U.S. patent application number 13/460442 was filed with the patent office on 2012-08-23 for tattoo removal and other dermatological treatments using multi-photon processing.
Invention is credited to Alexander John Smits, Szymon Suckewer.
Application Number | 20120215209 13/460442 |
Document ID | / |
Family ID | 40722386 |
Filed Date | 2012-08-23 |
United States Patent
Application |
20120215209 |
Kind Code |
A1 |
Smits; Alexander John ; et
al. |
August 23, 2012 |
Tattoo Removal and Other Dermatological Treatments using
Multi-Photon Processing
Abstract
A system and method for removing a portion of a tattoo using
multi-photon ablation is described. A localized, multi-photon
processing event is initiated within a vicinity of a pigment in
order to remove it. The multi-photon event requires a relatively
low energy, but very intense, pulse of light. The low amount of
energy per pulse allows ablation of the material to be highly
localized, with negligible thermal damage to surrounding material.
The multi-photon event may be initiated by focusing a suitable
electromagnetic pulse, such as a 2 mJ laser pulse having a pulse
duration of 100-300 femtoseconds, into a focal volume small enough
that the intensity exceeds 10.sup.11 Watts/cm.sup.2. A suitably
configured Ti:Sapphire solid state laser provides such pulses at
1-10 kHz. By repeating the multi-photon event along the location of
a tattoo, the tattoo may be removed with minimal damage to the
surrounding tissue.
Inventors: |
Smits; Alexander John;
(Princeton, NJ) ; Suckewer; Szymon; (Princton,
NJ) |
Family ID: |
40722386 |
Appl. No.: |
13/460442 |
Filed: |
April 30, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12136943 |
Jun 11, 2008 |
8187256 |
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13460442 |
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60944338 |
Jun 15, 2007 |
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60953826 |
Aug 3, 2007 |
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Current U.S.
Class: |
606/9 |
Current CPC
Class: |
A61B 18/203 20130101;
A61B 2017/00769 20130101; A61B 2018/00452 20130101 |
Class at
Publication: |
606/9 |
International
Class: |
A61B 18/20 20060101
A61B018/20 |
Claims
1. A method of removing a portion of a tattoo, comprising: locating
a position of a pigment defining said portion of said tattoo on or
within said patient; and initiating, using a femtosecond laser and
a computer controlled focusing element, a localized, multi-photon
processing event in, or within a vicinity of said pigment.
2. The method of claim 1 wherein initiating said localized,
multi-photon processing event further comprises: providing a pulse
of electromagnetic radiation; and focusing said pulse to a focal
volume such that an intensity of said electromagnetic radiation
within said focal volume exceeds 10.sup.11 W/cm.sup.2.
3. The method of claim 2 wherein said pulse of electromagnetic
radiation has a temporal pulse length in a range from 100 to 300
femtoseconds in duration.
4. The method of claim 3 wherein said pulse of electromagnetic
radiation has an energy that is equal to or less than 2 mJ.
5. The method of claim 3 wherein said pulse of electromagnetic
radiation has a bandwidth that is equal to or greater than 100
GHz.
6. The method of claim 3 further comprising setting said focal
volume of said focused pulse to substantially correspond to a
thickness of said pigment.
7. The method of claim 3 wherein said focal volume is equal to or
less than 500 .mu.m in diameter.
8. The method of claim 1 further comprising repeating initiating
said a localized, multi-photon processing event until said pigment
is removed.
9. The method of claim 2 wherein said pulse of electromagnetic
radiation has a temporal pulse length that is equal to or less than
100 femtoseconds in duration.
10. The method of claim 2 wherein said pulse of electromagnetic
radiation has a temporal pulse length that is equal to or less than
200 picoseconds in duration.
11. The method of claim 2 wherein said pigment is located within a
dermal layer of said patient.
12. The method of claim 11 wherein said locating said position of
said pigment further comprises locating an upper surface of said
patient's epidermis and wherein said focusing further comprises
locating said focal volume in a range of 10 .mu.m to 2000 .mu.m
below said upper surface.
13. The method of claim 12 wherein locating said focal volume
further comprises positioning a lens relative to said upper surface
of said patient's epidermis; and preventing initiation of said
localized, multi-photon processing event unless said lens is
located such that said focal volume will occur in said range of 10
.mu.m to 2000 .mu.m below said upper surface.
14. The method of claim 13 wherein said pigment is an inorganic
heavy metal salt, an inorganic heavy metal oxide, an azo-organic
pigment, or a polycyclic organic pigment.
15. An apparatus for removing a portion of a tattoo, comprising: a
femto-second laser; a pigment locating device for locating a
position of a pigment defining said portion of a tattoo; and a
computer for controlling the emission of a pulse of electromagnetic
radiation by said femto-second laser, and to control a focusing
device, containing at least one lens, so as to initiate a
localized, multi-photon process in or within a vicinity of said
pigment.
16. The apparatus of claim 15 wherein said pulse of electromagnetic
radiation has a temporal pulse length in the range of 100 to 300
femto-seconds in duration, a bandwidth that is equal to or greater
than 100 GHz; said focal volume corresponds substantially to a
thickness of said pigment; and said predetermined threshold is
equal to or greater than 10.sup.11 W/cm.sup.2.
17. The apparatus of claim 15 further comprising a visible light
beam for locating an upper surface of said patient's epidermis;
and, a feedback loop that prevents initiation of said localized,
multi-photon processing event unless said focusing lens is located
such that said focal volume would occur in said range of 10 .mu.m
to 2000 .mu.m below said upper surface.
18. The apparatus of claim 15 further comprising a computer
processor programmed to use a signal from visible light beam to
effect said feedback loop.
Description
CLAIM OF PRIORITY
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/136,943 filed on Jun. 11, 2008 by Smits et
al. titled "Tattoo Removal and other Dermatological Treatment using
Multi-photon processing", the contents of which are hereby
incorporated by reference.
[0002] This application is further related to, and claims priority
from, U.S. Provisional Patent application No. 60/944,388 filed on
Jun. 15, 2007 by Smits et al entitled "Tattoo Removal and other
Dermatological Treatment using Multi-photon processing" and to U.S.
Provisional Patent application No. 60/953,826 filed on Aug. 15,
2007 by Smits et al entitled "Tattoo Removal and other
Dermatological Treatment using Multi-photon processing" the entire
contents of both of which are hereby incorporated by reference.
FIELD OF THE INVENTION
[0003] The present invention relates to systems and methods for
dermatological treatment using multi-photon processing, and more
particularly to systems and methods for tattoo or blemish removal
using low energy (.about.2 mJ per pulse) focused, femtosecond
(fsec) laser light pulses.
BACKGROUND OF THE INVENTION
[0004] Tattooing is a well-known and wide spread practice of
marking or decorating human skin that is accomplished by injecting
colored pigment into small deep holes made in the skin. Tattoos may
have a wide range of colors and are relatively permanent. At
estimated 25 million people in the United States have at least one
such permanent tattoo, and with the current popularity of "body
art", estimates are that over 250,000 women are being tattooed each
year. The average age of people procuring a tattoo is approximately
18 years. These tattoos acquired in youth often become an
embarrassment in later life as tattoos are generally not well
received by the public and often create a barrier to employment or
social acceptance. There is, therefore, a significant demand for
the removal of tattoos.
[0005] Tattoo removal, however, is not easily accomplished. In
tattooing, pigments are injected into the dermis. This is the layer
of skin that lies immediately beneath the approximately one mm
thick epidermis, which is the dead, external surface layer of the
skin. The injected pigments initially tend to aggregate in the
upper dermis, close to the epidermis. Physical removal of tattoos,
therefore, requires abrading away the entire epidermis immediately
above the tattoo pigment. This may be a painful process and may
leave the subject with significant scarring. Over time, the tattoo
pigments may become encapsulated in fibroblasts and migrate deeper
into the dermis so that older tattoos, while a little duller, are
even more difficult to remove by abrasion.
[0006] With the advent of high power lasers, an alternative,
non-abrading method of removing tattoos that relies on thermal
photo-ablation has become possible. In tattoo removal based on
thermal photo-ablation, the laser wavelength is chosen so that the
tattoo pigment absorbs the laser light more readily than the
surrounding skin does. The laser pulses are then made powerful
enough so that the pigment heats up sufficiently to thermally
photo-ablate, i.e., to dissociate into small fragments. These
fragments are typically no longer colored and may be also
transported out of the dermis by macrophages or diffusion.
[0007] Tattoo pigments, however, cover a range of colors, including
black, white, blue, red, green, and others. Dark blue-black amateur
and professional tattoos usually contain amorphous carbon,
graphite, India ink, and organo-metallic dyes. There is, therefore,
no one laser most suitable for tattoo removal by thermal
photo-ablation. Tattoo removal is, therefore, currently
accomplished using a variety of lasers to induce thermal
photo-ablation including, but not limited to, Q-switched Nd:Yag
lasers typically operating at 1064 nanometer (nm) or 532 nm, with
5-20 nanosecond (nsec) pulse duration, Q-switched Alexandrite
lasers typically operating at 755 nm, with 100 nsec pulse duration,
and Q-switched Ruby lasers typically operating at 694 nm, with
20-40 nsec pulse duration.
[0008] All these lasers, collectively known as nano-second type
lasers, may be employed in a similar manner to remove tattoos.
Typically, a cream to numb the skin is applied to the patient prior
to the treatment to reduce the level of pain felt during the
treatment. Short pulses of the laser light, typically of the order
of 5 to 100 nsec, are then directed through the surface of the
subject's skin and are absorbed by the tattoo pigment. The light
breaks the pigment into particles by thermal photo-ablation. The
particles are small enough to be absorbed by the body.
[0009] The principal sources of trauma in the nsec laser treatment
of tattoos are the heating of the skin, which causes damage similar
to a second-degree burn, and the formation of highly localized
shock waves in the dermis that cause undesirable tissue damage.
After the treatment, the body's scavenger cells remove the
particles of pigment from the treated pigmented areas. The skin and
tissue damage then heals over the next several weeks. More then one
treatment is usually necessary to remove the entire tattoo. Some
scarring or color variations are likely to remain. Healing time
varies depending upon the size and depth of the tattoo, the
procedure used and the patient's healing process.
[0010] All the current laser procedures for tattoo removal are
painful, expensive, rarely 100% effective, may leave permanent
scarring and typically require multiple treatments spread over a
period of time.
[0011] What is needed is a tattoo removal system and method that is
more effective than the existing methods, does not leave permanent
scarring and is preferably not painful and can be accomplished in a
single treatment.
SUMMARY OF THE INVENTION
[0012] Briefly described, the present invention provides a system
and method for providing multi-photon processing treatment to a
patient.
[0013] In a preferred embodiment of the invention, a location of a
pigment on or within the patient is determined. The pigment may,
for instance, be a tattoo pigment of an unwanted tattoo, or it may
be some the pigment of a blemish or a pigment associated with some
unwanted growth such as, but not limited to, a carcinoma or a wart.
A localized, multi-photon processing event is then initiated within
a vicinity of the unwanted pigment in order to remove the
pigment.
[0014] A localized, multi-photon processing event is an event in
which a large number of photons--at least 5-10, and typically 100
or more--are absorbed simultaneously by a molecule or material.
Such multi-photon processing events require very intense light,
i.e., many photons in a small volume at the same time. Multi-photon
processing events, however, do not necessary require much energy
per pulse. The multi-photon processing events may result in the
dissociation of the absorbing molecule or material. This
photo-ablation, however, differs from thermal photo-ablation in
that the low amount of energy per pulse involved allows the process
to be very localized, and may result in no or negligible thermal
heating or shocking of any surrounding material. A localized,
multi-photon event may, for instance, be initiated by focusing
suitable pulses of electromagnetic radiation. For instance, by
focusing a 2 mJ pulse of laser light that has a temporal pulse
length in the range from 100 to 300 femtoseconds in duration to a
small enough focal volume that the intensity is equal to or greater
than 10.sup.11 Watts/cm.sup.2, a multi-photon processing event may
be initiated. Such pulses may be obtained from, for instance, a
suitably configured Titanium doped Sapphire (Ti:Sapphire) solid
state laser.
[0015] By using a high-repetition rate femtosecond laser, and
repeating the localized, multi-photon processing event initializing
along the location of the pigment in, for instance, a tattoo, the
entire tattoo may be removed with little or no damage to the
surrounding tissue. This process may be accomplished manually, or
under the guidance of a computer, or through a combination
thereof.
[0016] These and other features of the invention will be more fully
understood by references to the following drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic drawing of an exemplary apparatus of
the present invention for providing multi-photon processing
treatment.
[0018] FIG. 2 is a cross-sectional drawing of an exemplary delivery
wand of the present invention for providing multi-photon processing
treatment.
DETAILED DESCRIPTION
[0019] The present invention relates to systems and methods for
dermatological treatment using multi-photon processing events. In
particular, the present invention is directed to systems and
methods for tattoo or blemish removal using low power (.about.2 mJ
per pulse) focused, femtosecond laser light pulses to initiate
multi-photon processing events.
[0020] As described above, the laser light currently used in
procedures for tattoo removal typically interacts with the pigments
in the skin through a thermal photo-ablation process (also called a
thermal ablation process). This thermal photo-ablation process
occurs when the laser pulses have a relatively high energy but a
low intensity. As each pulse has a low density of photons, only
single photons are absorbed in any given absorption event. Each
absorption event supplies some heat to the pigment. By having
enough of these absorption events occur before the heat can be
dissipated, the pigment material may be heated to a high enough
temperature that the pigment undergoes thermal photo-ablation,
i.e., the pigment dissociates into particles small enough to be
absorbed by the body. After the thermal photo-dissociation of the
pigment, the accumulated heat diffuses out of the focal region,
causing undesirable heating, and possibly burning, of the
surrounding skin. The diffusing heat may, for instance, cause
trauma similar to a second-degree burn in the vicinity of the
treatment. In addition, the small volume of rapidly heated material
may also expand rapidly, generating highly localized shock waves in
the dermis that may also cause undesirable tissue damage.
[0021] When the intensity of the laser pulses is greatly increased,
however, the photo-ablation of materials changes to what is called
a "multi-photon" process. This is not a thermal process. In a very
high-intensity laser pulse, the density of photons is so great that
during a single absorption event, many photons are absorbed
simultaneously. The number of photons absorbed simultaneously by
the material in multi-photon ablation may be 10-100 photons or more
per molecule or atom (per few molecules or few atoms). The density
of photons in a pulse is so high that the number of photons
absorbed simultaneously is very large, hence photo-ablation may
occur even though the energy of the pulse is 2 mJ or less. This
amount of energy is sufficiently low that little or no damaging
thermal heating of the surrounding tissue occurs as the energy
diffuses out. This is in marked contrast to thermal ablation with
low-intensity pulsed lasers where only a single photon is absorbed
in any given absorption event, and the pulse energy necessary for
photo-ablation is sufficiently high that damaging heating of the
surrounding tissue occurs as the heat diffuse out.
[0022] "Few photon processes", i.e., processes that involve not
more than 3 photons in a single absorption event, also tend to
result in thermal ablation, even though few-photon processes are
sometimes inaccurately labeled "multi-photon processes" in some
literature.
[0023] For a multi-photon process, or multi-photon photo-ablation,
to be useful for treating skin discolorations and tattoos, the
intensity of the laser pulses needs to be sufficiently high. At the
same time, the energy content of each pulse needs to be
sufficiently low to avoid undesirable heating and shock wave
effects. One way to simultaneously achieve both the high intensity
and low energy is by using ultra-short laser pulses. In laser
physics, ultra-short pulses are typically defined to be pulses up
to 10 psec in duration, although some time pulses as long as 200
psec are termed ultra-short. For effective multi-photon processing,
a pulse duration in the range of 100 to 300 fsec is preferred,
where 1 fsec is equal to 10.sup.-15 sec. These ultra-short pulses
are significantly shorter than those produced by n-sec type lasers.
For instance, a 10 nsec laser pulse is 100,000 times longer than a
100 fsec laser pulse.
[0024] In addition to avoiding the heating of surrounding tissue,
the multi-photon ablation process is practically independent of the
pigment color as the process does not depend on differential
absorption by the pigment. Using multi-photon processing to remove
pigment from the skin does not, therefore, require using different
laser wavelengths for different pigments. This is in sharp contrast
to thermal photo-ablation processes where the wavelength needs to
be chosen carefully to maximize the interaction with the specific
pigment, or pigments, used in the tattoo, while allowing for
sufficient dermal penetration to reach the pigment and at the same
time avoiding absorption in the natural skin pigment, the
melanin.
[0025] In multi-photon ablation, the ablation rate for any
pigmented material at a given spot is typically only a function of
the number of laser pulses, i.e., the total energy, and does not,
typically, depend on the wavelength of the pulse.
[0026] Moreover, the multi-photon process of this invention is
readily directed below the skin with sufficient intensity and is
independent of the laser wavelength, in contrast with current
methods that use thermal photo-ablation.
[0027] Furthermore, in the present invention, high intensities on
target are easily achieved. As the laser wavelengths typically used
to initiate multi-photon processing events are in the infra-red,
they can penetrate deep into the dermis. The necessary high
intensities on target may therefore be accomplished by using, for
instance, a short focal length lens to focus the laser directly on
the pigment below the skin. In addition, the focal volume can be
made very small and typically less than 50 .mu.m in diameter and
depth. By adjusting the laser power and pulse duration, the
intensity within the focal volume can be made to exceed the
threshold intensity necessary for multi-photon processing while the
intensity near the skin surface may be kept too low for
multi-photon processing to occur. In this way, the pigment may be
multi-photon ablated while the surface of the skin is
undamaged.
[0028] A preferred embodiment of the invention will now be
described in detail by reference to the accompanying drawings in
which, as far as possible, like elements are designated by like
numbers.
[0029] Although every reasonable attempt is made in the
accompanying drawings to represent the various elements of the
embodiments in relative scale, it is not always possible to do so
with the limitations of two-dimensional paper. Accordingly, in
order to properly represent the relationships of various features
among each other in the depicted embodiments and to properly
demonstrate the invention in a reasonably simplified fashion, it is
necessary at times to deviate from absolute scale in the attached
drawings. However, one of ordinary skill in the art would fully
appreciate and acknowledge any such scale deviations as not
limiting the enablement of the disclosed embodiments.
[0030] FIG. 1 is a schematic drawing of an exemplary apparatus of
the present invention for providing multi-photon processing
treatment. The multi-photon processing treatment apparatus 10 may
include a femtosecond laser 12, a fiber optic 14, a delivery optic
16, a delivery wand 15, a positioning unit 23, a control computer
22 having a viewing monitor 24 and an input device 26, a guidance
light source 28, a mixing optic 30, a telescope 32 and a camera 34.
The input device 26 may, for instance, be a keyboard, a touch
screen, a mouse, a tablet or any other suitable computer input
device.
[0031] The femtosecond laser 12, for instance, may be a suitably
configured Titanium doped sapphire (Ti:Sapphire) solid state laser
as supplied by, for instance, Del Mar Photonics of Del Mar, Calif.
Such a laser may be configured to be a tunable laser operating over
a broad range of near infra-red wavelengths centered at 800 nm, and
emitting femtosecond pulses 13 having pulses with a temporal
duration in the range of 100 to 300 femtoseconds, a pulse energy of
0.5-2 mJ per pulse and a repetition rate of 1-10 kHz. As one
skilled in the art will realize, such a laser may be operated to
reasonable effect with pulses as long as 200 psec in duration. A
200 psec pulse would, however, require significantly higher energy
per pulse than for 100 fsec pulses. Pulses that are shorter than
200 psec are typically better for initiating multi-photon
processing events, and pulses in the range 100 to 300 femtoseconds
are preferred. For such ultra-short, high repetition rate pulse
lasers with pulse durations in the range 100 fsec up to 10 psec,
the total procedure time for treating a 1 cm.sup.2 tattoo is
expected to take only several minutes.
[0032] The femtosecond laser 12 may also or instead be a suitably
configured laser made using Cr doped Forsterite, or Er- and
Yb-doped fibers, or some combination thereof.
[0033] The femtosecond pulses 13 may be transmitted to the area of
interest 18 on the patient 20 via a delivery optic 16, a fiber
optic 14 and a delivery wand 15. The delivery optic 16 0001 may,
for instance, be a flat or focusing mirror used to direct the
femtosecond pulses 13 into the fiber optic 14. The fiber optic 14
may, for instance, be any glass or plastic fiber having the
requisite transparency to the femtosecond pulses 13. The fiber
optic 14 may be used to transport the femtosecond pulses 13 to the
delivery wand 15. The delivery wand 15 may be operated by hand, or
may be supported by a positioning unit 23 that may be under the
control of a control computer 22.
[0034] The delivery wand 15 may also deliver a guidance light beam
29. The mixing optic 30 may assist in delivering the guidance light
beam 29 to the fiber optic 14 or the delivery wand 15. The mixing
optic 30 may, for instance, be a suitable multilayer mirror that
reflects the guidance light beam 29 but is transparent to the
femtosecond pulses 13. The guidance light beam 29 may, for
instance, be from a Helium Neon laser, although any other laser
with an output in the visible spectrum would be suitable. The
guidance light source 28 may include a detector for monitoring how
much of the guidance light beam 29 is reflected back from the
surface of the patient 20. In this way a feed-back loop may be
established to monitor the distance between a focusing tip of the
delivery wand 15 and the patient 20.
[0035] FIG. 2 is a cross-sectional drawing of an exemplary delivery
wand 15 of the present invention for providing multi-photon
processing treatment. The delivery wand 15 may include a short
focal length lens 38, one or more micro-positioning elements 44 and
a fiber optic 14. The fiber optic 14 may deliver the femtosecond
pulses 13 and the guidance light beam 29 to the short focal length
lens 38. The short focal length lens 38 focuses the femtosecond
pulses 13 to a focal volume 40 that is positioned beneath a surface
of the patent 42 in the vicinity of the pigmented layer 46. The
pigmented layer 46 is typically located about 1 to 2 mm beneath the
surface of the patent 42.
[0036] The focal volume 40 may be 500 .mu.m in diameter or smaller.
In a preferred embodiment, the focal volume 40 may be made
substantially equal to the thickness of the pigmented layer 46 that
may be as small as 5 .mu.m.
[0037] The power density in the focal volume 40 typically needs to
be in the range of 10.sup.12-10.sup.13 W/cm.sup.2 in order to
initiate a multi-photon processing event. With very long wavelength
lasers such as, but not limited to, the 10 .mu.m wavelength
CO.sub.2 laser, multi-photon processing events may be initiated
when the power density in the focal volume 40 is in the range of
10'' Watts/cm.sup.2.
[0038] The delivery wand 15 may also deliver a guidance light beam
29 that may be a Helium Neon laser beam or some other suitable
visible light laser. A portion of the guidance light beam 29 may be
reflected off the surface of the patent 42 and back up the delivery
wand 15. This reflected portion of the guidance light beam 29 may
be detected by, for instance, a suitably located photo-diode. The
reflected portion of the guidance light beam 29 may then be used as
a feedback loop and used to control the location of the focal
volume 40 relative to the surface of the patent 42 using the
micro-positioning elements 44. The micro-positioning elements 44
may, for instance, be piezoelectric devices, or they may be MEMS
actuated devices or they may be micro-mechanical devices controlled
by, for instance, electric motors.
EXAMPLES OF USE OF THE INVENTION
Example 1
[0039] The use of multi-photon processing to remove tattoos has
been demonstrated using a pulsed Ti:Sapphire laser with a pulse
duration of approximately 100 fsec. A frozen pig foot obtained from
a butcher was thawed and a three color tattoo was laid down on the
skin (K & B Tattooing and Piercing, Hightstown, N.J.). The
colors were red, green, and black, and the tattoo measured
approximately 5 cm by 3 cm. Pig skin was chosen for the experiments
because it is anatomically and physiologically very similar to
human skin as detailed in, for instance, the article published by
Sullivan et al entitled "The pig as a model for human wound
healing", Wound Repair Regen. (2):66-76, 2001, the contents of
which are hereby incorporated by reference. This 100 fsec, 1 mJ per
pulse laser operating at 10 Hz repetition rate was focused at a
point about 100 to 200 .mu.m below the surface of the skin. A patch
of green dye was then treated. Similar results were obtained on red
dye and black dye, demonstrating that this particular broadband
laser was effective on all dyes tested here.
Example 2
[0040] The use of multi-photon processing to remove tattoos has
also been demonstrated using pulsed Ti:Sapphire laser with a pulse
duration of about 10 psec. A frozen pig foot obtained from a
butcher was thawed and a six color tattoo was laid down on the skin
(K & B Tattooing and Piercing, Hightstown, N.J.). The colors
were red, green, blue, orange, yellow and black, and the tattoo
measured approximately 5 cm by 3 cm. The laser had -10 mJ of energy
per pulse and was run at a 10 Hz repetition rate. The laser was
focused at a point about 100 to 200 .mu.m below the surface of the
skin. A section containing all colors of the tattoo was then
treated. The eradication of all dyes using this 10 psec laser was
clearly evident, although not as good as with 100 fsec laser.
Example 3
[0041] The multi-photon processing to remove tattoos was contrasted
with photo-thermal ablation removal of tattoos by using a nsec-type
laser with a pulse duration of about 10 nsec to remove a different
section of the same tattoo described in Example 2. The 5 nsec, 200
mJ/pulse Nd:YAG laser was focused at a point about 100 to 200 .mu.m
below the surface of the skin. The eradication of the some of the
dyes was clearly evident, but some dyes were not removed because
the wavelength of the laser (1.064 .mu.m) was not a good match to
the dye. Importantly, when enough laser energy was used to remove
the tattoo, the heating of the skin was intense and the skin damage
was severe, and sections of the skin were severely burnt. The
contrast with the treatments using ultra-short laser pulses
(Examples 1 and 2) was dramatic.
[0042] The multi-photon processing system and method of the present
invention, described and demonstrated above, permits the fast and
complete removal of tattoo pigments in the skin and other skin
discolorations with virtually no pain or scar formation using
multi-photon processing. The multi-photon processing system and
method also permits dermatological procedures, including cosmetic
procedures such as, but not limited to, the removal of blemishes,
liver spots, warts, acne, basal-cell-carcinoma, cutaneous T-cell
lymphoma or eczema, the treatment and mitigation of facial
scarring, and can be used in the processes of exfoliation and
dermabrasion. The effectiveness of the multi-photon photo-ablation
procedure is virtually independent of the laser wavelength.
Therefore the particular wavelength and bandwidth of the laser
pulses used may cover a very wide range. The wavelength may range
from 0.2 .mu.m to 10 .mu.m, but it can be as short as 0.11 .mu.m
and as long as 100 .mu.m, but is preferably in the range from 0.25
.mu.m to 1.06 .mu.m. The bandwidth can range from 10 GHz to 10 THz
(where 1 GHz is 10.sup.9 Hz, and 1 THz is 10.sup.12 Hz), but it can
be as small as 1 GHz and as large as 100 THz.
[0043] A clinical use of the multi-photon processing system and
method may proceed as follows. In a preliminary examination, a
tattoo may first be evaluated in terms of the extent of the
affected region, the depth of the dye layer, and the types of dyes
used in the tattoo. Other factors, such as the natural skin color
surrounding the tattoo, the age of the patient, the quality of
natural wound healing, and other factors including the patient's
general health may be noted. If it is decided to proceed with the
tattoo removal, the area where the tattoo is located may be held
firmly and securely in a comfortable position. A precise map of the
tattoo may then be created from a white light image of the tattoo
obtained by, for instance, a camera 34 that may be a Charge Coupled
Device (CCD) camera, and the imaging telescope 32 operating under
the control of the control computer 22. Using image processing
techniques, details of the physical location of the tattoo pigments
may be obtained, including the depth of the pigmented layers. Using
these parameters, a patient-specific procedure may be devised for
the tattoo removal using a suitable software program. This
computer-generated procedure may include calculating the necessary
laser parameters such as, but not limited to, the power per shot,
the number of shots, the repetition rate, the positioning and the
focusing requirements of the laser beam, the shot pattern and the
specific instructions for the laser positioning system.
[0044] In a manual treatment, the operator may choose the laser
parameters from the recommendations given in the computer-generated
procedure. The operator may then apply the laser pulses to the area
of area of interest 18 being treated using the specially designed
delivery wand 15. Progress may be monitored either by direct visual
inspection, or by the use of a camera 34 that may connected to a
viewing monitor 24 by means of the control computer 22.
[0045] In a computer-controlled treatment, the delivery wand 15 may
be directed to the area by a laser positioning system that may be
part of the positioning unit 23. The operator may monitor progress
either by direct visual inspection or by the use of the camera 34
connected to the viewing monitor 24. The camera may also be used in
all treatments, manual or computer-controlled to obtain and store
still or video images to record the progress of the removal
procedure. As multi-photon processing uses ultra-short pulsed
lasers, where ultra-short pulses are pulses up to 10 psec in
duration, and in some cases up to 200 psec in duration, although
the preferred pulse duration for such processing is in the range of
100 to 300 fsec, for which the beam energy may be in range of 0.5-2
mJ per pulse with laser repetition rate of around 1-10 kHz. For
such ultra-short, high repetition rate pulse lasers with pulse
durations in the range 100-300 fsec, the total procedure time for
treating a 1 cm.sup.2 tattoo is expected to take only several
minutes.
[0046] The laser pulses are transmitted to the area of interest 18
to be treated by a delivery wand 15 that is typically connected to
the femtosecond laser 12 using fiber optics. The delivery wand 15
may be operated manually or via the control computer 22 using a
computer-controlled positioning system. The delivery wand 15 may
house a short focal length lens 38 to focus the laser pulses below
the skin at the depth of the pigmented layer 46 comprising the
tattoo. The wand may also output a second laser beam that is a
guidance light beam 29. The guidance light beam 29 may, for
instance be a helium-neon laser although any other laser with an
output in the visible spectrum would be suitable. The second laser
beam provides a signal that can be used to monitor the distance
between the delivery wand 15 and the surface of the skin 42. The
guidance light beam 29 may also be used to infer the distance from
the short focal length lens 38 to the pigmented layer 46 containing
the tattoo. This signal may be used to generate a feedback control
output that will shut off the femtosecond laser pulses 13 when one
or both of these distances exceed some minimum and maximum limits.
For instance, the femtosecond pulses 13 may be blocked by, for
instance the delivery optic 16 if the distance from a front surface
of the short focal length lens 38 to the pigmented layer 46 is, for
instance, greater than 2 mm, or is outside a range of 0.5 to 2.5
mm. These limits are set to prevent undesirable interactions of the
laser with tissue outside the pigmented layers comprising the
tattoo, and also to ensure operator safety. The second laser beam
can also be used to illuminate the area of interest 18 being
treated, although other light sources may be used instead of or in
addition to the laser illumination.
[0047] Alternatively, the distance from the operating tip of the
delivery wand 15 to the pigmented layer 46 comprising the tattoo
may be set by an optically transparent spacer sheet.
[0048] In a further embodiment of the invention, the thickness of
this optically transparent spacer sheet may be set by prior visual
or computer inspection of the tattoo. The spacer sheet may be
positioned on the skin surface over the area to be treated, and the
wand may then move over the area to be treated while maintaining
contact with the spacer sheet.
[0049] The treated area may be evaluated after one round of laser
ablation. A further treatment may be advised, either immediately
following the first treatment, or after one or more days. Based on
experiments 1 and 2 described above, it is expected that most
individuals may only need a single treatment.
[0050] Although the invention has been described in language
specific to structural features and/or methodological acts, it is
to be understood that the invention defined in the appended claims
is not necessarily limited to the specific features or acts
described. Rather, the specific features and acts are disclosed as
exemplary forms of implementing the claimed invention.
[0051] Modifications may readily be devised by those ordinarily
skilled in the art without departing from the spirit or the scope
of the present invention.
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