Non-magnetic field line three-dimensional magnetic particle imaging method and system based on weak gradient coding

Abstract

The invention relates to the technical field of magnetic particle imaging, in particular to a non-magnetic field line three-dimensional magnetic particle imaging method and system based on weak gradient coding, and the method comprises the steps: driving a zero magnetic field line to carry out the spiral scanning of an imaging object; exciting a nonlinear response signal generated by magnetic particles of the imaging object; obtaining a two-dimensional image of magnetic particle concentration distribution in the imaging object; performing spatial position coding on the zero magnetic field line; obtaining target magnetic particle concentration distribution on the zero magnetic field line; and obtaining a three-dimensional image of the magnetic particle concentration distribution in the imaging object. According to the invention, the zero magnetic field line along the axial direction is constructed, and the Halbach permanent magnet array is driven to carry out visual field scanning of two-dimensional imaging. Two-dimensional imaging is carried out by adopting axial projection, then three-dimensional reconstruction is carried out under the guidance of the two-dimensional reconstruction image, and the three-dimensional reconstruction image is reconstructed by encoding the zero magnetic field line, that is, the three-dimensional image reconstruction can be completed only by scanning twice, and the imaging speed is higher compared with the traditional three-dimensional tomography.

Description

Technical Field

[0001] The invention relates to the technical field of magnetic particle imaging, and in particular to a method and system for three-dimensional magnetic particle imaging without magnetic field lines based on weak gradient encoding. Background Art

[0002] Magnetic particle imaging (MPI) technology uses the nonlinear response of magnetic nanoparticles in the magnetic field free zone of a high gradient magnetic field to obtain the distribution and concentration of magnetic nanoparticles in the body, and has the characteristics of high temporal resolution, high spatial resolution and high sensitivity. In addition, MPI does not display anatomical structures and has no background signal interference, so the signal intensity is directly proportional to the concentration of the tracer, which is a new imaging method with great potential for medical applications.

[0003] Magnetic particle imaging measures the nonlinear magnetization response signal of magnetic particles, and then obtains the magnetic particle distribution image based on the spatial encoding of the zero magnetic field region (Field Free Region, FFR). The gradient of the zero magnetic field region determines the spatial resolution of the magnetic particle imaging device. There are currently two methods for constructing the zero magnetic field region. The first is the zero magnetic field point (Field Free Point, FFP), which generates an FFP point in space through a pair of coils or permanent magnets with the same polarity relative to each other, and the sensing area is the weak magnetic field area near the FFP. The second is the zero magnetic field line (Field Free Line, FFL), which generates an FFL in space through a relatively more complex pair of coils or permanent magnets, and its sensing area is the weak magnetic field area near the FFL. Compared with FFP-type magnetic particle sensing imaging devices, FFL-type magnetic particle sensing imaging devices have more advantages in sensitivity.

[0004] The imaging method of zero magnetic field lines in the prior art includes: generating zero magnetic field lines, driving the zero magnetic field lines to move in a set direction; detecting the voltage signal generated on the surface of the object under test during the zero magnetic field line scanning process; determining the radius of the blood vessel according to the amplitude of the voltage signal and the set reference value; determining the position of the zero magnetic field lines at different times according to the voltage signal, and determining the position of the blood vessel centerline according to the position: imaging the blood vessel of the object under test based on the position of the blood vessel centerline and the radius. The prior art also has a magnetic particle imaging system based on magnetic field-free line scanning, which is intended to solve the problem that the sensitivity and resolution of the magnetic particle imaging system cannot meet the requirements. The system comprises a magnet group, an induction coil, an imaging bed, and a control and imaging device. The magnet group comprises two pairs of annular magnet pairs with axes arranged orthogonally and a cylindrical magnet; two annular magnets in the annular magnet pairs are coaxial; the cylindrical magnet is arranged in the enclosed space of the two pairs of annular magnets, and its axis passes through the orthogonal point of the axes of the two pairs of annular magnet pairs and is perpendicular to the plane formed by the axes of the two pairs of annular magnet pairs; the control and imaging device controls the magnetic field changes of each magnet in the magnet group according to the set control instructions, realizes the rotation and / or translation of the generated magnetic field-free line, and performs magnetic particle imaging according to the current signal generated in the induction coil by the induced magnetic field.

[0005] However, in the prior art, MPI uses multiple electromagnetic coil pairs to generate zero magnetic field areas, but the magnetic field leakage of multiple coil pairs is large, the generated selection field gradient value is limited, or the power consumption is increased to generate a high gradient field. These methods undoubtedly increase the cost of the equipment. In addition, the existing coil pairs and permanent magnet pairs generate anisotropic spatial selection fields, resulting in anisotropic characteristics of the reconstructed image, which seriously affects the imaging quality. In addition, when the electromagnetic coil drives the zero magnetic field area (FFP or FFL) to cover the imaging field of view scanning, when the spatial selection field gradient is large, the power consumption required for the driving field coil is very large. For example, for a 10cm imaging field of view and a 2 T / m spatial selection field, the power consumption required for the magnetic particle imaging device generally exceeds 70kW. The huge power consumption causes the coil to heat up seriously, which seriously affects the stability of the device. In addition, the driving coil generates a large alternating uniform magnetic field, so the coil will vibrate due to the changing Lorentz force, and the vibration will also cause the stability of the MPI device to deteriorate. At the same time, the electromagnetic coil drive design cost and power consumption cost are large. Secondly, when the existing FFL magnetic particle imaging device reconstructs three-dimensional imaging, it is necessary to complete two-dimensional tomography first, and then complete three-dimensional imaging through different section scanning, which results in a long three-dimensional scanning time.

[0006] Therefore, it is necessary to provide a method and system for three-dimensional magnetic particle imaging without magnetic field lines based on weak gradient encoding to solve the above problems. Summary of the invention

[0007] The present invention provides a three-dimensional magnetic particle imaging method and system without magnetic field lines based on weak gradient coding to solve the existing problems.

[0008] The present invention provides a method and system for three-dimensional magnetic particle imaging without magnetic field lines based on weak gradient encoding, which adopts the following technical solutions, including: A permanent magnetic array is used to generate zero magnetic field lines, and the zero magnetic field lines are driven to perform spiral scanning on the imaging object; Applying an alternating magnetic field to the imaging object during the spiral scanning process to stimulate the nonlinear response signal generated by the magnetic particles in the imaging object; Based on the nonlinear response signal generated by the magnetic particles of the imaging object, a two-dimensional image of the concentration distribution of the magnetic particles in the imaging object is obtained by using the X-space method; Applying a weak gradient magnetic field to the zero magnetic field line to encode the spatial position of the zero magnetic field line, wherein the range of the weak gradient magnetic field is 1 mT~5 mT; The magnetic particle concentration distribution on the zero magnetic field line is reconstructed according to the spatial position encoding and the nonlinear response signal to obtain the target magnetic particle concentration distribution on the zero magnetic field line; The target magnetic particle concentration distribution on the zero magnetic field line is fused with the magnetic particle concentration distribution in the two-dimensional image to obtain a three-dimensional image.

[0009] Preferably, the step of generating zero magnetic field lines by using a permanent magnet array is: using a Halbach permanent magnet array with K=2 to generate zero magnetic field lines, and the magnetic field gradient values ​​of the Halbach permanent magnet array in the symmetric direction are the same.

[0010] Preferably, an excitation coil is used to generate an alternating uniform magnetic field and excite magnetic particles of the imaging object to generate nonlinear response signals, and a gradient receiving coil is used to receive the nonlinear response signals of the magnetic particles.

[0011] Preferably, the step of imaging a two-dimensional image of the concentration distribution of magnetic particles in the object is: When performing spiral scanning on the imaging object, the scanning position of the zero magnetic field line is obtained in real time; After the scanning is completed, a two-dimensional image is obtained according to the trajectory formed by the scanning position of the zero magnetic field line and the non-linear response signals of the magnetic particles collected according to the two-dimensional spatial mapping.

[0012] Preferably, the step of encoding the spatial position of the zero magnetic field line is: A bias coil is used to generate a static weak gradient magnetic field; Different magnetic field strengths are assigned to each spatial position of the zero magnetic field line to obtain spatial position encoding Preferably, the step of obtaining the target magnetic particle concentration distribution on the zero magnetic field line is: Moving the zero magnetic field line to the two-dimensional reconstruction target area according to the two-dimensional reconstruction result; Acquire nonlinear response signals of magnetic particles at different positions on the zero magnetic field line at the position; Then, the nonlinear response signal is subjected to Fourier transformation to obtain the frequency signal and amplitude signal of the nonlinear response of the magnetic particles; According to the principle of nonlinear response of magnetic particles, and using the spatial position of magnetic particles on the zero magnetic field line and the frequency signal and amplitude signal corresponding to the spatial position, the spatial concentration distribution of each magnetic particle on the zero magnetic field line is reconstructed point by point according to the two-dimensional image results to obtain the target magnetic particle concentration distribution.

[0013] A three-dimensional magnetic particle imaging system without magnetic field lines based on weak gradient encoding, comprising: A supporting turntable on which a Halbach permanent magnet array is disposed; A three-dimensional mechanical arm assembly, the output end of which is provided with a support frame for placing an imaging object, and the three-dimensional mechanical arm assembly is used to place the imaging object in the Halbach permanent magnet array; A driving assembly, used for driving the supporting turntable to rotate, and driving the Halbach permanent magnet array on the supporting turntable to move radially along the supporting turntable, so that the zero magnetic field lines generated by the Halbach permanent magnet array perform spiral scanning on the imaging object; And an imaging module, which is used in the imaging method of the present invention to obtain a three-dimensional image of the imaging object.

[0014] Preferably, the imaging module comprises: An excitation unit, used for applying an alternating magnetic field to the imaging object during the spiral scanning process to excite the nonlinear response signal generated by the magnetic particles of the imaging object; A two-dimensional imaging unit, used for imaging a two-dimensional image of the concentration distribution of magnetic particles in the imaging object using an X-space method according to a nonlinear response signal generated by magnetic particles of the imaging object; A bias unit, used for applying a weak gradient magnetic field to the zero magnetic field line to encode the spatial position of the zero magnetic field line, wherein the range of the weak gradient magnetic field is 1mT~5mT; A magnetic particle concentration distribution reconstruction unit is used to reconstruct the magnetic particle concentration distribution on the zero magnetic field line according to the spatial position encoding and the nonlinear response signal to obtain the target magnetic particle concentration distribution on the zero magnetic field line; And a three-dimensional image unit is used to fuse the target magnetic particle concentration distribution with the magnetic particle concentration distribution in the two-dimensional image to obtain a three-dimensional image.

[0015] Preferably, the excitation unit comprises: An excitation link component, used to generate an alternating magnetic field to excite the nonlinear response of magnetic particles of an imaging object, comprising: a signal source, a power amplifier, a filter and an excitation coil; and a receiving link component for receiving a nonlinear response signal of a magnetic particle, comprising: a gradient receiving coil, a filter and a low noise amplifier, wherein the gradient receiving coil comprises: a receiving coil and a compensation coil; The gradient receiving coil is connected to the support through a connecting shaft, the excitation coil is concentrically sleeved outside the gradient receiving coil, the bias unit is a bias coil, and the bias coil is arranged at the connection between the gradient receiving coil and the connecting shaft.

[0016] Preferably, the drive assembly comprises: A rotating motor is suspended by a support frame, an output shaft of which is vertically arranged and is a hollow shaft, and a support turntable is horizontally arranged on the top of the output shaft, wherein a support is fixed on the support frame, a connecting shaft on the support is passed through the hollow shaft, and a gradient receiving coil at the end of the connecting shaft passes through the support turntable and is located in a Halbach permanent magnet array; And a linear motor, which is arranged at the bottom of the supporting turntable, and its output shaft is a lead screw. A slider arranged on the lead screw is slidably arranged in a guide groove opened on the supporting turntable, and the top of the slider is connected to a support seat arranged at the bottom of the Halbach permanent magnet array, and the support seat is slidably connected to a slide rail arranged at the top of the supporting turntable.

[0017] The beneficial effects of the present invention are: 1. A zero magnetic field line along the axial direction is constructed by adopting a Halbach permanent magnet array in the form of K=2, and the Halbach permanent magnet array is driven to perform field of view scanning for two-dimensional imaging. Axial projection is used for two-dimensional imaging, and then three-dimensional reconstruction is guided by the two-dimensional reconstructed image. The three-dimensional reconstructed image is reconstructed by encoding the zero magnetic field line. That is, in this process, the present invention uses a mechanically driven FFL to perform two-dimensional scanning, determine the two-dimensional plane position of the target, and then set the bias field to perform spatial encoding on the FFL, collect the signal on the FFL, and solve the target on the FFL line according to the FFL line coding system matrix. Then the reconstruction result on the FFL line is fused with the two-dimensional reconstruction result to obtain a three-dimensional imaging result. The method adopted by the present invention only needs two scans to complete the three-dimensional image reconstruction, and its imaging speed is faster than that of traditional three-dimensional tomography.

[0018] 2. The K=2 mode Halbach permanent magnet array is used to generate zero magnetic field lines. The K=2 mode Halbach permanent magnet array can effectively utilize the static magnetic field of each magnet, generate a large gradient field in a large field of view, and achieve zero power consumption. In addition, the magnetic field gradient values ​​of the permanent magnet array in the symmetric direction used in the present invention are the same, and an image with isotropic phase can be reconstructed, thereby improving the imaging quality.

[0019] 3. A three-axis mechanical drive is used to drive the zero magnetic field lines generated by the Halbach permanent magnet array to rotate, and two-dimensional scanning imaging can be achieved through rotation and translation. The support frame of the three-dimensional mechanical arm assembly is used to carry the imaging object to be measured, which drives the imaging object to be measured and uses FFL encoding to achieve three-dimensional imaging. The present invention uses mechanical drive to greatly reduce the power consumption required for the drive coil, and provides vibration during the mechanical scanning process through mechanical balance design, which solves the vibration phenomenon during the scanning process of the electromagnetic drive coil. The use of mechanical drive greatly reduces the power consumption and equipment cost of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a schematic diagram of the overall structure of a three-dimensional magnetic particle imaging system without magnetic field lines based on weak gradient encoding of the present invention; Figure 2 A top view of a three-dimensional magnetic particle imaging system without magnetic field lines based on weak gradient encoding according to the present invention; Figure 3 It is a structural schematic diagram of the Halbach permanent magnet array; Figure 4 The internal magnetic field distribution diagram of the Halbach permanent magnet array with K=2; Figure 5 This is the magnetic field density distribution diagram of the Halbach permanent magnet array with K=2; Figure 6 Schematic diagram of the scanning trajectory of the zero magnetic field line; Figure 7 It is a structural diagram of the excitation unit; Figure 8 This is the schematic diagram of the excitation unit; Fig. 9 is the schematic diagram of the bias unit; Fig.10 It is a schematic diagram of the two-dimensional X-space imaging process; Fig.11 Schematic diagram of the 3D reconstruction process; Fig.12 The present invention is a flow chart of a method for three-dimensional magnetic particle imaging without magnetic field lines based on weak gradient encoding.

[0022] In the figure: 1. Halbach permanent magnet array; 2. three-dimensional robotic arm assembly; 3. linear motor; 4. rotary motor; 5. bias coil; 6. excitation coil; 7. gradient receiving coil; 8. slip ring; 9. zero magnetic field line; 10. slide rail; 11. support turntable; 12. lead screw; 71. receiving coil; 72. compensation coil. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] A three-dimensional magnetic particle imaging system without magnetic field lines based on weak gradient encoding comprises: a supporting turntable 11, a three-dimensional mechanical arm component 2, a driving component and an imaging module, wherein a Halbach permanent magnet array 1 is arranged on the supporting turntable 11; a supporting frame for placing an imaging object is arranged at the output end of the three-dimensional mechanical arm component 2, and the three-dimensional mechanical arm component 2 is used to place the imaging object in the Halbach permanent magnet array 1; the driving component is used to drive the supporting turntable 11 to rotate, and drive the Halbach permanent magnet array 1 on the supporting turntable 11 to move radially along the supporting turntable 11, so that the zero magnetic field lines 9 generated by the Halbach permanent magnet array 1 perform a spiral scan on the imaging object; and the imaging module is used to obtain a three-dimensional image of the imaging object.

[0025] Specifically, the imaging module includes: an excitation unit, a two-dimensional image unit, a bias unit, a magnetic particle concentration distribution reconstruction unit and a three-dimensional image unit, wherein the excitation unit is used to apply an alternating magnetic field to the imaging object during the spiral scanning process to stimulate the nonlinear response signal generated by the magnetic particles of the imaging object; the two-dimensional image unit is used to obtain a two-dimensional image of the magnetic particle concentration distribution in the imaging object according to the nonlinear response signal generated by the magnetic particles of the imaging object and using the X-space method; the bias unit is used to apply a weak gradient magnetic field to the zero magnetic field line 9 to encode the spatial position of the zero magnetic field line 9, wherein the range of the weak gradient magnetic field is 1mT~5mT; the magnetic particle concentration distribution reconstruction unit is used to reconstruct the magnetic particle concentration distribution on the zero magnetic field line 9 according to the spatial position encoding and the nonlinear response signal to obtain the target magnetic particle concentration distribution on the zero magnetic field line 9; the three-dimensional image unit is used to fuse the target magnetic particle concentration distribution with the magnetic particle concentration distribution in the two-dimensional image to obtain a three-dimensional image of the magnetic particle concentration distribution.

[0026] Specifically, the excitation unit includes: an excitation link component and a receiving link component. The excitation link component is used to generate an alternating magnetic field to excite the nonlinear response of the magnetic particles of the imaging object. The excitation link component includes: a signal source, a power amplifier, a filter and an excitation coil 6; the receiving link component is used to receive the nonlinear response signal of the magnetic particles. The receiving link component includes: a gradient receiving coil 7, a filter and a low noise amplifier; wherein the gradient receiving coil 7 is connected to the support through a connecting shaft, such as Figure 7 As shown, the excitation coil 6 is concentrically sleeved outside the gradient receiving coil 7, the bias unit is the bias coil 5, and the bias coil 5 is arranged at the connection between the gradient receiving coil 7 and the connecting shaft; it should be noted that, as Figure 7 As shown, the bias coil 5 generates a static weak gradient magnetic field, which is referred to as the bias field in the present invention. The bias field is represented by Hdc, and the bias field strength decreases nonlinearly with the distance from the bias coil 5, as shown in FIG. Figure 8 As shown, the zero magnetic field line 9 (FFL) perpendicular to the bias coil 5 is spatially encoded, wherein the excitation coil 6 is wound with a spiral tube, the excitation coil generates an alternating uniform magnetic field and excites the magnetic particles of the imaging object to generate a nonlinear response signal; the gradient receiving coil is used to receive the nonlinear response signal of the magnetic particles. The excitation coil and the gradient receiving coil are coaxially placed. Figure 8 As shown, the gradient receiving coil 7 adopts a two-segment gradient coil, and the gradient receiving coil 7 includes: a receiving coil 71 and a compensation coil 72. Figure 8 The receiving coil 71 shown receives the nonlinear response signal of the magnetic particles. Figure 8 The compensation coil 72 is used to offset the feedthrough interference signal coupled from the excitation coil 6.

[0027] Specifically, the driving assembly includes: a rotary motor 4 and a linear motor 3, the rotary motor 4 is suspended by a support frame, the output shaft of the rotary motor 4 is vertically arranged and is a hollow shaft, and the support turntable 11 is horizontally arranged on the top of the output shaft, wherein the support is fixed on the support frame, the connecting shaft on the support is passed through the hollow shaft, and the gradient receiving coil at the end of the connecting shaft passes through the support turntable 11 and is located in the Halbach permanent magnet array 1; Figure 1 and Figure 2 As shown, the linear motor 3 is arranged at the bottom of the support turntable 11, and the output shaft of the linear motor 3 is a lead screw 12. The slider arranged on the lead screw 12 is slidably arranged in a guide groove opened on the support turntable 11, and the top of the slider is connected to the support seat arranged at the bottom of the Halbach permanent magnet array 1, and the support seat is slidably connected to the slide rail 10 arranged at the top of the support turntable 11, wherein a slip ring 8 is fixed at the bottom of the support frame, and the slip ring 8 is set on the connecting shaft, and the wires of the linear motor 3 are connected to the power supply through the slip ring 8.

[0028] An embodiment of a method for three-dimensional magnetic particle imaging without magnetic field lines based on weak gradient encoding of the present invention is as follows: Fig.12 As shown, including: S1, driving the zero magnetic field line to perform spiral scanning on the imaging object; Specifically, a permanent magnetic array is used to generate zero magnetic field lines 9, and the zero magnetic field lines 9 are driven to perform spiral scanning on the imaging object; Step 11: The step of using the permanent magnet array to generate zero magnetic field lines 9 is as follows: In this embodiment, the following Figure 3 The zero magnetic field line 9 (FFL) generated by the Halbach permanent magnet array 1 with K=2 shown in the figure can effectively utilize the static magnetic field of each magnet, can generate a large gradient field in a large field of view, and achieve zero power consumption. In addition, the magnetic field gradient values ​​of the Halbach permanent magnet array 1 used in this embodiment are the same in the symmetric direction, and an image with isotropic phase can be reconstructed, thereby improving the imaging quality. It should be noted that the spatial selection field magnetic field distribution and the zero magnetic field line 9 (FFL) generated by the Halbach permanent magnet array 1 with K=2 are shown in FIG. Figure 4 As shown; the spatial selection field magnetic field density distribution diagram is shown Figure 5 shown.

[0029] Step 12: Use the driving assembly to drive the support turntable 11 to rotate, and drive the Halbach permanent magnet array 1 on the support turntable 11 to move radially along the support turntable 11, so that the zero magnetic field line 9 generated by the Halbach permanent magnet array 1 performs a spiral scan on the imaging object. Figure 1 and Figure 2 As shown, the imaging object is first placed on the support frame set at the output end of the three-dimensional mechanical arm component 2, and then the imaging object is moved to the center of the Halbach permanent magnet array 1 by the three-dimensional mechanical arm component 2. Then, the rotating motor 4 of the driving component is used to drive the Halbach permanent magnet array 1 to perform circular motion around the center of the supporting turntable 11, that is, the zero magnetic field line 9 (FFL) generated by the zero-driven Halbach permanent magnet array 1 is performed in a circular motion around the center of the supporting turntable 11, and the linear motor 3 of the driving component drives the Halbach permanent magnet array 1 to move radially along the supporting turntable 11, that is, the zero magnetic field line 9 (FFL) generated by the Halbach permanent magnet array 1 is driven to move radially along the supporting turntable 11. The combination of the two movements makes the zero magnetic field line 9 (FFL) generated by the Halbach permanent magnet array 1 to spirally move around the center of the supporting turntable 11, thereby realizing spiral scanning of the imaging object. Among them, the trajectory diagram of the zero magnetic field line 9 (FFL) generated by the Halbach permanent magnet array 1 when performing spiral motion without magnetic field excitation is shown in FIG. Figure 6 shown.

[0030]

[0031] in, Indicates the rotation angle of the supporting turntable 11; Indicates the distance between the zero magnetic field line 9 and the center of the disk; represents the rotational angular velocity of the zero magnetic field line 9, represents the maximum distance that the zero magnetic field line 9 moves radially in the support turntable 11, is the radial movement distance of the zero magnetic field lines.

[0032] S2, nonlinear response signal generated by magnetic particles that excite the imaging object; An alternating magnetic field is applied to the imaging object during the spiral scanning process to excite the nonlinear response signal generated by the magnetic particles of the imaging object. In this embodiment, an excitation coil 6 is used to generate an alternating uniform magnetic field and excite the magnetic particles of the imaging object to generate a nonlinear response signal, and a gradient receiving coil 7 is used to receive the nonlinear response signal of the magnetic particles. The excitation coil 6 is a spiral tube coil or a Maxwell coil, such as Figure 8 As shown, the signal source passes through the power amplifier and the filter to input the frequency of the excitation coil 6. The current signal ,(in represents the current signal amplitude, represents the phase of the current signal, Represents the frequency of the current signal) can generate an alternating magnetic field with the same frequency, such as Figure 8 As shown, when the driving component drives the zero magnetic field line 9 generated by the Halbach permanent magnet array 1 to perform spiral motion, the alternating magnetic field generated by the excitation coil 6 excites the magnetic particles of the imaging object near the zero magnetic field line to generate a nonlinear response signal, and the gradient receiving coil 7 receives the nonlinear response signal of the magnetic particles (time domain signal), that is, the gradient receiving coil 7 obtains the nonlinear response signal generated by the alternating magnetic field generated by the excitation coil 6 to excite the magnetic particles of the imaging object.

[0033] S3, obtaining a two-dimensional image of the concentration distribution of magnetic particles in the imaging object; Specifically, based on the nonlinear response signal generated by the magnetic particles of the imaging object, the X-space method is used to obtain a two-dimensional image of the concentration distribution of the magnetic particles in the imaging object; it should be noted that the X-space reconstruction method is used to reconstruct the two-dimensional image based on the received nonlinear response signal (time domain signal).

[0034] In this embodiment, Fig. 9 As shown, during two-dimensional scanning, the driving component drives the zero magnetic field line 9 generated by the Halbach permanent magnet array 1 to perform spiral scanning, and obtains the scanning position of the zero magnetic field line 9 in real time; Figure 8As shown, while scanning, the AC signal of step S2 (the AC signal generated by the signal source and amplified by the first power amplifier and filtered by the filter) is input to the excitation coil 6 so that the excitation coil 6 generates an alternating magnetic field, and the alternating magnetic field excites the magnetic particles of the imaging object to generate a nonlinear response signal. Figure 8 The receiving coil 71 shown receives the nonlinear response signal of the magnetic particles. Figure 8 The compensation coil 72 is used to offset the feedthrough interference signal coupled from the excitation coil 6. After the scan is completed, the trajectory formed by the scanning position of the zero magnetic field line 9 and the non-linear response signal of the magnetic particles collected according to the two-dimensional spatial mapping are used to obtain a two-dimensional X-space imaging, and thus, a two-dimensional image of the imaging object is obtained.

[0035] S4, encoding the spatial position of the zero magnetic field line; A weak gradient magnetic field is applied to the zero magnetic field line 9 to encode the spatial position of the zero magnetic field line 9, wherein the range of the weak gradient magnetic field is 1 mT to 5 mT; after the two-dimensional scanning in step S3 is completed, as Figure 8 As shown, the bias coil 5 is turned on, and a DC signal is input into the bias coil 5. The DC signal generated by the signal generator is amplified by the second power amplifier and then input into the bias coil 5. Fig. 9 As shown, the bias coil 5 generates a static weak gradient magnetic field, which imparts a different magnetic field strength to each spatial position of the zero magnetic field line 9 in the figure, that is, spatial position encoding of the zero magnetic field line 9 is achieved.

[0036] S5, obtaining the target magnetic particle concentration distribution on the zero magnetic field line; Reconstructing the magnetic particle concentration distribution on the zero magnetic field line 9 according to the spatial position encoding and the nonlinear response signal to obtain the target magnetic particle concentration distribution on the zero magnetic field line 9; like Fig.11 As shown, during three-dimensional reconstruction, firstly, the zero magnetic field line 9 is moved to the two-dimensional reconstruction target area of ​​the area showing the magnetic particle concentration distribution according to the two-dimensional reconstruction result, and at the same time, the excitation coil 6, the bias coil 5 and the gradient receiving coil 7 are turned on, and the gradient receiving coil 7 receives the nonlinear response signals of the magnetic particles at different positions on the zero magnetic field line 9 at this position, and then the received nonlinear response signal is Fourier transformed to obtain the frequency signal and amplitude signal of the nonlinear response of the magnetic particles. At the same time, according to the nonlinear response principle of magnetic particles, U=S·C, wherein U represents the frequency domain voltage signal affected by the nonlinearity of the received magnetic particles, S represents the system matrix, which is a two-dimensional array, and the system matrix includes the spatial position information and the frequency signal corresponding to the spatial position, and C represents the spatial concentration distribution of the magnetic particles; as shown in FIG. Fig.10 As shown, by solving C = U·S -1The spatial concentration distribution of magnetic particles on the zero magnetic field line can be obtained. According to the principle of nonlinear response of magnetic particles, and using the spatial position of magnetic particles on the zero magnetic field line 9 and the frequency signal and amplitude signal corresponding to the spatial position, the spatial concentration distribution of each magnetic particle on the zero magnetic field line 9 is reconstructed point by point (points with magnetic particle distribution in the two-dimensional image) to obtain the target magnetic particle concentration distribution according to the two-dimensional image as the magnetic particle concentration distribution result.

[0037] S6, obtaining a three-dimensional image of the concentration distribution of magnetic particles in the imaging object; Specifically, according to the target magnetic particle concentration distribution on the zero magnetic field line 9, a dimension is added to the two-dimensional image to reconstruct the magnetic particle concentration distribution on the zero magnetic field line 9, and the three-dimensional reconstruction information of the magnetic particle spatial concentration distribution can be fused to obtain a fused three-dimensional image.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for three-dimensional magnetic particle imaging without magnetic field lines based on weak gradient encoding, characterized in that: include: A permanent magnetic array is used to generate zero magnetic field lines, and the zero magnetic field lines are driven to perform spiral scanning on the imaging object; Applying an alternating magnetic field to the imaging object during the spiral scanning process to stimulate the nonlinear response signal generated by the magnetic particles in the imaging object; Based on the nonlinear response signal generated by the magnetic particles of the imaging object, a two-dimensional image of the concentration distribution of the magnetic particles in the imaging object is obtained by using the X-space method; Applying a weak gradient magnetic field to the zero magnetic field line to encode the spatial position of the zero magnetic field line, wherein the range of the weak gradient magnetic field is 1 mT~5 mT; The magnetic particle concentration distribution on the zero magnetic field line is reconstructed according to the spatial position encoding and the nonlinear response signal to obtain the target magnetic particle concentration distribution on the zero magnetic field line; The target magnetic particle concentration distribution is fused with the magnetic particle concentration distribution in the two-dimensional image to obtain a three-dimensional image of the magnetic particle concentration distribution in the imaging object.

2. The method of three-dimensional magnetic particle imaging based on weak gradient encoding and free magnetic field lines according to claim 1, characterized in that: The steps of generating zero magnetic field lines by using a permanent magnet array are as follows: using a Halbach permanent magnet array with K=2 to generate zero magnetic field lines, and the magnetic field gradient values ​​of the Halbach permanent magnet array in the symmetric direction are the same.

3. The method of three-dimensional magnetic particle imaging based on weak gradient encoding and free magnetic field lines according to claim 1, characterized in that: An excitation coil is used to generate an alternating uniform magnetic field and excite magnetic particles of the imaging object to generate nonlinear response signals, and a gradient receiving coil is used to receive the nonlinear response signals of the magnetic particles.

4. The method of three-dimensional magnetic particle imaging based on weak gradient encoding and free magnetic field lines according to claim 1, characterized in that: The steps for imaging a two-dimensional image of the magnetic particle concentration distribution in an object are: When performing spiral scanning on the imaging object, the scanning position of the zero magnetic field line is obtained in real time; After the scanning is completed, a two-dimensional image is obtained according to the trajectory formed by the scanning position of the zero magnetic field line and the non-linear response signals of the magnetic particles collected according to the two-dimensional spatial mapping.

5. The method of three-dimensional magnetic particle imaging based on weak gradient encoding and free magnetic field lines according to claim 1, characterized in that: The steps to encode the spatial position of the zero magnetic field line are: A bias coil is used to generate a static weak gradient magnetic field; Different magnetic field strengths are assigned to each spatial position of the zero magnetic field line to obtain spatial position encoding.

6. The method of three-dimensional magnetic particle imaging based on weak gradient encoding and free magnetic field lines according to claim 1, characterized in that: The steps to obtain the target magnetic particle concentration distribution on the zero magnetic field line are: Moving the zero magnetic field line to the two-dimensional reconstruction target area according to the two-dimensional reconstruction result; Acquire nonlinear response signals of magnetic particles at different positions on the zero magnetic field line at the position; Then, the nonlinear response signal is subjected to Fourier transformation to obtain the frequency signal and amplitude signal of the nonlinear response of the magnetic particles; According to the principle of nonlinear response of magnetic particles, and using the spatial position of magnetic particles on the zero magnetic field line and the frequency signal and amplitude signal corresponding to the spatial position, the spatial concentration distribution of each magnetic particle on the zero magnetic field line is reconstructed point by point according to the two-dimensional image results to obtain the target magnetic particle concentration distribution.

7. A three-dimensional magnetic particle imaging system without magnetic field lines based on weak gradient encoding, characterized in that: include: A supporting turntable (11) on which a Halbach permanent magnet array (1) is arranged; A three-dimensional mechanical arm assembly (2), the output end of which is provided with a support frame for placing an imaging object, and the three-dimensional mechanical arm assembly (2) is used to place the imaging object in the Halbach permanent magnet array (1); A driving assembly, used for driving the supporting turntable (11) to rotate, and driving the Halbach permanent magnet array (1) on the supporting turntable (11) to move radially along the supporting turntable (11), so that the zero magnetic field lines (9) generated by the Halbach permanent magnet array (1) perform spiral scanning on the imaging object; And an imaging module, used for acquiring a three-dimensional image of an imaging object according to the imaging method according to any one of claims 1-6.

8. The three-dimensional magnetic particle imaging system based on weak gradient encoding and free magnetic field lines according to claim 7, characterized in that: The imaging module includes: An excitation unit, used for applying an alternating magnetic field to the imaging object during the spiral scanning process to excite the nonlinear response signal generated by the magnetic particles of the imaging object; A two-dimensional imaging unit, used for imaging a two-dimensional image of the concentration distribution of magnetic particles in the imaging object using an X-space method according to a nonlinear response signal generated by magnetic particles of the imaging object; A bias unit, used for applying a weak gradient magnetic field to the zero magnetic field line (9) to perform spatial position encoding on the zero magnetic field line (9), wherein the weak gradient magnetic field has a range of 1 mT to 5 mT; A magnetic particle concentration distribution reconstruction unit is used to reconstruct the magnetic particle concentration distribution on the zero magnetic field line (9) according to the spatial position encoding and the nonlinear response signal, so as to obtain the target magnetic particle concentration distribution on the zero magnetic field line (9); And a three-dimensional image unit is used to fuse the target magnetic particle concentration distribution with the magnetic particle concentration distribution in the two-dimensional image to obtain a three-dimensional image of the magnetic particle concentration distribution in the imaging object.

9. A three-dimensional magnetic particle imaging system based on weak gradient encoding and free magnetic field lines according to claim 8, characterized in that: The excitation unit includes: An excitation link component, used to generate an alternating magnetic field to excite the nonlinear response of magnetic particles of the imaging object, comprising: a signal source, a power amplifier, a filter and an excitation coil (6); and a receiving link component for receiving a nonlinear response signal of a magnetic particle, comprising: a gradient receiving coil (7), a filter and a low noise amplifier, wherein the gradient receiving coil (7) comprises: a receiving coil (71) and a compensation coil (72); The gradient receiving coil (7) is connected to the support via a connecting shaft, the excitation coil (6) is concentrically sleeved outside the gradient receiving coil, the bias unit is a bias coil (5), and the bias coil (5) is arranged at the connection between the gradient receiving coil (7) and the connecting shaft.

10. The three-dimensional magnetic particle imaging system based on weak gradient encoding and free magnetic field lines according to claim 7, characterized in that: The drive components include: A rotating motor (4) is suspended by a support frame, its output shaft is vertically arranged and is a hollow shaft, and a support turntable (11) is horizontally arranged on the top of the output shaft, wherein a support is fixed on the support frame, a connecting shaft on the support is inserted into the hollow shaft, and a gradient receiving coil (7) at the end of the connecting shaft passes through the support turntable (11) and is located in the Halbach permanent magnet array (1); And a linear motor (3), which is arranged at the bottom of the support turntable (11), and its output shaft is a lead screw (12), a slider arranged on the lead screw (12) is slidably arranged in a guide slot opened on the support turntable (11), and the top of the slider is connected to a support seat arranged at the bottom of the Halbach permanent magnet array (1), and the support seat is slidably connected to a slide rail (10) arranged at the top of the support turntable (11).

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