CN114403843A

CN114403843A - Two-dimensional magnetic particle imaging system

Info

Publication number: CN114403843A
Application number: CN202210086821.6A
Authority: CN
Inventors: 李檀平; 贾广; 胡凯; 黄力宇; 苗启广; 张昱
Original assignee: Xidian University
Current assignee: Xi'an Tiance Zhinao Electronic Technology Co ltd
Priority date: 2022-01-25
Filing date: 2022-01-25
Publication date: 2022-04-29

Abstract

The invention discloses a two-dimensional magnetic particle imaging system, which comprises: the flat plate structure is opposite to the imaging target position; an exciting coil and a receiving coil are arranged in the flat plate structure; the driving scanning unit is used for driving the exciting coil and the receiving coil in the flat plate structure to do spiral movement; including a plurality of data acquisition points during the helical movement; the magnetic field excitation unit is used for applying alternating current to an excitation coil in the flat plate structure once or for multiple times at each data acquisition point to generate different nonlinear and nonuniform excitation magnetic fields; the nonlinear and non-uniform excitation magnetic field acts on the excitation coil to generate an excitation magnetic field; the data acquisition unit is used for acquiring an induced voltage signal generated on a receiving coil in the flat plate structure at each data acquisition point; and the data imaging unit is used for carrying out magnetic particle imaging on the imaging target according to the induced voltage signals corresponding to all the data acquisition points. The invention realizes magnetic particle imaging with low power consumption, large visual field and high resolution.

Description

Two-dimensional magnetic particle imaging system

Technical Field

The invention belongs to the technical field of medical imaging, and particularly relates to a two-dimensional magnetic particle imaging system.

Background

With the development of nano biotechnology, medical imaging technology and targeted gene/drug transfection, biomedical imaging technology becomes an indispensable tool for targeted drug delivery and early tumor monitoring. Superparamagnetic nano-particles have the advantages of unique magnetic characteristics, good biocompatibility, magnetic non-viral vectors and the like, and have been widely applied to nuclear magnetic resonance imaging technology as contrast agents.

Magnetic Particle Imaging (MPI) technology was proposed by Gleich et al for the first time in 2005 to realize Imaging of Magnetic Particle concentration spatial distribution by using the nonlinear Magnetic response of superparamagnetic nanoparticles under excitation of an alternating Magnetic field. Compared with the traditional medical Imaging technology, such as medical Imaging technology, for example, Computed Tomography (CT), Magnetic Resonance Imaging (MRI), Single Photon Emission Computed Tomography (SPECT), MPI has the advantages of high sensitivity, high spatial resolution and high temporal resolution; the MPI realizes particle imaging through a static magnetic field and an oscillating magnetic field, and does not contact radioactive substances in the imaging process, so that ionizing radiation does not exist; because the tissue has diamagnetism and cannot generate interference signals for MPI imaging, the image contrast of particle concentration distribution is high, and the tissue receives wide attention.

Referring to fig. 1, in the conventional magnetic particle imaging, a magnetic field free region is generated by a selection field, the free region is moved by a focusing field, magnetic particles in the free region are excited by an excitation field, high-frequency harmonic signals emitted by the magnetic particles are collected by a receiving coil, and a spatial distribution image of the concentration of the magnetic particles in a human body is obtained by an image reconstruction algorithm. The existing magnetic particle imaging technology needs to detect the magnetic particle concentration information of a specific point or line in the human body each time. To obtain a signal at a specific point or line, it is necessary to use gradient coils to generate a small free field region, which may be either a point region (free field point) or a line (free field line). The magnetic particles in the free region of the magnetic field can be excited by the excitation magnetic field and contribute to the signal, while the magnetic particles outside the free region of the magnetic field are bound by the strong magnetic field and cannot be excited by the excitation magnetic field and do not contribute to the signal. Thus, the signal collected each time only comes from the magnetic field free area at a specific position, and the signal intensity depends on the magnetic particle concentration in the magnetic field free area. The magnetic particle imaging adopts a point-by-point scanning mode or a line-by-line scanning mode for imaging. The position of the free region of the magnetic field is changed by means of a focusing field or by means of mechanical movement. The position change locus of the magnetic field free region is generally a Lissajous curve and is generated by alternating magnetic fields in orthogonal directions. The Lissajous curve covers the whole imaging visual field, and an image of the whole visual field is obtained through interpolation.

However, in the existing two-dimensional magnetic particle imaging system, a magnetic field free area (point or line) is formed in the middle of a selection field by constructing the selection field and a focusing field, and the magnetic field free area is moved in the focusing field, so as to improve the image resolution, the magnetic field free point needs to be small enough, the magnetic field free line needs to be thin enough, and a large power consumption device is needed to generate a large enough current to generate a large gradient magnetic field; the imaging visual field size of the existing magnetic particle imaging technology is determined by a composite magnetic field formed by superposition of an excitation field and a selection field, the ratio of the excitation magnetic field intensity to the gradient of the selection field is generally used as the imaging visual field, the existing magnetic particle imaging is mainly applied to mouse imaging, the imaging visual field is 1 cm-3 cm, the required excitation magnetic field intensity is 15 mT-30 mT, the scanning visual field of a human body generally needs 20 cm-50 cm, and higher excitation magnetic field intensity is required, so that the realization is very difficult, and the expansion to clinical human body scanning is difficult.

Disclosure of Invention

In order to solve the above problems in the prior art, the present invention provides a two-dimensional magnetic particle imaging system. The technical problem to be solved by the invention is realized by the following technical scheme:

the embodiment of the invention provides a two-dimensional magnetic particle imaging system, which comprises a flat plate structure, a driving scanning unit, a magnetic field excitation unit, a data acquisition unit and a data imaging unit, wherein,

the flat plate structure is opposite to the imaging target position; an exciting coil and a receiving coil are arranged in the flat plate structure, the receiving coil is opposite to the imaging target position, and the exciting coil and the receiving coil are opposite;

the driving scanning unit drives the exciting coil and the receiving coil in the flat plate structure to spirally move from inside to outside by taking the corresponding projection positions of the imaging target on the plane where the exciting coil and the receiving coil are positioned as the center; including a plurality of data acquisition points during the helical movement;

the magnetic field excitation unit is used for applying alternating current to an excitation coil in the flat plate structure once or multiple times at each data acquisition point to generate different nonlinear and nonuniform excitation magnetic fields; wherein the amplitude of the current applied to the excitation coil in the flat plate structure at a time is gradually increased or decreased; the nonlinear and nonuniform excitation magnetic field acts on the excitation coil to generate an excitation magnetic field;

the data acquisition unit is used for acquiring an induced voltage signal generated on a receiving coil in the flat plate structure at each data acquisition point; wherein the induced voltage signal is generated under the change of the excitation magnetic field;

and the data imaging unit is used for carrying out magnetic particle imaging on the imaging target according to the induced voltage signals corresponding to all the data acquisition points.

In one embodiment of the invention, the plate structure is a cylindrical plate; an excitation coil and a receiving coil within the respective planar structures, comprising:

the excitation coil comprises a circular Homholtz coil;

the receiving coil comprises a circular Homholtz coil.

In one embodiment of the invention, the non-linear, non-uniform excitation magnetic field generated by the excitation coil is a cosine oscillating excitation magnetic field.

In one embodiment of the invention, the data imaging unit comprises a signal correction subunit, a signal feature extraction subunit, a one-dimensional data reconstruction subunit and a two-dimensional data reconstruction subunit, wherein,

the signal corrector subunit is used for correcting the induced voltage signal corresponding to each data acquisition point acquired by the data acquisition unit;

the signal characteristic extraction subunit is also used for extracting corresponding target acquisition data from the corrected induction voltage signal; the target acquisition data comprises a spike amplitude and/or 3 times fundamental frequency harmonic component of the signal;

the one-dimensional data reconstruction subunit is used for reconstructing to obtain one-dimensional magnetic particle concentration spatial distribution data of the corresponding data acquisition points according to the target acquisition data and the system matrix; the system matrix is used for representing the spatial distribution corresponding to target acquisition data of signals generated by magnetic particles with unit concentration under the action of the nonlinear and nonuniform excitation magnetic field;

and the two-dimensional data reconstruction subunit is used for reconstructing to obtain the two-dimensional magnetic particle concentration spatial distribution data of the imaging target by using a filtering back projection method according to the one-dimensional spatial distribution data of each data acquisition point.

In one embodiment of the invention, the target acquisition data further comprises signal spike area and full width at half maximum of the signal;

the signal correction subunit comprises a first signal correction module, a magnetic field correction module, and a second signal correction module, wherein,

the first signal correction module is used for correcting the peak amplitude and the full width at half maximum of the signal in the target acquisition data according to the signal area;

the magnetic field correction module is used for correcting the nonlinear and nonuniform excitation magnetic field according to the full width at half maximum of the signal;

the second signal correction module is used for correcting the peak amplitude and the full width at half maximum of the signal in the target acquisition data according to the full width at half maximum of the signal under the action of the corrected nonlinear and nonuniform excitation magnetic field, and correcting the system matrix according to the corrected nonlinear and nonuniform excitation magnetic field;

the corrected system matrix is used for representing the spatial distribution corresponding to target acquisition data of signals generated by magnetic particles with unit concentration under the action of a corrected nonlinear and nonuniform excitation magnetic field.

In an embodiment of the invention, the data imaging unit further comprises a relaxation deconvolution module;

the relaxation deconvolution module is used for carrying out deconvolution correction processing on the induction voltage signal corresponding to each data acquisition point acquired by the data acquisition unit under the action of the corrected nonlinear and nonuniform excitation magnetic field;

and the signal syndrome unit is also used for correcting the induced voltage signal after the deconvolution correction.

In an embodiment of the present invention, in the one-dimensional data reconstruction subunit, a formula of the one-dimensional magnetic particle concentration spatial distribution data of the corresponding data acquisition point is obtained by reconstructing according to the target acquisition data and the system matrix, and is represented as:

c＝g^-1u；

wherein the content of the first and second substances,

i₀,i₁,…,i_N+1representing N different magnitudes of current, r, applied to an excitation coil 101 in a flat configuration₀,r₁,…,r_N+1N data acquisition points representing an imaging region into which an imaging target is located; the specific u represents the target acquisition data corresponding to each data acquisition point, and the element u (i)_n) Indicating that a current i is applied to the exciting coil_nTarget acquisition data acquired in real time; g denotes a system matrix, of known quantity, the element g (i)_n,r_n) Magnetic particles representing unit concentration upon application of a current i_nTarget acquisition data component of the generated signal under the action of time-corresponding nonlinear and non-uniform excitation magnetic fieldR < th > of cloth in imaging area_nComponents of data acquisition points; c represents the reconstructed one-dimensional magnetic particle concentration spatial distribution data, and each element contained in the data is the magnetic particle concentration of each data acquisition point in the imaging region, and the element c (r)_n) Representing the r-th in the imaging area_nMagnetic particle concentration for each data acquisition spot.

In an embodiment of the present invention, in the two-dimensional data reconstruction subunit, the mathematical principle based on which the two-dimensional magnetic particle concentration spatial distribution data of the imaging target is reconstructed by using a filtered back projection method is radon transform.

In one embodiment of the invention, the imaging device further comprises an imaging target carrying device for carrying the imaging target;

a plurality of rectangular shielding coils are arranged in parallel in the imaging target bearing device; when the two-dimensional magnetic particle imaging system works, the shielding coils corresponding to the position of the imaging target up and down are closed, and the rest shielding coils are electrified and opened.

In one embodiment of the invention, when the magnetic field intensity of the excitation magnetic field is 15 mT-30 mT, the corresponding scanning visual field reaches 50 cm.

The invention has the beneficial effects that:

the invention provides a two-dimensional magnetic particle imaging system.A driving coil and a receiving coil in a flat plate structure make spiral movement from inside to outside by taking the corresponding projection positions of an imaging target on the plane where the driving coil and the receiving coil are positioned as the center, the spiral movement process comprises a plurality of data acquisition points, and the amplitude of current applied to the driving coil in the flat plate structure is gradually increased or decreased on each data acquisition point, so that a nonlinear and nonuniform driving magnetic field is generated.

Based on the nonlinear and nonuniform excitation magnetic field, the nonlinear and nonuniform magnetic field excitation is carried out on the magnetic particles in the whole space where the imaging target is located, all the magnetic particles in the whole space can contribute to the induced voltage on the winding coil, a magnetic field free area is not required to be arranged, and the position of the magnetic field free area is not required to be changed; the excitation coil and the receiving coil in the flat plate structure make spiral movement from inside to outside by taking the projection position of an imaging target on the plane where the excitation coil and the receiving coil are located as the center, and different currents are applied to the excitation coil in the flat plate structure, which is equivalent to that the excitation coil and the receiving coil in the flat plate structure carry out nonlinear and non-uniform excitation in multiple different space postures and multiple different magnetic field distribution states; when an exciting coil and a receiving coil in a flat plate structure are in a certain space attitude, the current in the exciting coil is changed, so that the magnetic field distribution can be shifted along the axial direction of the exciting coil, and one-dimensional space coding is realized; when the exciting coil and the receiving coil in the flat plate structure are in different space postures, the magnetic field strength sensed by the magnetic particles at the same position is different, so that the two-dimensional full-space coding is realized.

Based on the scanning mode, the two-dimensional magnetic particle imaging system provided by the invention can be used for magnetic particle imaging without setting a magnetic field free area; the position of the free area of the magnetic field is not required to be changed; the signals acquired each time are formed by superposing the signals generated after all the magnetic particles in the whole space are excited, and the imaging visual field does not need to be limited by the size of a free area of a magnetic field and the moving range as in the prior art, so that the imaging visual field can be matched with the size of a human body. In addition, the coils required for constructing the gradient field and the corresponding consumed power consumption can be omitted without arranging the magnetic field free area, and the equipment scale and the power consumption are reduced.

In addition, compared with the mode of executing scanning by almost taking the resolution of an imaging image as stepping in the prior art, the scanning stepping involved in the invention comprises stepping of current amplitude adjustment and stepping between adjacent data acquisition points in spiral movement, the scanning time required by executing scanning based on the stepping is far shorter than that of the prior art, the timeliness is higher, the relaxation effect of magnetic particles can be effectively reduced, the imaging result is clearer, and high-resolution magnetic particle imaging is realized.

In summary, the present invention does not need to use the selection field and the focusing field in the existing magnetic particle imaging technology, each point in the whole imaging space is a magnetic field free region, and can be excited by the magnetic field, that is, the signal acquired each time is formed by the superposition of the signals of the magnetic nanoparticles at all points in the whole space. The magnetic particle concentration distribution image of the imaging target is reconstructed by carrying out space coding on the full space, and the magnetic particle imaging with low power consumption, large visual field and high resolution is realized. The two-dimensional magnetic particle imaging system with low power consumption, large visual field and high resolution can be expanded to clinical human body scanning.

The present invention will be described in further detail with reference to the accompanying drawings and examples.

Drawings

FIG. 1 is a diagram illustrating magnetic field distribution in conventional magnetic particle imaging;

FIG. 2 is a schematic structural diagram of a two-dimensional magnetic particle imaging system according to an embodiment of the present invention;

FIGS. 3a to 3b are schematic structural diagrams of a flat plate structure according to an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of a data imaging unit in a two-dimensional magnetic particle imaging system according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a signal syndrome unit in a data imaging unit according to an embodiment of the present invention;

FIG. 6 is a schematic structural diagram of another data imaging unit in a two-dimensional magnetic particle imaging system according to an embodiment of the present invention;

FIG. 7 is a schematic diagram illustrating the effect of the correction process of the relaxation convolution according to the embodiment of the present invention;

fig. 8 is a schematic diagram of a corresponding two-dimensional magnetic particle concentration space reconstruction effect obtained by performing image reconstruction using the two-dimensional magnetic particle imaging system provided in the embodiment of the present invention.

Description of reference numerals:

10-a plate structure; 20-driving the scanning unit; 30-a magnetic field excitation unit; 40-a data acquisition unit; 50-a data imaging unit; 101-an excitation coil; 102-a receiving coil; 501-signal syndrome unit; 502-a signal feature extraction subunit; 503-a one-dimensional data reconstruction subunit; 504-two-dimensional data reconstruction subunit; 505-a relaxation deconvolution subunit; 5011-a first signal correction module; 5012-a magnetic field correction module; 5013-second signal correction module.

Detailed Description

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

Example one

In order to solve the problems of large power consumption, low spatial resolution, blurred reconstructed image, small visual field and difficult expansion to clinical human body scanning, etc. in the conventional two-dimensional magnetic particle imaging system, referring to fig. 2, an embodiment of the present invention provides a two-dimensional magnetic particle imaging system, which includes a flat plate structure 10, a driving scanning unit, a magnetic field excitation unit, a data acquisition unit and a data imaging unit, wherein,

the flat plate structure 10 is opposed to the imaging target position; an exciting coil and a receiving coil are arranged in the flat plate structure 10, the receiving coil is opposite to the position of an imaging target, and the exciting coil and the receiving coil are opposite;

the driving scanning unit drives the exciting coil and the receiving coil in the flat plate structure 10 to make a spiral movement from inside to outside by taking the corresponding projection positions of the imaging target on the plane where the exciting coil and the receiving coil are located as centers; including a plurality of data acquisition points during the helical movement;

a magnetic field excitation unit for applying an alternating current to the excitation coil in the slab structure 10 one or more times at each data acquisition point to generate different nonlinear, non-uniform excitation magnetic fields; wherein the current amplitude applied to the excitation coil in the flat plate structure 10 at a time is gradually increased or decreased; the nonlinear and non-uniform excitation magnetic field acts on the excitation coil to generate an excitation magnetic field;

a data acquisition unit for acquiring an induced voltage signal generated on a receiving coil in the flat plate structure 10 at each data acquisition point; wherein the induced voltage signal is generated under the change of the excitation magnetic field;

Next, each of the above units will be described in detail in the embodiments of the present invention.

From the above analysis, the existing two-dimensional magnetic particle imaging system forms a free magnetic field area (point or line) in the middle of the selection field by constructing the selection field and the focusing field, and moves the free magnetic field area by changing the size of the focusing field, so as to realize, for example, point-by-point scanning. However, in order to improve the image resolution, the magnetic particle imaging mode through selecting a field and a focusing field needs a magnetic field free point to be small enough and a magnetic field free line to be thin enough, so that a large power consumption device is needed to generate a large enough current and a large gradient magnetic field, which brings a power consumption problem and makes the magnetic particle imaging more difficult to extend to clinical human body scanning. Based on the problem, the embodiment of the present invention provides a way of cooperating with the flat plate structure 10, the driving scanning unit 20, and the magnetic field excitation unit 30 to generate a non-linear and non-uniform excitation magnetic field, and under the action of the non-linear and non-uniform excitation magnetic field, an induced voltage signal can be generated by using any point in space as a magnetic field free region without constructing a selection field and a focusing field, so as to provide for magnetic particle imaging. Specifically, the method comprises the following steps:

the flat plate structure 10 is opposed to the imaging target position, the exciting coil 101 and the receiving coil 102 are built in the flat plate structure 10, the receiving coil 102 is opposed to the imaging target position, and the exciting coil 101 and the receiving coil 102 in the flat plate structure 10 are opposed to each other. The exciting coil 101 is used for generating a nonlinear and non-uniform exciting magnetic field under the action of the magnetic field exciting unit 30; the receiving coil 102 is used for receiving the magnetic flux change caused by the magnetization response of the magnetic nanoparticles under the action of the nonlinear and non-uniform excitation magnetic field, and generating corresponding induced voltage signals for magnetic particle imaging. Wherein the imaging target carries magnetic particles.

Referring to fig. 3a to fig. 3b, the embodiment of the present invention exemplarily shows a structural schematic diagram of the flat plate structure 10: the plate structures 10 are all cylindrical plates; excitation coil 101 and receiving coil 102 within the corresponding flat plate structure 10: the excitation coil 101 comprises a circular helmholtz coil and the receiving coil 102 comprises a circular helmholtz coil. The flat plate structure 10 according to the embodiment of the present invention may be located directly above the imaging target as shown in fig. 3a, and the flat plate structure 10 may be located directly below the imaging target as shown in fig. 3b, where the position of the flat plate structure 10 is designed according to the actual environment requirement, and is not limited to the position shown in fig. 3a and 3b, for example, the flat plate structure may also be located on the left side or the right side of the same horizontal position as the imaging target. The flat plate structure 10 according to the embodiment of the present invention may be fixed in position by a fixing support, but is not limited to be fixed by the fixing support, and is not limited to be fixed in position, and the position of the flat plate structure 10 in the horizontal or vertical direction may also be adjusted by a mechanical control method.

The signal generated by the receiving coil 102 in the flat plate structure 10 according to the embodiment of the present invention includes a plurality of induced voltage signals generated under the action of a plurality of nonlinear and non-uniform excitation magnetic fields. In the process of generating signals, the driving scanning unit 20 drives the excitation coil 101 and the receiving coil 102 in the flat plate structure 10 to make a spiral movement from inside to outside with the projection positions of the imaging target on the planes where the excitation coil 101 and the receiving coil 102 are corresponding as the center, the movement track forms a spiral shape, and each movement is equivalent to regulating and controlling the spatial postures of the excitation coil 101 and the receiving coil 102. During the movement, the exciting coil 101 and the receiving coil 102 in the flat plate structure 10 can perform a spiral movement from inside to outside counterclockwise, or can perform a spiral movement from inside to outside clockwise. A plurality of data acquisition points are included in the spiral movement. For example, when a certain point is used as a starting point, one turn of clockwise rotation is performed, that is, the ending point is opposite to the starting point, so that the spiral movement makes 256 circular movements, and 256 data acquisition points are obtained in each circular movement, so that the flat plate structure 10 can form 256 × 256 data acquisition points, and different nonlinear and non-uniform excitation magnetic fields are applied to each data acquisition point.

The driving scanning unit 20 according to the embodiment of the present invention may be embedded in the flat plate structure 10; the excitation coil 101 and the receiving coil 102 in the corresponding flat plate structure 10 are respectively fixed on the driving scanning unit 20, and the driving scanning unit 20 drives the excitation coil 101 and the receiving coil 102 in the flat plate structure 10 to make a circular motion with the projection position as a central point to form a spiral track. The driving scanning unit 20 may also be independently electrically connected to the flat panel structure 10, and the driving scanning unit 20 may also drive the excitation coil 101 and the receiving coil 102 in the flat panel structure 10 to make a circular motion with the projection position as a central point to form a spiral track.

The driving scan unit 20 according to the embodiment of the present invention may include: a hardware driving module and a software control module; the hardware driving module drives the exciting coil 101 and the receiving coil 102 in the flat plate structure 10 to make a circular motion with the projection position as a central point to form a spiral track under the control of the software control module.

In practical applications, the software control module may be a control program running on a computer; the hardware driving module can comprise a rotating device and an electric driving unit which can drive the rotating device to move and is electrically connected with the software control module. The rotating apparatus may include a mechanical arm and a mechanical structure for fixing the positions of the excitation coil 101 and the receiving coil 102, and the mechanical structure is moved by the mechanical arm. In the embodiment of the present invention, a computer integrated in the two-dimensional magnetic particle imaging system may be referred to as a central control computer, and functions implemented by the central control computer are not limited to the software control module described herein, which will be described one by one subsequently.

In view of the structural features of the flat-plate structure 10, the non-linear and non-uniform excitation magnetic field acting at each data acquisition point is generated by the magnetic field excitation unit 30, specifically:

when the exciting coil 101 and the receiving coil 102 in the flat plate structure 10 are in a certain spatial attitude, in each data acquisition point, the same-direction alternating current is respectively applied to the exciting coil 101 in the flat plate structure 10 for one or more times to generate a nonlinear and non-uniform exciting magnetic field; the magnitude of the current applied to the excitation coil 101 in the flat plate structure 10 is increased or decreased stepwise each time. When an alternating current with a cocurrent current of gradually increasing or decreasing amplitude is applied to the excitation coil 101 for each data acquisition point, the excitation magnetic field generated by the excitation coil 101 in the flat plate structure 10 is distributed in a linearly decreasing manner, and the magnetic field distribution is shifted in position along the axial direction of the excitation coil 101, thereby realizing one-dimensional spatial encoding.

When the excitation coil 101 and the receiving coil 102 in the flat plate structure 10 are in different spatial postures, the magnetic field strength sensed by the magnetic particles at the same position is also different, so that two-dimensional full-space encoding is realized.

For each data acquisition point, embodiments of the present invention apply a unidirectional alternating current to the excitation coil 101 within the slab structure 10 one or more times, respectively, to generate a non-linear, non-uniform excitation magnetic field. For example, 256 different cocurrent alternating currents are applied to each data acquisition site, 256 × 256 nonlinear excitation magnetic fields are generated by the excitation coil 101 in the flat plate structure 10, and 256 × 256 induced voltage signals are generated under the action of each nonlinear, nonuniform excitation magnetic field. 256 × 256 induced voltage signals generated by the receiving coils 102 in the flat plate structure 10 are used for image reconstruction. Preferably, the current applied by the magnetic field excitation unit 30 is a cosine oscillating alternating current, but is not limited to a cosine oscillating alternating current.

In practical applications, the current excitation device 30 may be a digital ac power supply. The digital ac power supply may be integrated with a communication interface to communicate with the above-mentioned central control computer through a communication bus, so as to apply various magnitudes of current to the exciting coil 101 under the control of the central control computer. In another implementation, the current excitation device 30 may include a waveform generator and its corresponding front-end controller, and the waveform generator applies various magnitudes of current to the excitation coil 101 under the control of the front-end controller. It will be appreciated that the front-end director is also under the control of the central control computer. Specifically, the waveform generator boosts the voltage of the commercial power, rectifies the boosted alternating-current voltage into direct current, and obtains alternating current under a specific frequency through frequency conversion, wherein the specific frequency is preferably 3.0 KHz-35 KHz. The front-end controller pre-drives the scanning sequence issued by the central control computer so as to drive the power; the power drive is mainly to distribute current to the exciting coil under the high-voltage control of the frequency conversion output. In addition, the current applied to the exciting coil 101 can be fed back to the pre-driving circuit through a feedback loop, so that a closed-loop control is formed.

Compared with the figure 1, the magnetic field excitation structure is simpler and has higher application value in practical application scenes. In the traditional magnetic particle imaging, the magnetic particles in the free magnetic field area can be activated only by arranging the exciting coil/receiving coil and the like at the same time around the imaging target, but the invention only needs to carry out nonlinear magnetic field excitation on the magnetic particles in the whole space where the imaging target is located in a certain position relative to the imaging target, all the magnetic particles in the whole space are excited by adopting a mode of coaction of the flat plate structure 10, the driving scanning unit 20 and the magnetic field excitation unit 30, signals generated after excitation are superposed to form an induced voltage signal generated by the receiving coil 102, and the free magnetic field area does not need to be arranged.

After the flat plate structure 10, the driving scanning unit 20 and the magnetic field excitation unit 30 act together to generate induced voltage signals, the data acquisition unit 40 acquires the induced voltage signals generated on the receiving coil 102 in the flat plate structure 10 at each data acquisition point; wherein the induced voltage signal is generated under the change of the excitation magnetic field. Specifically, the method comprises the following steps:

the data acquisition unit 40 acquires an induced voltage signal generated on the receiving coil 102 in the flat plate structure 10 for each data acquisition point, and performs analog-to-digital conversion on the acquired induced voltage signal. The analog-to-digital conversion processing of the generated sensing signal comprises an analog signal processing part and a digital signal processing part: the analog signal processing part comprises the steps of carrying out low-noise amplification processing, receiving frequency mixing processing, high-frequency filtering processing, low-frequency filtering processing and ADC (analog-to-digital converter) conversion processing on the induced voltage signal generated on the receiving coil 102 in sequence; the digital signal processing part comprises the steps of carrying out Fourier transform processing, frequency spectrum analysis processing and fundamental frequency reduction processing on the signals output by the analog signal processing part in sequence to complete analog-to-digital conversion processing. The processing in the analog signal processing section and the digital signal processing section is a relatively conventional signal processing method, and will not be described in detail here.

In practical applications, the data acquisition device 40 may be a data acquisition device integrated with an Analog-to-Digital Converter (ADC), and can convert the induced voltage signal on the receiving coil 102 into a Digital signal for subsequent imaging processing.

And the data imaging unit 50 is used for performing magnetic particle imaging on the imaging target according to the induced voltage signals corresponding to all the data acquisition points. Referring to fig. 4, the data imaging unit 50 according to the embodiment of the present invention includes a signal correction subunit 501, a signal feature extraction subunit 502, a one-dimensional data reconstruction subunit 503, and a two-dimensional data reconstruction subunit 504, specifically:

in order to further improve the magnetic particle imaging accuracy, in the embodiment of the present invention, a signal corrector subunit 501 is added, where the signal corrector subunit 501 is used to perform correction processing on an induced voltage signal corresponding to each data acquisition point acquired by the data acquisition unit, specifically, target acquisition data corresponding to each induced voltage signal is subjected to correction processing, and the target acquisition data at this time may be extracted in advance by using the signal feature extraction subunit 502. The inventor finds that the correction can be carried out by utilizing the information of the peak area and the full width at half maximum of the signal included in the target acquisition data in the process of implementing the invention. Specifically, the method comprises the following steps:

when the target acquisition data includes the signal peak area of the signal, please refer to fig. 5, the signal correction subunit 501 may include a first signal correction module 5011, and the first signal correction module 5011 is configured to correct the peak amplitude and the full width at half maximum of the signal in the target acquisition data according to the signal area. The signal peak area of the signal is independent of the magnetic field intensity and is in direct proportion to the concentration of the magnetic particles. Therefore, no matter in the process of applying different current amplitudes to a single data acquisition point, or in the process of changing the data acquisition point or even changing the circular motion, the peak area of the signal acquired each time is actually a conservative value, assuming that the magnetic particle concentration distribution condition of the imaging target remains unchanged. In consideration of the fact that the magnetic particle concentration distribution of the actual imaging target is not changed in a short time and may be changed in a long time, the first signal correction module 5011 of the embodiment of the present invention corrects the target acquisition data according to the peak area of the signal in units of data acquisition points, so that the finally extracted target acquisition data can be better and more accurate.

The extracted signal peak area specifically refers to an area under a time domain curve of a signal, and data acquired in a time domain can be subjected to integration processing. Specifically, the method comprises the following steps: on each data acquisition point, acquiring a signal once when the current amplitude is converted once, and extracting the signal peak area of the signal; when the process of current amplitude adjustment is finished, namely after the scanning on the stop data acquisition point is finished, the signal areas of all acquired signals are compared, possible abnormity in the invisible magnetic field is found through the comparison result, the signals with abnormal signal areas are corrected, and various specific correction modes exist. For example, the excitation coil 101 may be re-applied with a current corresponding to the signal, so as to perform the acquisition again; or correcting the abnormal signal by using signals adjacent to the acquisition time, and the like.

When the target acquisition data further includes the full width at half maximum of the signal, please refer to fig. 5 again, the signal corrector subunit 501 in the embodiment of the present invention may further include a magnetic field correction module 5012 and a second signal correction module 5013. The magnetic field correction module 5012 is configured to correct a non-linear and non-uniform excitation magnetic field according to a full width at half maximum of a signal; the second signal correction module 5013 is configured to correct the peak amplitude and the full width at half maximum of the signal in the target acquisition data according to the full width at half maximum of the signal under the action of the corrected nonlinear and non-uniform excitation magnetic field. The inventors have found in the course of carrying out the invention that the full width at half maximum of the signal is independent of the magnetic particle concentration, but inversely related to the excitation magnetic field strength; therefore, by uniformly comparing the full widths at half maximum of all the actually acquired signals, the stability of the excitation magnetic field can be checked according to the comparison result, and possible abnormalities in the invisible magnetic field can be found, so that the data depended on by the final reconstructed image is ensured to be true and effective.

The full width at half maximum refers to the width of the corresponding time domain when the amplitude of the signal decreases to half. In consideration of the fact that the comparison efficiency of the full width at half maximum of the signals acquired in the whole scanning process is low, the second signal correction module 5013 in the embodiment of the present invention adopts a scheme of comparing the full width at half maximum in units of data acquisition points, and specifically, at each data acquisition point, a signal is acquired every time the current amplitude is changed, and the full width at half maximum of the signal is extracted; when the current amplitude adjustment process is finished, namely after the scanning on the data acquisition point is finished, the full widths at half maximum of all acquired signals are compared, and the abnormal full widths at half maximum are found, so that the possible abnormality in the invisible magnetic field is found. For the found abnormal magnetic field condition, the position of the exciting coil 101 is corrected by the magnetic field correction module 5012 to ensure the accurate change of the exciting magnetic field, and then under the action of the corrected exciting magnetic field, the target acquisition data is corrected according to the full width at half maximum of the signal, so that the finally extracted target acquisition data can be better and more accurate.

The second signal correction module 5013 according to this embodiment of the present invention is further configured to correct the system matrix according to the corrected nonlinear and nonuniform excitation magnetic field; the corrected system matrix is used for representing the spatial distribution corresponding to target acquisition data of signals generated by magnetic particles with unit concentration under the action of a corrected nonlinear and nonuniform excitation magnetic field. The system matrix is obtained by experiments in advance according to spatial distribution corresponding to target acquisition data of signals generated by magnetic particles with unit concentration under the action of a nonlinear and nonuniform excitation magnetic field, when the magnetic field is abnormal, the nonlinear and nonuniform excitation magnetic field is corrected, the corrected system matrix is measured in real time according to the corrected nonlinear and nonuniform excitation magnetic field, data reconstruction is performed according to the corrected system matrix, and the accuracy of data reconstruction is improved.

A signal feature extraction subunit 502, configured to extract corresponding target acquisition data from the corrected induced voltage signal; the target acquisition data includes a spike amplitude or 3 fundamental harmonic components of the signal. The corrected target acquisition data is extracted, and the corrected target acquisition data is more accurate for data reconstruction. The peak amplitude or 3 times fundamental frequency harmonic component of the preferred signal of the embodiment of the invention is used for the imageThe theoretical basis on which magnetic particle imaging is achieved based on the peak amplitude or 3 times fundamental frequency harmonic component of the signal is: the shape and size of the magnetization curve also differ according to the intensity of the excitation magnetic field, and the shape and size of the signal spikes also differ. Taking the example of the alternating current applied as cosine oscillation by the magnetic field excitation unit 30, the inventor found that, with the excitation magnetic field h (t) ═ Acos (2 pi ft) corresponding to the cosine oscillation alternating current, the peak amplitude u of the signal generated by the magnetic particles under their excitation is the peak amplitude u_peak3 times fundamental frequency harmonic component u of the signal in proportion to the intensity A of the excitation magnetic field and in proportion to the concentration c of the magnetic particles₃Is in a nonlinear relationship with the excitation magnetic field intensity A and is in direct proportion to the magnetic particle concentration c. Equations (1) and (2) show a simple proof of this theoretical basis:

wherein u is_peak(i_n) Is shown in the application of a current i_nThe peak amplitude of the time-corresponding signal, N the number of data acquisition points in the imaging region, f the frequency, m the magnetic moment of a single magnetic particle, μ₀The magnetic permeability in a vacuum is shown,

k_Bdenotes the Boltzmann constant, T^PRepresenting the absolute temperature of the imaged object, Δ V representing the volume size of the voxel at the data acquisition point, A (i)_n,r_n) Is shown in the application of a current i_nUnder the action of time-corresponding nonlinear and nonuniform excitation magnetic field in the imaging area_nExcitation magnetic field strength, s (r), at each data acquisition point_n) Representing the r-th in the imaging area_nSpatial sensitivity, c (r), of individual data acquisition site receiver coils 102_n) Representing the r-th in the imaging area_nMagnetic particle concentration, g (i) of individual data acquisition Point_n,r_n) Magnetic particles representing unit concentration upon application of a current i_nTarget acquisition data distribution of the generated signal under the action of time-corresponding nonlinear and non-uniform excitation magnetic fieldAt the r-th of the imaging area_nThe components of the individual data acquisition points.

Wherein u is₃(i_n) Is shown in the application of a current i_nThe time corresponds to the 3-fold fundamental harmonic component of the signal, Δ V represents the volume size of the voxel at the data acquisition point, f (A (i;)_n,r_n) Is indicated under application of a current i_nUnder the action of time-corresponding nonlinear and non-uniform excitation magnetic field in the imaging area_nFrequency, s (r), corresponding to the excitation field of the individual data acquisition points_n) Representing the r-th in the imaging area_nSpatial sensitivity, c (r), for individual data acquisition point receiving coils_n) Representing the r-th in the imaging area_nMagnetic particle concentration, g (i) of individual data acquisition Point_n,r_n) Magnetic particles representing unit concentration upon application of a current i_nUnder the action of time-corresponding nonlinear and non-uniform excitation magnetic field, the target acquisition data of the generated signal is distributed in the r-th position of the imaging area_nThe components of the individual data acquisition points.

Therefore, the peak amplitude and the 3 times fundamental frequency harmonic component of the signal are determined by the magnetic field intensity A and the magnetic particle concentration c together, so that the peak amplitude or the 3 times fundamental frequency harmonic component of the signal can be selected to be used for one-dimensional data reconstruction, and the peak amplitude and the 3 times fundamental frequency harmonic component of the signal can be selected to be used for one-dimensional data reconstruction together.

And a one-dimensional data reconstruction subunit 503, configured to reconstruct the one-dimensional magnetic particle concentration spatial distribution data of the corresponding data acquisition point according to the target acquisition data and the system matrix. The system matrix is used for representing the spatial distribution corresponding to target acquisition data of signals generated by magnetic particles with unit concentration under the action of a nonlinear and nonuniform excitation magnetic field. In the embodiment of the invention, in the one-dimensional data reconstruction, the peak amplitude and/or 3 times fundamental frequency harmonic component of a signal related to the concentration c of magnetic particles are/is utilized to reconstruct data. The specific data reconstruction process can be represented by the following formula:

c＝g^-1u (3)

in the formula (3), the first and second groups,

i0,i₁,…,i_N+1representing N different magnitudes of current, r, applied to an excitation coil 101 within the plate structure 10₀,r₁,…,r_N+1N data acquisition points representing an imaging region into which an imaging target is located. Wherein u represents the target acquisition data corresponding to each data acquisition point in each circular motion, wherein the element u (i)_n) Indicating that a current i is applied to the exciting coil 101_kThe meaning of the rest elements is analogized by the data acquired by the acquired target. Because the target acquisition data comprises the peak amplitude and/or 3 times fundamental frequency harmonic component of the signal, in the corresponding one-dimensional data reconstruction, when the peak amplitude of the signal is adopted for reconstruction, u (i) is used_n) The value is u corresponding to the formula (1)_peak(i_n) When the 3-fold fundamental harmonic component of the signal is used for reconstruction, u (i)_n) The value is u corresponding to formula (2)₃(i_n) (ii) a g represents a system matrix, being a known quantity, where g (i)_n,r_n) Magnetic particles representing unit concentration upon application of a current i_nUnder the action of time-corresponding nonlinear and non-uniform excitation magnetic field, the target acquisition data of the generated signal is distributed in the r-th position of the imaging area_nThe components of the data acquisition points and the meanings of the other elements are analogized; c represents the reconstructed one-dimensional magnetic particle concentration spatial distribution data, and each element contained in the data is the magnetic particle concentration of each data acquisition point in the imaging region, wherein c (r)_n) Representing the r-th in the imaging area_nMagnetic particle concentration for each data acquisition spot.

In practical applications, if the system matrix g is not very large, the system matrix g can be directly inverted according to the formula (3) shown above, and then the inverted system matrix g is invertedg^-1And reconstructing the magnetic particle concentration c by multiplying the target acquisition data u. If the system matrix g is huge and direct inversion is difficult, the elements in the magnetic particle concentration c can be used as the variables x to be solved, and a set of equations u (i) is constructed_n)＝g(i_n,r₀)x+g(i_n,r₁)x+…+g(i_n,r₁)x，n∈[0,N-1]And solving the set of equations in an iterative manner, thereby realizing the reconstruction of the magnetic particle concentration c according to the solving result. The iterative method is, for example, a common algebraic reconstruction method, a joint algebraic reconstruction method, a maximum likelihood expectation-maximization algorithm or an ordered subset expectation-maximization algorithm, etc.

It should be noted that, the existing Magnetic Particle Imaging (MPI) system also uses a system matrix to perform Magnetic Particle Imaging, but the system matrix is different from the system matrix proposed in the embodiment of the present invention: each element in a system matrix adopted by the existing two-dimensional magnetic particle imaging system comprises a group of Fourier components of a signal generated by a magnetic particle sample with known concentration at a certain data acquisition point in an imaging area, namely, each harmonic of the signal generated at the data acquisition point; in the embodiment of the invention, each element of the system matrix is the peak amplitude or 3 times fundamental frequency harmonic component of a signal generated by magnetic particles with unit concentration on a certain data acquisition point in the imaging area, and the system matrix is different from the system matrix adopted by the existing MPI system.

And simultaneously, when imaging is carried out by utilizing the peak amplitude and the 3-time fundamental frequency harmonic component, imaging is respectively carried out by adopting a formula (3), and the two obtained imaging results are fused. Specifically, each time target acquisition data is extracted from the induced voltage signal, the peak amplitude and 3-fold fundamental frequency harmonic components of the signal are extracted. And then, imaging by respectively utilizing the peak amplitude and the 3-time fundamental frequency harmonic component of the signal to obtain two imaging results. Then, the two imaging results are fused, that is, the two imaged images are subjected to image fusion, so that the reconstruction effect is further improved. The specific image fusion mode may include weighted fusion of pixels at the same position between images or other common image fusion modes.

And a two-dimensional data reconstruction subunit 504, configured to reconstruct, according to the one-dimensional spatial distribution data of each data acquisition point, two-dimensional magnetic particle concentration spatial distribution data of the imaging target by using a filtered back projection method. In practical applications, the filtered back-projection reconstruction method is commonly used in CT imaging reconstruction, and the mathematical principle behind the method is radon transform. The method for reconstructing the magnetic particle concentration distribution image by using the filtered back projection reconstruction method in the embodiments of the present invention is basically the same, and therefore, the description thereof is omitted here.

Further, referring to fig. 6, the data imaging unit 50 according to the embodiment of the present invention further includes a relaxation deconvolution subunit 505; a relaxation deconvolution subunit 505, configured to perform deconvolution correction processing on the induced voltage signal corresponding to each data acquisition point acquired by the data acquisition unit under the action of the corrected nonlinear and nonuniform excitation magnetic field; the signal corrector subunit 501 is further configured to perform correction processing on the induced voltage signal after the deconvolution correction processing. Referring to fig. 7, in the data reconstruction process, signal degradation is generally caused due to the relaxation effect. In the embodiment of the present invention, the relaxation effect deconvolution subunit 505 performs deconvolution processing on the target acquired data to reduce signal deformation caused by the magnetic particle relaxation effect, where the specific deformation mainly includes reduction of signal amplitude, and broadening and asymmetry of time domain, such as signal deformation indicated by a circle in fig. 7. Through deconvolution operation, target collected data can be corrected, signal deterioration is reduced, and finally extracted target features can be better and more accurate. After the correction processing based on deconvolution, the relevant correction and feature extraction processing are performed.

In practical applications, large size (30 nm-100 nm) magnetic particles are more prone to relaxation effects, so if the size of the magnetic particles in the imaged object is larger, the signal deformation can be mitigated by adding the relaxation effect deconvolution subunit 505.

In practical applications, the data imaging unit 50 may be an image imaging processing program module running on a central control computer. It should be understood that the central control computer in the embodiment of the present invention is not limited to a physical computer, and in practice, the program modules for implementing the image imaging processing and the coil control, the current control, and the like may be integrated or divided according to the computing power of the physical computer, which is not limited in the embodiment of the present invention.

In a medical application scenario, the central control computer of the two-dimensional magnetic particle Imaging System provided in the embodiment of the present invention may further communicate with a Radiology Information System (RIS) and an image archiving and Communication System (PACS) through a Digital Imaging and Communications in Medicine (DICOM) interface. The magnetic particle imaging system can be directly connected with a laser camera through a DICOM interface, so that the magnetic particle imaging result is subjected to laser printing.

Furthermore, the two-dimensional magnetic particle imaging system of the embodiment of the invention further comprises an imaging target bearing device, which is used for bearing the imaging target; a plurality of rectangular shielding coils are arranged in parallel in the imaging target bearing device; when the two-dimensional magnetic particle imaging system works, the shielding coils corresponding to the position of an imaging target up and down are closed, and the rest shielding coils are electrified and opened. Usually, the coil corresponding to the imaging target is a central region shielding coil, and the other coils are peripheral region shielding coils.

Here, the main role of the shield coil is to reduce external interference. For example, when the magnetic particle device is located in an environment where the shielding effect is poor, turning on the shielding coil may effectively saturate the magnetic particles existing in the region other than the non-imaging region, so that only the magnetic particles located in the imaging region are excited by the exciting coil 101. For example, when the two-dimensional magnetic particle imaging system is used for scanning and imaging a human body, the imaging target carrying device can be an examination table. In addition, when the two-dimensional magnetic particle imaging system is used for scanning and imaging an imaging target with irregular shape, the imaging target carrying device can also comprise a structure for clamping or fixing the imaging target. In practical application, the on-off control of the shielding coil can be controlled independently, and the linkage control can be realized through a central control computer and the scanning process.

When the output magnetic field abnormality occurs, a display device, an acoustic alarm device, or other prompting device may be included. Generally, the occurrence of magnetic field anomalies may be related to external disturbances; after the magnetic field abnormality is found, a higher level of shielding measures can be taken, such as opening shielding coils outside the imaging area, and the like, and the measurement of the system matrix is performed again, and then the scanning imaging is performed again.

In order to verify the effectiveness of the two-dimensional magnetic particle imaging system proposed by the embodiment of the present invention, the following experiment is performed.

An excitation coil 101 in the flat plate structure 10 is a circular Homholtz coil, the diameter of the excitation coil 101 is 40cm, the thickness and the width are both 5cm, the number of turns of the excitation coil 101 is 200 turns, the same-direction cosine alternating current is applied, a cosine alternating magnetic field of 15 mT-30 mT is generated in an imaging target area, the frequency is 25 KHz-35 KHz, the applied cosine alternating current is 20A-40A, the magnetic field of an axial component is uniformly distributed along a transverse plane, the variation range of the magnetic field intensity in the 20 cm-50 cm visual field range of a central area of the imaging target is less than 5%, and the constant magnetic field plane is ensured to be a plane and not a curved surface. The current of the excitation coil 101 at each data acquisition point is changed 256 times, and the current of the excitation coil 101 in the flat plate structure 10 is increased from 20A, increased by 0.78A each time and increased by 256 times, and is increased to 40A (or the current of the excitation coil 101 in the flat plate structure 10 is decreased from 40A, decreased by 0.78A each time and decreased by 256 times, and is decreased to 20A) all the time, so that the shape and the position of the magnetic field are changed 256 times independently. The shape and position of the magnetic field after each change are kept for a short time of 0.017ms, half cosine oscillation of excitation magnetic field (oscillation frequency is 30KHz) and signal acquisition are completed, then the next shape and position are changed, and 256 times of shape and position changes of the magnetic field are completed, wherein 4.267ms is needed. Correspondingly, after the subsequent data one-dimensional/two-dimensional reconstruction subunit performs data reconstruction, the obtained data is the one-dimensional/two-dimensional magnetic particle concentration distribution information along the axial direction of the exciting coil.

The receiving coil 102 in the flat plate structure 10 is a circular helmholtz coil, the diameter of the receiving coil 102 is 40cm, and the thickness and the width are both 5 cm. The distance between the excitation coil 101 and the receiving coil 102 is 5cm, abutting the excitation coil 101 in the axial direction within the flat plate structure 10.

When the flat structure 10 is located directly above the imaging target, one alternative: the flat plate structure 10 is a cylindrical flat plate, the diameter of the flat plate is 120cm, the thickness of the flat plate is 40cm, the driving scanning unit 20 drives the excitation coil 101 and the receiving coil 102 to make clockwise/anticlockwise spiral circular movement from inside to outside by taking the projection position of the imaging target corresponding to the plane where the excitation coil 101 and the receiving coil 102 are located as a center point, the scanning of 256 circles and 256 data acquisition points is completed totally, and the scanning time is 4.66 minutes; another alternative when the flat plate structure 10 is located directly below the imaging target: the flat plate structure 10 is a cylindrical flat plate, the diameter of the flat plate is 120cm, the thickness of the flat plate is 100cm, the driving scanning unit 20 drives the excitation coil 101 and the receiving coil 102 to make clockwise/counterclockwise spiral circular motion movement from inside to outside by taking the projection position of the imaging target corresponding to the plane where the excitation coil 101 and the receiving coil 102 are located as a center point, and scanning of 256 circles and 256 sampling points is completed together, and the scanning time is 4.66 minutes. 256 circular motions are performed through the exciting coil 101 and the receiving coil 102, 256 data acquisition points are acquired in each circular motion, 256 different alternating currents are correspondingly applied to each data acquisition point, 256 × 256 induced voltage signals are obtained in the flat plate structure 10, and image reconstruction is performed through the induced voltage signals obtained through the flat plate structure 10.

In addition, the imaging target carrying device of the embodiment of the invention can comprise an examination bed. The examining table can be provided with buttons for controlling the height and the movement of the examining table. A plurality of shielding coils are arranged in the examination bed: 15 shielding coils with the width of 10cm and the length of 30cm are arranged in the examination bed, the number of turns of the shielding coils is 200 turns, and the direct current is 30 amperes. The shielding coils are arranged in parallel along the examination bed, 2-5 shielding coils in the central area are closed during scanning, so that magnetic particles in the central area of an imaging target can be oscillated by the exciting coil 101 to generate an induced voltage signal, and the shielding coils at the other positions are opened to generate a 30mT nonlinear and non-uniform exciting magnetic field for saturation constraint of the magnetic particles in the peripheral area and avoid generation of interference signals.

Based on the above experimental conditions, the two-dimensional magnetic particle imaging system provided by the embodiment of the invention is used for image reconstruction, and the imaging effect is shown in fig. 8. Specifically, the method comprises the following steps:

in fig. 8, the upper side of fig. 8 is an original image, the left side of the lower side of fig. 8 is a schematic two-dimensional projection diagram of the original image, and the right side of the lower side of fig. 8 is a schematic two-dimensional reconstructed image obtained by reconstructing the original image by using the magnetic particle imaging system of the present invention. The imaging target adopted by the embodiment of the invention is a sample with magnetic particles distributed in a two-dimensional plane, the magnetic particles are distributed as an original image shown in the figure, a white area is an area with the magnetic particles distributed, and a black area is an area without the magnetic particles distributed. As can be seen from fig. 8, after the magnetic particle imaging method provided by the embodiment of the present invention is used for reconstruction, the two-dimensional image reconstructed by two-dimensional projection can clearly show the original magnetic particle distribution of the imaging target.

In the two-dimensional magnetic particle imaging system provided by the embodiment of the invention, the excitation coil 101 and the receiving coil 102 in the flat plate structure 10 make a spiral movement from inside to outside by taking the corresponding projection positions of the imaging target on the plane where the excitation coil and the receiving coil are located as the center, the spiral movement process comprises a plurality of data acquisition points, and the amplitude of the current applied to the excitation coil 101 in the flat plate structure 10 at each data acquisition point is gradually increased or decreased, so that a nonlinear and nonuniform excitation magnetic field is generated.

Based on the nonlinear and nonuniform excitation magnetic field, the nonlinear and nonuniform magnetic field excitation is carried out on the magnetic particles in the whole space where the imaging target is located, all the magnetic particles in the whole space can contribute to the induced voltage on the winding coil, a magnetic field free area is not required to be arranged, and the position of the magnetic field free area is not required to be changed; the excitation coil 101 and the receiving coil 102 in the flat plate structure 10 make a spiral movement from inside to outside with the projection position of the imaging target on the plane where the excitation coil 101 and the receiving coil 102 are located as the center, and different currents are applied to the excitation coil 101 in the flat plate structure 10, which is equivalent to that the excitation coil 101 and the receiving coil 102 in the flat plate structure 10 perform nonlinear and non-uniform excitation in multiple different spatial postures and multiple different magnetic field distribution states; when the exciting coil 101 and the receiving coil 102 in the flat plate structure 10 are in a certain spatial attitude, the current in the exciting coil 101 is changed, so that the magnetic field distribution can be shifted along the axial direction of the exciting coil 101, and one-dimensional spatial coding is realized; when the excitation coil 101 and the receiving coil 102 in the flat plate structure 10 are in different spatial postures, the magnetic field strength sensed by the magnetic particles at the same position is also different, so that two-dimensional full-space encoding is realized.

Based on the scanning mode, the two-dimensional magnetic particle imaging system provided by the invention can be used for magnetic particle imaging without setting a magnetic field free area; the position of the free area of the magnetic field is not required to be changed; the signal acquired each time is formed by superposing the signals generated after all the magnetic particles in the whole space are excited, and the imaging visual field is not limited by the size of a free area of a magnetic field and the moving range as in the prior art, so that the imaging visual field is not limited to small animals, such as mice, and can be matched with the size of a human body, such as a scanning visual field of 20 cm-50 cm which is usually required by human body scanning. And the coil required for constructing the gradient field and the corresponding consumed power consumption can be omitted without arranging the magnetic field free area, the equipment scale and the power consumption are reduced, and the scanning visual field of at least 50cm of the human body can be realized when the magnetic field intensity of the excitation magnetic field is 15 mT-30 mT.

In summary, the embodiments of the present invention do not use the selection field and the focusing field in the existing magnetic particle imaging technology, and each point in the entire imaging space is a free region of the magnetic field and can be excited by the magnetic field, that is, the signal acquired each time is formed by superimposing the signals of the magnetic nanoparticles at all points in the entire space. The magnetic particle concentration distribution image of the imaging target is reconstructed by carrying out space coding on the whole space and utilizing a system matrix and an image reconstruction method, so that the magnetic particle imaging with low power consumption, large visual field and high resolution is realized. The two-dimensional magnetic particle imaging system with low power consumption, large visual field and high resolution can be expanded to clinical human body scanning.

The two-dimensional magnetic particle imaging system provided by the embodiment of the invention can be applied to medical applications including but not limited to cardiovascular and cerebrovascular imaging, tumor imaging, stem cell tracking, red blood cell marking, immune cell marking, inflammatory cell monitoring and other targeted imaging. Compared with the existing blood vessel imaging technology, the embodiment of the invention does not need to perform digital subtraction when performing magnetic particle imaging, and has less motion artifacts. Compared with the existing PET and SPECT imaging technologies, the two-dimensional magnetic particle imaging system provided by the embodiment of the invention has higher sensitivity and image resolution, no ionizing radiation exists, and the production and storage of the tracer are easier.

In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples described in this specification can be combined and combined by those skilled in the art.

While the present application has been described in connection with various embodiments, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed application, from a review of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims

1. A two-dimensional magnetic particle imaging system is characterized by comprising a flat plate structure, a driving scanning unit, a magnetic field excitation unit, a data acquisition unit and a data imaging unit, wherein,

the driving scanning unit is used for driving the exciting coil and the receiving coil in the flat plate structure to spirally move from inside to outside by taking the corresponding projection positions of the imaging target on the plane where the exciting coil and the receiving coil are positioned as the center; including a plurality of data acquisition points during the helical movement;

2. A two-dimensional magnetic particle imaging system according to claim 1, wherein said plate structure is a cylindrical plate; an excitation coil and a receiving coil within the respective planar structures, comprising:

the excitation coil comprises a circular Homholtz coil;

the receiving coil comprises a circular Homholtz coil.

3. A two-dimensional magnetic particle imaging system according to claim 1, wherein the non-linear, non-uniform excitation magnetic field generated by the excitation coil is a cosine oscillating excitation magnetic field.

4. A two-dimensional magnetic particle imaging system according to claim 1, characterized in that said data imaging unit comprises a signal correction subunit, a signal feature extraction subunit, a one-dimensional data reconstruction subunit and a two-dimensional data reconstruction subunit, wherein,

5. The two-dimensional magnetic particle imaging system of claim 4 wherein the target acquisition data further comprises a signal peak area and a full width at half maximum of the signal;

6. A two-dimensional magnetic particle imaging system according to claim 5, wherein said data imaging unit further comprises a relaxation deconvolution module;

7. The two-dimensional magnetic particle imaging system of claim 4, wherein in the one-dimensional data reconstruction subunit, the one-dimensional magnetic particle concentration spatial distribution data formula of the corresponding data acquisition points is reconstructed according to the target acquisition data and the system matrix, and is represented as follows:

c＝g^-1u；

wherein the content of the first and second substances,

i₀,i₁,…,i_N+1representing N different magnitudes of current, r, applied to an excitation coil in a planar structure₀,r₁,…,r_N+1N data acquisition points representing an imaging region into which an imaging target is located; u represents the target acquisition data corresponding to each data acquisition point, element u (i)_n) Indicating that a current i is applied to the exciting coil_nTarget acquisition data acquired in real time; g denotes a system matrix, of known quantity, the element g (i)_n,r_n) Magnetic particles representing unit concentration upon application of a current i_nTime-corresponding non-linear, non-uniform excitation magnetic fieldUnder the action of the signal, the target acquisition data of the generated signal is distributed on the r-th of the imaging area_nComponents of data acquisition points; c represents the reconstructed one-dimensional magnetic particle concentration spatial distribution data, and each element contained in the data is the magnetic particle concentration of each data acquisition point in the imaging region, and the element c (r)_n) Representing the r-th in the imaging area_nMagnetic particle concentration for each data acquisition spot.

8. The two-dimensional magnetic particle imaging system of claim 4, wherein in the two-dimensional data reconstruction subunit, the mathematical principle based on which the two-dimensional magnetic particle concentration spatial distribution data of the imaging target is reconstructed by using a filtered back projection method is Radon transform.

9. A two-dimensional magnetic particle imaging system according to claim 1, further comprising an imaging target carrying means for carrying said imaging target;

10. A two-dimensional magnetic particle imaging system according to claim 1, characterized in that the corresponding scan field of view amounts to 50cm at a field strength of the excitation magnetic field of 15 mT-30 mT.