阅读说明：本技术 一种纳秒脉冲电场诱导热声信号处理方法及系统 (Nanosecond pulse electric field induced thermoacoustic signal processing method and system ) 是由 郭亮 姜文聪 王祥业 张超来 安政昂 宫礼坤 李政哲 宋立景 张秀龙 于 2020-03-13 设计创作，主要内容包括：本发明公开了一种纳秒脉冲电场诱导热声信号处理方法及系统,属于热声成像检测领域,目标体和A,B两个电极的极板间填充绝缘油,采用电极施加纳秒宽的脉冲电压,通过超声探头采集声信号；利用有限元方法求解得到目标体的电标位,再求解目标体内的电场强度和电流密度；目标体内的电场强度和电流密度与目标体的电导率分布有关；因目标体的热函数与其电导率分布有关,最终获得目标体声信号与电导率的分布关系。该方法具有高对比度、高分辨率、非接触测量、结构简单和穿透深度更大的优势。(The invention discloses a method and a system for processing nanosecond pulse electric field induced thermoacoustic signals, belonging to the field of thermoacoustic imaging detection.A target body and polar plates of two electrodes A and B are filled with insulating oil, the electrodes are adopted to apply nanosecond-wide pulse voltage, and an ultrasonic probe is used for acquiring acoustic signals; solving the electric potential mark position of the target body by using a finite element method, and then solving the electric field intensity and the current density in the target body; the electric field strength and current density within the target volume are related to the conductivity distribution of the target volume; because the thermal function of the target body is related to the conductivity distribution of the target body, the distribution relation between the acoustic signal of the target body and the conductivity is finally obtained. The method has the advantages of high contrast, high resolution, non-contact measurement, simple structure and larger penetration depth.)

1. A nanosecond pulse electric field induction thermoacoustic signal processing method is characterized in that insulating oil is filled between a target body and polar plates of an electrode A and an electrode B, nanosecond-wide pulse voltage U (t) is applied to the electrodes, and an ultrasonic probe is used for acquiring acoustic signals; solving the electric potential mark position of the target body by using a finite element method, and then solving the electric field intensity and the current density in the target body; the electric field intensity and the current density in the target body are related to the electric conductivity distribution of the target body, and the thermal function of the target body is related to the electric conductivity distribution of the target body, so that the distribution relation between the acoustic signal of the target body and the electric conductivity is finally obtained.

2. The processing method according to claim 1, characterized in that the specific processing steps comprise:

placing a target body in a target area, filling insulating oil with the conductivity of 0 between the target body and polar plates of two electrodes A and B, immersing an ultrasonic probe and the target body in the insulating oil, applying a nanosecond-wide pulse voltage U (t) to the target area by using the two electrodes A and B, and acquiring an acoustic signal by using the ultrasonic probe;

the target body is wrapped by the non-conductive medium, and the electric field in the target body is generated through electrolytic texture, so that the ampere law is met:

wherein the content of the first and second substances,is the Hamiltonian, J is the current density, J is the imaginary unit, E is the electric field strength,d is an electric displacement vector, t is time, omega is frequency, is dielectric constant, sigma is conductivity, the dielectric constant of a target body can be ignored relative to the conductivity because the conductivity in the insulating oil is 0, so that sigma can be ignored in the insulating oil^*The real part of (a), can be neglected in the target volume^*Imaginary part of, i.e. sigma^*＝σ；

Secondly, because the electric field in the target body is generated by electrolytic texture and the induced magnetic field is very small, the nanosecond pulse electric field induced thermoacoustic imaging can be described as being similar to electric quasi-static imaging

Wherein the content of the first and second substances,

thirdly, the electric mark position of the target area can be obtained through the above formula

the current density in the target body J is:

J＝σE (4)

the target body absorbs joule heat due to the passing of current, and the heat function H is

H(r,t)＝σE²(r,t) (5)

Fourthly, a thermal function image H (r, t) can be constructed through the formula, the target body can generate ultrasonic signals when absorbing joule heat expansion, and the wave equation satisfied by sound pressure is

Where p is the image of the sound source excited by the target volume, c₀Is the sound velocity in the insulating oil, beta is the volume coefficient of thermal expansion of the target, C_pIs the specific heat capacity of the target; the ultrasonic signal emitted by the target body is related to the distribution of the conductivity of the ultrasonic signal, and the conductivity of the target body can be obtained through the inversion of the acoustic signal.

3. The processing method of claim 2, wherein in nanosecond pulsed thermoacoustic imaging, the electric scale position of the target body is obtained by solving formula (2) with a finite element method, and the electric field intensity and the current density in the target body are solved by using formulas (3) and (4); the electric field intensity and the current density in the target body are related to the conductivity distribution of the target body, the electric field intensity and the current density of the area with higher conductivity are higher, and the value of the current density in the target body corresponds to the conductivity; the thermal function of the target body is related to the conductivity distribution of the target body obtained by the formulas (5 and 6), and the area with higher internal conductivity has larger thermal function and larger excited sound source, so that the intensity of the sound source corresponds to the conductivity distribution in the target body.

4. The process of claim 1 wherein the pulse voltage required to generate the induced electric field in the target is between 10 KV and 30KV and between 10 ns and 500ns in pulse width.

5. The processing method according to any one of claims 1 to 4, wherein a simple model and a complex model are respectively established by a nanosecond pulse thermoacoustic imaging method for simulation analysis, so as to provide theoretical guidance for actual detection of nanosecond pulse thermoacoustic imaging.

6. A method according to claim 5, characterized in that an electric field is induced in the target region, the interior of the target volume expands due to heating to generate an acoustic pressure p (r, t), the thermo-acoustic signal is received by an ultrasound probe placed around the target volume, and the thermo-acoustic signal (r, t) received by the ultrasound probe is the convolution of the acoustic pressure p (r, t) at the ultrasound transducer location and the impulse response function h (t) of the ultrasound probe, as known from the analysis of the positive acoustic field problem in inductive thermo-acoustic imaging

The formula (7) shows that the thermoacoustic signal ω (r, t) received by the ultrasonic probe can reflect the waveform of the original sound field and also includes the response characteristic of the ultrasonic probe.

7. A nanosecond pulsed electric field induced thermoacoustic imaging system, characterized in that processing is performed using the thermoacoustic signal processing method according to any of claims 1-6.

Technical Field

The invention belongs to the field of thermoacoustic imaging detection, and particularly relates to a nanosecond pulse electric field induced thermoacoustic signal processing method and system.

Background

The imaging technology aiming at the electrical characteristic parameters of the biological tissue has important significance, and is expected to be used in the field of biological detection, for example, a target body can be detected in advance and imaged before the biological tissue is abnormal. However, how to deeply acquire the electrical characteristic parameters of the target body to acquire the intermediate information and perform subsequent accurate processing is always a common problem in electrical characteristic parameter imaging.

At present, the techniques for imaging the electrical characteristic parameters of biological tissues mainly comprise magnetoacoustic imaging, microwave thermoacoustic imaging, induction type thermoacoustic imaging and the like. In the magnetoacoustic imaging, a target body is placed in a static magnetic field, the target body is excited by injected current or induced current, the current generates Lorentz force vibration under the action of the static magnetic field to form ultrasonic waves, and ultrasonic signals are detected.

Microwave thermoacoustic imaging adopts microwave signals to irradiate biological tissues to generate thermal effect to excite ultrasonic signals, ultrasonic is used as a carrier to reflect the difference of microwave absorptivity inside the biological tissues, and information of microwave absorption by the tissues is obtained, so that imaging is performed.

The induction type thermo-acoustic imaging applies an alternating magnetic field with the MHz magnitude to a conductive object through an exciting coil, an induction electric field is generated in the conductive object, joule heat is further generated, thermoelastic ultrasonic signals are excited, and the ultrasonic signals are detected to carry out imaging.

Disclosure of Invention

The invention aims to solve the problem that the prior art needs to be in direct contact with a target body and cannot deeply acquire information inside for subsequent imaging, and provides a nanosecond pulse electric field induced thermoacoustic signal processing method (nsPEFTAI for short), which has the advantages of high contrast, high resolution, non-contact measurement, simple structure and larger penetration depth.

The technical scheme provided by the invention is as follows:

a nanosecond pulse electric field induction thermoacoustic signal processing method comprises the steps that insulating oil is filled between a target body and polar plates of an electrode A and an electrode B, nanosecond-wide pulse voltage U (t) is applied to the electrodes, and an ultrasonic probe is used for collecting acoustic signals; solving the electric potential mark position of the target body by using a finite element method, and then solving the electric field intensity and the current density in the target body; the electric field intensity and the current density in the target body are related to the electric conductivity distribution of the target body, and the thermal function of the target body is related to the electric conductivity distribution of the target body, so that the distribution relation between the acoustic signal of the target body and the electric conductivity is finally obtained.

The specific treatment steps preferably include:

placing a target body in a target area, filling insulating oil with the conductivity of 0 between the target body and polar plates of two electrodes A and B, immersing an ultrasonic probe and the target body in the insulating oil, applying a nanosecond-wide pulse voltage U (t) to the target area by using the two electrodes A and B, and acquiring an acoustic signal by using the ultrasonic probe;

the target body is wrapped by the non-conductive medium, and the electric field in the target body is generated through electrolytic texture, so that the ampere law is met:

where ^ is a Hamiltonian, J is a current density, J is an imaginary unit, E is an electric field strength, D is an electric displacement vector, t is time, ω is a frequency, is a dielectric constant, and σ is an electric conductivity, and since the electric conductivity in the insulating oil is 0, the dielectric constant in the target can be ignored with respect to the magnitude of the electric conductivity, whereby σ can be ignored in the insulating oil^*The real part of (a), can be neglected in the target volume^*Imaginary part of, i.e. sigma^*＝σ；

Secondly, because the electric field in the target body is generated by electrolytic texture and the induced magnetic field is very small, the nanosecond pulse electric field induced thermoacoustic imaging can be described as being similar to electric quasi-static imaging

Wherein the content of the first and second substances,

is the electric potential, U is the voltage of the upper plate, r is the area, and belongs to the relation, sigma₁Is the plane of the high-voltage electrode plate₂In an infinitely large plane, sigma_3-6A plane at infinity, n being the normal unit vector of the boundary;

thirdly, the electric mark position of the target area can be obtained through the above formulaThe electric field strength within the target area can then be described as:

the current density in the target body J is:

J＝σE (4)

the target body absorbs joule heat due to the passing of current, and the heat function H is

H(r,t)＝σE²(r,t) (5)

Fourthly, a thermal function image H (r, t) can be constructed through the formula, the target body can generate ultrasonic signals when absorbing joule heat expansion, and the wave equation satisfied by sound pressure is

Where p is the image of the sound source excited by the target volume, c₀Is the sound velocity in the insulating oil, beta is the volume coefficient of thermal expansion of the target, C_pIs the specific heat capacity of the target; the ultrasonic signal emitted by the target body is related to the distribution of the conductivity of the ultrasonic signal, and the conductivity of the target body can be obtained through the inversion of the acoustic signal.

Preferably, in nanosecond pulse thermoacoustic imaging, a finite element method is used for solving a formula (2) to obtain an electric scale position of a target body, and then formulas (3) and (4) are used for solving electric field intensity and current density in the target body; the electric field intensity and the current density in the target body are related to the conductivity distribution of the target body, the electric field intensity and the current density of the area with higher conductivity are higher, and the value of the current density in the target body corresponds to the conductivity; the thermal function of the target body is related to the conductivity distribution of the target body obtained by the formulas (5 and 6), and the area with higher internal conductivity has larger thermal function and larger excited sound source, so that the intensity of the sound source corresponds to the conductivity distribution in the target body.

Preferably, the pulse voltage amplitude required to generate the induced electric field in the target is 10-30KV and the pulse width is 10-500 ns.

Preferably, a simple model and a complex model are respectively established by using a nanosecond pulse thermoacoustic imaging method for simulation analysis, so that theoretical guidance is provided for actual detection of nanosecond pulse thermoacoustic imaging.

More preferably, an electric field is induced in the target region, the interior of the target body expands due to heating to generate sound pressure p (r, t), the thermoacoustic signal is received by an ultrasonic probe arranged around the target body, and as can be seen from the analysis of the positive problem of the sound field in the induction type thermoacoustic imaging, the thermoacoustic signal (r, t) received by the ultrasonic probe is the convolution of the sound pressure p (r, t) at the position of the ultrasonic transducer and the impulse response function h (t) of the ultrasonic probe, namely

The formula (7) shows that the thermoacoustic signal ω (r, t) received by the ultrasonic probe can reflect the waveform of the original sound field and also includes the response characteristic of the ultrasonic probe.

The invention also provides a nanosecond pulse electric field induced thermoacoustic imaging system, which particularly adopts the thermoacoustic signal processing method for processing.

The comprehensive technical scheme and the comprehensive effect of the invention comprise:

the nanosecond pulse electric field induced thermoacoustic imaging inherits the advantages of no wound and high contrast of the traditional thermoacoustic imaging.

1. Compared with magnetoacoustic imaging, the method of the invention does not need a static magnetic field, saves magnet equipment and further reduces the equipment cost and complexity. The more important problem is that in the reconstruction process, the singularity problem of a sound source is avoided, and quick imaging is easier to realize.

2. The nsPEFTAI of the present invention allows for lower power for efficient imaging than microwave thermoacoustic imaging and has the potential for portable imaging. The reason is that the target body in the field is mostly non-magnetic, the response to the magnetic field is close to vacuum, and meanwhile, the frequency of the excitation source is reduced, so that the magnetic field penetrates deeper through the tissue and is not subjected to high-resistance shielding effects such as calcium-containing regions, the large reflection (the reflection coefficient is more than 70%) of other radiation methods is avoided, the influence of the electric field deposited inside the tissue with high dielectric constant is also avoided, and the energy conversion efficiency is improved.

3. Compared with the induction type thermo-acoustic imaging, the high-voltage pulse current is adopted as the excitation source, the condition that the induction electric field is reduced along with the increase of the distance from the excitation source is avoided, and the penetration depth is larger.

Drawings

Fig. 1 is a schematic structural diagram of an imaging system in a nanosecond pulsed electric field induced thermoacoustic signal processing method according to embodiment 1 of the present invention.

Fig. 2 is a schematic diagram of nanosecond pulse voltages in the method for processing a nanosecond pulsed electric field induced thermoacoustic signal according to embodiment 1 of the invention.

Fig. 3 is a simulation model diagram of the target body conductivity in the simulation analysis of the nanosecond pulsed electric field induced thermoacoustic signal processing method in embodiment 2 of the present invention, (a) a simple model, and (b) a complex model.

Fig. 4 is a schematic diagram of the electric field strength of a target simulation model in a simulation analysis of the nanosecond pulsed electric field induced thermoacoustic signal processing method according to the embodiment of the invention, (a) a simple model, and (b) a complex model.

Fig. 5 is a schematic view of current density of a target simulation model in simulation analysis of the nanosecond pulse electric field induced thermoacoustic signal processing method according to the embodiment of the invention, (a) a simple model, and (b) a complex model.

Fig. 6 is a diagram showing a distribution of a thermal function of a target simulation model at a time of 1 μ s in a simulation analysis of the nanosecond pulse electric field induced thermoacoustic signal processing method according to the embodiment of the invention, (a) a simple model, and (b) a complex model.

Fig. 7 is a diagram showing distribution curves of a thermal function of a target simulation model along a line of 0.035 at a time t of 1 μ s, which varies with x, in a simulation analysis of the nanosecond pulse electric-field-induced thermoacoustic signal processing method according to the embodiment of the invention, (a) a simple model, and (b) a complex model.

Fig. 8 shows simulated original acoustic signal diagrams, (a) a simple model, and (b) a complex model in simulation analysis of the nanosecond pulsed electric field induced thermoacoustic signal processing method according to the embodiment of the invention.

Fig. 9 shows a signal diagram received by a simulated ultrasonic probe in the simulation analysis of the nanosecond pulsed electric field induced thermoacoustic signal processing method according to the embodiment of the invention, (a) a simple model, and (b) a complex model.

Detailed Description

The invention is described in detail below with reference to the figures and the specific embodiments.