Current patterns for electrical impedance tomography

• US 5,381,333 A
• Filed: 07/23/1991
• Issued: 01/10/1995
• Est. Priority Date: 07/23/1991
• Status: Expired due to Term

• Current Assignee: Rensselaer Polytechnic Institute
• Original Assignee: Rensselaer Polytechnic Institute
• Inventors: Isaacson, David, Newell, Jonathan C., Gisser, David G.
• Primary Examiner(s): Hayes, Gail O.
• Assistant Examiner(s): Tkacs, Stephen R.
• Application Number:
  US07/734,591
• Time in Patent Office: 1,267 Days
• Field of Search: 128/734, 364/413.02, 364/413.13, 364/413.15
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0536 Impedance imaging, e.g. by tomography
• CPC Class Codes: G01R 27/26 Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
• CPC Class Codes: Y10S 128/922 including image analysis

Abstract

A method in electrical impedance tomography uses an adaptive repeated series of calculations and measurements to determine the best current pattern for a body having an initially unknown internal conductivity, for producing the best electrical impedance image for the body. Initially, an arbitrary current pattern and conductivity is utilized to generate a voltage pattern which is measured and compared with the theoretical voltage pattern based on the arbitrary conductivity and current patterns. When both the current pattern and the conductivity yielded by the process closely match values derived by measurements, the voltage pattern is used to produce the image.

Claims

1. In an electrical impedance tomography system that includes a body with an array of electrodes on its surface, a method for finding the values of an unknown distribution of conductivities from which an image may be formed, the method comprising:

(a) selecting an arbitrary guessed conductivity distribution and applying an arbitrary guessed set of current patterns to the electrodes to generate a voltage pattern on the array for each current pattern;

(b) measuring all electrode voltages for each current pattern applied;

(c) calculating values of all theoretical voltages that should have appeared on the electrodes for the body due to the arbitrary set of guessed current patterns and arbitrary guessed conductivity distribution;

(d) calculating a new set of current patterns based on differences between the measured and calculated voltage values;

(e) calculating the differences between electrode currents of the arbitrary set of current patterns and the calculated new set of current patterns, to form current differences;

(f) if any of the current differences are greater than a selected tolerance, applying the new set of current patterns to the electrode array and repeating steps (b) to (e);

(g) when the current differences are smaller than the selected tolerance, considering the new set of current patterns to be an optimal set of spatial current patterns, meaning that the optimal set of spatial current patterns can be used to best distinguish the actual conductivity distribution from that previously assumed, for a fixed limit on peak current values;

(h) testing whether any of the voltage differences between the measured and calculated values at the electrodes, using the optimal current patterns, are larger than a predetermined value;

(i) if so, computing a new conductivity distribution as a function of the new set of current patterns and the measured voltage values;

(j) repeating steps (b) to (g) using the new conductivity distribution to replace the previously assumed distribution in order to find a set of current patterns that better distinguishes the actual conductivity distribution from the new conductivity distribution; and

(k) repeating steps (h) to (J) as many times as are necessary to produce a calculated conductivity distribution whose calculated voltages are substantially identical to those measured, from which a conductivity image may be produced.