CN106885842B - A kind of Injection Current formula thermal acoustic imaging resistivity method for reconstructing - Google Patents

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

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CN106885842B
CN106885842B CN201710089730.7A CN201710089730A CN106885842B CN 106885842 B CN106885842 B CN 106885842B CN 201710089730 A CN201710089730 A CN 201710089730A CN 106885842 B CN106885842 B CN 106885842B
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objective body
formula
thermoacoustic
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resistivity
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CN106885842A (en
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李艳红
刘国强
夏正武
杨延菊
夏慧
李士强
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Institute of Electrical Engineering of CAS
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    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0093—Detecting, measuring or recording by applying one single type of energy and measuring its conversion into another type of energy
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/053—Measuring electrical impedance or conductance of a portion of the body
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/08—Detecting organic movements or changes, e.g. tumours, cysts, swellings
    • A61B8/0833—Detecting organic movements or changes, e.g. tumours, cysts, swellings involving detecting or locating foreign bodies or organic structures
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance

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 generated in imageable target body, cause to thermally expand, generate ultrasonic signal, ultrasonic signal is received with ultrasonic transducer, the ultrasonic signal received is handled and acquired, the resistivity image of objective body is obtained using resistivity image algorithm for reconstructing.Specific steps are as follows: 1, first obtain Injection Current formula thermoacoustic signal；2, the Injection Current formula thermoacoustic signal reconstruction objective body thermoacoustic source of acquisition is utilized；3, using thermoacoustic source, vector current potential is rebuild using nonlinear finite element method for solving；4, resistivity is rebuild using the vector current potential of reconstruction.

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, in particular to a kind of Injection Current formula resistivity image is rebuild Method.
Background technique
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 It is improved while existing contrast and resolution ratio.The multiple physical field imaging technique that electromagnetic field and ultrasound combine just allows for electromagnetism Field becomes the focus of people's research, magnetic the high contrast of tissue resistivity and the high-resolution characteristic of ultrasonic listening Thermal acoustic imaging is exactly a kind of emerging multiple physical field imaging technique.
Magnetic thermal acoustic imaging is the novel electrical impedance being put forward for the first time by the Feng of Nanyang Technological University in 2013 Imaging method, principle are as follows: by applying the alternating magnetic field of MHz magnitude to conductive imaging body, induction is generated inside objective body Electric field, and then Joule heat is generated, the ultrasonic signal of thermoelasticity is excited, detection ultrasonic signal is imaged.With microwave thermoacoustic imaging It compares, lower power is allowed efficiently to be imaged, and the potentiality with portable imaging, meanwhile, the frequency of driving source It reduces, so that magnetic field penetration tissue is deeper, the radiation also avoided.
As a kind of novel multiple physical field imaging method, Feng in 2013 imitates body using metallic copper, detects magnetic thermoacoustic Signal, and the thermoacoustic image that copper imitates body 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 generate 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, is proposed on the basis of heat content Resistivity method for reconstructing is still to use coil stimulating mode.Meanwhile extrinsic motivated coil generates time-varying magnetic field in objective body Middle generation secondary magnetic field and induced current, magnetic field and induced current act on while generating Lorentz force and Joule heat, i.e. magnetosonic is imitated It should be coexisted with magnetic thermoacoustic effect, how distinguish magneto-acoustic effect and magnetic thermoacoustic effect is to still need to solve the problems, such as.
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 and magnetic thermal acoustic imaging energisation mode, from the method for reconstructing that enthalpy counts to resistivity not It is identical.
Summary of the invention
The purpose of the present invention is overcome existing magnetic thermal acoustic imaging there are the shortcomings that, propose a kind of based on Injection Current formula thermoacoustic The resistivity method for reconstructing of imaging.The present invention rebuilds resistivity using thermoacoustic source, avoids magneto-acoustic effect during thermal acoustic imaging Interference, while using Injection Current formula motivate, thermoacoustic effect can be enhanced, it can be achieved that objective body resistivity image accurate weight It builds.
Injection Current formula thermal acoustic imaging principle are as follows: by injecting electrode to imageable target body Injection Current, in imageable target Joule heat is generated in body, causes to thermally expand, generates ultrasonic signal, ultrasonic signal is detected using ultrasonic transducer, according to detection Ultrasonic signal rebuilds thermoacoustic source and resistivity.
It includes four steps that the resistivity image of Injection Current formula thermal acoustic imaging of the present invention, which is rebuild: 1, obtaining injection electricity first Streaming thermoacoustic signal, i.e. detection ultrasonic signal；2, the Injection Current formula thermoacoustic signal reconstruction objective body thermoacoustic source of acquisition is utilized；3, Using thermoacoustic source, vector current potential is rebuild using nonlinear finite element method for solving；4, resistance is rebuild using the vector current potential of reconstruction Rate.
Resistivity image reconstruction process is described in detail below:
Step 1: obtaining Injection Current formula thermoacoustic signal
Driving source is by injecting electrode A and injecting electrode B to objective body injected pulse electric current, and objective body is under the function of current Joule heat is generated, and then generates thermal expansion, excitation ultrasound signal, ultrasonic signal is coupled to ultrasonic transducer by couplant, surpasses Sonic transducer receives amplification, the filtering, acquisition and storage for carrying out signal after signal by detection system, and ultrasonic transducer is being controlled Detection is scanned to objective body under device control processed；
Step 2: obtaining 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, csFor the velocity of sound in medium, CPFor the ratio of objective body (3) Thermal capacitance, β are the thermal expansion coefficient of objective body (3), and δ (t) is Dirac function, and S (r) is thermoacoustic source distribution, and t is the time,
Figure BDA0001228556740000022
For Laplacian；
The time reversal method reconstruction formula of thermoacoustic source distribution are as follows:
Wherein, R is scalar, R=| r '-r |, R is vector,
Figure BDA0001228556740000024
eRFor unit vector, r' is the position of ultrasonic probe It sets, r is thermoacoustic source position, SdIt is the plane where ultrasonic probe, p ' is first derivative of the acoustic pressure to the time, and n is the position r ' Sd's Normal vector, β are the thermal expansion coefficient of objective body；
Choose a certain fault plane z=z of objective body1, ultrasonic transducer carries out circular scanning on this fault plane, and acquisition is super Acoustical signal solves z=z 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, whole thermoacoustic on objective body (3) Source S can be obtained by interpolation on layered weighting calculating or the direction z；
Thermoacoustic source S is the function of resistivity and current density simultaneously, can be indicated are as follows:
S=ρ J2=ρ JJ (3)
Wherein, ρ is the resistivity of objective body, and J is current density distribution in objective body；
Step 3: solving vector current potential
According to current continuity theorem, the divergence of electric current is zero,
Figure BDA0001228556740000031
Vector current potential is introduced, then is had:
Figure BDA0001228556740000032
Wherein, T is vector current potential,
Figure BDA0001228556740000033
For the curl of vector current potential,
Figure BDA0001228556740000034
For Hamiltonian operator；
Using Ohm's law, J=σ E=E/ ρ then has:
Figure BDA0001228556740000035
Wherein, ρ is the resistivity of objective body,
Figure BDA0001228556740000036
For the curl of vector current potential.
It can be obtained by formula (3) and formula (4):
Formula (6) are substituted into formula (5), are obtained:
Figure BDA0001228556740000038
The boundary condition of satisfaction are as follows:
Figure BDA0001228556740000039
Wherein, ΓA,BFor injecting electrode position, ΓgTo remove the objective body boundary except electrode, A0For electrode and objective body Contact area, I are Injection Current, and n indicates the outer normal unit vector in region；
Thermoacoustic source S is substituted into formula (7), in conjunction with boundary condition (8), finite element model for solving is carried out, can rebuild and be sweared Measure current potential T；
Step 4: solving resistivity
Vector current potential T is substituted into formula (6), electricalresistivityρ can be rebuild.
Detailed description of the invention
Injection Current formula thermoacoustic signal acquisition schematic device involved in 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 detection systems, on 7 Position machine, 8 controllers, 9 sinks.
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, the Injection Current signal into objective body 3.Ultrasonic transducer 5 It is coupled between objective body 3 by couplant, the input terminal of the output end connecting detection system 6 of ultrasonic transducer 5, detection system 6 output end connects host computer 7, realizes image reconstruction in host computer 7.The rotation of ultrasonic transducer 5 is swept in the realization of controller 8 Retouch motion control.Objective body 3, injecting electrode A2, injecting electrode B4 and ultrasonic transducer 5 are placed in sink 9.
Injection Current formula thermal acoustic imaging principle are as follows: by injecting electrode to imageable target body Injection Current, in imageable target Joule heat is generated in body, causes to thermally expand, and is generated ultrasonic signal, is detected using ultrasonic transducer, according to the ultrasound of detection Signal rebuilds thermoacoustic source and resistivity.
It includes four steps that the resistivity image of Injection Current formula thermal acoustic imaging of the present invention, which is rebuild: 1, obtaining injection electricity first Streaming thermoacoustic signal, i.e. detection ultrasonic signal；2, the Injection Current formula thermoacoustic signal reconstruction objective body thermoacoustic source of acquisition is utilized；3, Using thermoacoustic source, vector current potential is rebuild using nonlinear finite element method for solving；4, resistance is rebuild using the vector current potential of reconstruction Rate.
Image reconstruction process is described in detail below:
Step 1: obtaining Injection Current formula thermoacoustic signal
Driving source 1 is by injecting electrode A2 and injecting electrode B4 to 3 injected pulse electric current of objective body, and objective body 3 is in electric current Effect is lower to generate Joule heat, and then generates thermal expansion, and excitation ultrasound signal, signal is coupled to ultrasonic transducer 5 by couplant, Ultrasonic transducer 5 passes through amplification, filtering, acquisition and storage that detection system 6 carries out signal, ultrasonic transducer after receiving signal 5 are scanned detection to objective body under the control of the controller 8；
Step 2: obtaining objective body thermoacoustic source
The acoustic pressure wave equation of known thermal acoustic imaging:
Figure BDA0001228556740000041
Wherein r is ultrasonic transducers locations, and p (r, t) is acoustic pressure, csFor the velocity of sound in medium, CPFor the ratio of objective body (3) Thermal capacitance, β are the thermal expansion coefficient of objective body (3), and δ (t) is Dirac function, and S (r) is thermoacoustic source distribution, and t is the time,
Figure BDA0001228556740000042
For Laplacian；
The time reversal method reconstruction formula of thermoacoustic source distribution are as follows:
Wherein, R is scalar, R=| r '-r |, R is vector,
Figure BDA0001228556740000044
eRFor unit vector, r' is the position of ultrasonic probe It sets, r is thermoacoustic source position, SdIt is the plane where ultrasonic probe, p ' is first derivative of the acoustic pressure to the time, and n is the position r ' Sd's Normal vector, β are the thermal expansion coefficient of objective body；
Choose a certain fault plane z=z of objective body1, ultrasonic transducer carries out circular scanning on this fault plane, and acquisition is super Acoustical signal solves z=z using equation (1), (2)1Thermoacoustic source distribution S (x, y, z on fault plane1), mobile ultrasonic transducer exists Scanning Detction is carried out on different fault planes, solves the thermoacoustic source distribution on different fault planes, overall thermal sound source S can on objective body 3 It is obtained by interpolation on layered weighting calculating or the direction z；
Thermoacoustic source S is the function of resistivity and current density simultaneously, can be indicated are as follows:
S=ρ J2=ρ JJ (3)
Wherein, ρ is the resistivity of objective body 3, and J is current density distribution in objective body 3；
Step 3: solving vector current potential
According to current continuity theorem, the divergence of electric current is zero,
Figure BDA0001228556740000051
Vector current potential is introduced, then is had:
Figure BDA0001228556740000052
Wherein, T is vector current potential,
Figure BDA0001228556740000053
For the curl of vector current potential,For Hamiltonian operator；
Using Ohm's law, J=σ E=E/ ρ then has:
Figure BDA0001228556740000055
Wherein, ρ is the resistivity of objective body,
Figure BDA0001228556740000056
For the curl of vector current potential.
It can be obtained by formula (3) and formula (4):
Formula (6) are substituted into formula (5), are obtained:
Figure BDA0001228556740000058
The boundary condition of satisfaction are as follows:
Figure BDA0001228556740000059
Wherein, ΓA,BFor injecting electrode position, ΓgTo remove the objective body boundary except electrode, A0For electrode and objective body Contact area, I are Injection Current, and n indicates the outer normal unit vector in region；
Thermoacoustic source S is substituted into formula (7), in conjunction with boundary condition (8), finite element model for solving is carried out, can rebuild and be sweared Measure current potential T；
Step 4: solving resistivity
Vector current potential T is substituted into formula (6), electricalresistivityρ can be rebuild.

Claims (1)

1. a kind of Injection Current formula thermal acoustic imaging resistivity method for reconstructing, which is characterized in that the Injection Current formula thermoacoustic electricity Thermal acoustic imaging principle of the resistance rate image rebuilding method based on Injection Current formula, it is electric to the injected pulse of imageable target body by electrode Stream, generates Joule heat in imageable target body, causes to thermally expand, and generates ultrasonic signal, receives ultrasonic signal with ultrasonic transducer, The ultrasonic signal received is handled and acquired, the resistivity map of objective body is obtained using resistivity image algorithm for reconstructing Picture；
The acquisition methods in thermoacoustic source are as follows: the acoustic pressure wave equation of known thermal acoustic imaging:
Figure FDA0001902247820000011
Wherein r is ultrasonic transducers locations, and p (r, t) is acoustic pressure, csFor the velocity of sound in medium, CPFor the specific heat capacity of objective body (3), β is the thermal expansion coefficient of objective body (3), and δ (t) is Dirac function, and S (r) is thermoacoustic source distribution, and t is the time,It is general to draw Lars operator；
Choose a certain fault plane z=z of objective body1, ultrasonic transducer carries out circular scanning on this fault plane, acquires 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, solves the thermoacoustic source distribution on different fault planes, overall thermal sound source S can be by being layered on objective body (3) Interpolation obtains in detection calculating or the direction z；
Thermoacoustic source S is the function representation of resistivity and current density simultaneously are as follows:
S=ρ J2=ρ JJ (3)
Wherein, ρ is the resistivity of objective body (3), and J is objective body (3) interior current density distribution；
The Injection Current formula thermal acoustic imaging resistivity method for reconstructing the following steps are included:
Step 1: obtaining 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 generated under the function of current, and then generates thermal expansion, and excitation ultrasound signal, ultrasonic signal is coupled to super by couplant Sonic transducer (5), ultrasonic transducer (5) pass through amplification, filtering, acquisition that detection system (6) carry out signal after receiving signal And storage, realize that image reconstruction, ultrasonic transducer (5) sweep objective body in the case where controller (8) control in host computer (7) Retouch detection；
Step 2: obtaining objective body thermoacoustic source
A pair of injecting electrode A (2), injecting electrode B (4) are used according to the first step, to after objective body Injection Current, it is swollen to cause heat It is swollen, acoustical signal is excited, detects sound pressure signal, overall thermal sound source on objective body is rebuild using sound pressure signal；
Step 3: solving vector current potential
According to current continuity theorem, the divergence of electric current is zero,
Figure FDA0001902247820000021
Vector current potential is introduced, then is had:
Figure FDA0001902247820000022
Wherein, T is vector current potential,
Figure FDA0001902247820000023
For the curl of vector current potential,For Hamiltonian operator；
Using Ohm's law, J=σ E=E/ ρ then has:
Figure FDA0001902247820000025
It can be obtained by formula (3) and formula (4):
Figure FDA0001902247820000026
Formula (6) are substituted into formula (5), are obtained:
The boundary condition of satisfaction are as follows:
Figure FDA0001902247820000028
Wherein, ΓA,BFor injecting electrode position, ΓgTo remove the objective body boundary except electrode, A0It is contacted for electrode with objective body Area, I are Injection Current, and n indicates the outer normal unit vector in region；
Thermoacoustic source S is substituted into formula (7), in conjunction with boundary condition (8), carries out finite element model for solving, can rebuild to obtain vector electricity Position T；
Step 4: solving resistivity
Vector current potential T is substituted into formula (6), electricalresistivityρ can be rebuild.
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CN111887807B (en) * 2020-03-13 2021-08-17 中国石油大学(华东) Nanosecond pulse electric field induced thermoacoustic signal processing method and system
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