Investigation of a body

• US 5,746,214 A
• Filed: 05/30/1995
• Issued: 05/05/1998
• Est. Priority Date: 10/30/1992
• Status: Expired due to Fees

• Current Assignee: British Technology Group Ltd. (Boston Scientific Corporation)
• Original Assignee: British Technology Group Ltd. (Boston Scientific Corporation)
• Inventors: Barber, David Charles, Brown, Brian Hilton
• Primary Examiner(s): Bahr, Jennifer
• Assistant Examiner(s): GILBERT, SAMUEL G
• Application Number:
  US08/416,717
• Time in Patent Office: 1,071 Days
• Field of Search: 128/693, 128/723, 128/734, 128/898, 128/897
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0536 Impedance imaging, e.g. by tomography

Abstract

A method of investigation of a body including applying interrogatory electrical signals at different frequencies to the body. First signals are obtained representing first electrical impedance measurements at the different frequencies. Second signals are obtained representing subsequent second electrical impedance measurements at the different frequencies after a change in the internal state of the body. Characteristics of part of the body are selectively determined in response to the first and second signals at the different frequencies. The invention has application in electrical impedance tomography techniques where the different frequency behavior of different parts of the body associated with temporal changes can be used to improve organ resolution and tissue differentiation.

Claims

1. A method of electrical impedance investigation of a body exhibiting a change in internal state, said method comprising:

applying to the body interrogatory electrical signals at different frequencies;

obtaining first signals representing first electrical impedance measurements at the different frequencies before said change in the internal state of the body;

obtaining second signals representing second electrical impedance measurements at the different frequencies after said change in the internal state of the body, wherein the first and second obtained signals are associated with a variation in two variables, said variables being (i) frequency and (ii) internal state of the body;

determining a change in said impedance measurements over a variation of one of said two variables;

determining a normalized change measurement from said change in said impedance measurements, said change in said impedance measurements being normalized with respect to a chosen reference impedance measurement;

determining a response, over a variation of said other of said variables, to said normalized change measurement; and

selectively determining characteristics of a part of said body from said response.

2. A method according to claim 1, wherein the change in the internal state of the body involves a change in geometry of at least part of said body.

3. A method according to claim 1 or claim 2, wherein said first electrical impedance measurements and said second electrical impedance measurements correspond to selected different points in a cyclic change in the internal state of the body.

4. A method according to claim 3, wherein the respective measurements are made at points selected to correspond substantially to peak and trough points in the cyclic change.

5. A method according to claim 1, wherein the obtained signals represent only a real part of the electrical impedance measurements.

6. A method according to claim 1, wherein the electrical impedance measurements are made at frequencies in the kHz range.

7. A method according to claim 6, wherein there is at least one order of numerical difference between the lowest and highest frequency.

8. A method according to any preceding claim 1, wherein the body is a human or animal body of a subject.

9. A method according to claim 8, wherein the body part is an organ or organs of the body.

10. A method according to claim 8 or claim 9, wherein the body has a trunk and the interrogatory electrical signals are applied to said trunk, said part of the body being the heart or at least one lung of the body.

11. A method according to claim 10, wherein said first electrical impedance measurements are made when the subject'"'"'s breath is held after inspiration and said second electrical impedance measurements are made when the subject'"'"'s breath is no longer held.

12. A method according to claim 9, wherein the respective signals are obtained by taking measurements in synchronization with a cyclic variation in the state of said part of the body.

13. A method according to claim 1, including using electrical impedance tomography (EIT) techniques to generate images of said part of the body by use of signals representing said characteristics of said part of the body.

14. A method of electrical impedance investigation of a body exhibiting a change in internal state, said method comprising:

applying to the body interrogatory electrical signals at different frequencies;

obtaining first signals representing first electrical impedance measurements at the different frequencies before said change in the internal state of the body;

obtaining second signals representing second electrical impedance measurements at the different frequencies after said change in the internal state of the body;

selectively determining characteristics of a part of said body from a response to a change in frequency of a differential variation between the first and second signals;

wherein the body is a human or animal body of a subject;

wherein said electrical signals are applied to the trunk of the body and the part of said body is the heart or at least one lung of the body; and

wherein said first electrical impedance measurements are made when the subject'"'"'s breath is held after inspiration and said second electrical impedance measurements are made when the subject'"'"'s breath is no longer held.

15. A method of electrical impedance investigation of a body exhibiting a change in internal state, said method comprising:

applying to the body interrogatory electrical signals at different frequencies;

obtaining first signals representing first electrical impedance measurements at the different frequencies before said change in the internal state of the body;

obtaining second signals representing second electrical impedance measurements at the different frequencies after said change in the internal state of the body;

selectively determining characteristics of a part of said body from a response to a change in frequency of a differential variation between the first and second signals; and

wherein electrical impedance techniques are used to generate images of said part of said body by use of signals representing said characteristics of said part of said body.