Electrical impedance tomography

• US 6,940,286 B2
• Filed: 12/28/2001
• Issued: 09/06/2005
• Est. Priority Date: 12/30/2000
• Status: Expired due to Term

• Current Assignee: University of Leeds
• Original Assignee: University of Leeds
• Inventors: Wang, Mi, Yin, Wuliang
• Primary Examiner(s): Nguyen, Vincent Q.
• Application Number:
  US10/250,327
• Publication Number:
  US 20040130338A1
• Time in Patent Office: 1,348 Days
• Field of Search: 324439-450, 324/600, 324/605, 324/609, 324/629, 600/393, 600/547, 378/21
• US Class Current: 324/450
• CPC Class Codes: A61B 5/0536 Impedance imaging, e.g. by tomography
• CPC Class Codes: G01N 27/20 Investigating the presence of flaws
• CPC Class Codes: G01N 27/24 Investigating the presence of flaws

Abstract

Methods and apparatus are provided for obtaining a representation of the distribution of electrical impedance within a multiphase flow with an electrically continuous or discontinuous principle flow contained within an electrically conductive solid ring electrode, including providing a plurality of mutually spaced electrical contacts mounted at the outside wall of the ring and electrically contacting with the ring, applying currents or voltages to the ring from the electrical contacts, generating a more homogeneous electric field distribution within the material, measuring voltage or current distribution alone the ring from other electrical contacts, relatively intensifying the imaging sensitivity at the central area of the sensing domain using a π/2 angle sensing strategy and reconstructing the representation of the impedance distribution using CG method with an error processing strategy.

Claims

1. A method of measuring the distribution of electrical impedance of a fluid, comprising:

surrounding the fluid with an electrically conductive ring electrode that comprises a plurality of metallic contacts embedded into the conductive ring and spatially distributed around the axis of the ring, in electric contact with an outside wall of the ring;

applying between two contacts, sequentially, an input electrical signal, which while applied to a pair of the contacts, causes respective output signals to be generated between any other pair of contacts;

measuring said output electrical signals between successive pairs of contacts, the contacts of each pair of contacts selected for signal generation and for signal reception, respectively, span an azimuthal angle of about π

/2 with respect to the axis of the conductive ring electrode.

2. A method according to claim 1 wherein the ring electrode has a higher conductivity compared to the principle flow or materials to be measured and it is employed as a ring electrode or part of a sensor body.

3. A method according to claim 2 wherein a relatively homogeneous electric field distribution is produced.

4. A method according to claim 1 wherein the electrically conductive ring comprises at least one of metal, conductive rubber and ceramics.

5. A method according to claim 1 wherein the plurality of metallic contacts penetrate through the outside wall of the ring.

6. A method according to claim 1, wherein a sensitivity distribution of a voltage measurement is intensified at a specific area in the whole of the sensing domain.

7. A method according to claim 1 further comprising deriving an intensified sensitivity matrix from a specific sensing strategy or a combination from a basic sensitivity matrix.

8. A method according to claim 7 wherein the basic sensitivity matrix is derived from equations 1 and 2:

$\begin{array}{cc}{Z}_{I,J}<br><br>\left(I_{M,N}\right)=\underset{m=M}{\overset{N-1}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\underset{i=I}{\overset{J-1}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>Z_{i,i+1}<br><br>\left(I_{m,m+1}\right)<br><br>\text{\hspace{1em}<br><br>}<br><br><br><br>\left(1\le <br><br>M<<br><br>N<<br><br>I<<br><br>J\le <br><br>\mathrm{number}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{electrode}\right)& \left(\mathrm{Equation}<br><br>\text{\hspace{1em}<br><br>}<br><br>1\right)\\ s_{I,J,k}<br><br>\left(I_{M,N}\right)=\underset{m=M}{\overset{N-1}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\underset{i=I}{\overset{J-1}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>s_{i,i+1,k}<br><br>\left(I_{m,m+1}\right)<br><br>\text{\hspace{1em}<br><br>}<br><br><br><br>\left(1\le <br><br>M<<br><br>N<<br><br>I<<br><br>J\le <br><br>\mathrm{number}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{electrodes}\right).& \left(\mathrm{Equation}<br><br>\text{\hspace{1em}<br><br>}<br><br>2\right)\end{array}$

9. A method according to claim 1 wherein the fluid is selected from a process material, a process fluid and a part of a human body.

10. A method according to claim 1 wherein the fluid has an electrically continuous or discontinuous phase, and wherein the electrically continuous phase is a miscible liquid and the discontinuous phase is in a foam formation or a half filled horizontal oil/water/gas stratified flow.

11. A method according to claim 1 wherein the ring electrode comprises a sensor with discrete electrode structure using an external resistor network connecting all electrodes.

12. A method according to claim 11 wherein a geometry and a conductivity of the conductive ring sensor is optimized using an illness measure of a sensitivity matrix.

13. A method according to claim 11 wherein the sensor comprises a conductive disk, with PCB as its connection.

14. A method according to claim 11 wherein the conductive sensor is made in micro-scale.

15. A method according to claim 14 wherein the micro-scale conductive sensor is made on silicon chips.

16. A method according to claim 15 wherein the micro-scale conductive sensor is integrated with a measurement and processing circuit.

17. A method according to claim 1 further comprising using a multi-step image reconstruction algorithm having an error processing method to reconstruct a conductivity distribution.

18. A method according to claim 17 wherein the following equation is used in the multi-step image reconstruction algorithm:

γ

=−

{overscore (s)}<sup>−

1</sup>·

e.

19. A method according to claim 18 wherein the error processing method uses the difference between the relative changes of forward solutions and measured results.

20. A method according to claim 19 wherein the following equation is used in the multi-step image reconstruction algorithm:

$e_j^{\left(n\right)}=\frac{V_j^{\mathrm{\prime <br><br>}}<br><br>\left({\mathrm{\sigma <br><br>}}^{\mathrm{\prime <br><br>}}\right)}{V_j<br><br>\left(\mathrm{\sigma <br><br>}\right)}-\frac{u_j^{\mathrm{\prime <br><br>}}<br><br>\left({\widehat{\mathrm{\sigma <br><br>}}}_k^{\left(n\right)}\right)}{u_j<br><br>\left({\widehat{\mathrm{\sigma <br><br>}}}_k^{\left(0\right)}\right)}.$

21. A method according to claim 19 wherein a CG method is used to solve linear equation in implementing both inverse solution and forward solution.

22. A method according to claim 21 wherein the following equation is used in the multi-step image reconstruction algorithm:

$A^{*}<br><br>x<br><br>\text{\hspace{1em}<br><br>}<br><br>1=\left[\begin{array}{c}1\\ 0\\ ·<br><br>\\ ·<br><br>\\ ·<br><br>\\ 0\end{array}\right],A^{*}<br><br>x<br><br>\text{\hspace{1em}<br><br>}<br><br>2=\left[\begin{array}{c}0\\ 1\\ ·<br><br>\\ \begin{array}{c}·<br><br>\\ ·<br><br>\\ 0\end{array}\end{array}\right],A^{*}<br><br>x<br><br>\text{\hspace{1em}<br><br>}<br><br>3=\left[\begin{array}{c}0\\ 0\\ 1\\ ·<br><br>\\ \begin{array}{c}·<br><br>\\ 0\end{array}\end{array}\right],\text{\hspace{1em}<br><br>}<br><br>\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>A^{*}<br><br>x<br><br>\text{\hspace{1em}<br><br>}<br><br>n=\left[\begin{array}{c}0\\ 0\\ ·<br><br>\\ \begin{array}{c}·<br><br>\\ ·<br><br>\\ 1\end{array}\end{array}\right].$

23. A method according to claim 22 wherein the following equation is used in the multi-step image reconstruction algorithm:

σ

=σ

₀* (1+γ

)=σ

₀*(1−

Λ

e).

24. An apparatus for measuring the distribution of electrical impedance of a fluid comprising:

a cylindrical electrically conductive ring electrode surrounding the fluid, the ring electrode comprising a plurality of metallic contacts embedded into the conductive ring and spatially distributed around the axis of the ring, in electric contact with an outside wall of the ring, the the metallic contacts being responsive to a sequentially applied input electrical signal, which while applied to a pair of the contacts, causes respective output signals to be generated between any other pair of contacts, the contacts of each pair of contacts selected for signal generation and for signal reception, respectively, span an azimuthal angle of about σ

/2 with respect to the axis of the conductive ring electrode.

25. A method of determining an internal structure of a body comprising:

surrounding a body fluid with an electrically conductive ring electrode that comprises a plurality of metallic contacts embedded into the conductive ring and spatially distributed around the axis of the ring, in electric contact with an outside wall of the ring;

applying between two contacts, sequentially, an input electrical signal, which while applied to a pair of the contacts, causes respective output signals to be generated between any other pair of contacts;

measuring said output electrical signals between successive pairs of contacts, the contacts of each pair of contacts selected for signal generation and for signal reception, respectively, span an azimuthal angle of about π

/2 with respect to the axis of the conductive ring electrode.