CN114052699A - Magnetic nanoparticle thermoacoustic imaging method and device based on single pulse magnetic field excitation - Google Patents

Magnetic nanoparticle thermoacoustic imaging method and device based on single pulse magnetic field excitation Download PDF

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CN114052699A
CN114052699A CN202111406206.0A CN202111406206A CN114052699A CN 114052699 A CN114052699 A CN 114052699A CN 202111406206 A CN202111406206 A CN 202111406206A CN 114052699 A CN114052699 A CN 114052699A
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刘洪家
李艳红
刘国强
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Abstract

A magnetic nanoparticle thermoacoustic imaging method and device based on single pulse magnetic field excitation are disclosed, wherein a thermoacoustic effect generation mechanism of magnetic nanoparticles under single pulse magnetic field excitation is deduced based on the Langmuir theory and the first law of thermodynamics. Based on the new mechanism, the single pulse magnetic field is applied to the body to be detected injected with the magnetic nano particles by using the vortex coil, so that the magnetic energy is generated in the magnetic nano particles, the magnetocaloric effect is further caused, and a thermoacoustic signal is excited by thermal expansion. And designing a 32-channel circumferential scanning device for receiving the thermoacoustic signals, collecting and processing the received thermoacoustic signals, and then acquiring a concentration image of the magnetic nanoparticles in the body to be detected by adopting an image reconstruction method. According to the invention, the concentration distribution of MNPs in the body to be measured can be reconstructed, and the 32-channel circumferential scanning device is used for receiving signals, so that the imaging time can be shortened.

Description

Magnetic nanoparticle thermoacoustic imaging method and device based on single pulse magnetic field excitation
Technical Field
The invention relates to the field of thermoacoustic imaging, in particular to a magnetic nanoparticle thermoacoustic imaging method and device based on single pulse magnetic field excitation.
Background
Small amount of Magnetic Nanoparticles (MNP)s) Has super-smoothThe magnetic and good biocompatibility can have targeting property under the action of an external magnetic field and can generate thermoacoustic effect, so the magnetic and good-biocompatibility magnetic-targeting thermo-acoustic imaging contrast agent is widely applied to the biomedical field, such as cell marking and separation, thermo-therapeutic treatment, imaging contrast agent and the like. Excitation of MNP by alternating magnetic fieldsThis phenomenon of thermoacoustic effect has been studied for use in the field of medical imaging, a phenomenon that is mediated by MNPsThe imaging method of coupling magnetic, thermal and acoustic multi-physical fields can obtain high resolution of ultrasonic imaging and high contrast generated by magnetic mediation.
Based on the Rosenssweig model, Piao Daqing et al propose a short-time alternating magnetic field-excited MNPs magnetic thermo-acoustic imaging method in 2013, and prove that the short-time alternating magnetic field excitation can induce MHz-level thermoelastic ultrasonic waves through simulation, and the mechanism of generating the thermo-acoustic effect is MNPsThe magnetic relaxation loss generated under the alternating magnetic field and the heat loss power (unit: W/kg) is given as:
Figure BDA0003372310000000011
in the formula of0For vacuum permeability, χ 0 is the magnetic susceptibility, ρ is the density, τ is the relaxation time, ω is0Is the angular frequency, H0Is the magnetic field intensity amplitude of the alternating magnetic field. In 2015, the university of southern ocean physiologists in singapore proposed a modulatable magnetocaloric imaging method for exciting MNPs with a short-time alternating magnetic field, which comprises the steps of firstly applying a bias magnetic field to make the magnetic susceptibility of MNPs zero, forcing the magnetocaloric process to fail to obtain a background field, then adopting a short-time alternating magnetic field with the frequency of 20MHz as an excitation signal, then acquiring a thermoacoustic signal and reconstructing an image, and finally making a difference between the reconstructed image and the background field, thereby further improving the contrast of the magnetothermoacoustic imaging method for exciting MNPs with the short-time alternating magnetic field. It is noted that the above thermoacoustic imaging methods for MNPs use short-time alternating magnetic field excitation, and the mechanism for generating thermoacoustic effect is magnetic relaxation loss according to heat loss power (SLP)CW) As can be seen from the formula, increasing the amplitude of the alternating magnetic field can enhance the thermoacoustic signal. However, because the excitation frequency of the short-time alternating magnetic field is in the MHz and GHz levels, the resonance matching is difficult, the amplitude of the current excitation signal is not high,the signal-to-noise ratio of the generated thermoacoustic signals is low, and the imaging quality needs to be improved. Meanwhile, the detuning problem of resonance matching needs to be considered under the complex electromagnetic environment.
Disclosure of Invention
The invention aims to overcome the defects of the conventional short-time alternating magnetic field excitation MNPs thermo-acoustic imaging method, provides a mechanism for generating a thermo-acoustic effect by exciting MNPs through a single pulse magnetic field, and provides a magnetic nanoparticle thermo-acoustic imaging method and a device based on single pulse magnetic field excitation based on the novel mechanism, which are used for reconstructing the concentration of MNPs in a body to be detected.
The invention provides a mechanism for generating the thermoacoustic effect of MNPs under the excitation of a single pulse magnetic field based on the Lawnian theory and the first law of thermodynamics. According to the new mechanism, the thermoacoustic imaging principle based on single pulse magnetic field excitation MNPs is provided as follows: a single pulse magnetic field (the pulse width is 500ns, the repetition frequency is 20Hz) is applied to the body to be detected injected with the magnetic nano particles by using the vortex coil, the MNPs can generate magnetization energy under the excitation of the single pulse magnetic field, further the magnetocaloric effect is generated, and then the thermoacoustic signals are excited by thermal expansion. And receiving the thermo-acoustic signal by using a 32-channel circumferential scanning device, carrying out signal acquisition and processing on the received thermo-acoustic signal, and then obtaining a concentration image of the magnetic nanoparticles in the body to be detected by adopting an image reconstruction method.
The invention provides the following technical scheme:
a magnetic nanoparticle thermoacoustic imaging method based on single pulse magnetic field excitation mainly comprises three steps: firstly, acquiring thermoacoustic signals of MNPs by a signal acquisition device; secondly, reconstructing the distribution of the thermoacoustic sources of the MNPs by using the obtained thermoacoustic signals; and thirdly, reconstructing the concentration distribution of MNPs by utilizing the spatial distribution of the thermal sound source. The specific process is as follows:
the first step is as follows: the signal acquisition device acquires the thermoacoustic signal of the magnetic nano particles
The pulse excitation source excites the object to be measured injected with MNPs through the vortex coil, the MNPs are magnetized under the action of the single pulse magnetic field, and then certain magnetization energy is formed, and the magnetization intensity of the MNPs is
Figure BDA0003372310000000021
Under adiabatic conditions, this part of the magnetization energy is converted into internal energy of MNPs, which causes magnetocaloric effect, and further excites a thermoacoustic signal by thermal expansion, and the thermoacoustic signal is received by a 32-channel circumferential scanning device. The thermoacoustic signals received by each ultrasonic transducer are processed by a preamplifier circuit, a filter circuit and a post-amplifier circuit, sampled and integrated and then stored in a data acquisition card to be used as original data for image reconstruction.
The second step is that: reconstruction of thermoacoustic source distribution of magnetic nanoparticles using acquired thermoacoustic signals
The sound pressure wave equation under adiabatic conditions is known:
Figure BDA0003372310000000022
wherein p (r, t) is sound pressure, csRepresents the speed of sound of the ultrasonic waves,
Figure BDA0003372310000000023
is Laplace operator, CpRepresents the specific heat capacity at constant pressure, beta is the coefficient of thermal expansion, Q (r) represents the source of the thermal sound, and δ' (t) is the derivative of the impulse function.
Under the excitation of a single pulse magnetic field, the internal energy change of the MNPs mainly comes from the accumulation of magnetization energy generated in the dynamic magnetization process. When MNPs are introduced into the magnetic field, the magnetic field energy increment in full space is:
Figure BDA0003372310000000024
due to the magnetization outside the region of MNPs
Figure BDA0003372310000000025
Is always zero, so the integration is limited to the space where the MNPs are located. In addition, for superparamagnetic MNPs,
Figure BDA0003372310000000031
and
Figure BDA0003372310000000032
is uniform, so that the magnetization energy density is as follows from equation (2)
Figure BDA0003372310000000033
B0Representing magnetic induction in vacuum
Figure BDA0003372310000000034
Of (d), M represents the magnetization
Figure BDA0003372310000000035
The amplitude of (c).
According to the first law of thermodynamics, under adiabatic conditions, the internal energy of magnetized MNPs changes dU W per unit volumemTherefore, the thermal sound source q (r) can be:
Figure BDA0003372310000000036
solving the sound pressure wave equation according to the Green function to obtain:
Figure BDA0003372310000000037
in the formula rdIs the position of the ultrasonic transducer, R is the position of the thermal sound source, and R ═ Rd-r | represents the distance of the thermal sound source to the ultrasound transducer. And obtaining a reconstruction expression of the thermal sound source according to a time reversal method:
Figure BDA0003372310000000038
in the formula SdFor the detection surface, n is r on the detection surfacedThe normal vector of the position. Setting a solving domain of the thermal sound source, dividing the solving domain into n multiplied by n square grid units, and solving the heat source moment through a formula (5)Array Qn×n。
The third step: reconstructing the concentration profile of magnetic nanoparticles
The magnetization of MNPs, which can be obtained according to the Langmuim theory, is:
M＝Nm0L(a) (6)
in the formula, N represents the concentration of MNPs solution, m0Represents the magnetic moments of the MNPs,
Figure BDA0003372310000000039
is a function of the number of langevin,
Figure BDA00033723100000000310
wherein kB is Boltzmann's constant, H represents the magnitude of the magnetic field strength, T0Is absolute temperature, μ0Is relative magnetic permeability;
since the Lambda function L (a) can be expanded in series into
Figure BDA00033723100000000311
When a < 1, the Langewan function can be simplified to
Figure BDA00033723100000000312
Further θ (r) can be expressed as:
Figure BDA00033723100000000313
are defined herein
Figure BDA00033723100000000314
Dispersing C according to the grid unit of the solution domain, wherein the expression is as follows:
Figure BDA00033723100000000315
and applying the matrix C by a nonlinear finite element methodn×nAnd (6) solving. MNPs concentration distribution matrix N according to formula (7)n×nThe expression of (a) is:
Figure BDA0003372310000000041
then the heat source matrix Qn×nSubstituting into formula (9), the concentration distribution of MNPs can be reconstructed.
Further, the first step specifically includes the steps of:
step 1:
initializing parameters: setting the number of signals needing to be acquired as m, wherein m is a positive integer multiple of 32, and setting a trigger signal as rising edge trigger;
step 2:
starting a pulse excitation source: applying a pulse current to the vortex coil to generate a single-pulse magnetic field in the imaging space, the magnetic induction intensity of the magnetic field being
Figure BDA0003372310000000042
And step 3:
the signal acquisition device receives thermoacoustic signals: adjusting the 32-channel circumferential scanning device to acquire signals on the selected fault plane through the ultrasonic transducer;
and 4, step 4:
the collected thermoacoustic signals are processed by a preamplifier circuit, a filter circuit and a post-amplifier circuit and then stored in a data acquisition card;
and 5:
judging whether the 32-channel circumference scanning device needs to rotate or not, and acquiring signals again:
the 32-channel circumference scanning device rotates through a connected stepping motor, and when n is equal to 1, the stepping motor does not need to act; when n is larger than 1, the upper computer is required to control the stepping motor to drive the 32-channel circumference scanning device to rotate for n-1 times, the step 3 is returned each time to obtain 32 thermo-acoustic signals again, and finally all the thermo-acoustic signals are sequenced according to the range from 0 degree to 360 degrees and then transmitted to the upper computer; wherein the content of the first and second substances,
Figure BDA0003372310000000043
the invention also provides a magnetic nanoparticle thermoacoustic imaging device based on single pulse magnetic field excitation, which mainly comprises a single pulse magnetic field excitation device, a signal acquisition device, a signal processing module and an image reconstruction module; wherein the excitation source device comprises a single pulse excitation source and a vortex coil;
the signal acquisition device comprises a stepping motor, a 32-channel circumferential scanning device and ultrasonic transducers, wherein the rotation of the 32-channel circumferential scanning device is controlled by the stepping motor, and the 32 ultrasonic transducers are fixedly arranged in the 32-channel circumferential scanning device, so that the 32-channel circumferential scanning device can simultaneously acquire 32 thermoacoustic signals, and the sampling efficiency is improved;
the signal processing module comprises a pre-amplification circuit, a filter circuit and a post-amplification circuit;
the reconstruction module comprises a data processing module and an image display module;
the imaging apparatus performs the imaging method as described above.
The imaging device collects data, then carries out normalization processing on the collected data, and then reconstructs a concentration image of MNPs through an image reconstruction method and displays the concentration image on an upper computer.
The reconstruction module reconstructs a concentration image of MNPs and displays the concentration image on an upper computer.
Furthermore, the 32-channel circumference scanning device is controlled to be arranged on different fault planes by adjusting the height connecting rod, so that the purpose of performing circumference scanning on different fault planes is achieved.
Further, the 32-channel circumference scanning device has 32 holes with equal spacing, which are used for placing 32 ultrasonic transducers respectively.
The invention has the following beneficial effects:
the invention provides a new mechanism for exciting MNPs (MNPs) by a single pulse magnetic field to generate a thermoacoustic effect, which can reconstruct the concentration distribution of the MNPs in a body to be detected, and designs a 32-channel circumferential scanning device for receiving signals, so that the imaging time can be shortened.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings required for the embodiments are briefly described below.
FIG. 1 is a schematic diagram of a magnetic nanoparticle thermoacoustic imaging device based on single-pulse magnetic field excitation according to the present invention;
FIG. 2 is a schematic diagram of a signal acquisition device and a 32-channel circular scanning device in accordance with an embodiment of the present invention;
FIG. 3 is a flowchart of the operation of an imaging device according to an embodiment of the invention.
In the figure: the device comprises an A1 pulse excitation source, an A2 vortex coil, an A3 body to be detected, an A4 upper computer, an A5 stepping motor, an A632 channel circumference scanning device, an A7 ultrasonic transducer, an A8 preamplification circuit, an A9 filter circuit, an A10 postamplification circuit, an A11 data processing module, an A12 image display module, a B1 height connecting rod, a B2 height connecting rod and a B3 height connecting rod.
Detailed Description
The invention will now be described more fully, in detail, with reference to the accompanying drawings, in which embodiments of the invention are shown.
As shown in fig. 1, the imaging device according to the reconstruction method of the present invention mainly includes a single-pulse magnetic field excitation device, a signal acquisition device, a signal processing module, and an image reconstruction module. The single-pulse magnetic field excitation device comprises a pulse excitation source A1 and a vortex coil A2, the diameter of the vortex coil A2 is 5cm, the number of turns is 4, the vortex coil A2 is placed at the bottom of a box, then an object to be detected A3 is placed in the box and is positioned right above the vortex coil A2, and the object to be detected A3 is isolated from the vortex coil A2 through air. A pulse excitation source A1 is arranged through an upper computer A4 to output a narrow pulse signal, the pulse excitation source A1 is connected with a vortex coil A2, single pulse current is generated in the vortex coil A2 through power amplification, and the single pulse current is used as an excitation signal to generate a single pulse magnetic field. The signal acquisition device is shown in fig. 2 and comprises a stepping motor A5, a 32-channel circumferential scanning device A6 and an ultrasonic transducer A7, wherein the 32-channel circumferential scanning device A6 is provided with 32 holes with equal intervals for placing the ultrasonic transducer, and a top thread hole M3 is arranged right above each hole and used for fixing the ultrasonic transducer. The 32-channel circular scanning device a6 can be controlled to rotate by the stepper motor a 5. The 32-channel circumferential scanning device A6 is controlled at different fault planes by adjusting height connecting rods (B1, B2 and B3), so that the aim of performing circumferential scanning on different fault planes is fulfilled. Among them, 32 ultrasonic transducers a7 need to be placed in a 32-channel circular scanning device a6, and each ultrasonic transducer a7 needs to be fixed with a jackscrew of M3. The signal processing module comprises a pre-amplification circuit A8, a filter circuit A9 and a post-amplification circuit A10. The ultrasonic transducer A7 is coupled with the body to be measured through oil or deionized water, and receives thermoacoustic signals by using the ultrasonic transducer A7. The received thermoacoustic signals are subjected to primary amplification through a preamplifier circuit A8, wherein the preamplifier circuit A8 adopts a low-noise amplifier with small amplification factor. The filter circuit A9 adopts a four-order Butterworth band-pass filter circuit to filter the thermoacoustic signal after the first-order amplification, and then the thermoacoustic signal after the filtering passes through a post-amplifier A10, wherein the amplifier mainly increases the amplification factor. Thus obtaining the thermoacoustic signal with high signal-to-noise ratio. The image reconstruction module comprises a data processing module A11 and an image display module A12. And storing the thermoacoustic signals passing through the signal detection module in a data acquisition card, carrying out normalization processing on the signals, transmitting the signals to an upper computer, acquiring a concentration image of MNPs (magnetic resonance spectroscopy) by an image reconstruction method, and finally displaying the concentration image on the upper computer.
Reconstructing a concentration image of MNPs mainly comprises three steps: firstly, acquiring thermoacoustic signals of MNPs by a signal acquisition device; secondly, reconstructing the distribution of the thermoacoustic sources of the MNPs by using the obtained thermoacoustic signals; and thirdly, reconstructing the concentration distribution of MNPs by utilizing the spatial distribution of the thermal sound source. The specific process is as follows:
the first step is as follows: the signal acquisition device acquires the thermoacoustic signal of the magnetic nano particles
The pulse excitation source A1 excites the object A3 to be measured injected with MNPs through a vortex coil, the MNPs are magnetized under the action of a single pulse magnetic field, and further certain magnetization energy is formed, and the magnetization intensity of the MNPs is
Figure BDA0003372310000000062
Under adiabatic conditions, this part of the magnetization energy is converted into internal energy of MNPs, causing magnetocaloric effect, and further exciting a thermoacoustic signal by thermal expansion, which is received by 32-channel circular scanning device a 6. The thermoacoustic signals received by each ultrasonic transducer A7 are processed by a preamplification circuit A8, a filter circuit A9 and a post-amplification circuit A10, sampled and integrated and then stored in a data acquisition card to be used as original data for image reconstruction.
The second step is that: reconstruction of thermoacoustic source distribution of magnetic nanoparticles using acquired thermoacoustic signals
The sound pressure wave equation under adiabatic conditions is known:
Figure BDA0003372310000000061
wherein p (r, t) is sound pressure, csRepresents the speed of sound of the ultrasonic waves,
Figure BDA0003372310000000071
is Laplace operator, CpRepresents the specific heat capacity at constant pressure, beta is the coefficient of thermal expansion, Q (r) represents the source of the thermal sound, and δ' (t) is the derivative of the impulse function.
Under the excitation of a single pulse magnetic field, the internal energy change of the MNPs mainly comes from the accumulation of magnetization energy generated in the dynamic magnetization process. When MNPs are introduced into the magnetic field, the magnetic field energy increment in full space is:
Figure BDA0003372310000000072
due to the magnetization outside the region of MNPs
Figure BDA0003372310000000073
Is always zero, so the integration is limited to the space where the MNPs are located. In addition, for superparamagnetic MNPs,
Figure BDA0003372310000000074
and
Figure BDA0003372310000000075
is uniform, so that the magnetization energy density is as follows from equation (2)
Figure BDA0003372310000000076
B0Representing the magnitude of the magnetic induction in vacuum and M representing the magnitude of the magnetization. According to the first law of thermodynamics, under adiabatic conditions, the internal energy of magnetized MNPs changes dU W per unit volumemTherefore, the thermal sound source q (r) can be:
Figure BDA0003372310000000077
solving the sound pressure wave equation according to the Green function to obtain:
Figure BDA0003372310000000078
in the formula rdIs the position of the ultrasonic transducer, R is the position of the thermal sound source, and R ═ Rd-r | represents the distance of the thermal sound source to the ultrasound transducer. And according to a time reversal method, reconstructing an expression of the thermal sound source:
Figure BDA0003372310000000079
in the formula SdFor the detection surface, n is r on the detection surfacedThe normal vector of the position. Setting a solving domain of the thermal sound source, dividing the solving domain into n multiplied by n square grid units, and solving a heat source matrix Q through a formula (5)n×n。
The third step: reconstructing the concentration profile of magnetic nanoparticles
The magnetization of MNPs, which can be obtained according to the Langmuim theory, is:
M＝Nm0L(a) (6)
in the formula, N represents the concentration of MNPs solution, m0Represents the magnetic moments of the MNPs,
Figure BDA00033723100000000710
is a function of the number of langevin,
Figure BDA00033723100000000711
wherein k isBIs Boltzmann constant, H represents the magnitude of the magnetic field strength, T0Is absolute temperature, μ0Is the relative permeability. Since the Lambda function L (a) can be expanded in series into
Figure BDA00033723100000000712
When a < 1, the Langewan function can be simplified to
Figure BDA0003372310000000081
And Q (r) can be expressed as:
Figure BDA0003372310000000082
are defined herein
Figure BDA0003372310000000083
Dispersing C according to the grid unit of the solution domain, wherein the expression is as follows:
Figure BDA0003372310000000084
and applying the matrix C by a nonlinear finite element methodn×nAnd (6) solving. MNPs concentration distribution matrix N according to formula (7)n×nThe expression of (a) is:
Figure BDA0003372310000000085
then the heat source matrix Qn×nSubstituting into formula (9), the concentration distribution of MNPs can be reconstructed.
Fig. 3 is a specific workflow of the image forming apparatus, and the working steps include:
step 1: initializing parameters: setting the number of signals to be acquired as m (m is a positive integer multiple of 32), the sampling frequency as 100MHz, the trigger type as rising edge trigger, and the sampling integral number of signal acquisition as 512;
step 2: starting the excitation device to generate a single-pulse magnetic field: starting a pulse excitation source A1, applying pulse current in a vortex coil A2 to generate a single pulse magnetic field in space with the magnetic induction intensity of
Figure BDA0003372310000000086
And step 3: the signal acquisition device acquires thermoacoustic signals: the height adjusting connecting rods (B1, B2 and B3) control the 32-channel circumferential scanning device A6 and the ultrasonic transducer A7 to acquire signals on the selected fault plane;
and 4, step 4: the collected thermoacoustic signals are processed through a pre-amplification circuit A8, a filter circuit A9 and a post-amplification circuit A10 and then stored in a data acquisition card;
and 5: it is determined whether the 32-channel circular scanning device a6 needs to be rotated and signal acquisition is performed again. The 32-channel circular scanning device a6 can be rotated by a stepping motor a5 connected thereto, and when n is 1, the stepping motor a5 does not need to be operated; when n is larger than 1, the upper computer A4 is required to control the stepping motor A5 to drive the 32-channel circumference scanning device A6 to rotate for n-1 times, the step 3 is returned each time to obtain 32 thermo-acoustic signals again, and finally all the thermo-acoustic signals are sequenced from 0 degree to 360 degrees and then transmitted to the upper computer A4; wherein the content of the first and second substances,
Figure BDA0003372310000000087
step 6: carrying out normalization processing on the data;
and 7: the density images of the MNPs were reconstructed by an image reconstruction method and displayed on the upper computer a 4.
The foregoing detailed description of the exemplary embodiments is provided to illustrate some of the relevant principles of the invention with reference to the accompanying drawings, and the scope of the invention is not limited to this exemplary embodiment. All possible alternative and modified embodiments according to the above description are considered to fall within the scope of the claimed invention.

Claims (8)

1. A magnetic nanoparticle thermoacoustic imaging method based on single pulse magnetic field excitation is characterized by comprising the following steps:
the first step, obtaining the thermo-acoustic signals of MNPs by a signal acquisition device, comprises:
the pulse excitation source excites the object to be measured injected with MNPs through the vortex coil, the MNPs are magnetized under the action of the single pulse magnetic field, and then certain magnetization energy is formed, and the magnetization intensity of the MNPs is
Figure FDA0003372309990000011
Under the adiabatic condition, the part of magnetization energy is converted into internal energy of MNPs to cause a magnetocaloric effect, and then thermoacoustic signals are excited by thermal expansion and are received by a 32-channel circumferential scanning device, the thermoacoustic signals received by each ultrasonic transducer are processed by a preamplifier circuit, a filter circuit and a post-amplifier circuit, and then are sampled and integrated and stored in a data acquisition card to serve as original data for image reconstruction;
secondly, reconstructing the space distribution of the thermoacoustic sources of the MNPs by using the acquired thermoacoustic signals;
thirdly, reconstructing the concentration distribution of MNPs by utilizing the space distribution of the thermoacoustic sources;
wherein the MNPs are magnetic nanoparticles.
2. The magnetic nanoparticle thermoacoustic imaging method based on single-pulse magnetic field excitation according to claim 1, wherein:
the first step specifically comprises the following steps:
step 1:
initializing parameters: setting the number of signals needing to be acquired as m, wherein m is a positive integer multiple of 32, and setting a trigger signal as rising edge trigger;
step 2:
starting a pulse excitation source: applying pulse current in the vortex coil to generate single pulse magnetic field with magnetic induction intensity of
Figure FDA0003372309990000012
And step 3:
the signal acquisition device receives thermoacoustic signals: adjusting the height of a 32-channel circumferential scanning device in the signal acquisition device to acquire signals on the selected fault plane through an ultrasonic transducer;
and 4, step 4:
the collected thermoacoustic signals are processed by a preamplifier circuit, a filter circuit and a post-amplifier circuit and then stored in a data acquisition card;
and 5:
judging whether the 32-channel circumference scanning device needs to rotate or not, and acquiring signals again:
the 32-channel circumference scanning device rotates through a connected stepping motor, and when n is equal to 1, the stepping motor does not need to act; when n is larger than 1, the upper computer is required to control the stepping motor to drive the 32-channel circumference scanning device to rotate for n-1 times, the step 3 is returned each time to obtain 32 thermo-acoustic signals again, and finally all the thermo-acoustic signals are sequenced according to the range from 0 degree to 360 degrees and then transmitted to the upper computer; wherein the content of the first and second substances,
Figure FDA0003372309990000021
3. the magnetic nanoparticle thermoacoustic imaging method based on single-pulse magnetic field excitation according to claim 2, wherein:
the reconstruction of the spatial distribution of the thermoacoustic source in the second step is realized by the following method:
the sound pressure wave equation under adiabatic conditions is known:
Figure FDA0003372309990000022
in the above formula, p (r, t) is sound pressure, csRepresents the speed of sound of the ultrasonic waves,
Figure FDA0003372309990000023
is Laplace operator, CpRepresents the specific heat capacity at constant pressure, beta is the coefficient of thermal expansion, Q (r) represents the source of the thermal sound, and delta' (t) is the derivative of the impulse function;
under the excitation of a single-pulse magnetic field, the MNPSThe internal energy change mainly comes from the accumulation of magnetization energy generated in the dynamic magnetization process when the MNP is magnetizedSAfter the magnetic field is introduced, the increment of the magnetic field energy in the whole space is as follows:
Figure FDA0003372309990000024
wherein the magnetization energy density is
Figure FDA0003372309990000025
B0Representing said magnetic induction
Figure FDA00033723099900000210
M represents said magnetization
Figure FDA0003372309990000026
The amplitude of (d);
under adiabatic conditions, the MNP being magnetized according to the first law of thermodynamicsSInternal energy change dU ═ W per unit volumemThus, a thermoacoustic source θ (r) is obtained as:
Figure FDA0003372309990000027
solving the sound pressure wave equation according to the Green function to obtain:
Figure FDA0003372309990000028
in the above formula, rdIs the position of the ultrasonic transducer, R is the position of the thermal sound source, and R ═ Rd-r | represents the distance of the thermal sound source from the ultrasonic transducer;
and further solving the formula (4) according to a time reversal method to obtain a reconstruction expression of the thermal sound source as follows:
Figure FDA0003372309990000029
in the above formula, SdFor the detection surface, n is r on the detection surfacedSetting the normal vector of the position, setting the solving domain of the thermal sound source, dividing the solving domain into n multiplied by n square grid units, and solving the heat source matrix Q through a formula (5)n×nThereby realizing the reconstruction of the space distribution of the thermoacoustic source.
4. The magnetic nanoparticle thermoacoustic imaging method based on single-pulse magnetic field excitation according to claim 3, wherein:
reconstructing MNP in the third stepSThe concentration distribution of (a) is realized by the following method:
obtaining MNP according to the Lagowan theorySThe magnetization of (A) is:
M＝Nm0L(a) (6)
in the above formula, N represents MNPSConcentration of solution, m0Represents MNPSThe magnetic moment of (a) is,
Figure FDA0003372309990000031
is a function of the number of langevin,
Figure FDA0003372309990000032
wherein k isBIs Boltzmann constant, H represents the magnitude of the magnetic field strength, T0Is absolute temperature, μ0Is relative magnetic permeability;
since the Lambda function L (a) can be expanded in series into
Figure FDA0003372309990000033
When a < 1, the Langewan function can be simplified to
Figure FDA0003372309990000034
And Q (r) can be expressed as:
Figure FDA0003372309990000035
are defined herein
Figure FDA0003372309990000036
Dispersing C according to the grid unit of the solution domain, wherein the expression is as follows:
Figure FDA0003372309990000037
for matrix C by nonlinear finite element methodn×nSolving is carried out;
MNP according to equation (7)SConcentration distribution matrix Nn×nThe expression of (a) is:
Figure FDA0003372309990000038
then the heat source matrix Qn×nSubstituting into formula (9) to reconstruct MNPSThe concentration distribution of (c).
5. A magnetic nanoparticle thermoacoustic imaging device based on single pulse magnetic field excitation is characterized in that:
the imaging device consists of a single pulse magnetic field excitation device, a signal acquisition device, a signal detection module and an image reconstruction module;
the single-pulse magnetic field excitation device comprises a single-pulse excitation source and a vortex coil;
the signal acquisition device comprises a stepping motor, a 32-channel circumferential scanning device and an ultrasonic transducer, wherein the rotation of the 32-channel circumferential scanning device is controlled by the stepping motor, and the ultrasonic transducer is fixedly arranged in the 32-channel circumferential scanning device, so that the 32-channel circumferential scanning device can simultaneously acquire 32 thermoacoustic signals, and the sampling efficiency is improved;
the signal processing module comprises a pre-amplification circuit, a filter circuit and a post-amplification circuit;
the reconstruction module comprises a data processing module and an image display module;
the imaging apparatus performs the imaging method of any one of claims 1-4.
6. The magnetic nanoparticle thermoacoustic imaging device based on single-pulse magnetic field excitation according to claim 5, wherein:
the reconstruction module reconstructs a concentration image of the MNPs and displays the concentration image on an upper computer.
7. The magnetic nanoparticle thermoacoustic imaging device based on single-pulse magnetic field excitation according to claim 5, wherein:
the 32-channel circumference scanning device is controlled at different fault planes by adjusting the height connecting rod, so that the purpose of performing circumference scanning on different fault planes is achieved.
8. The magnetic nanoparticle thermoacoustic imaging device based on single-pulse magnetic field excitation according to claim 5, wherein:
the 32-channel circumferential scanning device is provided with 32 equally spaced holes for respectively placing 32 ultrasonic transducers.
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116935139A (en) * 2023-08-07 2023-10-24 江南大学 River pollution monitoring method and system based on image reconstruction

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116935139A (en) * 2023-08-07 2023-10-24 江南大学 River pollution monitoring method and system based on image reconstruction

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