CN113812926A - Magneto-acoustic coupling imaging system and method based on laser Doppler vibration measurement - Google Patents
Magneto-acoustic coupling imaging system and method based on laser Doppler vibration measurement Download PDFInfo
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Abstract
The invention discloses a magneto-acoustic coupling imaging system and method based on laser Doppler vibration measurement, wherein the system comprises: the device comprises an excitation source, an excitation coil, a magnet, a laser Doppler vibration sensor, a guide rail and a control module; the excitation source generates an excitation current to the excitation coil; the exciting coil is positioned above the target body and is used for inducing induced eddy current in the target body under the action of exciting current; the magnets are respectively positioned above and below the target body and generate static magnetic fields; under the combined action of the induced eddy current and the static magnetic field, the target body generates vibration with the same frequency as the excitation source; the guide rail is arranged around the target body; the laser Doppler vibration sensor moves on the guide rail and collects vibration signals of a target body by 360 degrees; the control module is used for processing the vibration signal and carrying out three-dimensional reconstruction on the distribution of the electrical parameters in the target body according to the vibration signal. According to the invention, by detecting the high-frequency vibration information of the surface of the target body, the signal-to-noise ratio of the imaging method is improved, and the imaging spatial resolution is improved.
Description
Technical Field
The invention relates to the technical field of biomedical imaging, in particular to a magneto-acoustic coupling imaging system and method based on laser Doppler vibration measurement.
Background
Magneto-acoustic coupled imaging (MAT) is a functional imaging technique that does not damage the electrical properties of biological tissues. According to the method, a target body is placed in a static magnetic field and a pulse magnetic field, the pulse magnetic field generates eddy currents in the target body, the eddy currents generate Lorentz force under the action of the static magnetic field to trigger the target body to generate ultrasonic vibration, and MAT can reconstruct the spatial distribution of conductivity parameters in the target body through acquisition of acoustic signals. MAT technology can precede biological tissue structure changes, providing more effective tissue function information for early disease diagnosis.
Although MAT technology has been continuously developed in imaging theory and technology, many problems still remain to be researched. Currently, an ultrasonic probe based on a piezoelectric effect is commonly adopted in an MAT system to detect signals, the technology of the piezoelectric ultrasonic probe is mature, but the application of the piezoelectric ultrasonic probe to MAT imaging has the following problems:
(1) ultrasonic signals in MAT imaging are weak, and a sound field signal detection mode has a low signal-to-noise ratio. For example, a 1 μ A mm dipole moment is subject to a Lorentz force of only 10 at a magnetic field strength of 0.1T-10An N magnitude; in a 1T strong magnetic field, when the detection position of an elastic conductive sphere with the diameter of 10mm is 1mm far, the received ultrasonic pressure is 1/6N/m2(1/6×10-5atm), and the sound pressure amplitude is continuously reduced along with the increase of the detection distance; in the induction type MAT imaging, under the conditions of 1T magnetic field intensity, 1000V/m electric field and 0.5 mu s pulse width excitation signal, the calculation shows that when the detection distance of the elastic conductive sphere with the diameter of 10mm is 50mm, the ultrasonic pressure which can be detected is only 0.015 Pa.
(2) The central frequency of an ultrasonic probe used for MAT imaging is lower and is mostly below 10MHz, so that the spatial resolution of MAT is limited. According to the MAT imaging theory, the output ultrasonic signal and the excitation signal have the same frequency, the frequency of the excitation signal is a key factor for determining the spatial resolution of MAT, the sound velocity in biological tissues is about 1500m/s, and 1MHz excitation pulse signals (the pulse width is 1 mus) are frequently used in MAT experiments, so that the spatial resolution of MAT imaging is about 1500m/s multiplied by 1 mus to 1.5mm theoretically. Because the center frequency of the ultrasonic probe used in MAT is low, the spatial resolution of MAT imaging is limited to the mm order. Meanwhile, the ultrasonic probe has a narrow measurement frequency band, and a certain amount of other frequency information with tissue electrical characteristics can be missed during detection, so that the imaging reconstruction effect is further influenced.
(3) Interference of strong electromagnetic radiation to the ultrasound probe. An MAT imaging system generally adopts a static magnetic field of more than 0.1T and a 1MHz high-frequency pulse magnetic field, and the space environment of the MAT imaging is complex, and electromagnetic radiation is changed violently and has large interference. An ultrasonic probe based on a piezoelectric effect belongs to electromagnetic sensitive equipment, and in order to improve the signal to noise ratio, MAT needs to take an average signal waveform as final data after multiple (1000) measurements, so that the measurement time is longer.
Therefore, how to overcome the limitation problem existing in the aspect of signal acquisition in the current magnetoacoustic coupling imaging method is a problem that needs to be solved urgently by those skilled in the art.
Disclosure of Invention
In view of this, the invention provides a magnetoacoustic coupling imaging system based on laser doppler vibration measurement, which avoids electromagnetic interference in the conventional magnetoacoustic coupling imaging method by detecting high-frequency (10MHz magnitude) vibration information (such as displacement, velocity and acceleration) of the surface of a target body, improves the signal-to-noise ratio of the imaging method, improves the imaging spatial resolution, and obtains richer tissue electrical characteristic information by virtue of a wider frequency bandwidth.
In order to achieve the purpose, the invention adopts the following technical scheme:
a magneto-acoustic coupling imaging system based on laser Doppler vibration measurement comprises: the device comprises an excitation source, an excitation coil, a magnet, a laser Doppler vibration sensor, a guide rail and a control module;
wherein the excitation source generates an excitation current to the excitation coil under the control of the control module; the excitation coil is positioned above the target body and is used for inducing induced eddy current in the target body under the action of the excitation current; a pair of magnets for generating a static magnetic field, the magnets being disposed above and below the target body; the target body generates vibration with the same frequency as the excitation source under the combined action of the induced eddy current and the static magnetic field;
the guide rail is arranged around the target body; the laser Doppler vibration sensor is arranged on the guide rail, moves along the guide rail under the control of the control module and collects vibration signals of the target body in 360 degrees;
and the control module is used for processing the vibration signal and carrying out three-dimensional reconstruction on the distribution of the electrical parameters in the target body according to the vibration signal.
Preferably, in the aforementioned magneto-acoustic coupling imaging system based on laser doppler vibration measurement, the control module includes a filter amplifier, a data acquisition card, a main control unit, and a computer; the filter amplifier, the data acquisition card and the computer are electrically connected with the laser Doppler vibration sensor in sequence; the main control unit is electrically connected with the excitation source, the laser Doppler vibration sensor and the computer respectively;
the filter amplifier is used for filtering, denoising and amplitude amplification processing of the vibration signal;
the data acquisition card is used for collecting and uploading the processed vibration signals to the computer;
and the computer is used for performing three-dimensional reconstruction on the electrical parameter distribution in the target body according to the processed vibration signal, and performing parameter setting and operation management on the excitation source and the laser Doppler vibration sensor through the main control unit.
Preferably, in the aforementioned magneto-acoustic coupling imaging system based on laser doppler vibration measurement, the laser doppler vibration sensor includes a laser, a beam splitter, a reflection optical path, a reference optical path, an optical detector, a velocity demodulator, and a servo analysis module;
the laser is used for emitting laser beams; the beam splitter divides the laser beam into two beams, wherein one beam irradiates the target body through the reflection light path to generate reflected light and returns the reflected light to the optical detector; the other beam is used as reference light and is incident to the optical detector through the reference light path; the optical detector is used for mixing the reflected light and the reference light into pulse light, and performing photoelectric conversion on the pulse light to generate a pulse electric signal; the speed demodulator is used for demodulating the pulse electric signal to generate a speed signal; the servo analysis module is used for converting the speed signal into a displacement signal according to an integral calculation method.
Preferably, in the above magnetoacoustic coupled imaging system based on laser doppler vibration measurement, the reflection optical path includes a first reflective mirror, a second reflective mirror, a first transflective mirror, a lens and a third reflective mirror;
one of the laser beams split by the beam splitter is reflected by the first reflector and the second reflector in sequence, then passes through the first half-mirror and the lens, and then irradiates on the target body in a vibration state, and reflected light with frequency offset is generated under the Doppler effect;
the generated reflected light is irradiated into the optical detector after being converged by the lens and then sequentially passing through the first half-transmitting half-reflecting mirror and the third reflecting mirror to adjust the optical axis.
Preferably, in the above magnetoacoustic coupling imaging system based on laser doppler vibration measurement, the reference optical path includes an acousto-optic modulator and a second half mirror; the reference light is driven by the acousto-optic modulator to shift, and is irradiated into the optical detector after the optical axis of the reference light is adjusted by the second semi-transparent semi-reflective mirror.
Preferably, in the aforementioned magneto-acoustic coupled imaging system based on laser doppler vibration measurement, the acousto-optic modulator is an AOM bragg cell.
The invention also provides a magneto-acoustic coupling imaging method based on laser Doppler vibration measurement, which is suitable for the magneto-acoustic coupling imaging system based on laser Doppler vibration measurement and comprises the following steps:
setting parameters of the excitation source and the laser Doppler vibration sensor by using the control module;
generating a magnetic flux density vector B by using the magnet0The target body is placed in the static magnetic field space;
starting the excitation source to generate high-frequency excitation current to the excitation coil;
inducing induced eddy current with induced current density vector J in the target body by using annular excitation current generated by the excitation coil;
induced eddy current generates Lorentz force F ═ J in the presence of static magnetic fieldB0(ii) a Under the action of Lorentz force F, high-frequency vibration with the same frequency as the excitation source is generated inside the target body;
under the control of the control module, the laser Doppler vibration sensor moves along the track to perform 360-degree scanning detection on a target body to obtain a vibration signal of the target body;
and processing the vibration signal by using the control module, and performing three-dimensional reconstruction on the distribution of the electrical parameters in the target body according to the vibration signal.
Preferably, in the aforementioned method for magnetoacoustic coupled imaging based on laser doppler vibration measurement, the performing 360 ° scanning detection on the target body to obtain a vibration signal of the target body includes:
the emission frequency of the laser Doppler vibration sensor is f0And splitting the laser beam into two beams, wherein one beam is irradiated on the target body in a vibration state, and reflected light with the frequency fr is generated under the Doppler effect; the other beam is used as reference light;
the reference light is driven at a frequency fBModulating to shift frequency;
interfering the reflected light and the frequency-shifted reference light at the same spatial position, and mixing the reflected light and the frequency-shifted reference light into pulse light with a frequency f;
performing photoelectric conversion and frequency demodulation on the pulse light to obtain Doppler frequency fDMagnitude and vibration velocity of the target body proportional thereto; the calculation formula is as follows:
fD＝f-fB；
v＝λfD/2；
where v denotes a vibration velocity of the target body, and λ denotes a wavelength;
calculating the amplitude a of the target volume using:
A＝v/ω；
where ω denotes simple harmonic oscillation of the object at an angular frequency ω.
Preferably, in the aforementioned method for magnetoacoustic coupling imaging based on laser doppler vibration measurement, the relational model of surface vibration displacement caused by lorentz force in the target body is as follows:
wherein rho is density change caused by sound waves, and Cs is sound velocity in the target body; diameterVdr' is a volume division symbol; j (r') is the current density at the sound source; b is0(r') is the magnetic field strength at the acoustic source; t is time; r' is the position vector of the sound source; r isbIs the position vector of the detector on the surface of the target body.
Preferably, in the aforementioned method for magnetoacoustic coupled imaging based on laser doppler vibration measurement, the calculation formula of the electrical parameter inside the target volume is as follows:
wherein σ represents the electrical conductivity of the tissue within the target, J represents the induced current density vector, and B0Representing the static magnetic field flux density vector, B1The strength of the alternating magnetic field induced by J is shown.
Through the technical scheme, compared with the prior art, the invention discloses and provides the magneto-acoustic coupling imaging system and method based on the laser Doppler vibration measurement, which can overcome the limitation existing in the aspect of signal acquisition in the existing magneto-acoustic coupling imaging method, avoid suffering from electromagnetic interference in the traditional magneto-acoustic coupling imaging method by detecting the high-frequency (10MHz magnitude) vibration information (such as displacement, speed and acceleration) of the surface of the target body, improve the signal-to-noise ratio of the imaging method, improve the imaging spatial resolution and obtain richer tissue electrical characteristic information by means of wider frequency bandwidth.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a magnetoacoustic coupled imaging system based on laser Doppler vibration measurement according to the present invention;
fig. 2 is a schematic structural diagram of a laser doppler vibration sensor provided by the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, an embodiment of the present invention discloses a magnetoacoustic coupling imaging system based on laser doppler vibration measurement, including: the device comprises an excitation source 1, an excitation coil 2, a magnet 3, a laser Doppler vibration sensor 4, a guide rail 5 and a control module;
the excitation source 1 generates an excitation current to the excitation coil 2 under the control of the control module; the exciting coil 2 is positioned above the target body and is used for inducing induced eddy current in the target body under the action of exciting current; a pair of magnets 3 for generating a static magnetic field, each of which is located above and below the target body; under the combined action of the induced eddy current and the static magnetic field, the target body generates vibration with the same frequency as the excitation source;
the guide rail 5 is arranged around the object; the laser Doppler vibration sensor 4 is arranged on the guide rail 5, moves along the guide rail 5 under the control of the control module and collects vibration signals of a target body at 360 degrees;
the control module is used for processing the vibration signal and carrying out three-dimensional reconstruction on the distribution of the electrical parameters in the target body according to the vibration signal.
Specifically, the control module comprises a filter amplifier 6, a data acquisition card 7, a main control unit 8 and a computer 9; the filter amplifier 6, the data acquisition card 7 and the computer 9 are electrically connected with the laser Doppler vibration sensor 4 in sequence; the main control unit 8 is respectively electrically connected with the excitation source 1, the laser Doppler vibration sensor 4 and the computer 9;
the filter amplifier 6 is used for filtering, denoising and amplitude amplification processing of the vibration signals;
the data acquisition card 7 is used for collecting and uploading the processed vibration signals to the computer 9;
the computer 9 is used for performing three-dimensional reconstruction on the electrical parameter distribution in the target body according to the processed vibration signal, and performing parameter setting and operation management on the excitation source 1 and the laser Doppler vibration sensor 4 through the main control unit 8.
The process of detecting the vibration of the target body in the embodiment of the invention is as follows:
selecting a high-power current source with high repetition frequency as an excitation source 1; a circular excitation coil 2 is arranged on a target body, and pulse excitation signals in the excitation coil 2 induce induced eddy current with induced current density vector J in the target body; a pair of permanent magnets 3 are disposed on the upper and lower sides of the target body, respectively, to generate a magnetic flux density vector B0The target body is placed in the static magnetic field; the eddy current generates Lorentz force F ═ JXB under the action of static magnetic field0Inducing high-frequency vibration with the same frequency as the excitation source in the target body, and transmitting the vibration to the surface of the target body from the vibration source; the laser Doppler vibration sensor 4 emits detection laser to a target body, receives and acquires a laser signal reflected by the surface of the target body and carries out photoelectric detection and conversion; the laser Doppler vibration sensor 4 is arranged on the guide rail 5 and is used for scanning and measuring the surface of the target body by 360 degrees; filtering, noise removing and amplitude amplification preprocessing are carried out on a weak signal output by the vibration sensor 4 through a filter amplifier 6; the processed signals are collected by the data acquisition card 7 and uploaded to the computer 9; the computer 9 performs parameter setting and operation management on the excitation source 1 and the laser doppler vibration sensor 4 through the main control unit 8.
In one embodiment, as shown in fig. 2, the laser doppler vibration sensor 4 includes a laser a, an optical beam splitter BS1, a reflection optical path, a reference optical path, an optical detector B, a velocity demodulator C, and a servo analysis module D;
the laser A is used for emitting laser beams; the optical beam splitter BS1 splits the laser beam into two beams, one of which is irradiated onto the target via the reflected light path to generate reflected light and return to the optical detector B; the other beam is used as reference light and is incident to an optical detector B through a reference light path; the optical detector B is used for mixing the reflected light and the reference light into pulse light, and performing photoelectric conversion on the pulse light to generate a pulse electric signal; the speed demodulator C is used for demodulating the pulse electric signal to generate a speed signal; the servo analysis module D is used for converting the speed signal into a displacement signal according to an integral calculation method.
The reflection optical path comprises a first reflective mirror M1, a second reflective mirror M2, a first half mirror BS2, a lens E and a third reflective mirror M3;
one of the laser beams split by the beam splitter BSA is reflected by the first reflector M1 and the second reflector M2 in sequence, passes through the first half mirror BS2 and the lens E, and then irradiates on a target body in a vibration state, and generates reflected light with frequency offset under the doppler effect;
the generated reflected light is converged by the lens E, and then sequentially passes through the first half mirror BS2 and the third reflector M3 to adjust the optical axis, and then irradiates to the optical detector B.
The reference light path comprises an acousto-optic modulator F and a second half mirror BS 3; the reference light is driven by the acousto-optic modulator F to be shifted, and is irradiated into the optical detector B after the optical axis is adjusted by the second half mirror BS 3.
More advantageously, the acousto-optic modulator F is an AOM bragg cell.
The invention also discloses a magneto-acoustic coupling imaging method based on laser Doppler vibration measurement, which comprises the following steps:
firstly, parameter setting is carried out on an excitation source and a laser Doppler vibration sensor by using a control module;
step two, generating magnetic flux density vector by using magnetIs B0The target body is placed in the static magnetic field space;
step three, starting an excitation source to generate high-frequency excitation current to an excitation coil;
inducing induced eddy current with induced current density vector J in the target body by using annular exciting current generated by the exciting coil;
step five, generating Lorentz force F ═ JXB by the induced eddy current under the action of the static magnetic field0(ii) a Under the action of Lorentz force F, high-frequency vibration with the same frequency as that of the excitation source is generated inside the target body;
sixthly, under the control of the control module, the laser Doppler vibration sensor moves along the track to perform 360-degree scanning detection on the target body to obtain a vibration signal of the target body;
and seventhly, processing the vibration signals by using the control module, and performing three-dimensional reconstruction on the distribution of the electrical parameters in the target body according to the vibration signals.
In the sixth step, the laser doppler vibration sensor performs 360-degree scanning detection on the target body to obtain a vibration signal of the target body, and the specific detection process is as follows:
1. using a laser Doppler vibration sensor with a transmission frequency of f0The laser beam of (1) and splitting the laser beam into two beams, wherein one beam is irradiated on a target body in a vibration state, and reflected light with the frequency fr is generated under the Doppler effect; the other beam serves as a reference beam.
2. The reference light is driven at a frequency fBThen, modulation is performed to shift the frequency.
At BS1The reference beam is branched out to detect the directivity of the vibration. An acousto-optic modulator (AOM Bragg cell) is arranged in the reference light path and has a driving frequency fBSo that the reference light is frequency shifted and then passes through the half mirror BS3And adjusting the optical axis to irradiate the optical detector.
3. The reflected light and the frequency-shifted reference light interfere with each other at the same spatial position, and are mixed into pulsed light having a frequency f.
4. To pulseThe light is subjected to photoelectric conversion and frequency demodulation to obtain Doppler frequency fDMagnitude and vibration velocity of the target body proportional thereto; the calculation formula is as follows:
fD＝f-fB；
v＝λfD/2；
where v denotes the vibration velocity of the target body and λ denotes the wavelength.
fDThe derivation process of (1) is as follows:
in the laser Doppler vibration measuring sensor, a continuous wave He-Ne laser is used as a light source for multiple selection, and the output laser beam passes through a beam splitter BS1Split into two beams, one output beam is irradiated on the vibrating object, and the other beam is used as reference light. The outputted light passes through the mirror M1And M2Adjusting the optical axis, passing through the half mirror BS2And then passes through the lens to be irradiated on the vibration target body in a concentrated manner.
Frequency f0Is irradiated on the surface of an object having a vibration velocity v, and the frequency f of the reflected light is determined by the Doppler effectrComprises the following steps:
c is the speed of light, and the frequency of the illumination light changes due to the doppler effect. The Doppler frequency is:
since c > v, so
Because c is f0λ, so:
fD＝2v/λ (3)。
the Doppler-shifted reflected light is converged by the lens to obtain a focused beam, which is then transmitted through the BS2、M3The optical axis is adjusted. This beam of light is combined with the shifted reference light on the optical detectorOverlap, interference occurs. Frequency of reflected light fr＝f0+fDSince the light is photoelectrically converted by the optical detector, the beat frequency is f ═ f0+fD)-(f0-fB)＝fD+fBSo fD＝f-fB。
5. The amplitude a of the target is calculated using the following equation: a ═ v/ω;
where ω denotes simple harmonic oscillation of the object at an angular frequency ω.
The amplitude A derivation process specifically comprises:
assuming that the vibrating object vibrates in simple harmonic mode at the angular frequency omega, the surface speed of the vibrating object is as follows:
v＝Aω·cos(ωt) (4)
where a is amplitude, and since cos (ω t) is 1 when t → 0, a is v/ω.
Thus, for vibrations that are near simple harmonic vibrations, the displacement at high frequency vibrations can be calculated from equation (5) assuming that the vibration velocity and frequency are known.
In one embodiment, the relationship model of the Lorentz force induced surface vibration displacement in the target body is:
wherein rho is density change caused by sound waves, and Cs is sound velocity in the target body; diameterVdr' is a volume division symbol; j (r') is the current density at the sound source; b is0(r') is the magnetic field strength at the acoustic source; t is time; r' is the position vector of the sound source; r isbIs the position vector of the detector on the surface of the target body.
In one embodiment, the electrical parameter inside the target is calculated as:
wherein σ represents the targetInternal tissue conductivity, J denotes induced current density vector, B0Representing the static magnetic field flux density vector, B1The strength of the alternating magnetic field induced by J is shown.
The relation model of the surface vibration displacement caused by the Lorentz force in the target body and the specific derivation process of the electrical parameters in the target body are as follows:
and (3) a magnetoacoustic coupling imaging algorithm based on surface vibration information. When the magnetoacoustic coupling imaging technology is applied to an organism, the acoustic characteristics of biological tissues are very similar to those of fluid, and a sound field equation of magnetoacoustic coupling imaging can be researched by selecting a model with uniform acoustic characteristics from the acoustic theory of the fluid. Recording Lorentz force as F ═ J × B0J is the induced current density vector, B0Is the static magnetic field flux density vector, B1The intensity of the alternating magnetic field caused by J, csIs the sound velocity in the tissue body, and the density of the medium at rest is rho0Static pressure in the medium at rest is p0The density change due to the acoustic wave is ρ, the particle velocity in the medium is v, the displacement is u, and the sound pressure is p.
In the magnetic acoustic coupling imaging, the amplitude of sound waves in a medium is small, the sound pressure and density change is small, and a linear coupling equation can be derived:
the first of equation (6) is gradiented and multiplied by
Comprises the following steps:
the second equation in equation (6) is derived for t, with:
subtracting equations (7), (8) can eliminate the variable p, having:
further, defining the particle displacement as the integral u ═ vdt of the particle velocity, substituting equation (9) with:
will be provided with
Substituting into the first equation in equation (6) is:
therefore, the particle displacement (or velocity) can be obtained by solving equations (9) and (10), and further the sound pressure can be obtained by equation (11). Similarly, after the surface displacement (or velocity) of the target body is obtained by the measurement of the laser doppler vibrometer, the sound pressure information of the surface of the target body can be obtained through equation (11).
In MAT imaging, the wave equation describing the distribution of the acoustic pressure signal is:
using the green's function method, the analytical solution of equation (12) is obtained as:
where R and R 'are the position vectors of the detector and the sound source, respectively, and R ═ R-R' | is the distance between the source and the detector. Hypothesis testingThe detector is arranged on the surface r of the target bodybI.e. r ═ rbEquation (11) may be substituted into equation (13) to obtain a relational model of the surface vibration displacement induced by the lorentz force in the tissue as:
reconstruction to obtain J (r'). times.B0After (r'), the intra-tissue conductivity σ parameter can be calculated according to equation (15):
the embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. A magneto-acoustic coupling imaging system based on laser Doppler vibration measurement is characterized by comprising: the device comprises an excitation source, an excitation coil, a magnet, a laser Doppler vibration sensor, a guide rail and a control module;
wherein the excitation source generates an excitation current to the excitation coil under the control of the control module; the excitation coil is positioned above the target body and is used for inducing induced eddy current in the target body under the action of the excitation current; a pair of magnets for generating a static magnetic field, the magnets being disposed above and below the target body; the target body generates vibration with the same frequency as the excitation source under the combined action of the induced eddy current and the static magnetic field;
the guide rail is arranged around the target body; the laser Doppler vibration sensor is arranged on the guide rail, moves along the guide rail under the control of the control module and collects vibration signals of the target body in 360 degrees;
and the control module is used for processing the vibration signal and carrying out three-dimensional reconstruction on the distribution of the electrical parameters in the target body according to the vibration signal.
2. The magneto-acoustic coupling imaging system based on laser Doppler vibration measurement is characterized in that the control module comprises a filter amplifier, a data acquisition card, a main control unit and a computer; the filter amplifier, the data acquisition card and the computer are electrically connected with the laser Doppler vibration sensor in sequence; the main control unit is electrically connected with the excitation source, the laser Doppler vibration sensor and the computer respectively;
the filter amplifier is used for filtering, denoising and amplitude amplification processing of the vibration signal;
the data acquisition card is used for collecting and uploading the processed vibration signals to the computer;
and the computer is used for performing three-dimensional reconstruction on the electrical parameter distribution in the target body according to the processed vibration signal, and performing parameter setting and operation management on the excitation source and the laser Doppler vibration sensor through the main control unit.
3. The magnetoacoustic coupled imaging system based on laser Doppler vibration measurement is characterized in that the laser Doppler vibration sensor comprises a laser, a light beam splitter, a reflection light path, a reference light path, an optical detector, a speed demodulator and a servo analysis module;
the laser is used for emitting laser beams; the beam splitter divides the laser beam into two beams, wherein one beam irradiates the target body through the reflection light path to generate reflected light and returns the reflected light to the optical detector; the other beam is used as reference light and is incident to the optical detector through the reference light path; the optical detector is used for mixing the reflected light and the reference light into pulse light, and performing photoelectric conversion on the pulse light to generate a pulse electric signal; the speed demodulator is used for demodulating the pulse electric signal to generate a speed signal; the servo analysis module is used for converting the speed signal into a displacement signal according to an integral calculation method.
4. The magneto-acoustic coupling imaging system based on laser Doppler vibration measurement is characterized in that the reflection light path comprises a first reflector, a second reflector, a first half mirror, a lens and a third reflector;
one of the laser beams split by the beam splitter is reflected by the first reflector and the second reflector in sequence, then passes through the first half-mirror and the lens, and then irradiates on the target body in a vibration state, and reflected light with frequency offset is generated under the Doppler effect;
the generated reflected light is irradiated into the optical detector after being converged by the lens and then sequentially passing through the first half-transmitting half-reflecting mirror and the third reflecting mirror to adjust the optical axis.
5. The magnetoacoustic coupled imaging system based on laser Doppler vibration measurement is characterized in that the reference light path comprises an acousto-optic modulator and a second half mirror; the reference light is driven by the acousto-optic modulator to shift, and is irradiated into the optical detector after the optical axis of the reference light is adjusted by the second semi-transparent semi-reflective mirror.
6. The system of claim 5, wherein the acousto-optic modulator is an AOM Bragg cell.
7. A magnetoacoustic coupling imaging method based on laser Doppler vibration measurement, which is suitable for the magnetoacoustic coupling imaging system based on laser Doppler vibration measurement according to any one of claims 6, and is characterized by comprising the following steps:
setting parameters of the excitation source and the laser Doppler vibration sensor by using the control module;
generating a magnetic flux density vector B by using the magnet0The target body is placed in the static magnetic field space;
starting the excitation source to generate high-frequency excitation current to the excitation coil;
inducing induced eddy current with induced current density vector J in the target body by using annular excitation current generated by the excitation coil;
induced eddy current generates Lorentz force F ═ JXB under the action of static magnetic field0(ii) a Under the action of Lorentz force F, high-frequency vibration with the same frequency as the excitation source is generated inside the target body;
under the control of the control module, the laser Doppler vibration sensor moves along the track to perform 360-degree scanning detection on a target body to obtain a vibration signal of the target body;
and processing the vibration signal by using the control module, and performing three-dimensional reconstruction on the distribution of the electrical parameters in the target body according to the vibration signal.
8. The magnetoacoustic coupled imaging method based on laser doppler vibration measurement according to claim 7, wherein the performing 360 ° scanning detection on the target body to obtain the vibration signal of the target body includes:
the emission frequency of the laser Doppler vibration sensor is f0And splitting the laser beam into two beams, wherein one beam is irradiated on the target body in a vibration state, and reflected light with the frequency fr is generated under the Doppler effect; the other beam is used as reference light;
the reference light is driven at a frequency fBModulating to shift frequency;
interfering the reflected light and the frequency-shifted reference light at the same spatial position, and mixing the reflected light and the frequency-shifted reference light into pulse light with a frequency f;
performing photoelectric conversion and frequency demodulation on the pulse light to obtain Doppler frequency fDMagnitude and vibration velocity of the target body proportional thereto; the calculation formula is as follows:
fD＝f-fB；
v＝λfD/2；
where v denotes a vibration velocity of the target body, and λ denotes a wavelength;
calculating the amplitude a of the target volume using:
A＝v/ω；
where ω denotes simple harmonic oscillation of the object at an angular frequency ω.
9. The method of claim 7, wherein the relational model of the Lorentz force-induced surface vibration displacement in the target body is as follows:
wherein rho is density change caused by sound waves, and Cs is sound velocity in the target body; diameterVdr' is a volume division symbol; j (r') is the current density at the sound source; b is0(r') is the magnetic field strength at the acoustic source; t is time; r' is the position vector of the sound source; r isbIs the position vector of the detector on the surface of the target body.
10. The method of claim 7, wherein the electrical parameter inside the target is calculated by the following formula:
wherein σ represents the electrical conductivity of the tissue within the target, J represents the induced current density vector, and B0Representing the static magnetic field flux density vector, B1The strength of the alternating magnetic field induced by J is shown.
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