CN115120222A - Magnetic nanoparticle imaging system and method based on pre-polarization - Google Patents
Magnetic nanoparticle imaging system and method based on pre-polarization Download PDFInfo
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Abstract
The invention belongs to the technical field of biomedical imaging, and particularly relates to a magnetic nanoparticle imaging system and method based on pre-polarization, aiming at solving the problems that the existing magnetic nanoparticle imaging equipment depends on a differential receiving coil and is not robust to background interference signals. The invention comprises the following steps: the device comprises a group of pre-polarization coils, a group of gradient and horizontal scanning coils, a group of excitation and vertical scanning coils and a group of non-differential receiving coils, wherein the pre-polarization coils, the gradient and horizontal scanning coils, the excitation and vertical scanning coils and the non-differential receiving coils are used for pre-polarizing the magnetic nano particles in a semi-saturation state, exciting a magnetic field, spatially encoding the magnetic nano particles in the horizontal and vertical directions and inducing the change of magnetization intensity; and the signal acquisition and image reconstruction module is used for acquiring the induced voltage signals of a group of non-differential receiving coils in the three-dimensional tomography process of the imaging target and performing magnetic nanoparticle imaging reconstruction. The invention realizes the magnetization pulse signal detection and the magnetic nano particle imaging without background interference, and the robustness of the system is strong.
Description
Technical Field
The invention belongs to the technical field of biomedical imaging, and particularly relates to a magnetic nanoparticle imaging system and method based on pre-polarization.
Background
Magnetic nanoparticles are nano-scale particles with superparamagnetism, and are widely researched and applied as a novel medical imaging tracer agent in clinical problems of tumor detection, magnetic particle thermotherapy, targeted drug delivery and the like in recent years.
According to the langevin paramagnetic theory, the Magnetic nanoparticles can generate a nonlinear magnetization response containing odd harmonics under the excitation of an external alternating Magnetic field, and at the moment, odd harmonic signals except a fundamental frequency can be detected by using a receiving coil and used for image reconstruction, and the image reconstruction method is called Magnetic nanoparticle Imaging (MPI). The receiving coil in a conventional MPI apparatus is usually coaxial with the exciting coil, and the purpose of the receiving coil is to increase the receiving efficiency, but the problem is that the exciting magnetic field directly forms an induced voltage signal on the receiving coil, and the induced voltage signal is generally called as a background signal. Typically the background signal is several orders of magnitude higher than the response signal of the magnetic nanoparticles. Therefore, the receiving coil in the conventional MPI apparatus generally adopts a differential structure, and specifically is formed by connecting two coils with opposite winding directions in series, wherein one coil is close to the detection region, and the other coil is far from the detection region, so as to cancel the background signal as much as possible and avoid the loss of the magnetic nanoparticle response signal.
Although the differential receiving coil can theoretically completely cancel the background signal, since it is particularly sensitive to the number of turns and relative positions of the two coils, it is relatively weak in practical applications, and generally a trap filter is required to further suppress the fundamental frequency component. But the more critical problem is that due to the non-ideality of the excitation system, the excitation current is also mixed with higher harmonic interference caused by the nonlinear distortion of the system besides the fundamental frequency, and the harmonic interference and the odd harmonic signal of the magnetic nano particles are seriously mixed and cannot be removed by the traditional digital or analog filtering technology. If the harmonic interference is too large, the reconstructed image can generate serious artifacts.
In view of the above, there is also a lack in the art of a robust MPI imaging method without background signal interference. To this end, the present invention provides a magnetic nanoparticle imaging system and method based on pre-polarization.
Disclosure of Invention
In order to solve the above-mentioned problems in the prior art, that is, the problem that the existing magnetic nanoparticle imaging device relies on a differential receiving coil and is not robust to background interference signals, the present invention provides a magnetic nanoparticle imaging system based on pre-polarization, which includes:
the electromagnetic coil module comprises a group of pre-polarization coils, a group of gradient and horizontal scanning coils, a group of excitation and vertical scanning coils and a group of non-differential receiving coils, and is used for pre-polarizing the magnetic nanoparticles in a semi-saturation state, exciting a magnetic field, carrying out spatial encoding in the horizontal and vertical directions and inducing variation of magnetization intensity;
and the signal acquisition and image reconstruction module is used for acquiring induced voltage signals of the group of non-differential receiving coils in the three-dimensional tomography process of the imaging target and carrying out magnetic nanoparticle imaging reconstruction based on the induced voltage signals.
In some preferred embodiments, the set of pre-polarizing coils, after being supplied with a direct current, generate a uniform and co-directional pre-polarizing field in the field-of-view fault plane for making the magnetic nanoparticles inside the field of view in a half-saturation magnetization state.
In some preferred embodiments, the set of pre-polarizing coils is a Helmholtz coil structure or a solenoid structure.
In some preferred embodiments, the half-saturation magnetization state is:
the macroscopic magnetization direction of the magnetic nano particles is aligned along the axial direction of the field of view and is consistent with the external magnetic field, and the magnetic nano particles can rotate along with the external magnetic field in an incomplete magnetic saturation state.
In some preferred embodiments, the set of gradient and horizontal scanning coils, when supplied with direct current and low frequency alternating current, generate a dynamic gradient magnetic field along the horizontal direction of the field of view for spatial encoding along the horizontal direction of the field of view.
In some preferred embodiments, the set of gradient and horizontal scan coils is a maxwell coil structure.
In some preferred embodiments, the set of excitation and vertical scanning coils, after being supplied with high-frequency alternating current and low-frequency alternating current, are used for driving the magnetic nanoparticles to deflect and spatially encode along the vertical direction of the field of view.
In some preferred embodiments, the set of excitation and vertical scanning coils is a Helmholtz coil structure.
In some preferred embodiments, the windings of the set of non-differential receiving coils are wound in the same direction and coaxial with the set of pre-polarizing coils, and are used for inducing the change of horizontal magnetization caused by the deflection of the magnetic nano-particles.
In some preferred embodiments, the set of non-differential receive coils is of a solenoid configuration.
In another aspect of the present invention, a magnetic nanoparticle imaging method based on pre-polarization is provided, where the magnetic nanoparticle imaging method includes:
a uniform pre-polarizing field is configured along the horizontal direction of a field of view, so that the magnetic nano particles in the field of view reach a half-saturation magnetization state, and the magnetization direction is consistent with the pre-polarizing field;
configuring a uniform excitation magnetic field along the vertical direction of the field of view, so that the magnetic nanoparticles in the field of view in a semi-saturated magnetization state are deflected to and fro along the vertical direction;
a receiving coil is arranged along the horizontal direction of a visual field, and a horizontal direction magnetization pulse signal caused by the deflection of the magnetic nano particles is induced; the frequency of the change signal is 2 times of the frequency of the excitation magnetic field;
configuring a dynamic gradient magnetic field along the horizontal direction of a field of view, and carrying out space coding and induced voltage signal acquisition along the horizontal direction; configuring a low-frequency scanning magnetic field along the vertical direction of a field of view, and carrying out space coding and induced voltage signal acquisition along the vertical direction;
after the harmonic components of the induced voltage signals are respectively extracted, the amplitudes of the harmonic components are respectively projected to the space encoding track, and the magnetic nanoparticle imaging reconstruction is realized.
The invention has the beneficial effects that:
(1) the magnetic nano particle imaging system based on pre-polarization utilizes the pre-polarization field to make the macroscopic magnetization intensity of the magnetic nano particles consistent, then utilizes the orthogonal excitation magnetic field to drive the magnetic nano particles to deflect so as to change the original macroscopic magnetization intensity, generates the magnetization pulse signal, and then maps the magnetization pulse signal to the space coding track to realize imaging.
(2) The magnetic nano particle imaging system based on pre-polarization solves the problems of direct coupling and interference of an excitation magnetic field to a receiving coil in the traditional method, and realizes the magnetization pulse signal detection and magnetic nano particle imaging without background interference through the pre-polarization magnetic field and the orthogonal excitation magnetic field.
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Other features, objects and advantages of the present application will become more apparent upon reading of the following detailed description of non-limiting embodiments thereof, made with reference to the accompanying drawings in which:
FIG. 1 is a schematic diagram of the composition of a pre-polarized magnetic nanoparticle-based imaging system of the present invention;
FIG. 2 is a flow chart of an imaging method of an embodiment of the pre-polarized magnetic nanoparticle-based imaging system of the present invention.
Detailed Description
The present application will be described in further detail with reference to the following drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the relevant invention and not restrictive of the invention. It should be noted that, for convenience of description, only the portions related to the related invention are shown in the drawings.
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments with reference to the attached drawings.
The invention relates to a magnetic nanoparticle imaging system based on pre-polarization, which comprises:
the electromagnetic coil module comprises a group of pre-polarization coils, a group of gradient and horizontal scanning coils, a group of excitation and vertical scanning coils and a group of non-differential receiving coils, and is used for pre-polarizing the magnetic nano particles in a semi-saturation state, exciting a magnetic field, carrying out spatial coding along the horizontal direction and the vertical direction, and inducing the change of magnetization intensity;
and the signal acquisition and image reconstruction module is used for acquiring induced voltage signals of the group of non-differential receiving coils in the three-dimensional tomography process of the imaging target and carrying out magnetic nanoparticle imaging reconstruction based on the induced voltage signals.
In order to more clearly illustrate the pre-polarized magnetic nanoparticle-based imaging system of the present invention, the modules in the embodiment of the present invention are described in detail below with reference to fig. 1.
The magnetic nanoparticle imaging system based on pre-polarization in the first embodiment of the invention comprises an electromagnetic coil module and a signal acquisition and image reconstruction module, wherein each module is described in detail as follows:
the electromagnetic coil module comprises a group of pre-polarization coils, a group of gradient and horizontal scanning coils, a group of excitation and vertical scanning coils and a group of non-differential receiving coils, and is used for pre-polarizing the magnetic nano particles in a semi-saturation state, exciting a magnetic field, spatially encoding the magnetic nano particles in the horizontal and vertical directions and inducing the change of magnetization intensity.
Referring to fig. 1, which is a schematic diagram of the composition of a magnetic nanoparticle imaging system based on pre-polarization of the present invention, 1 represents a set of pre-polarization coils, 2 represents a set of gradient and horizontal scanning coils, 3 represents a set of excitation and vertical scanning coils, 4 represents a set of non-differential receiving coils, and FOV represents the field of view region.
And the group of pre-polarizing coils are of a Helmholtz coil structure or a solenoid structure, and after direct current is introduced, a uniform pre-polarizing field in the same direction is generated in the view field fault plane and is used for enabling the magnetic nano particles in the view field to be in a semi-saturated magnetization state.
The prepolarization field is a static magnetic field, and is different from a gradient field in the traditional MPI, the intensity distribution of the prepolarization field is uniform, and according to the Langmian paramagnetic theory, magnetic nanoparticles can generate magnetization response in the same direction under the action of an external magnetic field, and the magnetization intensity of the magnetic nanoparticles gradually approaches saturation and does not increase with the increase of the intensity of the external magnetic field. The semi-saturation magnetization state refers to that the intensity of the prepolarization field does not fully saturate the magnetic nanoparticles, but the magnetic nanoparticles can still change along with the change of the external magnetic field.
And the group of gradient and horizontal scanning coils are of a Maxwell coil structure, and generate a dynamic gradient magnetic field along the horizontal direction of the field of view after direct current and low-frequency alternating current are introduced, so that the dynamic gradient magnetic field is used for carrying out space encoding along the horizontal direction of the field of view.
The dynamic gradient magnetic field is that a low-frequency alternating magnetic field is configured on the basis of an original static gradient field, so that the position of a zero magnetic field point in the gradient magnetic field moves, and further space coding is realized.
And the group of excitation and vertical scanning coils are of Helmholtz coil structures and are used for driving magnetic nanoparticles to deflect and carrying out spatial encoding along the vertical direction of a view field after high-frequency alternating current and low-frequency alternating current are introduced.
Because the magnetic nano-particles are in a half-saturation magnetization state, when an orthogonal excitation magnetic field is applied, the magnetic nano-particles can periodically deflect along with the change of the excitation magnetic field. The high-frequency alternating current is used for generating an excitation magnetic field, and the low-frequency alternating current is used for driving a zero magnetic field point to move along the vertical direction, so that the spatial coding of the vertical direction is realized. The two alternating currents can be fed simultaneously into one coil or into both coils.
The winding directions of the group of non-differential receiving coils are the same, and the non-differential receiving coils are in a solenoid structure and coaxial with the group of pre-polarizing coils and are used for inducing the change of horizontal magnetization caused by the deflection of the magnetic nano particles.
The magnetic nanoparticles deflect resulting in a change in horizontal magnetization that generates a response signal frequency that is predominantly 2 times the excitation field frequency.
Since the orthogonal excitation magnetic field can flip the magnetic nano-particles aligned along the horizontal direction twice in one excitation period, and further induce the horizontal magnetization change twice, the response signal generated by the horizontal magnetization change will be 2 times of the frequency of the excitation magnetic field.
And the signal acquisition and image reconstruction module is used for acquiring induced voltage signals of the group of non-differential receiving coils in the three-dimensional tomography process of the imaging target and carrying out magnetic nanoparticle imaging reconstruction based on the induced voltage signals.
And magnetic nanoparticle imaging reconstruction is carried out based on the induced voltage signal, wherein the induced voltage signal is transmitted to an upper computer, and image reconstruction is realized after digital phase-sensitive detection is carried out to extract a magnetization pulse signal.
In a second embodiment of the present invention, as shown in fig. 2, a magnetic nanoparticle imaging method based on pre-polarization includes:
and step S10, configuring a uniform pre-polarizing field along the horizontal direction of the field of view, so that the magnetic nanoparticles in the field of view reach a half-saturation magnetization state, and the macroscopic magnetization direction is consistent with the pre-polarizing field.
Step S20, a uniform excitation magnetic field is arranged in the vertical direction of the field of view, and the magnetic nanoparticles in the half-saturation magnetization state in the field of view are reciprocally deflected in the vertical direction.
Step S30, configuring a receiving coil along the horizontal direction of the field of view, and inducing a horizontal direction magnetization pulse signal caused by the deflection of the magnetic nano particles; the frequency of the change signal is 2 times of the frequency of the excitation magnetic field.
And step S40, configuring a dynamic gradient magnetic field along the horizontal direction of the field of view, and carrying out space encoding and induced voltage signal acquisition along the horizontal direction.
And step S50, configuring a low-frequency scanning magnetic field along the vertical direction of the field of view, and carrying out space coding and induced voltage signal acquisition along the vertical direction.
And step S60, after the harmonic components of the induction voltage signals are respectively extracted, the amplitudes of the harmonic components are respectively projected to the spatial coding tracks, and the spatial distribution image of the magnetic nanoparticles is reconstructed, so that the imaging reconstruction of the magnetic nanoparticles is realized.
Although the foregoing embodiments describe the steps in the above sequential order, those skilled in the art will understand that, in order to achieve the effect of the present embodiments, the steps may not be executed in such an order, and may be executed simultaneously (in parallel) or in an inverse order, and these simple variations are within the scope of the present invention.
It can be clearly understood by those skilled in the art that, for convenience and brevity of description, the specific working process and related descriptions of the method described above may refer to the corresponding process in the foregoing system embodiment, and are not described herein again.
It should be noted that, the magnetic nanoparticle imaging system and method based on pre-polarization provided in the foregoing embodiments are only illustrated by the division of the functional modules, and in practical applications, the functions may be allocated to different functional modules according to needs, that is, the modules or steps in the embodiments of the present invention are further decomposed or combined, for example, the modules in the embodiments may be combined into one module, or further split into multiple sub-modules, so as 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 to be construed as unduly limiting the present invention.
An apparatus of a third embodiment of the invention comprises:
at least one processor; and
a memory communicatively coupled to at least one of the processors; wherein,
the memory stores instructions executable by the processor for execution by the processor to implement the pre-polarization based magnetic nanoparticle imaging methods described above.
A computer-readable storage medium of a fourth embodiment of the present invention stores computer instructions for execution by the computer to implement the pre-polarization based magnetic nanoparticle imaging method described above.
It can be clearly understood by those skilled in the art that, for convenience and brevity of description, the specific working processes and related descriptions of the storage device and the processing device described above may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.
Those of skill in the art would appreciate that the various illustrative modules, method steps, and modules described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that programs corresponding to the software modules, method steps may be located in Random Access Memory (RAM), memory, Read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. To clearly illustrate this interchangeability of electronic hardware and software, various illustrative components and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as electronic hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The terms "first," "second," and the like are used for distinguishing between similar elements and not necessarily for describing or implying a particular order or sequence.
The terms "comprises," "comprising," or any other similar term are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
So far, the technical solutions of the present invention have been described in connection with the preferred embodiments shown in the drawings, but it is easily understood by those skilled in the art that the scope of the present invention is obviously not limited to these specific embodiments. Equivalent changes or substitutions of related technical features can be made by those skilled in the art without departing from the principle of the invention, and the technical scheme after the changes or substitutions can be within the protection scope of the invention.
Claims (10)
1. A pre-polarization based magnetic nanoparticle imaging system, comprising:
the electromagnetic coil module comprises a group of pre-polarization coils, a group of gradient and horizontal scanning coils, a group of excitation and vertical scanning coils and a group of non-differential receiving coils, and is used for pre-polarizing the magnetic nano particles in a semi-saturation state, exciting a magnetic field, carrying out spatial coding along the horizontal direction and the vertical direction, and inducing the change of magnetization intensity;
and the signal acquisition and image reconstruction module is used for acquiring induced voltage signals of the group of non-differential receiving coils in the three-dimensional tomography process of the imaging target and carrying out magnetic nanoparticle imaging reconstruction based on the induced voltage signals.
2. The magnetic nanoparticle imaging system based on pre-polarization of claim 1, wherein the set of pre-polarization coils, after being energized with a direct current, generate a uniform and co-directional pre-polarization field in a field-of-view fault plane for keeping the magnetic nanoparticles inside the field-of-view in a half-saturation magnetization state.
3. The pre-polarization based magnetic nanoparticle imaging system of claim 2, wherein the set of pre-polarizing coils is a Helmholtz coil structure or a solenoid structure.
4. The magnetic nanoparticle imaging system based on pre-polarization of claim 1, wherein the set of gradient and horizontal scanning coils, after being supplied with direct current and low frequency alternating current, generate a dynamic gradient magnetic field along the horizontal direction of the field of view for spatial encoding along the horizontal direction of the field of view.
5. The pre-polarization based magnetic nanoparticle imaging system of claim 4, wherein the set of gradient and horizontal scan coils is a Maxwellian coil configuration.
6. The magnetic nanoparticle imaging system based on pre-polarization of claim 1, wherein the set of excitation and vertical scanning coils, after being supplied with high frequency alternating current and low frequency alternating current, are used for driving magnetic nanoparticles to deflect and spatially encode along a vertical direction of a field of view.
7. The pre-polarization based magnetic nanoparticle imaging system of claim 6, wherein the set of excitation and vertical scanning coils is a Helmholtz coil structure.
8. The pre-polarization based magnetic nanoparticle imaging system of claim 1, wherein the set of non-differential receiving coils are wound in the same direction and coaxial with the set of pre-polarization coils for inducing the change in horizontal magnetization caused by magnetic nanoparticle deflection.
9. The pre-polarization based magnetic nanoparticle imaging system of claim 8, wherein the set of non-differential receive coils is a solenoid structure.
10. A magnetic nanoparticle imaging method based on pre-polarization, the magnetic nanoparticle imaging method comprising:
a uniform pre-polarizing field is configured along the horizontal direction of a field of view, so that the magnetic nano particles in the field of view reach a half-saturation magnetization state, and the magnetization direction is consistent with the pre-polarizing field;
configuring a uniform excitation magnetic field along the vertical direction of the field of view, and enabling the magnetic nano particles in the half-saturation magnetization state in the field of view to deflect in a reciprocating manner along the vertical direction;
a receiving coil is arranged along the horizontal direction of a visual field, and a horizontal direction magnetization pulse signal caused by the deflection of the magnetic nano particles is induced; the frequency of the change signal is 2 times of the frequency of the excitation magnetic field;
configuring a dynamic gradient magnetic field along the horizontal direction of a field of view, and carrying out space coding and induced voltage signal acquisition along the horizontal direction; configuring a low-frequency scanning magnetic field along the vertical direction of a field of view, and carrying out space coding and induced voltage signal acquisition along the vertical direction;
after the harmonic components of the induced voltage signals are respectively extracted, the amplitudes of the harmonic components are respectively projected to the space encoding track, and the magnetic nanoparticle imaging reconstruction is realized.
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| CN115778354A (en) * | 2023-02-07 | 2023-03-14 | 北京航空航天大学 | Human body scale closed-hole MPI device based on radial-Cartesian track scanning |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115778354A (en) * | 2023-02-07 | 2023-03-14 | 北京航空航天大学 | Human body scale closed-hole MPI device based on radial-Cartesian track scanning |
| CN115778354B (en) * | 2023-02-07 | 2023-04-28 | 北京航空航天大学 | Human body scale closed-pore MPI device based on radial-Cartesian trajectory scanning |
| US11931135B1 (en) | 2023-02-07 | 2024-03-19 | Beijing University Of Aeronautics And Astronautics | Human-scale closed-bore MPI device based on radial-cartesian trajectory scanning |
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