetic pole directions. The magnetic pole directions of the two circular permanent magnets are crossed and stacked to form a pair of circular permanent magnets. All the circular permanent magnets are arranged with their magnetic pole directions crossed.

[0016] The magnetic field-free line inertia-free drive unit 7 is a coil coaxial with the magnetic field-free line generating unit 8, which is installed in the inner arm of the cylindrical scanning device. The length of the magnetic field-free line inertia-free drive unit 7 is greater than the translational range of the magnetic field-free line generating unit 8 in the first direction 1. The magnetic field-free line inertia-free drive unit 7 is used to generate a uniform magnetic field in the vertical direction after being energized.

[0017] The magnetic field-free line inertial drive unit 16 is a rotational displacement block used to control the magnetic field-free line generating unit 8 to rotate in the horizontal direction or translate in the first direction 1.

[0018] The current excitation unit 9 is a first circular coil, which is used to generate a scanning signal of the target waveform after a high-frequency excitation current is applied according to the required waveform.

[0019] The signal receiving unit 10 is a second circular coil, the size of which is within a preset range smaller than that of the first circular coil, and is used to receive magnetic particle response signals; the current excitation unit 9 and the signal receiving unit 10 in the cylindrical scanning device located in another position work together as a group;

[0020] The cylindrical scanning device located above has the same structure as the cylindrical scanning device located below, but they are oriented in opposite directions and are coaxial. The magnetic field line generating unit 8, the magnetic field line inertial drive unit 7, the magnetic field line inertial drive unit 16, the current excitation unit 9, and the signal receiving unit 10 are all coaxial, and except for the magnetic field line inertial drive unit 7, their rotation and translation are synchronized.

[0021] In some preferred embodiments, the non-magnetic field line generating unit 8 generates FFLs on a horizontal plane at the origin.

[0022] In some preferred embodiments, the external signal compensation module includes a compensation current excitation unit 11 and a compensation signal receiving unit 12;

[0023] The compensation current excitation unit 11 is the same size as the current excitation unit 9, and the compensation signal receiving unit 12 is the same size as the signal receiving unit 10.

[0024] The relative positions of the compensation current excitation unit 11 and the compensation signal receiving unit 12 are the same as the relative positions of the current excitation unit 9 and the signal receiving unit 10; the compensation current excitation unit 11 and the compensation signal receiving unit 12 located in another position work as a group; the current excitation unit 9 and the compensation current excitation unit 11 are connected in series through the excitation series cable 13, and the signal receiving unit 10 and the compensation signal receiving unit 12 are connected in series through the receiving series cable 14.

[0025] In some preferred embodiments, the electronic control module includes a displacement controller 17, a first power supply unit 18, a second power supply unit 19, and a third power supply unit 20;

[0026] The displacement controller 17 is used to drive the magnetic field-free linear inertial drive unit 16 to rotate or translate.

[0027] The first power supply unit 18 is used to supply power to the magnetic field-free, inertial-free drive unit 7;

[0028] The second power supply unit 19 is used to supply power to the current excitation unit 9 and the excitation unit 11 in the external compensation module;

[0029] The third power supply unit 20 is used to supply power to the platform 15.

[0030] In some preferred embodiments, the signal processing and image reconstruction module includes a signal processing unit 21 and an image reconstruction and display unit 22;

[0031] The signal processing unit 21 is connected to the signal receiving unit 10. The signal processing unit 21 includes a notch filter, an operational amplifier, and a signal acquisition card. It is used to filter out the direct feedthrough signal from the received magnetic particle response signal through the notch filter, and record the data through the acquisition card after passing through the operational amplifier to obtain the recorded data.

[0032] The image reconstruction and display unit 22 includes a data processing unit and an image display unit, used to reconstruct and display MPI images.

[0033] A second aspect of the present invention provides a magnetic field open-loop three-dimensional magnetic particle imaging method based on finite magnetic field resources. The method is implemented using the aforementioned magnetic field open-loop three-dimensional magnetic particle imaging device based on finite magnetic field resources, and includes:

[0034] Step S100: Determine the dimensions of system components based on the dimensions of the object under test, build the MPI imaging system, and define the MPI imaging field of view;

[0035] Step S200: Select a small sample filled with a high-concentration magnetic particle solution to scan each location point in the MPI imaging field of view, and rotate the magnetic field-free line uniformly between 0 and 180 degrees at each location point for repeated scanning. Based on the measured magnetic particle response signal, construct the MPI system matrix.

[0036] Step S300: The object to be tested is sent into the MPI imaging field of view via the stage 15;

[0037] Step S400: Scan the object under test layer by layer in a set order to obtain the time-domain magnetic particle response signal;

[0038] Step S500: Based on the time-domain magnetic particle response signal, perform a Fourier transform to obtain the frequency-domain magnetic particle response signal;

[0039] Step S600: Based on the MPI system matrix and the frequency domain magnetic particle response signal, construct the image reconstruction equation;

[0040] Step S700: Based on the image reconstruction equation, obtain the three-dimensional concentration distribution of magnetic particles.

[0041] In some preferred embodiments, step S200 specifically includes:

[0042] Step S210: Position the FFL at the bottom layer of the MPI imaging field of view;

[0043] Step S220: A preset sinusoidal current is passed into the magnetic field-free inertial drive unit 7 and the current excitation unit 9 to make the FFL scan all position points on the current horizontal plane.

[0044] Step S230: By controlling the non-magnetic field line inertial drive unit 7, the FFL is rotated by a preset angle. The method of step S220 is repeated to scan all position points on the current horizontal plane until a uniform rotation scan between 0 and 180 degrees on the current horizontal plane is completed. The non-magnetic field line inertial drive unit 16 is controlled to move the FFL up one layer.

[0045] Step S240: Repeat steps S220 to S230 until FFL completes scanning of all positions on the top layer, then move the small sample.

[0046] Step S250, repeat steps S220-S240 until the small sample traverses all locations in the MPI imaging field of view to obtain the time-domain magnetic particle response signal of the reference object.

[0047] Step S260: Based on the time-domain magnetic particle response signal of the reference object, perform Fourier transform to obtain the frequency-domain magnetic particle response signal of the reference object, and concatenate the frequency-domain magnetic particle response signals of the reference object to obtain the MPI system matrix.

[0048] In some preferred embodiments, the image reconstruction equation is:

[0049] Sc = u

[0050] S is the MPI system matrix, u is the frequency domain magnetic particle response signal, and c is the magnetic particle distribution vector c∈R to be determined. mn .

[0051] In some preferred embodiments, the image reconstruction equation is solved quickly using a method based on Kaczmarz iteration, specifically as follows:

[0052]

[0053] in, W is a weighted matrix, and row normalization of the system matrix is ​​performed using the energy of each row as an index, which can suppress components with poor signal-to-noise ratio; λ is a regularization parameter. This represents the L2 norm.

[0054] The above-described at least one technical solution adopted in the embodiments of this specification can achieve the following beneficial effects:

[0055] The method for generating an open field of view (FFL) using reverse magnetic pole arrangement, as used in this invention, eliminates the need for a high-power power supply module, avoids input current filtering, and eliminates the heat generation issue that may occur during prolonged operation, thus simplifying the system. Compared to elongated permanent magnets, it can generate a longer FFL, which is more advantageous for wide-field-of-view imaging. Attached Figure Description

[0056] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0057] Figure 1 A schematic diagram of the structure of an open three-dimensional magnetic particle imaging device based on magnetic field free lines provided in an embodiment of this specification;

[0058] Figure 2 A cross-sectional view of an open three-dimensional magnetic particle imaging device based on magnetic field free lines provided in one embodiment of this specification;

[0059] Figure 3 A simplified system diagram of an open three-dimensional magnetic particle imaging device based on magnetic field free lines provided in one embodiment of this specification;

[0060] Figure 4 This is a schematic diagram illustrating the effect of generating an FFL as provided in one embodiment of this specification;

[0061] Figure 5 This is a schematic diagram illustrating the effect of generating an FFL using a long strip permanent magnet in the prior art of this specification;

[0062] Figure 6 This is a schematic diagram illustrating the effect of generating an FFL using an electromagnetic coil in the prior art of this specification;

[0063] Figure 7 This is a schematic diagram illustrating the effect of an electromagnetic coil generating a uniform magnetic field according to an embodiment of this specification.

[0064] Figure 8 This is a schematic diagram illustrating the effect of rotating the FFL in the xy plane by rotating a permanent magnet, as provided in one embodiment of this specification.

[0065] Figure 9 This is a schematic diagram illustrating the effect of translating the FFL along the z-axis by translating the permanent magnet, as provided in one embodiment of this specification.

[0066] Figure 10This is a schematic diagram of the traditional arrangement and FOV of the open FFL receiver compensation coil in the prior art of this specification;

[0067] Figure 11 This is a schematic diagram of the arrangement and FOV of the external receiving compensation coil in one embodiment of this specification;

[0068] Figure 12 This is a flowchart illustrating the open three-dimensional magnetic particle imaging method based on magnetic field free lines according to the second embodiment of this specification.

[0069] Figure 13 This is a schematic diagram illustrating the principle of the open three-dimensional magnetic particle imaging method based on magnetic field free lines, as described in the second embodiment of this specification. Detailed Implementation

[0070] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0071] The technical solutions provided by the various embodiments of this application are described in detail below with reference to the accompanying drawings.

[0072] Figure 1 An open-type three-dimensional magnetic particle imaging device based on magnetic field free lines is provided as an embodiment of this specification. See also: Figure 1 , Figure 2 and Figure 3 The imaging device may include: a signal detection module, an electronic control module, an external signal compensation module, and a signal processing and image reconstruction module;

[0073] The signal detection module is configured to provide an open scanning environment by installing a magnetic field-free line generation unit 8, composed of circular permanent magnets arranged in two intersecting directions, and a signal receiving unit 10 in two coaxial cylindrical scanning devices that are symmetrically arranged vertically, thereby emitting an initial scanning signal and receiving magnetic particle response signals.

[0074] In this embodiment, the signal detection module specifically includes:

[0075] The system includes a stage 15, a magnetic field line generation unit 8, a magnetic field line inertial drive unit 7, a magnetic field line inertial drive unit 16, a current excitation unit 9, and a signal receiving unit 10.

[0076] Let the center point of two coaxial cylindrical scanning devices that are symmetrical about each other be the origin. Let the first direction 1 represent the vertical direction, and the second direction 2 and the third direction 3 represent two mutually perpendicular directions on the horizontal plane.

[0077] The stage 15 is a displacement bed used to fix the object to be measured and send it parallel into the imaging field of view of the device.

[0078] In the cylindrical scanning device located below:

[0079] The magnetic field-free line generation unit 8 is a pair of circular permanent magnets horizontally arranged in the middle of the cylindrical scanning device;

[0080] Each of the aforementioned circular permanent magnets, such as Figure 4 As shown, each is composed of two semi-circular permanent magnets with opposite magnetic pole directions. The magnetic pole directions of the two circular permanent magnets are crossed and stacked to form a pair of circular permanent magnets. All the circular permanent magnets are arranged with their magnetic pole directions crossed, as shown in the example. Figure 4 As shown in (a);

[0081] Traditional elongated permanent magnets generate FFLs such as Figure 5 As shown, the FFL generated by the electromagnetic coil is as follows Figure 6 As shown, compared with the FFL generated by the traditional permanent magnet shape, the FFL generated in this embodiment can have a larger range. Compared with the long strip permanent magnet, it can generate a longer FFL, which is more conducive to large field of view imaging.

[0082] The magnetic field-free line inertia-free drive unit 7 is a coil coaxial with the magnetic field-free line generating unit 8, which is installed in the inner arm of the cylindrical scanning device. The length of the magnetic field-free line inertia-free drive unit 7 is greater than the translational range of the magnetic field-free line generating unit 8 in the first direction 1. The magnetic field-free line inertia-free drive unit 7 is used to generate a uniform magnetic field in the vertical direction after being energized.

[0083] like Figure 7 As shown, this coil assembly can generate a wide-ranging uniform magnetic field along axis 1. When a certain frequency of alternating current in the same direction is simultaneously applied to both coils as required, it can drive the FFL to translate and scan in the xy direction, as shown. Figure 8 As shown.

[0084] The magnetic field-free line inertial drive unit 16 is a rotational displacement block used to control the magnetic field-free line generation unit 8 to rotate in the horizontal direction or translate in the first direction 1, such as... Figure 9 As shown;

[0085] The current excitation unit 9 is a first circular coil, which is used to generate a scanning signal of the target waveform after a high-frequency excitation current is applied to it according to the required waveform. The coil can be directly adjusted and replaced as needed. A high-frequency excitation current is applied to it according to the required waveform to generate the required waveform (sine wave, trapezoidal wave, square wave, etc.).

[0086] The signal receiving unit 10 is a second circular coil, the size of which is within a preset range smaller than that of the first circular coil, and is used to receive magnetic particle response signals; the current excitation unit 9 and the signal receiving unit 10 in the cylindrical scanning device located in another position work together; the magnetic particle response signal is a nonlinear response signal generated by magnetic particles in an alternating magnetic field.

[0087] The cylindrical scanning device located above has the same structure as the cylindrical scanning device located below, but they are oriented in opposite directions and are coaxial. The magnetic field line generating unit 8, the magnetic field line inertial drive unit 16, the current excitation unit 9, and the signal receiving unit 10 are all coaxial, and except for the magnetic field line inertial drive unit 7, their rotation and translation are synchronized.

[0088] The magnetic field-free line generation unit 8 generates an FFL on the horizontal plane between the current excitation unit 9 and the signal receiving unit 10, such as... Figure 4 As shown in b.

[0089] The electronic control module is used to control the position, intensity, and trajectory of the initial scanning signal emitted by the signal detection module;

[0090] In this embodiment, the electronic control module includes a displacement controller 17, a first power supply unit 18, a second power supply unit 19, and a third power supply unit 20;

[0091] The displacement controller 17 is used to drive the magnetic field-free linear inertial drive unit 16 to rotate or translate.

[0092] The first power supply unit 18 is used to supply power to the non-magnetic field line non-inertia drive unit 7. When working, it passes a sinusoidal current of the same magnitude and direction into the two coaxial coil non-magnetic field line non-inertia drive units 7 placed opposite each other, generating a uniform magnetic field that changes with time in space. After being superimposed with the gradient field, it can make the FFL translate in the xy plane.

[0093] The displacement controller 17 is connected to the magnetic field-free linear inertial drive unit 16, controlling the relatively placed permanent magnets to synchronously rotate and displace. When the permanent magnet rotates, the FFL (Field-Fluid Sensor) follows its rotation. Combined with the translation of the FFL in the xy plane, the position encoding of the magnetic particles in the xy plane can be achieved, enabling MPI two-dimensional imaging. When the permanent magnet displaces along the z-axis, the FFL follows its translation along the z-axis, achieving MPI three-dimensional imaging.

[0094] The second power supply unit 19 is used to supply power to the current excitation unit 9. The power supply unit 19 is connected to the current excitation unit 9. When working, it passes a high-frequency sinusoidal current of the same magnitude and direction into the two coaxial coil current excitation units 9 placed opposite each other, so as to excite the magnetic particles to generate a response signal.

[0095] The third power supply unit 20 is used to supply power to the platform 15.

[0096] The external signal compensation module is used to measure the direct feedthrough signal;

[0097] In this embodiment, the external signal compensation module includes a compensation current excitation unit 11 and a compensation signal receiving unit 12; the external signal compensation module in Figure 1 and Figure 2 In the diagram, 5 is the x-axis, 6 is the y-axis, and 4 is the z-axis.

[0098] The compensation current excitation unit 11 is the same size as the current excitation unit 9, and the compensation signal receiving unit 12 is the same size as the signal receiving unit 10.

[0099] The relative positions of the compensation current excitation unit 11 and the compensation signal receiving unit 12 are the same as the relative positions of the current excitation unit 9 and the signal receiving unit 10; the compensation current excitation unit 11 and the compensation signal receiving unit 12 located in another position work as a group.

[0100] In MPI systems, the receiving coil receives not only the response signal of the magnetic particles but also a direct feedthrough signal generated by the coaxial excitation coil. Therefore, a compensation coil needs to be added during the design phase. Under the same excitation and without a measured object, the direct feedthrough signal is measured, and subtracting this signal from the received signal yields the desired particle nonlinear response signal. In open MPI systems, the traditional arrangement of compensation coils is as follows: Figure 10 As shown in (a), because the compensation coil needs to measure the direct feedthrough signal in the absence of particles, the imaging field of view will be halved to a semicircle, as... Figure 10 As shown in (b). The external compensation method proposed in this invention is as follows: Figure 11 The imaging field of view shown in (a) is unaffected by the compensation coil and is a complete circle. Figure 11 As shown in (b). Furthermore, a greater distance between the compensation coil and the receiving coil reduces the impact of the compensation coil on the sensitivity of the imaging field of view, achieving a better effect.

[0101] The current excitation unit 9 and the compensation current excitation unit 11 are connected in series via an excitation series cable 13, and the signal receiving unit 10 and the compensation signal receiving unit 12 are connected in series via a receiving series cable 14.

[0102] The signal processing and image reconstruction module is used to process the magnetic particle response signal and the direct feedthrough signal to obtain a reconstructed image.

[0103] In this embodiment, the signal processing and image reconstruction module includes a signal processing unit 21 and an image reconstruction and display unit 22;

[0104] The signal processing unit 21 is connected to the signal receiving unit 10. The signal processing unit 21 includes a notch filter, an operational amplifier, and a signal acquisition card. It is used to filter out the direct feedthrough signal from the received magnetic particle response signal through the notch filter, and record the data through the acquisition card after passing through the operational amplifier to obtain the recorded data.

[0105] The image reconstruction and display unit 22 includes a data processing unit and an image display unit, used to reconstruct and display MPI images.

[0106] The second embodiment of the present invention, as follows: Figure 12 As shown, a magnetic field open-loop three-dimensional magnetic particle imaging method based on finite magnetic field resources is proposed, implemented using the aforementioned magnetic field open-loop three-dimensional magnetic particle imaging device based on finite magnetic field resources. The method includes:

[0107] Step S100: Based on the dimensions of the object under test, determine the dimensions of the system components, build the MPI imaging system, and define the MPI imaging field of view. In this embodiment, firstly, to ensure that the object under test can smoothly enter the device, determine the size of the open area in the middle of the device based on the maximum thickness of the target object under test; then adjust the material and thickness of the permanent magnet to adjust the intensity of its generated magnetic field, so that the magnetic field gradient within the imaging field of view matches the design value; to ensure the size of the scanning field of view, calculate the current amplitude required for the current excitation unit 9 and the inertial drive unit 7 without magnetic field lines during scanning. This completes the construction of the MPI imaging system and the determination of the MPI imaging field of view.

[0108] Step S200: A small-sized sample filled with a high-concentration magnetic particle solution is used to scan each location point in the MPI imaging field of view. At each location point, the sample is repeatedly scanned by uniformly rotating a magnetic field-free line between 0 and 179 degrees. Based on the measured magnetic particle response signal, the MPI system matrix is ​​constructed. In this embodiment, the small-sized sample is 1×1×1mm in size. 3 ;

[0109] In this embodiment, step S200 specifically includes:

[0110] Step S210: Position the FFL at the bottom layer of the MPI imaging field of view;

[0111] Step S220: A preset sinusoidal current is passed into the magnetic field-free inertial drive unit 7 and the current excitation unit 9 to make the FFL scan all position points on the current horizontal plane.

[0112] Step S230: By controlling the non-magnetic field line inertial drive unit 7, the FFL is rotated by a preset angle. The method of step S220 is repeated to scan all position points on the current horizontal plane until a uniform rotation scan between 0 and 180 degrees on the current horizontal plane is completed. The non-magnetic field line inertial drive unit 16 is controlled to move the FFL up one layer.

[0113] Step S240: Repeat steps S220 to S230 until FFL completes the scanning of all positions on the top layer and moves the small sample. In this embodiment, after completing the uniform rotation scan between 0 and 180 degrees on a horizontal plane, the two-dimensional system matrix of the current layer is obtained. After integrating all the two-dimensional system matrices, the MPI system matrix can be obtained.

[0114] Step S250, repeat steps S220-S240 until the small sample traverses all locations in the MPI imaging field of view to obtain the time-domain magnetic particle response signal of the reference object.

[0115] Step S260: Based on the time-domain magnetic particle response signal of the reference object, a Fourier transform is performed to obtain the frequency-domain magnetic particle response signal of the reference object. The frequency-domain magnetic particle response signals of the reference object are then concatenated to obtain the MPI system matrix. In the measurement at each position, the magnetic field-free linear inertial drive unit 16 measures every 1 degree from 0 to 180 degrees. The obtained time-domain signals are converted to the frequency domain by Fourier transform and concatenated to form the system matrix. Assuming that there are m positions on each surface, and a total of n planes, and 180nk frequency points are taken in each measurement, then the final three-dimensional system matrix is ​​S∈C. 180nk×mn ,like Figure 13 As shown.

[0116] Step S300: The object to be tested is sent into the MPI imaging field of view via the stage 15;

[0117] Step S400: Scan the object under test layer by layer according to the set sequence to obtain the time-domain magnetic particle response signal. Similar to the system matrix measurement step, first move the inertial drive unit 16 without magnetic field lines along the z-axis so that the FFL is located at the bottom of the imaging field of view. Pass a sinusoidal current into the inertial drive unit 7 without magnetic field lines and move the FFL on the xy plane for measurement. Then move the measurement upwards along the z-axis until all points in the entire imaging field of view have been measured. Each surface is also measured once every 1 degree from 0 to 179 degrees. The obtained time-domain signal is converted to the frequency domain by Fourier transform to obtain the signal u∈C of the object under test. 180nk .

[0118] Step S500: Based on the time-domain magnetic particle response signal, perform a Fourier transform to obtain the frequency-domain magnetic particle response signal;

[0119] Step S600: Based on the MPI system matrix and the frequency domain magnetic particle response signal, construct the image reconstruction equation;

[0120] The image reconstruction equation is:

[0121] Sc = u

[0122] S is the MPI system matrix, u is the frequency domain magnetic particle response signal, and c is the magnetic particle distribution vector c∈R to be determined. mn .

[0123] The image reconstruction equation is solved quickly using a method based on Kaczmarz iteration, specifically as follows:

[0124]

[0125] in, W is a weighted matrix, and row normalization of the system matrix is ​​performed using the energy of each row as an index, which can suppress components with poor signal-to-noise ratio; λ is a regularization parameter. This represents the L2 norm.

[0126] Step S700: Based on the image reconstruction equation, obtain the three-dimensional concentration distribution of magnetic particles.

[0127] The above description is merely an embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.

Claims

1. An open-type three-dimensional magnetic particle imaging device based on free lines of a magnetic field, characterized in that, The device includes: a signal detection module, an electronic control module, an external signal compensation module, and a signal processing and image reconstruction module; The signal detection module specifically includes: The system includes a stage (15), a magnetic field line generation unit (8), a magnetic field line inertial drive unit (7), a magnetic field line inertial drive unit (16), a current excitation unit (9), and a signal receiving unit (10). Let the center space point of two coaxial cylindrical scanning devices that are symmetrical about each other be taken as the origin. Let the first direction (1) represent the vertical direction, and the second direction (2) and the third direction (3) represent two mutually perpendicular directions on the horizontal plane. The stage (15) is a displacement bed; In the cylindrical scanning device located below: The magnetic field-free line generation unit (8) is a pair of circular permanent magnets horizontally arranged in the middle of the cylindrical scanning device; Each of the circular permanent magnets is composed of two semi-circular permanent magnets with opposite magnetic pole directions. The magnetic pole directions of the two circular permanent magnets are crossed and stacked to form a pair of circular permanent magnets. All the circular permanent magnets are arranged with their magnetic pole directions crossed. The magnetic field-free line inertial drive unit (7) is a coil coaxial with the magnetic field-free line generating unit (8) and installed in the inner arm of the cylindrical scanning device. The length of the magnetic field-free line inertial drive unit (7) is greater than the translational range of the magnetic field-free line generating unit (8) in the first direction (1). The magnetic field-free line inertial drive unit (7) is used to generate a uniform magnetic field in the vertical direction after being energized. The magnetic field-free line inertial drive unit (16) is a rotational displacement block used to control the magnetic field-free line generation unit (8) to rotate in the horizontal direction or translate in the first direction (1); The current excitation unit (9) is a first circular coil, which is used to generate a scanning signal of the target waveform after a high-frequency excitation current is applied according to the required waveform; The signal receiving unit (10) is a second circular coil, the size of which is smaller than that of the first circular coil, and is used to receive magnetic particle response signals; the current excitation unit (9) and the signal receiving unit (10) in the cylindrical scanning device located in another position work together; The cylindrical scanning device located above has the same structure as the cylindrical scanning device located below, but they are oriented oppositely and coaxial. The magnetic field line generating unit (8), the magnetic field line inertial drive unit (7), the magnetic field line inertial drive unit (16), the current excitation unit (9), and the signal receiving unit (10) are all coaxial, and except for the magnetic field line inertial drive unit (7), their rotation and translation are synchronized. The electronic control module is used to control the position, intensity, and trajectory of the initial scanning signal emitted by the signal detection module; The external signal compensation module is used to measure the direct feedthrough signal; The signal processing and image reconstruction module is used to process the magnetic particle response signal and the direct feedthrough signal to obtain a reconstructed image.

2. The open-type three-dimensional magnetic particle imaging device based on free lines of magnetic fields according to claim 1, characterized in that, The magnetic field-free line generation unit (8) generates an FFL on a horizontal plane between the current excitation unit (9) and the signal receiving unit (10).

3. The open-type three-dimensional magnetic particle imaging device based on magnetic field free lines according to claim 1, characterized in that, The external signal compensation module includes a compensation current excitation unit (11) and a compensation signal receiving unit (12). The compensation current excitation unit (11) is the same size as the current excitation unit (9), and the compensation signal receiving unit (12) is the same size as the signal receiving unit (10). The relative positions of the compensation current excitation unit (11) and the compensation signal receiving unit (12) are the same as the relative positions of the current excitation unit (9) and the signal receiving unit (10); The compensation current excitation unit (11) and the compensation signal receiving unit (12) located in another position work together; The current excitation unit (9) and the compensation current excitation unit (11) are connected in series via an excitation series cable (13), and the signal receiving unit (10) and the compensation signal receiving unit (12) are connected in series via a receiving series cable (14).

4. The open-type three-dimensional magnetic particle imaging device based on magnetic field free lines according to claim 1, characterized in that, The electronic control module includes a displacement controller (17), a first power supply unit (18), a second power supply unit (19), and a third power supply unit (20). The displacement controller (17) is used to drive the magnetic field-free linear inertial drive unit (16) to rotate or translate; The first power supply unit (18) is used to supply power to the non-magnetic field line non-inertial drive unit (7); The second power supply unit (19) is used to supply power to the current excitation unit (9) and the compensation current excitation unit (11); The third power supply unit (20) is used to supply power to the stage (15).

5. The open-type three-dimensional magnetic particle imaging device based on magnetic field free lines according to claim 1, characterized in that, The signal processing and image reconstruction module includes a signal processing unit (21) and an image reconstruction and display unit (22). The signal processing unit (21) is connected to the signal receiving unit (10). The signal processing unit (21) includes a notch filter, an operational amplifier, and a signal acquisition card. It is used to filter out the direct feedthrough signal of the received magnetic particle response signal through the notch filter, and record the data through the acquisition card after passing through the operational amplifier. The image reconstruction and display unit (22) includes a data processing unit and an image display unit, used to reconstruct and display MPI images.

6. A magnetic field open-loop three-dimensional magnetic particle imaging method based on limited magnetic field resources, characterized in that, The method is implemented using the open-type three-dimensional magnetic particle imaging device based on limited magnetic field resources as described in any one of claims 1-5, and includes: Step S100: Determine the dimensions of system components based on the dimensions of the object under test: an MPI imaging system can be built, and the MPI imaging field of view can be defined; Step S200: Select a small sample filled with a high-concentration magnetic particle solution to scan each location point in the MPI imaging field of view, and rotate the magnetic field-free line uniformly between 0 and 180 degrees at each location point for repeated scanning. Based on the measured magnetic particle response signal, construct the MPI system matrix. Step S300: The object to be tested is sent into the MPI imaging field of view through the stage (15); Step S400: Scan the object under test layer by layer in a set order to obtain the time-domain magnetic particle response signal; Step S500: Based on the time-domain magnetic particle response signal, perform a Fourier transform to obtain the frequency-domain magnetic particle response signal; Step S600: Based on the MPI system matrix and the frequency domain magnetic particle response signal, construct the image reconstruction equation; Step S700: Based on the image reconstruction equation, obtain the three-dimensional concentration distribution of magnetic particles.

7. The open-field three-dimensional magnetic particle imaging method based on limited magnetic field resources according to claim 6, characterized in that, Step S200 specifically includes: Step S210: Position the FFL at the bottom of the MPI imaging field of view; Step S220: A preset sinusoidal current is passed into the non-magnetic field line inertial drive unit (7) and the current excitation unit (9) to make the FFL scan all position points on the current horizontal plane. Step S230: By controlling the non-magnetic field line inertial drive unit (7), the FFL is rotated by a preset angle. The method of step S220 is repeated to scan all position points on the current horizontal plane until the uniform rotation scan between 0-180 degrees on the current horizontal plane is completed. The non-magnetic field line inertial drive unit (16) is controlled to move the FFL up one layer. Step S240: Repeat steps S220 to S230 until FFL completes scanning of all positions on the top layer, then move the small sample. Step S250, repeat steps S220-S240 until the small sample traverses all locations in the MPI imaging field of view to obtain the time-domain magnetic particle response signal of the reference object. Step S260: Based on the time-domain magnetic particle response signal of the reference object, perform Fourier transform to obtain the frequency-domain magnetic particle response signal of the reference object, and concatenate the frequency-domain magnetic particle response signals of the reference object to obtain the MPI system matrix.

8. The open-field three-dimensional magnetic particle imaging method based on limited magnetic field resources according to claim 6, characterized in that, The image reconstruction equation is: ； Let u be the frequency domain magnetic particle response signal, and represent the MPI system matrix. Let be the magnetic particle distribution vector to be determined. .

9. The open-field three-dimensional magnetic particle imaging method based on limited magnetic field resources according to claim 8, characterized in that, The image reconstruction equation is solved quickly using a method based on Kaczmarz iteration, specifically as follows: ； in, , It is a weighted matrix that normalizes the system matrix using the energy of each row as an indicator, which can suppress components with poor signal-to-noise ratio. For regularization parameters, This represents the L2 norm.

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