Magnetic particle imaging method based on mixed frequency magnetic field excitation

Abstract

The invention belongs to the technical field of magnetic particle imaging, and relates to a magnetic particle imaging method based on mixed-frequency magnetic field excitation, which comprises the following steps: acquiring a dotted magnetic nanoparticle sample and a to-be-imaged object, respectively applying a mixed-frequency excitation magnetic field in an imaging mode to the dotted magnetic nanoparticle sample and the to-be-imaged object, acquiring a mixed frequency magnetic field excitation-based system matrix and a mixed frequency domain magnetization response frequency spectrum signal; and inputting the system matrix and the mixed frequency domain magnetization response frequency spectrum signal into a concentration spatial distribution inversion model to perform concentration spatial distribution inversion of the magnetic nanoparticles, obtaining the concentration spatial distribution of the magnetic nanoparticles in the object to be imaged, and performing magnetic particle concentration distribution imaging. According to the invention, real-time high-resolution magnetic particle imaging can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of magnetic particle imaging, and in particular to a magnetic particle imaging method based on frequency mixing magnetic field excitation. Background Art

[0002] Magnetic particle imaging is a new type of medical imaging technology that uses magnetic nanoparticles as tracers. By measuring the magnetization response and spectrum of magnetic nanoparticles under the stimulation of an alternating magnetic field, it can perform three-dimensional quantitative imaging of the distribution of magnetic nanoparticles in the body. It has the advantages of real-time, high sensitivity, high spatial resolution, no tissue depth limitation, no radioactivity, and no tissue background signal interference. Since it was publicly reported, magnetic particle imaging technology is in a rapid development stage and has shown broad application prospects in research such as cell tracing, drug delivery, angiography, and tumor imaging.

[0003] In magnetic particle imaging technology, the presence and concentration of magnetic particles are determined by the magnetization response signal of superparamagnetic nanoparticles under an excitation magnetic field, and magnetic particle concentration distribution imaging is achieved by constructing a field free point FFP and performing spatial encoding. At present, magnetic nanoparticle imaging methods are mainly based on analytical methods or algebraic methods, and imaging inversion is performed through the x-space (spatial domain) information of the FFP position or the k-space (frequency domain) spectrum information of the magnetic nanoparticle magnetization response. The x-space imaging method based on analytical methods is widely used because of its simplicity, but its spatial resolution is relatively low. On the contrary, although the x-space imaging method based on algebraic methods can provide higher spatial resolution, its system matrix acquisition process is time-consuming.

[0004] Therefore, there is an urgent need for a magnetic nanoparticle imaging method that has both high resolution and real-time advantages in this field to promote the application of magnetic nanoparticle technology in clinical medicine. This new imaging method should simplify system complexity, reduce costs, and increase imaging speed without sacrificing image quality, making it more suitable for clinical applications. Summary of the invention

[0005] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to propose a magnetic particle imaging method based on mixed-frequency magnetic field excitation, which makes full use of the mixed-frequency magnetic field to excite rich mixed-frequency magnetization response spectrum information, and realizes real-time high-resolution imaging of the spatial distribution of magnetic nanoparticles, which is of great significance for realizing the clinical application of magnetic particle imaging.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A magnetic particle imaging method based on frequency mixing magnetic field excitation, comprising:

[0008] Obtain a sample of dot-shaped magnetic nanoparticles and the object to be imaged, apply a mixed-frequency excitation magnetic field in the imaging mode to the sample of dot-shaped magnetic nanoparticles and the object to be imaged respectively, and obtain a system matrix based on the mixed-frequency magnetic field excitation and a mixed-frequency domain magnetization response spectrum signal;

[0009] Input the system matrix and the mixed-frequency domain magnetization response spectrum signal into a concentration spatial distribution inversion model for inverting the concentration spatial distribution of magnetic nanoparticles, obtain the concentration spatial distribution of magnetic nanoparticles in the object to be imaged, and perform magnetic particle concentration distribution imaging.

[0010] Optionally, after obtaining the sample of dot-shaped magnetic nanoparticles and the object to be imaged, it includes:

[0011] Set the imaging mode and imaging parameters:

[0012] The imaging mode includes: a first mode and a second mode. The first mode is a three-dimensional mixed-frequency domain dimension, and the second mode is to set any one dimension as the spatial domain dimension and the remaining dimensions as the mixed-frequency domain dimensions;

[0013] The imaging parameters include: the pixel size of the imaging area and the mixed-frequency excitation magnetic field parameters.

[0014] Optionally, setting the imaging parameters includes:

[0015] Divide the imaging field of view region into the target number of pixels along the x-axis, y-axis, and z-axis directions, further set the sizes of the pixels in the x-axis, y-axis, and z-axis directions, and obtain the relationship between the volume of the imaging field of view region and the imaging field of view sizes in each dimension:

[0016]

[0017] Among them, is the volume of the imaging field of view region, , , are the imaging field of view sizes in each dimension;

[0018] Based on the relationship between the volume of the imaging field of view region and the imaging field of view sizes in each dimension, obtain the relationship between the imaging field of view sizes in each dimension and the pixel size:

[0019]

[0020] Among them, , , are the sizes of the pixels in the x-axis, y-axis, and z-axis directions, , , are the target numbers of pixels divided along the x-axis, y-axis, and z-axis directions;

[0021] Set the amplitudes of the excitation magnetic fields in the x-axis, y-axis, and z-axis directions, as well as the magnetic field gradients in each dimension, and determine the constraint relationship between the amplitude of the excitation magnetic field and the magnetic field gradient:

[0022]

[0023] Among them, H x 、H y 、H z are the amplitudes of the excitation magnetic fields in the x-axis, y-axis, and z-axis directions, and G x 、G y 、G z are the magnetic field gradients in each dimension.

[0024] Optionally, the expression of the mixed-frequency excitation magnetic field of the imaging mode is:

[0025]

[0026] Among them, H x 、H y 、H z are the amplitudes of the excitation magnetic fields in the x-axis, y-axis, and z-axis directions, f x 、f y 、f z are the excitation frequencies of the excitation magnetic fields in each dimension, is the phase of the excitation magnetic field in each dimension.

[0027] Optionally, obtaining the system matrix includes:

[0028] Place the punctate magnetic nanoparticle sample at the initial position within the imaging field of view, and apply a three-dimensional mixed-frequency excitation magnetic field to the punctate magnetic nanoparticle sample at the initial position to obtain the mixed-frequency domain magnetization response at the initial position;

[0029] During the process of obtaining the mixed-frequency domain magnetization response at the initial position, the high-frequency magnetic field excites the magnetic particles to generate magnetization response harmonics at the high-frequency doubling frequency, and the low-frequency magnetic field excites the magnetic particles to generate mixed-frequency magnetization response harmonics on both sides of each high-frequency doubling frequency;

[0030] Adjust the position of the punctate magnetic nanoparticle sample within the imaging field of view, apply a three-dimensional mixed-frequency excitation magnetic field at the target time until all pixel positions are traversed, obtain the mixed-frequency domain magnetization response spectrum at all pixel positions, and construct the system matrix based on the mixed-frequency domain magnetization response spectrum at all pixel positions.

[0031] Optionally, obtaining the mixed-frequency domain magnetization response spectrum at all pixel positions includes:

[0032]

[0033] Among them, is the spectral information of the mixed frequency-domain magnetization response at all pixel positions, is the m-th mixed-frequency magnetization response complex harmonic of the magnetic nanoparticles at the position.

[0034] Optionally, obtaining the mixed frequency-domain magnetization response spectral signal includes:

[0035]

[0036] where represents the m-th mixed-frequency magnetization response complex harmonic of the object to be imaged, represents the m-th mixed-frequency magnetization response complex harmonic of the mixed-frequency magnetization response signal u(x i , y j , z k , t).

[0037] Optionally, the expression of the concentration spatial distribution inversion model is:

[0038]

[0039] where is the spatial distribution of the magnetic particle concentration, is the mixed frequency-domain magnetization response spectral signal of the object to be imaged, is the system matrix based on the mixed-frequency magnetic field excitation.

[0040] Optionally, obtaining the spatial distribution of the magnetic nanoparticles includes:

[0041]

[0042] where is the spatial distribution of the magnetic nanoparticle concentration.

[0043] The beneficial effects of the present invention are:

[0044] The present invention makes full use of the rich spectral information of the mixed-frequency magnetization response under the mixed-frequency magnetic field excitation to realize real-time high-resolution imaging of the spatial distribution of magnetic nanoparticles. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0046] Figure 1Flowchart of a magnetic particle imaging method based on mixed-frequency magnetic field excitation according to an embodiment of the present invention. Detailed implementation manners

[0047] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0048] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0049] As Figure 1 shown, this embodiment discloses a magnetic particle imaging method based on mixed-frequency magnetic field excitation, including: obtaining a punctate magnetic nanoparticle sample and an object to be imaged, respectively applying a mixed-frequency excitation magnetic field in an imaging mode to the punctate magnetic nanoparticle sample and the object to be imaged, obtaining a system matrix based on mixed-frequency magnetic field excitation and a mixed-frequency domain magnetization response spectrum signal; inputting the system matrix and the mixed-frequency domain magnetization response spectrum signal into a concentration spatial distribution inversion model to perform inversion of the concentration spatial distribution of magnetic nanoparticles, obtaining the concentration spatial distribution of magnetic nanoparticles in the object to be imaged, and performing magnetic particle concentration distribution imaging.

[0050] Specifically, this embodiment discloses a magnetic particle imaging method based on mixed-frequency magnetic field excitation, including:

[0051] Step S10: Perform pixel segmentation in the imaging field of view area. The proposed method performs magnetic particle imaging based on the mixed-frequency domain magnetization response information of magnetic particles under mixed-frequency magnetic field excitation. For imaging, three-dimensional mixed-frequency domain information can be used to image the three-dimensional space, that is, a three-dimensional mixed-frequency domain imaging mode; or one of the dimensions can be set as the spatial domain dimension, and the remaining two dimensions can be set as the mixed-frequency domain dimensions for layer-by-layer imaging; set the imaging mode, pixel size, mixed-frequency excitation magnetic field parameters, etc.;

[0052] Step S20: Place the punctate magnetic nanoparticle sample in the imaging field of view area, and form a three-dimensional mixed-frequency excitation magnetic field by applying excitation magnetic fields with different frequencies that are mutually orthogonal in the mixed-frequency domain dimension. Change the spatial position of the magnetic nanoparticle sample to traverse the pixel positions in the imaging field of view area, and measure the mixed-frequency magnetization response harmonics at different positions to form a system matrix A based on mixed-frequency magnetic field excitation;

[0053] Step S30: Place the object to be imaged in the imaging field of view area, use the three-dimensional mixed-frequency magnetic field to excite the object to be imaged, and measure the mixed-frequency domain magnetization response spectrum signal U;

[0054] Step S40: Using the mixing frequency spectrum U measured in step S30 and the system matrix A obtained in S20, construct a mathematical model of the system matrix A, the spatial distribution C of magnetic particle concentration, and the magnetization response spectrum signal U in the mixed frequency domain, expressed as:

[0055]

[0056] Solving the above equation can invert the spatial distribution C of the magnetic nanoparticle concentration, thereby realizing the imaging of the magnetic particle concentration distribution.

[0057] Furthermore, after obtaining the punctiform magnetic nanoparticle sample, it includes: setting the imaging mode and imaging parameters: the imaging mode includes: the first mode and the second mode. The first mode is the three-dimensional mixed frequency domain dimension, and the second mode is to set any one dimension as the spatial domain dimension and the remaining dimensions as the mixed frequency domain dimensions; the imaging parameters include: the pixel size of the imaging area and the mixing excitation magnetic field parameters.

[0058] Furthermore, setting the imaging parameters includes:

[0059] Divide the imaging field of view region into the target number of pixels along the x-axis, y-axis, and z-axis directions, further set the sizes of the pixels in the x-axis, y-axis, and z-axis directions, and obtain the relationship between the volume of the imaging field of view region and the imaging field of view sizes of each dimension:

[0060]

[0061] Among them, is the volume of the imaging field of view region, , , are the imaging field of view sizes of each dimension;

[0062] Based on the relationship between the volume of the imaging field of view region and the imaging field of view sizes of each dimension, obtain the relationship between the imaging field of view sizes of each dimension and the pixel size:

[0063]

[0064] Among them, , , are the sizes of the pixels in the x-axis, y-axis, and z-axis directions, , , are the target number of pixels divided along the x-axis, y-axis, and z-axis directions;

[0065] Set the excitation magnetic field amplitudes in the x-axis, y-axis, and z-axis directions and the magnetic field gradients of each dimension, and determine the constraint relationship between the excitation magnetic field amplitude and the magnetic field gradient:

[0066]

[0067] Among them, H x 、H y 、H z are the amplitudes of the excitation magnetic fields in the x-axis, y-axis, and z-axis directions, in G x 、G y 、G z are the magnetic field gradients in each dimension.

[0068] Specifically, taking the mode of using the mixed frequency domain information of three dimensions for imaging as an example, step S10 includes:

[0069] Step S11: Set the imaging mode, use the mixed frequency domain information of three dimensions for magnetic particle imaging, divide the imaging area into I, J, and K pixels along the x-axis, y-axis, and z-axis directions respectively, and the total number of spatial pixels is I×J×K;

[0070] Step S12: Set the sizes of the pixels in the x / y / z-axis directions to be l x / l y / l z , then the relationship between the volume V Fov of the imaging field of view area and the imaging field of view sizes FOV x / FOV y / FOV z in each dimension is:

[0071]

[0072] Among them, the relationship between the imaging field of view size in each dimension and the pixel size is:

[0073]

[0074] Step S13: Set the amplitudes of the excitation magnetic fields in the x / y / z-axis directions to be H x / H y / H z , and the magnetic field gradients in each dimension to be G x / G y / G z , and the constraint relationship between the amplitude of the excitation magnetic field and the magnetic field gradient is:

[0075]

[0076] Furthermore, the expression of the mixed-frequency excitation magnetic field of the imaging mode is:

[0077]

[0078] Among them, H x 、H y 、Hz are the amplitudes of the excitation magnetic fields in the x-axis, y-axis, and z-axis directions, and f x , f y , f z are the excitation frequencies of the excitation magnetic fields in each dimension, is the phase of the excitation magnetic field in each dimension.

[0079] Furthermore, obtaining the system matrix includes: placing the punctiform magnetic nanoparticle sample at the initial position within the imaging field of view, applying a three-dimensional mixed-frequency excitation magnetic field to the punctiform magnetic nanoparticle sample at the initial position, and obtaining the magnetization response in the mixed-frequency domain at the initial position; during the process of obtaining the magnetization response in the mixed-frequency domain at the initial position, the high-frequency magnetic field excites the magnetic particles to generate magnetization response harmonics at the high-frequency doubling frequency, and the low-frequency magnetic field excites the magnetic particles to generate mixed-frequency magnetization response harmonics on both sides of each high-frequency doubling frequency; adjusting the position of the punctiform magnetic nanoparticle sample within the imaging field of view, applying the three-dimensional mixed-frequency excitation magnetic field at the target time until all pixel positions are traversed, obtaining the magnetization response spectra in the mixed-frequency domain at all pixel positions, and constructing the system matrix based on the magnetization response spectra in the mixed-frequency domain at all pixel positions.

[0080] Specifically, step S20 includes:

[0081] Step S21: Place the punctiform magnetic nanoparticle sample at the initial position (x 1 , y 1 , z 1 ), and set the three-dimensional alternating mixed-frequency excitation magnetic field as:

[0082]

[0083] where f x / f y / f z are the excitation frequencies of the excitation magnetic fields in each dimension, is the phase of the excitation magnetic field in each dimension, where the magnetic field with frequency f x is the high-frequency magnetic field, and the magnetic fields with frequencies f x , f y are the low-frequency magnetic fields;

[0084] Step S22: Apply the three-dimensional mixed-frequency excitation magnetic field to the magnetic nanoparticles at the initial position (x 1 , y 1 , z 1 ), and obtain the magnetization response u(x 1 , y 1 , z 1 , t) of the magnetic nanoparticles in the mixed-frequency domain;

[0085] Step S23: Adjust the position of the punctiform magnetic nanoparticle sample in the imaging field of view (x i , yj ,z k ), apply a three-dimensional mixed-frequency excitation magnetic field with an application time of T, and obtain the magnetic nanoparticle mixed-frequency domain magnetization response signal u(x i ,y j ,y k ,t) at each position within the time T until all pixel positions (x 1 ,y 1 ,z 1 )~(x I ,y J ,z K ) are traversed;

[0086] Step S24: Obtain the mixed-frequency domain magnetization response spectrum at the positions (x 1 ,y 1 ,z 1 )~(x I ,y J ,z K ), and form the system matrix A based on the spectrum.

[0087] Furthermore, obtaining the mixed-frequency domain magnetization response spectra at all pixel positions includes:

[0088]

[0089] Among them, is the mixed-frequency domain magnetization response spectrum information at all pixel positions, is the m-th mixed-frequency magnetization response complex harmonic of the magnetic nanoparticles at the position.

[0090] Specifically, step S24 includes:

[0091] Step S241: Perform a Fourier transform on the mixed-frequency domain magnetization response signal u(x i ,y j ,z k ,t) obtained by moving the punctiform magnetic nanoparticle sample to each pixel position within the imaging field of view, to obtain the mixed-frequency domain magnetization response spectrum information :

[0092]

[0093] Among them, the high-frequency magnetic field excites the magnetic particles to generate magnetization response harmonics at high-frequency multiples, and the low-frequency magnetic field excites the magnetic particles to generate mixed-frequency magnetization response harmonics on both sides of each high-frequency multiple. M is the total number of mixed-frequency harmonics, represents the magnetic nanoparticles at (x i ,y j ,z kThe m-th mixed-frequency magnetization response complex harmonic at the position.

[0094] Furthermore, obtaining the mixed-frequency domain magnetization response spectral signal includes:

[0095]

[0096] where represents the m-th mixed-frequency magnetization response complex harmonic of the object to be imaged, represents the m-th mixed-frequency magnetization response complex harmonic of the mixed-frequency magnetization response signal u(x i , y j , z k , t).

[0097] Furthermore, the expression of the concentration spatial distribution inversion model is:

[0098]

[0099] where is the magnetic particle concentration spatial distribution, is the mixed-frequency domain magnetization response spectral signal of the object to be imaged, is the system matrix based on the mixed-frequency magnetic field excitation.

[0100] Furthermore, obtaining the concentration spatial distribution of magnetic nanoparticles includes:

[0101]

[0102] where is the concentration spatial distribution of magnetic nanoparticles.

[0103] Specifically, step S30 includes:

[0104] Step S31: Place the object to be imaged in the imaging field of view area, and set the three-dimensional alternating mixed-frequency excitation magnetic field as:

[0105]

[0106] Step S32: Apply the three-dimensional mixed-frequency excitation magnetic field to the object to be imaged for a time T, and obtain the mixed-frequency domain magnetization response signal u(t) of the object to be imaged within the time T,

[0107] Step S33: Calculate the mixed-frequency domain magnetization response spectral matrix U of the object to be imaged using the magnetization response signal u(t) of the object to be imaged.

[0108] Step S331: Perform Fourier transform on the magnetization response signal u(t) of the object to be imaged under the three-dimensional mixed-frequency magnetic field excitation to obtain the mixed-frequency domain magnetization response spectrum of the object to be imaged:

[0109]

[0110] wherein represents the m-th mixed-frequency magnetization response complex harmonic of the object to be imaged. The harmonic components mainly include the magnetization response harmonics at the frequency multiples of the high-frequency magnetic field frequency and the mixed-frequency magnetization response harmonics on both sides of each high-frequency multiple;

[0111] Step S40 includes: performing image inversion based on the mixed-frequency magnetization response spectrum U of the object to be imaged obtained in step S30 and the imaging system matrix A obtained in step S20 to obtain the spatial distribution of the magnetic nanoparticle concentration:

[0112]

[0113] wherein, is the spatial distribution of the magnetic nanoparticle concentration.

[0114] Through the magnetic particle imaging method based on mixed-frequency magnetic field excitation proposed by the present invention, real-time high-resolution magnetic particle imaging can be realized, which can meet the biomedical application requirements such as cell tracing, angiography, and drug targeted delivery.

[0115] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A magnetic particle imaging method based on frequency mixing magnetic field excitation, characterized in that: include: Acquire a point-shaped magnetic nanoparticle sample and an object to be imaged, apply a mixed frequency excitation magnetic field of an imaging mode to the point-shaped magnetic nanoparticle sample and the object to be imaged, respectively, and acquire a system matrix based on the mixed frequency magnetic field excitation and a mixed frequency domain magnetization response spectrum signal; The system matrix and the mixed frequency domain magnetization response spectrum signal are input into a concentration spatial distribution inversion model to perform concentration spatial distribution inversion of magnetic nanoparticles, obtain the concentration spatial distribution of magnetic nanoparticles in the object to be imaged, and perform magnetic particle concentration distribution imaging.

2. The magnetic particle imaging method based on frequency mixing magnetic field excitation according to claim 1, characterized in that: After obtaining the dot-shaped magnetic nanoparticle sample and the object to be imaged, the method comprises: Set the imaging mode and imaging parameters: The imaging modes include: a first mode and a second mode, the first mode is a three-dimensional mixed frequency domain dimension, and the second mode is to set any one dimension as a space domain dimension and the remaining dimensions as mixed frequency domain dimensions; The imaging parameters include: imaging area pixel size and mixing excitation magnetic field parameters.

3. The magnetic particle imaging method based on frequency mixing magnetic field excitation according to claim 2, characterized in that: Setting the imaging parameters includes: The imaging field of view area is divided into target pixel numbers along the x-axis, y-axis and z-axis directions, and the size of the pixels in the x-axis, y-axis and z-axis directions is further set to obtain the relationship between the volume of the imaging field of view area and the size of the imaging field of view in each dimension: in, is the volume of the imaging field of view, , , is the imaging field size of each dimension; Based on the relationship between the imaging field of view area volume and the imaging field of view size of each dimension, the relationship between the imaging field of view size of each dimension and the pixel size is obtained: in, , , is the size of the pixel in the x-axis, y-axis and z-axis directions, , , is the number of target pixels for each segmentation along the x-axis, y-axis, and z-axis directions; Set the excitation magnetic field amplitudes in the x-axis, y-axis, and z-axis directions and the magnetic field gradients in each dimension, and determine the constraint relationship between the excitation magnetic field amplitude and the magnetic field gradient: Among them, H x , H y , H z is the excitation magnetic field amplitude in the x-axis, y-axis and z-axis directions, G x , G y , G z is the magnetic field gradient in each dimension.

4. The magnetic particle imaging method based on frequency mixing magnetic field excitation according to claim 1, characterized in that: The mixed frequency excitation magnetic field expression of the imaging mode is: Among them, H x , H y , H z is the excitation magnetic field amplitude in the x-axis, y-axis and z-axis directions, f x 、f y 、f z is the excitation frequency of the excitation magnetic field in each dimension, Excite the magnetic field phase for each dimension.

5. The magnetic particle imaging method based on frequency mixing magnetic field excitation according to claim 1, characterized in that: Acquiring the system matrix includes: Placing the point-shaped magnetic nanoparticle sample at an initial position within the imaging field of view, applying a three-dimensional frequency mixing excitation magnetic field to the point-shaped magnetic nanoparticle sample at the initial position, and acquiring a mixed frequency domain magnetization response at the initial position; In the process of obtaining the mixed frequency domain magnetization response at the initial position, the high frequency magnetic field excites the magnetic particles to generate magnetization response harmonics at the high frequency multiples, and the low frequency magnetic field excites the magnetic particles to generate mixed frequency magnetization response harmonics on both sides of each high frequency multiple; The position of the point-shaped magnetic nanoparticle sample in the imaging field of view is adjusted, and a three-dimensional frequency mixing excitation magnetic field of a target time is applied until all pixel positions are traversed, and the mixed frequency domain magnetization response spectrum at all pixel positions is obtained, and the system matrix is ​​constructed based on the mixed frequency domain magnetization response spectrum at all pixel positions.

6. The magnetic particle imaging method based on frequency mixing magnetic field excitation according to claim 5, characterized in that: Obtaining the mixed frequency domain magnetization response spectrum at all pixel locations includes: in, is the mixed frequency domain magnetization response spectrum information at all pixel positions, For magnetic nanoparticles The mth frequency mixing magnetization response complex harmonic at the position.

7. The magnetic particle imaging method based on frequency mixing magnetic field excitation according to claim 1, characterized in that: Acquiring the mixed frequency domain magnetization response spectrum signal comprises: in, represents the mth frequency-mixing magnetization response complex harmonic of the object to be imaged, represents the mixing response signal u(x i ,y j ,z k ,t)’s mth frequency mixing magnetization response complex harmonic.

8. The magnetic particle imaging method based on frequency mixing magnetic field excitation according to claim 1, characterized in that: The concentration spatial distribution inversion model expression is: in, is the spatial distribution of magnetic particle concentration, is the mixed frequency domain magnetization response spectrum signal of the object to be imaged, is the system matrix based on mixed frequency magnetic field excitation.

9. The magnetic particle imaging method based on frequency mixing magnetic field excitation according to claim 1, characterized in that: Obtaining the concentration spatial distribution of the magnetic nanoparticles includes: in, is the spatial distribution of the concentration of magnetic nanoparticles.

Images