# Patent

## Title
Treatment of skin by spatial modulation of thermal heating

## Abstract

Treating skin can include delivering a beam of radiation to a target region of the skin to cause a zone of thermal injury including a lateral pattern of varying depths of thermal injury distributed along the target region. The lateral pattern includes at least one first sub-zone of a first depth of thermal injury laterally adjacent to at least one second sub-zone of a second depth of thermal injury. The first depth is greater than the second depth. The at least one first sub-zone of the first depth and the at least one second sub-zone of the second depth extend from a surface of the target region of the skin to form a substantially continuous surface thermal injury. The at least one first sub-zone of the first depth and the at least one second sub-zone of the second depth are substantially heated to at least a critical temperature.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of and priority to U.S. Provisional Application Ser. No. 60/813,729 filed Jun. 14, 2006, which is owned by the assignee of the instant application and the disclosure of which is incorporated herein by reference in its entirety.


FIELD OF THE INVENTION
The invention relates generally to a skin treatment using radiation. In particular, the invention relates to a method for treating skin using a beam of radiation to cause spatially modulated thermal injury of the skin sufficient to elicit a healing response and improvement in the skin.
BACKGROUND OF THE INVENTION
Ablative resurfacing of skin with lasers can be an effective treatment for skin conditions such as wrinkles. However, ablative resurfacing can have undesirable post-treatment side effects. For example, crusting, oozing, erythema can last up to 5 weeks. Furthermore, permanent scarring is a possible long-term side effect of ablative resurfacing. Such side effects can be a deterrent to individuals who otherwise desire treatment.
Improved treatments with reduced side effects include forming sub-surface thermal damage of skin, while leaving the top layer intact by combining heating and surface cooling. However, the results of sub-surface methods can be less dramatic than those achieved by ablative resurfacing. Other improvements include fractional resurfacing techniques, that treat skin in discrete spots and leave the skin between the spots untreated.
Fractional resurfacing technologies can have advantages including lower incidences of side-effects and expedited healing. These advantages can result from the undamaged regions providing blood and nutrients to the adjacent damaged regions and accelerating the healing process. Ablative resurfacing and technologies that include inducing uniform damage corresponding to coverage of an entire region can include higher efficacy at the cost of increased side effects.
SUMMARY OF THE INVENTION
The invention, in various embodiments, combines many of the advantages of ablative resurfacing with those of fractional methods. Skin can be treated by delivering a beam of radiation to a target region to cause a zone of thermal injury. The zone can include a lateral pattern of varying depths of thermal injury distributed along the target region. The lateral pattern can include at least one first sub-zone of a first depth of thermal injury laterally adjacent to at least one second sub-zone of a second depth of thermal injury. The at least one first sub-zone of the first depth and the at least one second sub-zone of the second depth can extend from a surface of the target region of the skin to form a substantially continuous surface thermal injury.
A beam of radiation can have a modulated spatial profile such that the fluence, the intensity, and/or the wavelength delivered to the skin can be varied. The spatial profile determines the depth of thermal injury to the skin. A beam of radiation can be delivered to a region of skin to cause modulated spatial profile of temperature, such that the depth of damage to the skin is varied. An advantage of the invention is that a large target region can be formed with damaged regions adjacent to substantially undamaged regions within the target region, together with a substantially continuous surface thermal injury. The substantially undamaged regions can be undamaged or less damaged than the damaged regions. Other advantages include: improved treatment efficacy initiating from zones corresponding to deeper first damage zones, high coverage of a treatment region corresponding to deeper first damage zones and less deep second damage zones, improved efficacy relating to forming a substantially continuous surface thermal injury, and improved post-treatment healing initiating from zones corresponding to less deep second damage zones.
In one embodiment, the treatment can be used to treat wrinkles or for skin rejuvenation. However, the treatment is not limited to treating wrinkles or skin rejuvenation. A beam of radiation can be delivered non-invasively to affect the skin.
In one aspect, the invention features a method for treating skin including delivering a beam of radiation to a target region of the skin, to cause a zone of thermal injury including a lateral pattern of varying depths of thermal injury distributed along the target region. The lateral pattern includes at least one first sub-zone of a first depth of thermal injury laterally adjacent to at least one second sub-zone of a second depth of thermal injury. The first depth is greater than the second depth. The at least one first sub-zone of the first depth and the at least one second sub-zone of the second depth extend from a surface of the target region of the skin to form a substantially continuous surface thermal injury. Both the at least one first sub-zone of the first depth and the at least one second sub-zone of the second depth are substantially heated to at least a critical temperature to cause the thermal injury.
In another aspect, the invention features a method for treating skin including delivering a beam of radiation to a first portion of a target region of the skin, to heat the first portion to at least a critical temperature to cause a first thermal injury. The method also includes translating the beam of radiation to a second portion of the target region. Additionally, the method includes delivering the beam of radiation to the second portion of the target region, to heat the second portion to at least the critical temperature to cause a second thermal injury. The first thermal injury and the second thermal injury extend from a surface of the target region of the skin to form a substantially continuous surface thermal injury and form a lateral pattern of varying depths of thermal injury distributed along the target region.
In yet another aspect, the invention features an apparatus for treating skin including a source of a beam of radiation and a modulator. The modulator receives the beam of radiation and forms a modulated spatial profile of the beam including a first plurality of first regions at a first fluence and a second plurality of second regions at a second fluence. The first fluence is greater than the second fluence, and each first region is spaced from an adjacent first region by a respective second region. The apparatus also includes a device for delivering the beam of radiation to a target region of skin to cause a zone of thermal injury including a lateral pattern of varying depths of thermal injury distributed along the target region. The lateral pattern includes at least one first sub-zone of a first depth of thermal injury laterally adjacent to at least one second sub-zone of a second depth of thermal injury. The first depth is greater than the second depth. The at least one first sub-zone of the first depth and the at least one second sub-zone of the second depth extend from a surface of the target region of the skin to form a substantially continuous surface thermal injury. The at least one first sub-zone of the first depth and the at least one second sub-zone of the second depth are substantially heated to at least a critical temperature to cause the thermal injury.
In other examples, any of the aspects above, or any apparatus or method described herein, can include one or more of the following features.
In various embodiments, the lateral pattern has a substantially sinusoidal cross sectional injury profile. The method can include delivering the beam of radiation to the target region to form a one-dimensional lateral pattern of varying depths of thermal injury. The method can include delivering the beam of radiation to the target region to form a two-dimensional lateral pattern of varying depths of thermal injury. The first depth and the second depth can be between about 2 mm and about 0.02 mm. The first depth can be about 1.5 mm and the second depth can be about 0.05 mm.
In some embodiments, the critical temperature is below about 100° C., 95° C., 90° C., 85° C., 80° C., 75° C., 70° C., 65° C., 60° C., 55° C., or 50° C. The thermal injury can include at least one of ablation, coagulation, necrosis, and acute thermal injury of skin. The method can include heating the at least one first sub-zone and the at least one second sub-zone to substantially the same temperature.
In certain embodiments, the method includes cooling the surface of the skin, to control the surface thermal injury. The method can include cooling the surface of the skin, to prevent unwanted surface thermal injury. The method can include cooling the target region of skin to produce at least one first region at a first temperature and at least one second region at a second temperature, the first temperature being greater than the second temperature, the at least one first region corresponding to the at least one first sub-zone, and the at least one second region corresponding to the at least one second sub-zone. The method can include cooling the target region of skin to produce at least one first region cooled to a first depth and at least one second region cooled to a second depth, the first depth being less than the second depth, the at least one first region corresponding to the at least one first sub-zone, and the at least one second region corresponding to the at least one second sub-zone.
In various embodiments, the method includes delivering a beam of radiation having a first wavelength to the at least one first sub-zone to cause the first depth of thermal injury and a beam of radiation having a second wavelength to the at least one second sub-zone to cause the second depth of thermal injury. The method can include delivering a beam of radiation having a first fluence to the at least one first sub-zone to cause the first depth of thermal injury and a beam of radiation having a second fluence to the at least one second sub-zone to cause the second depth of thermal injury. The method can include delivering a beam of radiation having a first pulse duration to the at least one first sub-zone to cause the first depth of thermal injury and a beam of radiation having a pulse duration to the at least one second sub-zone to cause the second depth of thermal injury.
In some embodiments, the at least two first sub zones of the first depth are separated by a center to center distance of about 0.05 mm to about 20 mm. The at least one first sub-zone of the first depth can have an aspect ratio of diameter:depth up to about 0.1:10. The at least one second sub-zone of the second depth can have an aspect ratio of diameter:depth up to about 0.1:10.
In certain embodiments, the apparatus includes a cooling system for controllably cooling at least a portion of the target region of skin, to control the thermal injury within the target region. The apparatus can include a cooling system for cooling the target region of skin to produce at least one first region at a first temperature and at least one second region at a second temperature, the first temperature being greater than the second temperature, the at least one first region corresponding to the at least one first sub-zone, and the at least one second region corresponding to the at least one second sub-zone. In one embodiment, the apparatus includes a cooling system for cooling the target region of skin to produce at least one first region cooled to a first depth and at least one second region cooled to a second depth, the first depth being less than the second depth, the at least one first region corresponding to the at least one first sub-zone, and the at least one second region corresponding to the at least one second sub-zone.
Other aspects and advantages of the invention can become apparent from the following drawings and description, all of which illustrate the principles of the invention, by way of example only.



BRIEF DESCRIPTION OF THE DRAWINGS
The advantages of the invention described above, together with further advantages, may be better understood by referring to the following description taken in conjunction with the accompanying drawings. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention.
FIG. 1 shows an exemplary cross-section of skin.
FIG. 2 shows an exemplary embodiment of a system for treating skin.
FIGS. 3A-3B show views of an exemplary cross-section of a region of skin.
FIGS. 4A-4B show a relationship that can be used to control the temperature and thermal injury at a depth of a region of skin.
FIGS. 5A-5B shows examples of spatial modulation of a beam of radiation.
FIG. 6 shows an exemplary embodiment of a device for treating a region of skin.
FIGS. 7A-7C show exemplary treatments of skin using cooling.
FIGS. 8A-8B show exemplary embodiments of a surface of a treated region of skin with a pattern of varying depths of thermal injury.
FIG. 9 shows a ray trace of modulated electromagnetic radiation.
FIG. 10 shows a contour plot of energy density on skin created by modulated electromagnetic radiation.
FIG. 11 shows a plot of intensity variation across skin created by modulated electromagnetic radiation.



DESCRIPTION OF THE INVENTION
FIG. 1 shows an exemplary cross-section of skin 1 including a region of epidermis 2, a region of dermis 3, a region of subcutaneous tissue 4, and a surface of the skin 5. In one embodiment, the skin 1 can be a region of human skin with wrinkles. A beam of radiation 6 can be delivered to the skin 1 to treat at least a region of skin, including a region of epidermis 2 and/or a region of dermis 3. Skin treatments can include skin rejuvenation and treatments for wrinkles, vessels, pigmentation, scarring, and acne.
A therapeutic injury can be induced with electromagnetic radiation in the visible to infrared spectral region. A wavelength of light that penetrates into at least a portion of skin can be used. Chromophores can include blood (e.g., oxyhemoglobin and deoxyhemoglobin), collagen, melanin, fatty tissue, and water. Light sources can include lasers, light emitting diodes, or an incoherent source, and can be either pulsed or continuous. In one embodiment, a light source can be coupled to a flexible optical fiber or light guide, which can be introduced proximally to a target region skin. The light source can operate at a wavelength with depth of penetration into skin that is less than the thickness of the target region of skin.
In various embodiments, skin in a target region is heated to a critical temperature to cause thermal injury. In certain embodiments, the critical temperature is below about 100° C. In other embodiments, the critical temperature is below about 95° C., 90° C., 85° C., 80° C., 75° C., 70° C., 65° C., 60° C., 55° C., or 50° C. In one embodiment, the critical temperature is the temperature associated with ablation, coagulation, necrosis, and/or acute thermal injury of skin.
FIG. 2 shows an exemplary embodiment of a system 10 for treating skin. The system 10 can be used to non-invasively deliver a beam of radiation to a target region of skin. The system 10 includes an energy source 12 and a delivery system 13. In one embodiment, a beam of radiation provided by the energy source 12 is directed via the delivery system 13 to a target area. In the illustrated embodiment, the delivery system 13 includes a fiber 14 having a circular cross-section and a handpiece 16. A beam of radiation can be delivered by the fiber 14 to the handpiece 16, which can include an optical system (e.g., an optic or system of optics) to direct the beam of radiation to the target area. A user can hold or manipulate the handpiece 16 to irradiate the target area. The handpiece 16 can be positioned in contact with a skin surface, can be positioned adjacent a skin surface, can be positioned proximate a skin surface, can be positioned spaced from a skin surface, or a combination of the aforementioned. In the embodiment shown, the handpiece 16 includes a spacer 18 to space the delivery system 13 from the skin surface. In one embodiment, the spacer 18 can be a distance gauge, which can aid a practitioner with placement of the handpiece 16.
In various embodiments, the energy source 12 can be an incoherent light source, a coherent light source (e.g., a laser), a solid state laser, a diode laser, a fiber coupled diode laser array, an optically combined diode laser array, and/or a high power semiconductor laser. In some embodiments, two or more sources can be used together to effect a treatment. For example, an incoherent source can be used to provide a first beam of radiation while a coherent source provides a second beam of radiation. The first and second beams of radiation can share a common wavelength or can have different wavelengths. In an embodiment using an incoherent light source or a coherent light source, the beam of radiation can be a pulsed beam, a scanned beam, or a gated continuous wave (CW) beam.
In various embodiments, the source of electromagnetic radiation can include a fluorescent pulsed light (FPL) or an intense pulsed light (IPL) system. For example, the system can be a LIGHTSTATIONTM (by Candela Corporation of Wayland, Mass.), or an OMNILIGHTTM, NOVALIGHTTM, or PLASMALITETM system (by American Medical Bio Care of Newport Beach, Calif.). However, the source of electromagnetic radiation can also include a laser, a diode, a coherent light source, an incoherent light source, or any other source of electromagnetic radiation. FPL technologies can utilize laser-dye impregnated polymer filters to convert unwanted energy from a xenon flashlamp into wavelengths that enhance the effectiveness of the intended applications. FPL technologies can be more energy efficient and can generate significantly less heat than comparative IPL systems. A FPL system can be adapted to operate as a multi-purpose treatment system by changing filters or handpieces to perform different procedures. For example, separate handpieces allow a practioner to perform tattoo removal and other vascular treatments. An exemplary FPL system is described in U.S. Pat. No. 5,320,618, the disclosure of which is herein incorporated by reference in its entirety.
In various embodiments, the beam of radiation can have a wavelength between about 380 nm and about 2600 nm. In certain embodiments, the beam of radiation can have a wavelength between about 1,200 nm and about 2,600 nm, between about 1,200 nm and about 1,800 nm, or between about 1,300 nm and about 1,600 nm. In one embodiment, the beam of radiation has a wavelength of about 1,500 nm. In other embodiments, the beam of radiation has a wavelength up to about 2,100 nm or up to about 2,200 nm.
In various embodiments, the beam of radiation can have a fluence of about 1 J/cm2 to about 500 J/cm2. For a given wavelength of radiation, a range of effective fluences can be approximated. Because radiation of wavelength between about 380 nm and about 2600 nm is absorbed by water, and because skin is about 70% water, the absorption coefficient of skin can be approximated as 70% of the absorption coefficient of water. Because the absorption coefficient of water is a function of the wavelength of radiation, the desired fluence depends on the chosen wavelength of radiation. The fluence necessary to produce a desired damage depth can be approximated as the fluence that will raise the temperature to the critical temperature at the desired penetration depth, calculated as:

[3*μa*(μa+μs(1−g))]−0.5 

where μa, μs, and g are absorption coefficient, scattering coefficient, and the anisotropy factor of skin, respectively.








TABLE 1







Approximate fluence range to produce a first sub-zone of damage using a


given wavelength.










Wavelength (nm)
Fluence (J/cm2)







1180
100-498



1200
100-498



1220
109-545



1240
118-588



1260
116-582



1280
106-528



1300
 93-466



1320
 75-375



1340
 65-326



1360
 56-280



1380
 29-146



1400
19-96



1420
14-70



1440
11-54



1460
11-55



1480
15-73



1500
18-88



1520
 22-111



1540
 20-101



1560
 23-115



1580
 26-130



1600
 26-132



1620
 31-153



1640
 36-178



1660
 39-196



1680
 40-198



1700
 40-200



1720
 35-174



1740
 29-145



1760
 25-124



1780
 26-128



1800
 26-129



1820
 23-115



1840
 23-117



1860
 22-109



1880
10-50



1900
 5-23



1920
 3-14



1940
 3-13



1960
 3-15



1980
 3-17



2000
 4-22



2020
 6-28



2040
 7-35



2060
 8-40



2080
10-49



2100
12-58



2120
13-65



2140
15-76



2160
17-83



2180
18-90



2200
19-94



2220
19-96



2240
19-94



2260
18-90



2280
16-78



2300
14-69



2320
12-58



2340
10-49



2360
 8-42



2380
 7-36



2400
 6-31



2420
 5-26



2440
 5-23



2460
 4-20



2480
 4-18



2500
 3-17



2520
 3-15



2540
 3-14



2560
 3-13



2580
 2-12



2600
 2-10










In various embodiments, the fluence used to produce a second sub-zone of damage is less than the fluence used to produce a first sub-zone of damage. In certain embodiments, the fluence used to produce a second sub-zone of damage is about 10% of the fluence used to produce a first sub-zone of damage.
In various embodiments, a desired penetration depth of light into the skin (and a corresponding depth of thermal injury) can be targeted by selecting a wavelength of a beam of radiation. For example, a water absorption coefficient can be taken from G. M. Hale and M. R. Querry, “Optical constants of water in the 200 nm to 200 μm wavelength region,” Appl. Opt., 12, 555-563, (1973) and an Optical Penetration Depth (OPD) can be calculated using a diffusion approximation. As described above, μa of skin is taken as μa of water multiplied by 0.7. The product of scattering coefficient and (1-anisotropy factor) is taken as 12 cm−1.







TABLE 2







Approximate wavelength for a corresponding desired penetration depth.









lambda (nm)
OPD (microns)
OPD (mm)












1180
1896.68
1.90


1200
1896.68
1.90


1220
1989.42
1.99


1240
2071.04
2.07


1260
2058.80
2.06


1280
1957.11
1.96


1300
1832.38
1.83


1320
1631.35
1.63


1340
1399.75
1.40


1360
1110.54
1.11


1380
692.68
0.69


1400
431.17
0.43


1420
279.87
0.28


1440
226.74
0.23


1460
229.34
0.23


1480
288.97
0.29


1500
333.69
0.33


1520
393.98
0.39


1540
445.51
0.45


1560
512.22
0.51


1580
583.96
0.58


1600
651.32
0.65


1620
713.46
0.71


1640
785.79
0.79


1660
831.29
0.83


1680
836.88
0.84


1700
842.55
0.84


1720
773.46
0.77


1740
689.83
0.69


1760
626.39
0.63


1780
575.87
0.58


1800
580.12
0.58


1820
538.51
0.54


1840
492.55
0.49


1860
391.16
0.39


1880
213.05
0.21


1900
111.13
0.11


1920
67.16
0.07


1940
64.38
0.06


1960
72.32
0.07


1980
82.28
0.08


2000
106.81
0.11


2020
128.89
0.13


2040
156.06
0.16


2060
176.11
0.18


2080
211.15
0.21


2100
239.41
0.24


2120
262.39
0.26


2140
296.35
0.30


2160
319.62
0.32


2180
338.03
0.34


2200
349.91
0.35


2220
356.02
0.36


2240
349.28
0.35


2260
338.77
0.34


2280
304.49
0.30


2300
277.13
0.28


2320
240.27
0.24


2340
208.26
0.21


2360
183.15
0.18


2380
161.22
0.16


2400
142.20
0.14


2420
121.74
0.12


2440
109.92
0.11


2460
97.31
0.10


2480
87.44
0.09


2500
83.58
0.08


2520
74.66
0.07


2540
70.44
0.07


2560
66.71
0.07


2580
58.99
0.06


2600
51.05
0.05









FIG. 3A shows an exemplary cross-section 20 of a region of skin including a region of skin surface 22, a region of epidermis 24, a region of dermis 26, and a zone of thermal injury 28 including a pattern of varying depths of thermal injury. The pattern includes at least one first sub-zone 30 of a first depth of thermal injury adjacent to at least one second sub-zone 32 of a second depth of thermal injury. The first depth is greater than the second depth. In various embodiments, the depth 34 of thermal injury in the first sub-zone can be measured from the skin surface 22. In various embodiments, the depth 36 of thermal injury in the second sub-zone can be measured from the skin surface 22. In various embodiments, the diameter 38 of thermal injury in a sub-zone can be measured on the skin surface 22.
The at least one first sub-zone 30 of the first depth of thermal injury and the at least one second sub-zone 32 of the second depth of thermal injury extend from the surface 22 of the target region to form a substantially continuous surface thermal injury. The at least one first sub-zone 30 of the first depth and the at least one second sub-zone 32 of the second depth are substantially heated to at least a critical temperature to cause the thermal injury. In one embodiment, the temperature within the at least one first sub-zone 30 of the first depth and the at least one second sub-zone 32 can vary at or above the critical temperature and, accordingly, the degree of thermal injury can also vary at or above a pre-determined amount. In another embodiment, the temperature within the at least one first sub-zone 30 of the first depth and the at least one second sub-zone 32 can be substantially the same and, accordingly, the degree of thermal injury can also be substantially the same.
FIG. 3B shows a three-dimensional view of the cross-section 20 of the region of skin in FIG. 3A, including the region of skin surface 22 and a three-dimensional zone of thermal injury 28 including a pattern of varying depths of thermal injury. The exemplary pattern of varying depths of thermal injury is distributed contiguously along the surface 22 of the target region and includes a three-dimensional zone of thermal injury 28 having a pattern with the three-dimensional first sub-zone 30 of a first depth of thermal injury contiguous along the skin surface with the three-dimensional second sub-zone 32 of a second depth of thermal injury. In various embodiments, the depth 34 of thermal injury in the first sub-zone can be measured from the skin surface 22. In various embodiments, the depth 36 of thermal injury in the second sub-zone can be measured from the skin surface 22. In various embodiments, the diameter 38 of thermal injury in a sub-zone can be measured on the skin surface 22.
A first sub-zone of a first depth of thermal injury can improve the efficacy of treatment by including an acute thermal injury. A substantially continuous surface thermal injury can improve the efficacy of treatment by including surface ablation and/or inducing a surface peel. A second sub-zone of a second depth of thermal injury can improve post-treatment healing of skin. A second sub-zone of a second depth of thermal injury can improve post-treatment healing of an adjacent first sub-zone of a first depth of thermal injury. In various embodiments, treatment efficacy can be improved by forming first sub-zones of thermal injury adjacent to second sub-zones of thermal injury. In some embodiments, treatment efficacy can be improved by forming first sub-zones of thermal injury underlying a substantially continuous surface thermal injury. In certain embodiments, post-procedure healing can be improved by improved flow of blood and nutrients provided by a second sub-zone.
In various embodiments, a sub-zone of thermal damage can include a three-dimensional region of epidermis and/or a region of dermis. For example, in certain embodiments, a first sub-zone can include three-dimensional regions of epidermis and dermis, while a second sub-zone can include three-dimensional regions of epidermis.
In various embodiments, the pattern of thermal injury can be a continuously varying pattern (e.g., a sinusoidal-like or wave-like pattern when viewed in two-dimensions or an “egg carton” like pattern when viewed in three-dimensions). In some embodiments, the pattern of thermal injury can be a continuous surface injury with periodic or irregular regions of deeper thermal injury (e.g., a step-function like pattern when viewed in two dimensions). However, the pattern of thermal injury is not limited to any specific design. Contiguous regions in skin of subsurface injury without surface injury can be overlaid by discrete regions of added surface injury. In certain embodiments, contiguous regions of superficial injury can be overlaid by discrete regions of superficial tissue ablation.
In some embodiments, a three-dimensional pattern of varying depths and/or varying severity of thermal injury within skin can be formed. Regions of more deeply and/or severely injured skin can be contiguous with regions of less deeply and/or severely damaged skin. In certain embodiments, first regions of skin with sub-surface injury and without surface injury are formed. Such first regions can be contiguous with second regions of skin without sub-surface injury and with surface injury. In various embodiments, wounds in the skin that require long recovery periods are avoided. For example, effective treatment of skin can be provided without forming large or contiguous areas of acute injury or necrosis.
As a beam or radiation penetrates skin, the fluence (J/cm2) decreases in an approximately exponential fashion. The rate of decrease in fluence is dependent upon the absorption and scattering properties of skin. A local temperature increase due to absorbed radiation within the skin is a product of the local absorption coefficient and a local fluence divided by the volumetric specific heat. Since absorption and volumetric specific heat can be considered approximately constant within a region of skin, the local temperature rise can be considered proportional to the fluence.
Thermal damage to skin forms at temperatures at, or exceeding, a critical temperature (Tc). Little or no thermal damage to skin forms at temperatures below Tc. Therefore, depth of thermal damage to skin is approximately equal to the depth of skin that is exposed to a temperature of, or exceeding, Tc.
FIG. 4A shows a relationship that can be used to control the temperature at a depth of a region of skin. For a given temperature (T), a greater fluence can be selected if heating to a greater depth is desired and a lesser fluence can be selected if heating to a lesser depth is desired. This relationship can provide a method to control the depth to which a specific temperature is achieved.
FIG. 4B shows a relationship that can be used to control a depth of thermal injury to a region of skin. A lower fluence produces a smaller depth of thermal injury and a higher fluence produces a greater depth of thermal injury. For a given degree of damage, a greater fluence can be selected if a greater depth is desired and a lesser fluence can be selected if a lesser depth is desired. Therefore, by modulating the fluence, one can modulate the depth and temperature within a region of skin.
To form deeper sub-zones of thermal injury, more penetrating wavelengths of radiation can be used. More penetrating wavelengths can be combined with longer pulse durations to increase thermal damage. In certain embodiments, more penetrating wavelengths can be combined with surface cooling to spare overlying tissue.
To form shallower sub-zones of thermal injury, less penetrating wavelengths can be used. Less penetrating wavelengths can be combined with shorter pulse durations. Less penetrating wavelengths can be used without surface cooling or with moderate cooling. Less penetrating wavelengths can also be used with surface cooling to maintain a temperature about a Tc (e.g., allow formation of thermal injury, but prevent necrosis or acute thermal injury).
In various embodiments a beam of radiation with spatially varying intensity; a beam of radiation with spatially varying exposure time or pulse duration; a beam of radiation with spatially varying wavelengths wherein certain regions of the beam include a more penetrating wavelength and other parts include a less penetrating wavelength; and/or a beam of radiation with spatially varying wavelengths with preferential absorption in different skin structures (e.g., a beam including wavelengths with strong water absorption interspersed with wavelengths with strong blood absorption) can be delivered to a target region of the skin to cause a zone of thermal injury including a lateral pattern of varying depths.
In various embodiments, a pulse duration can be between about 1 ms and about 1 min. Shorter pulse durations can be between about 1 ms and about 100 ms. Longer pulse durations can be between about 100 ms and about 1 min.
In various embodiments, a depth of thermal injury in a deeper sub-zone can be up to about 2 mm. In certain embodiments, a depth of thermal injury in a shallower sub-zone can be up to about 50 μm. In one embodiment, deeper sub-zones having a depth of about 400-800 μm are adjacent to shallower sub-zones having a depth of about 50 μm. In another embodiment, deeper sub-zones having a depth of about 400-800 μm are adjacent to shallower sub-zones having a depth of about 25 μm. In still another embodiment, deeper sub-zones having a depth of about 1.5 mm are adjacent to shallower sub-zones having a depth of about 50 μm
In various embodiments, adjacent sub-zones of thermal damage distributed contiguously along the surface of the target region can correspond to about 100% coverage of the surface of the target region (e.g., a substantially continuous surface injury). In certain embodiments, adjacent sub-zones of thermal damage distributed contiguously along the surface of the target region can correspond to less than 100% coverage of the surface of the target region.
In various embodiments, the target region includes about 0.5% to about 99% sub-zones of greater depth. In one embodiment, the target region includes about 5% to about 50% sub-zones of greater depth. In one embodiment, the target region includes about 15% to about 30% sub-zones of greater depth.
In various embodiments, a diameter of a deeper sub-zone of thermal damage can be between about 20 μm and about 2 mm. In some embodiments, a diameter of a shallower sub-zone of thermal damage can be between about 100 μm and about 1000 μm. In various embodiments, spacing between deeper sub-zones can be between about 2 to about 5 times the diameter of the deeper sub-zone. In various embodiments, spacing between shallower sub-zones is the sum of the diameters of the deeper and the shallower sub-zones. In certain embodiments, a sub-zone of thermal damage can have an aspect ratio of diameter:depth greater than 1:2. In one embodiment, a sub-zone of thermal damage has an aspect ratio greater than 1:4. In another embodiment, a sub-zone of thermal damage can have an aspect ratio up to about 0.1:10.
FIG. 5A shows an example of spatial modulation of a beam of radiation. A single 40 beam of radiation is incident on a modulator 41, which forms a spatially modulated 42 beam of radiation 42. In various embodiments, the modulator 41 can be an optical device and/or an electromagnetic device. For example, the modulator 41 can be a lens, a micro lens array, a system of lenses, a diffractive optic in combination with a lens, or another optical device capable of varying the fluence of the beam of radiation 40. In certain embodiments, the modulator is an acousto-optic modulator. In certain embodiments, the single 40 beam can be modulated to form a plurality of discrete beams.
FIG. 5B shows another example of spatial modulation of a beam of radiation. A plurality 44 of beams of radiation are incident on a modulator 41, which forms the spatially modulated 42 beam of radiation. Regions of the discrete beams can overlap to form the spatially modulated beam of radiation 42.
In various embodiments, an optical fiber can be scanned over a surface of skin to deliver a spatially modulated beam of radiation to a target region of skin. In various embodiments, an optical fiber bundle can be used to deliver a plurality of beams of radiation. In certain embodiments, the optical fiber bundle can operate in a scanning mode over a surface of skin. In certain embodiments, the optical fiber bundle can operate in a stamping mode over a surface of skin. The diameter of a region of a surface of skin treated in each stamp can range from about 1 mm to about 50 mm. An optical fiber can be a fiber laser.
FIG. 6 shows an exemplary embodiment of a device for treating a region of skin. A cross-section of skin 50 includes a skin surface 51 and a region 52 of thermal injury underlying the surface 51. A source 53 of a beam of radiation is coupled to a modulator 54. The source 53 can scan 55 along to the skin surface 51, to deliver a beam of radiation 56 to a target region of skin. The modulator 54 can modulate the fluence, the intensity, or the wavelength of the beam 56 and/or the rate of translation of the source 53.
By varying the fluence, the intensity, or the wavelength of the beam 56, the depth of injury can be controlled. Increasing the intensity of the beam 56 delivered to skin 50 can form a deeper zone of injury, e.g., a first sub-zone 57. Decreasing the intensity of the beam 56 delivered to skin 50 can form a shallow zone of injury, e.g., a second sub-zone 58. Varying the fluence or the intensity of the beam 56 can form a modulated spatial pattern 59 of thermal injury in skin.
By varying the rate of translation along the skin, the depth of thermal injury can be controlled. Decreasing the rate over skin 50 can increase the total fluence delivered to a particular region, forming a deeper zone of injury, e.g., a first sub-zone 57. Increasing the rate over skin 50 can decrease the total fluence delivered to a particular region, forming a shallow zone of injury, e.g., a second sub-zone 57. Varying the rate of translation along the skin, can form a modulated spatial pattern 59 of thermal injury in skin.
In some embodiments, methods can include sequentially applying different combinations of radiation wavelength, intensity, or cooling such that a pattern of thermal injury achieved in a given pass is different than that achieved in a subsequent pass.
A cooling system can be used to modulate the temperature in a region of skin and/or minimize unwanted thermal injury to untargeted skin. For example, the delivery system 13 shown in FIG. 2 can be used to cool the skin before, during, or after delivery of radiation, or a combination of the aforementioned. Cooling can include contact conduction cooling, evaporative spray cooling, convective air flow cooling, or a combination of the aforementioned. Cooling can include applying a template to the skin and employing contact, evaporative, or convective cooling to cool at least an exposed portion of the skin. In one embodiment, the handpiece 16 includes a skin contacting portion that can be brought into contact with a region of skin. The skin contacting portion can include a sapphire or glass window and a fluid passage containing a cooling fluid. The cooling fluid can be a fluorocarbon type cooling fluid, which can be transparent to the radiation used. The cooling fluid can circulate through the fluid passage and past the window to cool the skin.
A spray cooling device can use cryogen, water, or air as a coolant. In one embodiment, a dynamic cooling device (e.g., a DCD available from Candela Corporation) can be used to cool the skin. For example, the delivery system 13 shown in FIG. 2 can include tubing for delivering a cooling fluid to the handpiece 16. The tubing can be connected to a container of a low boiling point fluid, and the handpiece can include a valve for delivering a spurt of the fluid to the skin. Heat can be extracted from the skin by virtue of evaporative cooling of the low boiling point fluid. In one embodiment, the fluid is a non-toxic substance with high vapor pressure at normal body temperature, such as a Freon or tetrafluoroethane.
By cooling only a portion of the target region or by cooling different portions of the target region to different extents, the degree of thermal injury of individual portions of the target region can be controlled. By cooling with spatially varying duration and/or by cooling with spatially varying temperature, the degree of thermal injury of individual portions of the target region can also be controlled.
FIG. 7A shows an exemplary treatment of skin using cooling. A cross-section of a region of skin 60 includes a skin surface 61. A cooling plate 62 is applied to the skin surface 61, and a region 63 of skin not in contact with the cooling plate 62 is formed. A beam of radiation 64 is delivered to the region of skin 60, to treat the skin.
The cooling plate 62 can be applied to the skin surface 61 prior to or during delivery of the beam of radiation 64. In some embodiments, the cooling plate 62 can have at least one open region, corresponding to the region 63 of skin not in contact with the cooling plate 62.
The cooling plate 62 can cool different regions of the target region to different extents thus modulating a spatial profile of temperature in the skin 60. For example, skin underlying the region 63 not in contact with the cooling plate 62 can be cooled to a first temperature, and skin underlying the cooling plate 62 can be cooled to a second temperature. The first temperature is greater than the second temperature.
In some embodiments, the cooling plate 62 can be continuous (e.g., not have open regions), but have regions of varying thickness. Thicker regions of the cooling plate can extract more heat from the skin than thinner regions, thus a deeper zone of thermal injury can be formed under the thinner regions.
In FIG. 7A skin region 66 represents a deeper zone of thermal injury. Skin region 68 represents a shallower zone of thermal injury, e.g., where the skin 60 is substantially undamaged.
FIG. 7B shows another exemplary treatment of skin using cooling. A cross-section of a treatment region of skin 70 is treated with a cryogen spray 71 and a beam 72 of radiation. At least a region of the skin surface 73 is in contact with a laser-transparent spray screen 74, which can be applied to the skin surface 73 prior to delivery of the cryogen spray 71. The cryogen spray 71 can be applied prior to or during delivery of the beam 72 of radiation to cool different regions of the target region to different extents.
The screen 74 can modulate a spatial profile of temperature in skin by preventing the cryogen spray 71 from reaching at least a region of the surface 73. In certain embodiments, the screen 74 is not used and the cryogen spray 71 is applied to the skin surface 73 in pools of varying depth. A deeper pool can extract more heat from the skin surface 73, thus forming a region of shallow injury when radiation is delivered.
In FIG. 7B the beam 72 of radiation is delivered to the surface 73 of skin with at least one underlying region 76 of skin of first temperature and at least one underlying region 77 of skin of second temperature. The first temperature is greater than the second temperature. Delivery of the beam 72 of radiation can increase the temperature in the target region. In a region 76 of skin of first temperature, delivery of the beam 72 of radiation can increase the temperature above a critical temperature, forming a first sub-zone 75 of thermal injury. In a region 77 of skin of second temperature, delivery of the beam of radiation can increase the temperature to a second temperature below the first temperature. In some embodiments, the region 77 of skin of second temperature can remain substantially undamaged. In some embodiments, the region 77 of skin of second temperature can form a second sub-zone 78 of thermal injury.
FIG. 7C shows yet another exemplary treatment of skin using cooling, specifically a skin surface 69 with at least one first 79 region and at least one second 89 region. The at least one first 79 region and at least one second 89 region can form a regular or irregular array. In one treatment, the target region can be cooled to produce at least one first 79 region at a first temperature and at least one second 89 region at a second temperature, the first temperature being greater than the second temperature. The at least one first 79 region can correspond to the at least one first sub-zone, and the at least one second 89 region corresponding to the at least one second sub-zone. In another example, the method can include cooling the target region of skin to produce at least one first 79 region cooled to a first depth and at least one second 89 region cooled to a second depth, the first depth being less than the second depth. The at least one first 79 region can correspond to the at least one first sub-zone, and the at least one second 89 region corresponding to the at least one second sub-zone. In general, the depth and/or temperature within the target region can be controlled by the duration and/or temperature of the cooling. For example, a greater duration can cool to a greater depth and a lower temperature can cool to a lower temperature.
Sub-zones of thermal damage can form different geometries. In various embodiments, sub-zone geometries can include cylinders, cones, cuboids, spheroids, ellipsoids, and ovoids. Any of these sub-zone geometries can be overlaid with, or combined with, a substantially continuous surface thermal injury.
FIG. 8A shows an exemplary embodiment of a surface 80 of a treated region of skin with a pattern of varying depths of thermal injury. A regular two-dimensional array of a plurality of sub-zones of a first depth 82 of thermal injury are adjacent to a plurality of sub-zone of a second depth 84 of thermal injury.
In another embodiment, a plurality of sub-zones of a first depth of thermal injury adjacent to a plurality of sub-zones of a second depth of thermal injury can form a one-dimensional array (e.g., a curvilinear pattern). Such a pattern can, for example, trace the contour of a wrinkle, vein, scar, or skin defect. In certain embodiments, methods can include varying a pattern over different parts of the skin to achieve different desired effects (e.g., to produce a pattern of surface injury in an area with surface wrinkles, while producing a pattern of sub-surface injury in an area for skin tightening with less surface injury).
FIG. 8B shows an exemplary embodiment of a surface 86 of a treated region of skin with a pattern of varying depths of thermal injury. An irregular array of a plurality of sub-zones of a first depth 87 of thermal injury are adjacent to a plurality of sub-zone of a second depth 88 of thermal injury.
FIG. 9 shows a ray trace 90 of modulated electromagnetic radiation. The electromagnetic radiation is represented by a plurality of rays 91, which are emitted from a fiber face 93. The rays 91 are imaged by two lenses 95 and then spatially modulated by a micro lens 97 array before delivery to the skin 99 surface. A first region 92 of the skin surface, upon which more rays 91 are incident, can correspond to a first sub-zone of a first depth of thermal injury. A second region 94 of the skin surface, upon which fewer rays 91 are incident, can correspond to a second sub-zone of a second depth of thermal injury.
FIG. 10 shows a contour plot 100 of energy density on skin created by modulated electromagnetic radiation. A position of high 101 energy density can correspond to a first sub-zone of a first depth of thermal injury and a position of low 102 energy density can correspond to a second sub-zone of a second depth of thermal injury. The legend 103 of the contour plot 100 shows the energy density in units of W/mm2. The contour plot 100 represents an area of about 7 mm by about 7 mm.
FIG. 11 shows a plot 110 of intensity variation across skin created by modulated electromagnetic radiation. The y-axis shows the intensity of energy in arbitrary units (a.u.) and the x-axis shows the position in microns. A position of high 111 energy density can correspond to a first sub-zone of a first depth of thermal injury and a position of low 112 energy density can correspond to a second sub-zone of a second depth of thermal injury.
While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

## Claims

1. A method for treating skin, the method comprising delivering a beam of radiation to a target region of the skin to cause a zone of thermal injury including a lateral pattern of varying depths of thermal injury distributed along the target region, the lateral pattern including at least one first sub-zone of a first depth of thermal injury laterally adjacent to at least one second sub-zone of a second depth of thermal injury, wherein (i) the first depth is greater than the second depth, (ii) the at least one first sub-zone of the first depth and the at least one second sub-zone of the second depth extend from a surface of the target region of the skin to form a substantially continuous surface thermal injury, and (iii) the at least one first sub-zone of the first depth and the at least one second sub-zone of the second depth are substantially heated to at least a critical temperature to cause the thermal injury.

2. The method of claim 1 wherein the lateral pattern has a substantially sinusoidal cross sectional injury profile.

3. The method of claim 1 further comprising delivering the beam of radiation to the target region to form a one-dimensional lateral pattern of varying depths of thermal injury.

4. The method of claim 1 further comprising delivering the beam of radiation to the target region to form a two-dimensional lateral pattern of varying depths of thermal injury.

5. The method of claim 1 wherein at least one of the first depth and the second depth are between about 2 mm and about 0.02 mm.

6. The method of claim 1 further comprising heating the at least one first sub-zone and the at least one second sub-zone to substantially the same temperature.

7. The method of claim 1 wherein the first depth is about 1.5 mm and the second depth is about 0.05 mm.

8. The method of claim 1 wherein the critical temperature is below about 100° C., 95° C., 90° C., 85° C., 80° C., 75° C., 70° C., 65° C., 60° C., 55° C., or 50° C.

9. The method of claim 1 wherein the thermal injury includes at least one of ablation, coagulation, necrosis, and acute thermal injury of skin.

10. The method of claim 1 further comprising cooling the surface of the skin, to control the surface thermal injury.

11. The method of claim 1 further comprising cooling the surface of the skin, to prevent unwanted surface thermal injury.

12. The method of claim 1 further comprising delivering a beam of radiation having a first wavelength to the at least one first sub-zone to cause the first depth of thermal injury and a beam of radiation having a second wavelength to the at least one second sub-zone to cause the second depth of thermal injury.

13. The method of claim 1 further comprising delivering a beam of radiation having a first fluence to the at least one first sub-zone to cause the first depth of thermal injury and a beam of radiation having a second fluence to the at least one second sub-zone to cause the second depth of thermal injury.

14. The method of claim 1 further comprising delivering a beam of radiation having a first pulse duration to the at least one first sub-zone to cause the first depth of thermal injury and a beam of radiation having a pulse duration to the at least one second sub-zone to cause the second depth of thermal injury.

15. The method of claim 1 further comprising at least two first sub zones of the first depth are separated by a center to center distance of about 0.05 mm to about 20 mm.

16. The method of claim 1 wherein the at least one first sub-zone of the first depth has an aspect ratio of diameter:depth up to about 0.1:10.

17. The method of claim 1 wherein the at least one second sub-zone of the second depth has an aspect ratio of diameter:depth up to about 0.1:10.