Rapid calibration method for magnetic particle imaging system matrix

Abstract

The invention belongs to the technical field of medical imaging detection, and particularly relates to a magnetic particle imaging system matrix rapid calibration method, which comprises the following steps: carrying out spatial discretization on an imaging area and setting magnetic particle imaging magnetic field configuration parameters; acquiring magnetic particle magnetization response frequency spectrum information under different field free point space positions; acquiring magnetic particle magnetization response frequency spectrum information under different magnetic particle spatial positions based on an equivalent substitution principle; and calculating and assembling to obtain a magnetic particle imaging system matrix. According to the symmetry of a magnetic particle imaging gradient magnetic field, magnetic particle space position mechanical movement is replaced by field free point space position movement, rapid calibration of a magnetic particle imaging system matrix is achieved, and the calibration time is remarkably shortened.

Description

Technical Field

[0001] The invention belongs to the technical field of medical imaging detection, and in particular relates to a method for rapid matrix calibration of a magnetic particle imaging system. Background Art

[0002] Magnetic nanoparticle imaging technology is a new type of medical imaging technology. It uses the nonlinear response of superparamagnetic iron oxide nanoparticles in an alternating magnetic field to highly sensitively locate and reconstruct the concentration distribution of magnetic nanoparticles in the field of view FOV. It has the characteristics of high resolution and high sensitivity. It has great application prospects in medical applications such as biological tissue imaging, cell tracing, thermal diagnosis, and angiography.

[0003] Matrix calibration of magnetic nanoparticle imaging system usually requires moving magnetic nanoparticle point samples to traverse various spatial positions in the imaging area. Therefore, the system matrix takes a long time and has high requirements on coil power consumption and heat dissipation system performance. Therefore, it is urgent to propose a fast calibration method for magnetic particle imaging system matrix. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a method for rapid calibration of the matrix of a magnetic particle imaging system, which significantly reduces the calibration time of the magnetic nanoparticle imaging matrix and promotes the application of magnetic nanoparticles in clinical medicine.

[0005] To achieve the above object, the present invention provides a method for rapid matrix calibration of a magnetic particle imaging system, comprising:

[0006] Discretize the imaging area spatially and set the magnetic field configuration parameters of magnetic particle imaging;

[0007] The magnetic nanoparticle point sample is driven by the magnetic field to traverse the magnetic particle imaging magnetic field, and the magnetic particle magnetization response spectrum information at different field free point spatial positions is obtained;

[0008] Converting the magnetic particle magnetization response spectrum information at different field free point spatial positions into the magnetic particle magnetization response spectrum information at different magnetic particle spatial positions;

[0009] The magnetic particle magnetization response spectrum information at the different magnetic particle spatial positions is calculated and assembled to obtain a magnetic particle imaging system matrix.

[0010] Optionally, the magnetic particle imaging magnetic field configuration parameters include an imaging area pixel grid size, a driving magnetic field size, and a scanning magnetic field size.

[0011] Optionally, spatially discretizing the imaging region and setting magnetic field configuration parameters for magnetic particle imaging include:

[0012] The imaging area is divided into pixel grids, and the magnetic nanoparticle point samples are placed in the imaging area. The total number of pixel grids in the three-dimensional space is ;

[0013] Set the size of a single pixel grid in the x-axis, y-axis, and z-axis directions to l respectively. x , l y , l z The size of the imaging field of view in the x-axis, y-axis and z-axis directions are FOV x FOV y FOV z , calculated as follows:

[0014] ;

[0015] Set the maximum magnetic field strength H of the scanning field in the x-axis direction x(max) , the maximum magnetic field intensity H of the scanning field in the y-axis direction y(max) and the maximum magnetic field strength H of the scanning field in the z-axis direction z(max) , the constraint expression between the maximum magnetic field intensity and the size of the imaging area is as follows:

[0016] ;

[0017] Among them, G x , G y and G z are the gradient magnitudes of the gradient field in the x-axis, y-axis, and z-axis directions respectively.

[0018] Optionally, obtaining the magnetization response spectrum information of magnetic particles at different field free point spatial positions includes:

[0019] S1. Place the magnetic nanoparticle sample in the imaging area and set the scanning magnetic field size;

[0020] S2, using a driving magnetic field to excite and obtain a magnetization response signal of the magnetic nanoparticles;

[0021] S3, adjusting the size of the scanning magnetic field to change the spatial position of the field free point. If the field free point has traversed the pixel grid divided by the imaging area, go to S4, otherwise return to S2;

[0022] S4. Obtain the magnetization response spectrum information of the magnetic particles at different field free point spatial positions.

[0023] Optionally, the equivalent substitution principle is used when converting the magnetization response spectrum information of magnetic particles at different field free point spatial positions into the magnetization response spectrum information of magnetic particles at different magnetic particle spatial positions.

[0024] Optionally, obtaining the magnetization response spectrum information of magnetic particles at different spatial positions of magnetic particles includes:

[0025] Calculate the spatial relative position relationship between the field free point and the magnetic particle measured at different field free point positions;

[0026] According to the spatial relative position relationship between the field free point and the magnetic particle, the magnetization response spectrum information of the magnetic particle at different spatial positions of the field free point is converted into the magnetization response spectrum information of the magnetic particle at different spatial positions of the magnetic particle.

[0027] Optionally, obtaining a magnetic particle imaging system matrix includes:

[0028] ;

[0029] Where A is the magnetic particle imaging system matrix; They are the magnetization response spectrum information of magnetic particles at different spatial positions of magnetic particles.

[0030] An electronic device comprises: a processor and a memory storing computer program instructions; when the processor executes the computer program instructions, the magnetic particle imaging system matrix rapid calibration method is implemented.

[0031] A computer storage medium stores computer program instructions, which, when executed by a processor, implement the magnetic particle imaging system matrix rapid calibration method.

[0032] Technical effect of the invention: The invention discloses a method for rapid calibration of the matrix of a magnetic particle imaging system, which comprehensively utilizes the symmetry of the gradient magnetic field of magnetic particle imaging to achieve equivalent substitution of the spatial position of the field free point and the spatial position of the magnetic particle; by reasonably setting the imaging area size, driving magnetic field strength, and scanning magnetic field strength, rapid calibration of the matrix of the magnetic particle imaging system is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0034] Figure 1 The present invention is a flowchart of a method for rapid matrix calibration of a magnetic particle imaging system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0036] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0037] like Figure 1 As shown, this embodiment provides a method for rapid calibration of a magnetic particle imaging system matrix, including:

[0038] Discretize the imaging area spatially and set the magnetic field configuration parameters of magnetic particle imaging;

[0039] The magnetic nanoparticle point sample is driven by the magnetic field to traverse the magnetic particle imaging magnetic field, and the magnetic particle magnetization response spectrum information at different field free point spatial positions is obtained;

[0040] Converting the magnetic particle magnetization response spectrum information at different field free point spatial positions into the magnetic particle magnetization response spectrum information at different magnetic particle spatial positions;

[0041] The magnetic particle magnetization response spectrum information at the different magnetic particle spatial positions is calculated and assembled to obtain a magnetic particle imaging system matrix.

[0042] Furthermore, the magnetic particle imaging magnetic field configuration parameters include the imaging area pixel grid size, the driving magnetic field size and the scanning magnetic field size.

[0043] Furthermore, the imaging area is spatially discretized and the magnetic field configuration parameters of the magnetic particle imaging are set, including:

[0044] The imaging area is divided into pixel grids, and the magnetic nanoparticle point samples are placed in the imaging area. The total number of pixel grids in the three-dimensional space is ;

[0045] Set the size of a single pixel grid in the x-axis, y-axis, and z-axis directions to l respectively. x , l y , l z The size of the imaging field of view in the x-axis, y-axis and z-axis directions are FOV x FOV y FOV z , calculated as follows:

[0046] ;

[0047] Set the maximum magnetic field strength H of the scanning field in the x-axis direction x(max) , the maximum magnetic field intensity H of the scanning field in the y-axis direction y(max) and the maximum magnetic field strength H of the scanning field in the z-axis directionz(max) , the constraint expression between the maximum magnetic field intensity and the size of the imaging area is as follows:

[0048] ;

[0049] Among them, G x , G y and G z are the gradient magnitudes of the gradient field in the x-axis, y-axis, and z-axis directions respectively.

[0050] Furthermore, obtaining the magnetization response spectrum information of magnetic particles at different field free point spatial positions includes:

[0051] S1. Place the magnetic nanoparticle sample in the imaging area and set the scanning magnetic field size;

[0052] S2, using a driving magnetic field to excite and obtain a magnetization response signal of the magnetic nanoparticles;

[0053] S3, adjusting the size of the scanning magnetic field to change the spatial position of the field free point. If the field free point has traversed the pixel grid divided by the imaging area, go to S4, otherwise return to S2;

[0054] S4. Obtain the magnetization response spectrum information of the magnetic particles at different field free point spatial positions.

[0055] Specifically, in this embodiment, a magnetic nanoparticle point sample is placed in the imaging field of view, a scanning magnetic field is applied to change the spatial position of the magnetic nanoparticle point sample so that it traverses the three-dimensional space pixel grid points, and a driving magnetic field is applied to measure and obtain the magnetic particle magnetization response spectrum information under different field free point spatial positions. The specific steps include:

[0056] Step S1: Place the magnetic nanoparticle point sample in the three-dimensional pixel grid in the imaging area At , set the scanning magnetic field magnitudes in the x, y and z directions to:

[0057] ;

[0058] At this time, the x-space position of the field free point is ;

[0059] Step S2: Using the driving module to excite and obtain the response signal based on the magnetic nanoparticles ;

[0060] Step S3: Adjust the magnitude of the scanning magnetic field in the x, y and z directions to change the x spatial position of the field free point , if the field free point has traversed all pixel grid points in the x space dimension ~ , then go to step S4, otherwise go to step S2;

[0061] Step S4: Using Fourier transform to obtain the magnetization response spectrum information of magnetic particles at different field free point spatial positions .

[0062] Furthermore, the equivalent substitution principle is used when converting the magnetization response spectrum information of magnetic particles at different field free point spatial positions into the magnetization response spectrum information of magnetic particles at different magnetic particle spatial positions.

[0063] Furthermore, obtaining the magnetization response spectrum information of magnetic particles at different spatial positions of magnetic particles includes:

[0064] Calculate the spatial relative position relationship between the field free point and the magnetic particle measured at different field free point positions;

[0065] According to the spatial relative position relationship between the field free point and the magnetic particle, the magnetization response spectrum information of the magnetic particle at different spatial positions of the field free point is converted into the magnetization response spectrum information of the magnetic particle at different spatial positions of the magnetic particle.

[0066] Specifically, the implementation process in this embodiment includes: calculating the signal-to-noise ratio SNR of each harmonic component of the signal magnetic nanoparticle magnetization response signal k , set the signal-to-noise ratio threshold to determine the harmonic number k to be used to construct the system matrix; according to the equivalent substitution formula, the magnetic particle magnetization response spectrum information at different field free point spatial positions is converted into Transformed into the magnetic particle magnetization response spectrum information at different magnetic particle spatial positions .

[0067] Further, obtaining a magnetic particle imaging system matrix includes:

[0068] ;

[0069] Where A is the magnetic particle imaging system matrix; They are the magnetization response spectrum information of magnetic particles at different spatial positions of magnetic particles.

[0070] The first aspect of the present invention proposes a method for rapid calibration of a magnetic particle imaging system matrix. The following description will be introduced using magnetic particle imaging based on spatial domain information as an example (i.e., the x-axis, y-axis, and z-axis all use scanning fields to change the spatial position of the field free point). When the scanning magnetic field intensity in the x-axis direction is , the magnetic field strength scanned in the y-axis direction is , the magnetic field intensity scanned in the z-axis direction is When , the spatial position of the field free point is It is expressed as:

[0071] ;

[0072] in, The specific position is determined by the scanning magnetic field strength in the x-axis, y-axis, and z-axis directions, i=1, 2, …, M; j= 1, 2, …, N; o= 1, 2, …, P; M represents the number of grids divided along the x-axis; N represents the number of grids divided along the y-axis; and P represents the number of grids divided along the z-axis.

[0073] The driving magnetic field module in the x-axis direction is used to apply high-amplitude excitation to receive the induced electromotive force signal in the coil. It is expressed as:

[0074] ;

[0075] in, Indicates spatial location The concentration space of magnetic nanoparticles at; The x-axis coordinate of the spatial position of the free point on the spot is , the y-axis coordinate is , the z-axis coordinate is , and the infinitesimal magnetic nanoparticles per unit concentration are placed When the magnetic nanoparticle imaging device system responds under the excitation of the driving magnetic field.

[0076] For the discretized imaging space, the spatial position of the field free point is Can be located in ~ Between, corresponding to the Cartesian coordinate system , where m = 1, 2, …, M; n = 1, 2, …, N; p = 1, 2, …, P. The induced electromotive force signal in the receiving coil is Fourier transformed to obtain the spectrum information of the magnetization response of the magnetic particles. The above expression is expressed in matrix form as follows:

[0077] ;

[0078] in, Representative signal The kth harmonic component of Representative signal The kth harmonic component of .

[0079] By using the above formula and choosing an appropriate regularization method to solve the inverse problem, the spatial distribution of the magnetic nanoparticle concentration of the imaged body can be obtained. In summary, the matrix of the magnetic nanoparticle imaging acquisition system usually needs to change the position of the field free point and the spatial position of the magnetic particle point sample so that both traverse the discretized spatial position. The method for rapid calibration of the magnetic particle imaging system matrix proposed in the present invention uses the rapid field free point spatial position movement to replace the mechanical movement of the magnetic particle spatial position based on the symmetry of the magnetic particle imaging gradient magnetic field, thereby achieving the following equivalent substitution:

[0080] .

[0081] Therefore, the proposed method for rapid calibration of the magnetic particle imaging system matrix does not require mechanical displacement to change the spatial position of the magnetic particle point sample. It only needs to enhance the intensity of the scanning field and change the spatial position of the field free point through the scanning field in a larger range, so that the spatial position of the field free point covers , that is, to obtain all the information of the system matrix. At this time, the spatial position index is expanded to m = -M, …, 1, 2, …, M; n = -N, …, 1, 2, …, N; p = -P, …, 1, 2, …, P.

[0082] This embodiment further provides an electronic device, which includes: a processor and a memory storing computer program instructions; when the processor executes the computer program instructions, the method for rapid matrix calibration of a magnetic particle imaging system is implemented.

[0083] This embodiment further provides a computer storage medium, on which computer program instructions are stored. When the computer program instructions are executed by a processor, the method for rapid matrix calibration of a magnetic particle imaging system is implemented.

[0084] The present invention discloses a method for rapid calibration of a magnetic particle imaging system matrix, which comprehensively utilizes the symmetry of the magnetic particle imaging gradient magnetic field to achieve equivalent substitution of the field free point spatial position and the magnetic particle spatial position; and realizes rapid calibration of the magnetic particle imaging system matrix by reasonably setting the imaging area size, driving magnetic field strength, and scanning magnetic field strength.

[0085] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for rapid calibration of a magnetic particle imaging system matrix, characterized in that: include: Discretize the imaging area spatially and set the magnetic field configuration parameters of magnetic particle imaging; The magnetic nanoparticle point sample is driven by the magnetic field to traverse the magnetic particle imaging magnetic field, and the magnetic particle magnetization response spectrum information at different field free point spatial positions is obtained; Converting the magnetic particle magnetization response spectrum information at different field free point spatial positions into the magnetic particle magnetization response spectrum information at different magnetic particle spatial positions; The magnetic particle magnetization response spectrum information at the different magnetic particle spatial positions is calculated and assembled to obtain a magnetic particle imaging system matrix.

2. The method for rapid matrix calibration of a magnetic particle imaging system as claimed in claim 1, characterized in that: The magnetic particle imaging magnetic field configuration parameters include the imaging area pixel grid size, the driving magnetic field size and the scanning magnetic field size.

3. The method for rapid matrix calibration of a magnetic particle imaging system according to claim 1, characterized in that: The spatial discretization of the imaging area and the setting of magnetic field configuration parameters for magnetic particle imaging include: The imaging area is divided into pixel grids, and the magnetic nanoparticle point samples are placed in the imaging area. The total number of pixel grids in the three-dimensional space is ; Set the size of a single pixel grid in the x-axis, y-axis, and z-axis directions to l respectively. x , l y , l z The size of the imaging field of view in the x-axis, y-axis and z-axis directions are FOV x FOV y FOV z , calculated as follows: ； Set the maximum magnetic field strength H of the scanning field in the x-axis direction x(max) , the maximum magnetic field intensity H of the scanning field in the y-axis direction y(max) and the maximum magnetic field strength H of the scanning field in the z-axis direction z(max) , the constraint expression between the maximum magnetic field intensity and the size of the imaging area is as follows: ； Among them, G x , G y and G z are the gradient magnitudes of the gradient field in the x-axis, y-axis, and z-axis directions respectively.

4. The method for rapid matrix calibration of a magnetic particle imaging system as claimed in claim 1, characterized in that: Obtaining the magnetization response spectrum information of magnetic particles at different field free point spatial positions includes: S1. Place the magnetic nanoparticle sample in the imaging area and set the scanning magnetic field size; S2, using a driving magnetic field to excite and obtain a magnetization response signal of the magnetic nanoparticles; S3, adjusting the size of the scanning magnetic field to change the spatial position of the field free point. If the field free point has traversed the pixel grid divided by the imaging area, go to S4, otherwise return to S2; S4. Obtain the magnetization response spectrum information of the magnetic particles at different field free point spatial positions.

5. The method for rapid matrix calibration of a magnetic particle imaging system as claimed in claim 1, characterized in that: The equivalent substitution principle is used to convert the magnetization response spectrum information of magnetic particles at different field free point spatial positions into the magnetization response spectrum information of magnetic particles at different magnetic particle spatial positions.

6. The method for rapid matrix calibration of a magnetic particle imaging system as claimed in claim 1, characterized in that: Obtaining the magnetic particle magnetization response spectrum information at different magnetic particle spatial positions includes: Calculate the spatial relative position relationship between the field free point and the magnetic particle measured at different field free point positions; According to the spatial relative position relationship between the field free point and the magnetic particle, the magnetization response spectrum information of the magnetic particle at different spatial positions of the field free point is converted into the magnetization response spectrum information of the magnetic particle at different spatial positions of the magnetic particle.

7. The method for rapid matrix calibration of a magnetic particle imaging system as claimed in claim 1, characterized in that: Obtain the Magnetic Particle Imaging System Matrix including: ； Where A is the magnetic particle imaging system matrix; They are the magnetization response spectrum information of magnetic particles at different spatial positions of magnetic particles.

8. An electronic device, characterized in that: The electronic device comprises: a processor and a memory storing computer program instructions; when the processor executes the computer program instructions, the method for rapid matrix calibration of a magnetic particle imaging system as described in any one of claims 1 to 7 is implemented.

9. A computer storage medium, characterized in that The computer storage medium stores computer program instructions, and when the computer program instructions are executed by the processor, the method for rapid matrix calibration of a magnetic particle imaging system according to any one of claims 1 to 7 is implemented.

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