Unilateral magnetic particle imaging system and method based on gradient bias magnetic field

Abstract

The invention relates to a single-side magnetic particle imaging system based on a gradient bias magnetic field. The single-side magnetic particle imaging system comprises a gradient bias coil, an exciting coil, a receiving coil and a compensating coil, the gradient bias coils are symmetrically distributed on the two sides outside the system, the excitation coils are symmetrically distributed on the two sides, different from the gradient bias coils, inside the system, and the receiving coil and the compensation coil are symmetrically distributed on the two sides, corresponding to the excitation coils, outside the system. According to the invention, the bias magnetic field changing along with the detection depth is generated in the depth direction, the FFR does not need to be constructed, the influence of the size of a free point of the magnetic field on the resolution is avoided, the detection depth and sensitivity are improved, and the resolution in the horizontal and depth directions is provided by utilizing the mutual constraint of spatial information at different positions.

Description

Technical Field

[0001] The present invention relates to the field of magnetic particle imaging, and in particular to a unilateral magnetic particle imaging system and method based on a gradient bias magnetic field. Background Art

[0002] Magnetic Particle Imaging (MPI) is an emerging tomographic imaging technology that can achieve fast and accurate imaging. This technology detects the nonlinear magnetization signal of superparamagnetic ironoxide nanoparticles (SPIONs) in a changing magnetic field, and then reconstructs the concentration distribution of particles in the area to be tested. At the same time, compared with other imaging methods, magnetic particle imaging equipment is easier to achieve high-resolution and high-sensitivity imaging, quantitative rapid dynamic scanning, and no ionizing radiation. Therefore, magnetic particle imaging equipment has broad application prospects in the fields of rapid clinical diagnosis and real-time intraoperative monitoring.

[0003] The unilateral MPI system concentrates all the hardware on one side of the system, has no restrictions on the volume of the imaged object, can provide local imaging for specific body parts, and has significant potential for clinical application. The spatial magnetic field of the unilateral MPI system consists of a driving field and a selection field, both of which are generated by a unilateral solenoid coil. The system consists of an external gradient coil and an internal excitation coil, as well as a receiving coil and a compensation coil at both ends of the system. The unilateral magnetic particle imaging system is not restricted by the size of the subject and also has the advantages of traditional magnetic particle imaging technology, making it the most promising solution for clinical application first. However, the magnetic field penetration depth of unilateral devices is limited, so they are mostly considered for the detection of sentinel lymph nodes in breast cancer patients and intraoperative guidance in breast-conserving surgery.

[0004] The unilateral MPI system based on FFR encoding (Field-Free Resonance Encoding) includes two methods: FFP (Field-Free Point, zero magnetic field point) / FFL (Field-Free Line, zero magnetic field line). By scanning the imaging area according to the scanning trajectory, the space in the imaging area can be spatially encoded. Among them, the scanning trajectory is divided into Lissajous trajectory and Cartesian trajectory. The first is the unilateral MPI encoding method based on FFP. Based on the unilateral structure, a double-layer reverse coil is used as the selection field to generate FFP in the depth direction. The excitation coil and the gradient coil are combined into one. By changing the current size of the inner and outer coils, the FFP is driven to move in the depth direction to achieve one-dimensional reconstruction. In order to realize two-dimensional FFP scanning, in addition to the coil that drives the one-dimensional FFP movement along the axis direction, a magnetic field perpendicular to the axis needs to be generated. Therefore, a pair of semicircular coils can be added in front of the selection field as a lateral driving field. The two semicircular coils can generate a magnetic field perpendicular to the axis direction in space through the reverse current, and the magnetic field strength changes accordingly when the current size is changed. The two sets of coils cooperate with each other to realize the movement of FFP in two-dimensional space. The single-sided MPI encoding method based on FFL uses two saddle-shaped coils placed side by side as selection coils. Currents in the same direction are passed through the two coils to generate a zero magnetic field line directly above the two coils. By changing the currents in the two coils, the position of the FFL can be moved horizontally. Another saddle-shaped coil is placed in the exact center of the two coils as a drive coil. High-frequency alternating current is passed through the drive coil to stimulate the nonlinear response of magnetic particles and move the position of the FFL up and down. Through the interaction of magnetic fields, the FFL can be moved and scanned within the imaging area, thereby realizing two-dimensional spatial encoding. Rotating the coil or phantom can achieve three-dimensional spatial encoding.

[0005] The single-sided MPI system based on FFR encoding has some difficult-to-overcome engineering problems. First, the selection field of FFP / FFL along the depth direction is usually composed of electromagnetic coils. When it is necessary to detect distant objects or high-resolution imaging, the volume of the coil will become huge and the power consumption will increase exponentially. At this time, the limitation of the volume and power of the single-sided MPI is an issue that must be considered. Secondly, the magnetic field distribution generated by the single-sided coil decays along the depth direction, which means that it is difficult to form an effective FFP / FFL at a deeper position. At this time, the magnetic field gradient near the FFR is small and the spatial resolution will be limited. At the same time, it is difficult to move the FFP / FFL along the depth direction, and it is difficult to detect magnetic particle signals in deep layers. The existence of these problems restricts the further development of the single-sided MPI system. Summary of the invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a unilateral magnetic particle imaging system and method based on a gradient bias magnetic field.

[0007] According to a first aspect of an embodiment of the present invention, a unilateral magnetic particle imaging system based on a gradient bias magnetic field is provided, the system comprising: a gradient bias coil, an excitation coil, a receiving coil and a compensation coil; the gradient bias coil is symmetrically distributed on two sides outside the system, the excitation coil is symmetrically distributed on two sides inside the system different from the gradient bias coil, and the receiving coil and the compensation coil are symmetrically distributed on two sides outside the system corresponding to the position of the excitation coil.

[0008] According to a second aspect of an embodiment of the present invention, a unilateral magnetic particle imaging method based on a gradient bias magnetic field is provided, the method comprising:

[0009] Collecting particle harmonic signals under various bias conditions as harmonic signal groups; wherein the various bias conditions are obtained by changing the current of the bias coil;

[0010] According to the harmonic signal group, constructing a basic system function of hybrid constraints;

[0011] Expanding the constrained basic system function according to the spatial positions of different sampling points to obtain an expanded system function;

[0012] Image reconstruction is performed according to the extended system function to obtain a spatial distribution image of the magnetic particle concentration.

[0013] Optionally, before collecting the particle harmonic signals under a plurality of bias conditions as the harmonic signal group, the method further comprises:

[0014] Acquiring a spatial particle voltage signal according to the phantom image and the magnetic field distribution of the gradient bias magnetic field;

[0015] Perform Fourier transform on the spatial particle voltage signal to obtain a particle harmonic signal.

[0016] Optionally, constructing a basic system function of a hybrid constraint according to the harmonic signal group includes:

[0017] Obtaining basic system functions under various bias conditions according to the harmonic signal group;

[0018] A basic system function with mixed constraints is obtained according to the basic system functions under the multiple bias conditions.

[0019] Optionally, performing image reconstruction according to the extended system function to obtain a spatial distribution image of magnetic particle concentration includes:

[0020] Collecting harmonic signal groups at the spatial positions of the different sampling points to obtain a total signal;

[0021] Image reconstruction is performed according to the total signal and the extended system function to obtain a spatial distribution image of the magnetic particle concentration.

[0022] Optionally, the basic system function reference of the hybrid constraint is expressed as follows:

[0023]

[0024] in, is the basic system function of the hybrid constraint, n represents the harmonic order, This represents the basic system function for the variable magnetic field construction of the nth harmonic.

[0025] Optionally, the basic system function reference is represented as follows:

[0026]

[0027] in, Indicates that a current A is passed through the bias magnetic field coil E After the position r M The nth harmonic particle harmonic signal at , E represents the number of different currents passing through the bias magnetic field, and M represents the number of positions in the discrete space.

[0028] Optionally, image reconstruction is performed according to the extended system function with reference to the following expression:

[0029]

[0030] Wherein, Img represents the spatial distribution image of the magnetic particle concentration, reshape(·) represents the rearrangement of the magnetic particle concentration distribution, represents the concentration distribution of magnetic particles in space, i represents the number of pixels of the abscissa in the two-dimensional imaging, and j represents the number of pixels of the ordinate in the two-dimensional imaging.

[0031] The technical solution provided by the present invention may include the following beneficial effects:

[0032] Through the above technical solution, a single-sided solenoid coil is used as a bias coil to generate a gradient bias magnetic field that decays along the depth direction in space. The gradient field amplitude is changed by changing the current of the bias coil, and then a system function between the particle signal at the spatial position and the changing gradient magnetic field is constructed. The spatial particle concentration distribution can be reconstructed without constructing an FFR for scanning, thereby having a smaller volume of the MPI coil. Considering that the distribution of the gradient magnetic field in space is symmetrically diffused, different positions have the same magnetic field strength in two-dimensional and three-dimensional space. In order to solve the problem that positions with the same magnetic field strength in two-dimensional and three-dimensional space cannot be spatially encoded, high-resolution two-dimensional imaging is finally achieved by collecting particle signals at different positions.

[0033] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0035] Figure 1 The figure is a schematic diagram of the coil structure of a unilateral magnetic particle imaging system based on a gradient bias magnetic field according to an exemplary embodiment.

[0036] Figure 2 It is a schematic diagram of the overall structure of a unilateral magnetic particle imaging system based on a gradient bias magnetic field according to an exemplary embodiment.

[0037] Figure 3 The present invention is a flow chart showing a method for unilateral magnetic particle imaging based on a gradient bias magnetic field according to an exemplary embodiment.

[0038] Figure 4 It is a flow chart of a single-sided magnetic particle imaging method based on a gradient bias magnetic field according to an exemplary embodiment.

[0039] Figure 5 is a schematic diagram of a basic system function according to an exemplary embodiment.

[0040] Figure 6 The present invention is a flow chart showing a method for unilateral magnetic particle imaging based on a gradient bias magnetic field according to an exemplary embodiment. DETAILED DESCRIPTION

[0041] In order to facilitate the understanding of the scheme of the present invention, the relevant state of the prior art and the inventive concept of the present invention are first briefly described.

[0042] In the prior art, a zero magnetic field line is generated in the traditional MPI, and an alternating pulsed magnetic field is generated in the direction of the zero magnetic field line, and the pulsed magnetic field is used to induce the relaxation attenuation signal of the magnetic particles; along the direction of the zero magnetic field line, by moving the position of the pulse coil or changing its current, the changing magnetic field traverses the entire imaging area in space, thereby obtaining the relaxation signal of the magnetic particles under different magnetic fields. By obtaining the voltage signal generated by the distribution of magnetic nanoparticles, the time domain attenuation area of ​​the voltage signal obtained in each half pulse oscillation cycle is used as the imaging parameter. The concentration distribution of magnetic nanoparticles can be reconstructed and imaged by constructing a system matrix using the particle signals and spatial position information under different magnetic fields.

[0043] In the prior art, there is also a method of using a flat plate structure with built-in excitation coils and receiving coils to generate a nonlinear and non-uniform excitation magnetic field according to a preset excitation magnetic field adjustment strategy; the excitation magnetic field adjustment strategy includes adjusting the positions of the excitation coils and receiving coils in the flat plate structure, and adjusting the current applied to the excitation coils in the flat plate structure; obtaining the induced voltage signal generated by the receiving coil under the nonlinear and non-uniform excitation magnetic field of the imaging target. A system matrix is ​​constructed based on the voltage signal of the magnetic particle distribution, and an image of the concentration distribution of the magnetic particles in the imaging target is reconstructed; wherein the system matrix is ​​used to characterize the spatial distribution corresponding to the target acquisition data generated by the unit concentration of magnetic particles under the excitation magnetic field; the target acquisition data includes the peak amplitude of the signal or 3 times the fundamental frequency harmonic component.

[0044] According to the above content, it is not difficult to see that most of the existing technical solutions are based on the methods proposed by the closed magnetic particle imaging equipment. At present, there is no solution for the unilateral MPI system to perform spatial encoding without selecting the field, that is, the field free zone. In combination with the above-mentioned existing technologies, in order to solve the problems of large equipment size, high power consumption, low spatial resolution and low sensitivity, the present invention proposes a unilateral magnetic particle imaging system and method based on a gradient bias magnetic field.

[0045] Figure 1 is a schematic diagram of a coil structure of a unilateral magnetic particle imaging system based on a gradient bias magnetic field according to an exemplary embodiment. Figure 1 As shown, the system includes: a gradient bias coil, an excitation coil, a receiving coil and a compensation coil; the gradient bias coil is symmetrically distributed on two sides outside the system, the excitation coil is symmetrically distributed on two sides inside the system different from the gradient bias coil, and the receiving coil and the compensation coil are symmetrically distributed on two sides outside the system corresponding to the position of the excitation coil.

[0046] It is understood that the excitation coil and the gradient magnetic field coil include but are not limited to: cylindrical solenoid coil, horn spiral coil, planar coil, and multilayer structure and the combination of the above structures. The signal receiving coil includes but is not limited to: cylindrical solenoid coil, horn spiral coil, planar coil, and multilayer structure and the combination of the above structures, and the specific selection depends on the usage scenario.

[0047] Figure 2 is a schematic diagram of the overall structure of a unilateral magnetic particle imaging system based on a gradient bias magnetic field according to an exemplary embodiment. Figure 2 As shown, in addition to the excitation coil 1, the gradient bias coil 2, the receiving coil 3 and the compensation coil 4, a water cooling tube 5 and a fine-tuning knob 6 may also be included; the water cooling tube 5 provides cooling for the coil during long-term operation to ensure the stability of the equipment, and the fine-tuning knob 6 is used to adjust the position of the compensation coil to better offset the fundamental frequency component.

[0048] It can be understood that the excitation coil, the gradient bias coil and the receiving coil for receiving the spatial particle signal are the basic components of the MPI device. Among them, the gradient bias coil applies different magnetic field strengths at different positions in space, which can encode the spatial position; the excitation coil generates an excitation signal to excite the particle signal in space; and the receiving coil receives the magnetization signal from all particles in space.

[0049] Figure 3 is a flow chart of a unilateral magnetic particle imaging method based on a gradient bias magnetic field according to an exemplary embodiment. Figure 3 As shown, the method may include the following steps:

[0050] S1. Collecting particle harmonic signals under various bias conditions as a harmonic signal group; wherein the various bias conditions are obtained by changing the current of the bias coil.

[0051] It can be understood that this method is applied to a unilateral magnetic particle imaging system, using the bias coil in the unilateral magnetic particle imaging system, changing the bias coil current, and obtaining a changing bias magnetic field in the imaging space. Following the changing bias conditions, particle harmonic signals under different bias conditions can be collected.

[0052] Optionally, before S1, the method may further include:

[0053] Acquiring a spatial particle voltage signal according to the phantom image and the magnetic field distribution of the gradient bias magnetic field;

[0054] Perform Fourier transform on the spatial particle voltage signal to obtain the particle harmonic signal.

[0055] It can be understood that, firstly, the spatial particle voltage signal is obtained according to the magnetic field distribution of the phantom image and the gradient bias magnetic field, and the spatial particle voltage signal is subjected to Fourier transformation, so that the particle harmonic signal containing the characteristic value of the high-order harmonic can be obtained, that is, after the spatial particle voltage signal is subjected to Fourier transformation, more than one harmonic signal is obtained. It is worth mentioning that the present invention uses the third harmonic of the nonlinear response of the magnetic particle as the characteristic value. Similarly, the present invention can also be represented by other parameters (3rd harmonic, 5th harmonic, mixed harmonic, signal peak, etc.) of other excitation waveforms (square wave, trapezoidal wave, triangle wave, etc.), and the time domain attenuation area of ​​square wave excitation is used as the characteristic value.

[0056] S2. Construct a basic system function of hybrid constraints based on the harmonic signal group.

[0057] Optionally, S2 may include:

[0058] Obtaining basic system functions under various bias conditions according to the harmonic signal group;

[0059] The basic system function of the mixed constraint is obtained according to the basic system functions under various bias conditions.

[0060] It can be understood that the harmonic signal of each spatial position is obtained according to the magnetic field distribution of the imaging space and the gradient bias magnetic field, and the basic system function is constructed by combining different bias magnetic fields as the column vector of the system function and different spatial positions as the row vector of the system function. Then, the basic system function of the hybrid constraint can be constructed based on the method of the variable gradient bias magnetic field system function according to the harmonic signal group composed of the particle harmonic signals containing different harmonic signals.

[0061] It can be understood that the basic principle of MPI signal generation relies on the nonlinear magnetization response of magnetic particles to an applied magnetic field H. When an excitation magnetic field of sufficient amplitude is applied, the magnetization response of the particles will be induced. Compared with the excitation magnetic field, the magnetization response of the particles will show an obvious high-order harmonic spectrum. First, define the sinusoidal excitation magnetic field H AC , and then a variable offset magnetic field H is applied in the direction of the excitation magnetic field DC , in order to study the change of particle high harmonics with the offset magnetic field. Since the magnetic field strength of the single-sided MPI device varies with the spatial position, the spatial position variable r is introduced into the magnetic field expression. Therefore, the excitation magnetic field can be expressed as follows:

[0062] H AC (r,t)=A0(r)cos(ω0t);

[0063] Where t represents the periodic time of the excitation magnetic field change, A0(r) represents the excitation magnetic field amplitude at the spatial position r, and ω0 is the excitation magnetic field frequency.

[0064] Since the frequency of the offset magnetic field is much lower than the frequency of the excitation magnetic field, in a short period, the offset magnetic field is only affected by the position r, which is denoted as H. DC (r), the variation range of the offset magnetic field is 0 <H DC (r)≤A1(r), where A1(r) represents the maximum offset magnetic field intensity at position r. At this time, the total magnetic field in the time domain can be expressed as follows:

[0065] H(r,t)=H DC (r)-H AC (r,t).

[0066] Optionally, the basic system function reference is expressed as follows:

[0067]

[0068] in, Indicates that a current A is passed through the bias magnetic field coil E After the position r M The nth harmonic particle harmonic signal at , E represents the number of different currents passing through the bias magnetic field, and M represents the number of positions in the discrete space. is the system function component, It is the signal representation in the frequency domain, which is obtained based on the total magnetic field H(r,t) in the time domain.

[0069] Optionally, after the signal is Fourier transformed, more than one harmonic signal is obtained. If different harmonic signals are combined, a basic system function of a hybrid constraint can be constructed based on a method of a variable gradient bias magnetic field system function. The basic system function of the hybrid constraint is represented as follows:

[0070]

[0071] in, is the basic system function of the mixed constraint, n represents the harmonic order, This represents the basic system function for the variable magnetic field construction of the nth harmonic.

[0072] It can be understood that the harmonic signal of each spatial position is obtained according to the magnetic field distribution of the imaging space and the gradient bias magnetic field, and the basic system function is constructed by combining different bias magnetic fields as the column vector of the system function and different spatial positions as the row vector of the system function. Then, the basic system function of the hybrid constraint can be constructed based on the method of the variable gradient bias magnetic field system function according to the harmonic signal group composed of the particle harmonic signals containing different harmonic signals.

[0073] S3. Expand the constrained basic system function through the spatial positions of different sampling points to obtain an extended system function.

[0074] S4. Perform image reconstruction according to the extended system function to obtain a spatial distribution image of the magnetic particle concentration.

[0075] Optionally, S4 may include:

[0076] Collecting harmonic signal groups at different spatial locations of sampling points to obtain a total signal;

[0077] Image reconstruction is performed based on the total signal and the extended system function to obtain the spatial distribution image of the magnetic particle concentration.

[0078] For example, the spatial particle concentration distribution can be solved based on the extended system function and the total signal as follows:

[0079] The characteristic value of the receiving coil voltage signal is decomposed into a spectrum signal by Fourier transforming the received voltage signal The spatial distribution of magnetic particles can be obtained based on the system function and the characteristic value of the voltage signal of the receiving coil. The relationship between and the spatial distribution c of magnetic particles can be expressed as:

[0080]

[0081] Since the number of frequency components and discrete spatial positions is often not the same, the system function is not a square matrix and cannot be calculated using matrix inversion. Linear equations are often used to solve the inverse problem and obtain the spatial distribution of magnetic particles. The least squares method is a commonly used method for solving non-square linear equations. It solves the approximate solution by minimizing the sum of squares of the residuals. Combined with the least squares method, the least squares problem for the MPI system can be expressed as:

[0082]

[0083] It can be understood that, by moving the device, the basic system function is expanded according to the spatial positions of different sampling points, thereby obtaining the extended system function.

[0084] Based on the system function constructed by the variable bias magnetic field, the extended system function is constructed by introducing the structural space information. The imaging space is mainly expanded along the sampling point direction, and then the spatial position of the system function is rearranged according to the spatial position relationship of the sampling points, so that the collected signal and the system function can correspond. The total signal for solution is constructed according to the harmonic signal group at different sampling point positions. In order to correspond to the extended system function, the spatial particle concentration distribution also needs to be expanded. The expanded concentration distribution is c extern , extended system functions and extended receiving voltage signal The relationship can be specifically expressed as follows:

[0085]

[0086] Solve c according to the system function solution method extern , and obtain the concentration distribution of magnetic particles in space in the selected FOV (Field of View) area

[0087] Magnetic particle concentration distribution based on the selected imaging area The rearrangement and image reconstruction reference are expressed as follows:

[0088]

[0089] Where Img represents the spatial distribution image of the magnetic particle concentration in the selected imaging area, reshape(·) represents the rearrangement of the magnetic particle concentration distribution, represents the concentration distribution of magnetic particles in space, i represents the number of pixels of the abscissa in the two-dimensional imaging, and j represents the number of pixels of the ordinate in the two-dimensional imaging.

[0090] It is worth mentioning that when reconstructing an image, you can also use a single sampling point to reconstruct the image first, and then perform image processing on multiple sampling points to reconstruct the image to obtain a two-dimensional high-resolution image, thereby replacing the step of extending the system function. The specific expression is shown in the following formula:

[0091]

[0092] Among them, Img Space Represented as the reconstructed image, Img k represents the reconstructed image when there is only a single sampling point k, reshift(Img,x,y) means that the image is moved by x pixels along the horizontal axis and y pixels along the vertical axis relative to the unilateral MPI system, keeping the imaging area unchanged and filling the missing parts with zeros, Sample(k) represents the spatial position corresponding to the sampling point, which is expressed in the formula as the unilateral MPI is moved by Sample(k) positions on the vertical axis relative to the imaging area. The final two-dimensional reconstructed image can be obtained by operating and processing the images reconstructed under all sampling points and summing them. The number of sampling points k directly affects the quality of the reconstructed image.

[0093] In one implementation, taking two-dimensional image reconstruction as an example, Figure 4 is a flow chart of a method for unilateral magnetic particle imaging based on a gradient bias magnetic field according to an exemplary embodiment. Figure 5 is a schematic diagram of a basic system function according to an exemplary embodiment. Figure 6 This is a flow chart of a unilateral magnetic particle imaging method based on a gradient bias magnetic field according to an exemplary embodiment. The specific process is as follows:

[0094] (1) An imaging area is selected, marked as a detection plane, and a number of sampling points at multiple spatial positions are set.

[0095] (2) A unilateral magnetic particle imaging system having an excitation coil, a bias coil, and a signal receiving and compensating coil is used to generate a nonlinear gradient magnetic field in the depth direction; magnetic field distributions of different intensities are obtained by adjusting the current of the gradient bias coil.

[0096] (3) Figure 5 and Figure 6 As shown, in the imaging area, the magnetic particles are under the gradient bias magnetic field, and the receiving coil receives the spatial particle voltage signal, and the harmonic signal of the particles in the space is obtained through Fourier transform. At this time, part of the system function can be obtained; there are different magnetic field distributions under different bias magnetic field conditions, and the harmonic signals under different bias magnetic fields can be expressed as harmonic signal groups, thereby forming a basic system function. According to the spatial position of different sampling points, the basic system function is expanded to obtain the extended system function.

[0097] (4) On the marked imaging plane, particle signals at different positions are collected along the calibrated sampling points; the collection process includes aligning the center of the receiving plane of the unilateral magnetic particle device with the sampling point and using the translation device to collect the total signal.

[0098] (5) Reconstructing the magnetic particle concentration distribution in the imaging area according to the total signal and the extended system function to obtain a two-dimensional reconstructed image.

[0099] It is worth mentioning that the present invention takes two-dimensional reconstruction as an example to demonstrate the strategy of constructing a system function by changing the bias magnetic field strength, and introduces spatial information constraints. The extended system function is constructed by the sampling point acquisition method to realize the two-dimensional image reconstruction method. The three-dimensional reconstruction of a specific area can also be realized. Only by collecting two-dimensional sampling point data in the sampling point part, three-dimensional magnetic particle imaging can be realized.

[0100] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0101] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0102] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A unilateral magnetic particle imaging system based on a gradient bias magnetic field, characterized in that: The system comprises: a gradient bias coil, an excitation coil, a receiving coil and a compensation coil; the gradient bias coil is symmetrically distributed on two sides outside the system, the excitation coil is symmetrically distributed on two sides inside the system different from the gradient bias coil, and the receiving coil and the compensation coil are symmetrically distributed on two sides outside the system corresponding to the position of the excitation coil.

2. A unilateral magnetic particle imaging method based on a gradient bias magnetic field, applied to a unilateral magnetic particle imaging system based on a gradient bias magnetic field, characterized in that: The method comprises: Collecting particle harmonic signals under various bias conditions as harmonic signal groups; wherein the various bias conditions are obtained by changing the current of the bias coil; According to the harmonic signal group, constructing a basic system function of hybrid constraints; Expanding the constrained basic system function according to the spatial positions of different sampling points to obtain an expanded system function; Image reconstruction is performed according to the extended system function to obtain a spatial distribution image of the magnetic particle concentration.

3. The method for unilateral magnetic particle imaging based on a gradient bias magnetic field according to claim 2, characterized in that: Before collecting the particle harmonic signals under various bias conditions as the harmonic signal group, the method further includes: Acquiring a spatial particle voltage signal according to the phantom image and the magnetic field distribution of the gradient bias magnetic field; Perform Fourier transform on the spatial particle voltage signal to obtain a particle harmonic signal.

4. The method for unilateral magnetic particle imaging based on a gradient bias magnetic field according to claim 3, characterized in that: The step of constructing a basic system function of a hybrid constraint according to the harmonic signal group includes: Obtaining basic system functions under various bias conditions according to the harmonic signal group; A basic system function with mixed constraints is obtained according to the basic system functions under the multiple bias conditions.

5. The method for unilateral magnetic particle imaging based on a gradient bias magnetic field according to claim 2, characterized in that: The image reconstruction is performed according to the extended system function to obtain a spatial distribution image of the magnetic particle concentration, including: Collecting harmonic signal groups at the spatial positions of the different sampling points to obtain a total signal; Image reconstruction is performed according to the total signal and the extended system function to obtain a spatial distribution image of the magnetic particle concentration.

6. The method for unilateral magnetic particle imaging based on a gradient bias magnetic field according to claim 4, characterized in that: The basic system function reference of the hybrid constraint is expressed as follows: in, is the basic system function of the hybrid constraint, n represents the harmonic order, This represents the basic system function for the variable magnetic field construction of the nth harmonic.

7. The method for unilateral magnetic particle imaging based on a gradient bias magnetic field according to claim 6, characterized in that: The basic system function reference is expressed as follows: in, Indicates that a current A is passed through the bias magnetic field coil E After the position r M The nth harmonic particle harmonic signal at , E represents the number of different currents passing through the bias magnetic field, and M represents the number of positions in the discrete space.

8. The method for unilateral magnetic particle imaging based on a gradient bias magnetic field according to claim 2, characterized in that: The image reconstruction reference according to the extended system function is expressed as follows: Wherein, Img represents the spatial distribution image of the magnetic particle concentration, reshape(·) represents the rearrangement of the magnetic particle concentration distribution, represents the concentration distribution of magnetic particles in space, i represents the number of pixels of the abscissa in the two-dimensional imaging, and j represents the number of pixels of the ordinate in the two-dimensional imaging.

Images