CN106885842A - A kind of Injection Current formula thermal acoustic imaging resistivity method for reconstructing - Google Patents

Abstract

A kind of Injection Current formula thermal acoustic imaging resistivity method for reconstructing, the thermal acoustic imaging principle based on electric current injection mode.By electrode to imageable target body injected pulse electric current, Joule heat is produced in imageable target body, cause thermal expansion, produce ultrasonic signal, ultrasonic signal is received with ultrasonic transducer, ultrasonic signal to receiving is processed and gathered, and the resistivity image of objective body is obtained using resistivity image algorithm for reconstructing.Concretely comprise the following steps：1st, Injection Current formula thermoacoustic signal is obtained first；2nd, using the Injection Current formula thermoacoustic signal reconstruction objective body thermoacoustic source for obtaining；3rd, using thermoacoustic source, vector current potential is rebuild using nonlinear finite element method for solving；4th, resistivity is rebuild using the vector current potential rebuild.

Description

A kind of Injection Current formula thermal acoustic imaging resistivity method for reconstructing

Technical field

The present invention relates to a kind of resistivity image method for reconstructing, more particularly to a kind of Injection Current formula resistivity image is rebuild Method.

Background technology

Due to the limitation of driving frequency, the sensitivity of the anti-imaging technique of traditional resistor and spatial resolution be not high.Single field There is its physical limitation, multiple physical field imaging provides resolution ratio by a kind of physical field, and another physical field provides contrast, real Improved while existing contrast and resolution ratio.The multiple physical field imaging technique that electromagnetic field and ultrasound are combined just allows for electromagnetism To the high-contrast and the high-resolution characteristic of ultrasonic listening of tissue resistivity, the focus as people's research, magnetic Exactly a kind of emerging multiple physical field imaging technique of thermal acoustic imaging.

Magnetic thermal acoustic imaging is the new electrical impedance proposed first in 2013 by the Feng of Nanyang Technological University Imaging method, its principle is：By applying the alternating magnetic field of MHz magnitudes to conductive imaging body, sensing is produced inside objective body Electric field, and then Joule heat is produced, excite the ultrasonic signal of thermoelasticity, detection ultrasonic signal to be imaged.With microwave thermoacoustic imaging Compare, it is allowed to which lower power is efficiently imaged, and with the potentiality of portable imaging, meanwhile, the frequency of driving source Reduce so that magnetic field penetration tissue is deeper, the radiation for also avoiding.

Used as a kind of new multiple physical field imaging method, Feng in 2013 imitates body, detects magnetic thermoacoustic using metallic copper Signal, and the thermoacoustic image of the imitative body of copper is obtained, resistivity image reconstruction is not carried out, and biological tissue is imitative different from metallic copper The Lorentz force that body, magnetic field and induced-current effect are produced is weaker.Patent " a kind of resistivity method for reconstructing of magnetic thermal acoustic imaging " (201410771496.2) a kind of resistivity method for reconstructing based on magnetic thermoacoustic effect is disclosed, it is proposed on the basis of heat content Resistivity method for reconstructing, is still using coil stimulating mode.Meanwhile, extrinsic motivated coil produces time-varying magnetic field in objective body Middle to produce secondary magnetic field and induced-current, magnetic field and induced-current effect produce Lorentz force and Joule heat, i.e. magnetosonic effect simultaneously Should be coexisted with magnetic thermoacoustic effect, how to distinguish magneto-acoustic effect and magnetic thermoacoustic effect is the problem for still needing to solve.

Based on this, using Injection Current formula thermal acoustic imaging method, magneto-acoustic effect can be avoided and magnetic thermoacoustic effect coexists and asks Topic, Injection Current formula thermal acoustic imaging is counted on the method for reconstructing of resistivity not with magnetic thermal acoustic imaging in energisation mode, from enthalpy It is identical.

The content of the invention

The purpose of the present invention is the shortcoming for overcoming existing magnetic thermal acoustic imaging to exist, and is proposed a kind of based on Injection Current formula thermoacoustic The resistivity method for reconstructing of imaging.The present invention rebuilds resistivity using thermoacoustic source, it is to avoid magneto-acoustic effect during thermal acoustic imaging Interference, while being encouraged using Injection Current formula, thermoacoustic effect can be strengthened, be capable of achieving the accurate weight of objective body resistivity image Build.

Injection Current formula thermal acoustic imaging principle is：By injecting electrode to imageable target body Injection Current, in imageable target Joule heat is produced in body, causes thermal expansion, produce ultrasonic signal, ultrasonic signal is detected using ultrasonic transducer, according to detection Ultrasonic signal rebuilds thermoacoustic source and resistivity.

The resistivity image of Injection Current formula thermal acoustic imaging of the present invention is rebuild includes four steps：1st, injection electricity is obtained first Streaming thermoacoustic signal, that is, detect ultrasonic signal；2nd, using the Injection Current formula thermoacoustic signal reconstruction objective body thermoacoustic source for obtaining；3、 Using thermoacoustic source, vector current potential is rebuild using nonlinear finite element method for solving；4th, resistance is rebuild using the vector current potential rebuild Rate.

Resistivity image process of reconstruction is described in detail below：

The first step：Obtain Injection Current formula thermoacoustic signal

, by injecting electrode A and injecting electrode B to objective body injected pulse electric current, objective body is under the function of current for driving source Joule heat is produced, and then produces thermal expansion, excitation ultrasound signal, ultrasonic signal is coupled to ultrasonic transducer by couplant, surpassed Sonic transducer receiving after signal carry out the amplification of signal, filtering, collection by detecting system and storing, and ultrasonic transducer is in control Detection is scanned to objective body under device control processed；

Second step：Obtain objective body thermoacoustic source

The acoustic pressure wave equation of known thermal acoustic imaging：

Wherein r is ultrasonic transducers locations, and p (r, t) is acoustic pressure, c_sIt is the velocity of sound in medium, C_PIt is the ratio of objective body (3) Thermal capacitance, β is the thermal coefficient of expansion of objective body (3), and δ (t) is Dirac function, and S (r) is thermoacoustic source distribution, and t is the time,For Laplacian；

The time reversal method reconstruction formula of thermoacoustic source distribution is：

Wherein, R is that scalar, R=| r '-r |, R are vector,e_RIt is unit vector, r' is the position of ultrasonic probe Put, r is thermoacoustic source position, S_dIt is the plane where ultrasonic probe, p ' is first derivative of the acoustic pressure to the time, and n is r ' positions S_d's Normal vector, β is the thermal coefficient of expansion of objective body；

Choose a certain fault plane z=z of objective body₁, ultrasonic transducer carries out circular scanning on this fault plane, and collection is super Acoustical signal, z=z is solved using equation (1) and formula (2)₁Thermoacoustic source distribution S (x, y, z on fault plane₁), mobile ultrasonic transduction Device carries out Scanning Detction on different fault planes, solves the thermoacoustic source distribution on different fault planes, overall thermoacoustic on objective body (3) Source S can be obtained by interpolation on layered weighting calculating or z directions；

Thermoacoustic source S is simultaneously the function of resistivity and current density, can be expressed as：

S=ρ J²=ρ JJ (3)

Wherein, ρ is the resistivity of objective body, and J is electric current distribution in objective body；

3rd step：Solve vector current potential

According to current continuity theorem, the divergence of electric current is zero,Vector current potential is introduced, is then had：

Wherein, T is vector current potential,It is the curl of vector current potential,It is Hamiltonian operator；

Using Ohm's law, J=σ E=E/ ρ then have：

Wherein, ρ is the resistivity of objective body,It is the curl of vector current potential.

Can be obtained by formula (3) and formula (4)：

By in formula (6) substitution formula (5), obtain：

The boundary condition of satisfaction is：

Wherein, Γ_A,BIt is injecting electrode position, Γ_gTo remove the objective body border outside electrode, A₀It is electrode and objective body Contact area, I is Injection Current, and n represents the outer normal unit vector in region；

Thermoacoustic source S is substituted into formula (7), with reference to boundary condition (8), finite element model for solving is carried out, you can reconstruction is sweared Amount current potential T；

4th step：Solve resistivity

Vector current potential T is substituted into formula (6), you can rebuild electricalresistivityρ.

Brief description of the drawings

Injection Current formula thermoacoustic signal acquisition schematic device involved by Fig. 1 method for reconstructing of the present invention；

In figure：1 driving source, 2 injecting electrode A, 3 objective bodies, 4 injecting electrode B, 5 ultrasonic transducers, 6 detecting systems, on 7 Position machine, 8 controllers, 9 tanks.

Specific embodiment

Below in conjunction with the drawings and specific embodiments, the present invention will be further described.

Driving source 1 connects injecting electrode A2 and injecting electrode B4, to Injection Current signal in objective body 3.Ultrasonic transducer 5 Coupled by couplant between objective body 3, the input of the output end connecting detection system 6 of ultrasonic transducer 5, detecting system 6 output end connection host computer 7, image reconstruction is realized in host computer 7.Controller 8 is realized sweeping the rotation of ultrasonic transducer 5 Retouch motion control.Objective body 3, injecting electrode A2, injecting electrode B4 and ultrasonic transducer 5 are placed in tank 9.

Injection Current formula thermal acoustic imaging principle is：By injecting electrode to imageable target body Injection Current, in imageable target Joule heat is produced in body, causes thermal expansion, produce ultrasonic signal, detected using ultrasonic transducer, according to the ultrasound of detection Signal, rebuilds thermoacoustic source and resistivity.

The resistivity image of Injection Current formula thermal acoustic imaging of the present invention is rebuild includes four steps：1st, injection electricity is obtained first Streaming thermoacoustic signal, that is, detect ultrasonic signal；2nd, using the Injection Current formula thermoacoustic signal reconstruction objective body thermoacoustic source for obtaining；3、 Using thermoacoustic source, vector current potential is rebuild using nonlinear finite element method for solving；4th, resistance is rebuild using the vector current potential rebuild Rate.

Image reconstruction process is described in detail below：

The first step：Obtain Injection Current formula thermoacoustic signal

, by injecting electrode A2 and injecting electrode B4 to the injected pulse electric current of objective body 3, objective body 3 is in electric current for driving source 1 Effect is lower to produce Joule heat, and then produces thermal expansion, and excitation ultrasound signal, signal is coupled to ultrasonic transducer 5 by couplant, Ultrasonic transducer 5 receives amplification, filtering, collection and the storage for carrying out signal after signal by detecting system 6, ultrasonic transducer 5 are scanned detection to objective body under the control of the controller 8；

Second step：Obtain objective body thermoacoustic source

The acoustic pressure wave equation of known thermal acoustic imaging：

Wherein r is ultrasonic transducers locations, and p (r, t) is acoustic pressure, c_sIt is the velocity of sound in medium, C_PIt is the ratio of objective body (3) Thermal capacitance, β is the thermal coefficient of expansion of objective body (3), and δ (t) is Dirac function, and S (r) is thermoacoustic source distribution, and t is the time,For Laplacian；

The time reversal method reconstruction formula of thermoacoustic source distribution is：

Wherein, R is that scalar, R=| r '-r |, R are vector,e_RIt is unit vector, r' is the position of ultrasonic probe Put, r is thermoacoustic source position, S_dIt is the plane where ultrasonic probe, p ' is first derivative of the acoustic pressure to the time, and n is r ' positions S_d's Normal vector, β is the thermal coefficient of expansion of objective body；

Choose a certain fault plane z=z of objective body₁, ultrasonic transducer carries out circular scanning on this fault plane, and collection is super Acoustical signal, using equation (1), (2), solves z=z₁Thermoacoustic source distribution S (x, y, z on fault plane₁), mobile ultrasonic transducer exists Scanning Detction is carried out on different fault planes, the thermoacoustic source distribution on different fault planes is solved, overall thermal sound source S can on objective body 3 Obtained by interpolation on layered weighting calculating or z directions；

Thermoacoustic source S is simultaneously the function of resistivity and current density, can be expressed as：

S=ρ J²=ρ JJ (3)

Wherein, ρ is the resistivity of objective body 3, and J is electric current distribution in objective body 3；

3rd step：Solve vector current potential

According to current continuity theorem, the divergence of electric current is zero,Vector current potential is introduced, is then had：

Wherein, T is vector current potential,It is the curl of vector current potential,It is Hamiltonian operator；

Using Ohm's law, J=σ E=E/ ρ then have：

Wherein, ρ is the resistivity of objective body,It is the curl of vector current potential.

Can be obtained by formula (3) and formula (4)：

By in formula (6) substitution formula (5), obtain：

The boundary condition of satisfaction is：

Wherein, Γ_A,BIt is injecting electrode position, Γ_gTo remove the objective body border outside electrode, A₀It is electrode and objective body Contact area, I is Injection Current, and n represents the outer normal unit vector in region；

Thermoacoustic source S is substituted into formula (7), with reference to boundary condition (8), finite element model for solving is carried out, you can reconstruction is sweared Amount current potential T；

4th step：Solve resistivity

Vector current potential T is substituted into formula (6), you can rebuild electricalresistivityρ.

Claims (1)

1. a kind of Injection Current formula thermal acoustic imaging resistivity method for reconstructing, it is characterised in that described Injection Current formula thermoacoustic electricity Conductance image rebuilding method is based on the thermal acoustic imaging principle of Injection Current formula, by electrode to imageable target body injected pulse electricity Stream, Joule heat is produced in imageable target body, causes thermal expansion, produces ultrasonic signal, and ultrasonic signal is received with ultrasonic transducer, Ultrasonic signal to receiving is processed and gathered, and the resistivity map of objective body is obtained using resistivity image algorithm for reconstructing Picture；

The acquisition methods in thermoacoustic source are：The acoustic pressure wave equation of known thermal acoustic imaging：

${\▿}^{2}p(r,t)-\frac{1}{{c_s}^2}\frac{{\∂}^2}{\∂t^2}p(r,t)=-\frac{\mathrm{\β}}{C_P}S\left(r\right){\mathrm{\δ}}^{\′}\left(t\right)---\left(1\right)$

Wherein r is ultrasonic transducers locations, and p (r, t) is acoustic pressure, c_sIt is the velocity of sound in medium, C_PIt is the specific heat capacity of objective body (3), β is the thermal coefficient of expansion of objective body (3), and δ (t) is Dirac function, and S (r) is thermoacoustic source distribution, and t is the time,It is La Pula This operator；

Choose a certain fault plane z=z of objective body₁, ultrasonic transducer carries out circular scanning on this fault plane, collection ultrasound letter Number, using equation (1), solve z=z₁Thermoacoustic source distribution S (x, y, z on fault plane₁), mobile ultrasonic transducer is in different tomographies Scanning Detction is carried out on face, the thermoacoustic source distribution on different fault planes is solved, overall thermal sound source S can be by being layered on objective body (3) Interpolation is obtained in detection calculating or z directions；

Thermoacoustic source S is simultaneously that the function representation of resistivity and current density is：

S=ρ J²=ρ JJ (3)

Wherein, ρ is the resistivity of objective body (3), and J is objective body (3) interior electric current distribution；

Described Injection Current formula thermal acoustic imaging resistivity method for reconstructing is comprised the following steps：

The first step：Obtain Injection Current formula thermoacoustic signal

Driving source (1) is by injecting electrode A (2) and injecting electrode B (4) to objective body (3) injected pulse electric current, objective body (3) Joule heat is produced under the function of current, and then produces thermal expansion, excitation ultrasound signal, ultrasonic signal is coupled to super by couplant Sonic transducer (5), ultrasonic transducer (5) to be received and carry out the amplification of signal, filtering by detecting system (6) after signal, gathers And storage, image reconstruction is realized in host computer (7), ultrasonic transducer (5) is swept under controller (8) control to objective body Retouch detection；

Second step：Obtain objective body thermoacoustic source

A pair of injecting electrode A (2), injecting electrode B (4) are used according to the first step, after objective body Injection Current, triggers heat swollen It is swollen, acoustical signal is excited, sound pressure signal is detected, overall thermal sound source on objective body is rebuild using sound pressure signal；

3rd step：Solve vector current potential

According to current continuity theorem, the divergence of electric current is zero,Vector current potential is introduced, is then had：

$J=\▿\×T---\left(4\right)$

Wherein, T is vector current potential,It is the curl of vector current potential,It is Hamiltonian operator；

Using Ohm's law, J=σ E=E/ ρ then have：

$\▿\×(\mathrm{\ρ}\▿\×T)=0---\left(5\right)$

Can be obtained by formula (3) and formula (4)：

$\mathrm{\ρ}=\frac{S}{\▿\×T\·\▿\×T}---\left(6\right)$

By in formula (6) substitution formula (5), obtain：

$\▿\×(\frac{S}{\▿\×T\·\▿\×T}\▿\×T)=0---\left(7\right)$

The boundary condition of satisfaction is：

$\left\{\begin{array}{c}\▿\×T\·n{|}_{{\mathrm{\Γ}}_{A,B}}=\±\frac{I}{A_0}\\ \▿\×T\·n{|}_{{\mathrm{\Γ}}_g}=0\end{array}\right.---\left(8\right)$

Wherein, Γ_A,BIt is injecting electrode position, Γ_gTo remove the objective body border outside electrode, A₀For electrode is contacted with objective body Area, I is Injection Current, and n represents the outer normal unit vector in region；

Thermoacoustic source S is substituted into formula (7), with reference to boundary condition (8), finite element model for solving is carried out, you can reconstruction obtains vector electricity Position T；

4th step：Solve resistivity

Vector current potential T is substituted into formula (6), you can rebuild electricalresistivityρ.