Apparatus for monitoring CHF patients using bio-impedance technique

• US 20040006279A1
• Filed: 07/03/2002
• Published: 01/08/2004
• Est. Priority Date: 07/03/2002
• Status: Active Grant

• Current Assignee: Tel Aviv University Future Technology Development L.P. (Tel Aviv University)
• Original Assignee: Tel Aviv University Future Technology Development L.P. (Tel Aviv University)
• Inventors: Arad (Abboud), Shimon
• Granted Patent: US 7,096,061 B2
• Time in Patent Office: Days
• US Class Current: 600/506
• CPC Class Codes: A61B 5/0044 for the heart
• CPC Class Codes: A61B 5/0536 Impedance imaging, e.g. by tomography
• CPC Class Codes: A61B 5/7289 Retrospective gating, i.e. associating measured signals or images with a physiological event after the actual measurement or image acquisition, e.g. by simultaneously recording an additional physiological signal during the measurement or image acquisition
• CPC Class Codes: A61B 6/541 involving acquisition triggered by a physiological signal

Abstract

A method for generating impedance images of the chest, comprising:

acquiring electrical data of the chest;

obtaining electrocardiograph data of a patient;

analyzing the electrocardiograph data to obtain information about breathing parameters at the time the electrical data was acquired; and

reconstructing at least one impedance image of the chest from the electrical data and the information about breathing parameters;

wherein the information about breathing parameters reduces the sensitivity of the at least one impedance image to breathing parameters.

Claims

1. A method for generating impedance images of the chest, comprising:

acquiring electrical data of the chest;

obtaining electrocardiograph data of a patient;

analyzing the electrocardiograph data to obtain information about breathing parameters at the time the electrical data was acquired; and

reconstructing at least one impedance image of the chest from the electrical data and the information about breathing parameters;

wherein the information about breathing parameters reduces the sensitivity of the at least one impedance image to breathing parameters.

2. A method according to claim 1, wherein reconstructing at least one impedance image comprises;

reconstructing at least one preliminary impedance image of the chest from the electrical data; and

correcting the at least one preliminary impedance images to form the at least one impedance image, taking into account the breathing parameters.

3. A method according to claim 1, wherein analyzing the electrocardiograph data comprises analyzing changes in RR intervals.

4. A method according to claim 1, wherein analyzing the electrocardiograph data comprises analyzing changes in a voltage measured at a same phase in each cardiac cycle.

5. A method according to claim 1, wherein analyzing the electrocardiograph data comprises analyzing the average over one or more cardiac cycles of a voltage measured by the electrocardiograph.

6. A method according to claim 2, wherein reconstructing at least one preliminary image comprises reconstructing a plurality of preliminary images, and correcting the at least one impedance images comprises sorting the preliminary images into a plurality of bins according to the breathing parameters.

7. A method according to claim 6, wherein sorting the preliminary images into bins comprises sorting according to the state of expansion of the lungs.

8. A method according to claim 6, wherein sorting the preliminary images into bins comprises sorting according to the elapsed time since the last maximum expansion of the lungs.

9. A method according to claim 6, wherein sorting the preliminary images into bins comprises sorting according to the elapsed time since the last minimum expansion of the lungs.

10. A method according to claim 6, wherein sorting the preliminary images into bins comprises sorting according to a cardiac volume.

11. A method according to claim 6, wherein sorting the preliminary images into bins comprises sorting according to a heart rate.

12. A method according to claim 6, wherein sorting the preliminary images into bins comprises sorting according to a phase of the cardiac cycle.

13. A method according to claim 1, wherein acquiring the electrical data comprises gating by the cardiac cycle.

14. A method according to claim 2, wherein correcting the at least one preliminary impedance images comprises averaging the impedance data acquired over one or more breathing cycles.

15. A method according to claim 2, wherein reconstructing at least one preliminary image comprises reconstructing a plurality of preliminary images for which the impedance data was acquired at a plurality of phases in the breathing cycle, and correcting the at least one preliminary impedance images comprises averaging the preliminary impedance images.

16. A method according to claim 1, and including measuring the air flow into the lungs, and calibrating the information about breathing parameters obtained from the electrocardiograph using said measured air flow.

17. A method according to claim 1, and including measuring the air flow out of the lungs, and calibrating the information about breathing parameters obtained from the electrocardiograph using said measured air flow.

18. A method according to claim 1, wherein reconstructing at least one impedance image of the chest comprises using a finite volume method.

32. A method according to claim 1, wherein acquiring electrical data of the chest comprises measuring potentials at a plurality of locations on the body, while known currents are applied at a plurality of locations on the body.

19. A method for generating an impedance image of the chest, comprising:

acquiring electrical data of the chest; and

using a finite volume method to calculate an impedance image from the electrical data.

20. A method according to claim 19, and including:

formulating an initial impedance image;

using a finite volume method to calculate an expected set of electrical data if the impedance distribution of the chest matched the initial impedance image;

determining a difference between the acquired electrical data and the expected electrical data; and

calculating a new impedance image based on said difference.

21. A method according to claim 20, wherein calculating an expected set of electrical data and calculating a new impedance image are iterated at least one time, using the new impedance image calculated in at least one previous iteration to calculate the expected set of electrical data in each iteration except the first iteration.

22. A method according to claim 21, wherein calculating an expected set of electrical data and calculating a new impedance image are iterated until the difference between the acquired electrical data and the expected set of electrical data is small enough to satisfy a stopping condition.

23. A method according to claim 20, wherein calculating the new impedance image comprises calculating with a Newton-Raphson method.

24. A method according to claim 20, wherein calculating the new impedance image comprises calculating with a modified Newton-Raphson method.

25. A method according to claim 20, wherein formulating the initial impedance image comprises ascribing typical impedances to different parts of the chest according to at least one image of the chest.

26. A method according to claim 25, wherein ascribing impedances according to at least one image of the chest comprises ascribing impedances according to at least one x-ray image.

27. A method according to claim 26, wherein ascribing impedances according to at least one x-ray image comprises ascribing impedances according to at least one x-ray computed tomography image.

28. A method according to claim 25, wherein ascribing impedance according to at least one image of the chest comprises ascribing impedances according to at least one magnetic resonance image.

29. A method according to claim 25, wherein ascribing impedances according to at least one image of the chest comprises ascribing impedances according to at least one ultrasound image.

30. A method according to claim 19, wherein using the finite volume method comprises inverting a matrix with a technique that is adapted for inverting sparse matrixes.

31. A method according to claim 30, wherein inverting a matrix comprises inverting a matrix with the successive over relaxation method.

33. A method for monitoring a congestive heart failure patient, comprising:

generating at least one impedance image of the patient'"'"'s chest;

acquiring electrocardiograph data of the patient; and

calculating a parameter characterizing medical treatment of the patient, from electrocardiograph data and at least one impedance image of the chest.

34. A method according to claim 33, wherein generating at least one impedance image comprises;

acquiring electrical data of the chest;

obtaining electrocardiograph data of a patient;

analyzing the electrocardiograph data to obtain information about breathing parameters at the time the electrical data was acquired; and

reconstructing at least one impedance image of the chest from the electrical data and the information about breathing parameters;

and wherein the information about breathing parameters reduces the sensitivity of the at least one impedance image to breathing parameters.

35. A method according to claim 34, wherein reconstructing at least one impedance image of the chest comprises using a finite volume method.

36. A method according to claim 33, wherein generating at least one impedance image comprises:

acquiring electrical data of the chest; and

using a finite volume method to calculate an impedance image from the electrical data.

37. A method according to claim 33, wherein calculating at least one parameter comprises calculating a recommended dose of a medication.

38. A method according to claim 37, wherein calculating a recommended dose of medication comprises calculating a recommended dose of a diuretic.

39. A method according to claim 33, wherein using the electrocardiograph data comprises using the QT interval.

40. A method according to claim 39, wherein using the QT interval comprises using the QT interval to detect hypokalemia.

41. A method according to claim 33, wherein using the electocardiograph data comprises using the U wave amplitude.

42. A method according to claim 41, wherein using the U wave amplitude comprises using the U wave amplitude to detect hypokalemia.

43. An apparatus for making corrected impedance images of the chest, comprising:

an impedance imaging data acquisition system which acquires impedance imaging data of the chest;

an electrocardiograph which obtains electrocardiograph data of a patient; and

a data analyzer which analyzes the electrocardiograph data to obtain information about breathing parameters at the time the impedance imaging data was acquired, and reconstructs, from the impedance imaging data and the information about breathing parameters, at least one impedance image of the chest with reduced sensitivity to breathing parameters.

44. An apparatus for making impedance images of the chest, comprising:

an impedance imaging data acquisition system which acquires impedance imaging data of the chest;

a data analyzer which reconstructs an impedance image of the chest from said impedance imaging data, using a finite volume method.