Tattoo removal - Lasers and Energy Devices for the Skin - page 79

Histologic evaluation of the created wounds revealed loss of
dermis and subcutaneous tissue up to a depth of 5 mm (128).
Because of the slow healing time (4.5 ± 1.5 weeks) (123) and
resultant thick, unsightly scars, most did not attempt complete
pigment removal in one session and instead treated more con-
servatively, relying on macrophage engulfment and transepi-
dermal removal of tattoo pigment during the healing phase
(128).
Originally used as a continuous beam, repetitive pulses of
50-200 ms or superpulsed CO 2 lasers became more acceptable,
with reports of good results in 29 of 30 tattoos after an average
of 2.4 treatments. Although only a 7% incidence of hypertro-
phic scarring was noted, vaporization confined to the tattoo
may result in a scar in its original shape; therefore feathering
into normal tissue is recommended. Power settings of 8-25 W
were common for repetitive treatments, with higher powers
more rapidly vaporizing the tissue.
Because of the common occurrence of residual tattoo pig-
ment after more superficial CO 2 laser vaporization, together
with the increasing risk of hypertrophic scarring with subse-
quent treatments, methods to improve the results of a single
treatment were explored. Although the concomitant use of
2% gentian violet to prolong the exudative phase following
superficial CO 2 laser vaporization did not increase efficacy,
50% urea paste did improve results (187), as was reported with
the argon laser (188).
In summary, the CO 2 laser removes tattoo pigment in much
the same way as the argon laser, although with higher fluencies
and more effi cient tissue vaporization with the CO 2 laser is
more efficient. Tattoo pigment is removed by direct tissue
vaporization, as well as by thermal necrosis of adjacent tissue
and through loss of pigment in the exudative healing phase.
Dermal tissue is reconstituted by fibrosis and scar tissue, and
although acceptable results can occasionally be obtained,
because there is a level of unpredictability and some scarring
usually occurs, the CO 2 is no longer a viable option for treating
unwanted tattoos.

much less than that required for the argon laser and that each
wavelength reacted only with complementary colors of tat-
too pigment. However, despite the short 1-ms pulse, wide-
spread tissue necrosis was observed, and tattoo lightening
occurred only as a result of significant dermal necrosis and
resultant fibrosis. The authors postulated that an even shorter
pulse in the nanosecond domain would interact best with the
micrometer-sized pigment granule's approximate thermal
relaxation time.
To destroy tattoo ink selectively, the best wavelength is cho-
sen to achieve selective absorption for that ink color while
minimizing the nonspecific thermal effects from the primary
endogenous chromophores, hemoglobin, and melanin. After
laser treatment, a small portion of the ink may be partially
extruded through the scale crust that forms following epider-
mal injury. A greater proportion of the ink particles may be
fragmented, released into the extracellular space, and elimi-
nated into the lymphatics or rephagocytosed as laser-altered
residual tattoo particles, perhaps with altered optical proper-
ties. With the advent of Q-switched lasers operating in the
nanosecond (billionth of a second, 10 −9 ) range, the promise of
scarless tattoo removal became a reality.

q-switched ruby laser
The ruby laser uses a synthetic ruby crystal as the active
medium and emits a wavelength of light at 694 nm, which has
a deep red color. In 1965, the earliest reports of tattoo-pigment
interaction with short-pulsed lasers were documented by
Goldman et al. (190,191) who compared the reaction of a
dark-blue tattoo to a Q-switched ruby laser with nanosecond
pulses with a microsecond-pulsed ruby laser. They found non-
specifi c thermal necrosis with microsecond impacts, whereas
nanosecond impacts produced only transient edema accompa-
nied by a peculiar whitening of the impact area, lasting about
30 minutes. No thermal necrosis was present but tattoo frag-
ments remained in the dermis. The mechanism of this reaction
was unknown but was not thought to be thermal because of
normal measurements taken with a thermistor. Because of the
reported retention of tattoo pigment, this modality was origi-
nally interpreted as a failure. Goldman, however, followed the
patient's progress and noted continued fading of the treated
area. Goldman was unable to continue this work because his
engineer was fatally electrocuted, and subsequently he aban-
doned the project. Only 3 years later, however, other investiga-
tors confi rmed and expanded these results (192,193) using a
Q-switched ruby laser to remove blue and black tattoo pig-
ments successfully without tissue damage. Biopsies performed
after 3 months showed absence of tattoo pigment and no evi-
dence of thermal damage. These effects were dose dependent,
with fl uences of 5.6 J/cm 2 or less, showing absence of thermal
damage but incomplete pigment removal. Higher fl uences led
to subepidermal blisters similar to a second-degree burn and
dermal fi brosis at 3 months, although pigment removal was
more complete. Subsequent studies (123,194) concluded that
this treatment modality was impractical because of the small
target areas and the risk of coagulation necrosis of tissue sur-
rounding the tattoo pigment.
Reid and coworkers (195) continued to study the Q-switched
ruby laser and in 1983 published an additional report on
removal of black pigment in professional and amateur tattoos.

quality-switched laser treatment
of tattoos
Anderson and Parrish's principle of selective photothermoly-
sis revolutionized the treatment of tattoos (189). The word
“photothermolysis” is derived from the Greek word “photo”
meaning light, “thermo” meaning heat, and “lysis” meaning
destruction. Thus, selective photothermolysis therefore refers
to the precise targeting of a structure using a specifi c wave-
length of light with the intention of absorbing light into that
target area alone. They proposed that if a wavelength was well
absorbed by the target and the pulse width was equal to or
shorter than the target's thermal relaxation time, the heat gen-
erated would be confined to the target and allow the sur-
rounding area to remain relatively untouched. The thermal
relaxation time is the time it takes a given target chromophore
(in this case, tattoo ink) to lose 50% of its absorbed heat
energy.
In one of the earliest studies, Diette et al. (55) examined
the effects of a tunable dye laser at three wavelengths
(505, 577, and 680 nm) using a 1-ms pulse to remove black,
blue, red, and white tattoo pigments. They found that the
threshold dose to induce the same histologic changes was