A Fast Calibration Method for the Matrix of a Magnetic Particle Imaging System

Abstract

The present invention belongs to the technical field of medical imaging detection, and particularly relates to a method for rapid calibration of a matrix of a magnetic particle imaging system, including: performing spatial discretization on an imaging region and setting magnetic particle imaging magnetic field configuration parameters; obtaining magnetic particle magnetization response spectrum information at different spatial positions of field-free points; obtaining magnetic particle magnetization response spectrum information at different magnetic particle spatial positions based on the principle of equivalent substitution; calculating and assembling to obtain a matrix of the magnetic particle imaging system. According to the symmetry of the magnetic particle imaging gradient magnetic field, the present invention uses the movement of the spatial position of the field-free point to replace the mechanical movement of the magnetic particle spatial position, realizes the rapid calibration of the matrix of the magnetic particle imaging system, and significantly shortens the calibration time.

Description

Technical Field

[0001] The present invention belongs to the technical field of medical imaging detection, and particularly relates to a method for quickly calibrating a matrix of a magnetic particle imaging system. Background Art

[0002] Magnetic nanoparticle imaging technology is a new type of medical imaging technology that 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 within the field of view (FOV). It features high resolution and high sensitivity, and has great application prospects in medical applications such as biological tissue imaging, cell tracing, thermotherapy diagnosis, and angiography.

[0003] Matrix calibration of a magnetic nanoparticle imaging system usually requires moving a magnetic nanoparticle point sample to traverse each spatial position in the imaging area. Therefore, the system matrix calibration takes a long time and has high requirements for coil power consumption and the performance of the cooling system. Therefore, there is an urgent need to propose a method for quickly calibrating a matrix of a magnetic particle imaging system. Summary of the Invention

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

[0005] To achieve the above object, the present invention provides a method for quickly calibrating a matrix of a magnetic particle imaging system, including:

[0006] Performing spatial discretization on the imaging area and setting magnetic particle imaging magnetic field configuration parameters;

[0007] Driving a magnetic nanoparticle point sample to traverse the magnetic particle imaging magnetic field through a magnetic field, and obtaining magnetic particle magnetization response spectrum information at different field-free point spatial positions;

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

[0009] Calculating and assembling the magnetic particle magnetization response spectrum information at different magnetic particle spatial positions to obtain a magnetic particle imaging system matrix.

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

[0011] Optionally, performing spatial discretization on the imaging area and setting magnetic particle imaging magnetic field configuration parameters includes:

[0012] Dividing the imaging area along the x-axis, y-axis, and z-axis directions into A pixel grid is formed, and the magnetic nanoparticle dot sample is placed within the imaging region. The total number of pixel grids in three-dimensional space is ;

[0013] Set the sizes of the single pixel grid in the x-axis, y-axis, and z-axis directions to be l x , l y , l z . The scale sizes of the imaging field of view in the x-axis, y-axis, and z-axis directions are FOV x , FOV y , FOV z , and the calculations are as follows:

[0014] ;

[0015] Set the maximum magnetic field strength H x(max) of the scanning field in the x-axis direction, the maximum magnetic field strength H y(max) of the scanning field in the y-axis direction, and the maximum magnetic field strength H z(max) of the scanning field in the z-axis direction. The constraint expressions between the maximum magnetic field strength and the size of the imaging region are as follows:

[0016] ;

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

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

[0019] S1. Place the magnetic nanoparticle dot sample within the imaging region and set the scanning magnetic field magnitude;

[0020] S2. Use the driving magnetic field for excitation to obtain the magnetic particle magnetization response signal;

[0021] S3. Adjust the scanning magnetic field magnitude to change the spatial position of the field-free point. If the field-free point has traversed the pixel grids divided in the imaging region, go to S4; otherwise, return to S2;

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

[0023] Optionally, the equivalent substitution principle is adopted when 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.

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

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

[0026] According to the spatial relative position relationship between the field-free points and the magnetic particles, convert 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.

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

[0028] ;

[0029] where A is the magnetic particle imaging system matrix; are respectively the magnetic particle magnetization response spectrum information at different magnetic particle spatial positions.

[0030] An electronic device, the electronic device includes: 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, on which computer program instructions are stored, and when the computer program instructions are executed by a processor, the magnetic particle imaging system matrix rapid calibration method is implemented.

[0032] Technical effects of the present invention: The present invention discloses a method for rapidly calibrating a magnetic particle imaging system matrix, comprehensively utilizes the symmetry of the magnetic particle imaging gradient magnetic field to realize the equivalent substitution of the field-free point spatial position and the magnetic particle spatial position; and realizes the rapid calibration of the magnetic particle imaging system matrix by reasonably setting the imaging region size, driving magnetic field strength, and scanning magnetic field strength. Description of the Drawings

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

[0034] Figure 1 is a schematic flowchart of a method for rapidly calibrating a magnetic particle imaging system matrix according to an embodiment of the present invention. Detailed Embodiments

[0035] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The following will refer to the drawings and combine the embodiments to detail this application.

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

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

[0038] Performing spatial discretization on the imaging region and setting magnetic particle imaging magnetic field configuration parameters;

[0039] Driving magnetic nanoparticle point samples through the magnetic particle imaging magnetic field by the magnetic field to obtain magnetic particle magnetization response spectrum information at different spatial positions of field-free points;

[0040] Converting the magnetic particle magnetization response spectrum information at different spatial positions of field-free points into magnetic particle magnetization response spectrum information at different spatial positions of magnetic particles;

[0041] Calculating and assembling the magnetic particle magnetization response spectrum information at different spatial positions of magnetic particles to obtain a magnetic particle imaging system matrix.

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

[0043] Furthermore, performing spatial discretization on the imaging region and setting magnetic particle imaging magnetic field configuration parameters includes:

[0044] Dividing the imaging region into pixel grids along the x-axis, y-axis, and z-axis directions, and placing magnetic nanoparticle point samples in the imaging region, with the total number of pixel grids in three-dimensional space being ;

[0045] Setting the sizes of a single pixel grid in the x-axis, y-axis, and z-axis directions to be l x , l y , l z , and the scale sizes of the imaging field of view in the x-axis, y-axis, and z-axis directions to be FOV x , FOV y , FOV z , and the calculation is as follows:

[0046] ;

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

[0048] ;

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

[0050] Further, obtaining the magnetic particle magnetization response spectrum information at different field-free point spatial positions includes:

[0051] S1. Place the magnetic nanoparticle dot sample in the imaging region and set the magnitude of the scanning magnetic field;

[0052] S2. Use the driving magnetic field for excitation to obtain the magnetic nanoparticle magnetization response signal;

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

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

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

[0056] Step S1: Place the magnetic nanoparticle dot sample at the three-dimensional space pixel grid in the imaging region, and set the magnitudes of the scanning magnetic fields in the x-direction, y-direction, and z-direction to:

[0057] ;

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

[0059] Step S2: Use the driving module for excitation to obtain the magnetic nanoparticle response signal ;

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

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

[0062] Furthermore, when 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 principle of equivalent substitution is adopted.

[0063] Furthermore, obtaining the magnetic particle magnetization response spectrum information at different magnetic particle spatial positions 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, convert 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.

[0066] Specifically, the implementation process in this embodiment includes: calculating the signal-to-noise ratio SNR of each harmonic component of the magnetization response signal of the signal magnetic nanoparticles k , setting a signal-to-noise ratio threshold to determine the number of harmonics k to be used for constructing the system matrix; according to the equivalent substitution formula, convert 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 .

[0067] Furthermore, obtaining the magnetic particle imaging system matrix includes:

[0068] ;

[0069] where A is the magnetic particle imaging system matrix; are the magnetic particle magnetization response spectrum information at different magnetic particle spatial positions respectively.

[0070] The first aspect of the present invention proposes a method for quickly calibrating a magnetic particle imaging system matrix. The following description will be introduced by taking magnetic particle imaging based on spatial domain information as an example (that is, the spatial position of the field-free point is changed by using scanning fields on the x-axis, y-axis, and z-axis). When the scanning magnetic field intensity in the x-axis direction is , the scanning magnetic field intensity in the y-axis direction is , and the scanning magnetic field intensity in the z-axis direction is , the spatial position where the field-free point is located is expressed as:

[0071] ;

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

[0073] Apply a high-amplitude excitation using the drive magnetic field module in the x-axis direction, and the induced electromotive force signal in the receiving coil is expressed as:

[0074] ;

[0075] Among them, represents the magnetic nanoparticle concentration space at the spatial position ; represents that when the x-axis coordinate of the spatial position of the field-free point is , the y-axis coordinate is , the z-axis coordinate is , and magnetic nanoparticles with an infinitesimal unit concentration volume are placed at , the system response of the magnetic nanoparticle imaging device under the drive magnetic field excitation.

[0076] For the discretized imaging space, the spatial position where the field-free point is located can be between ~ , corresponding to the Cartesian coordinate system , where m = 1, 2, …, M; n = 1, 2, …, N; p = 1, 2, …, P. Perform a Fourier transform on the induced electromotive force signal in the receiving coil to obtain the magnetic particle magnetization response spectrum information. The above expression is represented in matrix form as:

[0077] ;

[0078] Among them, represents the k-th harmonic component of the signal , represents the k-th harmonic component of the signal .

[0079] Using the above formula and selecting an appropriate regularization method to solve the inverse problem, the magnetic nanoparticle concentration spatial distribution of the object to be imaged can be obtained. In summary, usually, for the magnetic nanoparticle imaging acquisition system matrix, it is necessary 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 positions 。The fast calibration method for the matrix of the magnetic particle imaging system proposed by the present invention, according to the symmetry of the magnetic particle imaging gradient magnetic field, uses the spatial position movement of the fast field-free point to replace the mechanical movement of the magnetic particle spatial position, and realizes the following equivalent substitution:

[0080] 。

[0081] Therefore, for the proposed fast calibration method for the matrix of the magnetic particle imaging system, there is no need to mechanically displace to change the spatial position of the magnetic particle point sample. Only by increasing the intensity of the scanning field and changing the spatial position of the field-free point within a larger range through the scanning field, the spatial position of the field-free point can cover , that is, all the information of the system matrix is obtained. At this time, the spatial position index is extended to m = -M, …, 1, 2, …, M; n = -N, …, 1, 2, …, N; p = -P, …, 1, 2, …, P.

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

[0083] This embodiment also provides a computer storage medium, on which computer program instructions are stored, and when the computer program instructions are executed by a processor, the fast calibration method for the matrix of the magnetic particle imaging system is realized.

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

[0085] The above is only a preferred specific implementation manner 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 those skilled in the art within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for rapid calibration of a matrix in a magnetic particle imaging system, characterized in that, Including: Spatially discretize the imaging area and set the magnetic particle imaging magnetic field configuration parameters; Drive the magnetic nanoparticle dot sample through the magnetic particle imaging magnetic field by the magnetic field to obtain the magnetic particle magnetization response spectrum information at different spatial positions of the field-free points; Obtaining the magnetic particle magnetization response spectrum information at different spatial positions of the field-free points includes: S1. Place the magnetic nanoparticle dot sample in the imaging area and set the magnitude of the scanning magnetic field; S2. Use the driving magnetic field for excitation to obtain the magnetic particle magnetization response signal; S3. Adjust the magnitude 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 magnetic particle magnetization response spectrum information at different spatial positions of the field-free points; Convert the magnetic particle magnetization response spectrum information at different spatial positions of the field-free points into the magnetic particle magnetization response spectrum information at different spatial positions of the magnetic particles; when converting the magnetic particle magnetization response spectrum information at different spatial positions of the field-free points into the magnetic particle magnetization response spectrum information at different spatial positions of the magnetic particles, the equivalent substitution principle is adopted; Obtaining the magnetic particle magnetization response spectrum information at different spatial positions of the magnetic particles 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, convert the magnetic particle magnetization response spectrum information at different spatial positions of the field-free points into the magnetic particle magnetization response spectrum information at different spatial positions of the magnetic particles; Calculate and assemble the magnetic particle magnetization response spectrum information at different spatial positions of the magnetic particles to obtain the magnetic particle imaging system matrix; Obtaining the magnetic particle imaging system matrix includes: ； Among them, A is the matrix of the magnetic particle imaging system; They are respectively the magnetic particle magnetization response spectrum information at different magnetic particle spatial positions.

2. The method for quickly calibrating the magnetic particle imaging system matrix according to claim 1, wherein The magnetic particle imaging magnetic field configuration parameters include the pixel grid size of the imaging area, the magnitude of the driving magnetic field, and the magnitude of the scanning magnetic field.

3. The method for quickly calibrating the magnetic particle imaging system matrix according to claim 1, wherein Spatially discretizing the imaging area and setting the magnetic particle imaging magnetic field configuration parameters include: The imaging area is divided along the x-axis, y-axis, and z-axis directions into pixel grids, and the magnetic nanoparticle dot sample is placed within the imaging area. The total number of pixel grids in the three-dimensional space is ; Set the sizes of a single pixel grid in the x-axis, y-axis, and z-axis directions to be l x , l y , l z , and the scale sizes of the imaging field of view in the x-axis, y-axis, and z-axis directions are FOV x , FOV y , FOV z , and the calculation is as follows: ； Set the maximum magnetic field strength H of the scanning field in the x-axis direction x(max) and the maximum magnetic field strength 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 strength and the size of the imaging area is as follows: ； Among them, G x , G y and G z are respectively the gradient magnitudes of the gradient field in the x-axis direction, y-axis direction, and z-axis direction.

4. An electronic device, characterized in that, The electronic device includes: a processor and a memory storing computer program instructions; when the processor executes the computer program instructions, the method for quickly calibrating the magnetic particle imaging system matrix according to any one of claims 1-3 is implemented.

5. A computer storage medium, characterized in that, Computer program instructions are stored on the computer storage medium, and when the computer program instructions are executed by the processor, the method for quickly calibrating the magnetic particle imaging system matrix according to any one of claims 1-3 is implemented.

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