CN114601442A - Two-dimensional magnetic particle imaging method - Google Patents

Abstract

The invention discloses a two-dimensional magnetic particle imaging method, which comprises the following steps: generating a nonlinear and non-uniform excitation magnetic field by utilizing a flat plate structure with an internal excitation coil and a receiving coil according to a preset excitation magnetic field adjustment strategy; the excitation magnetic field adjustment strategy comprises the position adjustment of an excitation coil and a receiving coil in the flat plate structure and the adjustment of current applied to the excitation coil in the flat plate structure; acquiring an induced voltage signal generated by a receiving coil under the action of a nonlinear and nonuniform excitation magnetic field of an imaging target; the imaging target carries magnetic particles; according to the induced voltage signal and the system matrix, carrying out image reconstruction on the concentration distribution of the magnetic particles in the imaging target; the system matrix is used for representing the spatial distribution corresponding to target acquisition data generated by magnetic particles with unit concentration under the action of an excitation magnetic field; the target acquisition data includes a spike amplitude and/or 3 fundamental harmonic components of the signal. The particle imaging method can be extended to clinical human body scanning imaging.

Description

Two-dimensional magnetic particle imaging method

Technical Field

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

Background

Medical imaging and image processing play an extremely important role in the fields of application such as medical diagnosis, life science research, clinical treatment, and the like. Magnetic nanoparticle Imaging (MPI) is a brand new medical Imaging technology, and the technology completes the spatial distribution Imaging of Particle concentration by detecting the response of Super Paramagnetic Iron Oxide nanoparticles (SPIO) to an external Magnetic field, has the advantages of safety, no radiation, high contrast, high resolution, high sensitivity, quantitative detection and the like, and has wide application prospects in various medical fields of angiography, cell tracking and the like.

In the existing two-dimensional magnetic particle imaging method, a magnetic field free area is generated by a selection field, the free area is moved by a focusing field, magnetic particles in the free area 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 change in position of the free region of the magnetic field requires the use of a focusing or excitation field, or 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 conventional two-dimensional magnetic particle imaging method, a selection field and a focusing field are constructed, a magnetic field free region (point or line) is formed in the middle of the selection field, and the magnetic field free region is moved in the focusing field, so that the image resolution is improved by requiring a sufficiently small magnetic field free point and a sufficiently thin magnetic field free line, and a large power consumption device is required to generate a sufficiently large current. To meet the requirement of magnetic particle imaging of human body size, a strong selection field and excitation field are required, resulting in large power consumption, which is difficult to implement and difficult to extend to clinical human body scanning.

Disclosure of Invention

In order to solve the above problems in the prior art, the present invention provides a two-dimensional magnetic particle imaging method. 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 method, which comprises the following steps:

generating a nonlinear and non-uniform excitation magnetic field by utilizing a flat plate structure with an internal excitation coil and a receiving coil according to a preset excitation magnetic field adjustment strategy; the excitation magnetic field adjustment strategy comprises position adjustment of an excitation coil and a receiving coil in the flat plate structure and adjustment of current application of the excitation coil in the flat plate structure;

acquiring an induced voltage signal generated by the receiving coil under the action of a nonlinear and nonuniform excitation magnetic field of an imaging target; the imaging target carries magnetic particles;

according to the induced voltage signal and the system matrix, carrying out image reconstruction on the concentration distribution of the magnetic particles in the imaging target; the system matrix is used for representing the corresponding spatial distribution of induced voltage signals generated by magnetic particles with unit concentration under the action of the nonlinear and nonuniform excitation magnetic field; the target acquisition data includes a spike amplitude and/or a 3-fold fundamental harmonic component of a signal extracted from the induced voltage signal.

The invention has the beneficial effects that:

according to the two-dimensional magnetic particle imaging method, nonlinear and non-uniform magnetic field excitation is carried out on magnetic particles in the whole space where an imaging target is located, all the magnetic particles in the whole space can contribute to induced voltage on a winding coil, a magnetic field free area does not need to be arranged, and the position of the magnetic field free area does not need to be changed; the position adjustment of an exciting coil and a receiving coil in the flat plate structure and the adjustment of current application to the exciting coil in the flat plate structure are equivalent to the nonlinear and non-uniform excitation of the exciting coil and the receiving coil in the flat plate structure in various different spatial postures and various different magnetic field distribution states; when the exciting coil and the receiving coil in the flat plate structure are in a certain space attitude, the current applied by the exciting coil in the flat plate structure is changed, so that the magnetic field distribution can generate position deviation 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 magnetic field excitation mode, when the two-dimensional magnetic particle imaging method provided by the embodiment of the invention is used for magnetic particle imaging, a magnetic field free area does not need to be arranged; the position of the free area of the magnetic field is not required to be changed; the induction voltage signal acquired each time is formed by superposing signals generated after all magnetic particles in the whole space are excited, 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 for imaging, and the imaging visual field 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 adopted excitation magnetic field is 15 mT-30 mT.

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 method 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 schematic flow chart of a two-dimensional magnetic particle imaging method according to an embodiment of the present invention;

FIG. 2 is a diagram illustrating the magnetic field distribution in conventional magnetic particle imaging;

FIGS. 3(a) -3 (c) are schematic structural diagrams of a flat plate structure provided by an embodiment of the present invention;

FIG. 4 is a schematic flow chart of an image reconstruction process in a two-dimensional magnetic particle imaging method according to an embodiment of the present invention;

FIG. 5 is a flow chart of another image reconstruction process in a two-dimensional magnetic particle imaging method according to an embodiment of the present invention;

FIG. 6 is a flow chart of a further image reconstruction process in a two-dimensional magnetic particle imaging method according to an embodiment of the present invention;

FIG. 7 is a schematic flow chart illustrating a further image reconstruction process in a two-dimensional magnetic particle imaging method according to an embodiment of the present invention;

FIG. 8 is a schematic structural diagram of an imaging target carrying device in a two-dimensional magnetic particle imaging method according to an embodiment of the present invention;

fig. 9(a) to 9(b) are schematic diagrams illustrating the reconstruction effect of the two-dimensional magnetic particle density space obtained by reconstructing two original images by using the two-dimensional magnetic particle imaging method according to the embodiment of the present invention.

Description of reference numerals:

10-plate; 20-an excitation coil; 30-a receiving coil; 40-fixing the support.

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 problem that the conventional two-dimensional magnetic particle imaging method is difficult to expand to clinical human body scanning due to large power consumption, referring to fig. 1, an embodiment of the invention provides a two-dimensional magnetic particle imaging method, which comprises the following steps:

s10, generating a nonlinear and non-uniform excitation magnetic field according to a preset excitation magnetic field adjustment strategy by utilizing a flat plate structure with the built-in excitation coil 20 and the built-in receiving coil 30; the excitation field adjustment strategy includes adjustment of the position of the excitation coil 20 and the receiving coil 30 within the flat plate structure, and adjustment of the application of current to the excitation coil 20 within the flat plate structure.

Specifically, referring to fig. 2, the conventional two-dimensional magnetic particle imaging method forms a free magnetic field region (point or line) in the middle of a selection field by constructing the selection field and a focusing field, and moves the free magnetic field region by changing the magnitude of the focusing field, so as to implement, 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 embodiments of the present invention provide several alternatives for generating a nonlinear and nonuniform excitation magnetic field by using a flat plate structure, and any point in space is used as a free magnetic field area without constructing a selection field and a focusing field, so that an induced voltage signal can be generated under the excitation of the generated nonlinear and nonuniform excitation magnetic field.

Next, several proposed alternatives for generating a non-linear, non-uniform excitation magnetic field with a flat plate structure will be described in detail.

An alternative is provided in the embodiments of the present invention, please refer to fig. 3(a), the flat plate structure includes a flat plate 10, the flat plate 10 is opposite to the imaging target, specifically, the flat plate 10 is located right above the imaging target as shown in fig. 3 (a); the flat plate 10 has an exciting coil 20 and a receiving coil 30 built therein, the receiving coil 30 is opposed to a target position, and the exciting coil 20 is opposed to the receiving coil 30. The exciting coil 20 is used for generating various nonlinear and nonuniform exciting magnetic fields, and the receiving coil 30 is used for receiving the magnetic flux change caused by the magnetization response of the magnetic nanoparticles under the action of the nonlinear and nonuniform exciting magnetic fields and generating corresponding induced voltage signals for magnetic particle imaging. As shown in fig. 3(a), the plate 10 may be a cylindrical plate, and the excitation coil 20 and the receiving coil 30 in the plate 10 include a circular helmholtz coil, respectively.

Corresponding to the flat-plate structure shown in fig. 3(a), the embodiment of the present invention generates a non-linear, non-uniform excitation magnetic field according to a preset excitation magnetic field adjustment strategy, which includes:

the position adjustment of the exciting coil 20 and the receiving coil 30 in the flat plate structure comprises the following steps:

adjusting the exciting coil 20 and the receiving coil 30 in the flat plate 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 20 and the receiving coil 30 are located as centers;

the adjustment of the applied current to the excitation coil 20 in the flat structure comprises:

the amplitude of the co-current applied to the excitation coil 20 in the plate 10 is adjusted. Preferably, the manner of adjusting the amplitude of the cocurrent alternating current applied by the excitation coil 20 in the flat plate 10 includes: the amplitude of the co-current applied to the excitation coil 20 in the plate 10 is gradually increased or decreased.

Another alternative is provided in the embodiment of the present invention, please refer to fig. 3(b), the flat plate structure includes a flat plate 10, the flat plate 10 is opposite to the imaging target, specifically, the flat plate 10 is located right below the imaging target as shown in fig. 3 (b); the flat plate 10 has an exciting coil 20 and a receiving coil 30 built therein, the receiving coil 30 is opposed to a target position, and the exciting coil 20 is opposed to the receiving coil 30. The exciting coil 20 is used for generating various nonlinear and nonuniform exciting magnetic fields, and the receiving coil 30 is used for receiving the magnetic flux change caused by the magnetization response of the magnetic nanoparticles under the action of the nonlinear and nonuniform exciting magnetic fields and generating corresponding induced voltage signals for magnetic particle imaging. As shown in fig. 3(b), the plate 10 may be a cylindrical plate, and the excitation coil 20 and the receiving coil 30 in the plate 10 include a circular helmholtz coil, respectively.

Corresponding to the flat-plate structure shown in fig. 3(b), the embodiment of the present invention generates a non-linear, non-uniform excitation magnetic field according to a preset excitation magnetic field adjusting strategy, which includes:

the position adjustment of the exciting coil 20 and the receiving coil 30 in the flat plate structure comprises the following steps:

adjusting the exciting coil 20 and the receiving coil 30 in the flat plate 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 20 and the receiving coil 30 are located as centers;

the adjustment of the applied current to the excitation coil 20 in the flat plate structure includes:

the amplitude of the co-current applied to the excitation coil 20 in the plate 10 is adjusted. Preferably, the manner of adjusting the amplitude of the cocurrent alternating current applied by the excitation coil 20 in the flat plate 10 includes: the amplitude of the co-current applied to the excitation coil 20 in the plate 10 is gradually increased or decreased.

For the flat plate structure shown in fig. 3(a) and 3(b), a plurality of nonlinear and non-uniform excitation magnetic fields can be generated, and a plurality of induced voltage signals are generated under the action of different nonlinear and non-uniform excitation magnetic fields. In the process of generating the signal, due to the exciting coil 20 and the receiving coil 30 in the flat plate 10, the imaging target makes a spiral movement from inside to outside with the projection position of the plane where the exciting coil 20 and the receiving coil 30 are corresponding as the center, and each movement is equivalent to the adjustment of the spatial postures of the exciting coil 20 and the receiving coil 30. The spiral movement may be clockwise inside-out spiral movement or counterclockwise inside-out spiral movement. The spiral movement process includes a plurality of data acquisition points, for example, when a certain point is taken as a starting point, one turn of the clockwise spiral is performed, that is, the ending point is opposite to the starting point, so that the spiral movement performs a circular movement 256 times, and 256 data acquisition points are formed in each circular movement, so that the flat plate 10 can form 256 × 256 data acquisition points, and different nonlinear and nonuniform excitation magnetic fields are applied to each data acquisition point.

Applying a co-directional alternating current to the excitation coil 20 in the plate 10 one or more times at each data acquisition point in each circular motion to generate a non-linear, non-uniform excitation magnetic field; the amplitude of the current applied to the excitation coil 20 in the plate 10 is preferably increased or decreased stepwise each time. When the exciting coil 20 and the receiving coil 30 in the flat plate 10 are in a certain spatial attitude and alternating current with the equidirectional current amplitude gradually increasing or decreasing is applied to the exciting coil 20 for each data acquisition point, the exciting magnetic field generated by the exciting coil 20 in the flat plate 10 is in a linearly decreasing distribution state, so that the magnetic field distribution is subjected to position shift along the axial direction of the exciting coil 20, and one-dimensional spatial coding can be realized; when the excitation coil 20 and the receiving coil 30 in the flat panel 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 example, the excitation coil 20 and the receiving coil 30 in the flat plate 10 make 256 circular motions, each circular motion includes 256 data acquisition points, and 256 different equidirectional alternating currents are applied to each data acquisition point, so that the excitation coil 20 in the flat plate 10 generates 256 × 256 nonlinear and non-uniform excitation magnetic fields, and generates 256 × 256 induced voltage signals under the action of each excitation magnetic field. 256 x 256 induced voltage signals generated by the receiving coils 30 in the plate 10 are used for image reconstruction. Preferably, the current applied to the excitation coil 20 in the flat plate 10 is an alternating current oscillating in cosine, but is not limited to an alternating current oscillating in cosine.

An alternative is provided by embodiments of the present invention, referring to fig. 3(c), where the flat plate structure includes two flat plates 10, and the imaging target is located between the two flat plates 10; an exciting coil 20 and a receiving coil 30 are respectively arranged in the two flat plates 10; the excitation coil 20 and the receiving coil 30 in the two flat plates 10 are opposite, and the two receiving coils 30 are opposite. In the embodiment of the present invention, the position of the two flat plates 10 can be fixed by a fixing support 40, as shown in fig. 3(c), but the fixing is not limited to be fixed by the fixing support 40, and is not limited to be fixedly arranged, and the position of the two flat plates 10 in the horizontal or vertical direction can also be adjusted by a mechanical control manner.

Corresponding to the slab structure shown in fig. 3(c), the embodiment of the present invention generates a non-linear, non-uniform excitation magnetic field according to a preset excitation shimming strategy, which includes:

the position adjustment of the exciting coil 20 and the receiving coil 30 in the flat plate structure comprises the following steps:

adjusting the exciting coil 20 and the receiving coil 30 in the two flat plates 10 respectively, and performing spiral movement from inside to outside by taking the corresponding projection positions of the imaging target on the plane where the exciting coil 20 and the receiving coil 30 are located as centers; the direction of the helical movement of the excitation coil 20 and the receiving coil 30 in the two plates 10 is opposite.

The adjustment of the applied current to the excitation coil 20 in the flat plate structure includes:

respectively adjusting the amplitude of the equidirectional alternating current applied by the exciting coils 20 in the two flat plates 10; the amplitude adjustment directions of the equidirectional alternating currents applied by the exciting coils 20 in the two flat plates 10 are opposite. Preferably, the way of adjusting the amplitude of the cocurrent alternating current applied by the excitation coils 20 in the two flat plates 10 respectively includes: the magnitude of the current applied to the excitation coil 20 in one plate 10 is increased or decreased in steps, and the magnitude of the current applied to the excitation coil 20 in the other plate 10 is decreased or increased in steps.

For the flat plate structure shown in fig. 3(c), a plurality of non-linear and non-uniform excitation magnetic fields can be generated, and a plurality of induced voltage signals can be generated under the action of different excitation magnetic fields. In the process of generating the signals, the exciting coil 20 and the receiving coil 30 in the two flat plates 10 also make a spiral movement from inside to outside by taking the projection position of the imaging target on the plane where the exciting coil 20 and the receiving coil 30 are located as the center, and each movement is equivalent to the adjustment of the spatial postures of the exciting coil 20 and the receiving coil 30. Each movement corresponds to the opposite direction of the spiral movement of the two plates 10, for example, the exciting coil 20 and the receiving coil 30 in one plate 10 make a spiral movement from inside to outside counterclockwise, and the exciting coil 20 and the receiving coil 30 in the other plate 10 make a spiral movement from inside to outside clockwise. In the spiral moving process, a plurality of data acquisition points are included, for example, when a certain point is taken as a starting point, a clockwise spiral turns for one circle, that is, the end point is opposite to the starting point, one circular motion is completed, each circular motion process includes a plurality of data acquisition points, each flat plate 10 makes 256 circular motions, and 256 data acquisition points are formed in each circular motion, so that each flat plate 10 can form 256 × 256 data acquisition points, and each data acquisition point is acted on by a different nonlinear and non-uniform excitation magnetic field.

At each data acquisition point in each circular motion, applying the same-direction alternating current to the excitation coils 20 in the two flat plates 10 one or more times respectively generates a nonlinear, non-uniform excitation magnetic field, and adjusting the amplitude of the same-direction alternating current applied by the excitation coils 20 in the two flat plates 10 in opposite directions, for example, the amplitude of the current applied by the excitation coil 20 in one flat plate 10 is increased or decreased step by step, and the amplitude of the current applied by the excitation coil 20 in the other flat plate 10 is correspondingly decreased or increased step by step each time. When the exciting coil 20 and the receiving coil 30 in the two flat plates 10 are in a certain spatial attitude, and for each data acquisition point, an alternating current with the amplitude of the current in the same direction gradually increasing or decreasing is applied to the exciting coil 20 in one flat plate 10, and an alternating current with the amplitude of the current in the same direction gradually decreasing or increasing is applied to the exciting coil 20 in the other flat plate 10, the axial component of the exciting magnetic field generated between the exciting coils 20 in the two flat plates 10 will present a V-shaped distribution state in which the current linearly decreases first and then linearly increases second, or will present an a V-shaped distribution state in which the current linearly increases first and then linearly decreases second, and then the V-shaped distribution and the V-shaped distribution are collectively referred to as a V-shaped distribution, so that the magnetic field distribution is subjected to positional deviation along the axial direction of the exciting coil 20, thereby realizing one-dimensional spatial encoding; when the excitation coil 20 and the receiving coil 30 in the flat panel 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. Preferably, the current applied to the excitation coil 20 in the flat plate 10 is an alternating current oscillating in cosine, but is not limited to an alternating current oscillating in cosine.

At this time, since the curve of the magnetic field intensity with the applied magnetic field is a symmetric curve, only a half period of scanning is required. For example, the alternating current applied in the embodiment of the present invention is an alternating current oscillating in cosine, and the current amplitude goes through half period of cosine oscillation every time the current amplitude is adjusted. It is understood that the cosine oscillation period as referred to herein refers to the oscillation period of the cosine alternating current, and accordingly, the current amplitude refers to the maximum value of the alternating current within the oscillation period.

And, each plane perpendicular to the axial direction of the exciting coil 20 is one constant magnetic field plane. Furthermore, by increasing or decreasing the current of the excitation coil 20 in one plate 10 and simultaneously decreasing or increasing the current of the excitation coil 20 in the other plate 10, the "V" shaped magnetic field distribution causes a positional shift in the axial direction of the excitation coil 20, thereby realizing one-dimensional to two-dimensional spatial encoding.

Meanwhile, for each data acquisition point, the embodiment of the present invention applies the same-directional alternating current to the excitation coils 20 in the two plates 10 one or more times to generate the nonlinear and non-uniform excitation magnetic field, for example, the excitation coils 20 and the receiving coils 30 in the plates 10 make 256 circular motions, each circular motion includes 256 data acquisition points, and 256 different same-directional alternating currents are applied to each data acquisition point, so that the excitation coils 20 in the two plates 10 will generate 256 × 256 nonlinear and non-uniform excitation magnetic fields, respectively, and generate 256 × 256 induced voltage signals under the action of each excitation magnetic field. 256 × 256 induced voltage signals generated by the two plates 10 are used for image reconstruction.

Compared with the existing magnetic particle imaging technology, the embodiment of the invention can realize the nonlinear and nonuniform magnetic field excitation of the magnetic particles in the whole space where the imaging target is located only by adopting the magnetic field excitation mode formed by the flat plate structure provided by the embodiment of the invention at a certain position or certain positions relative to the imaging target without arranging a magnetic field free area.

S20, acquiring an induced voltage signal generated by the coil 30 under the action of a nonlinear and nonuniform excitation magnetic field of an imaging target; the imaging target carries magnetic particles.

Specifically, under the action of the nonlinear and non-uniform excitation magnetic field generated by any scheme of S10, all magnetic particles in the whole space are excited, and signals generated after excitation are superimposed to form an induced voltage signal generated by the receiving coil 30. The induced voltage signal is a signal after analog-to-digital conversion processing, and the analog-to-digital conversion processing 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 30 in sequence; the digital signal processing part comprises the steps of carrying out Fourier transform processing, spectrum analysis processing and fundamental frequency reduction processing on the signals output by the analog signal processing part in sequence to finish the analog-to-digital conversion processing of the final signal processing subunit. 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.

S30, reconstructing the image of the concentration distribution of the magnetic particles in the imaging target according to the induced voltage signal and the system matrix; the system matrix is used for representing the corresponding spatial distribution of induced voltage signals generated by magnetic particles with unit concentration under the action of a nonlinear and nonuniform excitation magnetic field; the target acquisition data is the peak amplitude and/or 3 times fundamental frequency harmonic component of the signal extracted from the induced voltage signal.

Specifically, a plurality of data acquisition points are included in the adjustment process of the excitation coil 20 and the reception coil 30 within the flat plate structure; correspondingly, according to the induced voltage signal and the system matrix, the image reconstruction is performed on the concentration distribution of the magnetic particles in the imaging target, referring to fig. 4, including the following steps:

s301, aiming at each data acquisition point, corresponding target acquisition data is extracted from the induced voltage signal.

Specifically, before image reconstruction, the method provided by the invention firstly extracts corresponding target acquisition data from the induced voltage signal for each data acquisition point for image reconstruction. Preferably the target acquisition data comprises the peak amplitude or 3 fundamental harmonic components of the signal.

The peak amplitude or 3 times fundamental frequency harmonic component of the preferred signal in the embodiment of the invention is used for image reconstruction, and the theoretical basis for realizing magnetic particle imaging based on the peak amplitude or 3 times fundamental frequency harmonic component of the signal is as follows: 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 applying an alternating current whose current is cosine oscillation to the excitation coil 20 in the flat plate 10, the inventor found that, by using the excitation magnetic field h (t) ═ Acos (2 pi ft) corresponding to the cosine oscillation alternating current, the signal peak u generated by the magnetic particles under the excitation thereof_peak3 times fundamental frequency harmonic component u in proportion to the intensity A of the exciting magnetic field and in proportion to the concentration c of 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 represents 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), for each data acquisition point receiver coil 30_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.

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 nonuniform excitation magnetic field, the r-th magnetic field is generated in the imaging region_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 each data acquisition point receiver coil 30_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 reconstructing a one-dimensional image, and the peak amplitude and the 3 times fundamental frequency harmonic component of the signal can be selected to be used for reconstructing the one-dimensional image together.

S302, performing corresponding one-dimensional image reconstruction on the concentration distribution of the magnetic particles in the imaging target according to the target acquisition data and the system matrix.

Specifically, according to the target acquisition data and the system matrix, the one-dimensional magnetic particle concentration spatial distribution of each data acquisition point is reconstructed. 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 present invention, the peak amplitude and/or 3 times fundamental frequency harmonic component of the signal related to the magnetic particle concentration c are preferably used for image reconstruction, and the image 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 the excitation coils 20 in the two plates 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 20_kThe meaning of the rest elements is analogized by the data acquired by the acquired target. Because the target acquisition data of the embodiment of the invention comprises the peak amplitude and/or 3 times fundamental frequency harmonic component of the signal, when the peak amplitude of the signal is adopted for reconstruction in the corresponding one-dimensional image reconstruction, u (i) is used_n) The value is u corresponding to 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, of known quantity, where g (i)_n,r_n) Magnetic particles representing unit concentrationAt the 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, which contains elements of magnetic particle concentration at each data acquisition point in the imaging region, where 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 inverted^-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, in the existing Magnetic Particle Imaging (MPI) method, a system matrix is also used for Magnetic Particle Imaging, but the method is different from the system matrix proposed in the embodiment of the present invention: the existing magnetic particle imaging system adopts a system matrix in which each element includes a set of fourier components of a signal generated by a magnetic particle sample with a known concentration at a certain data acquisition point in an imaging region, 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 and/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 a system matrix adopted by the existing MPI system.

In order to further improve the magnetic particle imaging accuracy, the embodiment of the present invention corrects the induced voltage signal acquired in S20 before image reconstruction. The inventor finds that, in the process of implementing the present invention, the induced voltage signals can be corrected by using the information of the peak area and the full width at half maximum of the signal included in the target collected data, and specifically, the corresponding target collected data extracted from each induced voltage signal can be corrected.

The embodiment of the invention provides an alternative scheme, when the target acquisition data further comprises the signal peak area and the full width at half maximum of the signal; referring to fig. 5, S302, according to the target acquisition data and the system matrix, performing corresponding one-dimensional image reconstruction on the concentration distribution of the magnetic particles in the imaging target, may include the following steps:

and S3021, correcting the peak amplitude and the full width at half maximum of the signal in the target acquisition data by using the signal peak area of the signal.

Specifically, the inventors analyzed that the signal peak area of the signal is independent of the magnetic field strength and is proportional to the magnetic particle concentration. 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 signal peak area on each data acquisition point is actually a conservative amount, 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 an actual imaging target is constant in a short time and may change in a long time, the embodiment of the invention corrects the peak amplitude and the full width at half maximum of a signal in target acquisition data according to the peak area of the signal by taking a data acquisition point as a unit, 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 20 may be reapplied with a current corresponding to the signal, so as to perform the acquisition again; or correct the abnormal signal by using signals adjacent to the acquisition time, and the like.

And S3022, performing corresponding one-dimensional image reconstruction on the concentration distribution of the magnetic particles in the imaging target according to the corrected target acquisition data and the system matrix.

Specifically, formula (3) is adopted, and the corrected target acquisition data and the system matrix are utilized to realize one-dimensional image reconstruction of the concentration distribution of the magnetic particles in the imaging target.

The embodiment of the invention provides another alternative, when the target acquisition data further comprises the signal peak area and the full width at half maximum of the signal; referring to fig. 6, S302 performs corresponding one-dimensional image reconstruction on the concentration distribution of the magnetic particles in the imaging target according to the target acquisition data and the system matrix, and may also include the following steps:

s302-1, correcting the peak amplitude and the full width at half maximum of the signal in the target acquisition data by using the signal peak area and/or the full width at half maximum of the signal.

Specifically, the correction of the peak amplitude and the full width at half maximum of the signal in the target acquisition data by the signal peak area of the signal is similar to the S3021 process, and is not described herein again.

When the target acquisition data also includes the full width at half maximum of the signal, the inventors have discovered in the course of practicing the invention that the full width at half maximum of the signal is independent of the magnetic particle concentration, but has an inverse relationship 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. Considering that the comparison efficiency of the full width at half maximum of the signals collected in the whole scanning process is lower, the embodiment of the invention adopts a scheme of comparing the full width at half maximum by taking the data collection points as units, and particularly, on each data collection point, the signals are collected once when the current amplitude is converted every time, and the full width at half maximum of the signals 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. The correction of the signal in which the full width at half maximum of the signal is abnormal can be carried out in various ways. For example, the excitation coil 20 may be applied with a current corresponding to the signal again, so as to perform the acquisition again; or correct the abnormal signal by using signals adjacent to the acquisition time, and the like.

S302-2, correcting the nonlinear and non-uniform excitation magnetic field by using the full width at half maximum of the signal.

Specifically, the full width at half maximum of the anomaly is found using S302-1, thereby finding the anomaly that may occur in the intangible magnetic field. For the found abnormal magnetic field condition, the position of the exciting coil 20 is corrected to ensure the accurate change of the exciting magnetic field, and then the corrected target acquisition data is obtained under the action of the corrected exciting magnetic field, so that the peak amplitude and the full width at half maximum of the signal in the target acquisition data are corrected, and the finally extracted target acquisition data can be better and more accurate.

S302-3, correcting the system matrix by using the corrected nonlinear and nonuniform excitation magnetic field; the corrected system matrix is used for representing the spatial distribution corresponding to the target acquisition data of the signals generated by the magnetic particles with unit concentration under the action of the corrected nonlinear and nonuniform excitation magnetic field.

Specifically, the system matrix in the embodiment of the present invention is a 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, which is obtained in advance through experiments, and when a 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, and one-dimensional image reconstruction is performed according to the corrected system matrix, so that the accuracy of image reconstruction can be improved.

S302-4, performing corresponding one-dimensional image reconstruction on the concentration distribution of the magnetic particles in the imaging target according to the corrected target acquisition data and the corrected system matrix.

Specifically, formula (3) is adopted, and the corrected target acquisition data and the corrected system matrix are used for realizing one-dimensional image reconstruction of the concentration distribution of the magnetic particles in the imaging target.

Another alternative is provided in the embodiment of the present invention, please refer to fig. 7, after S3023, the following steps may also be performed:

s302-5, carrying out deconvolution correction processing on the corrected target acquisition data by using the corrected nonlinear and nonuniform excitation magnetic field.

In particular, in image reconstruction, signal degradation is typically caused by relaxation effects. The embodiment of the invention reduces the signal deformation caused by the relaxation effect of magnetic particles by carrying out deconvolution processing on the target collected data, wherein the specific deformation mainly comprises the reduction of the signal amplitude, the broadening of a time domain, asymmetry and the like. Through deconvolution operation, target collected data can be corrected, signal deterioration caused by relaxation effect is reduced, and finally extracted target features can be better and more accurate.

After the correction processing based on deconvolution, the corresponding S302-4 is updated to be S302-6:

s302-6, performing corresponding one-dimensional image reconstruction on the concentration distribution of the magnetic particles in the imaging target according to the target acquisition data after the deconvolution correction processing and the corrected system matrix.

Specifically, formula (3) is adopted, and the target acquisition data after the deconvolution correction processing and the corrected system matrix are used for realizing the one-dimensional image reconstruction of the concentration distribution of the magnetic particles in the imaging target.

In practical applications, large size (30 nm-100 nm) magnetic particles are more prone to relaxation effects, so that 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.

S302, performing corresponding two-dimensional image reconstruction on the result of the one-dimensional image reconstruction by using a filtering back projection method.

Specifically, the embodiment of the invention reconstructs the two-dimensional magnetic particle concentration spatial distribution of the imaging target by utilizing a filtering back projection method for the one-dimensional image reconstruction result of each data acquisition point. Among them, the filtered back-projection reconstruction method is commonly used in CT imaging reconstruction, and the mathematical principle behind it 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.

It should be noted that, in the embodiment of the present invention, the reconstructed images of the one-dimensional image reconstruction and the two-dimensional image reconstruction are both the spatial distribution of the magnetic particle concentration in one dimension or two dimensions.

When the two-dimensional magnetic particle imaging method provided by the embodiment of the invention simultaneously utilizes the peak amplitude and the 3-time fundamental frequency harmonic component for imaging, the peak amplitude and the 3-time fundamental frequency harmonic component are respectively utilized for imaging, 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.

Further, referring to fig. 8, the two-dimensional magnetic particle imaging method according to the embodiment of the invention further includes generating a shielding magnetic field by using the shielding coil to saturate magnetic particles existing in the region outside the imaging region.

Specifically, the shielding coil is arranged in the imaging target bearing device and is parallel to a plurality of rectangular shielding coils; when the two-dimensional magnetic particle imaging method works, the shielding coils corresponding to the upper part and the lower part of the position of an imaging target are closed, and the rest shielding coils are electrified and opened. As shown in fig. 8, the thickened coil is a central region shielding coil corresponding to the imaging target, 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 saturation-confine magnetic particles present in a region other than the non-imaging region, so that only the magnetic particles located in the imaging region are excited by the exciting coil 20. For example, when the two-dimensional magnetic particle imaging method is used for scanning and imaging a human body, the imaging target carrying device can be an examination bed. In addition, when the two-dimensional magnetic particle imaging method is used for scanning and imaging an imaging target with an 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 method proposed by the embodiment of the present invention, the following experiment is performed with the flat plate structure shown in fig. 3 (c).

The exciting coils 20 in the two flat plates 10 are composed of a circular Homholtz coil, the diameter of each exciting coil 20 is 40cm, the thickness and the width are both 5cm, the number of turns of the exciting coil 20 is 200 turns, the distance between the two exciting coils 20 is 50cm, 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 3.0 KHz-35 KHz, the applied cosine alternating current is 20A-40A, the magnetic field of the 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 the central area of the imaging target is less than 5 percent, and the constant magnetic field plane is ensured to be a plane and not a curved surface. The current change times of the excitation coil 20 of each data acquisition point are 256, and the current of the excitation coil 20 in one flat plate 10 is increased from 20A to 256 times, wherein the current is increased by 0.78A each time till 40A; the current of the excitation coil 20 in the other plate 10 is reduced from 40A by 0.78A for a total of 256 times to 20A, so that the shape and position of the "V" shaped magnetic field are changed 256 times independently. The shape and position of the V-shaped 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 the shape and position change of the V-shaped magnetic field is completed 256 times, 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 excitation coil 20.

The receiving coils 30 in the two plates 10 consist of a circular helmholtz coil, each receiving coil 30 having a diameter of 40cm and a thickness and width of 5 cm. The two receiver coils 30 are spaced apart by 40cm and abut against the non-uniform exciter coil 20 in the axial direction in the two plates 10.

One flat plate 10 is a cylindrical flat plate 10, the diameter of the flat plate 10 is 120cm, the thickness of the flat plate 10 is 40cm, in the process of acquiring an induced voltage signal, an excitation coil 20 and a receiving coil 30 in the flat plate 10 perform circular motion by taking the projection position of an imaging target corresponding to the plane where the excitation coil 20 and the receiving coil 30 are located as a central point, counterclockwise spiral movement is performed from inside to outside, scanning of 256 data acquisition points with 256 circles is completed, and the scanning time is 4.66 minutes; similarly, the other flat plate 10 is a cylindrical flat plate 10, the diameter of the flat plate 10 is 120cm, the thickness of the flat plate 10 is 100cm, the excitation coil 20 and the receiving coil 30 in the flat plate 10 perform circular motion by taking the projection position of the imaging target on the plane where the excitation coil 20 and the receiving coil 30 are located as the center point, and perform clockwise spiral motion from inside to outside, that is, the excitation coils in the two flat plates 10 perform opposite direction and opposite position motions, so as to jointly complete the scanning of 256 sampling points at circumference, and the scanning time is 4.66 minutes. 256 circular motions are performed through the exciting coil 20 and the receiving coil 30, 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 respectively obtained on the two flat plates 10, and image reconstruction is performed through the induced voltage signals obtained by the two flat plates 10.

In addition, the imaging target carrying device of the embodiment of the invention can comprise an examination bed, and the examination bed can be provided with buttons for controlling the height and the movement of the examination bed. 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 20 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 to avoid generation of interference signals.

Based on the above experimental conditions, the two-dimensional magnetic particle imaging method proposed by the embodiment of the present invention is used for image reconstruction on two original images, and the imaging effect is shown in fig. 9(a) to 9(b), specifically:

in fig. 9(a), the upper side of fig. 9(a) is a first original image, the left side of the lower side of fig. 9(a) is a schematic two-dimensional projection diagram of the first original image, and the right side of the lower side of fig. 9(a) is a schematic two-dimensional reconstructed image obtained by performing image reconstruction on the first original image by using the magnetic particle imaging method 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. 9(a), 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 fig. 9(b), the upper side of fig. 9(b) is a second original image, the left side of the lower side of fig. 9(b) is a schematic two-dimensional projection diagram of the second original image, and the right side of the lower side of fig. 9(b) is a schematic two-dimensional reconstructed image obtained by performing image reconstruction on the second original image by using the magnetic particle imaging method of the present invention. The imaging target adopted by the embodiment of the invention is the head of a patient, and the original image is the magnetic resonance imaging of the head of the patient shot by using a magnetic resonance device; as can be seen from fig. 9(b), the mri includes images of other tissues inside the cranium, which are superimposed with the images of the vascular tissues; in contrast, in the two-dimensional image reconstructed by the magnetic particle imaging apparatus according to the two-dimensional projection provided by the embodiment of the present invention, only the vascular tissue with the magnetic particle distribution is shown.

Similarly, the plate structures shown in fig. 3(a) to 3(b) are adopted, and based on the experimental conditions similar to the plate structure shown in fig. 3(c), the magnetic particle imaging effects shown in fig. 9(a) to 9(b) can also be achieved, which are not described again here.

In the two-dimensional magnetic particle imaging method provided by the embodiment of the invention, nonlinear and non-uniform magnetic field excitation is performed on 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 receiving coil 30, and a magnetic field free area does not need to be arranged or the position of the magnetic field free area does not need to be changed; the position adjustment of the exciting coil 20 and the receiving coil 30 in the flat plate structure and the adjustment of the current applied to the exciting coil 20 in the flat plate structure are equivalent to the nonlinear and non-uniform excitation of the exciting coil 20 and the receiving coil 30 in the flat plate structure in various different spatial postures and various different magnetic field distribution states; when the exciting coil 20 and the receiving coil 30 in the flat plate structure are in a certain spatial attitude, the current applied by the exciting coil 20 in the flat plate structure is changed, so that the magnetic field distribution can be shifted along the axial direction of the exciting coil 20, and one-dimensional spatial coding is realized; when the excitation coil 20 and the receiving coil 30 in the flat plate structure 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 excitation mode, when the two-dimensional magnetic particle imaging method provided by the embodiment of the invention is used for magnetic particle imaging, a magnetic field free area is not required to be arranged; the position of the free area of the magnetic field is not required to be changed; the induction voltage signal acquired each time is formed by superposing signals generated after all magnetic particles in the whole space are excited, 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 for imaging, and the imaging visual field 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 adopted excitation magnetic field is 15 mT-30 mT.

In addition, compared with the mode of executing scanning by almost taking the resolution of an imaging image as a step in the prior art, the scanning step involved in the embodiment of the invention comprises the step of adjusting the current amplitude and the step between adjacent data acquisition points in the circular motion, the scanning time required for executing scanning based on the step 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 the magnetic particle imaging with high resolution is realized.

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 induced voltage signal obtained 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 method with low power consumption, large visual field and high resolution can be expanded to clinical human body scanning.

The two-dimensional magnetic particle imaging method 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 method provided by the embodiment of the invention has higher sensitivity and image resolution, no ionizing radiation and easier production and storage of the tracer.

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 (10)

1. A method of two-dimensional magnetic particle imaging, comprising:

generating a nonlinear and non-uniform excitation magnetic field by utilizing a flat plate structure with an internal excitation coil and a receiving coil according to a preset excitation magnetic field adjustment strategy; the excitation magnetic field adjustment strategy comprises position adjustment of an excitation coil and a receiving coil in the flat plate structure and adjustment of current application of the excitation coil in the flat plate structure;

acquiring an induced voltage signal generated by the receiving coil under the action of a nonlinear and nonuniform excitation magnetic field of an imaging target; the imaging target carries magnetic particles;

according to the induced voltage signal and the system matrix, carrying out image reconstruction on the concentration distribution of the magnetic particles in the imaging target; the system matrix is used for representing the spatial distribution corresponding to target acquisition data generated by magnetic particles with unit concentration under the action of the nonlinear and nonuniform excitation magnetic field; the target acquisition data includes a spike amplitude and/or a 3-fold fundamental harmonic component of a signal extracted from the induced voltage signal.

2. A two-dimensional magnetic particle imaging method according to claim 1, wherein said plate structure comprises a plate, said plate being opposite to said imaging target location; an exciting coil and a receiving coil are arranged in the flat plate, the receiving coil is opposite to the imaging target position, and the exciting coil is opposite to the receiving coil;

correspondingly, the nonlinear and nonuniform excitation magnetic field is generated according to a preset excitation magnetic field adjustment strategy, and the method comprises the following steps:

the position adjustment of the exciting coil and the receiving coil in the flat plate structure comprises the following steps:

adjusting the exciting coil and the receiving coil in the flat plate to make 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 positioned as the center;

the adjustment of the current applied to the excitation coil in the flat plate structure comprises:

and adjusting the amplitude of the equidirectional alternating current applied by the excitation coil in the flat plate.

3. A two-dimensional magnetic particle imaging method according to claim 2, wherein adjusting the amplitude of the in-plane alternating current applied by the excitation coil comprises:

the amplitude of the cocurrent alternating current applied to the excitation coil in the flat plate is gradually increased or decreased.

4. A two-dimensional magnetic particle imaging method according to claim 1 wherein said plate structure comprises two plates, said imaging target being located between said two plates; an exciting coil and a receiving coil are respectively arranged in the two flat plates; the excitation coils and the receiving coils in the two flat plates are opposite in position, and the two receiving coils are opposite in position;

correspondingly, the nonlinear and nonuniform excitation magnetic field is generated according to a preset excitation magnetic field adjustment strategy, and the method comprises the following steps:

the position adjustment of the exciting coil and the receiving coil in the flat plate structure comprises the following steps:

adjusting the two excitation coils and the two receiving coils in the flat plates respectively, and performing spiral movement from inside to outside by taking the corresponding projection positions of the imaging target on the planes of the excitation coils and the receiving coils as centers; the spiral moving directions of the exciting coil and the receiving coil in the two flat plates are opposite;

the adjustment of the current applied to the excitation coil in the flat plate structure comprises:

adjusting the amplitude of the equidirectional alternating current applied by the exciting coils in the two flat plates respectively; the amplitude adjustment directions of the equidirectional alternating currents applied by the two excitation coils in the flat plate are opposite.

5. A two-dimensional magnetic particle imaging method according to claim 4 wherein the manner of adjusting the amplitude of the co-directional alternating current applied by the two in-plane excitation coils separately comprises:

the amplitude of the current applied to the exciting coil in one flat plate is gradually increased or decreased, and the amplitude of the current applied to the exciting coil in the other flat plate is correspondingly gradually decreased or increased.

6. A two-dimensional magnetic particle imaging method according to claim 1, characterized in that a plurality of data acquisition points are included in the adaptation of the excitation coil and the receiving coil within the slab structure;

according to the induced voltage signal and the system matrix, carrying out image reconstruction on the concentration distribution of the magnetic particles in the imaging target, wherein the image reconstruction comprises the following steps:

for each data acquisition point, extracting corresponding target acquisition data from the induced voltage signal;

performing corresponding one-dimensional image reconstruction on the concentration distribution of the magnetic particles in the imaging target according to the target acquisition data and the system matrix;

and performing corresponding two-dimensional image reconstruction on the result of the one-dimensional image reconstruction by using a filtering back projection method.

7. A two-dimensional magnetic particle imaging method according to claim 6, wherein the corresponding one-dimensional image reconstruction formula for the concentration distribution of magnetic particles in the imaged object is expressed 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 in said plate structure₀,r₁,…,r_N+1N data acquisition points representing a division of an imaging region in which the 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 said excitation coil_nThe acquired and extracted target acquisition data; g denotes a system matrix, of known quantity, the element g (i)_n,r_n) Magnetic particles representing unit concentration under applied 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_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. A two-dimensional magnetic particle imaging method according to claim 6 wherein said target acquisition data further comprises signal peak area and full width at half maximum of the signal;

the performing corresponding one-dimensional image reconstruction on the concentration distribution of the magnetic particles in the imaging target according to the target acquisition data and the system matrix comprises:

correcting the peak amplitude and the full width at half maximum of the signal in the target acquisition data by using the signal peak area of the signal;

and performing corresponding one-dimensional image reconstruction on the concentration distribution of the magnetic particles in the imaging target according to the corrected target acquisition data and the system matrix.

9. A two-dimensional magnetic particle imaging method according to claim 6 wherein said target acquisition data further comprises signal peak area and full width at half maximum of the signal;

the performing corresponding one-dimensional image reconstruction on the concentration distribution of the magnetic particles in the imaging target according to the target acquisition data and the system matrix comprises:

correcting the peak amplitude and the full width at half maximum of the signal in the target acquisition data by using the signal peak area and/or the full width at half maximum of the signal;

correcting for a non-linear, non-uniform excitation magnetic field using a full width at half maximum of the signal;

correcting the system matrix by using 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 the magnetic particles with unit concentration under the action of the corrected nonlinear and nonuniform excitation magnetic field;

and performing corresponding one-dimensional image reconstruction on the concentration distribution of the magnetic particles in the imaging target according to the corrected target acquisition data and the corrected system matrix.

10. A two-dimensional magnetic particle imaging method according to claim 9, further comprising:

carrying out deconvolution correction processing on the corrected target acquisition data by using the corrected nonlinear and nonuniform excitation magnetic field;

the corresponding one-dimensional image reconstruction of the concentration distribution of the magnetic particles in the imaging target according to the corrected target acquisition data and the corrected system matrix comprises the following steps:

and performing corresponding one-dimensional image reconstruction on the concentration distribution of the magnetic particles in the imaging target according to the target acquisition data subjected to the deconvolution correction processing and the corrected system matrix.

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