Tissue cooling rod for laser surgery

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.

Testing of the Devices

The reader should understand that devices according to the present invention work by destroying living tissue. Hopefully the destroyed tissue is unwanted tissue and is quickly replaced by new tissue produced by the body's natural ability to repair damaged and destroyed skin tissue. Care should be taken to minimize unwanted tissue destruction. Applicants recommend that tests be performed prior to use of the device in the manner disclosed above. A test station could be constructed using a plastic material having thermal properties similar to human skin and equipping it with fast response thermocouples located at various depths and positions below the surface. The thermocouples should be connected to the real time monitors so that the technician and the patient can see the thermal effects produced by the device prior to actual use on the patient.

CRYOGENICALLY COOLED SELF CONTAINED WINDOW

A second embodiment involves the use of a cryogenically cooled diamond cooling element as shown in FIGS. 5A and 5B. The device consists of copper holder 24, which has a cryogenic container 21. Synthetic diamond cooling element 23 is in the shape of a flattened cylinder and contains a circular groove through which cryogenic mist flows. The mist exits at the exit port 26.

The flattened diamond rod is transparent to the laser beam. It is applied to the part of the cleaned skin to be treated. The nozzle valve opens the shutter and the cryogenic spray flows to the chamber around this window. When the window is cold the “ready” light will be switched-on. The energy delivery procedure can be started. This device is good for the large area irradiation such as subsurface tumor interstitial thermotherapy with a high frequency electromagnetic radiation.

PATERNED COOLING ELEMENT FOR MASKING PORTIONS OF TISSUE

A third embodiment for practicing this invention is to use a patterned rod to the surface of the skin in order to have damaged and healthy areas under the skin surface. FIGS. 3A and 3B show rod 31 with the perpendicular grooves 32 filled with copper stripes 33.

A laser light is sent through the cooled rod to the surface of the skin does not penetrate through the copper stripes. But the contacting surface of the rod has an almost uniform temperature distribution. It means that the surface of the skin is cooled uniformly. But under skin damage is not uniform having irradiated and not irradiated healthy spots. The reason to have these healthy untouched spots around the damaged tissue is to use the capacity of healthy spot tissue and cells for the fast immune response and wound healing process.

SELF COLLIMATED COOLING ELEMENT

This embodiment is essentially the same as the first one described above except that the rod tip, which is connected to the fiber optics has concave form for the self-collimating beam properties. FIG. 4 shows a cooling element with the lens-type tip surface. For such an element, it does not require a collimated lens and can be replaced by the transparent disk-type window in the oil chamber.

HORIZONTAL AND ANACHROMATIC COOLING ELEMENT

This embodiment is essentially the same as the first one described above except that the cylindrical element is placed in the cooling chamber horizontally (see FIGS. 6A and 6B). The reader should note that the rod could be of different shapes to provide desired beam profiles on the skin surface or to focus the beam. The focal point (or focal line) could be under the skin to help concentrate the beam energy in target locations.

TISSUE DESTRUCTION WITH FREEZING

The device disclosed herein can be used in reverse. That is, surface tissue destruction can be provided by the very cold surface of the tip of the sapphire rod. Preferably, the skin is pre-warmed with a low energy laser pulse of about one-half the values specified above which should cause no damage but will provide warmth which will minimize tissue destruction caused below the surface. This process is good for freezing of warts and certain types of surface skin cancers.

PRE AND POST COOLING

In an additional embodiment pre and post cooling is provided by transparent circular part 20 as shown in FIG. 9 preferably comprised of sapphire. In this case the exhaust from chamber 17 flows through port 21 onto the surface of the circular sapphire part 20 to cool it. This cool surface which will be at a temperature above 0 C prevents the epidermis from being overheated from the hotter lower dermis. This permits the technician to move the laser beam rapidly across the skin surface. The illuminated portion of the skin is both pre-cooled and post-cooled.

PLATE TYPE COOLING ELEMENT

Another preferred embodiment is shown in FIGS. 10A and B. Solenoid valve 50 is controlled by microprocessor 52 to provide a controlled spray from cryogen can 53 on sapphire plate 54 which cools skin surface 565. The temperature of plate 54 is monitored using thermocouple 58. Temperature data is displayed on display 60. The operator has manual control of the spray with switch 62 as desired or the spray can be automatically controlled with processor 52 based on temperature data from thermocouple 58. In a preferred process the operator holds a laser device in one hand and the cooling device in the other. He moves the cooling device in the direction of arrow 64 and the laser beam is directed as shown at 66. As in the paragraph above sapphire plate 54 provides both pre and post cooling as the cooling device is moved along the skin surface. FIG. 10B shows a bottom view of plate 54. In this example the laser beam applicator (not shown specifically) and the cooling device are handled separately, but they could be mounted together as one unit.

OTHER EMBODIMENTS

It is very important for all of these embodiments and in other embodiments that will be apparent to persons skilled in the art that the cooling rod has a very high thermoconductivity coefficient and low absorption of the irradiating light. The substance used for the cryogenic cooling can be chosen based on the particular application. The important thing is to use a proper time of cooling in order to reach a required low temperature of the tissue at the required depth. Persons skilled in the art will recognize that certain material and configuration of the rod, container, coolant and connector will be preferred for different skin type, different lesions and different applications. The reader should note that the preferred embodiment of this invention can be used without this laser to provide cryogenic treatment to surface skin lesions. The same skin cooling can be provided with about 1/10 the cryogen as direct open spray. An important application of the device for cryogenic treatment is to promote lymphatic drainage by cold therapy. Skin rejuvenation begins with flushing of the lymphatic system to remove dead proteins and other debris. Thermal receptors in the lymphatic system are effectively stimulated by the presence of cold applied to the skin surface. Current techniques for lymphatic drainage by cold therapy include spray and ice, both of which are messy and offer poor control of the skin temperature. The device shown in FIGS. 10A and B is useful for lymphatic drainage due to its compact hand held design, disposable canisters and accurate control of the skin temperature.

While the above description contains many specifications, the reader should not construe these as limitations on the scope of the invention, buy merely as exemplifications of preferred embodiments thereof. Those skilled in the art will envision many other possible variations are within its scope. Accordingly the reader is requested to determine the scope of the invention by the appended claims and their legal equivalents, and not by the examples which have been given.

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 of treating skin tissue, comprising:

generating laser light at a wavelength that in skin tissue is primarily absorbed by water;

transmitting the laser light through a transparent material contained in a hand-held unit;

placing the hand-held unit in contact with skin tissue; and

converting the laser light from a beam to an irradiation pattern such that a portion of the laser light irradiates and damages a first tissue portion, a second portion of the laser light irradiates and damages a second tissue portion, and a portion of tissue between the first and second tissue portions is undamaged by the laser light.

30. The method of claim 29 wherein converting the laser light from the beam to the irradiation pattern comprises:

masking the laser light.

31. The method of claim 29 further comprising:

cooling the transparent material; and

placing the cooled transparent material in contact with the skin tissue during irradiation of the skin tissue by the laser light.

32. The method of claim 31 further comprising:

cryogenically cooling the transparent material.

33. The method of claim 29 further comprising:

cooling the transparent material; and

placing the cooled transparent material in contact with the skin tissue so as to provide pre-cooling, post-cooling, or both pre-cooling and post-cooling of the skin tissue.

34. The method of claim 29 wherein the transparent material cools the temperature of the skin tissue at a depth of 100 μm beneath the surface and the laser light heats the temperature of the skin tissue at a depth of 400 μm beneath the surface to above 70° C.

35. The method of claim 29 further comprising:

focusing the laser light beneath the surface of the skin tissue with a focusing element.

36. The method of claim 35, wherein the focusing element comprises a collimating lens.

37. The method of claim 29 wherein the transparent material focuses the laser light.

38. The method of claim 29 wherein the transparent material is slid across the tissue.

39. The method of claim 29 further comprising:

measuring the temperature of the skin tissue with a temperature monitoring element.

40. The method of claim 39, further comprising:

using the measured temperature to control delivery of a power of the laser light to provide proper regulation of tissue temperature.

41. The method of claim 40, further comprising:

cooling the transparent material, and using the measured temperature to control an amount of cooling applied to the transparent material.

42. The method of claim 41, wherein an amount of cooling is controlled so that a temperature of the skin tissue is not below 0 degrees C for more than 1 second.

43. The method of claim 29, wherein the transparent material includes a lens-type tip surface for focusing the laser light.

44. The method of claim 29 further comprising:

using the laser light to treat wrinkles.

45. The method of claim 29 wherein the laser light is generated with an Er:Glass laser.

46. The method of claim 29 wherein the laser light is generated with a laser lasing at a wavelength of approximately 1.54 μm.

47. The method of claim 29 wherein the laser light is generated with a laser with a wavelength that is absorbed more strongly by blood than by tissue surrounding blood vessels.

48. The method of claim 29 wherein the laser light is generated with a pulse duration of about 2-200 ms.

49. The method of claim 48, wherein the laser light is generated with a pulse duration of about 50-200 ms.

50. The method of claim 29 wherein the hand-held unit converts the laser light from a beam to a regular irradiation pattern such that irradiation of the skin tissue causes a regular pattern of spots of damaged tissue with undamaged tissue between the spots of damaged tissue.

51. The method of claim 29, wherein a plurality of undamaged tissue portions is created, an arrangement of the undamaged and damaged tissue portions is such that the undamaged tissue portions are around the damaged tissue portions allowing a capacity of the undamaged tissue portions to create a fast immune response and wound healing process for the damaged tissue portions.

52. The method of claim 29, further comprising:

using a battery to power the hand-held unit, the hand-held unit being portable.

53. The method of claim 29, further comprising:

using the laser light to treat spider veins.

54. The method of claim 29, further comprising:

using the laser light to treat telagiactasia.

55. The method of claim 29, further comprising:

using the laser light to treat skin tumor angiogenesis.

56. The method of claim 29, further comprising:

using the laser light to coagulate hair follicular blood vessels.

57. The method of claim 29, further comprising:

using the laser light to destroy living tissue.

58. The method of claim 29, wherein the laser light is generated at a pulse rate between 0.5 Hz and 2 Hz.

59. The method of claim 29, wherein the laser light produces an energy fluence of between 25 J/cm2 and 140 J/cm2.

60. The method of claim 29, further comprising:

focusing the laser light using a cylindrical element.

61. 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.

62. The method of claim 29, further comprising:

controlling a power of the laser light so as to reach a penetration depth in the skin tissue of up to 1-1.5 mm.

63. The method of claim 29, wherein the laser light causes irreversible changes in the first and second tissue portions.

64. A method of treating wrinkles in skin tissue, comprising:

generating laser light with an Er:Glass laser lasing at a wavelength of approximately 1.54 μm;

transmitting the laser light through a transparent material contained in a hand-held unit;

placing the transparent material in contact with the skin tissue;

converting the laser light from a beam to an irradiation pattern that irradiates and damages a pattern of spots of skin tissue, with undamaged tissue between the spots of damaged tissue;

cooling the transparent material; and

placing the cooled transparent material in contact with the skin tissue during irradiation of the skin tissue by the laser light.

65. The method of claim 64 wherein the hand-held unit converts the laser light from a beam to a regular irradiation pattern such that irradiation of the skin tissue causes a regular pattern of spots of damaged tissue with undamaged tissue between the spots of damaged tissue.

66. The method of claim 64 wherein

the step of generating laser light comprises the Er:Glass laser generating pulses of laser light;

transmitting the laser light through a fiber optic cable to the hand-held unit; and

the hand-held unit converting the laser light from the beam to a regular rectilinear irradiation pattern such that irradiation of the skin tissue causes a regular rectilinear pattern of spots of damaged tissue with undamaged tissue between the spots of damaged tissue.

67. The method of claim 66 further comprising:

the step of generating laser light comprises the Er:Glass laser generating pulses of laser light at a pulse repetition rate of between approximately 0.5-1.0 Hz; and

placing the cooled transparent material in contact with the skin tissue before, during and after irradiation of the skin tissue by the laser light.