CN114403842A

CN114403842A - Magnetic particle imaging device

Info

Publication number: CN114403842A
Application number: CN202210086820.1A
Authority: CN
Inventors: 李檀平; 贾广; 胡凯; 黄力宇; 苗启广; 张艺飞
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 magnetic particle imaging apparatus, comprising: the signal generating unit is used for generating an induced voltage signal under the action of a nonlinear and nonuniform excitation magnetic field; the signal generating unit comprises an upper flat plate and a lower flat plate which are opposite in position; an exciting coil and a receiving coil are arranged in the upper flat plate and the lower flat plate; the driving scanning unit drives the exciting coil and the receiving coil in the upper flat plate and the lower flat plate to do circular motion; the directions of the circular motion are opposite each time; each circular motion comprises a plurality of data acquisition points; the magnetic field excitation unit is used for applying equidirectional alternating current to the excitation coils in the upper flat plate and the lower flat plate to generate a nonlinear and non-uniform excitation magnetic field at each data acquisition point in each circular motion; and the data acquisition and imaging unit is used for acquiring induced voltage signals generated on the receiving coils of the upper and lower flat plates at each data acquisition point in each circular motion so as to acquire target acquisition data and perform magnetic particle imaging. The invention realizes magnetic particle imaging with low power consumption, large visual field and high resolution.

Description

Magnetic particle imaging device

Technical Field

The invention belongs to the technical field of medical imaging, and particularly relates to magnetic particle imaging equipment.

Background

How to accurately and objectively locate tumors and other targets in clinical diagnosis and detection has been an international research hotspot and challenging problem. The existing medical Imaging technologies such as Computed Tomography (CT), Magnetic Resonance Imaging (MRI), Single-Photon Emission Computed Tomography (SPECT) and other methods have the problems of large harm, poor positioning, low precision and the like. In recent years, a new tracer-based Imaging method, Magnetic Particle Imaging (MPI) has been proposed.

By utilizing the tomography technology, MPI can accurately position tumors or other target objects by detecting the spatial concentration distribution of superparamagnetic iron oxide nanoparticles (SPIOs) harmless to human bodies, and has the characteristics of two/three-dimensional imaging, high space-time resolution and high sensitivity. In addition, MPI does not show anatomical structures and is free of background signal interference, so the intensity of the signal is directly proportional to the concentration of the tracer, a new approach with potential for medical applications. The magnetic particle has magnetic core size in 10-60 nm range and generates high frequency harmonic signal with the change of the exciting magnetic field. Magnetic particle imaging generates a magnetic field free area through a selection field, moves the free area through a focusing field, excites magnetic particles in the free area through an excitation field, collects high-frequency harmonic signals emitted by the magnetic particles through a receiving coil, and obtains a spatial distribution image of the concentration of the magnetic particles in a human body through 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, the existing magnetic particle imaging apparatus has the following problems:

(1) and large power consumption: the existing magnetic particle imaging device forms a magnetic field free area (point or line) in the middle of a selection field by constructing the selection field and a focusing field, and moves the magnetic field free area in the focusing field.

(2) The spatial resolution is low: the image resolution of the current medical imaging scanning technology can basically reach 0.5mm, and the image resolution of the current magnetic particle imaging technology can only reach 5mm under a field of view of 20 cm.

(3) And blurring the reconstructed image: the relaxation effects of the magnetic particles cause a lag and delay in the movement of the free region of the magnetic field, resulting in a blurred reconstructed image.

(4) And small visual field: the imaging field of view of the existing magnetic particle imaging technology is determined by a composite magnetic field formed by superposing an excitation field and a selection field, and the ratio of the excitation field strength to the gradient of the selection field is generally used as the imaging field of view. At present, 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 usually needs 20 cm-50 cm, the high excitation magnetic field intensity is required, and the realization is difficult.

(5) Difficult extension to clinical body scans: in order to satisfy the human body size magnetic particle imaging, a strong selection field and excitation field are needed, resulting in large power consumption, which is very difficult to realize. Meanwhile, the image spatial resolution of the existing magnetic particle imaging technology is too low or the field of view is too small, so that the requirement of clinical diagnosis is difficult to meet. All existing magnetic particle imaging techniques are difficult to extend to clinical body scanning.

Disclosure of Invention

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

the embodiment of the invention provides magnetic particle imaging equipment, which comprises a signal generating unit, a driving scanning unit, a magnetic field excitation unit and a data acquisition and imaging unit, wherein,

the signal generating unit is used for generating an induced voltage signal under the action of a nonlinear and non-uniform excitation magnetic field; the signal generating unit comprises an upper flat plate structure and a lower flat plate structure which are opposite in position, and an imaging target is positioned between the upper flat plate structure and the lower flat plate structure; the upper flat plate structure and the lower flat plate structure are respectively internally provided with an exciting coil and a receiving coil, the exciting coil and the receiving coil in the upper flat plate structure and the lower flat plate structure are opposite in position, and the two receiving coils are opposite in position;

the driving scanning unit drives the exciting coil and the receiving coil in the upper flat plate structure and the lower flat plate structure respectively to do one or more times of circular motion by taking the corresponding projection positions of the imaging target on the plane where the exciting coil and the receiving coil are located as the center; the circumferential motion directions of the exciting coil and the receiving coil in the upper flat plate structure and the lower flat plate structure are opposite each time; each circular motion process comprises a plurality of data acquisition points;

the magnetic field excitation unit is used for applying alternating currents in the same direction to the excitation coils in the upper flat plate structure and the lower flat plate structure for one time or multiple times to generate different nonlinear and nonuniform excitation magnetic fields at each data acquisition point in each circular motion; the amplitude of the current applied by the exciting coil in the upper flat plate structure is gradually increased or decreased every time, and the amplitude of the current applied by the exciting coil in the lower flat plate structure is correspondingly gradually decreased or increased;

the data acquisition and imaging unit is used for respectively acquiring induced voltage signals generated on the receiving coils in the upper flat plate structure and the lower flat plate structure at each data acquisition point in each circular motion so as to acquire corresponding target acquisition data, and carrying out magnetic particle imaging on the imaging target according to the target acquisition data.

The invention has the beneficial effects that:

the invention provides magnetic particle imaging equipment, wherein exciting coils and receiving coils in an upper flat plate structure and a lower flat plate structure move along different circumferences, each circumferential movement process comprises a plurality of data acquisition points, the amplitude of current applied by the exciting coil in the upper flat plate structure is gradually increased or decreased at each data acquisition point, and the amplitude of current applied by the exciting coil in the corresponding lower flat plate structure is correspondingly gradually decreased or increased, so that a generated nonlinear and nonuniform exciting magnetic field can be linearly decreased and then linearly increased along the axial component of each exciting coil and is distributed in a V shape.

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 coils and the receiving coils in the upper flat plate structure and the lower flat plate structure do one or more times of circular motion by taking the projection positions of the imaging target on the planes of the excitation coils and the receiving coils as the center, and different currents are applied to the excitation coils in the upper flat plate structure and the lower flat plate structure, which is equivalent to that the excitation coils and the receiving coils in the upper flat plate structure and the lower flat plate structure do nonlinear and non-uniform excitation in multiple different spatial postures and multiple different magnetic field distribution states; when the exciting coil and the receiving coil in the upper flat plate structure and the lower flat plate structure are in a certain space attitude, the current in the exciting coil is changed, so that the position of the V-shaped 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 upper flat plate structure and the lower flat plate structure are in different space postures, the magnetic field intensity 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 magnetic particle imaging equipment 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 circular motion, 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. Such a low power, large field of view, high resolution magnetic particle imaging apparatus can be extended to clinical 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 structural diagram of a magnetic particle imaging apparatus according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a signal generating unit according to an embodiment of the present invention;

FIG. 3 is a schematic structural diagram of a data acquisition and imaging unit in a magnetic particle imaging apparatus according to an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of another data acquisition and imaging unit in the magnetic particle imaging apparatus according to the embodiment of the present invention;

FIG. 5 is a schematic structural diagram of a signal corrector subunit in the data acquisition and imaging unit provided in the embodiment of the present invention;

FIG. 6 is a schematic structural diagram of another data acquisition and imaging unit in the magnetic particle imaging apparatus according to the 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 structural diagram of an imaging target carrying device in a magnetic particle imaging apparatus according to an embodiment of the present invention;

FIG. 9 is a schematic diagram of a system matrix provided by an embodiment of the invention;

fig. 10a to 10c are schematic diagrams of the two-dimensional magnetic particle concentration space reconstruction effect corresponding to image reconstruction performed under three conditions by using the magnetic particle imaging apparatus provided in the embodiment of the present invention.

Description of reference numerals:

10-a signal generating unit; 20-driving the scanning unit; 30-a magnetic field excitation unit; 40-a data acquisition and imaging unit; 101-upper plate structure; 102-a lower plate structure; 103-a fixed support; 104-an excitation coil; 105-a receiving coil; 401-a signal processing subunit; 402-a signal feature extraction subunit; 403-one-dimensional data reconstruction subunit; 404-a two-dimensional data reconstruction subunit; 405-a signal syndrome unit; 406-a relaxation deconvolution subunit; 4051-a first signal correction module; 4052-magnetic field correction module; 4053-a 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 difficulty in expanding to clinical human body scanning, etc. in the conventional magnetic particle imaging apparatus, referring to fig. 1, an embodiment of the present invention provides a magnetic particle imaging apparatus, including: a signal generating unit 10, a drive scanning unit 20, a magnetic field excitation unit 30 and a data acquisition and imaging unit 40, wherein,

the signal generating unit 10 is used for generating an induced voltage signal under the action of a nonlinear and nonuniform excitation magnetic field; the signal generating unit 10 includes an upper plate structure 101 and a lower plate structure 102 which are opposite in position, and an imaging target is located between the upper plate structure 101 and the lower plate structure 102; an excitation coil 104 and a receiving coil 105 are respectively arranged in the upper flat plate structure 101 and the lower flat plate structure 102, the excitation coil 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 are opposite in position, and the two receiving coils 105 are opposite in position;

the driving scanning unit 20 drives the exciting coil 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 respectively to make one or more circular motions with the corresponding projection positions of the imaging target on the plane where the exciting coil 104 and the receiving coil 105 are located as the center; the circular motion directions of the excitation coil 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 are opposite each time; each circular motion process comprises a plurality of data acquisition points;

the magnetic field excitation unit 30 is used for applying equidirectional alternating currents to the excitation coils 104 in the upper flat plate structure 101 and the lower flat plate structure 102 respectively one or more times to generate different nonlinear and nonuniform excitation magnetic fields at each data acquisition point in each circular motion; wherein, each time the amplitude of the current applied by the exciting coil 104 in the upper flat plate structure 101 is gradually increased or decreased, the amplitude of the current applied by the exciting coil 104 in the lower flat plate structure 102 is correspondingly gradually decreased or increased;

the data acquisition and imaging unit 40 is configured to acquire induced voltage signals generated on the receiving coils 105 in the upper flat plate structure 101 and the lower flat plate structure 102 at each data acquisition point in each circular motion to acquire corresponding target acquisition data, and perform magnetic particle imaging on an imaging target according to the target acquisition data.

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

As can be seen from the above, the existing magnetic particle imaging apparatus forms a free magnetic field region (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 region by changing the magnitude 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 signal generating unit 10, the driving scanning unit 20, and the magnetic field exciting unit 30 to generate a non-linear and non-uniform exciting magnetic field, and under the action of the non-linear and non-uniform exciting magnetic field, an induced voltage signal can be generated by taking any point in space as a magnetic field free area without constructing a selection field and a focusing field. Specifically, the method comprises the following steps:

the signal generating unit 10 includes an upper plate structure 101 and a lower plate structure 102 which are opposite in position, and an imaging target is located between the upper plate structure 101 and the lower plate structure 102; the upper flat plate structure 101 and the lower flat plate structure 102 are respectively provided with an exciting coil 104 and a receiving coil 105, the exciting coil 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 are opposite, and the receiving coils 105 are opposite. The excitation coil 104 is used for generating a nonlinear and non-uniform excitation magnetic field under the action of the magnetic field excitation unit 30; the receiving coil 105 is used for receiving the magnetic flux change caused by the magnetization response of the magnetic nanoparticles under the action of a 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. 2, an exemplary structural diagram of a signal generating unit 10 according to an embodiment of the present invention is shown: the upper flat plate structure 101 and the lower flat plate structure 102 are both cylindrical flat plates; excitation coil 104 and receiving coil 105 within respective upper and lower plate structures 101 and 102: the excitation coil 104 comprises a circular helmholtz coil and the receiving coil 105 comprises a circular helmholtz coil. The upper plate structure 101 and the lower plate structure 102 of the embodiment of the invention may be fixed in position by a fixing support 103, as shown in fig. 2, but not limited to being fixed by the fixing support 103, and not limited to being fixed in position, and the positions of the upper plate structure 101 and the lower plate structure 102 in the horizontal or vertical direction may also be adjusted by a mechanical control manner.

The signal generating unit 10 according to the embodiment of the present invention generates signals including 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 exciting coil 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 respectively to make one or more circular motions with the projection positions of the imaging target on the plane where the exciting coil 104 and the receiving coil 105 correspond as the center, the multiple circular motions form a spiral movement from inside to outside, and each movement is equivalent to regulating and controlling the spatial postures of the exciting coil 20 and the receiving coil 30. Each time the circular motion directions of the excitation coil 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 are opposite, for example, the excitation coil 104 and the receiving coil 105 in the upper flat plate structure 101 make a counterclockwise spiral movement from inside to outside, and the excitation coil 104 and the receiving coil 105 in the lower flat plate structure 102 make a clockwise spiral movement from inside to outside. A plurality of data acquisition points are included during each circular motion. For example, the upper plate structure 101 performs a circular motion 256 times, each circular motion has 256 data acquisition points, so that the upper plate structure 101 can form 256 × 256 data acquisition points, each data acquisition point acts on a different nonlinear and non-uniform excitation magnetic field, the corresponding lower plate structure 102 performs a circular motion 256 times, each circular motion has 256 data acquisition points, so that the lower plate structure 102 can form 256 × 256 data acquisition points, and each data acquisition point acts on a different nonlinear and non-uniform excitation magnetic field.

The driving scanning unit 20 according to the embodiment of the present invention may be respectively embedded in the upper flat plate structure 101 and the lower flat plate structure 102; the excitation coil 104 and the receiving coil 105 in the corresponding upper flat plate structure 101 and the lower flat plate structure 102 are respectively fixed on the driving scanning unit 20, and the driving scanning unit 20 respectively drives the excitation coil 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 to make one or more circular motions with the projection position as a central point. The driving scanning unit 20 may also be independently electrically connected to the upper flat plate structure 101 and the lower flat plate structure 102, and the driving scanning unit 20 may also respectively drive the excitation coil 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 to make one or more circular motions with the projection position as the center point.

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 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 to make one or more circular motions with the projection position as a central point 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 device may include a mechanical arm and a mechanical structure for fixing the positions of the excitation coil 104 and the receiving coil 105, and the mechanical structure is moved by the mechanical arm. In the embodiment of the present invention, a computer integrated in the magnetic particle imaging apparatus 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.

In view of the structural features of the signal generating unit 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 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 are in a certain spatial attitude, at each data acquisition point in each circular motion, applying an equidirectional alternating current to the exciting coil 104 in the upper flat plate structure 101 and the lower flat plate structure 102 respectively one or more times to generate a nonlinear and non-uniform exciting magnetic field; each time the amplitude of the current applied by the excitation coil 104 in the upper flat plate structure 101 increases or decreases, the amplitude of the current applied by the excitation coil 104 in the lower flat plate structure 102 decreases or increases. For each data acquisition point, when the same-direction alternating current is respectively applied to the exciting coils 104, the axial components of the exciting magnetic field generated between the exciting coils 104 of the upper flat plate structure 101 and the lower flat plate structure 102 in the exciting coils 104 will respectively present a V-shaped distribution state in which the linear decrease is performed first and then the linear increase is performed later, or will present an a-shaped distribution state in which the linear increase is performed first and then the linear decrease is performed later, and the V-shaped distribution and the a-shaped distribution are collectively referred to as a V-shaped distribution later, so that the magnetic field distribution is subjected to positional deviation along the axial direction of the exciting coils 20, thereby realizing one-dimensional spatial coding.

When the excitation coil 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 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.

In the embodiment of the present invention, the current applied by the magnetic field excitation unit 30 is preferably a cosine-oscillating alternating current, but is not limited to a cosine-oscillating alternating current. 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 104 is one constant magnetic field plane. Furthermore, by increasing or decreasing the current of the excitation coil 104 in the upper flat plate structure 101 and simultaneously decreasing or increasing the current of the excitation coil 104 in the lower flat plate structure 102, the "V" shaped magnetic field distribution causes the position of the excitation coil 104 to be shifted in the axial direction, thereby realizing one-dimensional to two-dimensional spatial encoding.

Meanwhile, for each data acquisition point, if the present embodiment applies the same-directional alternating current to the excitation coils 104 in the upper plate structure 101 and the lower plate structure 102 multiple times to generate a non-linear and non-uniform excitation magnetic field, for example, 256 different same-directional alternating currents are applied to each data acquisition point, the excitation coils 104 in the upper plate structure 101 and the lower plate structure 102 will generate 256 × 256 non-linear and non-uniform excitation magnetic fields, respectively, and generate 256 × 256 induced voltage signals under the action of each non-linear and non-uniform excitation magnetic field. 256 × 256 induced voltage signals generated by the upper plate structure 101 and the lower plate structure 102, respectively, are used for image reconstruction.

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 104 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, the waveform generator applying currents of various amplitudes to the excitation coil 104 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 magnitude of the current applied to the excitation coil 104 can be fed back to the pre-drive through a feedback loop, thereby forming a closed loop control.

Compared with the existing magnetic particle imaging technology, the embodiment of the invention only needs to be at certain positions relative to the imaging target, the mode of the invention adopting the combined action of the flat plate structure 10, the drive scanning unit 20 and the magnetic field excitation unit 30 can realize the nonlinear and nonuniform magnetic field excitation of the magnetic particles in the whole space where the imaging target is located, all the magnetic particles in the whole space are excited, and the signals generated after excitation are superposed to form the induced voltage signal generated by the receiving coil 102 without setting a magnetic field free area.

After the signal generating unit 10, the driving scanning unit 20, and the magnetic field excitation unit 30 act together to generate induced voltage signals, the data acquisition and imaging unit 40 respectively acquires the induced voltage signals generated on the receiving coils 105 in the upper flat plate structure 101 and the lower flat plate structure 102 at each data acquisition point in each circular motion to acquire corresponding target acquisition data, and performs magnetic particle imaging on the imaging target according to the target acquisition data. Referring to fig. 3, the data acquisition and imaging unit 40 according to the embodiment of the present invention includes a signal processing subunit 401, a signal feature extraction subunit 402, a one-dimensional data reconstruction subunit 403, and a two-dimensional data reconstruction subunit 404, specifically:

and the signal processing subunit 401 is configured to perform analog-to-digital conversion processing on the induced voltage signals generated on the receiving coil 105 connected to the upper flat plate structure 101 and the lower flat plate structure 102, respectively, for each data acquisition point in each circular motion. 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 105 in sequence; the digital signal processing section includes a processing unit for performing fourier transform processing, spectrum analysis processing, and fundamental frequency reduction processing on the signal output from the analog signal processing section in sequence to complete the analog-to-digital conversion processing of the final signal processing subunit 401. 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.

A signal feature extraction subunit 402, configured to extract corresponding target acquisition data from the analog-to-digital converted induced voltage signal; the target acquisition data includes a spike 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 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 signal peak u generated by the magnetic particle 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 sampling 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 sample 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 of data sampling point, s (r)_n) Representing the r-th in the imaging area_nSpatial sensitivity, c (r) to which each data sample point receives coil 105_n) Representing the r-th in the imaging area_nMagnetic particle concentration of each data sample point, 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 each data sample point.

Wherein u is₃(i_n) Is shown in the application of a current i_nTime corresponds to 3 fundamental harmonic components of the signal, Δ V represents the volume size of the voxel at the data sample 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 each data sample point_n) Representing the r-th in the imaging area_nSpatial sensitivity, c (r) for each data sample point receiving coil_n) Representing the r-th in the imaging area_nMagnetic particle concentration of each data sample point, 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 each data sample point.

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 403, configured to reconstruct, according to the peak amplitude and/or 3-fold fundamental frequency harmonic component of the signal and the system matrix, one-dimensional magnetic particle concentration spatial distribution data of the corresponding data acquisition point in each circular motion. 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 times different magnitude currents, r, applied to the excitation coil 104 in the upper and

lower plate structures

101 and 102₀,r₁,…,r_N+1N data sampling points representing an imaging region into which an imaging target is divided. 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 current i is applied to excitation coil 104_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 imagingR th of region_nThe components of the data sampling points, the meanings of the other elements and the like; c represents the reconstructed one-dimensional magnetic particle concentration spatial distribution data, and each element contained in the data spatial distribution data is the magnetic particle concentration on each data sampling point in the imaging area, wherein c (r)_n) Representing the r-th in the imaging area_nMagnetic particle concentration of each data sample point.

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.

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.

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 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 sampling point in an imaging area, namely, each harmonic of the signal generated at the data sampling 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 sampling point in an imaging area, and the system matrix is different from a system matrix adopted by the existing MPI system.

And a two-dimensional data reconstruction subunit 404, configured to reconstruct, according to the one-dimensional spatial distribution data of each data acquisition point in each circular motion, two-dimensional magnetic particle concentration spatial distribution data of the imaging target by using a filtering back projection method. 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.

In order to further improve the magnetic particle imaging accuracy, in the embodiment of the present invention, before performing feature extraction, a signal is first corrected, and a signal corrector subunit 405 is added, please refer to fig. 4, in which the data acquisition and imaging unit 40 in the embodiment of the present invention further includes the signal corrector subunit 405; and a signal corrector subunit 405, configured to perform correction processing on the analog-to-digital converted induced voltage signal. 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 collected data includes a signal peak area of the signal, please refer to fig. 5, the signal corrector subunit 405 includes a first signal correction module 4051, and the first signal correction module 4051 is configured to correct a peak amplitude and a full width at half maximum of the signal in the target collected 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 4051 according to 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 target acquisition data extracted finally 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 104 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 a full width at half maximum of the signal, please refer to fig. 5 again, the signal corrector subunit 405 according to the embodiment of the present invention further includes a magnetic field correction module 4052 and a second signal correction module 4053, where the magnetic field correction module 4052 is configured to correct the nonlinear and non-uniform excitation magnetic field according to the full width at half maximum of the signal; and the second signal correction module 4053 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. Considering 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 4053 in the embodiment of the present invention adopts a scheme of comparing the full width at half maximum with data acquisition points as a unit, and specifically, at each data acquisition point, a signal is acquired every time the current amplitude is converted, 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 104 is corrected by the magnetic field correction module 4052 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 4053 according to the 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.

Further, referring to fig. 6, the data acquisition and imaging unit 40 according to the embodiment of the present invention further includes a relaxation deconvolution subunit 406; a relaxation deconvolution subunit 406, configured to perform deconvolution correction processing on the analog-to-digital converted induced voltage signal under the action of the corrected nonlinear and non-uniform excitation magnetic field; the signal syndrome unit 405 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 406 performs deconvolution processing on the target acquired data to reduce signal deformation caused by the relaxation effect of the magnetic particles, 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 406.

In practical applications, the data acquisition and imaging unit 40 may be a data acquisition device including an Analog-to-Digital Converter (ADC) and 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 magnetic particle Imaging apparatus 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.

Further, referring to fig. 8, the magnetic particle imaging apparatus according to the embodiment of the present invention further includes an imaging target bearing device, configured to bear an imaging target; a plurality of rectangular shielding coils are arranged in parallel in the imaging target bearing device; when the magnetic particle imaging equipment 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. 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 within the imaging region are excited by the exciting coil 104. For example, when the magnetic particle imaging apparatus is used for scanning imaging of a human body, the imaging target carrying device may be an examination table. In addition, when the magnetic particle imaging device 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 magnetic particle imaging apparatus proposed by the embodiment of the present invention, the following experiment is explained.

The exciting coils 104 in the upper flat plate structure 101 and the lower flat plate structure 102 are composed of a circular Homholtz coil, the diameter of each exciting coil 104 is 40cm, the thickness and the width are both 5cm, the number of turns of the exciting coil 104 is 200 turns, the distance between the two exciting coils 104 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 visual field range of 20 cm-50 cm in the 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 change time of the excitation coil 104 of each data acquisition point is 256 times, the current of the excitation coil 104 in the upper flat plate structure 101 is increased from 20A, each time is increased by 0.78A, and the current is increased for 256 times till 40A; the current of the excitation coil 104 in the lower plate structure 102 is decreased from 40A to 0.78A for a total of 256 times, and then 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 exciting coil.

The receiving coils 105 in the upper plate structure 101 and the lower plate structure 102 are respectively composed of a circular helmholtz coil, the diameter of each receiving coil 105 is 40cm, and the thickness and the width are both 5 cm. The distance between the two receiver coils 105 is 40cm, and the upper flat structure 101 and the lower flat structure 102 are respectively abutted against the excitation coil 104 in the axial direction.

The upper flat plate structure 101 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 exciting coil 104 and the receiving coil 105 to wind a central point of an imaging target, circular motion is carried out on a plane where the exciting coil 104 and the receiving coil 105 are located, anticlockwise spiral motion is carried out from inside to outside, scanning of 256 circles and 256 data sampling points is completed totally, and the scanning time is 4.66 minutes; similarly, the lower flat plate structure 102 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 104 and the receiving coil 105 to make circular motion around the projection position of the imaging target corresponding to the plane where the excitation coil 104 and the receiving coil 105 are located as the center point, and makes clockwise spiral motion from inside to outside, that is, the scanning of 256 circles with 256 sampling points is completed together with the movement of the coil in the upper flat plate in the opposite direction and the opposite position, and the scanning time is 4.66 minutes. 256 circular motions are performed through the exciting coil 104 and the receiving coil 105, 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 from the upper flat plate structure 101 and the lower flat plate structure 102, and image reconstruction is performed through the induced voltage signals obtained from the upper flat plate structure 101 and the lower flat plate structure 102.

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 104 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 magnetic particle imaging apparatus provided in the embodiment of the present invention is used to reconstruct an image, a system matrix used in image reconstruction is shown in fig. 9, and an imaging effect is shown in fig. 10a to 10 c. Specifically, the method comprises the following steps:

in fig. 10a and 10b, the imaging target is a sample in which magnetic particles are distributed in a two-dimensional plane, the magnetic particles are distributed as an original image as shown in the figure, white areas are areas having magnetic particles distributed, and black areas are areas having no magnetic particles distributed; it can be seen that the two-dimensional image reconstructed from the two-dimensional projection can clearly show the original magnetic particle distribution of the imaging target.

In fig. 10c, the imaging target is a patient's head, and the original image is obtained by magnetic resonance imaging of the patient's head using a magnetic resonance apparatus; it can be seen that the magnetic resonance imaging contains 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.

In the magnetic particle imaging apparatus provided by the embodiment of the present invention, the exciting coil 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 move along different circumferences, each circumferential movement process includes a plurality of data acquisition points, at each data acquisition point, the amplitude of the current applied by the exciting coil 104 in the upper flat plate structure 101 is gradually increased or decreased, and the amplitude of the current applied by the exciting coil 104 in the corresponding lower flat plate structure 102 is correspondingly gradually decreased or increased, so that the generated nonlinear and nonuniform exciting magnetic field can be linearly decreased first and then linearly increased along the axial component of each exciting coil 104, and is distributed in a "V" shape.

Based on the nonlinear and nonuniform excitation magnetic field, the embodiment of the invention carries out nonlinear and nonuniform magnetic field excitation 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 receiving coil 105, and 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 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 perform one or more circular motions with the projection position of the imaging target on the plane where the excitation coil 104 and the receiving coil 105 are located as the center, and different currents are applied to the excitation coil 104 in the upper flat plate structure 101 and the lower flat plate structure 102, which is equivalent to that the excitation coil 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 perform nonlinear and non-uniform excitation in multiple different spatial postures and multiple different magnetic field distribution states; when the exciting coil 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 are in a certain spatial attitude, the current in the exciting coil 104 is changed, so that the position of the V-shaped magnetic field distribution along the axial direction of the exciting coil 104 can be shifted, and one-dimensional spatial coding is realized; when the excitation coil 104 and the receiving coil 105 in the upper flat plate structure 101 and the lower flat plate structure 102 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 magnetic particle imaging equipment provided by the embodiment of the invention does not need to be provided with a magnetic field free area for magnetic particle imaging; 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 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 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. Such a low power, large field of view, high resolution magnetic particle imaging apparatus can be extended to clinical body scanning.

The magnetic particle imaging device provided by the embodiment of the invention can be used in medicine, 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 magnetic particle imaging device provided by the embodiment of the invention has higher sensitivity and image resolution, does not have ionizing radiation, and is easier to produce and store tracers.

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 magnetic particle imaging apparatus comprising a signal generating unit, a drive scanning unit, a magnetic field excitation unit, and a data acquisition and imaging unit, wherein,

the magnetic field excitation unit is used for applying alternating currents in the same direction to the excitation coils in the upper flat plate structure and the lower flat plate structure for one time or multiple times at each data acquisition point in each circular motion to generate different nonlinear and nonuniform excitation magnetic fields; the amplitude of the current applied by the exciting coil in the upper flat plate structure is gradually increased or decreased every time, and the amplitude of the current applied by the exciting coil in the lower flat plate structure is correspondingly gradually decreased or increased;

2. The magnetic particle imaging apparatus of claim 1 wherein the upper plate structure and the lower plate structure are both cylindrical plates;

an excitation coil and a receiving coil within the corresponding upper plate structure and lower plate structure, comprising:

the excitation coil comprises a circular Homholtz coil;

the receiving coil comprises a circular Homholtz coil.

3. The magnetic particle imaging apparatus of claim 1, wherein the driving scanning units are built in the upper plate structure and the lower plate structure, respectively;

and the exciting coil and the receiving coil which correspond to the upper flat plate structure and the lower flat plate structure are respectively fixed on the driving scanning unit.

4. The magnetic particle imaging apparatus of claim 1, wherein the data acquisition and imaging unit comprises a signal processing subunit, a signal feature extraction subunit, a one-dimensional data reconstruction subunit, and a two-dimensional data reconstruction subunit, wherein,

the signal processing subunit is configured to perform analog-to-digital conversion processing on the induced voltage signals generated on the winding coils in the upper flat plate structure and the lower flat plate structure respectively for each data acquisition point in each circular motion;

the signal characteristic extraction subunit is used for extracting corresponding target acquisition data from the induction voltage signal subjected to analog-to-digital conversion processing; 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 the one-dimensional magnetic particle concentration spatial distribution data of the corresponding data acquisition points in each circular motion according to the peak amplitude and/or 3 times fundamental frequency harmonic component of the signal 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 each circular motion.

5. The magnetic particle imaging apparatus of claim 4 wherein the data acquisition and imaging unit further comprises a signal syndrome unit;

the signal corrector subunit is used for correcting the induction voltage signal after the analog-to-digital conversion treatment;

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

6. The magnetic particle imaging apparatus of claim 5 wherein the target acquisition data further comprises a signal peak area and a full width at half maximum of the signal;

the signal correction subunit comprises a first signal correction module, and 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.

7. The magnetic particle imaging apparatus of claim 6, wherein the signal corrector subunit further comprises a magnetic field correction module and a second signal correction module, wherein,

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;

and 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 non-uniform excitation magnetic field.

8. The magnetic particle imaging apparatus of claim 7, wherein the second signal correction module is further configured to correct the system matrix according to the corrected non-linear, non-uniform 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.

9. The magnetic particle imaging apparatus of claim 7 wherein the data acquisition and 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 after the analog-to-digital conversion processing 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.

10. The magnetic particle imaging apparatus according to claim 1, further comprising 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 magnetic particle imaging equipment 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.