CN104644219A - Power density imaging method based on acousto-electric effect - Google Patents

Abstract

The invention provides a power density imaging method based on an acousto-electric effect, comprising the following steps that a discrete electrode array is uniformly or non-uniformly fixed at the outer side of a to-be-detected biological tissue; a region encircled by the electrode array is taken as a measurement object field; a focused ultrasound transducer is vertical to the measurement object field, the position of the focused ultrasound transducer is adjusted, and focal spots of the focused ultrasound transducer are positioned on the measurement object field; a region covered by each focal spot on the measurement object field is called as a focusing domain. Focused ultrasound emitted by the focused ultrasound transducer disturbs the conductivity of the biological tissue in each focusing domain; a voltage vector is measured by utilization of the boundary of the electrode array measurement; a power density value of each focusing domain is calculated according to a power density calculation formula; when the focused ultrasound transducer finishes the disturbance to each focusing domain, a power density distribution diagraph of the measurement object field is obtained by means of utilizing the power density value of each focusing domain and combining the position information of each focusing domain. The power density imaging method based on the acousto-electric effect has the advantage that the medium distribution spatial resolution of the measurement object field can be improved.

Description

Based on the power density formation method of acoustoelectric effect

Technical field

The invention belongs to technical field of imaging, relate to multiple physical field hybrid imaging technology, specifically a kind of power density formation method based on acoustoelectric effect.

Background technology

Each tissue of human body (organ) has different electrology characteristics, and some pathological phenomenons and physiological activity all can cause the change of tissue electrology characteristic, and therefore biological tissue carries abundant physiology and pathological information.By certain technological means, rebuild the electrology characteristic of biological tissue or dielectric distribution image, and then analyze and the physiology of postgraduate's object and pathological condition, there is very high practical value clinically.

Electrical impedance tomography technology (Electrical Impedance Tomography, EIT) be chromatography imaging technique based on electrical characteristics sensitive mechanism, it is by electricity means, judges the electrical characteristics distribution of object in sensitivity field, and then obtains the distributed image of this interior medium.In imaging process, the receptible small safe current of end user's body, and do not use nucleic or shooting, to human body without ionization or radiation effects; In addition, its structure is simple, measurement is convenient, cheap, is applicable to being applied to medical treatment generaI investigation and carrying out long-term medical image monitoring to patient, is the technological means having very much application and research to be worth.Nearly decades, scholar extensively studied EIT, and it all makes much progress in theory, hardware, software, algorithm etc.

But because the inverse problem of EIT dielectric distribution image reconstruction has serious ill-posedness, cause reconstructed image spatial resolution and precision all very low, limit its application and development.Study new method and obtain the basic method that more effective information is solution EIT low spatial resolution, low precision.

In bio-electrical impedance imaging field, researcheres are while improving experimental design and improvement algorithm for reconstructing, attempt, from the angle of physic field coupling, electrical impedance imaging is combined with other imaging techniques the effective information increasing imaging, thus improve the spatial resolution of image.

Acoustoelectric effect refers to, the ultrasound wave focused on causes pressure to change in Medium Propagation, cause the mechanical compress in regional area (focal zone) cycle and lax (being determined by hyperacoustic frequency), cause the minute elastic deformation of regional area, thus cause local conductivity to change.

Electricity and ultra sonic imaging combine by the formation method based on acoustoelectric effect, improve the spatial resolution of measured object field electrical parameter distribution.H Zhang in 2004 and L V Wang (Acousto-electric tomography, H Zhang and L V Wang, " Proceedings of SPIE ", 2004,5320:145-149) in the meeting of optical field, deliver acoustic-electric formation method, the method utilizes the positioning function of focus supersonic different with the acoustic-electric modulation signal of different medium, directly reconstructs electrical conductivity spatial distribution according to the position of ultrasonic beam and the power of acoustoelectric signal.Biological tissue's electrical impedance imaging method of Chinese patent (CN 103156604A) also openly supersonic synergic in 2013.

The people such as the Ragnar Olafsson of the U.S. propose the Current density imaging based on acoustoelectric effect, acoustoelectric signal is utilized to rebuild measured object field internal current source distributed intelligence (Ultrasound Current Source Density Imaging based on acoustoelectric effect, Ragnar Olafsson, RussellS.Witte, Sheng-Wen Huang and Matthew O ' Donnell, IEEETRANSACTIONS ON BIOMEDICAL ENGINEERING, 2008, 55 (7): 1840-1848) (Measurement of a 2D electric dipole filed using the acousto-electric effect, Ragnar Olafsson, Russell S.Witte and Matthew O ' Donnell, Proc.SPIE 6513, Medical Imaging 2007:Ultrasonic Imaging and Signal Processing, 65130S (March 12, 2007), doi:10.1117/12.712448, San Diego, CA|February 17,2007).2013 Chinese patent (CN 103156605A) also disclose a kind of biological tissue's Current density imaging based on acoustoelectric effect.

People (the Electrical impedance tomography by elastic deformation such as French researcher Ammari in 2008, HAmmari, E Bonnetier, Y Capdeboscq, M Tanter and M Fink, SIAM Journal on Applied Mathematics, 2008,68:1557-1573) mathematical theory, obtain local power density by the electrical impedance tomography boundary survey value derivation through ultrasonic modulation, and this information is reconstructed the distribution of conductivity of measured object field as intermediate quantity.This research work relates to power density, but due to power density computation formula be derive based on small size inclusions extended method to obtain, the computing formula of power density is only applicable to the interior zone measuring thing field, there is limitation in actual use.Further, this work is in pure mathematics theoretical basis, and based on the calculating of continuous electrode model realization power density, and actual measuring system can only use dispersive electrode model.The people such as Ammari are (Resolution andstability analysis in acousto-electric imaging in the research work of 2012, H Ammari, J Garnier and W Jing, Inverse Problem, 2012,28,084005), use approximate power density computation formula, although the scope of application of power density to be expanded to whole measurement thing field, affect the computational accuracy of power density.

The above-mentioned existing work relating to power density is just rebuild power density intermediate variable as electrical conductivity, does not have power density as independently formation method research; The computing formula of the accurate power density proposed is only applicable to the interior zone measuring thing field, there is limitation in actual use, although and approximate after power density computation formula be applicable to whole measurement thing field, affect computational accuracy; The calculating of existing power density is all in pure theory and based on continuous electrode model, and actual measuring system can only use dispersive electrode model.

Summary of the invention

The object of the invention is the deficiency existed for above-mentioned prior art, a kind of power density formation method based on acoustoelectric effect is proposed, the method is on dispersive electrode model basis, using power density imaging as one independently imaging means, coupling ultrasonic on electricity basis, by concentration ultrasonic to the disturbance focusing on territory medium, obtains the power density information measuring thing field, form power density distribution image, thus reach the object improving and measure thing field dielectric distribution spatial resolution.For achieving the above object, the technical solution used in the present invention is to provide a kind of power density formation method based on acoustoelectric effect.Comprise the following steps:

A kind of power density formation method based on acoustoelectric effect, discrete electrod-array is uniformly or non-uniformly fixed on the outside of tested biological tissue by the method, the region that electrod-array surrounds is for measuring thing field, focused transducer is perpendicular to measurement thing field, regulate its position, the focal spot of focused transducer is positioned at and measures on thing field, the region that focal spot covers on measurement thing field is called focusing territory.The concentration ultrasonic that focused transducer is launched produces disturbance to the electrical conductivity focusing on Yu Chu biological tissue, the boundary survey voltage vector utilizing electrod-array to measure, according to power density computation formula, calculate the power density values focusing on territory place, when after the disturbance that focused transducer completes each focusing territory, utilize each to focus on the power density values at territory place, focus on the positional information in territory in conjunction with each, obtain the power density distribution figure measuring thing field, comprise following step:

1) focal spot size and the sound pressure level P of focused transducer is measured

Make microphone aim at focused transducer, and make the sensing unit of microphone be in the focal spot place of focused transducer, measure the sound pressure level P obtaining focal spot place, regulate the position of microphone, measure the focal spot size of focused transducer;

2) measurement thing field is divided into I and focuses on territory, determine that each focuses on the positional information in territory, and concentration ultrasonic intends the scanning sequency each being focused on to territory

According to measuring thing field size and step 1) in measure the focal spot size obtained, measurements thing field is divided into I and focuses on territory, division principle is: focused transducer can complete the scanning to whole measurement thing field, and respectively focusing territory is not overlapping.Record the two-dimensional position information that each focuses on territory, i.e. the coordinate (x, y) in each focusing territory, and determine that concentration ultrasonic intends focusing on each scanning sequency in territory, from 1 to I;

3) without in focus ultrasonic situation, electrical stimuli and measurement are carried out to measurement thing field, obtains boundary survey voltage vector φ (x, y)

By applying current excitation or voltage drive on exciting electrode, realize applying electrical stimuli to measurement thing field, collection Opposed Current encourages, neighboring voltage is measured and boundary voltage in each measurement electrode under the measurement pattern do not measured of exciting electrode, form boundary survey voltage vector φ (x, y), complete and once encourage measuring process;

4) in focus ultrasonic situation, focus supersonic wave disturbance each focusing territory i, carries out electrical stimuli, measurement to measurement thing field simultaneously again, obtains boundary survey voltage vector φ _i(x, y)

By focused transducer perpendicular to measurement thing field, to each focusing territory i (1≤i≤I), while focus supersonic wave disturbance, all complete a step 3) in the excitation measuring process of electrod-array, measure the boundary survey voltage vector φ of thing field when obtaining focus supersonic this focusing territory of wave disturbance _i(x, y);

5) define the product that power density is electrical conductivity and electric field intensity square, utilize step 3) and step 4) measure the boundary voltage signal psi (x, y) and φ that obtain respectively _i(x, y), by the power density values of i position, following formulae discovery each focusing territory, is designated as S _i(x, y):

$S_i(x,y)=-{\left[{\∫\∫}_{\mathrm{\Ω}}^{\mathrm{kP}}\right]}^{-1}{\∫}_{\∂\mathrm{\Ω}}({\mathrm{\φ}}_i(x,y)-\mathrm{\φ}(x,y))j(x,y)\mathrm{dx}$

Wherein, k=10 ^-9for the acoustoelectric effect coefficient of medium; J (x, y) is step 3) in be applied to outer normal direction electric current density on exciting electrode, be the ratio of exciting current and exciting electrode area; Ω is for measuring thing field; for measuring thing border outside the venue;

6) power density distribution image S (x, y) of whole measurement thing field is obtained

Focus on the power density values of position, territory by each, integrating step 1) in each focus on the positional information in territory, obtain power density distribution image S (x, y) of whole measurement thing field.

The present invention is owing to taking above technical scheme, and it has the following advantages:

(1) compared with traditional electrical impedance tomography technology, the present invention is coupling ultrasonic on electricity basis, based on acoustoelectric effect principle, by the disturbance of concentration ultrasonic to whole measurement thing field dielectric distribution, obtain the power density information measuring thing field, form power density image, thus reach the object improving and measure thing field dielectric distribution spatial resolution.

(2) the present invention proposes new power density computation formula, and this formula, compared to existing power density computation formula, namely overcomes existing computing formula limitation in actual use, ensures computational accuracy again.

(3) one of the advantage of power density imaging of the present invention to carry out reverse temperature intensity, directly rebuilds, avoid a lot of problems that the reconstruction of conventional electrical imaging inverse problem can run into, such as unstable, less qualitative etc.

(4) the present invention adopts dispersive electrode model, and compared to continuous electrode model, the electrode of this kind of form is easier to realize in actual measuring system, and follow-up hardware circuit and software design are also more simple.

(5) power density image height depends on distribution of conductivity, and it can reflect physiology and the pathological condition of biological tissue of human body, for biomedical measurement provides a kind of high-resolution measurement means newly.

Accompanying drawing explanation

The following drawings describes the embodiment selected by the present invention, is exemplary drawings and non exhaustive or restricted, wherein:

Fig. 1 is principle schematic of the present invention;

Fig. 2 is operational flowchart of the present invention;

Fig. 3 is the excitation instrumentation plan of measurement thing of the present invention dispersive electrode array outside the venue;

Fig. 4 is that concentration ultrasonic of the present invention is to the schematic diagram focusing on territory dielectric conductance rate disturbance;

The geometric model figure that Fig. 5 (a) is arranged for simulation example of the present invention;

Fig. 5 (b) is corresponding illustraton of model 5 (a) the power density image under 1-9 electrode excitation boundary condition of simulation example of the present invention;

Fig. 5 (c) imitates corresponding illustraton of model 5 (a) the power density image under 5-13 electrode excitation boundary condition of actual example for the present invention;

Detailed description of the invention

Be described in detail of the present invention below in conjunction with drawings and Examples.(whether the words needs deletes)

Below in conjunction with drawings and Examples, the power density formation method based on acoustoelectric effect of the present invention is illustrated, be intended to describe as embodiments of the invention, be not can manufactured or utilize unique forms, also should comprise within the scope of the invention the embodiment that other can realize identical function.

The power density formation method that the present invention is based on acoustoelectric effect is formed primarily of four parts, as shown in Figure 1: (1) obtains the dispersive electrode array measuring thing field information.Dispersive electrode array is fixed on outside biological tissue, and the region that electrod-array surrounds is measures thing field.Dispersive electrode array is used for applying electrical stimuli to measurement thing field, and detects corresponding measurement thing field boundary voltage signal.(2) focus supersonic wave generating device.Focused transducer, perpendicular to measurement thing field, produces concentration ultrasonic under focused transducer driving device drives.The focal spot of focused transducer is positioned to be measured on thing field, and the region that focal spot covers on measurement thing field becomes focusing territory.(3) data acquisition and procession unit.Its task is the boundary survey voltage signal gathering the reflected measurement thing field dielectric distribution state that dispersive electrode array exports fast in real time, completes corresponding demodulation, Filtering Processing, to obtain the information of direct reflection field change.(4) image reconstruction unit.Its task uses power density computation formula, according to boundary survey voltage signal, obtains the two dimensional image of measured object field, make people directly see the power density image of measured object field over the display.Based on the power density formation method of acoustoelectric effect operational flowchart as shown in Figure 2, probably can be divided into following step:

(1) focal spot size and the sound pressure level P in the focusing territory of focused transducer is measured.

Make microphone aim at transducer, and make the sensing unit of microphone be in the focus place of transducer, measure the sound pressure level P obtaining focus point.Regulate the position of microphone, the focal spot size in the focusing territory of measurement transducer.

(2) measurement thing field is divided into I and focuses on territory, determine that each focuses on the positional information in territory, and concentration ultrasonic intends the scanning sequency each being focused on to territory.

According to measuring thing field and focusing on the size of focal spot in territory, measurements thing field is divided into I and focuses on territory, division principle is: focused transducer can complete the scanning to whole measurement thing field, and respectively focusing territory is not overlapping.Record the positional information that each focuses on territory, and determine that concentration ultrasonic intends focusing on each scanning sequency in territory, from 1 to I.

(3) without under focus ultrasonic disturbance, electrical stimuli, measurement are carried out to measurement thing field, obtains boundary survey voltage vector $\mathrm{\φ}(x,y)=u(x,y){|}_{\∂\mathrm{\Ω}}.$

Dispersive electrode array evenly or is anisotropically fixed on measures thing side outside the venue, is used for applying electrical stimuli to measurement thing field, and detects corresponding measurement thing field boundary voltage signal.Apply current excitation to dispersive electrode, and obtain the corresponding boundary voltage signal measuring the interior media distributed intelligence of thing field, its mathematical model is:

$\left\{\begin{array}{cc}\▿\·(\mathrm{\σ}(x,y)\▿u(x,y))=0& \mathrm{in\Ω}\\ \mathrm{\σ}(x,y)\frac{\∂u(x,y)}{\∂n}=j(x,y)& \mathrm{on}\∂\mathrm{\Ω}\end{array}\right.$

Wherein, Ω measures thing field, measure thing border outside the venue, σ (x, y), u (x, y) are respectively thing field internal conductance rate, Potential Distributing, and n is normal vector outside border, and j (x, y) is the outer normal direction electric current density of exciting electrode.

Electrode shape can be circular or square, but is not limited to these shapes.Thing field, 16 equally distributed rectangle measurement electrode are measured for circle, the two dimension current excitation of thing field, voltage measurement process are as shown in Figure 3, for 1-9 electrode excitation, current excitation is applied to the electrode being numbered 1, the electrode being numbered 9 is ground electrode, measure and the electromotive force value difference calculated on other adjacent electrodes as the boundary voltage data φ (x, y) do not had in focus supersonic wave disturbance situation, so φ (x, y) is the vector of 1*12 dimension.

(4) in focus ultrasonic situation, focus supersonic wave disturbance i-th focuses on territory, again carries out electrical stimuli, measurement to measurement thing field simultaneously, obtains boundary survey voltage vector φ _i(x, y).

Focused transducer is perpendicular to the two-dimensional imaging cross section measuring thing field, and focus supersonic wave disturbance i-th focuses on territory, 1≤i≤I.According to acoustoelectric effect principle, concentration ultrasonic produces disturbance to the electrical conductivity that i-th focuses on territory, and meets

δσ(x,y)＝k·P·σ(x,y)

Wherein, the conductivity variations amount that δ σ (x, y) causes for concentration ultrasonic effect, σ (x, y) is medium initial conductivity distribution in thing field, and P measures the sound pressure level obtained, k=10 in step (1) ^-9for the acoustoelectric effect coefficient of medium.Fig. 4 is that concentration ultrasonic is to the schematic diagram focusing on territory dielectric conductance rate disturbance.

While concentration ultrasonic focuses on disturbance i-th focusing territory, the excitation measuring process of the middle electrod-array of completing steps (3), measures the boundary survey voltage vector φ of thing field when obtaining focus supersonic this focusing territory of wave disturbance again _i(x, y), its mathematical model is:

$\left\{\begin{array}{cc}\▿\·({\mathrm{\σ}}_i(x,y)\▿u_i(x,y))=0& \mathrm{in\Ω}\\ {\mathrm{\σ}}_i(x,y)\frac{{\∂u}_i(x,y)}{\∂n}=j(x,y)& \mathrm{on}\∂\mathrm{\Ω}\end{array}\right.$

Wherein, σ _i(x, y)=σ (x, y)+δ σ (x, y) is the distribution of conductivity behind focus supersonic wave disturbance i-th focusing territory, u _i(x, y) is the Potential Distributing behind focusing territory, i-th, focus supersonic wave disturbance thing field.

(5) thing field boundary voltage vector φ (x, y) and φ measuring respectively and obtain is utilized in step (3) and step (4) _i(x, y), focuses on the power density values in territory by following formulae discovery i-th,

$S_i(x,y)=-{\left[{\∫\∫}_{\mathrm{\Ω}}^{\mathrm{kP}}\right]}^{-1}{\∫}_{\∂\mathrm{\Ω}}({\mathrm{\φ}}_i(x,y)-\mathrm{\φ}(x,y))j(x,y)\mathrm{dx}$

S _i(x, y) is and measures the power density values that i-th, thing field focuses on territory.

(6) judge whether transducer completes the disturbance to all focusing territories, and obtain the corresponding power density values focusing on position, territory.If completed, then implementation step (7); If do not completed, then change the position, focusing territory of focus supersonic wave disturbance, make i=i+1, and jump to step (4).

Intend, at the focusing domain information measuring the interscan generation of thing field, judging whether transducer completes the focusing disturbance to all focusing territories according to the concentration ultrasonic determined in step (2), and obtain the corresponding power density values focusing on position, territory.If completed, then implementation step (7); If do not completed, then change the position, focusing territory of focus supersonic wave disturbance, even i=i+1, and jump to step (4).

(7) power density distribution image S (x, y) of whole measurement thing field is obtained.

Focused on the power density values of position, territory by each, the positional information in each focusing territory in integrating step (1), obtains power density distribution image S (x, y) of whole measurement thing field.The geometric model that Fig. 5 (a) is arranged for emulation, background conductance rate is 0.5s/m, and dielectric conductance rate is 2s/m.Fig. 5 (b) is depicted as the power density image of this model under 1-9 electrode excitation boundary condition.

(8) change exciting electrode, obtain the power density image under Different electrodes excitation.

Change the exciting electrode in step (3), be set to 5-13 electrode excitation, namely current excitation is applied to the electrode being numbered 5, be numbered the electrode ground connection of 13, then step (3), (4), (5), (6), (7) are repeated, obtain the power density diagram under 5-13 electrode excitation boundary condition, as shown in Fig. 5 (c).

The derivation of power density computation formula:

When not having focus supersonic wave disturbance, for measurement thing field Ω, under electrical stimuli, field domain internal conductance rate distribution σ (x, y) and Potential Distributing u (x, y) meet following Laplace's equation:

$\left\{\begin{array}{cc}\▿\·(\mathrm{\σ}(x,y)\▿u(x,y))=0& \mathrm{in\Ω}\\ \mathrm{\σ}(x,y)\frac{\∂u(x,y)}{\∂n}=j(x,y)& \mathrm{on}\∂\mathrm{\Ω}\end{array}\right.---\left(1\right)$

Namely, under not having focus supersonic wave disturbance, boundary survey voltage is

When concentration ultrasonic focuses on disturbance measurement ω region, thing field, according to acoustoelectric effect principle, focus on territory place electrical conductivity and change, meet

δσ(x,y)＝k·P·σ(x,y) (2)

Namely the electrical conductivity after disturbance is σ _ω(x, y)=σ (x, y)+δ σ (x, y).

Because measure thing field electrical conductivity generation minor variations, under identical electrical stimuli, corresponding Potential Distributing u _ωthere is minor variations in (x, y), i.e. u _ω(x, y)=u (x, y)+δ u (x, y), the two meets Laplace's equation

$\left\{\begin{array}{cc}\▿\·({\mathrm{\σ}}_{\mathrm{\ω}}(x,y)\▿u_{\mathrm{\ω}}(x,y))=0& \mathrm{in\Ω}\\ {\mathrm{\σ}}_{\mathrm{\ω}}(x,y)\frac{{\∂u}_{\mathrm{\ω}}(x,y)}{\∂n}=j(x,y)& \mathrm{on}\∂\mathrm{\Ω}\end{array}\right.---\left(3\right)$

Namely, during focus supersonic wave disturbance ω region, boundary survey voltage is so, measure initial electrical conductivity, the Potential Distributing in thing field, and each self-corresponding disturbance quantity caused due to focus supersonic wave disturbance meets

▽((σ(x,y)+δσ(x,y))▽(u(x,y)+δu(x,y)))＝0 (4)

Formula (4) is launched, and ignores higher order term and obtain

▽(σ(x,y)▽(δu(x,y)))＝-▽((δσ(x,y))▽u(x,y)) (5)

U (x, y) is multiplied by formula (6) both sides, according to green theorem, obtains following approximate expression

${\∫\∫}_{\mathrm{\Ω}}\mathrm{\δ\σ}(x,y)\▿u(x,y)\·\▿u(x,y)=-{\∫}_{\∂\mathrm{\Ω}}\mathrm{\δu}(x,y)\·\mathrm{\σ}(x,y)\frac{\∂u(x,y)}{\∂\stackrel{\→}{n}}---\left(6\right)$

Because $\mathrm{\δu}(x,y){|}_{\∂\mathrm{\Ω}}=u_{\mathrm{\ω}}(x,y){|}_{\∂\mathrm{\Ω}}-u(x,y){|}_{\∂\mathrm{\Ω}}={\mathrm{\φ}}_{\mathrm{\ω}}(x,y)-\mathrm{\φ}(x,y),$ Again because the definition of power density is

S(x,y)＝σ(x,y)|▽u(x,y)| ²(7)

Bring formula (2) into formula (6), following power density computation formula can be obtained

$S_i(x,y)=-{\left[{\∫\∫}_{\mathrm{\Ω}}^{\mathrm{kP}}\right]}^{-1}{\∫}_{\∂\mathrm{\Ω}}({\mathrm{\φ}}_i(x,y)-\mathrm{\φ}(x,y))j(x,y)\mathrm{dx}---\left(8\right)$

From formula (8), on the right of equation, Part I is the coefficient determined by focused transducer parameter and dielectric distribution characteristic, and Part II is have, without the boundary survey magnitude of voltage measuring thing field under focus supersonic wave disturbance.So, boundary survey magnitude of voltage should be utilized directly to rebuild based on power density formation method of acoustoelectric effect, need not reverse temperature intensity be carried out, the problems such as what avoid that the reconstruction of conventional electrical imaging inverse problem can run into is such as unstable, less qualitative.

Power density formation method based on acoustoelectric effect of the present invention, it is mainly used in biological tissue's dielectric distribution imaging, but also can be applicable to other measured mediums of acoustoelectric effect.

Schematic above the present invention and embodiment thereof to be described; this description is not restricted; shown in accompanying drawing is also one embodiment of the present invention; if any those of ordinary skill in the art when not departing from the invention aim; without create shape design the version similar with the present invention or embodiment, all should protection scope of the present invention be belonged to.

Claims (1)

1. the power density formation method based on acoustoelectric effect, discrete electrod-array is uniformly or non-uniformly fixed on the outside of tested biological tissue by the method, the region that electrod-array surrounds is for measuring thing field, focused transducer is perpendicular to measurement thing field, regulate its position, the focal spot of focused transducer is positioned at and measures on thing field, the region that focal spot covers on measurement thing field is called focusing territory.The concentration ultrasonic that focused transducer is launched produces disturbance to the electrical conductivity focusing on Yu Chu biological tissue, the boundary survey voltage vector utilizing electrod-array to measure, according to power density computation formula, calculate the power density values focusing on territory place, when after the disturbance that focused transducer completes each focusing territory, utilize each to focus on the power density values at territory place, focus on the positional information in territory in conjunction with each, obtain the power density distribution figure measuring thing field, comprise following step:

1) focal spot size and the sound pressure level P of focused transducer is measured

Make microphone aim at focused transducer, and make the sensing unit of microphone be in the focal spot place of focused transducer, measure the sound pressure level P obtaining focal spot place, regulate the position of microphone, measure the focal spot size of focused transducer;

2) measurement thing field is divided into I and focuses on territory, determine that each focuses on the positional information in territory, and concentration ultrasonic intends the scanning sequency each being focused on to territory

According to measuring thing field size and step 1) in measure the focal spot size obtained, measurements thing field is divided into I and focuses on territory, division principle is: focused transducer can complete the scanning to whole measurement thing field, and respectively focusing territory is not overlapping.Record the two-dimensional position information that each focuses on territory, i.e. the coordinate (x, y) in each focusing territory, and determine that concentration ultrasonic intends focusing on each scanning sequency in territory, from 1 to I;

3) without in focus ultrasonic situation, electrical stimuli and measurement are carried out to measurement thing field, obtains boundary survey voltage vector φ (x, y)

By applying current excitation or voltage drive on exciting electrode, realize applying electrical stimuli to measurement thing field, collection Opposed Current encourages, neighboring voltage is measured and boundary voltage in each measurement electrode under the measurement pattern do not measured of exciting electrode, form boundary survey voltage vector φ (x, y), complete and once encourage measuring process;

4) in focus ultrasonic situation, focus supersonic wave disturbance each focusing territory i, carries out electrical stimuli, measurement to measurement thing field simultaneously again, obtains boundary survey voltage vector φ _i(x, y)

By focused transducer perpendicular to measurement thing field, to each focusing territory i (1≤i≤I), while focus supersonic wave disturbance, all complete a step 3) in the excitation measuring process of electrod-array, measure the boundary survey voltage vector φ of thing field when obtaining focus supersonic this focusing territory of wave disturbance _i(x, y);

5) define the product that power density is electrical conductivity and electric field intensity square, utilize step 3) and step 4) measure the boundary voltage signal psi (x, y) and φ that obtain respectively _i(x, y), by the power density values of i position, following formulae discovery each focusing territory, is designated as S _i(x, y):

$S_i(x,y)=-{\left[{\∫}_{\mathrm{\Ω}}\mathrm{kP}\right]}^{-1}{\∫}_{\∂\mathrm{\Ω}}({\mathrm{\φ}}_i(x,y)-\mathrm{\φ}(x,y))j(x,y)\mathrm{dx}$

Wherein, k=10 ^-9for the acoustoelectric effect coefficient of medium; J (x, y) is step 3) in be applied to outer normal direction electric current density on exciting electrode, be the ratio of exciting current and exciting electrode area; Ω is for measuring thing field; for measuring thing border outside the venue;

6) power density distribution image S (x, y) of whole measurement thing field is obtained

Focus on the power density values of position, territory by each, integrating step 1) in each focus on the positional information in territory, obtain power density distribution image S (x, y) of whole measurement thing field.