Relative impedance measurement

• US 20070038078A1
• Filed: 07/08/2005
• Published: 02/15/2007
• Est. Priority Date: 07/08/2005
• Status: Active Grant

• Current Assignee: Biosense Webster Incorporated (Johnson & Johnson)
• Original Assignee: Biosense Webster Incorporated (Johnson & Johnson)
• Inventors: Osadchy, Daniel
• Granted Patent: US 7,848,787 B2
• Time in Patent Office: Days
• US Class Current: 600/424
• CPC Class Codes: A61B 2034/2053 Tracking an applied voltage gradient
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/0538 invasively, e.g. using a catheter
• CPC Class Codes: A61B 5/06 Devices, other than using radiation, for detecting or locating foreign bodies for removing same A61B17/50 ; determining position of probes within or on the body of the patient
• CPC Class Codes: A61B 5/063 using impedance measurements
• CPC Class Codes: A61B 5/6885 Monitoring or controlling sensor contact pressure

Abstract

A method for calibrating impedance includes coupling at least first, second, and third electrodes at respective locations to a surface of a body of a subject. A first current passing through the body between the first and second body-surface electrodes is measured, and a second current passing through the body between the first and third body-surface electrodes is measured. From the first and second currents, a contact factor is derived that is indicative of the impedance between at least one of the body-surface electrodes and the surface of the body. Also described are methods for sensing the position of a probe and for detecting tissue contact based on a relation between currents from the probe to body-surface electrodes.

Claims

1. A method for calibrating impedance, comprising:

coupling at least first, second, and third electrodes at respective locations to a surface of a body of a subject;

measuring a first current passing through the body between the first and second body-surface electrodes;

measuring a second current passing through the body between the first and third body-surface electrodes; and

deriving a contact factor indicative of the impedance between at least one of the body-surface electrodes and the surface of the body using the first and second currents.

2. The method according to claim 1, wherein deriving the contact factor comprises determining a value of relative impedance using a relation between the first current and a sum of the first and second currents.

3. The method according to claim 2, wherein deriving the contact factor comprises determining three or more values of the relative impedance and solving a set of linear equations whose parameters comprise the three or more values and distances between the body-surface electrodes.

4. The method according to claim 1, and comprising:

inserting a probe comprising a fourth electrode into the body;

measuring a third current through the body between the fourth electrode and at least one of the body-surface electrodes; and

sensing a position of the probe responsively both to the contact factor of the at least one body-surface electrode and to the third current.

5. The method according to claim 4, wherein sensing the position comprises determining a relative distance between the probe and the at least one body-surface electrode.

6. The method according to claim 1, wherein at least one of the first, second, and third body-surface electrodes comprises an adhesive conductive patch.

7. A method for position sensing, comprising:

inserting a probe comprising a probe electrode into a body of a subject;

measuring a first current passing through the body between the probe electrode and a first body-surface electrode coupled to a surface of the body;

measuring a second current passing through the body between the probe electrode and a second body-surface electrode coupled to the surface of the body;

calculating a relation between the first and second currents; and

tracking movement of the probe within the body responsively to the relation.

8. The method according to claim 7, wherein calculating the relation comprises determining a value of relative impedance between the probe electrode and each of the body-surface electrodes.

9. The method according to claim 8, wherein determining the value of relative impedance comprises finding a quotient of the first current and the sum of the first and second currents.

10. The method according to claim 7, wherein calculating the relation comprises determining at least two values of relative impedance between the probe electrode and the first and second body-surface electrodes and solving a set of linear equations whose parameters comprise the at least two values.

11. The method according to claim 7, wherein tracking the movement of the probe comprises determining that a change in the first and second currents that does not significantly change the relation between the first and second currents is indicative of contact of the probe electrode with tissues of varying impedance within the body, and not due to the movement of the probe.

12. The method according to claim 11, wherein the relation between the first and second currents is indicative of a relative impedance between the probe and the first and second body-surface electrodes.

13. A method for detecting tissue contact, comprising:

inserting a probe comprising a probe electrode into a body of a subject, whereby the probe electrode makes contact with a tissue inside the body;

measuring a first current passing through the body between the probe electrode and a first body-surface electrode coupled to a surface of the body;

measuring a second current passing through the body between the probe electrode and a second body-surface electrode coupled to the surface of the body;

calculating a relation between the first and second currents; and

detecting, responsively to the relation, contact between the probe and the tissue.

14. The method according to claim 13, wherein detecting the contact between the probe and the tissue comprises measuring a change in the first and second currents that does not change the relation between the first and second currents.

15. The method according to claim 13, and comprising tracking a position of the probe in the body responsively to the first and second currents and correcting the position responsively to detecting the contact between the probe and the tissue.

16. Apparatus for calibrating impedance, comprising:

at least first, second and third electrodes adapted to be coupled at respective locations to a surface of a body of a subject; and

a control unit, adapted to measure a first current passing through the body between the first and second body-surface electrodes, to measure a second current passing through the body between the first and third body-surface electrodes, and to derive a contact factor indicative of the impedance between at least one of the body-surface electrodes and the surface of the body using the first and second currents.

17. The apparatus according to claim 16, wherein the control unit is adapted to derive the contact factor by determining a value of relative impedance, using a relation between the first current and a sum of the first and second currents.

18. The apparatus according to claim 16, wherein the control unit is adapted to determine three or more values of the relative impedance and to derive a contact factor by solving a set of linear equations whose parameters comprise the three or more values and distances between the body-surface electrodes.

19. The apparatus according to claim 16, and comprising a probe adapted to be inserted into the body, wherein the probe comprises a fourth electrode, and wherein the control unit is further adapted to measure a third current through the body between the fourth electrode and at least one of the body-surface electrodes, and to sense a position of the probe responsively both to the contact factor of the at least one of the body-surface electrodes and to the third current.

20. The apparatus according to claim 19, wherein the control unit is adapted to sense the position by determining a relative distance between the probe and the at least one body-surface electrode.

21. Apparatus for position sensing, comprising:

a probe comprising a probe electrode and adapted to be inserted into a body of a subject;

first and second body-surface electrodes adapted to be coupled at respective locations to a surface of a body of a subject; and

a control unit, adapted to measure a first current passing through the body between the probe electrode and the first body-surface electrode, to measure a second current passing through the body between the probe electrode and the second body-surface electrode, to calculate a relation between the first and second currents, and to track movement of the probe within the body responsively to the relation.

22. The apparatus according to claim 21, wherein the control unit is adapted to track movement of the probe by determining a value of relative impedance between the probe electrode and each of the body-surface electrodes.

23. The apparatus according to claim 22, wherein the control unit is adapted to determine the value of relative impedance by calculating a quotient of the first current and the sum of the first and second currents.

24. The apparatus according to claim 22, wherein the control unit is adapted to derive at least two values of relative impedance and to track movement of the probe by solving a set of linear equations whose parameters comprise the values of the relative impedance.

25. The apparatus according to claim 22, wherein the control unit is adapted to determine that a change in the first and second currents that does not significantly change the relation between the first and second currents is indicative of contact of the probe electrode with tissues of varying impedance within the body, and not due to the movement of the probe.

26. The apparatus according to claim 25, wherein the relation between the first and second currents is indicative of a relative impedance between the probe and the first and second body-surface electrodes.

27. Apparatus for detecting tissue contact, comprising:

a probe comprising a probe electrode adapted to be inserted into a body of a subject, and to make contact with a tissue inside the body;

first and second body-surface electrodes adapted to be coupled at respective locations to a surface of a body of a subject; and

a control unit adapted to measure a first current passing through the body between the probe electrode and the first body-surface electrode, to measure a second current passing through the body between the probe electrode and a second body-surface electrode, to calculate a relation between the first and second currents, and to detect, responsively to the relation, contact between the probe and the tissue.

28. The apparatus according to claim 27, wherein the control unit is adapted to detect the contact between the probe and the tissue by sensing a change in the first and second currents while sensing no change in the relation between the first and second currents.

29. The apparatus according to claim 27, wherein the control unit is adapted to track a position of the probe in the body responsively to the first and second currents and to correct the position responsively to detecting the contact between the probe and the tissue.