Magnetic particle imaging method, system and device based on harmonic orthogonal projection

Abstract

The present invention belongs to the field of biomedical imaging technology, and specifically relates to a magnetic particle imaging method, system, and device based on harmonic orthogonal projection, which aims to solve the problem that the existing magnetic particle imaging method cannot achieve fast and high-resolution imaging under high driving magnetic field and low gradient magnetic field conditions. The method of the present invention includes: collecting magnetic particle time domain signals; grid discretizing the synthetic scanning path of the scanning magnetic field; transforming the collected magnetic particle time domain signals in the time-frequency domain; projecting the instantaneous harmonic components onto the corresponding discrete grid to obtain harmonic orthogonal projection images of different frequencies; constructing a small sample prior harmonic orthogonal projection image, and then constructing projection convolution kernels of different frequencies; using the projection convolution kernel to deconvolve the harmonic orthogonal projection image to obtain a spatial distribution image of magnetic particles. The present invention improves the spatial resolution of magnetic particle imaging and realizes fast and high-resolution imaging of the spatial distribution of magnetic particles under strong excitation magnetic field conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of biomedical imaging, and in particular relates to a magnetic particle imaging method, system and equipment based on harmonic orthogonal projection. Background Art

[0002] Magnetic particles are nanoscale particles with superparamagnetism. In recent years, they have been widely studied and applied as a new type of medical imaging tracer in tumor detection, magnetic particle thermal therapy, targeted drug delivery and other issues.

[0003] The basic process of the traditional magnetic particle imaging (MPI) method is: 1. First, a high-field static gradient magnetic field is used to construct a magnetic field-free region (FFR) in the imaging space. This region can be a magnetic field-free point (FFP) or a magnetic field-free line (FFL). In the FFR, the magnetic particles are in a non-saturated state and can generate a magnetization response signal; 2. Apply a high-frequency driving magnetic field to rotate the magnetic moment of the magnetic particles in the FFR, thereby generating a magnetization response signal. At the same time, the FFR will move as the driving field strength increases, realizing rapid scanning of the FFR in the imaging space; 3. When there are driving magnetic fields in two or three directions, the FFR will perform two-dimensional or three-dimensional scanning in the imaging space; 4. The magnetization response signal of the magnetic particles is sensed by the receiving coil, and the magnetic particle concentration distribution can be reconstructed in combination with the image reconstruction algorithm.

[0004] At present, the MPI reconstruction algorithms mainly include the system matrix method and the X-space method:

[0005] The basic principle of the system matrix method is to establish a system matrix S between the magnetic particle signal U and the concentration c, further solve the equation U=Sc, and calculate the spatial distribution of the magnetic particle concentration c. However, the existing problem is that the acquisition process of the system matrix is ​​very cumbersome, requiring repeated movement of magnetic particle samples for measurement, and regular repeated debugging and calibration, which is very time-consuming. In addition, a large number of matrix operations will slow down the imaging speed, which is not conducive to real-time imaging.

[0006] The X-space method is a relatively simple and fast MPI reconstruction method. The particle distribution can be reconstructed by deconvolving the time domain signal and projecting it onto the FFR scanning trajectory. However, the existing problem is that when the driving magnetic field strength is increased to increase the scanning range, the magnetic particles will be affected by the strong driving magnetic field and produce a relaxation effect. This will cause delays and distortions in the time domain signal, which will in turn cause the reconstructed image to be misplaced and blurred, reducing the spatial resolution of the image. On the other hand, the particle signal intensity is also proportional to the field strength of the driving field. If you want to perform high-sensitivity magnetic particle imaging, you must increase the driving field strength. Therefore, it is difficult for the X-space-based rapid imaging method to take into account both spatial resolution and sensitivity.

[0007] In summary, the current magnetic particle imaging reconstruction method cannot achieve fast high-resolution imaging under high driving magnetic field and low gradient magnetic field conditions. This will restrict the development of magnetic particle imaging technology in the field of clinical applications. Based on this, the present invention proposes a magnetic particle imaging method based on harmonic orthogonal projection. Summary of the invention

[0008] In order to solve the above-mentioned problems in the prior art, that is, to solve the problem that the existing magnetic particle imaging method cannot achieve fast and high-resolution imaging under high driving magnetic field and low gradient magnetic field conditions, the present invention proposes a magnetic particle imaging method based on harmonic orthogonal projection, which is applied to a magnetic particle imaging device, wherein the magnetic particle imaging device comprises a permanent magnet pair, a scanning coil group, a sample moving bed, and an image reconstruction device; the scanning coil group comprises two pairs of annular scanning coil pairs and two cylindrical coils; the two annular scanning coils in the annular scanning coil pair are coaxial and the axes are orthogonal; the two cylindrical coils, one is an excitation coil and the other is a receiving coil, are coaxially arranged in the enclosed space of the two pairs of annular scanning coil pairs; the magnetic particle imaging device takes the axis direction of the cylindrical coil as the x direction and the longitudinal direction of the axis of the cylindrical coil as the z direction; the permanent magnet pair is arranged between the annular scanning coil pair and the cylindrical coil in the z direction; the method comprises:

[0009] Step S100, constructing a gradient magnetic field using a permanent magnet pair to form a magnetic field-free region, and passing an alternating current through two pairs of annular scanning coils to generate a scanning magnetic field; when generating a scanning magnetic field, the magnetic particles are excited by the excitation coil, and the time domain signals of the magnetic particles are collected by the receiving coil;

[0010] Step S200, discretizing a composite scanning path of a scanning magnetic field in at least one direction into a grid, wherein each discrete grid corresponds to an imaging voxel; the composite scanning path refers to a scanning path when scanning magnetic fields in two or more directions work simultaneously;

[0011] Step S300, performing time-frequency domain transformation on the collected magnetic particle time domain signal to obtain instantaneous harmonic components of the magnetic particle signal at different times;

[0012] Step S400, performing spatiotemporal projection on the instantaneous harmonic component according to a preset spatiotemporal coding rule, projecting the projected component onto a corresponding discrete grid, and obtaining harmonic orthogonal projection images of different frequencies;

[0013] Step S500, combining the methods of steps S100 to S400, constructing a small sample prior harmonic orthogonal projection image; after the construction, constructing projection convolution kernels of different frequencies based on the small sample prior harmonic orthogonal projection image;

[0014] Step S600, using projection convolution kernels of different frequencies to perform deconvolution processing on the harmonic orthogonal projection images of different frequencies obtained in step S400, and finally obtaining a spatial distribution image of the magnetic particles.

[0015] In some preferred embodiments, the magnetic particle time domain signal is collected by:

[0016] When alternating current is passed through the two pairs of annular scanning coils, scanning magnetic fields in two directions are applied simultaneously with different frequencies or phases, and the magnetic field-free points will be quickly scanned in the two-dimensional space along the set trajectory, and after a period of time T, the entire yz plane two-dimensional space will be traversed;

[0017] While scanning the point without magnetic field, the excitation coil is used to generate a continuous high-frequency excitation magnetic field to excite the magnetization response signal of the magnetic particles, and the receiving coil is used to sense and collect the magnetization response signal, that is, the magnetic particle time domain signal.

[0018] In some preferred implementations, the time-frequency domain transform is any one of a piecewise Fourier transform, a short-time Fourier transform, and a wavelet transform.

[0019] In some preferred embodiments, the instantaneous harmonic components of the magnetic particle signal at different times are obtained by:

[0020] The time length T of the magnetic particle time domain signal generated in the scanning process of the entire yz plane two-dimensional space and the number N of voxels set in the spatial distribution image of the magnetic particles to be reconstructed are obtained, and the magnetic particle time domain signal is divided into T / N segments;

[0021] Each segment of magnetic particle time domain signal is transformed into time-frequency domain separately to obtain N groups of instantaneous harmonic components of different frequencies.

[0022] In some preferred embodiments, a small sample priori harmonic orthogonal projection image is constructed by:

[0023] Before the formal scanning imaging, a magnetic particle sample whose size is no larger than the imaging voxel of the spatial distribution image of the magnetic particles to be reconstructed is placed in the imaging space of the magnetic particle imaging device; then the method of steps S100 to S400 is executed to obtain harmonic orthogonal projection images of different frequencies as small sample prior harmonic orthogonal projection images.

[0024] In some preferred embodiments, projection convolution kernels of different frequencies are constructed based on the small sample prior harmonic orthogonal projection image, and the method is:

[0025] Construct the projection convolution kernel according to the imaging space and resolution scale requirements;

[0026] Specifically: The reconstructed harmonic orthogonal projection image It can be regarded as the point spread function of the real particle distribution ρ(y) and different frequencies The three obtained by convolution have the following relationship:

[0027]

[0028] Among them, t n represents the nth time point, y(t n ) represents the spatial coordinates of the FFP at the nth time point, f k represents the kth frequency, and y represents the distribution coordinates of the real particles;

[0029] Based on the above theory, the method for constructing the projection convolution kernel is: if the desired resolution is Pmm, a small sample with a width not greater than Pmm, which can also be called the minimum unit voxel, is used to obtain the orthogonal harmonic projection image according to the method of step S100-step S400; according to the above formula, at this time that is because It is the point spread function corresponding to the smallest unit voxel, so it is called the projected convolution kernel.

[0030] In some preferred embodiments, the instantaneous harmonic component is subjected to spatiotemporal projection according to a preset spatiotemporal encoding rule, and the method is as follows:

[0031]

[0032] Among them, TFS (t n , f k ) represents the instantaneous harmonic component, which is a function of time and frequency. Specifically, it represents the instantaneous harmonic component of the kth frequency at the nth moment. represents the phase corresponding to the instantaneous harmonic component, Indicates the instantaneous scanning speed of FFP, S R [y(t n )] represents the sensitivity of the receiving coil corresponding to the instantaneous displacement point, The one-dimensional harmonic projection image representing different frequencies is a function of space and frequency;

[0033] If there are two scanning magnetic fields in two directions, then according to the above projection rules, two-dimensional harmonic projection images IMG (f k ):

[0034]

[0035] Among them, y N represents the Nth y-space coordinate, z M represents the Mth z-space coordinate;

[0036] The weighted combination of harmonic orthogonal projection images of different frequencies is:

[0037]

[0038] in, It represents the harmonic orthogonal projection images of different frequencies after individual normalization. f0 represents the frequency of the excitation magnetic field, which is called the fundamental frequency. (2k-1)f0 represents the odd multiple frequency, also called the odd harmonic frequency. IMG CH It represents the weighted combined harmonic projection image after normalization and polarity correction of all odd-frequency harmonic projection images.

[0039] The second aspect of the present invention proposes a magnetic particle imaging system based on harmonic orthogonal projection, the system comprising: a signal acquisition module, a grid discretization module, a time-frequency domain transformation module, a projection module, a convolution kernel construction module, and an image reconstruction module;

[0040] The signal acquisition module is configured to construct a gradient magnetic field using a permanent magnet pair to form a magnetic field-free area, and to pass an alternating current through two pairs of annular scanning coils to generate a scanning magnetic field; when the scanning magnetic field is generated, the magnetic particles are excited by the excitation coil, and the time domain signals of the magnetic particles are collected by the receiving coil;

[0041] The grid discretization module is configured to discretize the synthetic scanning path of the scanning magnetic field in at least one direction into a grid, wherein each discrete grid corresponds to an imaging voxel; the synthetic scanning path refers to a scanning path when the scanning magnetic fields in two or more directions work simultaneously;

[0042] The time-frequency domain transformation module is configured to perform time-frequency domain transformation on the collected magnetic particle time domain signal to obtain the instantaneous harmonic components of the magnetic particle signal at different times;

[0043] The projection module is configured to perform spatiotemporal projection of the instantaneous harmonic component according to a preset spatiotemporal encoding rule, project the projected image onto a corresponding discrete grid, and obtain orthogonal projection images of harmonics of different frequencies;

[0044] The convolution kernel construction module is configured to construct a small sample priori harmonic orthogonal projection image by combining the signal acquisition module-projection module method; after the construction, a projection convolution kernel of different frequencies is constructed based on the small sample priori harmonic orthogonal projection image;

[0045] The image reconstruction module is configured to perform deconvolution processing on the harmonic orthogonal projection images of different frequencies acquired by the projection module using projection convolution kernels of different frequencies, and finally obtain a spatial distribution image of the magnetic particles.

[0046] According to a third aspect of the present invention, an electronic device is proposed, comprising: at least one processor; and a memory communicatively connected to at least one of the processors; wherein the memory stores instructions executable by the processor, and the instructions are used to be executed by the processor to implement the above-mentioned magnetic particle imaging method based on harmonic orthogonal projection.

[0047] According to a fourth aspect of the present invention, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores computer instructions, and the computer instructions are used to be executed by the computer to implement the above-mentioned magnetic particle imaging method based on harmonic orthogonal projection.

[0048] Beneficial effects of the present invention:

[0049] The present invention improves the spatial resolution of magnetic particle imaging and realizes rapid high-resolution imaging of the spatial distribution of magnetic particles under strong excitation magnetic field conditions.

[0050] The present invention uses instantaneous harmonic components instead of traditional time domain signals for projection reconstruction, avoiding the problem of time domain signal distortion caused by particle relaxation effects, and can improve the spatial resolution of magnetic particle imaging under strong excitation magnetic field conditions. Compared with traditional imaging methods, it not only improves the signal-to-noise ratio, but also takes into account the image resolution, and at the same time has a fast imaging speed, which is conducive to the application in the field of real-time imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings.

[0052] Figure 1 It is a schematic flow chart of a magnetic particle imaging method based on harmonic orthogonal projection according to an embodiment of the present invention;

[0053] Figure 2 A schematic diagram of a framework of a magnetic particle imaging method based on harmonic orthogonal projection according to an embodiment of the present invention;

[0054] Figure 3 is a schematic structural diagram of a magnetic particle imaging device according to an embodiment of the present invention;

[0055] Figure 4 It is a structural diagram of a computer system of an embodiment of the present invention that is suitable for implementing an electronic device of an embodiment of the present application. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] The present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It should be noted that, in the absence of conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0058] A magnetic particle imaging method based on harmonic orthogonal projection according to a first embodiment of the present invention is applied to a magnetic particle imaging device, wherein the magnetic particle imaging device comprises a permanent magnet pair, a scanning coil group, a sample moving bed, and an image reconstruction device; the scanning coil group comprises two pairs of annular scanning coil pairs and two cylindrical coils; two annular scanning coils in the annular scanning coil pairs are coaxial and their axes are orthogonal; two cylindrical coils, one is an excitation coil and the other is a receiving coil, are coaxially arranged in the enclosed space of the two pairs of annular scanning coil pairs; the magnetic particle imaging device takes the axis direction of the cylindrical coil as the x direction and the longitudinal direction of the axis of the cylindrical coil as the z direction; the permanent magnet pair is arranged between the annular scanning coil pair and the cylindrical coil in the z direction; Figure 1 As shown, the method includes:

[0059] Step S100, constructing a gradient magnetic field using a permanent magnet pair to form a magnetic field-free region, and passing an alternating current through two pairs of annular scanning coils to generate a scanning magnetic field; when generating a scanning magnetic field, the magnetic particles are excited by the excitation coil, and the time domain signals of the magnetic particles are collected by the receiving coil;

[0060] Step S200, discretizing a composite scanning path of a scanning magnetic field in at least one direction into a grid, wherein each discrete grid corresponds to an imaging voxel; the composite scanning path refers to a scanning path when scanning magnetic fields in two or more directions work simultaneously;

[0061] Step S300, performing time-frequency domain transformation on the collected magnetic particle time domain signal to obtain instantaneous harmonic components of the magnetic particle signal at different times;

[0062] Step S400, performing spatiotemporal projection on the instantaneous harmonic component according to a preset spatiotemporal coding rule, projecting the projected component onto a corresponding discrete grid, and obtaining harmonic orthogonal projection images of different frequencies;

[0063] Step S500, combining the methods of steps S100 to S400, constructing a small sample prior harmonic orthogonal projection image; after the construction, constructing projection convolution kernels of different frequencies based on the small sample prior harmonic orthogonal projection image;

[0064] Step S600, using projection convolution kernels of different frequencies to perform deconvolution processing on the harmonic orthogonal projection images of different frequencies obtained in step S400, and finally obtaining a spatial distribution image of the magnetic particles.

[0065] In order to more clearly illustrate the magnetic particle imaging method based on harmonic orthogonal projection of the present invention, each step in an embodiment of the method of the present invention is described in detail below with reference to the accompanying drawings.

[0066] The present invention provides a magnetic particle imaging method based on harmonic orthogonal projection, which is applied to a magnetic particle imaging device. The magnetic particle imaging device, such as Figure 3 As shown, it includes a coil or permanent magnet pair for generating a gradient magnetic field, and a scanning coil group; the scanning coil group includes two pairs of annular scanning coil pairs and two cylindrical coils;

[0067] The first permanent magnet 1 and the second permanent magnet 2 form a permanent magnet pair; the magnetic fields generated by the first permanent magnet 1 and the second permanent magnet 2 have opposite polarities. According to the principle of magnetic field vector superposition, a magnetic field-free region 10 is generated in the center of the imaging space 9. The magnetic particles are in a non-saturated state in the magnetic field-free region 10 and can be magnetized by an external magnetic field to generate a magnetization response signal.

[0068] The first annular scanning coil 3 and the second annular scanning coil 4 constitute a first scanning coil group, and the first annular scanning coil 5 and the second annular scanning coil 6 constitute a second scanning coil group; the cylindrical coil 7 is an excitation coil, which is used to generate a high-frequency alternating magnetic field to excite the magnetization response signal of the magnetic particles; the cylindrical coil 8 is a receiving coil, which is used to sense the magnetization response signal, and the two cylindrical coils are arranged in the enclosed space of the two pairs of annular scanning coils. The cylindrical coils 7 and 8 are coaxially arranged, and their axes are made to be the first axis, the first annular scanning coil 3 and the second annular scanning coil 4 are coaxially arranged in parallel, and their axes are made to be the second axis, the first annular scanning coil 5 and the second annular scanning coil 6 are coaxially arranged in parallel, and their axes are made to be the third axis, and the second axis and the third axis are orthogonal.

[0069] The present invention takes the direction of the first axis as the x direction (in other embodiments, in addition to the x direction, excitation coils and receiving coils in other directions can also be set at appropriate positions to increase the amount of detected information), the first axis passes through the orthogonal point of the second axis and the third axis, and the first axis is perpendicular to the plane formed by the second axis and the third axis (yz plane). That is, the first annular scanning coil 3 and the second annular scanning coil 4 can generate a scanning magnetic field in the z direction after an alternating current is passed through them, that is, the magnetic field-free point is controlled to move alternately along the z direction; the first annular scanning coil 5 and the second annular scanning coil 6 can generate a scanning magnetic field in the y direction after an alternating current is passed through them, that is, the magnetic field-free point is controlled to move alternately along the y direction. When the scanning magnetic fields in two directions are applied simultaneously and there is a certain frequency or phase difference, the magnetic field-free point will scan the entire yz plane along the set trajectory, recording different spatial positions at different times, and realizing two-dimensional space-time coding. If an x-direction scanning coil is added, three-dimensional scanning and space-time coding can be realized in the same way.

[0070] In addition, the sample moving bed, image reconstruction device, signal transmission module, signal acquisition and processing module, and power supply module in the present invention;

[0071] The sample moving bed is used to deliver the imaging object from the outside of the scanning coil group to the inside of the receiving coil, and can be moved arbitrarily in three directions by a three-axis mechanical arm or motor control;

[0072] The signal transmission module includes a resonant circuit at the excitation end, an amplifying and filtering circuit at the receiving end, and current, voltage, temperature and other sensor devices. The resonant circuit is used to reduce the reactive power of the excitation coil and reduce the power output demand of the power supply. The amplifying and filtering circuit is used to amplify and filter the signal received by the receiving coil. The current, voltage, temperature and other sensors are mainly used to monitor the working status of each coil.

[0073] The signal acquisition and processing module includes a data acquisition circuit, a storage device, and a software processing module; the data acquisition circuit mainly performs the function of analog-to-digital conversion, converting the amplified and filtered analog signal into a digital signal and transmitting it to the storage unit. The software processing module is mainly used to perform various online or offline processing on the stored data.

[0074] The power supply module includes a signal generator, a power amplifier, and a low-voltage AC / DC power supply. The signal generator and the power amplifier are combined to form the coil power supply. The signal generator generates the required waveform signal, which is transmitted to the power amplifier for amplification, and then outputs the voltage and current of the power required by the coil. The low-voltage AC / DC power supply is mainly used to power various sensors, amplifier filters and other components.

[0075] The image reconstruction device includes a data calculation unit and an image display unit. The data calculation unit is mainly used to calculate and process the collected data according to the image reconstruction algorithm to obtain the final magnetic particle image data. The image display unit is mainly used to perform color visualization of the magnetic particle image data.

[0076] The specific process of reconstructing the spatial distribution image of magnetic particles by the above-mentioned magnetic particle imaging device is as follows:

[0077] Step S100, constructing a gradient magnetic field using a permanent magnet pair to form a magnetic field-free region, and passing an alternating current through two pairs of annular scanning coils to generate a scanning magnetic field; when generating a scanning magnetic field, the magnetic particles are excited by the excitation coil, and the time domain signals of the magnetic particles are collected by the receiving coil;

[0078] In this embodiment, firstly, two coils or permanent magnets 1 and 2 with opposite magnetic field polarities are used to generate a gradient magnetic field in the imaging space. The center of the gradient magnetic field is a magnetic field-free region, which can be a magnetic field-free point (FFP) or a magnetic field-free line (FFL). The present invention is described by taking FFP as an example. The magnetic nanoparticles are in a non-saturated state at the FFP and can be magnetized to generate a magnetization response.

[0079] Then, an alternating current is passed through the annular scanning coils 3, 4, 5, and 6, and the alternating magnetic fields in two directions are superimposed, which causes the FFP to scan rapidly in the two-dimensional space, and traverse the entire two-dimensional space after a period of time T. Through the scanning trajectory prepared in advance, it is easy to know the spatial position corresponding to the FFP at different times.

[0080] At the same time, the excitation coil 7 is used to generate a continuous high-frequency excitation magnetic field to continuously excite the magnetic particles during the movement of the FFP, but only the particles at the FFP will generate a response signal. Then, the receiving coil 8 is used to collect the time domain signal of the magnetic particles, and the length of the time domain signal is time T.

[0081] Step S200, discretizing a composite scanning path of a scanning magnetic field in at least one direction into a grid, wherein each discrete grid corresponds to an imaging voxel; the composite scanning path refers to a scanning path when scanning magnetic fields in two or more directions work simultaneously;

[0082] In this embodiment, the number of voxels N set for obtaining the spatial distribution image of magnetic particles to be reconstructed is discretized into N grids for the synthetic scanning path of the scanning magnetic field. The scanning magnetic field can be in two, three or more directions for realizing multi-dimensional scanning and spatial encoding.

[0083] Step S300, performing time-frequency domain transformation on the collected magnetic particle time domain signal to obtain instantaneous harmonic components of the magnetic particle signal at different times;

[0084] In this embodiment, the length of the time domain signal generated by the entire scanning process is T, and then divided into T / N segments. According to the space-time coding trajectory, each segment of the signal corresponds to a discrete grid. Each segment is transformed into the time-frequency domain separately, and each segment of the signal will obtain a group of instantaneous harmonic components of different frequencies, and finally N groups of instantaneous harmonic components will be obtained.

[0085] The time-frequency domain transformation is any one of segmented Fourier transform, short-time Fourier transform, and wavelet transform.

[0086] Step S400, performing spatiotemporal projection on the instantaneous harmonic component according to a preset spatiotemporal coding rule, projecting the projected component onto a corresponding discrete grid, and obtaining harmonic orthogonal projection images of different frequencies;

[0087] The spatiotemporal coding rule refers to the mapping relationship between the established time domain and the space domain. For example, in the present invention, a permanent magnet is first used to generate a magnetic field-free point, and then the magnetic field-free point is driven to move along a specific path under the action of a scanning magnetic field, and scanned point by point, so that each moment corresponds to a spatial position. Then, the time domain signal detected in real time is converted into an instantaneous harmonic component according to step S300, and then the instantaneous harmonic components at different moments are projected back to the spatial position according to the corresponding relationship between time and space.

[0088] The specific process of space-time projection is as follows:

[0089]

[0090] Among them, TFS (t n , f k ) represents the instantaneous harmonic component, which is a function of time and frequency. Specifically, it represents the instantaneous harmonic component of the kth frequency at the nth moment. represents the phase corresponding to the instantaneous harmonic component, Indicates the instantaneous scanning speed of FFP, S R [y(t n )] represents the sensitivity of the receiving coil corresponding to the instantaneous displacement point, The one-dimensional harmonic projection image representing different frequencies is a function of space and frequency.

[0091] In this embodiment, N groups of instantaneous harmonic components are projected onto N discrete grids in a one-to-one correspondence. Assuming that each group of instantaneous harmonic components contains K frequencies, K harmonic orthogonal projection images of different frequencies will eventually be obtained.

[0092] If there are two scanning magnetic fields in two directions, then according to the above projection rules, two-dimensional harmonic projection images IMG (f k ):

[0093]

[0094] Among them, y N represents the Nth y-space coordinate, z M represents the Mth z-space coordinate;

[0095] The space-time projection direction is orthogonal to the excitation direction. The excitation direction is the direction of the magnetic field generated by the excitation coil, which is the x direction in this embodiment; the space-time projection direction and the scanning direction are the y or z direction in this example.

[0096] Harmonic orthogonal projection images of different frequencies can be weighted combined. Here is an example of weighted combination:

[0097]

[0098] in, It represents the harmonic orthogonal projection images of different frequencies after individual normalization. f0 represents the frequency of the excitation magnetic field, which is called the fundamental frequency. (2k-1)f0 represents the odd multiple frequency, also called the odd harmonic frequency. IMG CH It represents the weighted combined harmonic projection image after normalization and polarity correction of all odd-frequency harmonic projection images.

[0099] Step S500, combining the methods of steps S100 to S400, constructing a small sample prior harmonic orthogonal projection image; after the construction, constructing projection convolution kernels of different frequencies based on the small sample prior harmonic orthogonal projection image;

[0100] In this embodiment, the specific process of constructing a small sample priori harmonic orthogonal projection image is as follows:

[0101] Before the formal scanning imaging, a magnetic particle sample whose size is no larger than the imaging voxel of the spatial distribution image of the magnetic particles to be reconstructed is placed in the imaging space of the magnetic particle imaging device; then the method of steps S100 to S400 is executed to obtain K harmonic orthogonal projection images of different frequencies as small sample prior harmonic orthogonal projection images.

[0102] According to the imaging space and resolution scale requirements, the projection convolution kernel is constructed; specifically:

[0103] Reconstructed harmonic orthogonal projection image It can be regarded as the point spread function of the real particle distribution ρ(y) and different frequencies The three obtained by convolution have the following relationship:

[0104]

[0105] Among them, t n represents the nth time point, y(t n) represents the spatial coordinates of the FFP at the nth time point, f k represents the kth frequency, and y represents the distribution coordinates of the real particles;

[0106] Based on the above theory, the method for constructing the projection convolution kernel is: if the desired resolution is Pmm, a small sample with a width not greater than Pmm, which can also be called the minimum unit voxel, is used to obtain the orthogonal harmonic projection image according to the method of steps S100 to S400. According to the above formula, at this time that is because It is the point spread function corresponding to the smallest unit voxel, so it is called the projected convolution kernel.

[0107] The benefit of constructing a projection convolution kernel is that by deconvolving the orthogonal harmonic projection image of any sample using the projection convolution kernel, an approximate real particle distribution can be obtained, which will improve the imaging resolution.

[0108] Step S600, using projection convolution kernels of different frequencies to perform deconvolution processing on the harmonic orthogonal projection images of different frequencies obtained in step S400, and finally obtaining a spatial distribution image of the magnetic particles.

[0109] A magnetic particle imaging system based on harmonic orthogonal projection according to a second embodiment of the present invention is as follows: Figure 2 As shown, the system includes: a signal acquisition module 100, a grid discretization module 200, a time-frequency domain transformation module 300, a projection module 400, a convolution kernel construction module 500, and an image reconstruction module 600;

[0110] The signal acquisition module 100 is configured to construct a gradient magnetic field using a permanent magnet pair to form a magnetic field-free region, and to pass an alternating current through two pairs of annular scanning coils to generate a scanning magnetic field; when generating a scanning magnetic field, the magnetic particles are excited by the excitation coil, and the time domain signals of the magnetic particles are collected by the receiving coil;

[0111] The grid discretization module 200 is configured to discretize the synthetic scanning path of the scanning magnetic field in at least one direction into a grid, where each discrete grid corresponds to an imaging voxel; the synthetic scanning path refers to the scanning path when the scanning magnetic fields in two or more directions work simultaneously;

[0112] The time-frequency domain transformation module 300 is configured to perform time-frequency domain transformation on the collected magnetic particle time domain signal to obtain the instantaneous harmonic components of the magnetic particle signal at different times;

[0113] The projection module 400 is configured to perform spatiotemporal projection of the instantaneous harmonic component according to a preset spatiotemporal encoding rule, project the instantaneous harmonic component onto a corresponding discrete grid, and obtain harmonic orthogonal projection images of different frequencies;

[0114] The convolution kernel construction module 500 is configured to construct a small sample priori harmonic orthogonal projection image by combining the method of the signal acquisition module 100-projection module 400; after the construction, a projection convolution kernel of different frequencies is constructed based on the small sample priori harmonic orthogonal projection image;

[0115] The image reconstruction module 600 is configured to perform deconvolution processing on the harmonic orthogonal projection images of different frequencies acquired by the projection module 400 using projection convolution kernels of different frequencies, and finally obtain a spatial distribution image of magnetic particles.

[0116] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process and related instructions of the system described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0117] It should be noted that the magnetic particle imaging system based on harmonic orthogonal projection provided in the above embodiment is only illustrated by the division of the above functional modules. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the modules or steps in the embodiments of the present invention can be decomposed or combined. For example, the modules in the above embodiment can be combined into one module, or further divided into multiple sub-modules to complete all or part of the functions described above. The names of the modules and steps involved in the embodiments of the present invention are only for distinguishing the modules or steps, and are not regarded as improper limitations of the present invention.

[0118] An electronic device according to the third embodiment of the present invention comprises at least one processor; and a memory communicatively connected to at least one of the processors; wherein the memory stores instructions executable by the processor, and the instructions are used to be executed by the processor to implement the magnetic particle imaging method based on harmonic orthogonal projection as claimed in the claim above.

[0119] A fourth embodiment of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer instructions, and the computer instructions are used to be executed by the computer to implement the above-mentioned magnetic particle imaging method based on harmonic orthogonal projection.

[0120] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process and related instructions of the electronic device and computer-readable storage medium described above can refer to the corresponding process in the aforementioned method example and will not be repeated here.

[0121] Reference below Figure 4 , which shows a structural diagram of a computer system of a server suitable for implementing the method, system, and device embodiments of the present application. Figure 4The server shown is merely an example and should not bring any limitation to the functions and scope of use of the embodiments of the present application.

[0122] like Figure 4 As shown, the computer system includes a central processing unit (CPU) 401, which can perform various appropriate actions and processes according to the program stored in the read-only memory (ROM) 402 or the program loaded from the storage part 408 to the random access memory (RAM) 403. Various programs and data required for system operation are also stored in the RAM 403. The CPU 401, ROM 402 and RAM 403 are connected to each other through a bus 404. An input / output (I / O) interface 405 is also connected to the bus 404.

[0123] The following components are connected to the I / O interface 405: an input section 406 including a keyboard, a mouse, etc.; an output section 407 including a cathode ray tube (CRT), a liquid crystal display (LCD), etc., and a speaker; a storage section 408 including a hard disk, etc.; and a communication section 409 including a network interface card such as a LAN (Local Area Network) card, a modem, etc. The communication section 409 performs communication processing via a network such as the Internet. A drive 410 is also connected to the I / O interface 405 as needed. A removable medium 411, such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, etc., is installed on the drive 410 as needed so that a computer program read therefrom is installed into the storage section 408 as needed.

[0124] In particular, according to an embodiment of the present disclosure, the process described above with reference to the flowchart can be implemented as a computer software program. For example, an embodiment of the present disclosure includes a computer program product, which includes a computer program carried on a computer-readable medium, and the computer program includes a program code for executing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from the network through the communication part 409, and / or installed from the removable medium 411. When the computer program is executed by the central processing unit (CPU) 401, the above-mentioned functions defined in the method of the present application are executed. It should be noted that the above-mentioned computer-readable medium of the present application can be a computer-readable signal medium or a computer-readable storage medium or any combination of the above two. The computer-readable storage medium can be, for example, - but not limited to - a system, device or device of electricity, magnetism, light, electromagnetic, infrared, or semiconductor, or any combination of the above. More specific examples of computer-readable storage media may include, but are not limited to, an electrical connection with one or more conductors, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In the present application, a computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in combination with an instruction execution system, an apparatus or a device. In the present application, a computer-readable signal medium may include a data signal propagated in a baseband or as part of a carrier wave, which carries a computer-readable program code. Such propagated data signals may take a variety of forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the above. A computer-readable signal medium may also be any computer-readable medium other than a computer-readable storage medium, which may send, propagate, or transmit a program for use by or in combination with an instruction execution system, an apparatus or a device. The program code contained on the computer-readable medium may be transmitted using any appropriate medium, including but not limited to: wireless, wire, optical cable, RF, etc., or any suitable combination of the above.

[0125] Computer program code for performing the operations of the present application may be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages, such as Java, Smalltalk, C++, and conventional procedural programming languages, such as "C" or similar programming languages. The program code may be executed entirely on the user's computer, partially on the user's computer, as a separate software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0126] The flow chart and block diagram in the accompanying drawings illustrate the possible architecture, function and operation of the system, method and computer program product according to various embodiments of the present application. In this regard, each box in the flow chart or block diagram can represent a module, a program segment or a part of a code, and the module, the program segment or a part of the code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some implementations as replacements, the functions marked in the box can also occur in a sequence different from that marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flow chart, and the combination of the boxes in the block diagram and / or flow chart can be implemented with a dedicated hardware-based system that performs a specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0127] The terms "first", "second", etc. are used to distinguish similar objects rather than to describe or indicate a particular order or sequence.

[0128] The term "comprise" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that includes a list of elements includes not only those elements but also other elements not expressly listed, or also includes elements inherent to such process, method, article, or apparatus / device.

[0129] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A magnetic particle imaging method based on harmonic orthogonal projection, applied to a magnetic particle imaging device, the magnetic particle imaging device comprising a permanent magnet pair, a scanning coil group, a sample moving bed, and an image reconstruction device; the scanning coil group comprises two pairs of annular scanning coil pairs and two cylindrical coils; two annular scanning coils in the annular scanning coil pair are coaxial and their axes are orthogonal; two cylindrical coils, one is an excitation coil and the other is a receiving coil, are coaxially arranged in the enclosed space of the two pairs of annular scanning coil pairs; the magnetic particle imaging device takes the axis direction of the cylindrical coil as the x direction and the longitudinal direction of the axis of the cylindrical coil as the z direction; the permanent magnet pair is arranged between the annular scanning coil pair and the cylindrical coil in the z direction; it is characterized in that The method includes: Step S100, constructing a gradient magnetic field using a permanent magnet pair to form a magnetic field-free region, and passing an alternating current through two pairs of annular scanning coils to generate a scanning magnetic field; when generating a scanning magnetic field, the magnetic particles are excited by the excitation coil, and the time domain signals of the magnetic particles are collected by the receiving coil; Step S200, discretizing a composite scanning path of a scanning magnetic field in at least one direction into a grid, wherein each discrete grid corresponds to an imaging voxel; the composite scanning path refers to a scanning path when scanning magnetic fields in two or more directions work simultaneously; Step S300, performing time-frequency domain transformation on the collected magnetic particle time domain signal to obtain instantaneous harmonic components of the magnetic particle signal at different times; Step S400, performing spatiotemporal projection on the instantaneous harmonic component according to a preset spatiotemporal coding rule, projecting the projected component onto a corresponding discrete grid, and obtaining harmonic orthogonal projection images of different frequencies; Step S500, combining the methods of steps S100 to S400, constructing a small sample prior harmonic orthogonal projection image; after the construction, constructing projection convolution kernels of different frequencies based on the small sample prior harmonic orthogonal projection image, the method is: Construct the projection convolution kernel according to the imaging space and resolution scale requirements; Specifically: The reconstructed harmonic orthogonal projection image is the point spread function of the real particle distribution ρ(y) and different frequencies The three obtained by convolution have the following relationship: Among them, t n represents the nth time point, y(t n ) represents the spatial coordinates of the FFP at the nth time point, f k represents the kth frequency, and y represents the distribution coordinates of the real particles; The method for constructing the projection convolution kernel is: if the desired resolution is Pmm, a small sample with a width not greater than Pmm, which can also be called the minimum unit voxel, is used to obtain an orthogonal harmonic projection image according to the method of steps S100 to S400; at this time that is because It is the point spread function corresponding to the smallest unit voxel, so it is called the projected convolution kernel; Step S600, using projection convolution kernels of different frequencies to perform deconvolution processing on the harmonic orthogonal projection images of different frequencies obtained in step S400, and finally obtaining a spatial distribution image of the magnetic particles.

2. The magnetic particle imaging method based on harmonic orthogonal projection according to claim 1, characterized in that: The magnetic particle time domain signal is collected by: When alternating current is passed through the two pairs of annular scanning coils, scanning magnetic fields in two directions are applied simultaneously with different frequencies or phases, and the magnetic field-free points will be quickly scanned in the two-dimensional space along the set trajectory, and after a period of time T, the entire yz plane two-dimensional space will be traversed; While scanning the point without magnetic field, the excitation coil is used to generate a continuous high-frequency excitation magnetic field to excite the magnetization response signal of the magnetic particles, and the receiving coil is used to sense and collect the magnetization response signal, that is, the magnetic particle time domain signal.

3. The magnetic particle imaging method based on harmonic orthogonal projection according to claim 2, characterized in that: The time-frequency domain transformation is any one of segmented Fourier transform, short-time Fourier transform, and wavelet transform.

4. The magnetic particle imaging method based on harmonic orthogonal projection according to claim 3, characterized in that: The method for obtaining the instantaneous harmonic components of the magnetic particle signal at different times is as follows: The time length T of the magnetic particle time domain signal generated in the scanning process of the entire yz plane two-dimensional space and the number N of voxels set in the spatial distribution image of the magnetic particles to be reconstructed are obtained, and the magnetic particle time domain signal is divided into T / N segments; Each segment of magnetic particle time domain signal is transformed into time-frequency domain separately to obtain N groups of instantaneous harmonic components of different frequencies.

5. The magnetic particle imaging method based on harmonic orthogonal projection according to claim 1, characterized in that: Construct a small sample prior harmonic orthogonal projection image, the method is: Before the formal scanning imaging, a magnetic particle sample whose size is no larger than the imaging voxel of the spatial distribution image of the magnetic particles to be reconstructed is placed in the imaging space of the magnetic particle imaging device; then the method of steps S100 to S400 is executed to obtain harmonic orthogonal projection images of different frequencies as small sample prior harmonic orthogonal projection images.

6. The magnetic particle imaging method based on harmonic orthogonal projection according to claim 4, characterized in that: The instantaneous harmonic component is subjected to space-time projection according to a preset space-time encoding rule, and the method is as follows: Among them, TFS (t n , f k ) represents the instantaneous harmonic component, which is a function of time and frequency. Specifically, it represents the instantaneous harmonic component of the kth frequency at the nth moment. represents the phase corresponding to the instantaneous harmonic component, Indicates the instantaneous scanning speed of FFP, S R [y(t n )] represents the sensitivity of the receiving coil corresponding to the instantaneous displacement point, The one-dimensional harmonic projection image representing different frequencies is a function of space and frequency; If there are two scanning magnetic fields in two directions, the two-dimensional harmonic projection images IMG (f k ): Among them, y N represents the Nth y-space coordinate, z M represents the Mth z-space coordinate; The weighted combination of harmonic orthogonal projection images of different frequencies is: in, It represents the harmonic orthogonal projection images of different frequencies after individual normalization. f0 represents the frequency of the excitation magnetic field, which is called the fundamental frequency. (2k-1)f0 represents the odd multiple frequency, also called the odd harmonic frequency. IMG CH It represents the weighted combined harmonic projection image after normalization and polarity correction of all odd-frequency harmonic projection images.

7. A magnetic particle imaging system based on harmonic orthogonal projection, characterized in that: The system includes: a signal acquisition module, a grid discretization module, a time-frequency domain transformation module, a projection module, a convolution kernel construction module, and an image reconstruction module; The signal acquisition module is configured to construct a gradient magnetic field using a permanent magnet pair to form a magnetic field-free area, and to pass an alternating current through two pairs of annular scanning coils to generate a scanning magnetic field; when the scanning magnetic field is generated, the magnetic particles are excited by the excitation coil, and the time domain signals of the magnetic particles are collected by the receiving coil; The grid discretization module is configured to discretize the synthetic scanning path of the scanning magnetic field in at least one direction into a grid, wherein each discrete grid corresponds to an imaging voxel; the synthetic scanning path refers to a scanning path when the scanning magnetic fields in two or more directions work simultaneously; The time-frequency domain transformation module is configured to perform time-frequency domain transformation on the collected magnetic particle time domain signal to obtain the instantaneous harmonic components of the magnetic particle signal at different times; The projection module is configured to perform spatiotemporal projection of the instantaneous harmonic component according to a preset spatiotemporal encoding rule, project the projected image onto a corresponding discrete grid, and obtain orthogonal projection images of harmonics of different frequencies; The convolution kernel construction module is configured to construct a small sample priori harmonic orthogonal projection image by combining the signal acquisition module-projection module method; after the construction, a projection convolution kernel of different frequencies is constructed based on the small sample priori harmonic orthogonal projection image; The image reconstruction module is configured to perform deconvolution processing on the harmonic orthogonal projection images of different frequencies acquired by the projection module using projection convolution kernels of different frequencies, and finally obtain a spatial distribution image of the magnetic particles; Among them, the projection convolution kernels of different frequencies are constructed based on the small sample prior harmonic orthogonal projection image, and the method is: Construct the projection convolution kernel according to the imaging space and resolution scale requirements; Specifically: The reconstructed harmonic orthogonal projection image is the point spread function of the real particle distribution ρ(y) and different frequencies The three obtained by convolution have the following relationship: Among them, t n represents the nth time point, y(t n ) represents the spatial coordinates of the FFP at the nth time point, f k represents the kth frequency, and y represents the distribution coordinates of the real particles; The method for constructing the projection convolution kernel is: if the desired resolution is Pmm, a small sample with a width not greater than Pmm, which can also be called the minimum unit voxel, is used to obtain an orthogonal harmonic projection image according to the method of steps S100 to S400; at this time that is because It is the point spread function corresponding to the smallest unit voxel, so it is called the projected convolution kernel.

8. An electronic device, characterized in that: include: at least one processor; and a memory communicatively coupled to at least one of the processors; The memory stores instructions executable by the processor, and the instructions are used to be executed by the processor to implement the magnetic particle imaging method based on harmonic orthogonal projection as described in any one of claims 1 to 6.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to be executed by a computer to implement the magnetic particle imaging method based on harmonic orthogonal projection according to any one of claims 1 to 6.

Images