U.S. patent application number 14/964987 was filed with the patent office on 2016-04-07 for system and method for microablation of tissue.
The applicant listed for this patent is LUMENIS LTD.. Invention is credited to Ray Choye, Vladimir Lemberg.
Application Number | 20160095660 14/964987 |
Document ID | / |
Family ID | 44799291 |
Filed Date | 2016-04-07 |
United States Patent
Application |
20160095660 |
Kind Code |
A1 |
Choye; Ray ; et al. |
April 7, 2016 |
SYSTEM AND METHOD FOR MICROABLATION OF TISSUE
Abstract
The present invention generally relates to the field of laser
treatment of tissue, and particularly, to a system and method for
creating microablated channels in skin. The present invention is
more particularly directed to treating subsurface tissue through
the created channels.
Inventors: |
Choye; Ray; (Belmont,
CA) ; Lemberg; Vladimir; (Santa Clara, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LUMENIS LTD. |
Yokneam Ilit |
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IL |
|
|
Family ID: |
44799291 |
Appl. No.: |
14/964987 |
Filed: |
December 10, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14735172 |
Jun 10, 2015 |
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14964987 |
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12799064 |
Apr 15, 2010 |
9078680 |
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14735172 |
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11730017 |
Mar 29, 2007 |
8496696 |
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12799064 |
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60791194 |
Apr 12, 2006 |
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60850628 |
Oct 11, 2006 |
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Current U.S.
Class: |
606/9 |
Current CPC
Class: |
A61B 18/203 20130101;
A61B 2018/00577 20130101; A61B 2017/00057 20130101; A61B 2018/00994
20130101; A61B 2018/00458 20130101; A61B 2018/00642 20130101; A61B
2018/00452 20130101 |
International
Class: |
A61B 18/20 20060101
A61B018/20 |
Claims
1. An apparatus for treating human skin tissue including fractional
treatment patterns, comprising: a first application device
configured to direct light energy to the skin tissue of a patient
to cause at least one microchannel to be formed in the skin; a
second transdermal substance delivery device configured to deliver
one or more substances to the skin tissue of the patient and into
the at least one microchannel formed; and a programmed controller
configured to: control application of energy from the first
application device to form the at least one microchannel, and
control delivery of one or more substances to the at least one
microchannel.
2. The apparatus of claim 1, wherein the second application device
includes: a source to store the one or more substances and a
delivery device to deliver the one or more substances.
3. The apparatus of claim 1, wherein the one or more substances
include one or more of: vitamins, drugs, ointments, acids, healing
substances, chemical peeling agents, collagen modification agents,
fillers and stem cells.
4. The apparatus of claim 2, wherein the delivery device comprises
an ultrasonic delivery device.
5. The apparatus of claim 1, wherein the at least one microchannel
includes a plurality of microchannels and wherein the delivery
device delivers the one or more substances to: the bottom of the at
least one microchannel formed, the walls of the at least one
microchannel formed, or both.
6. The apparatus of claim 1, wherein the controller is configured
to select the depth of the at least one microchannel into the human
skin tissue.
7. The apparatus of claim 1, wherein the light energy is laser
light energy.
8. The apparatus of claim 1, wherein the controller is configured
to cause the at least one microchannel to be formed followed by the
controlled delivery of the one or more substances.
9. The apparatus of claim 1, wherein the one or more substances are
fluid substances.
10. The apparatus of claim 1, further comprising a device for
applying a stretch to the human skin tissue, the controller causing
the device to stretch the tissue, one of prior to or after the
controller causes the first application device to form the at least
one channel.
11. The apparatus of claim 1, wherein the first application device
is an ablative laser device.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/735,172, filed Jun. 10, 2015, which is a
continuation of U.S. patent application Ser. No. 12/799,064, filed
Apr. 15, 2010, now U.S. Pat. No. 9,078,680, granted on Jul. 14,
2015, which is a continuation-in-part of U.S. patent application
Ser. No. 11/730,017 filed Mar. 29, 2007, now U.S. Pat. No.
8,496,696, granted on Jul. 30, 2013, which claims priority to U.S.
Ser. No. 60/791,194, filed on Apr. 12, 2006, U.S. Ser. No.
60/850,628, filed on Oct. 11, 2006, and U.S. Ser. No. 60/832,964,
filed on Jul. 25, 2006. These applications are incorporated by
reference in their entireties.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to the field of
laser treatment of tissue, and particularly, to a system and method
for creating microablated channels in skin. The present invention
is more particularly directed to treating subsurface tissue through
the created channels. By doing treating subsurface tissue through
uniquely created channels, skin may be treated with heretofore
unrealized results.
[0004] 2. Description of the Related Art
[0005] Skin is primarily made of an outer layer, or epidermis, that
has a depth of approximately 100/an from the outer surface of the
skin and an inner layer, or dermis, that has depth of approximately
3000 fm from the outer surface of the skin. As used herein, "dermal
tissue" or "skin" refers to both the dermis and epidermis
layers.
[0006] There is ongoing demand for procedures to improve skin
defects. Such improvements include reducing wrinkles, reducing
dyschromia (a variety of abnormalities or irregularities of skin
color resulting from, inter alia, irregular pigment distribution,
dilated blood vessels, etc.) and etc. A wide variety of skin
treating techniques have been introduced in recent years for
attempting to achieve this objective. The skin treating techniques
that have been employed may be generally categorized into two
general types of treatment: ablative laser skin resurfacing ("LSR")
and non-ablative collagen remodeling ("NCR"). LSR generally may
result in fairly extensive thermal damage to either the epidermis
and/or the dermis. NCR, on the other hand, is designed to avoid
thermal damage of the epidermis.
[0007] Nevertheless, LSR is an effective laser treatment for
treating skin. A typical LSR procedure comprises thermally damaging
a region of the epidermis 100 and a corresponding lower region of
the dermis 110 for promoting wound healing. Electromagnetic energy
120 is directed towards a region of skin, thereby ablating the skin
and removing both epidermal tissue and dermal tissue. Combining LSR
with a pulsed laser, for example a CO2 or an Er:YAG laser, is
typically referred to as laser resurfacing or ablative resurfacing.
This is considered to be an effective treatment protocol photo aged
or chronically aged skin, scars, superficial pigmented lesions,
stretch marks, and/or superficial skin lesions. Major drawbacks
include, however, edema, oozing, and burning discomfort up to the
first fourteen (14) days after treatment. Such drawbacks are
unacceptable for many patients. A further problem with LSR
procedures is that they are relatively painful. Therefore, they
generally require an application of a significant amount of
analgesia. While LSR of relatively small areas can be performed
under local anesthesia, LSR procedures that include relatively
large areas frequently require general anesthesia or nerve blockage
by multiple anesthetic injections.
[0008] Another limitation of LSR is that ablative laser resurfacing
generally cannot be performed on the patients having dark
complexions. Ablation of pigmented epidermis tissue can cause
severe cosmetic disfigurement to patients having a dark complexion.
Such disfigurement can last from several weeks up to years. This is
generally considered to be unacceptable by most patients and
physicians. Yet another limitation of LSR is that ablative
resurfacing generally has a greater risk of scarring in areas other
than the face and result in an increased incidence of an
unacceptable scar formation because the recovery from skin injury
within these areas is not very effective.
[0009] Several NCR techniques have attempted to overcome the
aforesaid problems associated with LSR procedures. These techniques
may be variously referred to as non-ablative resurfacing,
non-ablative subsurfacing, or non-ablative skin remodeling. Such
NCR techniques generally use non-ablative lasers, flash lamps, or
radio frequency current for damaging the dermal tissue and avoiding
damage to the epidermal tissue. NCR techniques apply the concept
that it is the thermal damage of the dermal tissues that is thought
to induce wound healing. This results in biological repair and the
formation of new dermal collagen which in turn can result in
decreased photoaging related structural damage. Avoiding the
epidermal damage by using NCR techniques may also decrease both the
severity and the duration of treatment related side effects, for
example, post procedural oozing, crusting, pigment changes, and the
incidence of infections.
[0010] Treating skin using the NCR method involves heating
selective portions of dermal tissue within the dermal layer for
inducing wound healing without damaging the epidermis above. By
cooling the surface of the skin and focusing electromagnetic
energy, for example a laser beam, a selected dermal damaged region
can be achieved while leaving the epidermis undamaged. Using
non-ablative lasers for damaging the dermis while leaving the
epidermis undamaged is common to NCR treatment methods. Generally,
using non-ablative lasers result in deeper dermal penetration
depths as compared to the ablative lasers than the
superficially-absorbed ablative Er:YAG and CO2 lasers used in
typical LSR procedures. Further, when NCR techniques are used, they
generally do not have the undesirable side effects characteristic
of the LSR treatment, such as the risk of scarring or infection.
Examples of NCR techniques and apparatus are disclosed by Anderson
et al. in U.S. Patent Publication No. 2002/0161357.
[0011] Although these NCR techniques may avoid epidermal damage, a
major drawback of this method is its limited effectiveness. For
example, this is significantly less improvement of photoaged skin
or scars after the NCR treatment than when LSR ablative techniques
is used. In fact, even when multiple NCR treatments are employed,
improvement in the patient's skin is often far below expectations.
In addition, improvement is often delayed for several months when a
series of treatment procedures are used. Although NCR techniques
have been found to be moderately effective for wrinkle removal,
they have generally not been found to be effective for
dyschromia.
[0012] Another problem with using a NCR technique is the limited
the breadth of acceptable treatment parameters for safe and
effective treatment of dermatological disorders. This is because
NCR procedures generally rely on an optimum coordination of laser
energy and cooling parameters. This results in an unfavorable
temperature profile in the skin. An unfavorable temperature profile
consequently results in either no therapeutic effect on one hand,
or scar formation due to the overheating of a relatively large
volume of the tissue, on the other.
[0013] A problem that is common to both ablative and non-ablative
resurfacing procedures is that they do not significantly use
keratinocytes, which play an active role in the wound healing
response. Keratinocytes release cytokines when the keratinocyte is
damaged. Cytokines encourage wound healing. For example, during
ablative resurfacing procedures, keratinocytes are removed from the
skin along with the epidermis. This removes keratinocytes entirely
from the healing process altogether. During non-ablative
procedures, keratinocytes, located in the epidermis, are not
damaged at all and thus do not release cytokines for aiding the
healing process.
[0014] Accordingly, there is now provided with this invention an
improved system and method for treating skin that effectively
overcomes the aforementioned difficulties and longstanding problems
inherent in using either a LSR or a NCR procedure. These problems
have been solved in a simple, convenient, and highly effective way
by which to treat skin.
SUMMARY OF THE INVENTION
[0015] In one aspect, the invention provides a method for treating
tissue using a laser system with pulsed light output comprising
indicating by a user at least two of: (i) a desired total light
output energy, (ii) a desired average light output power, or (iii)
a desired duration of laser application. The method further
includes controlling the laser by the system in order to achieve
the selected conditions (i), (ii), or (iii) specified by the user,
and directing the light output of the laser to the tissue to be
treated over the desired duration.
[0016] Implementations of the invention may include one or more of
the following features. The laser system has a control for power
that may be used to produce a population inversion, wherein the
control varies between on and off states, and a population
inversion may be produced when the control is varied from an off
state to an on state. The system may vary this control between on
and off states at least four times in order to achieve the selected
conditions (i), (ii), or (iii). The layer system may have at least
two attenuating elements and the system may place at least one of
these at least two attenuating elements in the path of the laser's
output in order to achieve the desired energy or average power or
duration. Implementations of the invention may also include one or
more of the following features. The light output of the laser may
be ablative during a portion of the time that it is directed to the
tissue and non-ablative during another portion of the time that it
is directed to the tissue. Light output of the laser may be
directed to the tissue through a mirror, an optical fiber, a prism,
or another optical element. As a result of the light output power
being directed to tissue, a channel may be ablated in the tissue
having a predetermined width and predetermined height. A thermal
affected zone of predetermined volume and shape may be created
proximate said channel. The tissue may have a surface through which
the light output power passes and the thermal affected zone may
have a cross section in a plane parallel to that surface, which
increases in diameter with the plane's distance from that surface,
such that, the diameter of the cross section increases with
distance from that surface for a range of distances to the
surface.
[0017] Implementations of the invention may further include one or
more of the following features. The method may further comprise
administering a treatment through the channel. The output light
power may raise the temperature of at least a portion of the tissue
into which it is directed above 100.degree. C. The system may
measure the laser's light output power. The measured light output
power may be used in a feedback control system in order to decide
when to change the control from an on state to an off state or vice
versa. The desired average light output power may be no greater
than about 10% of the maximum instantaneous light output power
which the laser is capable of producing. The light output power may
deviate by no more than 10% from the desired average light output
power during at least about 90% of the time that the laser is
producing light output in response to the user's setting. The
system may select from a set of discrete attenuation values the
attenuation closest to the desired level.
[0018] In another aspect, the invention provides a system for
treating tissue with light comprising a laser with pulsed light
output and a digital controller for the laser. The digital
controller implements a user interface which permits a user to
select at least two of: (i) a total energy to be applied to the
tissue, and (ii) a duration of the application of light to the
tissue, and (iii) a desired average power level to be applied to
the tissue. The digital controller controls the laser's light
output to achieve the conditions (i), (ii), or (iii) specified by
the user.
[0019] Implementations of the invention may include one or more of
the following features. The light with which the tissue is treated
may have a wavelength of at least about 9 .mu.m. The laser may be
capable of producing a pulsed light output with at least about 200
W peak light power.
[0020] In further aspect, the invention provides a system for
treating tissue with light comprising a laser with pulsed light
output, an optical system for directing the light output of the
laser to the tissue, and a digital controller for the laser. The
laser comprises a pumping mechanism and a control for that
mechanism which can be varied between an on state and an off state.
Varying the control from the off state to the on state may produce
a population inversion. The digital controller is programmed to
vary the control from the off state to the on state and back to the
off state a plurality of times. The light output power of the laser
does not fall to zero between the first transition to the off state
and the last transition to the on state.
[0021] Implementations of the invention may include one or more of
the following features. The digital controller may be programmed to
receive from a user at least one numerical value and to compute
from the at least one numerical value a desired light output power.
The average light output power of the laser between the first
transition to the off state and the last transition to the on state
may lie within about 10% of the desired light output power.
[0022] According to one aspect of the invention, a method for
treating tissue is disclosed. The method comprises applying
electromagnetic radiation to the tissue for ablating a channel
therein having a predetermined width and predetermined depth. The
method includes non-ablatively heating tissue on the bottom of the
channel with electromagnetic radiation and creating a thermal
affected zone of predetermined volume proximate said channel.
According to another aspect of the invention, a system for treating
tissue, is disclosed which comprises an electromagnetic radiation
source and an electromagnetic radiation emitting device for
applying the electromagnetic radiation to the tissue for forming a
channel therein having a predetermined width, predetermined depth,
and a thermal affected zone of predetermined volume proximate said
channel.
[0023] As will be appreciated by those persons skilled in the art,
a major advantage provided by the present invention is full control
of: depth of treatment, the amount and placement of heat, and the
amount and placement of channels. It is therefore an object of the
present invention to rejuvenate skin and reduce wrinkles, scars,
dyschromia and other conditions such as melasma and
hyperpigmentation. It is another object to provide a channel with
or without heat for delivery other therapy (vitamins, drugs, etc).
Additional objects of the present invention will become apparent
from the following description.
[0024] In a further aspect of the invention, a method for treating
tissue using a laser system with pulsed light output is provided.
In this method, a user indicates at least two of a desired total
light output energy, a desired average light output power, or a
desired duration of laser application. The system controls the
laser in order achieve the selected conditions specified by the
user and directs the light output of the laser to the tissue to be
treated over the desired duration. The system may achieve the
conditions with the aid of attenuating elements which it can place
in the path of the laser's light output. Alternatively, the system
may achieve the conditions by repeatedly turning on and off the
power in the laser's pumping system, causing the laser's light
output power to be maintained in the vicinity of a specified
level.
[0025] The method and apparatus of the present invention will be
better understood by reference to the following detailed discussion
of specific embodiments and the attached figures which illustrate
and exemplify such embodiments.
BRIEF DESCRIPTION OF THE FIGURES
[0026] The patent or application file contains at least one color
photograph. Copies of this patent or patent application with color
photograph(s) will be provided by the Office upon request and
payment of the necessary fee.
[0027] A specific embodiment of the present invention will be
described with reference to the following drawings, wherein:
[0028] FIG. 1 is a schematic illustration of a microablation method
and system in accordance with an embodiment of the invention;
[0029] FIGS. 2A, 2B, 2C, and 2D are schematic illustrations of
sequential stages of microablation and treatment in accordance with
an embodiment of the invention;
[0030] FIGS. 3A, 3B, 3C, and 3D are schematic illustrations of
sequential stages of microablation in accordance with an embodiment
of the invention;
[0031] FIGS. 4A, 4B, 4C, and 4D are schematic illustrations of
tissue manipulation in accordance with an embodiment of the
invention;
[0032] FIG. 5 is a schematic illustration of tissue treatment
according to an embodiment of the invention;
[0033] FIG. 6 is a schematic flow chart of a method of producing
microablation on a tissue in accordance with an embodiment of the
invention; and
[0034] FIG. 7 is a schematic flow chart of a method of producing
microablation on a tissue in accordance with an embodiment of the
invention.
[0035] FIG. 8 depicts exemplary optical power output versus time
curve for a laser system having pulsed output which is useful in
microablation;
[0036] FIG. 9 depicts schematically a way to control optical output
power of a laser by turning the pumping system power on and
off;
[0037] FIG. 10 depicts schematically the use of pumping system
power control to apply initially the normal high power pulse of
optical energy which the laser natively produces, followed by a
selected period of sub-ablation energy;
[0038] FIGS. 11A-11C depict schematically various attenuator
arrangements;
[0039] FIGS. 12A-12F depict graphical representations of laser
waveforms;
[0040] FIG. 13 is a color photograph of an irradiated
polyacrylamide gel using varying laser pulse duration and power;
and
[0041] FIG. 14 is a flow diagram of a method of treating skin using
a laser system with pulsed light output.
DETAILED DESCRIPTION OF THE INVENTION
[0042] The following preferred embodiment as exemplified by the
drawings is illustrative of the invention and is not intended to
limit the invention as encompassed by the claims of this
application. A system and method for treating skin is disclosed
herein. In skin tissue, for example, proteins such as collagen
reside in the dermal layer of the skin. The microchannel disclosed
in an embodiment of the present invention may itself target and
alter the collagen fibers within the dermis as an effective
treatment for wrinkles of the skin.
[0043] Alternatively, an embodiment of the microchannel disclosed
herein may create a passage through which targeted tissue is
treated.
[0044] As shown generally in FIG. 1, an embodiment of the present
invention provides a system and method for performing microscopic
ablation or partial microablation of e.g. tissue, and forming a
microchannel through a surface of tissue to treat subsurface
tissue. The microchannel may provide access to subsurface tissue
targeted for a prescribed treatment, or the microchannel itself may
provide a prescribed treatment. In some embodiments of the present
invention, the microchannel may produce partial lateral
denaturation of proteins (e.g. collagen) within the walls and/or at
the bottom of the channel.
[0045] According to some embodiments of the invention, a tissue
ablation system 1 may include a laser unit 2 and a laser emitting
device 3 for ablating a microchannel 6 into a tissue 5, for
example, for applying a treatment thereto as will be described
below in detail. The microchannel 6 may be, e.g. a column, a well,
a hole, or the like, created in the tissue 5 by ablating the tissue
5 by the laser emitting device 3 and the laser beam 4, for example,
an ablating laser beam. Microablation of the tissue 5 may result in
ablation of the microchannel. Microablation of the tissue may also
result in dissipation of heat from the heated and evaporated tissue
by the tissue surrounding the resultant microchannel 6. Thus,
ablation of the tissue 5, producing the microchannel 6, may result
in a thermal affected zone 7 surrounding the walls and/or bottom of
the microchannel 6. The thermal affected zone 7 is generally
indicative of damaged tissue and of tissue necrosis (the death of
cells) in particular. As used herein, "damaged" is defined as
inducing cell death in one or more regions of the dermal tissue of
interest ("lethal damage"), or stimulating the release of
cytokines, heat shock proteins, and other wound healing factors
without stimulating necrotic cell death ("sublethal damage").
[0046] Selection of the laser beam 4 may also be based on the
absorptive qualities of the tissue 5 to be treated. The absorptive
properties of the tissue 5 to be treated may dictate or influence
specific the type of laser or the characteristics of that laser
suitable for a particular treatment for and/or microchannel. For
example, certain lasers may reach depths unable to be reached by
other types of lasers. As an example, an ablative laser may reach
up to any depth required while non-ablative lasers may be unable to
penetrate skin below, for example, about 50 pm. Similarly, it may
be difficult to reach energy doses with one type of laser that are
easily reached with others. Of course, as is well known in the art,
if the wavelength is altered, the corresponding absorption level of
the skin treatment area will be altered. Therefore, as long as the
fluence described herein is maintained for achieving the
microablation disclosed herein, different lasers having different
characteristics may be used for achieving the same or similar
results disclosed.
[0047] The microchannel 6 may be characterized by certain
parameters, for example, diameter D and depth h. The diameter D of
the microchannel and the depth h of the microchannel generally may
be controlled by the energy characteristics of the laser. Such
energy characteristics include, for example, wavelength, power, and
the beam profile of the laser. Characteristics of the beam profile
of the laser include, for example, pulse width, pulse duration, and
pulse frequency). Furthermore, the profile and volume of the
thermal affected zone may be formed by using different laser beam
characteristics, such as chosen wavelength, energy of individual
pulse or defined sequence of pulses, duration of each pulse, power
distribution, shape of the laser spot, and the like, as will be
outlined in detail below.
[0048] In some embodiments of the invention, the diameter of the
ablated microchannel 6 may range from about 10 .mu.m to about 500
.mu.m, preferably in the range from about 50 pm to about 250 1.1 m.
Microchannel diameter D may depend on the type of laser used and
other parameters, for example, the elasticity of the skin. It has
been found that the bottom of the formed microchannel is often
conical due to the elastic forces of the skin as well as the power
energy distribution of the spot formed by the laser.
[0049] The depth of the microchannel may be determined by the
attending physician based upon the treatment required or selected
by the physician. For example, treatment of collagen (collagen
remodeling) typically located at a depth in the range from about
200 .tm to about 2 mm from the surface of skin tissue may be
desired. Treatment of blood vessels may necessitate a microchannel
extending up to approximately 0.5 mm, which is where blood vessels
are typically located. The microchannel 6 may therefore be created
in accordance with an embodiment of this invention to a
predetermined depth h to effect treatment to collagen or blood
vessels or any other portion of the dermis selected by the
attending physician. According to some embodiments of the present
invention, the laser device 4 may produce the microchannel 6
reaching, for example, in the range from about 100 tm to about 3 mm
in depth below the surface of the tissue 5.
[0050] Any suitable type of laser may be used, for ablating the
microchannel, for example, CO2 laser, Er:YAG, Tm:YAG, Tm fiber
laser, Er fiber laser, Ho fiber laser, etc. or any other laser type
as is well known in the art which may match a predetermined
operational parameter such as, for example, optical absorption by
tissue and intensity of laser that are strong enough to ablate
small volumes with minimal lateral damage. The laser emitting
device 3 may therefore be adapted for emitting an ablative laser
beam 4 having any suitable power level and/or spot size and/or
other associated characteristics. The laser power level may range,
for example, in the range from about 0.5 mJ to about 250 mJ. The
spot size of the laser beam 4 on the tissue surface may range, for
example, in the range from about 10 p.m to about 50. For example, a
CO2 laser may use a spot size ranging from about 80 p.m to about
150 p.m for ablative treatment and preferably about 80 p.m.
[0051] In some embodiments of the present invention, the ablation
may be produced by a continuous wave laser, by a single pulse of a
laser, or by a series of pulses. The selection of these forms may
depend, for example, upon the depth of the microchannel required,
the diameter of the microchannel, as well as the size of the
thermal affected zone, that is, the width of the lateral damage. In
an embodiment using a continuous wave laser, for example, an
ablating laser operating in a wavelength of 10.6 nm, the laser
emitting device 3 may be operated at a power level of, e.g., in the
range from about 1.0 W to about 250 W for a duration of, e.g., in
the range from about 0.02 msec to about 500 msec. In an embodiment
using a pulsed CO2 laser, for example, a series of, for example, 10
pulses, each having a duration of, for example in the range from
about 0.05 msec to about 100 msec may be fired at an energy level
of, e.g. in the range from about 0.2 mJ to about 20 mJ. In an
embodiment using a pulsed laser, a series of pulses, each having a
duration of from about 0.05 msec to about 100 msec may be fired may
be fired at an energy level of in the range from about 0.2 mJ to
about 20 mJ. In skin, for example, applying a pulsed laser as
indicated above may result in a microchannel 6 of a diameter in the
range of from about 80 tm to about 100 gm, a depth in the range of
from about 300 1-ffil to about 500 gm, and a thermal affected zone
of lateral width in the range of from about 20 gm to about 300 gm.
Additionally, as described below in an embodiment of the invention,
a series of pulses, of pulsed laser may be fired at the tissue 5 to
further deepen the microchannel 6, created as identified above. The
microchannel 6 may be deepened to a desired depth, preferably to
the level of the tissue to be non-ablatively treated. It should be
noted that the diameter of the deepened microchannel 6 may be in
the same range or different range as the previously created
microchannel in the same location.
[0052] In some embodiments of the invention, the microablation
channel 6 may be sculpted by employing different pulse
characteristics of the laser beam. Pulse characteristics of a laser
beam, e.g. laser beam 4, may further include different energy
profiles. As mentioned above, the depth h of the microchannel and
the resulting width of lateral damage and the profile of the
thermal affected zone 7 may be controlled by different laser beam
characteristics. For example, the laser beam 4 may have
characteristics resulting in the thermal affected zone 7 having a
substantially constant width (linear profile) 7. It will be
recognized that some embodiments of the invention may have a
thermal affected zone 7 profile different from the one depicted in
FIG. 1. Furthermore, it is now possible to produce a microchannel 6
according to embodiments of the present invention with a minimal
thermal affected zone 7, e.g. a width in the range from about 1 gm
to about 5 liM with the use of the Er:YAG laser.
[0053] In some embodiments of the present invention, the laser unit
2 may include a controller 12 able to control the laser emitting
device 3, and an input interface 13 capable of receiving input
parameters from user of system 1. Such input parameters may be for
defining microablation treatment parameters, for example. User
input parameters to the interface 13 may further include the
microchannel depth, the spatial location of the microchannel 6 on
the tissue surface 1, etc. Parameters may be provided at the input
interface 13 by an operator of the system, for example, a
physician, or alternatively, through an imager program detailed
below. The controller 12 may be able to perform at least one of the
following functions, as will be described in more detail below: (a)
identifying at least one location for treatment; (b) selecting
treatment(s) for each of at least one location; (c) operating a
laser and directing mechanism to produce the at least one
microablation; and (d) delivering the selected treatment(s) at the
at least one site.
[0054] Reference is now made to FIGS. 2A, 2B, 2C, and 2D which
schematically illustrate sequential stages of microablation and
treatment in accordance with an embodiment of the invention.
According to an embodiment of the invention, it may be desirable to
apply treatment to tissue which may be, for example, in the
hypodermis 10 in a way that substantially maintains the profile of
the thermal affected zone throughout the treatment protocol. As it
is desirable to minimize the necrosis of tissue at the surface 11,
it may be beneficial to apply a plurality of laser pulses onto the
tissue 5 in order to reach a depth of treatment area in the
hypodermis 10. As illustrated in FIG. 2A, the microchannel 6
created by a first ablative laser pulse, may have the desired
thermal affected zone 7, e.g. linear profile of constant width, for
example, a minimal width, and may have a depth of h1 that is not
sufficiently deep to provide treatment to the hypodermis 10. A
second ablative laser pulse may be applied through microchannel 6
of FIG. 2A to deepen the microchannel 6 having a minimal thermal
affected zone to a depth h2 into, for example, the dermis 9 of the
tissue 5, while maintaining the predetermined minimal thermal
affected zone profile, as illustrated in FIG. 2B. Finally, as
indicated in FIG. 2C, a third ablative laser pulse may be applied
through the microchannel 6 of FIG. 2B to deepen the microchannel 6
having a minimal thermal affected zone 7 further to a depth h3 into
the targeted hypodermis layer 10, while maintaining the
predetermined thermal affected zone profile 7. Alternatively, if a
non-ablative pulse is applied after the profile depicted in FIG.
2B, the profile may appear as depicted in FIG. 2D. According to
some embodiments of the invention, a delay representing a minimum
time, e.g. 1 to 100 msec, may pass between each laser pulse,
thereby allowing relevant portions of tissue 5 to cool down between
each pulse. This delay may be between any succession of laser
pulses whether they are ablative or non-ablative. It is preferable
to have a delay after an ablative laser pulse. To allow for cooling
of tissue 5, the minimum time between pulses may be determined
according to, for example, a predetermined tissue relaxation time
which may define, e.g. the time required to dissipate a certain
amount of heat absorbed by, e.g. the tissue 5, during a laser pulse
applied by the laser device 3. The delay may also allow venting of
ablative tissue and or gases that may have developed during an
ablative pulse of light. Accordingly, if a time of an applied pulse
is shorter than the tissue relaxation time and the beam has a top
hat profile a very low amount of heat may dissipate through walls
of the microchannel 6.
[0055] A beam profile that would conform to an inverted top bat may
be preferable in some embodiments of the present invention for
forming a channel with well defined side walls, minimal
microchannel diameter, and a minimal thermal affected zone.
Typically, a beam has a Gaussian power distribution across the
diameter of its spot. Since the power on the edges of such a spot
is less than the power in the center of the spot, it is often
difficult to form a straight walled channel or hole. By having a
beam profile that has a uniform power distribution across its spot
(a top hat profile) it will be easier to form a straight walled
channel.
[0056] In some embodiments of the invention, upon producing the
microchannel and clearing a path to the treatment site, a wide
variety of types of treatment may be delivered to the site, as
detailed below. In some embodiments, the treatment may be
non-ablative laser treatment. Such non-ablative laser treatment may
be used, for example, for remodeling collagen. As is more
particularly illustrated in FIG. 2D, a non-ablative laser treatment
may be delivered to the tissue 5 in the dermis 9 after the
microchannel 6 has been created. The path created for the
non-ablative heating of the target tissue may follow embodiments of
the invention detailed above regarding FIGS. 2A, or 2B and/or 2C.
That is, heating of subsurface tissue by a non-ablative laser
through the created microchannel may be through a microchannel that
was created by one or by more that one ablative pulses. Laser
treatment by the laser beam 4 may be applied to the tissue 5 in the
dermis 9, whereby the tissue 5 is heated to a temperature below
that at which the tissue is ablated though heated to a temperature
sufficient to denature collagen, for example, in the range of from
about 50.degree. C. to about 67.degree. C. The non-ablative laser
beam 4 may further create a thermal affected zone of denatured
collagen 17, without tissue ablation, whereby collagen is heated.
The collagen thereupon contracts, thus removing wrinkles. The
non-ablative laser beam 4 may further be applied to targeted tissue
for removing pigmentation, treating blood vessels, and other
treatments, as is well known to those skilled in the art.
[0057] Accordingly, it will be appreciated that the use of the
microchannel 6 of the present invention as a conduit for applying
non-ablative heat to targeted subsurface tissue, enables the
heating of the subsurface tissue to be treated without excessively
damaging non-targeted tissue, for example, the surface tissue.
Further, the thermal affected zone may be additionally controlled
by having non-ablative heating applications interposed between
ablative treatments for creating a larger thermal affected zone 17
deep in the tissue, for example in the dermis 9.
[0058] Reference is now additionally made to FIGS. 3A, 3B, 3C, and
3D which schematically illustrate sequential stages of treatment in
microablation channels in accordance with embodiments of the
invention. In accordance with to some embodiments of the invention,
it may be desirable to create a predetermined non-uniform thermal
affected zone profile and/or lateral width damaged area along the
depth of the channel. In other embodiments of the invention, an
area of tissue in the dermis 9 may be, treated for forming a
predetermined thermal affected zone having a profile different from
the profile of the thermal affected zone in the epidermis 8 near
the surface. As is more particularly illustrated in FIG. 3A, the
microchannel 6 having a predetermined thermal affected zone and/or
profile 7a and a depth h1 may be created by a first ablative laser
pulse. As illustrated in FIG. 2D, a second laser non-ablative laser
pulse may heat the bottom of the microchannel 6 thereby damaging a
spherical area surrounding the bottom of the channel to a depth h3,
reaching for example, beyond the dermis 9. This second pulse may
have different characteristics than the first pulse, producing a
thermal affected zone having a different area and/or profile than
the first pulse and resulting in the profile illustrated in FIG.
2D. When a second ablative laser pulse (that is, the third pulse to
this treatment area) is applied through the damaged tissue on the
bottom of the microchannel, a profile 7b as depicted in FIG. 3B is
formed. Thus, FIG. 3B depicts an ablative laser pulse applied
subsequent to the non-ablative laser pulse which formed the profile
depicted in FIG. 2D. Alternating ablative laser treatment with
non-ablative laser treatment may result, for example, in a
microchannel having a thermal affected profile as illustrated in
FIG. 3C. It will be understood that a microchannel may be produced
to any depth and by any number of pulses for creating a series of
predetermined thermal affected zones that may vary along the depth
of the microchannel. In this way, a predetermined thermal affected
zone profile along the microchannel 6 is formed. It is thus
possible to build a variety of predetermined thermal affected zone
areas and/or profiles along the wall and/or the bottom of the
microablated channel, using a sequence of pulses with different
parameters (e.g. energy and duration or wavelength) and employing
the natural thermal conductivity of tissue. For example, in another
embodiment of the invention, an ablative laser pulse applied to the
tissue 5 may have characteristics producing a thermal affected zone
having an area and/or profile 7d as illustrated in FIG. 3D. The
thermal affected zone 7d in FIG. 3D illustrates that the thermal
affected zone area may decrease along the depth of the channel,
according to predetermined laser beam parameters. Of course, once
the depth of the tissue targeted for treatment is reached, the
non-ablative heating of the tissue should preferably commence.
[0059] In some embodiments of the present invention, the creation
of the microchannel 6 with the desired thermal affected zone
profile 7 along the walls and/or bottom of the microchannel 6 may
itself be the desired treatment method. Additionally or
alternatively, creating the microchannel 6 itself may facilitate
the desired treatment method, by providing access directly to a
subcutaneous site for treatment. For example, upon completion of
the microchannel, a substance may be delivered to the treatment
site by any means, including for example, ultrasonic delivery.
Additionally or alternatively, the microchannel may serve as a
conduit for transdermal substance delivery, for example, for
diffusion, electrophoresis, ointments, acids, healing substances,
chemical peeling agents, collagen modification agents, fillers,
stem cells, or any variety of administering medicines and the like.
It will be noted that the depth of the microchannel need not be the
only or even the primary treatment site; rather the treatment site
may be any and all sites along the walls and/or bottom of the
microchannel adjacent to or proximate the microchannel.
[0060] In some embodiments of the invention, the controller 12 may
provide 3 a command via a signal 14 to the laser device for
applying a pulse or series of pulses to the tissue 5. The
controller may provide a variety of commands to the laser device 3,
for example, the sequence and duration of pulses to apply to the
tissue 5. The controller may also select form a variety of laser
sources for applying a desired sequence of ablative and
non-ablative laser applications to a particular site. The
controller may also prescribe the desired delay between the laser
applications. Furthermore, the controller 12 enables the laser
emitting device 3 to deliver precise multi-spot ablation to
selective portions of tissue in accordance with preselected
treatment protocols as is well known by the physician.
[0061] In some embodiments, more than one microchannel may be
produced substantially concurrently or in rapid sequence on the
tissue 5, for example, by directing the laser emitting device 3
from one predetermined site to another of the tissue 5, applying a
pulse at each site and returning precisely to the previously
treated site so as to apply the next pulse in the sequence. Thus,
while the tissue 5 at one microchannel is cooling, the controller
12 may send a command to the laser device 3 to move among one or
more sites on the tissue 5 for creating a plurality of
microchannels at a plurality of sites. Such a device may use, for
example, a laser scanner. Such scanners may operate in accordance
with the teachings in U.S. Pat. Nos. 5,713,902; 5,957,915; and
6,328,733, all of which are incorporated herein by reference. For
example, at a first scanning sequence, the laser device 3 may
provide the laser beam 4 on the first site resulting in a
microchannel of depth h1. The controller 12 may then move the laser
device 3 to a second site to produce thereon a microchannel having
a depth h1. This process may continue until the laser device 3
performed on each location has a microchannel resulting in depth
h1. The controller 12 may then proceed to provide the laser beam 4
on a microchannel site further ablating a microchannel resulting in
another microchannel of depth h2 directly below the first
microchannel site. Alternatively, the second laser application may
be a non-ablative laser beam. The controller 12 may then move the
laser device 3 to a second site to produce a microchannel of depth
h2. This process may continue until the laser device 3 performed on
each microchannel location of depth h1 a second laser beam pulse
resulting in a microchannel of depth h2. Of course, the order of
the second beam across the selected treatment sites may be in a
different order or sequence than the first pass. Alternative
scanning sequences may apply laser beam pulses repeatedly at a
location, then moving to another location to apply laser pulses. It
may not be necessary that the same series of pulses
(characteristics including duration and power) be applied at each
location in the sequence and any number of series of pulses may be
applied to tissue at various locations.
[0062] In some embodiments of the invention, the tissue 5 may be
manipulated and the laser emitting device 3 positioned for applying
the laser beam 4 to the tissue 5. For example, the skin tissue to
be treated may be lifted and the laser beam 4 may be applied from
the side. Furthermore, the controller 12 may direct the laser
emitting device 3 to apply the laser beam 3 to the tissue 5 from a
variety of angles from the perpendicular.
[0063] In another embodiment of the invention, it may be desirable
to increase the amount of radiation per unit of surface area of the
tissue 5. For example, the tissue 5 may be stretched prior to
applying laser beam 4 to the tissue. Referring to FIG. 4A, laser
beam 4 may be applied to unstretched tissue 5 over a surface area
19 of tissue. The tissue 5 may be stretched in a variety of
directions as selected by the physician, for example, the lateral
direction, manually or by some device applying a stretch 20, prior
to producing the microchannel 6 as detailed above in an embodiment
of the invention. Referring to FIG. 4B, applying stretch 20 to the
tissue 5, effectively increases the amount of radiation per unit
surface area 19 of the tissue 5. The microchannel 6 (FIG. 4C)
created in the stretched tissue 5 will possess dimensions and
characteristics as detailed above. Release of the tissue stretch
13, may result in a relaxed tissue 5 wherein the microchannel 6 now
possesses a smaller diameter D' (i.e. D'<D; Ref. FIG. 4D). The
reduction in microchannel diameter may also be a function of tissue
properties, for example, tissue elasticity, tissue hydrated
conditions, and the thickness of the stratum corneum. Thus, by
stretching the skin prior to a laser beam is applied, the area of
damaged skin may be further reduced. Stretching the skin has many
advantages beyond just minimizing the amount of damaged skin. For
example, by stretching the skin during the application of an
ablative laser for creating a microchannel, the diameter of the
microchannel will be further reduced. In this way, infection has a
smaller entrance point and the chance for infection may be further
minimized. Stretching the skin during the application of the laser
beam (both an ablative laser beam and a non-ablative laser beam)
provides additional advantages, for example, better penetration,
better evacuation of vapors, and being less sensitive to the
position of the target relative to the applied beam.
[0064] The system may also include an imager to enable a user to
view the tissue area and to choose a treatment site. For example,
the imager and an image processor may be used to determine the
wrinkle topology of a tissue. For example, by using the imager
combined with the application of polarized light, the outline,
depth, and profile of the skin's topology may be more precisely
determined. The wrinkle topology may be provided to the input
interface 13 to communicate with the controller 12 and send a
signal 14 to the laser device 3 to maximize the aim of the laser
device 3 to the target tissue 5. The wrinkle topology may be used
to measure the effectiveness of the treatment as well as used for
identifying targeted sites that may require additional
treatment.
[0065] An imager may also be used to generate optical feedback,
either manually to the eye of the user, or automatically to an
image processor, in order to return the laser to a previously
treated site. The processor may process the image obtained from the
imager for providing information to the controller for varying the
treatment locations, the particular laser to be used, the laser
spot size, the spot location, etc. In this manner, if the patient
moved between pulses, an imager and processor may enable returning
the laser to the precise site of the previous pulse. Use of an
imager to optically track or determine tissue position may be used
in concert with the process described above of the sequential
creation of microchannels, as is well known to those skilled in the
art.
[0066] As shown in FIG. 5, in another embodiment of the invention,
the microchannel may be used to facilitate treatment to
subcutaneous tissue by a means other than through the microchannel
itself. The void of the microchannel may act as a barrier, or
insulating separation of air, between layers of tissue on either
side of the microchannel. Therefore, a microchannel may be used in
conjunction with radio frequency (RF) energy treatment to allow
driving a current below the microchannel. As illustrated, the
microchannel 6 is created according to an embodiment of the present
invention detailed above, having a width W, a length L, and a depth
h. In this embodiment, the microchannel depth h reaches into the
dermis of the tissue and the targeted tissue is beneath the
microchannel 6 in the dermis 9.
[0067] Radio frequency electrodes 15 and 16 may be applied to the
tissue at opposite sides of the microchannel 6. When RF current 18
is applied, the insulating (non-conducting) property of the
microchannel 6 requires the current to flow between electrodes 15
and 16, below the microchannel depth h, directing the current to
deeper tissue than would have occurred in the absence of the
microchannel 6. The length L of the microchannel should preferably
be at least twice its depth (2D) so that the applied current may go
through the targeted tissue and not find an alternate path of less
resistance. The length of the microchannel in this embodiment of
the invention may be in the range of from about 100 pm to about 500
iirn, and preferably about 300 gm. Accordingly, it will be
appreciated that by using the microchannels of the present
invention, the heating of deeper layers of tissue may be achieved
without damaging the surface tissue. It will further be appreciated
that controlling the dimensions of the microchannel, e.g., the
depth, width, and/or length of the microchannels may define the
treatment provided by the treatment device, e.g., the RF
electrodes, to the treatment layer of the tissue. It will be noted
that by concentrating the current, the microchannel may provide for
increased current density at the desired treatment site. A similar
approach may be used for heating and followed shrinkage of collagen
fibers at a predetermined depth.
[0068] Creating a microchannel into the tissue for reaching an area
of targeted treatment may also be achieved without an ablative
laser. For example, a microchannel may be created mechanically with
a heated microneedle. After the microchannel is thus formed,
non-ablative treatment may be applied.
[0069] Reference is now made to FIG. 6, which schematically
illustrates a flow-chart of a method for performing micro-ablation
on a tissue in accordance with an embodiment of the invention. As
indicated at block 601, the method may include, for example,
positioning the laser device for performing microchannel ablation.
For example, the user of the system 1 may initially position the
laser device 3 relative to the skin 5 to enable creating the
microchannel at a desired location. As indicated at block 602, the
method may also include, for example, determining the depth of the
microchannel. For example, the user may determine that the desired
depth of the microchannel 6 (FIGS. 2A, 2B and 2C) is h3. As
indicated at block 603, the method may also include, for example,
determining the width of the microchannel and/or the thermal
affected zone. For example, the user may determine that the desired
width of the microchannel 6 is D (FIG. 1) and the desired thermal
affected zone profile may vary as in 7a, 7b, 7c, and 7d (FIGS. 3A,
3B, 3C and 3D). The density of microchannels (e.g., number of
channels per area) can also be determined. The wavelength for the
different stages of the ablation may also be determined. As
indicated at block 604, the method may also include, for example,
producing a microchannel. For example, the laser device 3 may emit
a laser beam and may thereby produce the microchannel 6 in the
tissue 5. As indicated at block 605, the method may also include,
for example, applying treatment onto a microchannel location. For
example, applying heat treatment to affect collagen at bottom of
microchannel 6 (FIG. 2D). It will be recognized that the step of
applying treatment is optional and need not be practiced in every
embodiment of the invention.
[0070] FIG. 7 depicts a flow chart method in accordance with
embodiments of the present invention. At block 700, the orientation
of the tissue 5 is selected for treatment, the tissue, e.g. skin is
stretched, lifted, or left natural. At block 701, image analysis of
the tissue surface is performed, for example, to create wrinkle
topology, to provide information to the controller 12 (FIG. 1) in
order to maximize laser orientation. It will be recognized that the
step of image analysis is optional and need not be practiced in
every embodiment of the invention. At blocks 702 and 703, the depth
and width of the microchannels may be determined respectively, for
example, based on the treatment program selected or selected by the
operator. At block 704, the thermal affected zone (e.g. area and/or
diameter of necrosis) may be determined, for example, by setting
the pulse duration, pulse energy, the number of pulses, or the
density of the pulses based on the treatment program, or based on
selection by the operator. At block 705, the area of collagen
shrinkage (i.e. thermal affected zone 17) may be determined (FIG.
2D). At block 706, a treatment pattern or program may be
determined, for example, by the operator of the device selecting an
appropriate program. At block 707, the size of the microchannel
pattern may be determined, for example, automatically by scanning,
or based on the treatment program, or by an operator selecting the
appropriate pattern size. At block 708, the fill factor, for
example, the density of the microchannels on the tissue, may be
determined, for example, automatically by the device, e.g., based
on the treatment program, or by selection by the operator of the
device. At block 709, the device may be positioned on the tissue,
and at block 710, the treatment may be performed by forming the
microchannels, and/or applying any other desired treatment.
[0071] In a further aspect of the invention, systems are provided
for control of the lasers used in microablation. As is well known
lasers comprise a laser medium, a pumping system to generate a
population inversion in the medium, and optics to pass certain
photons repeatedly through the medium and to allow a usually narrow
beam of light to exit the medium. The pumping system may be, for
example, a set of electrodes and associated controls which create a
glow discharge in a gas by supplying DC or RF energy to the gas,
with the discharge producing a population inversion. For background
on lasers see generally Jeff Hecht, Laser Guidebook (2nd ed. 1992)
and Orazio Svelto, Principles of Lasers (David Hanna trans. 4th ed.
1998).
[0072] In systems for laser microablation one may advantageously,
for example, a CO2 laser in which initiation of laser action
produces a high optical power output pulse, for example having a
peak output power of 300 W. An exemplary optical power output of
such a system over time is shown in FIG. 8. Lasers having pulsed
optical output suitable for laser microablation have been marketed
by the assignee of this application, for example, under the name
UltraPulse.RTM.. The assignee's laser products include RF excited
slab CO2 lasers of the waveguide type.
[0073] In existing systems for laser microablation it is common to
present the user (normally a physician) with an interface whereby
the user chooses an output energy. This energy may, for example, be
on the order of tens of millijoules, for example in the range of
about 5 mJ to about 50 mJ.
[0074] A microablation system could provide the desired number of
millijoules in the following manner. As part of the system design,
one determines a curve of the light power output over time of the
laser when a predetermined voltage step waveform is applied to the
pumping system. On the basis of that curve, for a series of time
values t one calculates the area under the curve from time 0 (onset
of voltage applied to pumping system) to time t. That area under
the curve will represent the amount of light energy that the system
will output if started at time 0 and shut down at time t. From the
series of areas under the curve for time values t, one can
calculate by interpolation for any desired energy output a time
value which will produce that energy output. Thus, for any energy,
the system can calculate how long to apply power to the pumping
system to produce that energy.
[0075] Alternatively, the system could start the application of
energy to the pumping system and measure the light output power of
the system. The system could integrate the light power output of
the system over time (e.g., using some numerical integration
algorithm) and turn off the energy input to the pumping system when
the integrated power since turn-on reaches the desired energy
level. The system might take into account the turn-off transient of
the light power output when the pumping system shuts down and so
shut down slightly short of the desired energy to compensate for
that transient.
[0076] It is desirable to extend the capability of such systems
whereby the user chooses both a desired amount of light energy and
a duration over which the energy is applied. With this capability,
the system described above based on the integrated optical power
output would potentially not be adequate because it might have to
stop short of the user's selected duration in order to meet the
total energy constraint.
[0077] It is therefore desirable to have the ability to reduce
reliably the output light energy level of the laser being used,
even when it employs a roughly fixed input energy level to the
pumping system and has a roughly fixed light power output curve as
a function of time when that fixed input energy level is applied to
the pumping system.
[0078] Given the curve of output light energy versus time described
above, the system can calculate the degree of attenuation necessary
to achieve both the desired energy output and the desired duration
of action t. The system can, for example, determine the duration
tfull to produce the desired energy output without attenuation, and
then attenuate by tfulilt to deliver the desired energy output over
the chosen interval.
[0079] There are a number of reasons why the user of a laser
microablation system would want to be able to vary the duration as
well as the energy delivered by the system. One important reason is
that a longer duration administration of the same energy can have
quite different effects on tissue. As discussed above, there is in
tissue both ablative and non-ablative damage. A rough
differentiation between these two types of damage can be made
according to whether the tissue temperature reaches the boiling
point of water, in which case the damage in portions of tissue
where that occurs would be ablative. Because heat is conducted away
from the area where the relatively thin laser beam enters tissue,
if the energy is being applied more slowly the tissue will not
reach the boiling point of water and the damage will tend to be
non-ablative. As discussed above and depicted in FIGS. 1-5, where
non-ablative damage occurs it will tend also to have a different
shape which may be more desirable in achieving the desired effect
on tissue.
[0080] In addition to varying the duration during which the optical
power is applied, control over the optical power may also be used
to apply initially the normal high power pulse of optical energy
which the laser natively produces, followed by a selected period of
sub-ablation energy. The sub-ablation energy as discussed above
produces a different kind of alteration of tissue from the initial
pulse. This alteration is referred to sometimes as "coagulation."
The ability to choose a particular power level and duration
following the initial high power pulse opens the way to a much more
precise control of the non-ablative damage.
[0081] For cosmetic purposes, for example, it can be desired to
have primarily non-ablative damage located shortly below the
surface of the skin, as schematically depicted for example in FIG.
3C.
[0082] It is also possible with control over output optical power
to generate, for example, double high-power pulses of optical
energy separated by a period in which a non-ablative level of
optical power is applied.
[0083] One method which is possible for controlling the output
energy level of the laser is to place a set of attenuators at the
output of the laser. For example, one could have a set of
attenuators which have attenuation values of about 10%, about 20%,
about 30%, about 40%, about 50%, about 60%, about 70%, about 80%,
or about 90%. Alternatively, one could have an arrangement in which
a smaller number of attenuators is employed with two or more
attenuators being put in the path of the beam in order to achieve a
greater degree of attenuation than what one attenuator can
produce.
[0084] A variety of mechanical arrangements may be employed to
place an attenuator in the path of the laser beam. For example,
referring to FIG. 11A, a rotational arrangement 200 may include a
shaft (not shown) that moves until an attenuator 202 is in place
and then moves to take the attenuator 202 out of the path of the
laser beam 201. Alternatively, as shown in FIG. 11B, a
solenoid-based arrangement 220 may involve linear motion of an
attenuator 204 in the laser beam path 201. With the rotational
arrangement, a number of different attenuators of different degrees
of attenuation can be attached to the shaft and the appropriate
attenuator rotated into place.
[0085] In a system with a fixed set of attenuation percentages, the
system might for example choose the percentage which is closest to
that calculated as described above and utilize that percentage.
Alternatively, the system might modify the time duration somewhat
from the desired duration to achieve the exact energy chosen by the
user with that closest feasible attenuation. Alternatively, the
system might choose the smallest attenuation percentage which is
greater than that calculated as described above, or the largest
attenuation which is less than that calculated as described
above.
[0086] Attenuators for light are known in the art. The precise form
and structure of the attenuator for use with a laser microablation
system will depend very much on the wavelength of the laser output,
because different materials have different frequency responses over
the broad range of frequencies for which lasers are available. The
laser used in a laser microablation system will generally output a
fairly narrow wavelength range corresponding to the set of
wavelengths of transitions that take place as part of the laser
action. For example, CO2 lasers produce light at wavelengths from
about 9 tim to about 11 [tin. The strongest light output from a CO2
laser will tend to be at about 10.6 p.m. The precise form and
structure of the attenuator will also depend on the optical power
level being used, for example milliwatts or watts or hundreds of
watts, since the attenuator itself should not be altered by the
energy which it is absorbing. For CO2 and other relatively powerful
infrared lasers metal screens work well as attenuators.
[0087] In addition to attenuators which have a fixed degree of
attenuation such as 60%, it is also possible to employ attenuators
that have a degree of attenuation which is electronically
controllable. Commercial acousto-optic and electro-optic modulators
206 are available, for example.
[0088] In an alternative technique for varying both duration and
light energy provided by a laser microablation system, it is
possible to turn the energy of the laser's pumping system on and
off repeatedly. For example, in the case of a gas laser system
which creates a population inversion by delivering DC or RF
electrical energy through electrodes to a gas, the delivery of DC
or RF electrical energy can be turned on and off repeatedly.
[0089] If the times at which the pumping energy is turned off and
then turned back on are chosen appropriately, it is possible to
operate the laser system at a chosen average optical power output
well below the peak power, e.g., via pulse width modulation. It is
possible, for example, to operate the system between about 1% and
about 100% of peak power, or between about 10% and about 100% of
peak power, with optical power output being chosen as desired.
[0090] The duty cycle applied to the pumping system may vary, for
example, between about 20% and about 80%, or between about 40% and
about 60%. Frequencies up to about 50 kHz are conveniently employed
for turning on and off the pumping system power. FIG. 9 depicts
schematically how one can control optical output power by turning
the pumping system power on and off In that figure we see in dashed
lines the initial transient as depicted in FIG. 8. We also see
above the pumping system power as it is turned on and off. We see
the resulting system optical output power oscillating around a
power level substantially lower than the peak.
[0091] FIG. 10 depicts the use of pumping system power control to
apply initially the normal high power pulse of optical energy which
the laser natively produces, followed by a selected period of
sub-ablation energy. We see that the pumping system energy is
initially turned on and held on so that the normal high power pulse
is produced. After a period of time, the periodic turning on and
off begins so as to produce the period of sub-ablation energy.
[0092] There are various ways to decide when to turn the pumping
power on and off in order to produce a desired optical output
power. With equipment in place for measuring the optical output
power of the system, it would be possible to use a feedback loop in
which, for example, the times of the on-off and off-on transitions
in the pumping system power are varied in order to maintain the
average light power output close to the precise level desired, or
for other control purposes. Any of a wide variety of feedback
control algorithms known to persons of skill in the art may be
employed. Reference may be made, for example, to Gene Franklin et
al., Feedback Control of Dynamic Systems (6th ed. 2009). Control
could be, for example, a simple thermostat-like control in which
power to the pumping system is turned off when instantaneous output
optical power exceeds the desired level plus a percentage, and
turned back on when instantaneous output optical power falls below
the desired level plus a percentage. More complicated feedback
controls in which, for example, the total energy delivered so far
is computed and influences the decision to turn the power to the
pumping system on or off may also be employed.
[0093] One may, alternatively, simply choose empirically the first
turn-off time and the duty cycle to achieve each of a range of
desired optical output powers with the laser in a particular system
or with representative such lasers, and then program those times
and duty cycles into the system's electronics for subsequent use in
the field. Alternatively, one might use a measured transient output
power waveform in response to an energy square wave applied to the
pumping system. This measurement will produce a turn-on transient
waveform and a turn off transient waveform. These waveforms may be
characterized, for example, by time constants. For the turn-off
transient, the time constant might be, for example, the time
required for the waveform to fall to 1/2 of its original value. One
could assume that, with on-off control of the pumping system input,
the transient after the first turn-off will follow the measured
turn-off transient and the transient after the first turn-on will
follow the measured turn-on transient, and so choose a first
turn-off time and duty cycle such that the output power predicted
with the assumption will oscillate around a desired output
power.
[0094] With the use of on-off driving of the pumping system power
as described above, it is possible that there would be substantial
fluctuation in the output power of the laser about the desired
average power. Such fluctuation is generally not problematic in
applications involving tissue ablation, since the thermal time
constant of tissue is approximately 1 ms, and so fluctuations above
approximately 1 kHz do not have a significant thermal effect.
[0095] Nonetheless, if it is desired to reduce fluctuations in the
optical power output when using on-off driving of the pumping
system, one way to achieve this would be to increase the frequency
of the on-off driving waveform, reducing the ripple in the optical
power output.
EXAMPLE
[0096] It is to be understood that the following example of the
present invention is not intended to restrict the present invention
since many more modifications may be made within the scope of the
claims without departing from the spirit thereof.
[0097] A study was conducted that consisted of two research
criteria. The first criterion evaluated different laser energy
doses on 47 consecutive samples of skin. The doses ranged from 5
m.T to 200 mJ. The width and depth of the ablated "column" was
measured as well as the surrounding width and depth of necrosis.
The second criterion compared the effects of doses ranging from 5
mJ to 20 mJ on the arms of selected volunteers. These evaluations
were recorded immediately after the firing of the laser; at one
hour; one day and four days.
[0098] Summary of Results or Findings
[0099] The depth and diameter of the ablated columns correlated in
a linear fashion with the dose. The column depth could be directly
controlled and ranged from 180 to 1378 microns, depending on the
dose level. Despite the wide range of dosing parameters, the column
diameter was tightly confined and only ranged from 34-106 microns
with most of column diameters being in the 50-70 micron range.
Necrosis depth ranged from 27-213 microns. Necrosis width was
extremely confined and ranged only from 19-55 microns.
Histologically, the ablated columns produced by 5 mJ and 10 mJ
pulses reached the mid- to deep-dermis; columns only penetrated to
the fat at the highest dose (200 mJ). On doses of 5, 10, and 20 mJ,
the resultant skin erythema and edema was evident at 1-2 days, but
the mild to moderate erythema faded by the fourth day. There were
no cases of necrosis.
[0100] Conclusions Reached
[0101] Utilizing histologic evaluation, it is a novel carbon
dioxide based microablation device can produce selective digital
injury to dermal collagen using very low energy levels. The
collateral necrosis is very limited. Preliminary clinical
evaluation using low energy doses demonstrates mild to moderate
erythema that fades at four days. These findings will be used to
determine the dosing for future clinical studies.
[0102] Although the particular embodiments shown and described
above will prove to be useful in many applications in the skin
treatment art to which the present invention pertains, further
modifications of the present invention will occur to persons
skilled in the art. All such modifications are deemed to be within
the scope and spirit of the present invention as defined by the
appended claims.
Example 1
[0103] It is to be understood that the following example of the
invention is not intended to restrict or to limit the invention
because many more modifications may be made within the scope of the
claims without departing from the spirit thereof.
[0104] A study was conducted that consisted of two research
criteria. The first criterion evaluated different laser energy
doses on 47 consecutive samples of skin. The doses ranged from 5 mJ
to 200 mJ. The width and depth of the ablated "column" was measured
as well as the surrounding width and depth of necrosis. The second
criterion compared the effects of doses ranging from 5 mJ to 20 mJ
on the arms of selected volunteers. These evaluations were recorded
immediately after the firing of the laser; at one hour; one day and
four days.
[0105] Summary of Results or Findings
[0106] The depth and diameter of the ablated columns correlated in
a linear fashion with the dose. The column depth could be directly
controlled and ranged from 180 to 1378 microns, depending on the
dose level. Despite the wide range of dosing parameters, the column
diameter was tightly confined and only ranged from 34-106 microns
with most of column diameters being in the 50-70 micron range.
Necrosis depth ranged from 27-213 microns. Necrosis width was
extremely confined and ranged only from 19-55 microns.
Histologically, the ablated columns produced by 5 mJ and 10 mJ
pulses reached the mid- to deep-dermis; columns only penetrated to
the fat at the highest dose (200 mJ). On doses of 5, 10, and 20 mJ,
the resultant skin erythema and edema was evident at 1-2 days, but
the mild to moderate erythema faded by the fourth day. There were
no cases of necrosis.
[0107] Conclusions Reached
[0108] Utilizing histologic evaluation, it is a novel carbon
dioxide based microablation device can produce selective digital
injury to dermal collagen using very low energy levels. The
collateral necrosis is very limited. Preliminary clinical
evaluation using low energy doses demonstrates mild to moderate
erythema that fades at four days. These findings will be used to
determine the dosing for future clinical studies.
[0109] Although the particular embodiments shown and described
above will prove to be useful in many applications in the skin
treatment art to which the present invention pertains, further
modifications of the present invention will occur to persons
skilled in the art. All such modifications are deemed to be within
the scope and spirit of the present invention as defined by the
appended claims.
Example 2
[0110] The following descriptions of the invention are provided as
illustrative examples only and are not intended to limit or to
restrict the invention. It is to be understood that the following
examples of the invention are not intended to restrict or to limit
the invention because many more modifications may be made within
the scope of the claims without departing from the spirit
thereof.
[0111] Referring to FIGS. 12A-12F, a demonstration of the "pulse
width modulation" techniques is described and FIGS. 12A-12F provide
graphs illustrating laser output responses to control inputs. By
modulating the control to the laser, one can turn the pumping
system on and off, turning a high power CO2 laser into a low
average power laser. A lab demonstration was constructed with
different pulse train structures to demonstrate different modulated
laser output profiles which may result in a controlled thermal
response. FIG. 12A illustrates a typical output of a high powered
CO2 laser. The upper waveform, identified as #1 in the graph, is
the control input and the lower waveform, identified as # 2 in the
graph, is the laser output. The high power nature of the laser
output to a typical control is shown.
[0112] With this waveform, one would expect the thermal response
depicted in FIG. 1.
[0113] The graph of FIG. 12B shows a typical output of a high
powered CO2 laser with a modulated control resulting in a low
average power output. The upper waveform, labeled #1 in the graph,
is the control input and the lower waveform, labeled #2 in the
graph, is the laser output. The low power nature of the laser
output to this modulated control is shown. With this waveform, one
would expect the thermal response depicted in FIG. 2A.
[0114] FIG. 12C illustrates a graph that shows an output of a high
powered CO2 laser. The upper waveform, labeled #1 in the graph, is
the control input and the lower waveform, labeled #2 in the graph,
is the laser output. This graph shows the variable nature of the
pulse shape due to the control modulation of varying duty cycles
and duration. The high power exposure of the laser output followed
with a low power exposure is shown. With this waveform one would
expect the thermal response depicted in FIG. 2D.
[0115] The graph of FIG. 12D shows the output of a high powered CO2
laser. The upper waveform, labeled #4 in the graph, is the control
input and the lower waveform, labeled #1 is the laser output. In
this example, the variable nature of the pulse shape due to the
control modulation of varying duty cycles and duration is
illustrated. In contrast to FIG. 12C, the low power exposure of the
laser output followed with a high power exposure is shown. With
this waveform one would expect the thermal response depicted in
FIG. 2B.
[0116] FIG. 12E illustrates a graph indicating one of the more
unique outputs of a modulated high powered CO2 laser. The upper
waveform, labeled #4 in the graph, is the control input and the
lower waveform, labeled #1 is the laser output. In this example,
the variable nature of the pulse shape due to the control
modulation of varying duty cycles and duration is shown. The high
power exposure of the laser output is followed with a low power
exposure and followed with another high power exposure. With this
waveform one would expect the thermal response depicted in FIG.
3B.
[0117] The graph of FIG. 12F shows one of the more unique outputs
of a modulated high powered CO2 laser. The upper waveform, labeled
#4 in the graph, is the control input and the lower waveform,
labeled #1 is the laser output. In this example, one can see the
variable nature of the pulse shape due to the control modulation of
varying duty cycles and duration. The high power exposure of the
laser output is followed with a low power exposure and followed
with another high power exposure followed with another low power
exposure. With this waveform one would expect the thermal response
depicted in FIG. 3C.
Example 3
[0118] The following description of the invention is provided as an
illustrative example only and is not intended to limit or to
restrict the invention. It is to be understood that the following
example of the invention is not intended to restrict or to limit
the invention because many more modifications may be made within
the scope of the claims without departing from the spirit
thereof.
[0119] Referring to FIG. 12, an experiment was performed,
demonstrating the effect of pulse duration and peak power on the
tissue response. Three exposures of equal energy, equal spot size,
but differing pulse duration were exposed into a polyacrylide gel,
containing a high concentration of the target water chromophore.
Left is shortest pulse (20 us), middle is a medium pulse (300 us),
and right is longest pulse (1000 us). FIG. 13 demonstrates the
varying depth of ablation and additional lateral thermal damage of
the lower power exposures.
[0120] Conclusions Reached.
[0121] High power exposures translate to deep ablation
capabilities, while low power exposures ablate less and leave more
thermal damage. One may conclude that, if combining low and high
power combinations, one can achieve thermal damage deeper and/or
vary the thermal damage zones for a multitude of depths.
[0122] Referring to FIG. 14, in a further aspect the invention
provides a method 300 for treating tissue using a laser system with
pulsed light output, as described above. The method 300, however,
is exemplary only and not limiting. The method 300 may be altered,
e.g., by having stages added, removed or rearranged.
[0123] At phase 302, the method includes selecting at least two of:
(i) a desired total light output energy, (ii) a desired average
light output power, or (iii) a desired duration of laser
application.
[0124] At phase 304, the method further includes controlling the
laser by the system in order to achieve the selected conditions
(i), (ii), or (iii) specified by the user.
[0125] At phase 306, the method includes directing the light output
of the laser to the tissue to be treated over the desired
duration.
[0126] At stage 308, the method includes varying a control for
power, which produces a population inversion, between on and off
states, such that, a population inversion may be produced when the
control is varied from an off state to an on state.
[0127] It will be appreciated by persons of ordinary skill in the
art that according to some embodiments of the present invention
other applications according to the principles of the present
invention are possible and are in the scope of this application.
While certain features of the invention have been illustrated and
described herein, many modifications, substitutions, changes, and
equivalents will now occur to those of ordinary skill in the art.
It is, therefore, to be understood that the appended claims are
intended to cover all such modifications and changes as fall within
the true spirit of the invention.
[0128] All patents, patent applications, and publications mentioned
herein are hereby incorporated by reference in their entireties.
However, where a patent, patent application, or publication
containing express definitions is incorporated by reference, those
express definitions should be understood to apply to the
incorporated patent, patent application, or publication in which
they are found, and not to the remainder of the text of this
application, in particular the claims of this application.
* * * * *