Method and apparatus for plasma-mediated thermo-electrical ablation

• US 20030208200A1
• Filed: 05/03/2002
• Published: 11/06/2003
• Est. Priority Date: 05/03/2002
• Status: Active Grant

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Inventors: Palanker, Daniel V., Vankov, Alexander B.
• Granted Patent: US 6,780,178 B2
• Time in Patent Office: Days
• US Class Current: 606/45
• CPC Class Codes: A61B 18/042 using additional gas becoming plasma
• CPC Class Codes: A61B 18/14 Probes or electrodes therefor
• CPC Class Codes: A61B 2018/00577 Ablation
• CPC Class Codes: A61B 2018/00601 Cutting
• CPC Class Codes: A61B 2018/00625 Vaporization
• CPC Class Codes: A61B 2018/1213 creating an arc
• CPC Class Codes: A61B 2018/122 ionizing, with corona
• CPC Class Codes: A61B 2018/1472 for use with liquid electrolyte, e.g. virtual electrodes
• CPC Class Codes: H05H 1/48 using an arc H05H1/26 takes precedence
• CPC Class Codes: H05H 2245/32 Surgery, e.g. scalpels, blades or bistoury; Treatments inside the body

Abstract

An apparatus and method for cutting a material including conducting and non-conducting materials such as biological tissue, cellulose or plastic while the material is submerged in a conductive liquid medium. The apparatus has a cutting electrode with an elongate cutting portion having an aspect ratio (length to width) of 1 or more and a return electrode. The two electrodes are immersed in the conductive medium and a voltage is applied between them to heat the medium, thus producing a vapor cavity around the elongate cutting portion and ionizing a gas inside the vapor cavity to produce a plasma. The voltage applied between the electrodes is modulated in pulses having a modulation format selected to minimize the size of the vapor cavity, its rate of formation and heat diffusion into the material while the latter is cut with an edge of the elongate cutting portion. The modulation format includes pulses ranging in duration from 10 μs to 10 ms, as well as minipulses and micropulses, as necessary. The apparatus and method of invention allow the user to perform efficient thermal ablation and electrosurgical procedures in particular at power levels as low as 10 mW with minimal thermal and cavitation damage.

Claims

1. A method for cutting a material submerged in a conductive liquid medium, said method comprising:

a) providing a cutting electrode having an elongate cutting portion;

b) providing a return electrode;

c) immersing said cutting electrode and said return electrode in said conductive liquid medium;

d) applying a voltage between said cutting electrode and said return electrode such that said conductive liquid medium is heated to produce a vapor cavity around said elongate cutting portion and to ionize a gas inside said vapor cavity to produce a plasma;

e) modulating said voltage in pulses having a modulation format selected to minimize the size of said vapor cavity, a rate of formation of said vapor cavity, and a heat diffusion into said material; and

f) cutting said material with an edge of said elongate cutting portion.

2. The method of claim 1, wherein said format comprises pulses having a pulse duration selected in the range substantially between 10 μ

s and 10 ms.

3. The method of claim 2, wherein each of said pulses comprises minipulses having a minipulse duration selected in the range between 0.1 and 10 μ

s and an interval between said minipulses selected in the range between 0.1 and 10 μ

s.

4. The method of claim 3, wherein each of said minipulses comprises micropulses having a micropulse duration selected in the range between 0.1 and 1 μ

s.

5. The method of claim 3, wherein said interval is shorter than a lifetime of said vapor cavity.

6. The method of claim 3, wherein said minipulse duration and a peak power are adjusted to permit spark discharges and to prevent arc discharges.

7. The method of claim 3, wherein said minipulses exhibit alternating positive and negative polarities.

8. The method of claim 2, wherein the voltage of said pulses is varied during said pulse duration, such that a low voltage is applied for electro-chemical generation of said gas and a high voltage is applied for generation of said plasma.

9. The method of claim 1, wherein said voltage and said format are selected such that the temperature of said elongate cutting portion and said plasma are maintained significantly above the boiling temperature of water.

10. The method of claim 9, wherein the temperature of said elongate cutting portion is maintained between about 100 and 1,000°

C.

11. The method of claim 1, further comprising preventing charge transfer to said material.

12. The method of claim 1, wherein said material is selected from the group consisting of biological tissue, cellulose and plastics.

13. The method of claim 1, wherein said elongate cutting portion has an aspect ratio of length to width larger than 1.

14. The method of claim 13, wherein said aspect ratio is larger than 5.

15. The method of claim 1, wherein said elongate cutting portion has a width between 1 and 250 microns.

16. The method of claim 15, wherein said elongate cutting portion has a width between 10 and 100 microns.

17. The method of claim 1, wherein said elongate cutting portion is a wire with diameter between 1 and 250 microns.

18. The method of claim 17, wherein said elongate cutting portion is a wire with diameter between 10 and 100 microns.

19. An apparatus for cutting a material submerged in a conductive liquid medium, said apparatus comprising:

a) a cutting electrode having an elongate cutting portion;

b) a return electrode;

c) a voltage source for applying a voltage between said cutting electrode and said return electrode such that when said cutting electrode and said return electrode are immersed in said conductive liquid medium said conductive liquid medium is heated to produce a vapor cavity around said elongate cutting portion and to ionize a gas inside said vapor cavity to produce a plasma; and

d) a pulse control for modulating said voltage in pulses of a modulation format selected to minimize the size of said vapor cavity, a rate of formation of said vapor cavity, and heat diffusion into said material.

20. The apparatus of claim 19, wherein said pulse control comprises a peak power control and a duration control and said format comprises pulse power, pulse duration and pulse interval.

21. The apparatus of claim 20, further comprising a low impedance line connecting the output of said voltage source and said elongate cutting portion for producing micropulses.

22. The apparatus of claim 19, wherein said material is selected from the group consisting of biological tissues, cellulose and plastics.

23. The apparatus of claim 19, wherein said elongate cutting portion has a width between 1 μ

m and 250 μ

m.

24. The apparatus of claim 23, wherein said width ranges between 10 μ

m and 100 μ

m.

25. The apparatus of claim 19, wherein said elongate cutting portion has a circular cross section.

26. The apparatus of claim 19, wherein said elongate cutting portion has at least one bend.

27. The apparatus of claim 19, wherein said elongate cutting portion forms a loop.

28. The apparatus of claim 19, wherein said cutting electrode comprises a wire electrode.

29. The apparatus of claim 28, further comprising a means for advancing and retracting said wire electrode.

30. The apparatus of claim 19, wherein said material comprises biological tissue and said apparatus further comprises a device for preventing charge transfer to said biological tissue.

31. The apparatus of claim 30, wherein said device comprises an RC-circuit.

32. The apparatus of claim 30, wherein said elongate cutting portion is designed for capsulotomy and said biological tissue comprises eye tissue.

33. The apparatus of claim 19, wherein said elongate cutting portion has an aspect ratio of length to width larger than 1.

34. The method of claim 33, wherein said aspect ratio is larger than 5.