Layer stripping process for impedance imaging

• US 5,390,110 A
• Filed: 07/09/1991
• Issued: 02/14/1995
• Est. Priority Date: 07/09/1991
• Status: Expired due to Term

• Current Assignee: Rensselaer Polytechnic Institute
• Original Assignee: Rensselaer Polytechnic Institute
• Inventors: Isaacson, Eli L., Isaacson, David, Somersalo, Erkki, Cheney, Margaret
• Primary Examiner(s): Huntley, David M.
• Application Number:
  US07/727,075
• Time in Patent Office: 1,316 Days
• Field of Search: 64/413.01, 64/413.02, 64/413.13, 64/413.14, 128/734
• US Class Current: 600/407
• 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: G16H 50/50 for simulation or modelling of medical disorders
• CPC Class Codes: Y10S 128/922 including image analysis

Abstract

A method for the impedance imaging of a three-dimensional body utilizes electrtodes on the outer surface of the body which receive a set of current patterns. The resulting voltage patterns are measured at the outer boundary of the body. Synthesized resulting patterns are then calculated for inner boundaries of the body, each at a selected incremental distance inwardly of the outer boundary. The synthesis step is repeated for successive inner boundaries until the center of the body is reached. The measured and synthesized patterns are utilized to calculate or otherwise find various medium properties in the body, such as the electric conductivity and electric permittivity for the body. These impedance characteristics based on the measured and synthesized patterns are used to produce an image of the body.

Claims

1. A method of creating an impedance image of a volume of a body, the volume having a selected number of finite dimensions and the volume varying in at least one of conductivity and permittivity characteristics in all of the selected number of finite dimensions, the body having an outer boundary, the method comprising:

(a) applying a set of current or voltage patterns to the outer boundary to create actual resulting and respective voltage or current patterns at the outer boundary;

(b) measuring the actual resulting and respective voltage or current patterns at the outer boundary;

(c) finding at least one of the conductivity and permittivity characteristics at the outer boundary of the body based only on the resulting patterns and information about the outer boundary;

(d) calculating synthesized resulting and respective voltage or current patterns for a first inner boundary which is at a selected incremental distance inward of the outer boundary as a function of the measuring and finding steps only;

(e) finding said characteristics at the inner boundary of the body based on the calculated resulting patterns;

(f) calculating synthesized and respective voltage or current patterns for a second inner boundary of the body which is at the selected incremental distance inward of the first inner boundary, as a function of the calculating step (d) and the finding step (e);

(g) repeating steps (e) and (f) for additional inner boundaries until the selected incremental distance inward reaches a selected depth in the body, the repeated calculating of step (f) also being a function of at least one previous step (f); and

(h) using said characteristics obtained to form an image of the body from the outer boundary to the selected depth.

2. A method according to claim 1 including a regularization method.

3. A method according to claim 2 including regularizing by expressing the resulting patterns as discrete trigonometric functions having a plurality of modes each containing some information for a particular boundary, determining which mode for each calculated pattern contains least information for a particular boundary, and dropping the mode containing least information.

4. A method according to claim 1, wherein the selected depth is the center of the body.

5. A method according to claim 1 including applying the set of current or voltage patterns through a plurality of electrodes on the outer boundary of the body and measuring the actual resulting and respective voltage or current patterns at the electrodes.

6. A method of creating an impedance image of a volume of a body, the volume having a selected number of finite dimensions and the volume having at least some of conductivity and permittivity characteristics, the body having an outer boundary, the method comprising:

(a) applying a set of current or voltage patterns to the outer boundary to create actual resulting and respective voltage or current patterns at the outer boundary;

(b) measuring the actual resulting and respective voltage or current patterns at the outer boundary;

(c) finding at least one of the conductivity and permittivity characteristics at the outer boundary of the body based only on the resulting patterns and information about the outer boundary;

(d) calculating synthesized resulting and respective voltage or current patterns for a first inner boundary which is at a selected incremental distance inward of the outer boundary as a function of the measuring and finding steps only;

(e) finding said characteristics at the inner boundary of the body based on the calculated resulting patterns;

(f) calculating synthesized and respective voltage or current patterns for a second inner boundary of the body which is at the selected incremental distance inward of the first inner boundary, as a function of the calculating step (d) and the finding step (e);

(g) repeating steps (e) and (f) for additional inner boundaries until the selected incremental distance inward reaches a selected depth in the body, the repeated calculating of step (f) also being a function of at least one previous step (f); and

(h) using said characteristics obtained to form an image of the body from the outer boundary to the selected depth.