Method for calculating impedance and apparatus utilizing same

• US 6,730,079 B2
• Filed: 07/22/2002
• Issued: 05/04/2004
• Est. Priority Date: 07/22/2002
• Status: Active Grant

• Current Assignee: Project Trojan Intellectual Property Acquisition, LLC
• Original Assignee: Medtronic Vidamed, Inc.
• Inventors: Lovewell, James G.
• Primary Examiner(s): PEFFLEY, MICHAEL F
• Application Number:
  US10/201,401
• Publication Number:
  US 20040015160A1
• Time in Patent Office: 652 Days
• Field of Search: 606/32-34, 606/37-42, 128/898
• US Class Current: 606/34
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 18/1482 having a long rigid shaft for accessing the inner body transcutaneously in minimal invasive surgery, e.g. laparoscopy
• CPC Class Codes: A61B 2018/00702 Power or energy
• CPC Class Codes: A61B 2018/00875 Resistance or impedance

Abstract

A method for calculating the impedance in a first circuit coupling a first radio frequency electrode to a radio frequency controller where the first electrode is disposed in tissue in the vicinity of a second radio frequency electrode coupled to a second circuit. The impedance IMP of the first circuit is measured when energy is being supplied to both electrodes. The impedance IMP₀ of the first circuit is also measured when energy is being supplied to the first electrode but not to the second electrode, and subtracted from the impedance value IMP to determine a delta value IMP_Δ. The impedance IMP² of the first circuit is then measured when energy is being supplied to both electrodes. The impedance delta value IMP_Δ is subtracted from the impedance value IMP² to arrive at a calculated impedance value for the first circuit. A computer-readable memory and apparatus utilizing the method are provided.

Claims

1. A method for calculating impedance in a first circuit coupling a first radio frequency electrode to a radio frequency controller where the first radio frequency electrode is disposed in tissue of a mammalian body in the vicinity of a second radio frequency electrode coupled to a second circuit distinct from the first circuit comprising the steps of measuring the impedance of the first circuit to determine an impedance value IMP when radio frequency energy is being supplied to the first and second radio frequency electrodes, measuring the impedance of the first circuit to determine an impedance value IMP₀ when radio frequency energy is being supplied to the first radio frequency electrode but not to the second radio frequency electrode, subtracting the impedance value IMP₀ from the impedance value IMP to determine an impedance delta value IMP_Δ

, remeasuring the impedance of the first circuit to determine an impedance value IMP² when radio frequency energy is being supplied to the first and second radio frequency electrodes and subtracting the impedance delta value IMP_Δ

from the impedance value IMP² to arrive at a calculated impedance value for the first circuit.

2. The method of claim 1 wherein the first and second radio frequency electrodes are first and second needle electrodes.

3. The method of claim 2 wherein the first and second needle electrodes are slidably carried by an elongate probe member introduceable into the urethra of a human male for treatment of the tissue of the prostate.

4. The method of claim 2 wherein a temperature sensor is carried by each of the first and second needle electrodes.

5. The method of claim 1 further comprising the step of adjusting the radio frequency energy supplied to the first radio frequency electrode as a function of the calculated impedance.

6. The method of claim 1 wherein the remeasuring and subtracting steps are repeated.

7. The method of claim 6 wherein the remeasuring and subtracting steps are repeated for a predetermined length of time.

8. The method of claim 1 further comprising the step of performing a medical procedure on the tissue.

9. The method of claim 8 wherein the steps of measuring the impedance of the first circuit to determine the impedance value IMP when radio frequency energy is being supplied to the first and second radio frequency electrodes, measuring the impedance of the first circuit to determine the impedance value IMP₀ when radio frequency energy is being supplied to the first radio frequency electrode but not to the second radio frequency electrode and subtracting the impedance value IMP₀ from the impedance value IMP to determine the impedance delta value IMP_Δ

are repeated after a predetermined event during the procedure.

10. The method of claim 9 wherein the predetermined event is an elapse of a length of time.

11. The method of claim 9 wherein the predetermined event is a change in the radio frequency energy supplied to one of the first and second radio frequency electrodes.

12. The method of claim 1 wherein the second circuit is coupled to the radio frequency controller.

13. A computer-readable memory for use with a radio frequency controller and a first circuit to couple a first radio frequency electrode to the controller and a second radio frequency electrode coupled to a second circuit distinct from the first circuit, the memory containing a computer program for causing the controller to calculate an impedance in the first circuit when the first radio frequency electrode is disposed in tissue of a mammalian body in the vicinity of the second radio frequency electrode by measuring the impedance of the first circuit to determine an impedance value IMP when radio frequency energy is being supplied to the first and second radio frequency electrodes, measuring the impedance of the first circuit to determine an impedance value IMP₀ when radio frequency energy is being supplied to the first radio frequency electrode but not to the second radio frequency electrode, subtracting the impedance value IMP₀ from the impedance value IMP to determine an impedance delta value IMP_Δ

, remeasuring the impedance of the first circuit to determine an impedance value IMP² when radio frequency energy is being supplied to the first and second radio frequency electrodes and subtracting the impedance delta value IMP_Δ

from the impedance value IMP² to arrive at a calculated impedance value for the first circuit.

14. The computer-readable memory of claim 13 wherein the computer program further causes the controller to adjust the radio frequency energy being supplied to the first radio frequency electrode as a function of the calculated impedance.

15. A radio frequency controller for use with a first circuit to couple a first radio frequency electrode to the controller and with a second radio frequency electrode coupled to a second circuit distinct from the first circuit comprising a computer-readable memory containing a computer program for causing the controller to calculate an impedance in the first circuit when the first radio frequency electrode is disposed in tissue of a mammalian body in the vicinity of the second radio frequency electrode by measuring the impedance of the first circuit to determine an impedance value IMP when radio frequency energy is supplied to the first and second radio frequency electrodes, measuring the impedance of the first circuit to determine an impedance value IMP₀ when radio frequency energy is being supplied to the first radio frequency electrode but not to the second radio frequency electrode, subtracting the impedance value IMP₀ from the impedance value IMP to determine an impedance delta value IMP_Δ

, remeasuring the impedance of the first circuit to determine an impedance value IMP² when radio frequency energy is being supplied to the first and second radio frequency electrodes and subtracting the impedance delta value IMP_Δ

from the impedance value IMP² to arrive at a calculated impedance value for the first circuit, and a central processing unit coupled to the memory for executing the program in the memory.

16. The radio frequency controller of claim 15 wherein the program in the memory further causes the controller to adjust the radio frequency energy being supplied to the first radio frequency electrode as a function of the calculated impedance.