High definition electrical impedance tomography

• US 20020138019A1
• Filed: 03/09/2001
• Published: 09/26/2002
• Est. Priority Date: 10/03/1997
• Status: Active Grant

• Current Assignee: Quantic Electroscan, Inc.
• Original Assignee: Quantic Electroscan, Inc.
• Inventors: Strobel, Guye S., Mu, Zhen, Wexler, Alvin, Murugan, Rajen Manicon
• Granted Patent: US 6,745,070 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0536 Impedance imaging, e.g. by tomography

Abstract

A method of imaging an object contained in a medium, having a specific impedance which is different from the specific impedance of the medium, comprising applying current to the medium at various locations at a surface of the medium, extracting current at other locations, detecting voltages produced by the current which has passed through the medium from the surface of the medium at various other locations, successively determining a location and shape and conductivity of the object with increasing accuracy by processing values of the detected voltages, determining a region in the medium in which the object is located from values of the detected voltages which are within upper and lower threshold values, applying acceleration procedures to the conductivities within the region in the course of iterative refinement of these values in the course of an imaging procedure, subsequently restricting further determination of the location of the object with increasing accuracy to voltages obtained from the region of the medium in which the object is located, and displaying an image on an axis using the restricted location determination values.

Claims

1. A method of imaging objects contained in a media, having a specific impedance which is different from the specific impedance of the medium, comprising applying current to the medium at various locations at a surface of the medium, extracting current at other locations, detecting voltages produced by the current which has passed through the medium from the surface of the medium at various other locations, successively determining a location of the object with increasing accuracy by processing values of the detected voltages determining a region in the medium in which the object is located from values of the detected voltages, successively determining a location and shape and conductivity of the object with increasing accuracy by processing values of the detected current, determining a pattern of convergence, selecting an appropriate function which approximates the determined pattern, extrapolating the function to a limit of an infinite number of iterations, and displaying an image illustrating the extrapolated functions on an axis at locations of the pattern of convergence.

2. A method as defined in claim 1 including determining and displaying two dimensional image slices of adjacent portions of the medium so as to form a three dimensional image of the object in the medium.

3. A method of imaging one or more objects as claimed in claim 1, wherein said process of determining said region, determining said pattern of convergence and imaging said objects includes:

a) modelling recovered potential and conductivity distributions using the non-linear least-squares fitting scheme of Levenberg-Marquardt iteratively,

b) deriving the iteration number at which the algorithm converges by substituting the known potential distribution into the mathematical relation, thereafter using the derived number of iterations to derive the corresponding conductivity distribution,

c) correcting the derived conductivity distribution by re-initializing step a) using the derived conductivity distribution as the initial starting conductivity distribution and

d) recursively adjusting the parameters of the model to obtain the best fit parameters.