Pre-polarization-based magnetic nanoparticle imaging system and method

Abstract

The present invention belongs to the field of biomedical imaging technology, and specifically relates to a magnetic nanoparticle imaging system and method based on pre-polarization, aiming to solve the problems that existing magnetic nanoparticle imaging devices rely on differential receiving coils and are not robust to background interference signals. The present invention includes: a group of pre-polarizing 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, which are used for pre-polarizing magnetic nanoparticles to a semi-saturated state, exciting a magnetic field and spatially encoding along the horizontal and vertical directions, and inducing changes in magnetization intensity; a signal acquisition and image reconstruction module, which is used to acquire the induced voltage signals of a group of non-differential receiving coils during the three-dimensional tomographic scanning of the imaging target, and perform magnetic nanoparticle imaging reconstruction. The present invention realizes the detection of magnetization pulse signals without background interference and magnetic nanoparticle imaging, and the system has strong robustness.

Description

Background Art

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

[0003] According to the Langevin paramagnetic theory, magnetic nanoparticles will produce nonlinear magnetization responses containing odd harmonics under the stimulation of an external alternating magnetic field. At this time, the odd harmonic signals other than the fundamental frequency can be detected by using a receiving coil, and the signal is used for image reconstruction. The above image reconstruction method is called magnetic nanoparticle imaging (MPI). The receiving coil in the traditional MPI device is usually coaxial with the excitation coil, and its purpose is to increase the receiving efficiency, but the problem that comes with it is that the excitation magnetic field will directly form an induced voltage signal on the receiving coil, and this induced voltage signal is generally called the background signal. Usually the background signal is several orders of magnitude higher than the response signal of the magnetic nanoparticles. Therefore, the receiving coil in the traditional MPI device generally adopts a differential structure, which is specifically composed of two coils with opposite winding directions connected in series, one of which is close to the detection area and the other is far away from the detection area. Its purpose is to offset the background signal as much as possible and avoid the loss of the response signal of the magnetic nanoparticles.

[0004] Although the differential receiving coil can completely cancel the background signal in theory, it is particularly sensitive to the number of winding turns and relative position of the two coils, so its robustness is poor in practical applications. Generally, a notch filter is required to further suppress the fundamental frequency component. However, the more critical problem is that due to the non-ideality of the excitation system, the excitation current is mixed with high-order harmonic interference caused by the nonlinear distortion of the system in addition to the fundamental frequency. This harmonic interference is seriously mixed with the odd harmonic signal of the magnetic nanoparticles and cannot be removed by traditional digital or analog filtering technology. If the harmonic interference is too large, it will cause serious artifacts in the reconstructed image.

[0005] In summary, the art still lacks 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 prepolarization. Summary of the invention

[0006] In order to solve the above-mentioned problem 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 prepolarization, the magnetic nanoparticle imaging system comprising:

[0007] The electromagnetic coil module includes a set of pre-polarization coils, a set of gradient and horizontal scanning coils, a set of excitation and vertical scanning coils, and a set of non-differential receiving coils, which are used for pre-polarizing the magnetic nanoparticles to a semi-saturated state, exciting the magnetic field, spatially encoding along the horizontal and vertical directions, and inducing the change of magnetization intensity;

[0008] The signal acquisition and image reconstruction module is used to acquire the induced voltage signals of the set of non-differential receiving coils during the three-dimensional tomography of the imaging target, and perform magnetic nanoparticle imaging reconstruction based on the induced voltage signals.

[0009] In some preferred embodiments, after passing a direct current through the set of pre-polarization coils, a co-directional and uniform pre-polarization field is generated within the field of view tomographic plane, which is used to make the magnetic nanoparticles inside the field of view in a semi-saturated magnetization state.

[0010] In some preferred embodiments, the set of pre-polarization coils is of a Helmholtz coil structure or a solenoid structure.

[0011] In some preferred embodiments, the semi-saturated magnetization state is:

[0012] The macroscopic magnetization direction of the magnetic nanoparticles is aligned along the field of view axis and is consistent with the externally applied magnetic field, and it is an incomplete magnetic saturation state that can rotate with the externally applied magnetic field.

[0013] In some preferred embodiments, after passing a direct current and a low-frequency alternating current through the set of gradient and horizontal scanning coils, a dynamic gradient magnetic field is generated along the horizontal direction of the field of view, which is used for spatial encoding along the horizontal direction of the field of view.

[0014] In some preferred embodiments, the set of gradient and horizontal scanning coils is of a Maxwell coil structure.

[0015] In some preferred embodiments, after passing a high-frequency alternating current and a low-frequency alternating current through the set of excitation and vertical scanning coils, it is used to drive the magnetic nanoparticles to deflect and perform spatial encoding along the vertical direction of the field of view.

[0016] In some preferred embodiments, the set of excitation and vertical scanning coils is of a Helmholtz coil structure.

[0017] In some preferred embodiments, the winding directions of the set of non-differential receiving coils are the same, and they are coaxial with the set of pre-polarization coils, which are used to sense the change of the horizontal magnetization intensity caused by the deflection of the magnetic nanoparticles.

[0018] In some preferred embodiments, the set of non-differential receiving coils is of a solenoid structure.

[0019] On the other hand, the present invention proposes a magnetic nanoparticle imaging method based on pre-polarization, and the magnetic nanoparticle imaging method includes:

[0020] Configure a uniform pre-polarization field along the horizontal direction of the field of view, so that the magnetic nanoparticles in the field of view reach the semi-saturated magnetization state, and the magnetization direction is consistent with the pre-polarization field;

[0021] Configure a uniform excitation magnetic field along the vertical direction of the field of view, so that the magnetic nanoparticles in the semi-saturated magnetization state in the field of view deflect reciprocally along the vertical direction;

[0022] Configure a receiving coil along the horizontal direction of the field of view to sense the intensity change of the horizontal magnetization pulse signal caused by the deflection of the magnetic nanoparticles; the intensity change of the horizontal magnetization pulse signal caused by the deflection of the magnetic nanoparticles has a frequency twice that of the excitation magnetic field frequency;

[0023] Configure a dynamic gradient magnetic field along the horizontal direction of the field of view to perform spatial encoding along the horizontal direction and collect induction voltage signals; configure a low-frequency scanning magnetic field along the vertical direction of the field of view to perform spatial encoding along the vertical direction and collect induction voltage signals;

[0024] After extracting the harmonic components of the induction voltage signal respectively, project the amplitudes of the harmonic components onto the spatial encoding trajectory respectively to realize the reconstruction of magnetic nanoparticle imaging.

[0025] Advantages of the present invention:

[0026] (1) The magnetic nanoparticle imaging system based on pre-polarization of the present invention makes the macroscopic magnetization of magnetic nanoparticles consistent by using the pre-polarization field, and then uses an orthogonal excitation magnetic field to drive the deflection of magnetic nanoparticles to change the original macroscopic magnetization, generating a magnetization pulse signal, and then maps the magnetization pulse signal into the spatial encoding trajectory to realize imaging. Since the direction of the magnetization pulse signal is orthogonal to the direction of the excitation field, the interference signal of the excitation magnetic field on the receiving coil is greatly reduced, and the robustness of the system is improved.

[0027] (2) The magnetic nanoparticle imaging system based on pre-polarization of the present invention overcomes the problems of direct coupling and interference of the excitation magnetic field on the receiving coil in the traditional method, and realizes the detection of magnetization pulse signals without background interference and magnetic nanoparticle imaging through the pre-polarization magnetic field and the orthogonal excitation magnetic field. Description of the Drawings

[0028] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects and advantages of the present application will become more obvious:

[0029] Figure 1 is a schematic diagram of the composition of the magnetic nanoparticle imaging system based on pre-polarization of the present invention;

[0030] Figure 2 It is a schematic diagram of the imaging method process of an embodiment of the magnetic nanoparticle imaging system based on prepolarization of the present invention. Specific embodiments

[0031] The present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related invention and are not intended to limit the invention. Additionally, it should be noted that for the sake of convenience of description, only parts related to the relevant invention are shown in the drawings.

[0032] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and embodiments.

[0033] A magnetic nanoparticle imaging system based on prepolarization of the present invention, the magnetic nanoparticle imaging system includes:

[0034] The electromagnetic coil module includes a set of prepolarization coils, a set of gradient and horizontal scanning coils, a set of excitation and vertical scanning coils, and a set of non-differential receiving coils, and is used for performing semi-saturation state prepolarization of magnetic nanoparticles, exciting a magnetic field and spatially encoding along the horizontal and vertical directions, and inducing changes in magnetization intensity;

[0035] The signal acquisition and image reconstruction module is used for acquiring the induced voltage signals of the set of non-differential receiving coils during the three-dimensional tomography of the imaging target, and performing magnetic nanoparticle imaging reconstruction based on the induced voltage signals.

[0036] For a clearer description of the magnetic nanoparticle imaging system based on prepolarization of the present invention, the following combines Figure 1 Each module in the embodiment of the present invention will be described in detail.

[0037] The magnetic nanoparticle imaging system based on prepolarization of the first embodiment of the present invention includes an electromagnetic coil module and a signal acquisition and image reconstruction module, and each module is described in detail as follows:

[0038] The electromagnetic coil module includes a set of prepolarization coils, a set of gradient and horizontal scanning coils, a set of excitation and vertical scanning coils, and a set of non-differential receiving coils, and is used for performing semi-saturation state prepolarization of magnetic nanoparticles, exciting a magnetic field and spatially encoding along the horizontal and vertical directions, and inducing changes in magnetization intensity.

[0039] As Figure 1As shown in the figure, it is a schematic diagram of the composition of the magnetic nanoparticle imaging system based on pre-polarization of the present invention. 1 represents a group of pre-polarization coils, 2 represents a group of gradient and horizontal scanning coils, 3 represents a group of excitation and vertical scanning coils, 4 represents a group of non-differential receiving coils, and FOV represents the field of view area.

[0040] A group of pre-polarization coils is of Helmholtz coil structure or solenoid structure. After passing a direct current, a co-directional and uniform pre-polarization field is generated within the field of view section plane, which is used to make the magnetic nanoparticles within the field of view in a semi-saturated magnetization state.

[0041] The pre-polarization field is a static magnetic field, which is different from the gradient field in traditional MPI. The intensity distribution of the pre-polarization field is uniform. According to Langevin paramagnetic theory, it can be known that magnetic nanoparticles will generate a magnetization response in the same direction under the action of an external magnetic field, and with the increase of the external magnetic field intensity, its magnetization intensity gradually tends to saturation and no longer increases. The semi-saturated magnetization state described here means that the intensity of the pre-polarization field does not completely saturate the magnetic nanoparticles, but the magnetic nanoparticles can still change with the change of the external magnetic field.

[0042] A group of gradient and horizontal scanning coils is of Maxwell coil structure. After passing a direct current and a low-frequency alternating current, a dynamic gradient magnetic field is generated along the horizontal direction of the field of view, which is used for spatial encoding along the horizontal direction of the field of view.

[0043] The dynamic gradient magnetic field refers to configuring a low-frequency alternating magnetic field on the basis of the original static gradient field, so that the position of the zero magnetic field point in the gradient magnetic field moves, thereby realizing spatial encoding.

[0044] A group of excitation and vertical scanning coils is of Helmholtz coil structure. After passing a high-frequency alternating current and a low-frequency alternating current, it is used to drive the deflection of magnetic nanoparticles and perform spatial encoding along the vertical direction of the field of view.

[0045] Since the magnetic nanoparticles are in a semi-saturated magnetization state, when an orthogonal excitation magnetic field is applied, the magnetic nanoparticles will deflect periodically with the change of the excitation magnetic field. The high-frequency alternating current is used to generate the excitation magnetic field, and the low-frequency alternating current is used to drive the zero magnetic field point to move along the vertical direction to realize spatial encoding in the vertical direction. These two alternating currents can be passed into one coil simultaneously or into two coils separately.

[0046] A group of non-differential receiving coils has the same winding direction and is of solenoid structure, and is coaxial with the group of pre-polarization coils, which is used to sense the change of the horizontal magnetization intensity caused by the deflection of magnetic nanoparticles.

[0047] For the change of the horizontal magnetization intensity caused by the deflection of magnetic nanoparticles, the frequency of the generated response signal is mainly twice the frequency of the excitation magnetic field.

[0048] Since the orthogonal excitation magnetic field will flip the magnetic nanoparticles aligned in the horizontal direction twice within one excitation period, thereby causing the horizontal magnetization intensity to change twice, the response signal generated by the change in the horizontal magnetization intensity will be twice the frequency of the excitation magnetic field.

[0049] A signal acquisition and image reconstruction module, which is used to acquire the induced voltage signals of the group of non-differential receiving coils during the three-dimensional tomography of the imaging target, and perform magnetic nanoparticle imaging reconstruction based on the induced voltage signals.

[0050] Performing magnetic nanoparticle imaging reconstruction based on the induced voltage signals means transmitting the induced voltage signals to a host computer, performing digital phase-sensitive detection to extract the magnetization pulse signals, and then realizing image reconstruction.

[0051] The magnetic nanoparticle imaging method according to the second embodiment of the present invention, as Figure 2 shown, the magnetic nanoparticle imaging method includes:

[0052] Step S10, arranging a uniform pre-polarization field along the horizontal direction of the field of view, so that the magnetic nanoparticles in the field of view reach a semi-saturated magnetization state, and the macroscopic magnetization direction is consistent with the pre-polarization field.

[0053] Step S20, arranging a uniform excitation magnetic field along the vertical direction of the field of view, so that the magnetic nanoparticles in the semi-saturated magnetization state in the field of view deflect reciprocally along the vertical direction.

[0054] Step S30, arranging receiving coils along the horizontal direction of the field of view to sense the intensity change of the horizontal magnetization pulse signal caused by the deflection of the magnetic nanoparticles; the frequency of the intensity change of the horizontal magnetization pulse signal caused by the deflection of the magnetic nanoparticles is twice the frequency of the excitation magnetic field.

[0055] Step S40, arranging a dynamic gradient magnetic field along the horizontal direction of the field of view to perform spatial encoding along the horizontal direction and acquire the induced voltage signals.

[0056] Step S50, arranging a low-frequency scanning magnetic field along the vertical direction of the field of view to perform spatial encoding along the vertical direction and acquire the induced voltage signals.

[0057] Step S60, after respectively extracting the harmonic components of the induced voltage signals, project the amplitudes of the harmonic components onto the spatial encoding trajectories respectively to reconstruct the spatial distribution image of the magnetic nanoparticles and realize magnetic nanoparticle imaging reconstruction.

[0058] Although the steps have been described in the above order in the foregoing embodiments, those skilled in the art can understand that, in order to achieve the effects of this embodiment, the different steps do not have to be executed in such an order, and they can be executed simultaneously (in parallel) or in a reversed order, and these simple changes are all within the protection scope of the present invention.

[0059] Those skilled in the art can clearly understand that, for the convenience and conciseness of description, the specific working processes and related descriptions of the methods described above can refer to the corresponding processes in the foregoing system embodiments, and will not be elaborated herein.

[0060] It should be noted that the pre-polarized magnetic nanoparticle imaging system and method provided in the above embodiments are only illustrated by dividing the above functional modules. In practical applications, the above functions can be allocated to different functional modules as needed, that is, the modules or steps in the embodiments of the present invention can be further decomposed or combined. For example, the modules in the above embodiments can be combined into one module, or further split into multiple sub-modules to complete all or part of the functions described above. For the names of the modules and steps involved in the embodiments of the present invention, they are only used to distinguish each module or step, and are not regarded as an improper limitation of the present invention.

[0061] An apparatus according to a third embodiment of the present invention includes:

[0062] At least one processor; and

[0063] A memory communicatively connected to at least one of the processors; wherein,

[0064] The memory stores instructions executable by the processor, and the instructions are used to be executed by the processor to implement the above-mentioned pre-polarized magnetic nanoparticle imaging method.

[0065] A computer-readable storage medium according to a fourth embodiment of the present invention stores computer instructions, and the computer instructions are used to be executed by the computer to implement the above-mentioned pre-polarized magnetic nanoparticle imaging method.

[0066] Those skilled in the art can clearly understand that, for the convenience and conciseness of description, the specific working processes and related descriptions of the storage device and the processing device described above can refer to the corresponding processes in the foregoing method embodiments, and will not be elaborated herein.

[0067] Those skilled in the art should be able to realize that the modules and method steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of both. The programs corresponding to the software modules and method steps can be placed in a random access memory (RAM), internal memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium well-known in the technical field. To clearly illustrate the interchangeability of electronic hardware and software, the composition and steps of each example have been generally described according to functions in the above description. Whether these functions are executed in the form of electronic hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0068] The terms "first", "second", etc. are used to distinguish similar objects, rather than to describe or represent a specific order or sequence.

[0069] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, so that a process, method, article, or device / equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent in these processes, methods, articles, or devices / equipment.

[0070] So far, the technical solution of the present invention has been described in combination with the preferred embodiments shown in the 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 pre-polarization based magnetic nanoparticle imaging system, characterized in that, The magnetic nanoparticle imaging system includes: The electromagnetic coil module includes 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, which are used for pre-polarizing the magnetic nanoparticles to a semi-saturated state, exciting a magnetic field, spatially encoding along the horizontal and vertical directions, and sensing the change in magnetization intensity; After passing a direct current through the group of pre-polarization coils, a co-directional and uniform pre-polarization field is generated within the field of view tomographic plane, which is used to make the magnetic nanoparticles inside the field of view in a semi-saturated magnetization state; After passing a direct current and a low-frequency alternating current through the group of gradient and horizontal scanning coils, a dynamic gradient magnetic field is generated along the horizontal direction of the field of view, which is used for spatial encoding along the horizontal direction of the field of view; After passing a high-frequency alternating current and a low-frequency alternating current through the group of excitation and vertical scanning coils, it is used to drive the magnetic nanoparticles to deflect and perform spatial encoding along the vertical direction of the field of view; The winding directions of the group of non-differential receiving coils are the same and coaxial with the group of pre-polarization coils, which are used to sense the change in the horizontal magnetization intensity caused by the deflection of the magnetic nanoparticles; The signal acquisition and image reconstruction module is used to acquire the induced voltage signals of the group of non-differential receiving coils during the three-dimensional tomographic scanning of the imaging target, and perform magnetic nanoparticle imaging reconstruction based on the induced voltage signals.

2. The magnetic nanoparticle imaging system based on pre-polarization according to claim 1, wherein The group of pre-polarization coils is of a Helmholtz coil structure or a solenoid structure.

3. The magnetic nanoparticle imaging system based on pre-polarization according to claim 1, wherein The group of gradient and horizontal scanning coils is of a Maxwell coil structure.

4. The magnetic nanoparticle imaging system based on pre-polarization according to claim 1, characterized in that, The group of excitation and vertical scanning coils is of a Helmholtz coil structure.

5. The magnetic nanoparticle imaging system based on pre-polarization according to claim 1, wherein The group of non-differential receiving coils is of a solenoid structure.

6. A magnetic nanoparticle imaging method based on pre-polarization, characterized in that, The magnetic nanoparticle imaging method includes: Configure a uniform pre-polarization field along the horizontal direction of the field of view to make the magnetic nanoparticles in the field of view reach a semi-saturated magnetization state, and the magnetization direction is consistent with the pre-polarization field; Configure a uniform excitation magnetic field along the vertical direction of the field of view to make the magnetic nanoparticles in the semi-saturated magnetization state in the field of view deflect reciprocally along the vertical direction; Configure a receiving coil along the horizontal direction of the field of view to sense the intensity change of the horizontal magnetization pulse signal caused by the deflection of the magnetic nanoparticles; the intensity change of the horizontal magnetization pulse signal caused by the deflection of the magnetic nanoparticles has a frequency that is twice the frequency of the excitation magnetic field; Configure a dynamic gradient magnetic field along the horizontal direction of the field of view to perform spatial encoding along the horizontal direction and acquire the induced voltage signal; configure a low-frequency scanning magnetic field along the vertical direction of the field of view to perform spatial encoding along the vertical direction and acquire the induced voltage signal; After respectively extracting the harmonic components of the induced voltage signals, project the amplitudes of the harmonic components onto the spatial encoding trajectories respectively to achieve magnetic nanoparticle imaging reconstruction.

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