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Medical
Lasers
Since their development in
1960, lasers have become powerful and indispensible
tools, used in almost every aspect of technology.
Laser applications in medicine and surgery have
similarly evolved, and while medical lasers have never
become the "magic ray" that some had hoped,
they have become powerful and indispensible tools in
clinical practice as well.
There are many medical laser systems
available today, but they all use the principal of
selective photothermolysis , which means getting the
right amount of the right wavelength of laser energy
to the right tissue to damage or destroy only that
tissue, and nothing else .
*
The right wavelength: Most medical laser devices
deliver only one wavelength of laser light, and the
laser surgeon must choose the right wavelength for the
specific tissue involved. Some lasers can be "frequency
doubled", and can deliver two wavelengths of
laser light, and a very few are tuneable over a narrow
range of wavelengths. Some lasers can be used in
different modes, for example, Q-Switched and
long-pulse.
* The
right amount of laser energy : Almost all medical
lasers allow the laser surgeon to adjust the power
setting and duration of the laser pulse. As a general
rule, the length of the laser pulse is as important as
the wavelength or the power setting in determining its
medical use. Lasers can operated in continuous wave
(CW) or pulsed mode. CW lasers emit a steady beam for
as long as the laser medium is excited. If this steady
beam is held on tissue longer than the thermal
relaxation time , excessive heat will be conducted
into normal tissue, which may delay healing and
increase scarring. All CW lasers may be pulsed, either
mechanically using a shutter, or by electronic or
photonic means. Pulsed lasers emit light in individual
pulses, which may be long-pulsed (thousandths of a
second) or short-pulse (millionths of a second).
Q-Switching allows the laser to store energy between
pulses, enabling very high power output.
* Getting
the laser energy there: The laser surgeon uses a "
delivery device" to get the laser energy to the
tissue. These devices include special fiberoptic
cables with handpieces, or articulated arms, in which
specially reflecting mirrors are mounted in tubes
which rotate about the axis of the mirrors. The laser
light is reflected from mirror to mirror through the
tube out to the patient. Special devices may be
attached to the handpieces of either fiberoptic cables
or articulated arms, including slit lamps for use on
the eye, operating microscopes for use in the ear and
throat, insulated fibers for use with endoscopes in
gastrointestinal and bronchial surgery, and Scanners,
which scan the laser beam in a preset pattern and
limit the time a CW laser beam dwells on the target
tissue.
Presented below is an overview of
medical lasers currently in general use. Certain
lasers are only used for very specific conditions.
Some conditions can be treated many ways, including by
several different lasers, as well as by non-laser
methods. Medical Lasers are not magic-they are only
tools, and one should always select the right tool for
the right job!
CO2 Laser:
Often referred to as the "Surgical Laser",
the action of the CO2 laser most resembles traditional
surgery. Unlike any other medical laser, its action on
tissue is directly visible as it's used. The CO2 Laser
was the first laser widely used by surgeons, and is
still the most used of all the medical lasers.
Strongly absorbed by water, which constitutes over 80%
of soft tissue, the CO2 laser emits continuous wave
(CW) or pulsed far infrared light at 10,600 nanometers
(nm), which can be focused into a thin beam and used
to cut like a scalpel, or defocused to vaporize,
ablate, or shave soft tissue. The CO2 Laser may be
operated in pulsed mode or used with scanning devices
to precisely control the depth and area of ablation.
Uses include:
Removal of benign
skin lesion, such as moles, warts, keratoses
As a
"laser scalpel" in patients or body areas
prone to bleeding
"No-Touch" removal of
tumors, especially of the brain and spinal cord.
Laser surgery for snoring
Shaving, dermabrading,
and resurfacing scars, rhinophyma, skin irregularities
Cosmetic Laser Resurfacing for Wrinkles
Argon Laser: One
of the first lasers to be used clinically , the Argon
(or argon-ion) laser is a continuous wave (CW) gas
laser that emits blue-green light at 488 and 514 nm.
Argon laser light is strongly absorbed by hemoglobin
and melanin. Although the beam may be mechanically
pulsed, there's significant non-selective heating in
surrounding tissues, thus increasing the chance of
scar formation. Delivery is through a fiberoptic cable
to a handpiece, slit lamp, or operating microscopye.
Uses include:
retinal and inner ear
surgery
treatment of thick or nodular port wine
birthmarks
facial spider veins
small dark
moles (junctional nevi)
cherry hemangioma
YAG Lasers: YAG
lasers use a Y ttrium-A luminum-G arnet crystal rod as
the lasing medium. Dispersed in the YAG rod are atoms
of rare earth elements, such as neodymium ( Nd),
Erbium ( Er ) or Holmium (Ho ), which are responsible
for the different properties of each laser. All YAG
lasers may be operated in continuous,/pulsed, or
Q-Switched mode, although a particular medical device
is usually only capable of one or the other.
Continuous and pulsed delivery is through fiberoptic
cables, either bare-fiber or through handpiece or
scanners, and Q-Switched delivery, because of the very
high power, is through an articulated arm.
* Nd:YAG Laser:
A true workhorse, the Nd:YAG emits a near-infrared
invisible light at 1064nm or 1320nm. It may be
delivered in CW or "long pulsed"
(millisecond domain) mode through a fiber to a
sapphire tip to cut tissue, or because of its deep
penetration, used to directly coagulate tissue. The
Q-Switched Nd:YAG is effective for black tattoo ink ,
and has been used with fair results for hair removal.
Millisecond-range Nd:YAG laser light is very effective
for long-term hair removal.
* KTP Laser:
When Nd:YAG laser light at 1064 nm is passed through a
potassium-titanyl-phosphate ( KTP) crystal, the
wavelength is halved to 532 nm, a brilliant green
light used in CW mode to cut tissue, in pulsed mode
for vascular lesions including facial and leg veins,
and in Q-Switched mode for red/orange tattoo pigment.
Delivery is through an insulated fiber, fiber
handpiece, scanner, or microscope for CW/pulsed mode,
and articulating arm for Q-Switched mode.
* Er:YAG Laser: Often referred to as
the "Erbium" laser, it emits a mid-infrared
beam at 2940 nm, which coincides with the absorption
peak for water. Its principal use is to ablate tissue
for cosmetic laser resurfacing for wrinkles. The
Erbium laser has been advertised to offer advantages
of reduced redness, decreased side effects and rapid
healing compared to the pulsed or scanned CO2 laser,
but does so by its limited penetration into tissue,
which limits the results compared to the more
versatile CO2 laser. It has also been used as a dental
drill substitute to prepare cavities for filling.
* Ho:YAG Laser: Relatively new to
the medical/dental fields, the Ho:YAG laser emits a
mid-infrared beam at 2070 nm. It's principal use is to
precisely ablate bone and cartilage, with many
applications in orthopedics for arthroscopy, urology
for lithotripsy (removal of kidney stones), ENT for
endoscopic sinus surgery, and spine surgery for
endoscopic disc removal. The Ho:YAG laser was recently
approved for TURP (prostate removal).
Ruby Laser: The
Ruby laser emits red light with a wavelength of 694
nm. The lasing medium is a synthetic ruby crystal of
aluminum oxide and chromium atoms, which is excited by
flashlamps. The first laser system to be built by T.
H. Maiman in 1960, early ruby laser systems were used
for retinal surgery, but weren't suitable for
dermatologic work until the development of Q-Switching
technology in the mid 1980's. Ruby laser light is
strongly absorbed by blue and black pigment, and by
melanin in skin and hair. Modern ruby laser systems
are available in Q-Switched mode, with an articulating
arm, "free running" (millisecond range) mode
with a fiber optic cable delivery, or as dual mode
lasers. Current uses include:
Treatment of tattoos
(Q-Switched mode)
Treatment of pigmented lesions
including freckles, liver spots, Nevus of Ota,
cafe-au-lait spots (Q-Switched mode)
Laser Hair
Removal (free-running mode)
Alexandrite Laser:
Similar to the Ruby Laser, the Alexandrite
Laser contains a rod of synthetic chrysoberyl, a
gemstone discovered in Russia in 1830 on Czar
Alexander II's 13th birthday. It emits a deep red
light at 755 nm, and has properties similar to the
ruby laser. It's slightly longer wavelength permits
slightly deeper penetration into skin, with slightly
less absorption by melanin. Prinicipal uses include
laser hair removal in millisecond-range pulsed mode,
and tattoo removal in Q-Switched mode.
Pulsed Dye Laser: Because
the yellow light at 577-585 nm coincides with the peak
absorption of hemoglobin in blood, the Pulsed Dye
Laser (PDL) is useful to treat vascular lesions. A
lasing medium of rhodamine dye is excited by
flashlamps, emitting a pulse in the range of 450
microseconds (1500 microseconds in some of the newer
PDL's), just less than the thermal relaxation time of
minute blood vessels. Originally developed in the late
1980's, the Pulsed Dye Laser became the preferred
laser for the treatment of vascular lesions, including
spider veins, strawberry birthmarks and port wine
stains, replacing the Argon Laser because of the PDL's
decreased heat damage and decreased chance of
scarring. However, the PDL's short pulse and high
absorption ruptures the targeted blood vessels,
causing unsightly purpura (black and blue marks) which
can last up to 2 weeks. Currently, less expensive,
more reliable green light lasers such as the KTP and
other Frequency doubled Nd:YAG are used for most
vascular lesions. The Pulsed Dye Laser remains the
treatment of choice for:
Port Wine Stains,
especially in infants and children
Laser
treatment of thick, red scars
Copper Vapor Laser:
Vaporized copper bromide is the lasing medium in the
Copper Vapor Laser (CVL) , which emits yellow light at
577 nm and green light at 511 nm, delivered through a
fiberoptic cable. Unlike the PDL, there is no purpura
because of the longer pulse duration. However, a long
warm up time and short laser cavity life make the CVL
a less popular choice than the PDL for vascular
lesions .
Diode Lasers:
Diode lasers are solid state devices similar in
construction to LED's. The familiar "laser
pointers" are in fact diode lasers. Diode lasers
used clinically emit near-infrared light in the
800-900 nm range. Currently their prinicipal
application is in millisecond-range pulsed mode for
laser hair removal, and for periodontal surgery. Other
applications include treatment of leg and facial
veins. Diode bars are also used to excite or "pump"
more traditional laser media, for example YAG rods.
Because of their relative simplicity and low
maintenance requirements, Diode lasers and
diode-pumped solid state lasers will be used more in
the near future as more wavelengths become available.
Excimer Lasers:
Noble gas:Halide, or Excimer Lasers, emit invisible
ultraviolet (UV) light that triggers a photochemical
reaction on the target tissue. This very short
wavelength is capable of high resolution and
microscopic surgery-note the letters etched into the
human hair at right. The most common medical
application is the Argon:Fluorine (Ar:F) laser at 193
nm, used for PRK and LASIK (Laser in-situ
Keratomilieusis) vision correction. The laser beam is
delivered through an operating microscope integrated
with the the laser housing and operating table.
Excimer laser radiation shows great promise for
cardiac revascularization and lithotripsy, but is
currently limited by the lack of durable UV-capable
fiberoptic delivery devices. |
