Fast single harmonic magnetic particle imaging device and method based on perpendicular magnetization

Abstract

The present invention provides a rapid single harmonic magnetic particle imaging device and method based on perpendicular magnetization. This device uses orthogonal sensing coils instead of single receiving coils to acquire multidimensional single harmonic magnetic particle signals for joint reconstruction, achieving full electromagnetic scanning. Therefore, while improving the quality of single harmonic magnetic particle images, the present invention facilitates rapid imaging of single harmonic MPI, alleviates the problem of inaccurate reconstructed images caused by the mutual cancellation of certain harmonic signals, and can improve image reconstruction quality under single harmonic reconstruction. Compared with traditional single harmonic magnetic particle imaging methods, the present invention achieves full electromagnetic scanning, which facilitates rapid single harmonic magnetic particle imaging; and effectively utilizes perpendicular magnetization signals to achieve accurate imaging.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomedical imaging, and in particular relates to a fast single harmonic magnetic particle imaging device and method based on perpendicular magnetization. Background Art

[0002] Magnetic particle imaging (MPI) uses the response of magnetic particles to high-frequency magnetic fields to generate images. These responses are typically broadband and can be affected by noise or coupling with the excitation magnetic field. The advent of narrowband MPI reduces the bandwidth requirements and makes it easier to obtain images with a higher signal-to-noise ratio.

[0003] Single-harmonic MPI is a further improvement on narrowband MPI, requiring only a single harmonic of the received signal, typically the third harmonic. Single-harmonic MPI generates an excitation magnetic field in a certain dimension to induce a response from magnetic particles. Mechanical or electromagnetic movement is then used to gradually traverse the scanning area across the entire field of view (FOV). The order in which the FOV is traversed is recorded, and the collected third harmonics are interpolated to create a harmonic distribution map. This map is then deconvolved to obtain a concentration map of the magnetic particles within the FOV. The point spread function (PSF) is pre-acquired using the same method for point-like phantoms.

[0004] The existing single harmonic MPI has the following disadvantages:

[0005] First, in single-harmonic MPI, traditional equipment uses mechanical scanning or partial electronic scanning to achieve imaging. An image with a size of 71 pixels × 41 pixels (approximately 14.2 mm × 8.2 mm field of view (FOV)) requires 5 minutes to scan. The long scanning time makes rapid imaging impossible.

[0006] Secondly, in traditional single harmonic MPI, the harmonic signals from superparamagnetic iron oxide nanoparticles (SPIONs) at the edge of the field of view (FOV) cannot be received, resulting in a smaller effective field of view.

[0007] Finally, due to the unique distribution of the PSF in the excitation direction in single-harmonic magnetic particle imaging, some harmonic signals can cancel each other, causing artifacts in the reconstructed image. However, current single-harmonic and narrow-band MPI devices only use single harmonic signals in the same direction as the excitation coil to reconstruct images.

[0008] Perpendicular magnetization is another way to improve the signal-to-noise ratio of magnetic particle signals because perpendicular magnetization and the excitation magnetic field are decoupled. It receives nonlinear response signals from magnetic particles in the direction perpendicular to the excitation field. In 2022, KJ et al. developed a narrowband MPI method based on a single harmonic, which reconstructs the image by deconvolution with the point spread function (PSF) of the third harmonic. This scheme relies on the mechanical movement of the free field point (FFP), and an image with a size of 71 pixels × 41 pixels (approximately 14.2 mm × 8.2 mm field of view (FOV)) will take 5 minutes to scan. Perpendicular magnetization is now reported to be used for high-sensitivity signal detection in MPS (magnetic particle spectrum) because the perpendicular magnetization signal is naturally decoupled from the excitation magnetic field. Weaver proposed in 2015 that perpendicular magnetization can be applied to MPI imaging and verified it in simulation.

[0009] The existing perpendicular magnetization has the following disadvantages:

[0010] First, existing perpendicular magnetization is mostly used to improve the signal-to-noise ratio of the MPS signal, ignoring the role of the additional information of the perpendicular magnetization. Moreover, this method (MPS) cannot perform imaging and only achieves signal detection.

[0011] Secondly, the existing simulation-based perpendicular magnetization scheme has complex hardware equipment, cumbersome scanning methods and low imaging efficiency. Summary of the Invention

[0012] In order to solve the above problems existing in the prior art, the present invention provides a fast single harmonic magnetic particle imaging device and method based on perpendicular magnetization. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0013] The present invention provides a fast single harmonic magnetic particle imaging device based on perpendicular magnetization, comprising:

[0014] A permanent magnet pair is formed by a first permanent magnet 1 and a second permanent magnet 2 being arranged opposite to each other; the magnetic fields generated by the first permanent magnet 1 and the second permanent magnet 2 have opposite polarities; thereby, a magnetic field-free region 11 is generated in the center of the imaging plane 10; a first Helmholtz drive coil 3 is arranged on the lower surface of the first permanent magnet 1, and a second Helmholtz drive coil 4 is arranged on the upper surface of the second permanent magnet 2, the first Helmholtz drive coil 3 and the second Helmholtz drive coil 4 being arranged opposite to each other to form a first pair of drive coil groups; a third Helmholtz drive coil 5 and a fourth Helmholtz drive coil 6 are arranged opposite to each other; the two pairs of drive coil groups are arranged orthogonally, and low-frequency sinusoidal alternating currents are respectively passed through them, so that the magnetic field-free region 11 moves in the imaging plane 10 to achieve the effect of scanning magnetic particles;

[0015] The solenoid coil 7 is an excitation coil, which is fed with a high-frequency sinusoidal alternating current signal to generate an excitation magnetic field to excite the magnetic particles to generate magnetic particle signals. The solenoid coil 8 is coaxially arranged with the solenoid coil 7. The solenoid coil 8 is a parallel receiving coil for receiving magnetic particle signals in the excitation direction. The saddle-shaped sensing coil 9 is arranged orthogonally to the solenoid coil 8. The saddle-shaped sensing coil 9 is a vertical receiving coil for receiving magnetic particle signals in a direction perpendicular to the excitation direction. The solenoid coil 8 and the saddle-shaped sensing coil 9 constitute an orthogonal sensing coil group. An imaging plane 10 exists between the saddle-shaped sensing coil 9, and a magnetic field-free region 11 exists at the center of the imaging plane 10.

[0016] The axis of the solenoid coil 7 is the x-axis, the axis of the saddle-shaped sensing coil 9 is the y-axis, and the axis perpendicular to the imaging plane 10 is the z-direction. The first permanent magnet 1, the second permanent magnet 2, the first Helmholtz drive coil 3, the second Helmholtz drive coil 4, and the saddle-shaped sensing coil 9 are arranged parallel to the y-axis; the third Helmholtz drive coil 5, the fourth Helmholtz drive coil 6, the solenoid coil 7, and the solenoid coil 8 are arranged parallel to the x-axis, and the x-axis, y-axis, and z-axis are arranged orthogonally in pairs.

[0017] The present invention provides a fast single harmonic magnetic particle imaging method based on perpendicular magnetization, characterized in that a fast single harmonic magnetic particle imaging device based on perpendicular magnetization is used, and the fast single harmonic magnetic particle imaging method based on perpendicular magnetization includes:

[0018] S100, using a permanent magnet pair to construct a gradient magnetic field, thereby generating a magnetic field-free region in the center of the imaging device; and supplying alternating current to two pairs of drive coils to generate a drive magnetic field; supplying alternating current to the excitation coils to excite the magnetic nanoparticles to generate magnetic particle signals, and obtaining magnetic particle signals in the excitation direction and perpendicular direction through an orthogonal sensing coil group;

[0019] S200, processing the magnetic particle signals sensed by the orthogonal sensing coils to obtain instantaneous single harmonic signals at different times;

[0020] S300, synthesizing the scanning trajectories of the driving magnetic fields in two directions, and performing grid discretization on the synthesized scanning trajectory;

[0021] Wherein, each discrete grid corresponds to an imaging pixel; the synthesized scanning trajectory is the scanning path when the driving magnetic fields in two directions work simultaneously;

[0022] S400: Mapping the instantaneous single harmonic signal to the corresponding discrete grid in sequence according to time, and performing image interpolation processing to obtain the single harmonic original image;

[0023] S500: For both the object to be imaged and the point-shaped phantom, steps S100-S400 are executed to pre-collect the point spread functions of the point-shaped phantom in the excitation direction and the vertical direction, and to collect a single harmonic native image of the object to be imaged, and system matrices are constructed based on the point spread functions in the excitation direction and the vertical direction respectively; the system matrices constructed based on the excitation direction and the vertical direction are used as single harmonic convolution kernels respectively;

[0024] S600: using each single harmonic convolution kernel to perform a deconvolution operation on the single harmonic native image of the object to be imaged in S400 in the corresponding direction to achieve joint reconstruction, and obtain the final magnetic nanoparticle spatial concentration distribution map, thereby completing fast and high-quality imaging of the object to be imaged.

[0025] Beneficial effects of the present invention:

[0026] The present invention provides a rapid single harmonic magnetic particle imaging device and method based on perpendicular magnetization. By replacing a single receiving coil with an orthogonal sensing coil, the device acquires multidimensional single harmonic magnetic particle signals for joint reconstruction, and achieves full electromagnetic scanning. Therefore, while improving the image quality of single harmonic magnetic particles, the present invention facilitates rapid, high-quality imaging of single harmonic MPI, alleviates the problem of inaccurate reconstructed images caused by the mutual cancellation of certain harmonic signals, and can improve image reconstruction quality under single harmonic reconstruction. Compared with traditional single harmonic magnetic particle imaging methods, the present invention achieves full electromagnetic scanning, which is conducive to rapid single harmonic magnetic particle imaging; it effectively utilizes perpendicular magnetization signals to achieve accurate imaging. In short, the present invention can achieve rapid, high-quality imaging of single harmonic magnetic particles.

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic cross-sectional view of the structure of a fast single harmonic magnetic particle imaging device based on perpendicular magnetization provided by the present invention;

[0029] Figure 2 is a schematic diagram of a signal acquisition and processing module in an external device connected to an imaging device provided by the present invention;

[0030] Figure 3 This is a schematic flow chart of the method for rapid single harmonic magnetic particle imaging based on perpendicular magnetization provided by the present invention;

[0031] Figure 4 Schematic diagram of a single harmonic convolution kernel provided by the present invention;

[0032] Figure 5 This is a reconstruction result diagram of a "-" shaped phantom placed along the excitation direction (X direction) provided by the present invention;

[0033] Figure 6 This is a reconstruction result diagram of a “|”-shaped phantom placed along the vertical direction (Y direction) provided by the present invention. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0035] The present invention provides a fast single harmonic magnetic particle imaging device based on perpendicular magnetization, comprising: a permanent magnet pair, a drive coil group, an excitation coil, and an orthogonal sensing coil group; the drive coil group comprises two Helmholtz drive coil pairs; the excitation coil is a cylindrical solenoid coil; the orthogonal sensing coil group comprises a pair of saddle-shaped sensing coils and a cylindrical solenoid sensing coil;

[0036] like Figure 1 As shown, a permanent magnet pair is formed by a first permanent magnet 1 and a second permanent magnet 2 arranged opposite to each other; the magnetic fields generated by the first permanent magnet 1 and the second permanent magnet 2 have opposite polarities; thereby, a magnetic field-free region 11 is generated in the center of the imaging plane 10; a first Helmholtz drive coil 3 is arranged on the lower surface of the first permanent magnet 1, and a second Helmholtz drive coil 4 is arranged on the upper surface of the second permanent magnet 2, and the first Helmholtz drive coil 3 and the second Helmholtz drive coil 4 are arranged opposite to each other to form a first pair of drive coil groups; a third Helmholtz drive coil 5 and a fourth Helmholtz drive coil 6 are arranged opposite to each other; the two pairs of drive coil groups are arranged orthogonally, and low-frequency sinusoidal alternating currents are respectively passed through them, so that the magnetic field-free region 11 moves in the imaging plane 10 to achieve the effect of scanning magnetic particles;

[0037] The solenoid coil 7 is an excitation coil, which is fed with a high-frequency sinusoidal alternating current signal to generate an excitation magnetic field to excite the magnetic particles and generate magnetic particle signals. The solenoid coil 8 is coaxially arranged with the solenoid coil 7 and is a parallel receiving coil for receiving the magnetic particle signals in the excitation direction. The saddle-shaped sensing coil 9 is arranged orthogonally to the solenoid coil 8 and is a vertical receiving coil for receiving the magnetic particle signals in the vertical direction. The solenoid coil 8 and the saddle-shaped sensing coil 9 constitute an orthogonal sensing coil group. An imaging plane 10 exists between the saddle-shaped sensing coil 9, and a magnetic field-free region 11 exists at the center of the imaging plane 10.

[0038] The axis of the solenoid coil 7 is the x-axis, the axis of the saddle-shaped sensing coil 9 is the y-axis, and the axis of the vertical imaging plane 10 is the z-direction. The first permanent magnet 1, the second permanent magnet 2, the first Helmholtz drive coil 3, the second Helmholtz drive coil 4, and the saddle-shaped sensing coil 9 are arranged parallel to the y-axis; the third Helmholtz drive coil 5, the fourth Helmholtz drive coil 6, the solenoid coil 7, and the solenoid coil 8 are arranged parallel to the x-axis, and the x-axis, y-axis, and z-axis are arranged orthogonally in pairs.

[0039] The permanent magnet pair in the present invention can also be implemented using Maxwell coils, and the solenoid-shaped receiving coil can also be implemented using a Helmholtz coil pair.

[0040] The vertical magnetization-based rapid single harmonic magnetic particle imaging device provided by the present invention is electrically connected to an external device, and the external device includes: a power supply module, a magnetic particle phantom delivery platform module, a signal acquisition and processing module, and an image reconstruction module;

[0041] The power supply module includes a signal generator, a power amplifier, and an excitation coil impedance matching circuit. On the one hand, the signal generator generates the required low-frequency driving waveform signal, which is input into the power amplifier for amplification and then input into the driving coil. On the other hand, the signal generator generates the required high-frequency excitation waveform signal, which is amplified by the power amplifier and then input into the excitation coil through the excitation coil impedance matching circuit.

[0042] A magnetic particle phantom delivery platform module is used to deliver the imaging object from outside the single harmonic imaging device to the imaging plane 10, and imaging can be completed using a fast single harmonic magnetic particle imaging device based on perpendicular magnetization;

[0043] like Figure 2 As shown, the signal acquisition and processing module includes a high-pass filter circuit, a low-noise amplifier circuit, a phase-locked amplifier circuit and a synchronous acquisition card. The high-pass filter circuit is used to filter the direct feedthrough of the excitation signal; the low-noise amplifier is used to amplify the particle signal; the phase-locked amplifier is used to extract the single harmonic particle signal; and the synchronous acquisition card is used to collect the single harmonic particle signal.

[0044] The signal acquisition and processing module is a single harmonic link. The method of extracting harmonic signals in this link is not limited to using a phase-locked amplifier, but can also include a digital phase-locked method.

[0045] The image reconstruction module includes a data calculation unit and an image display unit. The data calculation unit is used to reconstruct the single harmonic particle signal collected from the acquisition card to obtain a reconstructed particle concentration distribution map; the image display unit is used to visualize the reconstructed particle distribution map.

[0046] The present invention provides a method for rapid single harmonic magnetic particle imaging based on perpendicular magnetization, characterized in that a rapid single harmonic magnetic particle imaging device based on perpendicular magnetization is used, referring to Figure 3 As shown, the rapid single harmonic magnetic particle imaging method based on perpendicular magnetization includes:

[0047] S100, using a permanent magnet pair to construct a gradient magnetic field, thereby generating a magnetic field-free region in the center of the imaging device; and supplying alternating current to two pairs of drive coils to generate a drive magnetic field; supplying alternating current to the excitation coils to excite the magnetic nanoparticles to generate magnetic particle signals, and acquiring magnetic particle signals in the excitation direction and perpendicular direction through orthogonal sensing coils;

[0048] In this embodiment, a gradient magnetic field is generated on the imaging plane 10 by using the first permanent magnet 1 and the second permanent magnet 2, thereby generating a magnetic field-free region FFR. When an alternating current is applied to two pairs of annular drive coils formed by the Helmholtz drive coils 3, 4, 5, and 6, driving magnetic fields in two directions are generated. The two driving magnetic fields have different frequencies. Under the action of the driving magnetic field, the magnetic field-free region FFR is rapidly scanned along a predetermined scanning trajectory in the two-dimensional plane, traversing the entire xy two-dimensional plane after a period of time T.

[0049] At the same time as the FFR scanning in the magnetic field-free area begins, a continuous high-frequency alternating current is passed through the excitation coil 7 to generate an excitation magnetic field to excite the magnetic nanoparticles, thereby generating magnetic particle signals; and the solenoid coil 8 and the saddle-shaped sensing coil 9 are used to collect the magnetic particle signals in the excitation direction and the vertical direction respectively.

[0050] S200, processing the magnetic particle signals sensed by the orthogonal sensing coils to obtain instantaneous single harmonic signals at different times;

[0051] In this embodiment, the magnetic particle signal collected by the orthogonal sensing coil group passes through a single harmonic receiving link (signal acquisition and processing module), which is a high-pass filter circuit, a low-noise amplifier circuit, a phase-locked amplifier circuit, and a synchronous acquisition card in sequence. After acquisition and processing, a single harmonic magnetic particle signal can be obtained.

[0052] S300, synthesizing the scanning trajectories of the driving magnetic fields in two directions, and performing grid discretization on the synthesized scanning trajectory;

[0053] Wherein, each discrete grid corresponds to an imaging pixel; the synthesized scanning trajectory is the scanning path when the driving magnetic fields in two directions work simultaneously;

[0054] In this embodiment, S300 includes:

[0055] S301, respectively collecting the current signals I of the driving magnetic field in two directions x (t), I y (t);

[0056] S302, I x (t), I y (t) After discretization and scaling to various spatial locations of the plane grid;

[0057] Among them, Ix (t), I y The spatial position of (t) on the discrete grid is represented by POS(x i ,y j ); i, j = 1 to N; N is the number of predefined pixels in two dimensions of the XOY plane of the imaging area;

[0058] S303, I x (t), I y (t) The formed scanning trajectory is synthesized and the synthesized scanning trajectory is discretized into a grid.

[0059] S400: Mapping the instantaneous single harmonic signal to a corresponding discrete grid in sequence according to time, and performing image interpolation to obtain a single harmonic native image;

[0060] In this embodiment, S400 includes:

[0061] The instantaneous single harmonic signal Signal(t i ) is mapped to the corresponding discrete grid in sequence according to time to obtain a single harmonic native image; the mapping method is:

[0062] The instantaneous single harmonic signal Signal(t i ) and t at the same time i The spatial position POS(x i ,y j ) is mapped one by one to obtain the particle distribution img(x i ,y j ), and perform image interpolation processing, and finally the particle distribution is composed into a single harmonic native image, which is expressed as:

[0063]

[0064] Among them, x N ,y N They represent the i-th and j-th x and y positions on the discretized grid of the imaging plane XOY, respectively.

[0065] S500: For both the object to be imaged and the point-shaped phantom, steps S100-S400 are executed to pre-collect the point spread functions of the point-shaped phantom in the excitation direction and the vertical direction, and to collect a single harmonic native image of the object to be imaged, and system matrices are constructed based on the point spread functions in the excitation direction and the vertical direction respectively; the system matrices constructed based on the excitation direction and the vertical direction are used as single harmonic convolution kernels respectively;

[0066] In this embodiment, S500 includes:

[0067] S501: Place the point-shaped phantom into the imaging plane 10 and execute the steps S100-S400 to obtain the point spread function (PSF) in the excitation direction and the vertical direction. ∥ (x i ,y j ), PSF ⊥ (x i ,y j ), and placing the object to be imaged in the imaging plane 10, and performing steps S100-S400 to obtain a single harmonic native image of the object to be imaged;

[0068] The magnetic nanoparticles of the point-shaped phantom are no larger than the physical size represented by a single pixel in the image of the object to be imaged; ∥ (x i ,y j )=IMG ∥ (x i ,y j ), PSF ⊥ (x i ,y j )=IMG ⊥ (x i ,y j );

[0069] S502, based on the spatial invariance of the point spread function, the point spread functions in two directions are moved pixel by pixel on the imaging plane to obtain the system matrix in the corresponding direction;

[0070] S503, rearrange the system matrices in the two directions, and use the rearrangement results as the single harmonic convolution kernel A in the direction. || and A ⊥ , specifically:

[0071] First define the PSF ∥expand (x, y) is a matrix of all zeros, with a dimension of 2N×2N, where x, y = 1 to 2N; let PSF ∥expand (i, j) = PSF ∥ (x i ,y j ), where i, j = N / 2 to 3N / 2, PSF ∥ (x i ,y j ) is an N×N matrix; then, A can be obtained by the following steps: ij :PSF ∥expand (k, l), k=i~N+i-1, l=j~N+j-1, (i, j=1~N) and transpose it into N×1 matrix A N×1 ,Right now Finally, we get the excitation convolution kernel A∥ =(A 11 ,...,A N1 , A 12 ,...,A N2 ,...,A NN ); Similarly, we can get the vertical convolution kernel A ⊥ .

[0072] S600: using each single harmonic convolution kernel to perform a deconvolution operation on the single harmonic native image of the object to be imaged in S400 in the corresponding direction to achieve joint reconstruction, and obtain the final magnetic nanoparticle spatial concentration distribution map, thereby completing fast and high-quality imaging of the object to be imaged.

[0073] In this embodiment, S600 includes:

[0074] In step S601, deconvolution operations are performed on the single harmonic native image of the object to be imaged in step S400 in the vertical direction and the excitation direction using each single harmonic convolution kernel to achieve joint reconstruction. The joint reconstruction process is described by the following set of equations:

[0075]

[0076] Among them, A || and A ⊥ Represents the single harmonic convolution kernel in the excitation direction and vertical direction, M || and M ⊥ Represents the single harmonic distribution received in the excitation direction and the vertical direction, that is, the single harmonic native image;

[0077] S602 , inversely calculating c through an iterative reconstruction algorithm to obtain a final reconstructed spatial distribution map of the magnetic nanoparticles, thereby completing the image reconstruction for the object to be measured.

[0078] The above steps S100-S600 can be shown in the flowchart Figure 2 To depict.

[0079] In order to verify the effectiveness of the single harmonic imaging method based on perpendicular magnetization proposed in the embodiment of the present invention, the following experiment can be used for illustration.

[0080] Permanent magnets 1 and 2 of the same polarity generate a gradient magnetic field, with a Y-direction gradient of 2.5 T / m and X and Z-direction gradients of 1.25 T / m. A 25 kHz, 9 A sinusoidal current is passed through excitation coil 7, generating an excitation field of 5 mT. A 1 Hz, approximately 20 A peak sinusoidal current is passed through drive coils 3 and 4 in the first drive coil group, generating a 37.5 mT magnetic field. A 50 Hz, approximately 20 A peak sinusoidal current is passed through drive coils 5 and 6 in the second drive coil group, generating an 18.8 mT magnetic field. This creates an imaging area (FOV) of approximately 2.5 cm × 2.5 cm on imaging plane 10.

[0081] A mechanical translation stage is used to move a point-shaped phantom no larger than the reconstruction pixel point to the FOV area and keep it still. Finally, the Y-direction and X-direction magnetic particle signals are received by the excitation direction and vertical direction sensing coils respectively, and then pass through the single harmonic receiving link, such as Figure 3 As shown, single harmonic signals in the Y and X directions with high signal-to-noise ratio are extracted.

[0082] Based on the above experimental conditions, the single harmonic magnetic particle imaging method based on perpendicular magnetization proposed in the embodiment of the present invention is used to process the above single harmonic signal to obtain the single harmonic convolution kernel mentioned in step S500, and the X and Y directions correspond to A respectively. ∥ Single harmonic convolution kernel, A ⊥ Single harmonic convolution kernel, the result is as follows Figure 4 .

[0083] In addition, using the same experimental conditions as above, the phantom was replaced with a "one" phantom distributed along the X-axis and Y-axis to perform reconstruction using the single harmonic magnetic particle reconstruction method of the present invention; the imaging effect was compared. Figures 5-6 As shown in the figure, it can be seen that in the reconstructed image using a single-axis sensing coil to receive magnetic particle signals, no matter whether the X-direction or Y-direction magnetic particle signals are used for reconstruction, there is always a missing image in the other direction; the present invention uses vertical magnetization to realize single harmonic magnetic particle image joint reconstruction, which effectively solves the problem of reconstruction missing and improves the accuracy of reconstruction.

[0084] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0085] Although the present application is described herein with reference to various embodiments, those skilled in the art will be able to understand and implement other variations of the disclosed embodiments in practicing the claimed application by reviewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality.

[0086] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A fast single harmonic magnetic particle imaging method based on perpendicular magnetization, characterized in that: Using a fast single harmonic magnetic particle imaging device based on perpendicular magnetization, the fast single harmonic magnetic particle imaging method based on perpendicular magnetization includes: S100, using a permanent magnet pair to construct a gradient magnetic field, thereby generating a magnetic field-free region in the center of the imaging device; and supplying alternating current to two pairs of drive coils to generate a drive magnetic field; supplying alternating current to the excitation coils to excite the magnetic nanoparticles to generate magnetic particle signals, and obtaining magnetic particle signals in the excitation direction and perpendicular direction through an orthogonal sensing coil group; S200, processing the magnetic particle signals sensed by the orthogonal sensing coils to obtain instantaneous single harmonic signals at different times; S300, synthesizing the scanning trajectories of the driving magnetic fields in two directions, and performing grid discretization on the synthesized scanning trajectory; Wherein, each discrete grid corresponds to an imaging pixel; the synthesized scanning trajectory is the scanning path when the driving magnetic fields in two directions work simultaneously; S400: Mapping the instantaneous single harmonic signal to the corresponding discrete grid in sequence according to time, and performing image interpolation processing to obtain the single harmonic original image; S500: For both the object to be imaged and the point-shaped phantom, steps S100 to S400 are executed to pre-collect the point spread functions of the point-shaped phantom in the excitation direction and the vertical direction, and to collect a single harmonic native image of the object to be imaged, and to construct system matrices based on the point spread functions in the excitation direction and the vertical direction, respectively; the system matrices constructed based on the point spread functions in the excitation direction and the vertical direction are respectively used as single harmonic convolution kernels; the constructing of the system matrices based on the point spread functions in the excitation direction and the vertical direction includes: based on the spatial invariance of the point spread functions, the point spread functions in the two directions are respectively moved pixel by pixel on the imaging plane to obtain the system matrices in the corresponding directions; S600: using each single harmonic convolution kernel to perform a deconvolution operation on the single harmonic native image of the object to be imaged in S400 in the corresponding excitation direction or perpendicular direction to achieve joint reconstruction, thereby obtaining a final magnetic nanoparticle spatial concentration distribution map, thereby completing fast and high-quality imaging of the object to be imaged; S600 includes: In step S601, deconvolution operations are performed on the single harmonic native image of the object to be imaged in step S400 in the vertical direction and the excitation direction using each single harmonic convolution kernel to achieve joint reconstruction. The joint reconstruction process is described by the following set of equations: Among them, A || and A ⊥ Represents the single harmonic convolution kernel in the excitation direction and vertical direction, M || and M ⊥ Represents the single harmonic distribution received in the excitation direction and vertical direction; S602 , inversely calculating c through an iterative reconstruction algorithm to obtain a final reconstructed spatial distribution map of the magnetic nanoparticles, thereby completing the image reconstruction for the object to be measured.

2. The method for rapid single harmonic magnetic particle imaging based on perpendicular magnetization according to claim 1, characterized in that: include: A permanent magnet pair is formed by a first permanent magnet (1) and a second permanent magnet (2) being arranged opposite to each other; the magnetic fields generated by the first permanent magnet (1) and the second permanent magnet (2) have opposite polarities; thereby a magnetic field-free region (11) is generated at the center of an imaging plane (10); a first Helmholtz drive coil (3) is arranged on the lower surface of the first permanent magnet (1), and a second Helmholtz drive coil (4) is arranged on the upper surface of the second permanent magnet (2); the first Helmholtz drive coil (3) and the second Helmholtz drive coil (4) are arranged opposite to each other to form a first pair of drive coil groups; A third Helmholtz drive coil (5) and a fourth Helmholtz drive coil (6) are arranged opposite to each other; the two pairs of drive coil groups are arranged orthogonally, and low-frequency sinusoidal alternating currents are respectively passed through, so that the magnetic field-free region (11) moves in the imaging plane (10) to achieve the effect of scanning magnetic particles; A high-frequency sinusoidal alternating current signal is passed through the excitation coil (7) to generate an excitation magnetic field for exciting magnetic particles to generate magnetic particle signals; a solenoid coil (8) is coaxially arranged with the excitation coil (7), and the solenoid coil (8) is a parallel receiving coil for receiving magnetic particle signals in the excitation direction; a saddle-shaped sensing coil (9) is arranged orthogonally to the solenoid coil (8), and the saddle-shaped sensing coil (9) is a vertical receiving coil for receiving vertical magnetic particle signals perpendicular to the excitation direction; the solenoid coil (8) and the saddle-shaped sensing coil (9) constitute an orthogonal sensing coil group; an imaging plane (10) is present between the saddle-shaped sensing coil (9), and a magnetic field-free region (11) is present at the center of the imaging plane (10); The axis of the excitation coil (7) is the x-axis, the axis of the saddle-shaped sensing coil (9) is the y-axis, the axis perpendicular to the imaging plane (10) is the z-direction, the first permanent magnet (1), the second permanent magnet (2), the first Helmholtz drive coil (3), the second Helmholtz drive coil (4), and the saddle-shaped sensing coil (9) are arranged parallel to the y-axis; the third Helmholtz drive coil (5), the fourth Helmholtz drive coil (6), the excitation coil (7), and the solenoid coil (8) are arranged parallel to the x-axis, and the x-axis, y-axis, and z-axis are arranged orthogonally in pairs.

3. The method for rapid single harmonic magnetic particle imaging based on perpendicular magnetization according to claim 2, characterized in that: The vertical magnetization-based rapid single harmonic magnetic particle imaging device is electrically connected to an external device, which includes: a power supply module, a magnetic particle phantom delivery platform module, a signal acquisition and processing module, and an image reconstruction module; The power supply module includes a signal generator, a power amplifier, and an excitation coil impedance matching circuit. On the one hand, the signal generator generates the required low-frequency driving waveform signal, which is input into the power amplifier for amplification and then input into the driving coil. On the other hand, the signal generator generates the required high-frequency excitation waveform signal, which is amplified by the power amplifier and then input into the excitation coil through the excitation coil impedance matching circuit. A magnetic particle phantom delivery platform module is used to deliver an imaging object from outside the single harmonic imaging device to an imaging plane (10), and imaging can be completed using a fast single harmonic magnetic particle imaging device based on perpendicular magnetization; The signal acquisition and processing module includes a high-pass filter circuit, a low-noise amplifier circuit, a phase-locked amplifier circuit and a synchronous acquisition card. The high-pass filter circuit is used to filter the direct feedthrough of the excitation signal; the low-noise amplifier is used to amplify the particle signal; the phase-locked amplifier is used to extract the single harmonic particle signal; and the synchronous acquisition card is used to collect the single harmonic particle signal. The image reconstruction module includes a data calculation unit and an image display unit. The data calculation unit is used to reconstruct the single harmonic particle signal collected from the acquisition card to obtain a reconstructed particle concentration distribution map; the image display unit is used to visualize the reconstructed particle concentration distribution map.

4. The method for rapid single harmonic magnetic particle imaging based on perpendicular magnetization according to claim 3, characterized in that: S100 includes: A gradient magnetic field is generated on an imaging plane (10) by using a first permanent magnet (1) and a second permanent magnet (2), thereby generating a magnetic field-free region (11). When an alternating current is passed through two pairs of annular driving coils formed by Helmholtz driving coils (3), (4), (5), and (6), driving magnetic fields in two directions are generated. The two driving magnetic fields have different frequencies, so that the magnetic field-free region (11) is rapidly scanned along a predetermined scanning trajectory in a two-dimensional plane under the action of the driving magnetic field, and traverses the entire xy two-dimensional plane after a time T. When scanning begins in the magnetic field-free region (11), a continuous high-frequency alternating current is passed through the excitation coil (7) to generate an excitation magnetic field to excite the magnetic nanoparticles, thereby generating magnetic particle signals; and the solenoid coil (8) and the saddle-shaped sensing coil (9) are used to respectively collect magnetization response signals in the excitation direction and the perpendicular direction.

5. The method for rapid single harmonic magnetic particle imaging based on perpendicular magnetization according to claim 3, characterized in that: S300 includes: S301, respectively collecting the current signals I of the driving magnetic field in two directions x (t), I y (t); S302, I x (t), I y (t) After discretization and scaling to various spatial locations of the plane grid; Among them, I x (t), I y The spatial position of (t) on the discrete grid is represented by POS(x i ,y j ); i, j = 1 to N; N is the number of predefined pixels in two dimensions of the XOY plane of the imaging area; S303, I x (t), I y (t) The formed scanning trajectory is synthesized and the synthesized scanning trajectory is discretized into a grid.

6. The method for rapid single harmonic magnetic particle imaging based on perpendicular magnetization according to claim 5, characterized in that: S400 includes: The instantaneous single harmonic signal Signal(t i ) is mapped to the corresponding discrete grid in sequence according to time, and image interpolation is performed to obtain a single harmonic native image; the mapping method is: The instantaneous single harmonic signal Signal(t i ) and t at the same time i The spatial position POS(x i ,y j ) is mapped one by one to obtain the particle distribution img(x i ,y j ), and perform image interpolation processing, and finally the particle distribution is composed into a single harmonic native image, which is expressed as: Among them, x N ,y N They represent the i-th and j-th x and y positions on the discretized grid of the imaging plane XOY, respectively.

7. The method for rapid single harmonic magnetic particle imaging based on perpendicular magnetization according to claim 5, characterized in that: S500 includes: S501, place the point-shaped phantom into the imaging plane (10), and execute the method according to steps S100-S400 to obtain the point spread function PSF in the excitation direction and the vertical direction / / (x i ,y j ), PSF ⊥ (x i ,y j ), and placing the object to be imaged in the imaging plane (10), and performing the steps S100-S400 to obtain a single harmonic native image of the object to be imaged; The magnetic nanoparticles of the point-shaped phantom are no larger than the physical size represented by a single pixel in the image of the object to be imaged; / / (x i ,y j )=IMG / / (x i ,y j ), PSF ⊥ (x i ,y j )=IMG ⊥ (x i ,y j ); S502, based on the spatial invariance of the point spread function, the point spread functions in two directions are moved pixel by pixel on the imaging plane to obtain the system matrix in the corresponding direction; S503, rearrange the system matrices in the two directions, and use the rearrangement results as the single harmonic convolution kernel A in the direction. || and A ⊥ .

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