U.S. patent application number 10/160579 was filed with the patent office on 2003-04-03 for thermal quenching of tissue.
Invention is credited to Baumgardner, Jonathan M., Koop, Dale E., Weiss, Robert A..
Application Number | 20030065313 10/160579 |
Document ID | / |
Family ID | 23433781 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030065313 |
Kind Code |
A1 |
Koop, Dale E. ; et
al. |
April 3, 2003 |
Thermal quenching of tissue
Abstract
The present invention provides a system for achieving erythema
and/or mild edema in an upper layer of skin, without causing
blisters, and without the risk of high fluence levels or critical
need for cooling.
Inventors: |
Koop, Dale E.; (Woodside,
CA) ; Baumgardner, Jonathan M.; (Auburn, CA) ;
Weiss, Robert A.; (Hunt Valley, MD) |
Correspondence
Address: |
Rutan & Tucker LLP
Suite 1400
611 Anton Blvd.
Costa Mesa
CA
92626
US
|
Family ID: |
23433781 |
Appl. No.: |
10/160579 |
Filed: |
May 31, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10160579 |
May 31, 2002 |
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09364275 |
Jul 29, 1999 |
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6451007 |
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Current U.S.
Class: |
606/9 |
Current CPC
Class: |
A61B 18/203 20130101;
A61B 2018/00011 20130101; A61B 2018/00452 20130101; A61B 2018/00041
20130101; A61B 18/20 20130101 |
Class at
Publication: |
606/9 |
International
Class: |
A61B 018/20 |
Claims
What is claimed is:
1. A device for treatment of skin, comprising: an energy delivery
system that directs energy to a target tissue for a predetermined
time period and at a predetermined fluence such that a peak
temperature reached in the target tissue causes a thermally
mediated response resulting in transient erythema and/or mild
edema, without blistering.
2. The device of claim 1, fuirther comprising cooling means for
cooling a surface of the tissue after exposure to the energy.
3. The system of claim 1, wherein the energy is electromagnetic
energy with a wavelength about 1.3 microns.
4. The system of claim 1, wherein the cooling means delivers
cryogenic fluids to the target tissue or structure together with
tissues adjacent to the target tissue or structure.
5. The system of claim 1, wherein the predetermined fluence on the
skin surface is less than about 30 joules per square centimeter and
the predetermined time period is greater than 10 milliseconds.
6. The system of claim 1, wherein the energy is ultrasound.
7. The system of claim 1, wherein the energy is electromagnetic
radiation.
8. The system of claim 1, wherein the energy is provided by a
laser.
9. The system of claim 1, wherein the energy is provided by at
least one a flashlamp and a filament lamp.
10. The system of claim 1, wherein the energy comprises waves
having a wavelength between a microwave and an ultraviolet wave,
inclusive.
11. The system of claim 1, wherein the cooling means delivers a
short spurt of cryogenic fluid subsequent to delivery of the
energy.
12. The system of claim 1, wherein the energy has a pulse width
between about 1 nanosecond and about 10 seconds.
13. The system of claim 1, wherein erythema and/or mild edema is
achieved without the risk of high fluence levels or critical need
for cooling.
14. The system of claim 11, wherein the cooling means commences
delivery of the cryogenic fluid after the peak temperature is
reached in the target tissue.
15. The system of claim 11, wherein the cooling means provides
cooling beginning after the heating of target tissue to treatment
temperature.
16. A method for treatment of skin, comprising: selecting a source
of energy in which attenuation of the energy as it passes through
the skin is a function of depth; heating the skin with the energy
source for a predetermined time period and with a predetermined
fluence such that the energy causes thermal mediated injury in skin
below the epidermis resulting in transient erythema but does not
blister the epidermis.
17. The method of claim 16, using light energy having a wavelength
at about 1.3 microns.
18. The method of claim 16, wherein the treatment is repeated
serially with more than one day between any successive
treatments.
19. The method of claim 16, using light energy having a wavelength
between 1100 nm and 270 nm.
20. The method of claim 16, in which the selective thermally
mediated treatment of the target tissue or structures is for the
treatment of vascular tissue.
21. The method of claim 16, in which the selective thermally
mediated treatment of the target tissue or structures is for the
treatment of tissue containing collagen.
22. The method of claim 16, in which the selective thermally
mediated treatment of the target tissue or structures is for the
treatment of cartilage.
23. The method of claim 16, in which the selective thermally
mediated treatment of the target tissue or structures is for the
treatment of tissue containing pigment.
24. The method of claim 16, in which the selective thermally
mediated treatment of the target tissue or structures is for the
hair removal treatment.
25. A method for treatment of acne scars in skin, comprising:
heating the target skin portion with a source of energy which is
uniformly attenuated with depth in skin for a predetermined time
period and predetermined fluence such that the exposure time of the
epidermis and the peak temperature reached by the epidermis are
such that the epidermnis does not blister; and causing thermally
mediated injury in skin below the epidermis resulting in transient
erythema to initiate a healing response which improves the
appearance of the acne scars.
26. A method for treatment of photo damaged skin, comprising:
heating the skin with a source of energy which is uniformly
attenuated with depth in skin for a predetermined time period and
predetermined fluence such that the exposure time of the epidermis
and the peak temperature reached by the epidermis are such that the
epidermis does not blister; and causing thermal mediated injury in
skin below the epidermis resulting in transient erythema to
initiate a healing response which improves the appearance of the
photo damaged skin.
27. A method for treatment of wrinkled skin, comprising: heating
the skin with a source of energy which is uniformly attenuated with
depth in skin for a predetermined time period and predetermined
fluence such that the exposure time of the epidermis and the peak
temperature reached by the epidermis are such that the epidermis
does not blister; and causing thermal mediated injury in skin below
the epidermis resulting in transient erythema to initiate a healing
response which improves the appearance of the wrinkled skin.
28. A method of thermal quenching of surface tissue during
selective thermally mediated treatment of target tissue or
structures, the method comprising the steps of: delivering energy
to the target tissue or structures to increase the temperature of
the target tissue or structures to a predetermined treatment
temperature, thereby, resulting in transient erythema; and cooling
the surface tissue or other tissue adjacent the target tissue or
structures to prevent excessive heating of the surface tissue or
other tissue adjacent the target tissue.
29. The method of claim 28 in which the step of cooling is
initiated after elevation of the target tissue or structures to
treatment temperature.
30. The method of claim 28 in which the step of cooling is
initiated prior to elevation of the target tissue or structures to
treatment temperature.
31. The method of claim 28 in which the step of cooling is
initiated concurrently with elevation of the target tissue or
structures to treatment temperature.
32. The method of claim 28 in which the step of cooling is
initiated subsequent to an increase in the temperature of the
surface tissue or other tissue adjacent the target tissue or
structures.
33. The method of claim 28 in which the pulsed electromagnetic
energy is delivered at a rate of between about 50 Joules per square
centimeter and about 150 Joules per square centimeter.
34. The method of claim 28 in which the pulsed electromagnetic
energy has a pulse width of between about 5 milliseconds and about
200 milliseconds.
35. The method of claim 28 in which the step of cooling includes
delivery of refrigerant to the surface tissue for a period of
between about 10 milliseconds and about 30 milliseconds.
36. The method of claim 28 in which the step of cooling the surface
tissue or other tissue adjacent the target tissue or structures is
performned using passive cooling means.
37. The method of claim 28 in which the step of cooling the surface
tissue or other tissue adjacent the target tissue or structures is
performed using dynamic cooling means.
38. The method of claim 28 wherein the target tissue or structures
is veins and in which the treatment is vascular treatment.
39. The method of claim 28 wherein the target tissue or structures
is hair follicles and wherein the treatment is hair removal.
40. The method of claim 37 wherein the dynamic cooling means cools
the surface tissue or other tissue adjacent the target tissue or
structures by delivering a liquid refnigerant to the surface tissue
or other adjacent the target tissue or structures.
41. The method of claim 28 wherein the target tissue or structures
is tissue containing pigmentation and in which the treatment is
modification of the pigmentation.
42. The method of claim 37 in which the dynamic cooling means cools
the surface tissue or other tissue adjacent the target tissue or
structures by delivering a liquid refrigerant to the surface tissue
or other tissue adjacent the target tissue or structures.
43. The method of claim 42 in which the liquid refrigerant is
delivered to the surface tissue or other tissue adjacent the target
tissue or structures for a period of time between about 10
milliseconds and about 30 milliseconds.
Description
[0001] This application claims the benefit of U.S. patent
application Ser. No. 09/364,275 filed Jul. 29, 1999 incorporated
herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention is related to the delivery of laser or other
source of thermal energy to biological or other tissue for
treatment therein.
BACKGROUND OF THE INVENTION
[0003] It is sometimes desirable to cause heat affected changes in
a selected structure in tissue, such as a vein or hair follicle
without causing heat affected changes in tissue adjacent to the
selected structure. Selective photothermalysis is a method of
irradiating with a laser or pulsed light source that is
preferentially absorbed by a pre-selected target. The amount of
energy or fluence delivered to the target is chosen such that the
temperature rise in the targeted region results in an intended
thermal treatment of the target.
[0004] Heating of the epidermis may occur during treatment of the
target and several methods have been described for cooling the
surface of skin during and prior to treatment to minimize the risk
of thermal injury to tissue adjacent to the targeted veins. One
early method included pre-cooling with ice for several minute prior
to treatment. U.S. Pat. No. 5,282,797 issued Feb. 1, 1994 to Chess
describes a method of circulating cooling fluid over a transparent
plate in contact with the treatment area to cool the epidermis
during treatment. U.S. Pat. No. 5,344,418 issued Sep. 6, 1994 to
Ghaffari describes a method whereby a coolant is used for a
predetermined time interval in coordination with the delivery of
laser energy to optimize the cooling of the epidermis and minimize
cooling of the targeted vessel. U.S. Pat. No. 5,814,040 issued Sep.
29, 1998 to Nelson et al. describes a cooling method whereby a
cryogenic spurt is applied for a predetermined short time directly
onto the skin in the target region. The time period for cooling is
confined only to the epidermis while leaving the temperature of
deeper port wine stains substantially unchanged. Many of the
cooling methods may limit the amount of significant thermal damage
to the epidermis during treatment.
[0005] It may be desirable to shrink collagen in order to reduce
the appearance of undesirable conditions of the skin such as acne
scars and wrinkles. The following U.S. patents to Sand teach
controlled thermal shrinkage of collagen fibers in the cornea using
light at wavelengths between 1.8 and 2.55 microns: U.S. Pat. No.
4,976,709, Class No. 606/5, issued Dec. 11, 1990; U.S. Pat. No.
5,137,530; U.S. Pat. No. 5,304,169; U.S. Pat. No. 5,374,265; and
U.S. Pat. 5,484,432.
[0006] U.S. Pat. No. 5,810,801, class no. 606/9 issued Sep. 22,
1998 to Anderson et al. teaches a method and apparatus for treating
wrinkles in skin by targeting tissue at a level between 100 microns
and 1.2 millimeters below the surface, to thermally injure collagen
without causing erythema, by using light at wavelengths between 1.3
and 1.8 microns. Because of the high scattering and absorption
coefficients, precooling is utilized to prevent excess heat build
up in the epidermis when targeting the region of 100 microns to 1.2
mm below the surface. Specific laser and cooling parameters are
selected so as to avoid erythema and achieve improvement in
wrinkles as the long term result of a treatment.
SUMMARY OF THE INVENTION
[0007] The present invention provides a system for achieving
erythema and/or mild edema in an upper layer of skin, without
causing blisters, and without the risk of high fluence levels or
critical need for cooling.
[0008] The invention uses a source of thermal energy, which may be
infrared in the wavelength range of 1100 nm to 2.9 nm, to cause
thermally mediated effects in skin. The systems and methods are
directed toward heating the skin with a source of energy which is
uniformly attenuated with depth in skin for a predetermined time
period and predetermined fluence so that the exposure time of the
epidermis and the peak temperature reached by the epidermis are
such that the epidermis does not blister but the thermally mediated
injury in the skin below the epidermis causes a transient erythema
to initiate a healing response. By achieving erythema and/or mild
edema in an upper layer of skin, the system precludes the risk of
high fluence levels or critical need for cooling. The dosage and
time period of application are adjusted to prevent excess
accumulation of heat in the epidermis, which would cause tissue
damage. Thermal quenching is used to remove latent heat from the
treatment site to prevent thermal damage to the tissue. Collagen
remodeling is induced by distributing the laser energy over a
series of more benign treatments spaced weeks apart.
[0009] It is therefore an advantage and an object of the present
invention to provide an improved system for selectively cooling
tissue during photothermal treatment.
[0010] It is a further advantage of the present invention to
provide such a system which uses dynamic cooling to quench heat
build up during and after photothermal treatment.
[0011] It is a further advantage of the present invention to
provide such a system which selectively heats a subsurface
structure in tissue and subsequently quenches heat build up in
non-target tissue.
[0012] It is a further advantage of the present invention to reduce
the level of pulsed energy needed for treatment by minimizing
precooling of the tissue.
[0013] It is a further advantage of the present invention to
provide such a system which selectively heats a subsurface
structure in skin to cause thermal affected changes in said
subsurface structure without significant epithelial damage due to
subsequent heating from the target region.
[0014] It is a further advantage of the present invention to
provide such a system which selectively heats vascular lesions in
tissue and quenches subsequent heat build up in epithelial
tissue.
[0015] It is a further advantage of the present invention to
provide such a system which selectively heats hair follicles in
tissue and quenches subsequent heat build up in epithelial
tissue.
[0016] It is a further advantage of the present invention to
require less cooling of the target area than is typically required,
resulting in more efficient heating of the selected target and less
thermal damage to surrounding tissue.
[0017] In a preferred embodiment, the system for generating light
energy is a laser system such as but not limited to a solid-state
laser, including but not limited to a neodymium-doped
yttrium-aluminum-garnet (Nd:YAG) laser.
[0018] In additional preferred embodiments, the system for
generating light energy is a gas discharge flashlamp or an
incandescent-type filament lamp.
[0019] The energy from the generating system may be directed into
or coupled to a delivery device such as but not limited to a fiber
optic or articulated arm for transmitting the light energy to the
target tissue.
[0020] The light energy may be focused on tissue with a focusing
lens or system of lenses.
[0021] The surface of the tissue may be cooled with a cooling
device including but not limited to an irrigating solution, a spray
or flow of refrigerant or other cryogenic material, or a
transparent window cooled by other active means, or other dynamic
or passive cooling means.
[0022] The tissue may be preheated with a heating device such as,
but not limited to an intense light source, a flashlamp, a filament
lamp, laser diode, other laser source, electrical current, or other
electromagnetic or mechanical energy which penetrates into layers
of tissue beneath the surface. The preheating can occur
simultaneously or just prior to the surface cooling of tissue from
the cooling device such that the tissue preheating results in a
temperature rise in underlying layers of tissue, and a temperature
profile results. The pulsed application of energy from the energy
delivery device results in a temperature profile that
preferentially heats a selected structure or target in tissue, and
the post cooling prevents thermal damage to tissue adjacent to that
structure. This also reduces the overall pulse energy level needed
of the pulsed treatment device due to the fact that a desirable
temperature profile exists prior to delivery of the pulsed
treatment energy.
[0023] The tissue may be post cooled with a dynamic cooling device
such as, but not limited to a pulse, spray or other flow of
refrigerant such that the post cooling occurs after a temperature
rise in an underlying targeted structure and a temperature profile
results such that the pulsed application of energy from the energy
delivery device results in a temperature profile that preferential
heats a selected structure in tissue without subsequent undesirable
heating to tissue adjacent to that structure from thermal
conduction.
[0024] Numerous other advantages and features of the present
invention will become readily apparent from the following detailed
description of the invention and the embodiments thereof, from the
claims and from the accompanying drawings.
[0025] Various objects, features, aspects and advantages of the
present invention will become more apparent from the following
detailed description of preferred embodiments of the invention,
along with the accompanying drawings in which like numerals
represent like components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a representative schematic block diagram of a
preferred embodiment of a system for thermal quenching of tissue of
the present invention.
[0027] FIG. 2 is a more detailed representative schematic block
diagram of a preferred embodiment of the delivery device shown in
FIG. 1 of the present invention.
[0028] FIG. 3 is a representative sample data plot of the
temperature of surface tissue and target tissue achieved by methods
and systems of the prior art having precooling.
[0029] FIG. 4 is a representative sample data plot of the
temperature of surface tissue and target tissue achieved by a
preferred embodiment of the method and system of the present
invention such as shown in FIGS. 1 and 2 having precooling.
[0030] FIG. 5 is a representative sample data plot of the
temperature of surface tissue and target tissue achieved by a
preferred embodiment of the method and system of the present
invention such as shown in FIGS. 1 and 2 without precooling.
DETAILED DESCRIPTION
[0031] The description that follows is presented to enable one
skilled in the art to make and use the present invention, and is
provided in the context of a particular application and its
requirements. Various modifications to the disclosed embodiments
will be apparent to those skilled in the art, and the general
principals discussed below may be applied to other embodiments and
applications without departing from the scope and spirit of the
invention. Therefore, the invention is not intended to be limited
to the embodiments disclosed, but the invention is to be given the
largest possible scope which is consistent with the principals and
features described herein.
[0032] FIG. 1 is a representative schematic block diagram of a
preferred embodiment of a system 100 for thermal quenching of
tissue of the present invention. Operation of energy source 102 to
produce energy for delivery by the system 100 is controlled
according to control signal 104 from control system 106. Control
system 106 includes a physician interface 108 for operating the
system. Said interface 108 optionally includes a footswitch for
energy delivery, display and interactive and/or menu driven
operation utilizing operator input, prompts, etc. Additional energy
delivery control interface means shall be known to those skilled in
the art.
[0033] In a preferred embodiment, energy source 102 is a neodymium
doped yttrium-aluminum-garnet (Nd:YAG) laser, energized by a
flash-lamp or laser diode. Energy source 102 is controlled by
control system 106 which comprises the software and electronics to
monitor and control the laser system, and interface 108. The beam
of laser energy 110 from the energy source 102 is directed into a
delivery device 112 which may be an optical fiber, a fiber bundle
or articulated arm, etc.
[0034] Modern instruments to provide dynamic cooling of the surface
layers of tissue or other materials are well suited to these
applications. A coolant spray can be provided through a handpiece
or it could be provided with another separate device. Finally, a
connection to a computer and the control system 106 of the energy
source 102 will allow the system 100 to utilize electronic or other
thermal sensing means and obtain feedback control signals for the
handpiece. An optimum cooling strategy might be one that uses a
post-irradiation cooling spurt that provides cooling or dissipation
of the epidermal heat generated by absorption of energy in the
non-isotropic skin, optionally containing various pigmentation
levels. An appropriate cryogen spray would be liquid nitrogen or
tetrafluoroethane, C.sub.2H.sub.2F.sub.4, an environmentally
compatible, non-toxic, non-flammable freon substitute. In clinical
application the distance between the aperture of the spray valve
and the skin surface should be maintained at about 20
millimeters.
[0035] In a preferred embodiment of the present invention, upon
delivery of laser energy onto the surface and therethrough, the
target tissue will be raised to the optimal treatment temperature
and generally not any higher, in an adequately rapid process, with
the surface temperature of the skin remaining at a temperature
below the threshold for damage temperature. It will be understood
that the threshold for damage temperature is the temperature below
which the skin or other tissue can be elevated without causing
temporary or permanent thermal damage, and above which the tissue
may undergo either transient or long term thermally induced
physiological change. As described, the wavelength of irradiated
light energy is selectively absorbed by hemoglobin or hair
follicles, or other tissue with pigmentation or chromophores of a
certain type, but passes through the surface and overlying/adjacent
tissue to the target tissue with minimal absorption. However, once
the target tissue or structure becomes elevated in temperature,
surrounding and adjacent tissue will become hot due to conduction
of heat from the target tissue or structures. Post-irradiation
cooling can then be initiated, and tissue other than the target
tissue is prevented from increasing in temperature beyond the
threshold of damage or adverse effect. Adverse effects of elevated
tissue surface temperature include discomfort or pain, thermal
denaturing of proteins and necrosis of individual cells at the
surface only, or deeper tissue ablation potentially leading to
hyperplasia, scarring, or hyperpigmentation, a proliferation of
cells formed in response to the induced trauma. In a preferred
embodiment of the method of the present invention, heating and
subsequent post-cooling are performed in a predetermined timing
sequence, optionally with the use of timer circuits and/or other
controller means.
[0036] Thus, it will be obvious to those skilled in the art that a
passive heat sink includes glass or sapphire tip probes, and other
types of devices to lay on the surface of the skin. It will also be
obvious that a dynamic type of heat sink will refer to those
actively cooled by flowing gas or liquid, jets or spurts of coolant
such as freon, and other active types of heat exchangers suitable
for surface cooling while irradiating sub-surface portions of
collagen tissue. U.S. Pat. No. 5,820,626 issued Oct. 13, 1998 to
Baumgardner and U.S. application Ser. No. 08/938,923 filed Sep. 26,
1997 by Baumgardner et al., both incorporated herein by reference
in their entireties, teach a cooling laser handpiece with
refillable coolant reservoir, and can be utilized as a handpiece
for delivery device 112 and heat sink 114.
[0037] FIG. 2 is a more detailed representative schematic block
diagram of a preferred embodiment of the delivery device 112 shown
in FIG. 1 of the present invention. The energy from the energy
source 102 is directed into delivery device 112 via a delivery
channel 130 which may be a fiber optic, articulated arm, or an
electrical cable etc. At the distal end of delivery device 112 is a
energy directing means 131 for directing the pulsed energy toward
the surface tissue 116 and overlaying tissue 118 overlaying the
target tissue or structure 120. A nozzle 134 is useful for
directing coolant from reservoir 135 to the tissue 118, and a valve
136 for controlling the coolant interval. A temperature sensor 137
may be used to monitor the temperature rise of the target tissue
118. Control system 106 monitors the temperature signal from sensor
137 and controls valve 136 and energy source 102. Reservoir 135 may
be in the delivery device 112 or elsewhere, and contains a
refrigerant which may be applied to surface tissue 120 by spraying
said refrigerant from cooling nozzle 124 in conjunction with
delivery of pulsed treatment energy to the patient.
[0038] FIG. 3 is a representative sample data plot of the
temperature of surface tissue 116 and target tissue 120 achieved by
methods and systems of the prior art having precooling. The
waveforms are representative of oscilloscope-type traces which
reproduce signals generated by one or more thermal detectors. In
general, with precooling the coolant is applied just prior to the
delivery to the pulsed energy. Waveform 240 indicates the periods
of time and associated temperatures of the target tissue and the
surface tissue during the processes of the prior art. Initially, as
indicated by time period 241, the temperature of the surface tissue
116 as well as the target tissue 120, as shown in FIGS. 1 and 2,
are at T.sub.s and T.sub.t respectively. It will be understood that
typically the skin surface is at a temperature somewhat below
actual body temperature. Typically, this range might be between
about 28 and about 34 degrees Celsius. Furthermore, a target vein,
hair follicle or other structure can be assumed to be at about or
somewhat just below 37 degrees Celsius, or actual body temperature.
Once the refrigerant is applied to surface tissue 116 by opening
valve 136 during a subsequent time period 244, the temperature
T.sub.s drops to a level determined by the length of time 244 for
which the surface tissue 120 is exposed to the coolant. By way of
example, for time periods of about 30 milliseconds, T.sub.s may
drop from a typical temperature of about 32 degrees Celsius to just
above 0 degrees Celsius. However, as the target tissues 120 is
deeper than the surface 116, initially T.sub.t is not significantly
affected and may drop by only a few degrees. A short delay 245
following delivery of refrigerant may be used, and is typically
between 0 and 100 milliseconds. This allows time for cooling of at
least a layer of epidermis to a depth of 50 to 250 micrometers.
Following time periods 244 and optional period 245, the pulsed
energy is applied over predetermined or other time period 246. The
time period 246 depends on the size of the target and the fluence
delivered, as indicated by principles of selective
photothermalysis. For example, in experiments with an Nd:YAG laser
operating at 1064 nanometers, one application of a 10 millisecond
period and a fluence of 50 joules per square centimeter was
sufficient to treat small blood vessels, and fluences of up to 150
joules per square centimeter and time periods of up to 200
milliseconds are useful for treating larger vessels of 1 to 3
millimeters in cross-section. During period 246 T.sub.t increases
to a therapeutically effective value, whereas T.sub.s remains below
the threshold indicated as 250 for patient discomfort or tissue
damage.
[0039] Subsequent to treatment, the target tissue 116 cools by
conduction of thermal energy to adjacent overlaying tissue 118
including the surface tissue 116, with a resultant temperature rise
in the target tissue 120 dependant on the size and depth of the
target tissue 120. As T.sub.t equalizes with surrounding tissue,
the T.sub.s may rise above the level of patient discomfort and even
cause damage to surface tissue 116.
[0040] FIG. 4 is a representative sample data plot of the
temperature of surface tissue 116 and target tissue 120 achieved by
a preferred embodiment of the method and system of the present
invention such as shown in FIGS. 1 and 2 having precooling. The
method of the present invention includes the process of precooling
surface tissue 116 and target tissue 120 slightly, followed by a
short time period 245 and subsequent delivery of thermal energy to
the body during time period 246 such as shown in FIG. 3. In the
present invention, however, refrigerant is also applied subsequent
to the energy pulse by opening valve 136 as desired or as
indicated, thus keeping T.sub.s below the threshold for damage
temperature 250. FIG. 4 shows a pulse of coolant applied during
time period 248 which is subsequent to the application of pulsed
energy during period 246. This results in thermal quenching of the
surface tissue 116. The thermal quenching pulse or other flow of
refrigerant or other means for cooling is applied after the
beginning of treatment period 246 and may be initiated before or
after the end of time period 246. It is important that the peak or
highest temperature of the surface tissue 116 never rise above the
threshold for damage temperature 250. The time point at which the
peak temperature in the surface tissue 116 is achieved is dependant
on the size and depth of the target 120.
[0041] In one experimental example, cryogenic fluid was applied to
the surface tissue 116 within 10 milliseconds of the end of the
energy pulse of time period 246 and for a duration 248 of 20
milliseconds. For vascular treatment with an Nd:YAG laser with
pulse widths of 5 milliseconds to 200 milliseconds, the period of
thermal quenching 248 preferably 10 milliseconds to 30 milliseconds
immediately after the treatment energy. This sequence significantly
reduced patient discomfort compared to treatment with out thermal
quenching. The effect of thermal quenching is not dependant on
pre-cooling and may be used as the only method of cooling in many
cases.
[0042] FIG. 5 is a representative sample data plot of the
temperature of surface tissue and target tissue achieved by a
preferred embodiment of the method and system of the present
invention such as shown in FIGS. 1 and 2 without precooling. As in
the method shown in FIG. 4, the thermal quenching pulse or other
flow of refrigerant or other means for cooling over time period 248
is applied after the beginning of treatment period 246 and may be
initiated before or after the end of time period 246. It is
important that the peak or highest temperature of the surface
tissue 116 never rise above the threshold for damage temperature
250.
[0043] The present invention requires less cooling of the target
tissue, structure or area during the treatment phase than is
typically required, resulting in more efficient heating of the
selected target and less thermal damage to surrounding tissue.
[0044] It will be understood that while numerous preferred
embodiments of the present invention are presented herein, numerous
of the individual elements and finctional aspects of the
embodiments are similar. Therefore, it will be understood that
structural elements of the numerous apparatus disclosed herein
having similar or identical function may have like reference
numerals associated therewith.
[0045] In a preferred embodiment of the present invention,
re-heating of tissue, especially target or subsurface tissue can be
useful. U.S. application Ser. No. 09/185,490 filed Nov. 3, 1998 by
Koop et al. entitled Subsurface Heating of Tissue teaches methods
and systems for performing subsurface heating of material and
tissue, and is incorporated herein by reference in its entirety.
With these methods and apparatus, target or subsurface tissue is
preheated to an elevated, non-destructive temperature which is
somewhat below that of treatment. Thereafter, the temperature of
the target tissue or structures is raised to treatment temperature.
Once this second increase in temperature is achieved, the target
tissue or structures will conduct heat into the body, especially to
adjacent tissue and surface tissue, at which time the post-cooling
of the present invention can be initiated so as to prevent damage
to adjacent tissue or dermis or other surface tissue.
[0046] In one embodiment the invention utilizes an Nd:YAG laser at
1320 nm wavelength, (such as the CoolTouch 130, CoolTouch Corp.,
Auburn Calif.) as the source of treatment energy. At 1320 nm the
absorption depth in tissue is such that energy is deposited
throughout the upper dermis, with most absorption in the epidermis
and upper dermis, a region including the top 200 to 400 microns of
tissue. The energy falls off approximately exponentially with the
highest level of absorbed energy in the epidermis. Optical heating
of skin follows exposure to the laser energy. If the time of
exposure to the laser is very short compared to the time required
for heat to diffuse out of the area exposed, the thermal relaxation
time, than the temperature rise at any depth in the exposed tissue
will be proportional to the energy absorbed at that depth. However,
if the pulse width is comparable or longer to the thermal
relaxation time of the exposed tissue than profile of temperature
rise will not be as steep. Conduction of thermal energy occurs at a
rate proportional to the temperature gradient in the exposed
tissue. Lengthening the exposure time will reduce the maximum
temperature rise in exposed tissue.
[0047] For instance, at 1.3 microns the laser pulse width may be
set to 30 milliseconds and fluence to less than 30 joules per
square centimeter. This prevents excessive heat build up in the
epidermis, which is approximately the top 100 microns in skin. The
papillary dermis can then be heated to a therapeutic level without
damage to the epidermis. The epidermis will reach a temperature
higher than but close to that of the papillary dermis.
[0048] The epidermis is more resilient in handling extremes of
temperature than most other tissue in the human body. It is
therefore possible to treat the papillary dermis in conjunction
with the epidermis without scarring or blistering, by treating both
layers with laser energy and allowing a long enough exposure time
such that the thermal gradient between the epidermis and underlying
layers remains low. In this way the underlying layers can be
treated without thermal damage to the epidermis.
[0049] It is known that thermal damage in tissue is time dependant
and brief exposures to high temperature levels may be tolerated in
situations where long exposures are lethal or injurious.
Terminating the exposure of the epidermis to elevated temperatures
will decrease the risk of damage to the epidermis. In this
invention thermal quenching is used to terminate the exposure of
the epidermis to elevated temperatures. In this embodiment cryogen
spray cooling is use to reduce the epidermal temperature following
the exposure to laser radiation. The laser heats the epidermis and
lower layers simultaneously because of penetration of the laser
energy into tissue. The cryogen cooling works from the top surface
and heat flows out of the lower layers by conduction over a time
period equivalent to the thermal relaxation time at each depth of
tissue. As a result the epidermis is heated for a shorter time
period than the papillary dermis or other deeper layers.
[0050] In this invention a top layer of tissue can be protected by
limiting the time of exposure to elevated temperatures, and deeper
layers are protected by the attenuation of light energy in tissue
water.
[0051] The depth of protection due to cooling is determined by the
degree of cooling and the time delay after laser exposure. In the
embodiment described here 30 milliseconds of cooling spray is
applied without delay, (within 5 milliseconds), after the
termination of the laser exposure. The cooling may be delayed to
cause longer thermal exposures of the surface. The amount of
cooling is enough to reduce the temperature of the surface to
non-therapeutic levels. Higher cooling levels will terminate heat
build up deeper in tissue.
[0052] A wavelength of 1.3 microns is used in this embodiment to
treat the middle layers of skin. Other wavelengths such as 1.45 or
2.1 microns may by used to treat more superficial layers of skin by
this method. It is important that the wavelength is chosen such
that there is absorption in tissue water such that the energy
attenuation versus depth is fairly uniform over an area of skin.
The range of wavelengths longer than 1100 nm in the infrared have
this property. It is important that the energy source used for this
invention is uniformly attenuated with depth in tissue. Ultrasound,
microwaves, and RF electrical current are examples.
[0053] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which the present invention belongs.
Although any methods and materials similar or equivalent to those
described can be used in the practice or testing of the present
invention, the preferred methods and materials are now described.
All publications and patent documents referenced in the present
invention are incorporated herein by reference.
[0054] While the principles of the invention have been made clear
in illustrative embodiments, there will be immediately obvious to
those skilled in the art many modifications of structure,
arrangement, proportions, the elements, materials, and components
used in the practice of the invention, and otherwise, which are
particularly adapted to specific environments and operative
requirements without departing from those principles. The appended
claims are intended to cover and embrace any and all such
modifications, with the limits only of the true purview, spirit and
scope of the invention.
[0055] The description that follows is presented to enable one
skilled in the art to make and use the present invention, and is
provided in the context of a particular application and its
requirements. Various modifications to the disclosed embodiments
will be apparent to those skilled in the art, and the general
principals discussed below may be applied to other embodiments and
applications without departing from the scope and spirit of the
invention. Therefore, the invention is not intended to be limited
to the embodiments disclosed, but the invention is to be given the
largest possible scope which is consistent with the principals and
features described herein.
[0056] In a preferred embodiment of the present invention,
re-heating of tissue, especially target or subsurface tissue can be
useful. U.S. application Ser. No. 09/185,490 filed Nov. 3, 1998 by
Koop et al. teaches methods and systems for performing subsurface
heating of material and in incorporated herein by reference in its
entirety. In these methods, target or subsurface tissue is
preheated to an elevated, non-destructive temperature which is
somewhat below that of treatment. Thereafter, the temperature of
the target tissue or structures is raised to treatment temperature.
Once this second increase in temperature is achieved, the target
tissue or structures will conduct heat into the body, especially to
adjacent tissue and surface tissue, at which time the post-cooling
of the present invention can be initiated so as to prevent damage
to adjacent tissue or dermis or other surface tissue.
[0057] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which the present invention belongs.
Although any methods and materials similar or equivalent to those
described can be used in the practice or testing of the present
invention, the preferred methods and materials are now described.
All publications and patent documents referenced in the present
invention are incorporated herein by reference.
[0058] While the principles of the invention have been made clear
in illustrative embodiments, there will be immediately obvious to
those skilled in the art many modifications of structure,
arrangement, proportions, the elements, materials, and components
used in the practice of the invention, and otherwise, which are
particularly adapted to specific environments and operative
requirements without departing from those principles. The appended
claims are intended to cover and embrace any and all such
modifications, with the limits only of the true purview, spirit and
scope of the invention.P
[0059] Thus, specific embodiments and applications of thermal
quenching of tissue have been disclosed. It should be apparent,
however, to those skilled in the art that many more modifications
besides those already described are possible without departing from
the inventive concepts herein. The inventive subject matter,
therefore, is not to be restricted except in the spirit of the
appended claims. Moreover, in interpreting both the specification
and the claims, all terms should be interpreted in the broadest
possible manner consistent with the context. In particular, the
terms "comprises" and "comprising" should be interpreted as
referring to elements, components, or steps in a non-exclusive
manner, indicating that the referenced elements, components, or
steps may be present, or utilized, or combined with other elements,
components, or steps that are not expressly referenced.
* * * * *