CN116965795A - High-sensitivity magnetic particle imaging system and method - Google Patents
High-sensitivity magnetic particle imaging system and method Download PDFInfo
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Abstract
The invention provides a high-sensitivity magnetic particle imaging system and a method, wherein superparamagnetic particles are detected through abrupt change of harmonic phases; because the phase mutation deflects 180 degrees in extremely short time, compared with the traditional MPI signal detection, the phase mutation (namely, the differentiation of the phase to the time) is used as a response signal to obtain a higher detection signal amplitude, so that the signal to noise ratio is greatly improved, and the sensitivity of the system for detecting superparamagnetic particles is remarkably improved; the invention can detect the change of the surrounding environment property of the superparamagnetic particles with high sensitivity through the drift of the phase mutation position, thereby leading the sensitivity of the invention in detecting the change of the tissue microenvironment to be obviously higher than the traditional MPI.
Description
Technical Field
The invention relates to the technical field of magnetic particle imaging, in particular to a magnetic particle imaging system and method with high sensitivity.
Background
Magnetic particle imaging (Magnetic particle imaging, MPI) is a non-invasive, functional imaging technique free of ionizing radiation damage, which has been applied in the fields of tumor imaging, angiography, inflammation imaging, cell labeling, etc. Conventional MPI systems enable detection of response signals of changes in the spatial position, concentration and surrounding environment of superparamagnetic particles by detecting the nonlinear response of superparamagnetic particles (e.g., superparamagnetic iron oxide nanoparticles) in an alternating magnetic Field, and spatial scanning and spatial encoding of Field Free Points (FFPs) or Field Free Lines (FFLs). The improvement of the detection sensitivity of MPI to superparamagnetic particles is helpful for detecting the enrichment of superparamagnetic particle probes in early stage of diseases, thereby realizing early diagnosis of related diseases; the improvement of the response sensitivity of MPI to environmental changes is helpful to reveal the change of the tissue microenvironment at the focus in the disease evolution process, thereby providing basis for the research of related disease mechanism and the research and development of medicines.
The sensitivity of the traditional MPI system is limited by factors such as magnetic particle magnetization response speed, system noise, detection coil sensitivity and the like, and further improvement of the MPI sensitivity is realized by measures such as reducing the system noise, increasing the magnetic particle magnetization response speed, improving the detection coil sensitivity and the like. Along with the continuous optimization of the MPI system, the means for improving the sensitivity gradually approach an extreme value, so that the engineering difficulty for improving the MPI sensitivity is obviously increased. The sensitivity of MPI detection of superparamagnetic particles is difficult to break through further at present. In addition, the conventional MPI system mainly detects the change of the surrounding tissue environment by detecting the relaxation change of the superparamagnetic particles, and the sensitivity of the MPI to detect the change of the tissue environment is still insufficient due to the difficulty in measuring the relaxation of the superparamagnetic particles in the MPI and the low signal-to-noise ratio.
Disclosure of Invention
The invention provides a high-sensitivity magnetic particle imaging system and a high-sensitivity magnetic particle imaging method, which detect superparamagnetic particles and changes of surrounding tissue environments thereof through phase mutation of harmonic signals of the superparamagnetic particles and aim to greatly improve the sensitivity of detecting the superparamagnetic particles and the changes of the surrounding tissue environments thereof.
To this end, a first object of the present invention is to propose a magnetic particle imaging system of high sensitivity comprising:
the excitation circuit module is used for generating current and introducing the current into the electromagnetic coil module;
the electromagnetic coil module is used for generating a gradient magnetic field, a gradient bias magnetic field, a scanning magnetic field and an excitation magnetic field and detecting response signals of magnetic particles;
the receiving circuit module is used for receiving the detection signal of the electromagnetic coil module, filtering interference signals in the detection signal and amplifying magnetic particle response signals in the detection signal;
and the signal acquisition and processing module is used for acquiring the detection signals imported by the receiving circuit module, and performing signal processing and image reconstruction.
The excitation circuit module comprises a multichannel signal generator, a first power amplifier, a second power amplifier, a third power amplifier, a fourth power amplifier, a fifth power amplifier, a sixth power amplifier, a resonance circuit and wires; one end of the first power amplifier, one end of the second power amplifier, one end of the third power amplifier, one end of the fourth power amplifier, one end of the fifth power amplifier and one end of the sixth power amplifier are all connected with the multichannel signal generator through wires, and the other end of the first power amplifier is connected with one end of the resonance circuit; wherein, the liquid crystal display device comprises a liquid crystal display device,
the multi-channel signal generator is used for generating a first sinusoidal signal, a second sinusoidal signal, a first adjustable direct current signal, a second adjustable direct current signal, a third adjustable direct current signal and a fourth adjustable direct current signal;
the first sinusoidal signal is a high-amplitude high-frequency signal and is amplified by the first power amplifier to generate an excitation magnetic field in the X-axis direction; the second sinusoidal signal is a high-amplitude low-frequency signal and is amplified by the second power amplifier to generate a scanning magnetic field in the Z-axis direction;
the first adjustable direct current signal and the second adjustable direct current signal are low-amplitude direct current signals, the first adjustable direct current signal is amplified through the third power amplifier, and the second adjustable direct current signal is amplified through the fourth power amplifier and is used for generating a gradient magnetic field with a low gradient value in the X-axis direction;
the third adjustable direct current signal and the fourth adjustable direct current signal are high-amplitude direct current signals, the third adjustable direct current signal is amplified through the fifth power amplifier, the fourth adjustable direct current signal is amplified through the sixth power amplifier and is used for generating a gradient magnetic field with a high gradient value in the Y-axis direction, so that a non-magnetic field line and a selective magnetic field of the MPI are formed;
the resonance circuit is connected in series with the first power amplifier and is used for reducing the impedance value of the system in a high-frequency excitation state.
Wherein the solenoid module includes: the device comprises an excitation coil, a first scanning coil, a second scanning coil, a first gradient magnetic field scanning coil, a second gradient magnetic field scanning coil, a first selection magnetic field coil, a second selection magnetic field coil and a receiving coil; wherein, the liquid crystal display device comprises a liquid crystal display device,
the exciting coil and the resonance circuit are connected in series with the first power amplifier and are used for generating an exciting magnetic field in an imaging field area, namely: a high-frequency sinusoidal alternating magnetic field excited along the X-axis direction for exciting a response signal of the magnetic particles;
the second scanning coil, the first scanning coil and the second power amplifier are connected in series and are used for generating a scanning magnetic field, namely: an alternating magnetic field in the Z-axis direction;
the first gradient magnetic field scanning coil is connected with the other end of the third power amplifier, the second gradient magnetic field scanning coil is connected with the other end of the fourth power amplifier, the first gradient magnetic field scanning coil and the second gradient magnetic field scanning coil are a pair of coils and are used for generating gradient bias magnetic fields in an imaging visual field, namely: a gradient magnetic field with a low gradient value along the X-axis direction, and realizing the spatial scanning of the gradient magnetic field along the X-axis direction through current regulation;
the first magnetic field selecting coil is connected with the other end of the fifth power amplifier, the second magnetic field selecting coil is connected with the other end of the sixth power amplifier, the first magnetic field selecting coil and the second magnetic field selecting coil are a pair of coils and are used for generating a gradient magnetic field with high gradient value along the Y-axis direction in an imaging visual field, so that no magnetic field line and a selective magnetic field of MPI are formed, and spatial scanning of the no magnetic field line in the Y-axis direction is realized through current regulation;
the receiving coil is used for receiving response signals of the superparamagnetic particles in the imaging field of view.
The exciting coil and the receiving coil are two collinear solenoids, and the first scanning coil and the second scanning coil form a Helmholtz coil; the first gradient magnetic field scanning coil and the second gradient magnetic field scanning coil are two coaxial circular coils; the first selection field coil and the second selection field coil are two coaxial racetrack coils.
Wherein the receiving circuit module includes: a trap circuit and a pre-amplifier; wherein, the liquid crystal display device comprises a liquid crystal display device,
the trap circuit and the preamplifier are connected in series with the receiving coil; the trap circuit is used for filtering feed-through signals induced by the receiving coil; the preamplifier is used for amplifying the detection signal after the feed-through signal is removed, so as to amplify the response signal of the superparamagnetic particles.
The signal acquisition and processing module comprises a data acquisition card and a computer; wherein, the liquid crystal display device comprises a liquid crystal display device,
the data acquisition card is used for converting the detection signal into a digital signal and storing the digital signal into the computer; the computer is used for signal processing, image reconstruction and system control.
A second object of the present invention is to provide a magnetic particle imaging method with high sensitivity, comprising:
applying an excitation magnetic field to the selection magnetic field to excite the magnetization response signals of the superparamagnetic particles in the non-magnetic field lines; simultaneously, the gradient bias magnetic fields are overlapped, so that the excitation magnetic fields received by the superparamagnetic particles at different positions in the non-magnetic field lines contain bias of different degrees; the amplitude scanning of the gradient bias magnetic field is realized through the current regulation and control of the first gradient magnetic field scanning coil and the second gradient magnetic field scanning coil, so that the scanning of excitation bias degrees at different positions without magnetic field lines is realized, and the scanning A in the X-axis direction is further completed;
the scanning of the non-magnetic field line along the Y-axis direction is realized through the current regulation and control of the first selective magnetic field coil and the second selective magnetic field coil, so that the B scanning on the XY plane is completed;
scanning of the non-magnetic field lines along the Z-axis direction is achieved by applying the scanning magnetic field, and therefore three-dimensional space scanning is completed;
performing Fourier transform on the data acquired in the scanning process A, and extracting phase signals of one or more harmonic frequency points; using a differential value of the phase signal with respect to time as a response signal for the superparamagnetic particles; meanwhile, according to an excitation bias value required by harmonic frequency point phase mutation and the distribution of the gradient bias magnetic field, calculating the spatial position of the phase mutation in the non-magnetic field line; mapping the response signal to a spatial position with abrupt phase change, thereby realizing image reconstruction of A scanning;
mapping the image signals of the A scanning to the spatial positions of the non-magnetic field lines, mapping the A scanning images of different positions along with the spatial scanning of the non-magnetic field lines, and realizing the image reconstruction of the B scanning and the three-dimensional spatial scanning through the splicing of the A scanning images.
Compared with the prior art, the high-sensitivity magnetic particle imaging system provided by the invention detects superparamagnetic particles through abrupt change of harmonic phases; because the phase mutation deflects 180 degrees in extremely short time, compared with the traditional MPI signal detection, the phase mutation (namely, the differentiation of the phase to the time) is used as a response signal to obtain a higher detection signal amplitude, so that the signal to noise ratio is greatly improved, and the sensitivity of the system for detecting superparamagnetic particles is remarkably improved; the invention can detect the change of the surrounding environment property of the superparamagnetic particles with high sensitivity through the drift of the phase mutation position, thereby leading the sensitivity of the invention in detecting the change of the tissue microenvironment to be obviously higher than the traditional MPI.
Drawings
The invention and/or additional aspects and advantages will be apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which:
fig. 1 is a schematic structural diagram of a magnetic particle imaging system with high sensitivity according to the present invention.
Fig. 2 is a schematic diagram of connection between an excitation circuit module and an electromagnetic coil module in a high-sensitivity magnetic particle imaging system according to the present invention.
Fig. 3 is a schematic diagram illustrating an implementation of a top-view tangential plane of an electromagnetic coil module in a high-sensitivity magnetic particle imaging system according to the present invention.
Fig. 4 is a schematic diagram of an implementation of a main view section of an electromagnetic coil module in a high-sensitivity magnetic particle imaging system according to the present invention.
Fig. 5 is a schematic diagram showing connection between an electromagnetic coil module, a receiving circuit module and a signal acquisition and processing module in the magnetic particle imaging system with high sensitivity.
Detailed Description
Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative and intended to explain the present invention and should not be construed as limiting the invention.
As shown in fig. 1, a high-sensitivity magnetic particle imaging system according to an embodiment of the present invention includes:
an excitation circuit module 110 for generating and passing current into the electromagnetic coil module 120;
as shown in fig. 2, the excitation circuit module 110 includes a multi-channel signal generator 111, a first power amplifier 112, a second power amplifier 113, a third power amplifier 114, a fourth power amplifier 115, a fifth power amplifier 116, a sixth power amplifier 117, a resonance circuit 118, and wires; one end of the first power amplifier 112, the second power amplifier 113, the third power amplifier 114, the fourth power amplifier 115, the fifth power amplifier 116 and the sixth power amplifier 117 are all connected with the multichannel signal generator 111 through wires, and the other end of the first power amplifier 112 is connected with one end of the resonance circuit 118; wherein, the liquid crystal display device comprises a liquid crystal display device,
the multi-channel signal generator 111 is configured to generate a first sinusoidal signal, a second sinusoidal signal, a first adjustable dc signal, a second adjustable dc signal, a third adjustable dc signal, and a fourth adjustable dc signal;
the first sinusoidal signal is a high-amplitude high-frequency signal, and is amplified by the first power amplifier 112, so as to generate an excitation magnetic field in the X-axis direction; the second sinusoidal signal is a high-amplitude low-frequency signal, and is amplified by the second power amplifier 113, so as to generate a scanning magnetic field in the Z-axis direction;
the first adjustable direct current signal and the second adjustable direct current signal are low-amplitude direct current signals, the first adjustable direct current signal is amplified by the third power amplifier 114, and the second adjustable direct current signal is amplified by the fourth power amplifier 115 to generate a gradient magnetic field with a low gradient value in the X-axis direction;
the third adjustable direct current signal and the fourth adjustable direct current signal are high-amplitude direct current signals, the third adjustable direct current signal is amplified by the fifth power amplifier 116, the fourth adjustable direct current signal is amplified by the sixth power amplifier 117, and the fourth adjustable direct current signal is used for generating a gradient magnetic field with a high gradient value in the Y-axis direction, so that no magnetic field line and a selective magnetic field of MPI are formed;
the resonant circuit 118 is connected in series with the first power amplifier 112 for reducing the impedance of the system in the high frequency excitation state.
The electromagnetic coil module 120 is used for generating a gradient magnetic field, a gradient bias magnetic field, a scanning magnetic field and an exciting magnetic field, and detecting response signals of magnetic particles.
As shown in fig. 3 and 4, the electromagnetic coil module 120 includes: an excitation coil 50, a first scan coil 70, a second scan coil 80, a first gradient magnetic field scan coil 10, a second gradient magnetic field scan coil 20, a first selection magnetic field coil 30, a second selection magnetic field coil 40, and a receiving coil 60; wherein, the liquid crystal display device comprises a liquid crystal display device,
the exciting coil 50 and the resonance circuit 118 are connected in series with the first power amplifier 112 for generating an exciting magnetic field in an imaging field of view, that is: a high-frequency sinusoidal alternating magnetic field excited along the X-axis direction for exciting a response signal of the magnetic particles;
the second scan coil 80, the first scan coil 70 and the second power amplifier 113 are connected in series for generating a scan magnetic field, that is: an alternating magnetic field in the Z-axis direction;
the first gradient magnetic field scanning coil 10 is connected to the other end of the third power amplifier 114, the second gradient magnetic field scanning coil 20 is connected to the other end of the fourth power amplifier 115, and the first gradient magnetic field scanning coil 10 and the second gradient magnetic field scanning coil 20 are a pair of coils for generating a gradient bias magnetic field in an imaging field of view, namely: a gradient magnetic field with a low gradient value along the X-axis direction, and realizing the spatial scanning of the gradient magnetic field along the X-axis direction through current regulation;
the first magnetic field selecting coil 30 is connected to the other end of the fifth power amplifier 116, the second magnetic field selecting coil 40 is connected to the other end of the sixth power amplifier 117, the first magnetic field selecting coil 30 and the second magnetic field selecting coil 40 are a pair of coils for generating a gradient magnetic field with high gradient value along the Y-axis direction in the imaging field of view, thereby forming a non-magnetic field line and a magnetic field selecting of the MPI, and realizing the spatial scanning of the non-magnetic field line in the Y-axis direction through current regulation;
the receiving coil 60 is arranged to receive a response signal of the superparamagnetic particles in the imaging field of view.
Wherein the exciting coil 50 and the receiving coil 60 are two collinear solenoids, and the first scanning coil 70 and the second scanning coil 80 constitute a helmholtz coil; the first gradient magnetic field scanning coil 10 and the second gradient magnetic field scanning coil 20 are two coaxial circular coils; the first selection field coil 30 and the second selection field coil 40 are two coaxial racetrack coils.
The receiving circuit module 130 is configured to receive the detection signal of the electromagnetic coil module 120, filter the interference signal in the detection signal, and amplify the magnetic particle response signal in the detection signal.
As shown in fig. 5, the receiving circuit module 130 includes: a trap circuit and a pre-amplifier; wherein, the liquid crystal display device comprises a liquid crystal display device,
the trap circuit, the preamplifier and the receiving coil 60 are connected in series; the trap circuit is used for filtering feed-through signals induced by the receiving coil 60; the preamplifier is used for amplifying the detection signal after the feed-through signal is removed, so as to amplify the response signal of the superparamagnetic particles.
The signal acquisition and processing module 140 is configured to acquire the detection signal imported by the receiving circuit module 130, and perform signal processing and image reconstruction.
As shown in fig. 5, the signal acquisition and processing module 140 includes a data acquisition card and a computer; wherein, the liquid crystal display device comprises a liquid crystal display device,
the data acquisition card is used for converting the detection signal into a digital signal and storing the digital signal into the computer; the computer is used for signal processing, image reconstruction and system control.
The imaging principle of the imaging system of the invention is as follows: the superparamagnetic particles are magnetized under the action of an excitation magnetic field and generate magnetic moment which changes along with the change of the amplitude and the direction of the excitation magnetic field; the change in magnetic moment in the coil produces a response signal for the superparamagnetic particle; the relation between the response amplitude (M) of the magnetic moment and the amplitude (H) of the excitation magnetic field can be expressed by Langevin equation:
M（H）=coth(a×H)-1/ (a×H) （1）
where a is a constant related to the properties of the superparamagnetic particles, temperature, ambient viscosity, bozmann constant, permeability, etc. As can be seen from equation (1), the magnetic moment of the superparamagnetic particles responds non-linearly under excitation of a high amplitude sinusoidal alternating magnetic field, thereby generating a non-linear response signal that can be induced by the detection coil. The frequency spectrum of the nonlinear response signal contains a fundamental frequency signal and its odd harmonics. When a bias magnetic field is applied to a high-amplitude sinusoidal alternating excitation magnetic field, the excitation magnetic field (H) can be expressed as:
H= H0×sin(2×Π×f×t)+A（Ａ≠０） （2）
wherein H0 is the excitation amplitude, f is the excitation frequency, t is the time, and A is the bias magnetic field amplitude. When the H-excited superparamagnetic particle signal is used, the bias magnetic field makes the positive and negative signals of the nonlinear response signal asymmetric, so that the frequency spectrum of the nonlinear response signal is changed. As the bias magnetic field a increases gradually, the harmonic phase of the response signal undergoes a 180 degree abrupt change at a critical point, the value of a corresponding to the critical point being related to the harmonic order. If a time-varying gradient bias magnetic field is applied in one dimension, different magnetic field bias values can be formed at various spatial locations at each point in time. Under the condition, when the phase mutation of a certain harmonic is detected, the amplitude (A) of the bias magnetic field when the phase mutation occurs can be deduced through the harmonic times and the formula (1), and then the position where the phase mutation occurs can be calculated through the amplitude and the gradient value of A, so that one-dimensional space coding and imaging are realized.
In this technique, the two-dimensional and three-dimensional spatial encoding and imaging principles are as follows: on the basis of the one-dimensional imaging magnetic field, adding a selective magnetic field of MPI to form a non-magnetic field line and a saturated magnetic field area; in the magnetic field line-free region, the magnetic response signal of the superparamagnetic particles can be excited smoothly, however, the magnetic response signal of the saturation magnetic field region is suppressed; therefore, the A scanning along the non-magnetic field line can be realized through the one-dimensional space coding and imaging method; meanwhile, two-dimensional and three-dimensional space coding and imaging are realized through space scanning without magnetic field lines and space mapping of a plurality of A-scanning.
The imaging technology principle in the invention has similarities and differences with the traditional FFL type MPI technology principle. The method is similar in that both realize partial spatial coding through the suppression of magnetic response signals by a selective magnetic field; both use a high-amplitude excitation magnetic field to excite the magnetic response signal of the superparamagnetic particles, and realize detection of the superparamagnetic particles by the nonlinear response of the superparamagnetic particles to the excitation magnetic field. The difference is that the imaging technique in the invention uses a sine alternating magnetic field with a bias magnetic field for excitation instead of the standard sine alternating magnetic field used in the traditional FFL type MPI technique; the imaging technique in the present invention uses the phase mutation of the response signal as the response signal of the superparamagnetic particles, instead of the response signal amplitude used in the conventional FFL MPI technique; the imaging technique of the present invention uses gradient bias magnetic fields to spatially encode the response signals in the non-magnetic field lines, however, since there is no such function in the conventional FFL MPI technique, three-dimensional spatial encoding is required by rotation of the non-magnetic field lines.
The invention adopts the technical proposal, and has the following advantages:
the invention breaks through the theoretical framework of the traditional MPI, and changes the mutation of harmonic phase to detect superparamagnetic particles; because the phase mutation deflects 180 degrees in extremely short time, compared with the traditional MPI signal detection, the phase mutation (namely, the differentiation of the phase to the time) is used as a response signal to obtain a higher detection signal amplitude, so that the signal to noise ratio is greatly improved, and the sensitivity of the system for detecting superparamagnetic particles is remarkably improved;
superparamagnetic particles (e.g., superparamagnetic magnetic nanoparticles) detect changes in tissue microenvironment, and may be designed as probes that respond to changes in the surrounding environment; when the environment of the probe is changed or the probe encounters a detected molecule, the magnetization property is changed, namely: a in the formula (1) is changed; the phase mutation signal used in the invention is extremely sensitive to the change of a, and the weak change of a can lead to the drift of the phase mutation position, thereby leading to the change of the image; therefore, the change of the surrounding environment property of the superparamagnetic particles can be detected with high sensitivity through the drift of the phase mutation position, so that the sensitivity of the invention in detecting the change of the tissue microenvironment is obviously higher than that of the traditional MPI.
In addition, the present invention provides a magnetic particle imaging method of high sensitivity, comprising:
applying the excitation magnetic field generated by the excitation coil 50 to the selection magnetic fields generated by the first selection magnetic field coil 30 and the second selection magnetic field coil 40; the excitation magnetic field is a high-frequency sinusoidal alternating magnetic field and is used for exciting magnetization response signals of superparamagnetic particles in the non-magnetic field lines; the gradient bias magnetic fields generated by the first gradient magnetic field scanning coil 10 and the second gradient magnetic field scanning coil 20 are simultaneously overlapped on the selection magnetic field and the excitation magnetic field, so that the excitation magnetic fields received by the superparamagnetic particles at different positions in the non-magnetic field lines contain bias of different degrees; meanwhile, the amplitude scanning of the gradient bias magnetic field is realized through the current regulation and control of the first gradient magnetic field scanning coil 10 and the second gradient magnetic field scanning coil 20, so that the scanning of the excitation bias degree at each position of the non-magnetic field line is realized, and the A scanning in the X-axis direction is further completed.
The scanning of the non-magnetic field lines along the Y-axis direction is achieved by the current regulation of the first selection magnetic field coil 30 and the second selection magnetic field coil 40, thereby completing the B-scanning on the XY plane.
By applying the scanning magnetic field generated by the first scanning coil 70 and the second scanning coil 80, scanning of the non-magnetic field lines in the Z-axis direction is achieved, thereby completing three-dimensional space scanning.
Performing Fourier transform on the data acquired in the scanning process A, and extracting phase signals of one or more harmonic frequency points; using the differential value of the phase signal with respect to time as a response signal for the superparamagnetic particles; meanwhile, calculating the spatial position of the phase mutation in the non-magnetic field line according to the excitation bias value required by the harmonic frequency point phase mutation and the distribution of the gradient bias magnetic field; mapping the response signal to the spatial position of the phase mutation, thereby realizing image reconstruction of A scanning.
Mapping the image signals of the A scanning to the spatial positions of the non-magnetic field lines, mapping the A scanning images of different positions along with the spatial scanning of the non-magnetic field lines, and realizing the image reconstruction of the B scanning and the three-dimensional spatial scanning through the splicing of the A scanning images.
Preferably, the frequency of the excitation magnetic field is 20K-30K Hz;
preferably, the scanning frequency of the gradient bias magnetic field is 40-60 Hz;
preferably, the scanning frequency of the non-magnetic field lines along the Y-axis direction is 2-3 Hz;
preferably, the scanning frequency of the non-magnetic field lines along the Z-axis direction is 0.1-0.15 and Hz;
preferably, the power amplifier used is AE technology 7548;
preferably, the sampling rate of the data acquisition card is not less than 2 MS/s;
preferably, the pre-amplifier used is a low noise voltage pre-amplifier.
In summary, the present invention provides an innovation in imaging principles and methods, including: (1) The method comprises the steps of (1) taking phase mutation which is more sensitive to superparamagnetic particles and environmental changes thereof as a response signal, replacing the traditional method of taking the amplitude of a sensing signal as the response signal, (2) realizing space coding and three-dimensional imaging by spatial scanning of the position where the phase mutation is located, realizing high-sensitivity MPI imaging, and finally obviously improving the sensitivity of an MPI system for detecting the superparamagnetic particles and the environmental changes thereof.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means 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 present invention. In this specification, schematic representations of the terms are not necessarily directed 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, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In the description of the present invention, the meaning of "plurality" means at least two, for example, two, three, etc., unless specifically defined otherwise.
Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps of the process, and additional implementations are included within the scope of the preferred embodiment of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order from that shown or discussed, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the embodiments of the present invention.
Although embodiments of the present invention have been shown and described above, it will be understood that the embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the embodiments by one of ordinary skill in the art within the scope of the invention.
Claims (6)
1. A high sensitivity magnetic particle imaging system, comprising:
the excitation circuit module is used for generating current and introducing the current into the electromagnetic coil module;
the electromagnetic coil module is used for generating a gradient magnetic field, a gradient bias magnetic field, a scanning magnetic field, a non-magnetic field line, a selection magnetic field and an excitation magnetic field and detecting response signals of magnetic particles; wherein, the liquid crystal display device comprises a liquid crystal display device,
applying an excitation magnetic field to the selection magnetic field to excite the magnetization response signals of the superparamagnetic particles in the non-magnetic field lines; simultaneously, the gradient bias magnetic fields are overlapped, so that the excitation magnetic fields received by the superparamagnetic particles at different positions in the non-magnetic field lines contain bias of different degrees; the amplitude scanning of the gradient bias magnetic field is realized through the current regulation and control of the gradient magnetic field scanning coil, so that the scanning of the excitation bias degree at different positions of the non-magnetic field line is realized, and the first scanning in the X-axis direction is further completed;
scanning of the non-magnetic field lines along the Y-axis direction is achieved through current regulation and control of the magnetic field coils, and therefore second scanning on the XY plane is achieved;
scanning of the non-magnetic field lines along the Z-axis direction is achieved by applying the scanning magnetic field, and therefore three-dimensional space scanning is completed;
the receiving circuit module is used for receiving the detection signal of the electromagnetic coil module, filtering interference signals in the detection signal and amplifying magnetic particle response signals in the detection signal, and guiding the detection signal into the signal acquisition and processing module; wherein, the liquid crystal display device comprises a liquid crystal display device,
performing Fourier transform on the data acquired in the first scanning process, and extracting phase signals of one or more harmonic frequency points; using a differential value of the phase signal with respect to time as a response signal for the superparamagnetic particles; meanwhile, according to an excitation bias value required by harmonic frequency point phase mutation and the distribution of the gradient bias magnetic field, calculating the spatial position of the phase mutation in the non-magnetic field line; mapping the response signal to a spatial position of the phase mutation, thereby realizing image reconstruction of the first scan;
the signal acquisition and processing module is used for acquiring the detection signals imported by the receiving circuit module, and performing signal processing and image reconstruction; wherein, the liquid crystal display device comprises a liquid crystal display device,
mapping the image signals of the first scanning to the spatial positions of the non-magnetic field lines, mapping out the first scanning images of different positions along with the spatial scanning of the non-magnetic field lines, and realizing the image reconstruction of the second scanning and the three-dimensional spatial scanning through the splicing of the first scanning images.
2. The high sensitivity magnetic particle imaging system of claim 1, wherein the excitation circuit module comprises a multichannel signal generator, a first power amplifier, a second power amplifier, a third power amplifier, a fourth power amplifier, a fifth power amplifier, a sixth power amplifier, a resonant circuit, and wires; one end of the first power amplifier, one end of the second power amplifier, one end of the third power amplifier, one end of the fourth power amplifier, one end of the fifth power amplifier and one end of the sixth power amplifier are all connected with the multichannel signal generator through wires, and the other end of the first power amplifier is connected with one end of the resonance circuit; wherein, the liquid crystal display device comprises a liquid crystal display device,
the multi-channel signal generator is used for generating a first sinusoidal signal, a second sinusoidal signal, a first adjustable direct current signal, a second adjustable direct current signal, a third adjustable direct current signal and a fourth adjustable direct current signal;
the first sinusoidal signal is a high-amplitude high-frequency signal and is amplified by the first power amplifier to generate an excitation magnetic field in the X-axis direction; the second sinusoidal signal is a high-amplitude low-frequency signal and is amplified by the second power amplifier to generate a scanning magnetic field in the Z-axis direction;
the first adjustable direct current signal and the second adjustable direct current signal are low-amplitude direct current signals, the first adjustable direct current signal is amplified through the third power amplifier, and the second adjustable direct current signal is amplified through the fourth power amplifier and is used for generating a gradient magnetic field with a low gradient value in the X-axis direction;
the third adjustable direct current signal and the fourth adjustable direct current signal are high-amplitude direct current signals, the third adjustable direct current signal is amplified through the fifth power amplifier, the fourth adjustable direct current signal is amplified through the sixth power amplifier and is used for generating a gradient magnetic field with a high gradient value in the Y-axis direction, so that a non-magnetic field line and a selective magnetic field of the MPI are formed;
the resonance circuit is connected in series with the first power amplifier and is used for reducing the impedance value of the system in a high-frequency excitation state.
3. The high sensitivity magnetic particle imaging system of claim 2, wherein said electromagnetic coil module comprises: the device comprises an excitation coil, a first scanning coil, a second scanning coil, a first gradient magnetic field scanning coil, a second gradient magnetic field scanning coil, a first selection magnetic field coil, a second selection magnetic field coil and a receiving coil; wherein, the liquid crystal display device comprises a liquid crystal display device,
the exciting coil and the resonance circuit are connected in series with the first power amplifier and are used for generating an exciting magnetic field in an imaging field area, namely: a high-frequency sinusoidal alternating magnetic field excited along the X-axis direction for exciting a response signal of the magnetic particles;
the second scanning coil, the first scanning coil and the second power amplifier are connected in series and are used for generating a scanning magnetic field, namely: an alternating magnetic field in the Z-axis direction;
the first gradient magnetic field scanning coil is connected with the other end of the third power amplifier, the second gradient magnetic field scanning coil is connected with the other end of the fourth power amplifier, the first gradient magnetic field scanning coil and the second gradient magnetic field scanning coil are a pair of coils and are used for generating gradient bias magnetic fields in an imaging visual field, namely: a gradient magnetic field with a low gradient value along the X-axis direction, and realizing the spatial scanning of the gradient magnetic field along the X-axis direction through current regulation;
the first magnetic field selecting coil is connected with the other end of the fifth power amplifier, the second magnetic field selecting coil is connected with the other end of the sixth power amplifier, the first magnetic field selecting coil and the second magnetic field selecting coil are a pair of coils and are used for generating a gradient magnetic field with high gradient value along the Y-axis direction in an imaging visual field, so that no magnetic field line and a selective magnetic field of MPI are formed, and spatial scanning of the no magnetic field line in the Y-axis direction is realized through current regulation;
the receiving coil is used for receiving response signals of the superparamagnetic particles in the imaging field of view.
4. A high sensitivity magnetic particle imaging system according to claim 3, wherein said excitation coil and said receiving coil are two collinear solenoids, said first scanning coil and said second scanning coil constituting a helmholtz coil; the first gradient magnetic field scanning coil and the second gradient magnetic field scanning coil are two coaxial circular coils; the first selection field coil and the second selection field coil are two coaxial racetrack coils.
5. A high sensitivity magnetic particle imaging system according to claim 3, wherein said receive circuit module comprises: a trap circuit and a pre-amplifier; wherein, the liquid crystal display device comprises a liquid crystal display device,
the trap circuit and the preamplifier are connected in series with the receiving coil; the trap circuit is used for filtering feed-through signals induced by the receiving coil; the preamplifier is used for amplifying the detection signal after the feed-through signal is removed, so as to amplify the response signal of the superparamagnetic particles.
6. The high sensitivity magnetic particle imaging system of claim 1, wherein the signal acquisition and processing module comprises a data acquisition card and a computer; wherein, the liquid crystal display device comprises a liquid crystal display device,
the data acquisition card is used for converting the detection signal into a digital signal and storing the digital signal into the computer; the computer is used for signal processing, image reconstruction and system control.
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