Method for cryogenically treating tissue below the skin surface

Abstract

A laser treatment device and process with controlled cooling. The device contains a cooling element with high heat conduction properties, which is transparent to the laser beam. A surface of the cooling element is held in contact with the tissue being treated while at least one other surface of the cooling element is cooled by the evaporation of a cryogenic fluid. The cooling is coordinated with the application of the laser beam so as to control the temperatures of all affected layers of tissues. In a preferred embodiment useful for removal of wrinkles and spider veins, the cooling element is a sapphire plate. A cryogenic spray cools the top surface of the plate and the bottom surface of the plate is in contact with the skin. In preferred embodiments the wavelength of the laser beam is chosen so that absorption in targeted tissue is low enough so that substantial absorption occurs throughout the targeted tissue. In a preferred embodiment for treating large spider veins with diameters in the range of 1.5 mm, Applicants use an Er:Glass laser with a wavelength of 1.54 microns.

Description

where skin density is about 1.15 g/cm³ and specific heat of skin about 3.8J/Cgm.

Effect of skin surface cooling on temperature distribution in skin have been estimated by solving heat transfer equation in semi infinite skin tissue with boundary conditions corresponding to constant −5° C. temperature of the surface (or other constant temperature of the sapphire rod). Temperature distribution in ° C. in skin then can be calculated by formula:
T(z,t)=37*erf(z/2 αct),
where erf refers to the Gausian error function, and z is the depth into the tissue, t is time lapse in seconds from the start of the contact skin cooling and α=10⁻⁴(cm²/sec) is thermal diffusivity of skin dermis. Skin temperature was found by superposition of laser heating and surface cooling effects.

Various elaborate computer programs are available for more precise estimate of temperature distribution within the skin as a function of time. Applicants have made analysis using a Monte-Carlo computer code specifically modified for skin thermodynamic analysis and some of the results are shown in FIGS. 7A1-7 and 7B1-7 which were discussed above. Cooling experiments have been performed by using different configurations of the cooling element for the different applications. For these applications, one of the alternative embodiments is recommended.

Claims

1. A laser system for tissue treatment, comprising:

A) A hand-held portable battery powered tissue cooling unit comprising:

1) a cooling transmitting element comprised of material transparaent to light at a nominal wavelength and having high thermal conductivity and having a contact surface for contacting a surface of tissue being treated,

2) a cryogenic container mounted within or on said cooling unit,

3) a cryogen contained in said container,

4) a cryogenic cooling chamber for cooling at least one surface of said cooling element, said chamber having an entrance port communicating with said container and an exit port,

5) a battery powered cryogenic control means for permitting a flow of vaporizing cryogen from said container into said chamber to cool said at least one surface in order to remove heat from said tissue surface and to produce desired temperature distribution in target tissue being treated, and

6) a battery mounted on or within said cooling unit for providing power to said control means, and

B) a source of laser light defining a nominal wavelength arranged to transmit said laser light through said cooling transmitting element.

2. A laser system as in claim 1 and further comprising a temperature-monitoring element mounted adjacent to but insulated from said contact surface for monitoring tissue surface temperature.

3. A laser system as in claim 1 and further comprising a temperature-monitoring element configured to monitor temperature of said cooling element.

4. A laser system as in claim 1 and further comprising a processor programmed for controlling said source of laser light and said flow of cryogen.

5. A laser system as in claim 1 wherein said source of laser light is a free running mode Er:Glass pulse laser.

6. A laser system as in claim 1 wherein said source of laser light is a Nd:YAG laser.

7. A laser system as in claim 6 wherein said Nd:YAG laser is arranged to operate at a pulse width of about 50 ms.

8. A laser system as in claim 6 wherein said Nd:YAG laser is arranged to operate at a pulse width of about 100 to 200 ms.

9. A laser system as in claim 1 wherein said cooling transmitting element is sapphire plate and substantially all cooling of said plate is through a single non-circumferential surface.

10. A laser system as in claim 1 wherein said cooling transmitting element is sapphire rod defining a circumferential surface and substantially all cooling is through said circumferential surface.

11. A laser system as in claim 1 wherein said cooling transmitting element is a diamond plate.

12. A laser system as in claim 1 wherein said cooling transmitting element is a diamond rod.

13. A laser system as in claim 1 wherein said cooling transmitting element is a patterned rod.

14. A laser system as in claim 1 wherein said cooling transmitting element has a concave form for self-collimating beam properties.

15. A laser system as in claim 1 wherein said cooling transmitting element is a cylindrical rod mounted horizontally.

16. A process for treating tissue, comprising the steps of:

A) generating from a source a laser light defining a nominal wavelength,

B) transmitting said laser light through a hand-held portable battery operated tissue cooling unit comprising a cooling transmitting element comprised of material transparent to light at said nominal wavelength and having high thermal conductivity and having a contact surface for contacting a surface of tissue being treated,

C) inserting cryogen from a cryogenic container, mounted on or within said cooling unit, into a cryogenic cooling chamber for said cooling element, said chamber having an entrance port communicating with said container and an exit port,

17. A process as in claim 16, further comprising the additional step of sliding said cooling element across surface of tissue while applying laser radiation through a portion of said cooling transmitting element so as to provide pre, during and post cooling of said tissue.

18. A process as in claim 17, further comprising the step of controlling said source of laser light and said flow of cryogen with a processor programmed with a control algorithm.

19. A process as in claim 17, wherein said method is for the purpose of treating spider veins.

20. A hand-held portable battery powered tissue cooling unit, useful for both cryogenic tissue treatment and for cooling tissue during laser treatment, comprising:

A) a cooling transmitting element comprised of material transparent to light at a nominal wavelength and having high thermal conductivity and having a contact surface for contacting a surface of tissue being treated,

B) a cryogenic container mounted on or within said cooling unit,

C) a cryogen contained in said container,

D) a cryogenic cooling chamber for cooling at least one surface of said cooling element, said chamber having an entrance port communicating with said container and an exit port,

E) a battery powered cryogenic control means for permitting a flow of vaporizing cryogen from said container into said chamber to cool said at least one surface in order to remove heat from said tissue surface and to produce desired temperature distribution in target tissue being treated, and

F) a battery mounted on or within said cooling unit providing power to said control means.

21. A cooling unit as in claim 20 wherein said cooling transmitting element is comprised of sapphire.

22. A cooling unit as in claim 20 wherein said cooling transmitting element is comprised of diamond.

23. A cooling unit as in claim 20 wherein said control means includes a temperature detector.

24. A cooling unit as in claim 23 wherein said temperature detector is a thermocouple.

25. A cooling unit as in claim 24 wherein said cryogenic container is a replaceable container.

26. A cooling unit as in claim 25 wherein said control means comprises a microprocessor for providing a controlled spray from said cryogenic container.

27. A cooling unit as in claim 26 wherein said cooling transmitting element comprises a sapphire plate and wherein said microprocessor is programmed to provide a controlled spray from said cryogen container onto said sapphire plate.

28. A cooling unit as in claim 27 wherein said cryogen is tetrafluoethan.

29. A method for cryogenically treating tissue below a skin surface, comprising:

placing a hand-held unit in contact with the skin surface;

cryogenically cooling the skin surface by contacting the skin surface with a material which has high thermal conductivity;

monitoring a temperature of either the material or the skin surface; and

controlling an amount of time the hand-held unit is in contact with the skin surface and an amount of cooling applied in order to cryogenically reach a desired temperature of the tissue at a desired depth below the skin surface, which is lower than a temperature before treatment, to promote lymphatic drainage by cold therapy.

30. The method of claim 29, wherein the temperature of the material is monitored.

31. The method of claim 29, wherein the temperature of the skin surface is monitored.

32. The method of claim 29, wherein the temperature is monitored with a thermocouple.

33. The method of claim 32, wherein the temperature of the skin surface is controlled so as to not fall below 0 degrees Centigrade for more than one second.

34. The method of claim 29, wherein the cooling results in skin rejuvenation.

35. The method of claim 29, wherein the amount of cooling applied is automatically controlled in response to the monitored temperature.

36. The method of claim 29, wherein the tissue below the skin surface is destroyed without any significant damage to the skin surface.

37. The method of claim 29, wherein the tissue comprises epidermal tissue.

38. The method of claim 29, wherein the material is cooled by evaporation of a cryogenic fluid.

39. The method of claim 29, wherein the cooling results in either removal of wrinkles or removal of spider veins.

40. The method of claim 29, wherein a temperature of all desired tissue layers being treated are controlled.

41. The method of claim 29, wherein cooling of the skin tissue is accompanied by no heating with laser light or other heating mechanism.

42. The method of claim 29, further comprising:

cleaning the skin surface with alcohol prior to placing the hand-held unit in contact with the skin.

43. The method of claim 29, further comprising:

heating the skin surface.

44. The method of claim 43, wherein the skin surface is heated prior to being cooled.

45. The method of claim 43, wherein the skin surface is heated as it is cooled.

46. The method of claim 29, wherein the material has a convex surface that contacts the skin surface.

47. The method of claim 29, wherein the material has a planar surface that contacts the skin surface.

48. The method of claim 29, wherein the cooling results in cryogenic treatment of skin surface lesions.

49. A method for cryogenically treating tissue below a skin surface, comprising:

placing a hand-held unit in contact with the skin surface;

cryogenically cooling the skin surface by contacting the skin surface with a material which has high thermal conductivity;

monitoring a temperature of either the material or the skin surface; and

controlling an amount of time the hand-held unit is in contact with the skin surface and an amount of cooling applied in order to cryogenically reach a desired temperature of the tissue at a desired depth below the skin surface, which is lower than a temperature before treatment, to promote lymphatic drainage by cold therapy,

wherein cooling of the skin tissue is accompanied by no heating with laser light or other heating mechanism.

50. The method of claim 49, wherein the temperature of the material is monitored.

51. The method of claim 49, wherein the temperature of the skin surface is monitored.

52. The method of claim 49, wherein the temperature is monitored with a thermocouple.

53. The method of claim 49, wherein the temperature of the skin surface is controlled so as to not fall below 0 degrees Centigrade for more than one second.

54. The method of claim 49, wherein the cooling results in skin rejuvenation.

55. The method of claim 49, wherein the amount of cooling applied is automatically controlled in response to the monitored temperature.

56. The method of claim 49, wherein the tissue below the skin surface is destroyed without any significant damage to the skin surface.

57. The method of claim 49, wherein the tissue comprises epidermal tissue.

58. The method of claim 49, wherein the material is cooled by evaporation of a cryogenic fluid.

59. The method of claim 49, wherein the cooling results in either removal of wrinkles or removal of spider veins.

60. The method of claim 49, wherein a temperature of all desired tissue layers being treated are controlled.

61. The method of claim 49, further comprising:

cleaning the skin surface with alcohol prior to placing the hand-held unit in contact with the skin.

62. The method of claim 49, further comprising:

heating the skin surface.

63. The method of claim 62, wherein the skin surface is heated prior to being cooled.

64. The method of claim 62, wherein the skin surface is heated as it is cooled.

65. The method of claim 49, wherein the material has a convex surface that contacts the skin surface.

66. The method of claim 49, wherein the material has a planar surface that contacts the skin surface.

67. The method of claim 49, wherein the cooling results in cryogenic treatment of skin surface lesions.