Narrowband-based multi-harmonic magnetic particle imaging method

Abstract

The invention relates to the technical field of medical imaging, in particular to a narrowband-based multi-harmonic magnetic particle imaging method, which comprises the following steps of: determining a magnetic particle imaging area, and acquiring a first area and a second area according to the magnetic particle imaging area; placing a magnetic nanoparticle sample in the first area, externally applying a magnetic field, and extracting harmonic signals to construct a system matrix; placing a measured object in the second area and externally applying a magnetic field, and extracting harmonic signals to construct a harmonic signal matrix of the measured object; and according to the system matrix and the harmonic signal matrix of the measured object, constructing an equation to be solved and carrying out inversion solution to obtain an image of magnetic nanoparticle concentration distribution. Compared with a broadband imaging technology, the narrow-band imaging technology is adopted, the requirement for the bandwidth of a magnetic particle imaging system is lowered, and the problem of insufficient bandwidth under high-frequency excitation is solved.

Description

Technical Field

[0001] The present invention relates to the field of medical imaging technology, and particularly to a narrow-band based multi-harmonic magnetic particle imaging method. Background Art

[0002] Magnetic particle imaging (MPI) is a new type of medical imaging technology. By measuring the magnetic response spectrum of magnetic nanoparticles, the spatial distributions of multi-parameters such as the concentration of magnetic nanoparticles and the concentration of biomarkers are inverted, and it can be applied to the early diagnosis of tumors, the real-time monitoring of the treatment process, and the accurate evaluation of the treatment effect. Compared with existing medical imaging technologies, such as magnetic resonance imaging (MRI), CT, ultrasound, etc., magnetic particle imaging technology has the characteristics of high sensitivity, high time-space resolution, no tissue depth limitation, and no radioactivity, showing great potential in various biomedical applications.

[0003] According to the bandwidth of the received signal, MPI technology can be divided into two methods: narrow-band magnetic particle imaging and wide-band magnetic particle imaging. However, the wide-band magnetic particle imaging method requires receiving signals in a wider frequency spectrum range, which has high requirements for the bandwidth of the magnetic particle imaging system, increasing the complexity of system design and the difficulty of noise processing. Based on the single-harmonic narrow-band imaging method, the single harmonic is interfered by the feed-through signal, restricting the further improvement of its signal-to-noise ratio; since only one harmonic imaging is used to construct the system matrix for imaging, the obtained spectral information is insufficient, restricting the further improvement of its resolution.

[0004] Based on the above technical problems, the present invention provides a narrow-band based multi-harmonic magnetic particle imaging method. Summary of the Invention

[0005] The object of the present invention is to provide a narrow-band based multi-harmonic magnetic particle imaging method, which constructs a system matrix by using the narrow-band multi-harmonic method, solves the problem of insufficient spectral information obtained by narrow-band single harmonic, improves the data measurement dimension, effectively improves the detection sensitivity and imaging resolution of the magnetic particle imaging system, and the implementation process is convenient and concise.

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

[0007] A narrow-band based multi-harmonic magnetic particle imaging method, comprising:

[0008] Determine the magnetic particle imaging region, and divide the first region and the second region according to the low-frequency sinusoidal scanning magnetic field;

[0009] Place the magnetic nanoparticle sample in the first region and apply an external magnetic field, and extract harmonic signals to construct a system matrix;

[0010] Place the object to be measured in the second region and apply an external magnetic field, extract the harmonic signals to construct the harmonic signal matrix of the object to be measured;

[0011] According to the system matrix and the harmonic signal matrix of the object to be measured, construct the equation to be solved and perform inversion to obtain the image of the magnetic nanoparticle concentration distribution.

[0012] Optionally, placing the magnetic nanoparticle sample in the first region and applying an external magnetic field, the extraction of harmonic signals to construct the system matrix includes:

[0013] Divide the first region into a grid of several imaging units, apply a high-frequency excitation magnetic field and a low-frequency scanning magnetic field in a preset direction, and move the magnetic nanoparticle sample of unit volume to traverse the entire first region to construct the system matrix, where the system matrix includes the specific harmonic kf0 and sideband harmonic signals kf0±nf1 of the magnetic nanoparticle sample of unit volume in each imaging unit in the first region, n = 1, 2…, N, where k is an integer greater than or equal to 2, f0 represents the frequency of the high-frequency excitation magnetic field, f1 represents the frequency of the low-frequency scanning magnetic field, and N is the largest integer at which sideband harmonic signals are detected.

[0014] Optionally, obtaining the specific harmonic and sideband harmonic signals includes:

[0015] Place the magnetic nanoparticle sample of unit volume in the imaging unit in the first region and apply a high-frequency excitation magnetic field and a low-frequency scanning magnetic field in a preset direction to obtain the voltage signal generated by the magnetization response signal;

[0016] Perform Fourier transform on the voltage signal generated by the magnetization response signal to obtain the specific harmonic and sideband harmonic signals.

[0017] Optionally, placing the object to be measured in the second region and applying an external magnetic field, the extraction of harmonic signals to construct the harmonic signal matrix of the object to be measured includes: dividing the second region into a grid of several imaging units, applying a high-frequency excitation magnetic field and a low-frequency scanning magnetic field in a preset direction, and moving the object to be measured to traverse the entire second region to construct the harmonic signal matrix of the object to be measured, where the harmonic signal matrix of the object to be measured includes the specific harmonic and sideband harmonic signals of the object to be measured in each imaging unit in the second region.

[0018] Optionally, the equation to be solved includes:

[0019] U = A·c;

[0020] where U is the harmonic signal matrix of the object to be measured, A is the system matrix, and c is the magnetic nanoparticle concentration distribution.

[0021] Optionally, the inversion solution of the equation to be solved includes: performing Tikhonovz regularization on the equation to be solved, and using an algebraic reconstruction algorithm to solve the standardized equation to be solved, so as to obtain an image of the magnetic nanoparticle concentration distribution.

[0022] Optionally, performing Tikhonovz regularization on the equation to be solved includes:

[0023] ;

[0024] where α is the regularization parameter, I is the identity matrix, A H is the adjoint matrix of the system matrix A, and c is the magnetic nanoparticle concentration distribution.

[0025] The beneficial effects of the present invention are as follows:

[0026] 1. The present invention adopts the narrowband imaging technology. Compared with the broadband imaging technology, the requirement for the bandwidth of the magnetic particle imaging system is reduced, and the problem of insufficient bandwidth faced under high-frequency magnetic field excitation is solved.

[0027] 2. The present invention adopts the method of constructing the system matrix with multiple harmonics. Compared with the narrowband single-harmonic magnetic particle imaging method, by increasing the number of measured harmonics, richer spectral information is obtained, and the image resolution can be improved.

[0028] 3. The harmonic frequencies adopted by the present invention are the k-th harmonic and sideband harmonic signals. The sideband harmonic signals have a higher signal-to-noise ratio (SNR) than the k-th harmonic, and the sensitivity of the magnetic particle imaging system can be improved. Description of the Drawings

[0029] 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, other drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 is a flowchart of a narrowband-based multi-harmonic magnetic particle imaging method according to an embodiment of the present invention;

[0031] Figure 2 is for an embodiment of the present invention N x = 2, N y = 2, a schematic diagram of the division of the two-dimensional imaging area of narrowband-based multi-harmonic magnetic particles;

[0032] Figure 3 is a basic principle diagram of narrowband-based multi-harmonic magnetic particle imaging according to an embodiment of the present invention;

[0033] Figure 4 For Embodiment N of the present invention x = 2, N y = 2, N z = 1, schematic diagram of three-dimensional imaging region division of multi-harmonic magnetic particles based on narrowband. Specific embodiments

[0034] 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.

[0035] 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 embodiments.

[0036] As Figure 1 shown, this embodiment provides a multi-harmonic magnetic particle imaging method based on narrowband, including:

[0037] Determine the magnetic particle imaging region, and obtain the first region and the second region according to the magnetic particle imaging region;

[0038] Place a unit volume of magnetic nanoparticle sample in the first region and apply an external magnetic field, extract the harmonic signal to construct a system matrix;

[0039] Place the object to be measured in the second region and apply an external magnetic field, extract the harmonic signal to construct a harmonic signal matrix of the object to be measured;

[0040] According to the system matrix and the harmonic signal matrix of the object to be measured, construct an equation to be solved and perform inversion to obtain an image of the magnetic nanoparticle concentration distribution.

[0041] Specifically, determine the range FOV of the imaging region of the magnetic particle imaging system x × FOV y × FOV z , determine the amplitude, waveform, phase, and direction of the low-frequency scanning magnetic field and the high-frequency excitation magnetic field. The direction of the low-frequency scanning magnetic field can be any one of the x, y, or z axes, and the direction of the high-frequency excitation magnetic field can also be any one of the x, y, or z axes. Divide the first region I and the second region II according to it; determine the size of the first region I including: along the direction of the low-frequency scanning magnetic field and the range of the imaging region, and the size in the remaining directions is twice the range of the imaging region; determine the size of the second region II including: along the direction of the low-frequency scanning magnetic field becomes the size of 1 pixel unit, and the size in the remaining directions remains the same as the range of the imaging region.

[0042] Further, place the magnetic nanoparticle sample in the first region and apply an external magnetic field. Extracting the harmonic signals to construct the system matrix includes:

[0043] Divide the first region into a grid, dividing it into several imaging units. Apply a high-frequency excitation magnetic field and a low-frequency scanning magnetic field in a preset direction and move the magnetic nanoparticle sample with a unit volume to traverse the entire first region to construct the system matrix. Among them, the system matrix includes the specific harmonic and sideband harmonic signals of the magnetic nanoparticle sample with a unit volume in each imaging unit in the first region.

[0044] Furthermore, obtaining the specific harmonic and sideband harmonic signals includes:

[0045] Place the magnetic nanoparticle sample with a unit volume in the imaging unit in the first region and apply a high-frequency excitation magnetic field and a low-frequency scanning magnetic field in a preset direction to obtain the voltage signal generated by the magnetization response signal;

[0046] Perform Fourier transform on the voltage signal generated by the magnetization response signal to obtain the specific harmonic kf0 and sideband harmonic signals kf0±nf1, n = 1, 2…, N. Among them, k is an integer greater than or equal to 2, f0 represents the frequency of the high-frequency excitation magnetic field, f1 represents the frequency of the low-frequency scanning magnetic field, and N is the maximum integer detected by the sideband harmonic signal.

[0047] Specifically, constructing the system matrix in this embodiment includes:

[0048] Step S1: Perform grid division processing on the first region I and divide it into several imaging units;

[0049] Step S2: Place the magnetic nanoparticle sample with a unit volume in the first region I and apply a high-frequency excitation magnetic field and a low-frequency scanning magnetic field in a preset direction. For example, apply a high-frequency excitation magnetic field in the x direction and a low-frequency scanning magnetic field in the y direction;

[0050] Step S3: The detection coil collects the magnetization response signal generated by the object to be measured, and through Fourier transform, extracts the harmonic and sideband harmonic signals of a specific frequency;

[0051] Step S4: Drive the three-dimensional mechanical displacement stage to adjust the position of the magnetic nanoparticle sample with a unit volume in the first region I. If the magnetic nanoparticle sample with a unit volume has traversed all imaging units, go to step S5; otherwise, go to step S2;

[0052] Step S5: According to the harmonic signals and sideband harmonic signals of the specific frequency extracted in step S3, construct the system matrix A.

[0053] Further, place the object to be measured in the second region and apply an external magnetic field, and extract harmonic signals to construct a harmonic signal matrix of the object to be measured, including: dividing the second region into a grid, dividing it into a number of imaging units, applying a high-frequency excitation magnetic field and a low-frequency scanning magnetic field in a preset direction, and moving the spatial position of the object to be measured to traverse the entire second region to construct a harmonic signal matrix of the object to be measured, where the harmonic signal matrix of the object to be measured includes specific harmonics and sideband harmonic signals of each imaging unit of the object to be measured in the second region.

[0054] Specifically, constructing the harmonic signal matrix of the object to be measured includes:

[0055] S1: Perform grid division processing on the second region II, divide it into a number of imaging units, and the size of the imaging units is the same as that of the imaging units in the first region I;

[0056] S2: Place the object to be measured in the second region II and apply a high-frequency excitation magnetic field in the x direction and a low-frequency scanning magnetic field in the y direction to it;

[0057] S3: The detection coil collects the magnetization response signal generated by the object to be measured, and after Fourier transform, extracts specific harmonics and sideband harmonic signals;

[0058] S4: Drive the three-dimensional mechanical displacement stage to adjust the position of the object to be measured in the second region II. If the object to be measured has traversed all the imaging units in the second region II, go to step S5; otherwise, go to step S2;

[0059] S5: According to the specific harmonics and sideband harmonic signals extracted in step S3, obtain the harmonic signal matrix U of the object to be measured.

[0060] Further, the equation to be solved includes:

[0061] U = A·c;

[0062] where U is the harmonic signal matrix of the object to be measured, A is the system matrix, and c is the magnetic nanoparticle concentration distribution.

[0063] Further, performing inversion solution on the equation to be solved includes: standardizing the equation to be solved, and using the algebraic reconstruction algorithm to solve the standardized equation to be solved to obtain an image of the magnetic nanoparticle concentration distribution.

[0064] Standardizing the equation to be solved includes:

[0065] ;

[0066] where α is the regularization parameter, I is the identity matrix, and A H is the adjoint matrix of the system matrix A, and c is the magnetic nanoparticle concentration distribution.

[0067] The multi - harmonic magnetic particle imaging method based on narrow - band in this embodiment, together with the method of noise matching, has a signal - to - noise ratio better than that of the k - th harmonic. This method has relatively low requirements for the bandwidth of the magnetic particle imaging system, and is relatively simple to design and implement, which can solve the problem of insufficient bandwidth faced under high - frequency magnetic field excitation. This method constructs the system matrix by using multi - harmonics. Compared with the single - harmonic narrow - band magnetic particle imaging method, by increasing the number of measured harmonics, it obtains richer spectral information, which is of great significance for improving image resolution.

[0068] The following will further illustrate the method of this embodiment by applying the multi - harmonic magnetic particle imaging method based on narrow - band to two - dimensional imaging:

[0069] Step S10: Determine the range FOV of the field of view (FOV) of the magnetic particle imaging system x ×FOV y , and divide it into (2N x + 1)×(2N y + 1) imaging units. Among them, N x and N y are positive integers; Use the magnetic particle imaging system to apply a gradient magnetic field H G (x, y) to the imaging area, apply a low - frequency sinusoidal scanning magnetic field H s (t)=H s sin(2πf1t) in the y - direction of the imaging area, and apply a high - frequency sinusoidal excitation magnetic field H ac (t)=H ac sin(2πf0t) in the x - direction. The low - frequency sinusoidal scanning magnetic field controls the movement of the zero - magnetic - field point, and the high - frequency excitation magnetic field drives the particles to generate magnetization response signals, where H s and f1 are the amplitude and frequency of the low - frequency scanning magnetic field respectively, H ac and f0 are the amplitude and frequency of the high - frequency excitation magnetic field respectively, t is time, and the total magnetic field H(x, y, t) can be expressed as:

[0070] ;

[0071] Step S20: According to the direction of the sinusoidal scanning magnetic field H s , divide the range of the first region I as 2FOV x ×FOV y , and the range of the second region II as FOV x ; Perform grid division processing on the first region I. The size of the imaging unit is consistent with the field of view (FOV), and divide it into (4N x + 1)×(2N y+(1) imaging unit; The second region II is divided into a grid. The size of the imaging unit is consistent with the imaging field of view (FOV), and it is divided into (2N x +1)×1 imaging units; As Figure 2 shown, it represents when N x is 2 and N y is 2, the size relationship of the imaging field of view (FOV), the first region I, and the second region II. Place a unit volume of SPION sample in the first region I and apply a total magnetic field H(x, y, t).

[0072] When a unit volume of SPION sample is located at the position (x a , y b ), the generated magnetization response signal can be described mathematically by the Langevin equation:

[0073] ;

[0074] where M s is the saturation magnetization, is the Langevin function ℒ(x)=coth(x)-1 / x, is the ratio of the magnetic energy of a particle with magnetic moment m to the thermal energy given by the Boltzmann constant k B and temperature T, and μ0 is the vacuum permeability. According to Faraday's law of electromagnetic induction, the detection coil collects the voltage signal generated by this magnetization response signal which can be expressed as:

[0075] ;

[0076] where s(x, y) is the spatial sensitivity of the receiving coil, and V is the spatial volume element covered by the detection coil and related to the magnetization response signal. The voltage signal after Fourier transform processing can be expressed as:

[0077] ;

[0078] where i is the imaginary unit, and a m,n represents the Fourier coefficient of the mf0+nf1 frequency component. M and N respectively represent the maximum integers of the integer multiple harmonic signals and sideband harmonic signals that can be detected. According to the hardware design of the magnetic particle imaging system, the kth harmonic kf0 and sideband harmonic signals kf0±nf1 (n = 1, 2…, N) are extracted for imaging, where k is an integer greater than or equal to 2.

[0079] Drive the three-dimensional mechanical displacement stage to adjust the position of the SPION sample per unit volume in the first region I until all imaging units in the first region I are traversed, and construct the system matrix A, which can be expressed as:

[0080] ;

[0081] where u0(x a , y b ) represents the position of the SPION sample per unit volume at (x a , y b ) in the first region I. When x a ∈ (-2N x , 2N x ), y b ∈ (-N y , N y ), the kth harmonic kf0 and sideband harmonic signals kf0 ± nf1 (n = 1, 2..., N) are extracted.

[0082] Step S30: The SPION concentration distribution of the object under test is c(x, y). Place the object under test in the second region II, record its position , and apply the total magnetic field H(x, y, t). The magnetization response signal M(x, y, t) generated by the object under test; the detection coil collects the magnetization response signal M(x, y, t), and the generated voltage signal is processed by Fourier transform to extract the kth harmonic kf0 and sideband harmonic signals kf0 ± nf1 (n = 1, 2..., N). In this embodiment, the third harmonic 3f0 and sideband harmonic signals 3f0 ± nf1 (n = 1,..., N) are extracted; drive the three-dimensional mechanical displacement stage to adjust the position of the object under test in the second region II until all imaging units in the second region II are traversed, and calculate the harmonic signal matrix U of the object under test, which can be expressed as:

[0083] ;

[0084] where, represents the kth harmonic and sideband harmonic signals extracted when the object under test is at the position in region II, and the superscript T represents the transpose.

[0085] Step S40: Based on the system matrix A and the harmonic signal matrix U of the object under test, construct the equation to be solved:

[0086] ;

[0087] Perform Tikhonov regularization on the equation U = A·c:

[0088] ;

[0089] where α is the regularization parameter, I is the identity matrix, and A H is the adjoint matrix of the system matrix A. Solve this equation using the algebraic reconstruction algorithm (ART algorithm) to inversely obtain the image of the magnetic nanoparticle concentration distribution c.

[0090] The following further illustrates the method of this embodiment by applying the narrowband multi-harmonic magnetic particle imaging method to three-dimensional imaging:

[0091] Step S10: Determine the range FOV of the field of view (FOV) of the magnetic particle imaging system x ×FOV y ×FOV z , divide it into (2N z +1) layers, and each layer is divided into (2N x +1)×(2N y +1) imaging units, where N z is a positive integer; use the magnetic particle imaging system to apply a gradient magnetic field H G (x,y) to the imaging area, apply a low-frequency sinusoidal scanning magnetic field H s (t)=H s sin(2πf1t) in the y direction of the imaging area, apply a high-frequency sinusoidal excitation magnetic field H ac (t)=H ac sin(2πf0t) in the x direction. The low-frequency sinusoidal scanning magnetic field controls the movement of the zero magnetic field point, and the high-frequency excitation magnetic field drives the particles to generate a magnetization response signal, where H s and f1 are the amplitude and frequency of the low-frequency scanning magnetic field respectively, H ac and f0 are the amplitude and frequency of the high-frequency excitation magnetic field respectively, t is the time, and the total magnetic field H(x,y,z,t) can be expressed as:

[0092] ;

[0093] Step S20: As Figure 4 shown, according to the direction of the sinusoidal scanning magnetic field H s , divide the range of the first region I to be 2FOV x ×FOV y ×2FOV z , and the range of the second region II to be FOV x ×FOV z; Perform mesh division on the first region I. Keep the imaging unit size consistent with the imaging field of view, and divide it into (4N z +1) layers, with each layer having (4N x +1)×(2N y +1) imaging units.

[0094] Place a unit volume of SPION sample in the first region I and apply a total magnetic field H(x, y, z, t). When the unit volume of SPION sample is at a certain position (x a , y b , z c ) in space, a magnetization response signal M0(x a , y b , z c , t) is generated. According to Faraday's law of electromagnetic induction, the detection coil collects the voltage signal generated by this magnetization response signal. The voltage signal is processed by Fourier transform, and the kth harmonic kf0 and sideband harmonic signals kf0±nf1 (n = 1, 2…, N) are extracted for imaging, where k is an integer greater than or equal to 2. Drive the three-dimensional mechanical displacement stage to adjust the position of the unit volume of SPION sample in the first region I until all the imaging units in the first region I are traversed, and calculate and construct the system matrix A. The system matrix A can be expressed as:

[0095] ;

[0096] Among them, represents the two-dimensional system matrix when the unit volume of SPION sample is in the N z layers in the first region I.

[0097] Step S30: Perform mesh division on the second region II. Keep the imaging unit size consistent with the imaging field of view (FOV), and divide it into (2N x +1)×(2N z +1) imaging units. The SPION concentration distribution of the object to be measured is c(x, y). Place the object to be measured in the second region II and apply a total magnetic field H(x, y, z, t). The magnetization response signal M(x, y, z, t) generated by the object to be measured; the detection coil collects the magnetization response signal, and the generated voltage signal is processed by Fourier transform, and the third harmonic 3f0 and sideband harmonic signals 3f0±nf1 (n = 1,…, N) are extracted; drive the three-dimensional mechanical displacement stage to adjust the position of the object to be measured in the second region II until all the imaging units in the second region II are traversed, and calculate the harmonic signal matrix U of the object to be measured. U can be expressed as:

[0098] ;

[0099] Among them, represents the two-dimensional harmonic signal matrix of the SPION sample per unit volume at N z layers in the second region II.

[0100] Step S40: Based on the system matrix A and the harmonic signal matrix U of the object to be measured, construct the equation to be solved:

[0101] ;

[0102] Perform Tikhonov regularization on the equation U = A·c:

[0103] ;

[0104] where α is the regularization parameter, I is the identity matrix, and A H is the adjoint matrix of the system matrix A. Solve this equation using the algebraic reconstruction algorithm (ART algorithm) to inversely obtain the image of the magnetic nanoparticle concentration distribution c.

[0105] Based on the basic principle of narrowband multi-harmonic magnetic particle imaging, as Figure 3 shown. For two-dimensional imaging, in the xy plane, apply a gradient magnetic field H G to generate FFP and perform spatial encoding. In the x direction, apply a high-frequency excitation magnetic field H with a frequency of f0 ac to excite SPION. In the y direction, apply a scanning magnetic field H with a low frequency f1 s to scan FFP along the y-axis. Under the action of the gradient magnetic field, SPIONs at different positions within the imaging field of view (FOV) will generate different magnetization response signals M0. The detection coil collects this magnetization response signal, and the generated voltage signal is processed by Fourier transform to generate a spectral signal around the third harmonic 3f0.

[0106] The present invention adopts the narrowband imaging technology, which reduces the requirement for the bandwidth of the magnetic particle imaging system compared with the broadband imaging technology and solves the problem of insufficient bandwidth faced under high-frequency excitation. The present invention adopts the method of constructing the system matrix with multi-harmonics, constructs the system matrix using the kth harmonic and the surrounding spectrum, and obtains richer spectral information by increasing the number of measured harmonics, thereby improving the image resolution and making the detection limit of the magnetic particle imaging system lower.

[0107] The embodiments described above 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 narrow-band based multi-harmonic magnetic particle imaging method, characterized in that, Including: Determine the magnetic particle imaging region, and divide it into a first region and a second region according to a low-frequency sinusoidal scanning magnetic field; Place the magnetic nanoparticle sample in the first region and apply an external magnetic field, and extract harmonic signals to construct a system matrix; Place the object to be measured in the second region and apply an external magnetic field, and extract harmonic signals to construct a harmonic signal matrix of the object to be measured; According to the system matrix and the harmonic signal matrix of the object to be measured, construct an equation to be solved and perform inverse solution to obtain an image of the magnetic nanoparticle concentration distribution.

2. The narrow-band based multi-harmonic magnetic particle imaging method according to claim 1, wherein Placing the magnetic nanoparticle sample in the first region and applying an external magnetic field, and extracting harmonic signals to construct a system matrix includes: Divide the first region into a grid, divide it into several imaging units, apply a high-frequency excitation magnetic field and a low-frequency scanning magnetic field in a preset direction and move the magnetic nanoparticle sample with a unit volume to traverse the entire first region, and construct the system matrix, where the system matrix includes the specific harmonic kf0 and sideband harmonic signals kf0±nf1 of the magnetic nanoparticle sample with a unit volume in each imaging unit in the first region, n = 1, 2…, N, where k is an integer greater than or equal to 2, f0 represents the frequency of the high-frequency excitation magnetic field, f1 represents the frequency of the low-frequency scanning magnetic field, and N is the largest integer detected by the sideband harmonic signals.

3. The multi-harmonic magnetic particle imaging method based on narrowband according to claim 2, wherein Obtaining the specific harmonic and sideband harmonic signals includes: Place the magnetic nanoparticle sample with a unit volume in the imaging unit in the first region and apply a high-frequency excitation magnetic field and a low-frequency scanning magnetic field in a preset direction to obtain a voltage signal generated by the magnetization response signal; Perform Fourier transform on the voltage signal generated by the magnetization response signal to obtain the specific harmonic and sideband harmonic signals.

4. The narrowband-based multi-harmonic magnetic particle imaging method according to claim 3, wherein Placing the object to be measured in the second region and applying an external magnetic field, and extracting harmonic signals to construct a harmonic signal matrix of the object to be measured includes: Divide the second region into a grid, divide it into several imaging units, apply a high-frequency excitation magnetic field and a low-frequency scanning magnetic field in a preset direction and move the object to be measured to traverse the entire second region, and construct the harmonic signal matrix of the object to be measured, where the harmonic signal matrix of the object to be measured includes the specific harmonic and sideband harmonic signals of the object to be measured in each imaging unit in the second region.

5. The narrowband-based multi-harmonic magnetic particle imaging method according to claim 1, wherein The equation to be solved includes: U = A·c; where U is the harmonic signal matrix of the object to be measured, A is the system matrix, and c is the magnetic nanoparticle concentration distribution.

6. The multi-harmonic magnetic particle imaging method based on narrowband according to claim 1, characterized in that Performing inverse solution on the equation to be solved includes: performing Tikhonovz regularization on the equation to be solved, and using an algebraic reconstruction algorithm to solve the standardized equation to be solved to obtain an image of the magnetic nanoparticle concentration distribution.

7. The narrow-band based multi-harmonic magnetic particle imaging method according to claim 6, wherein Performing Tikhonovz regularization on the equation to be solved includes: ； where α is the regularization parameter, I is the identity matrix, A H is the adjoint matrix of the system matrix A, and c is the concentration distribution of magnetic nanoparticles.

Images