Biomedical Engineering Reference
In-Depth Information
q-switched alexandrite laser
The third Q-switched laser developed for the treatment of
tattoos has a wavelength of 755 nm (222-225) and uses a
synthetic version of a semiprecious stone, alexandrite, as the
active medium. Reflectance studies at 755 nm suggest excellent
absorption by black pigment, good absorption by blue and
green, and poor absorption by red pigments, as confirmed by
preliminary studies performed on tattooed guinea pigs and
harvested human skin (226). This corroborates previous
findings from preliminary trials on Yucatan miniature pigs,
where one treatment session provided excellent results in
removal of black ink, good results with blue and green, and
poor results with red ink. Efficacy was fluence related; 8 J/cm
2
was more effective than 6 J/cm
2
, which was more effective than
4 J/cm
2
, and 2 J/cm
2
was ineffective (124).
In contrast to previous reports using the Q-switched ruby and
Nd:YAG lasers, histologic clearing correlated with clinical clear-
ing. Similar to reports with the other Q-switched lasers, fragmen-
tation of tattoo pigment was followed by macrophage engulfment
and gradual clearing of the pigment, but with clinically clear tat-
toos devoid of ink histologically. Interestingly, tattoo pigment
became progressively altered during this process, initially appear-
ing as very sharp-bordered grains of pigment in clumps and tak-
ing on a progressively more amorphous form and lighter color
within the macrophages. No clinical or histologic reaction in col-
lagen, scarring, or atrophy was seen in laser-treated sites.
The Q-switched alexandrite laser was initially studied with 30
tattoos using fluences of 4.5-8.0 J/cm
2
. Test sites using three
fluences up to 6 J/cm
2
were evaluated at 4 weeks. The appropri-
ate fluence was then selected and treatment begun. A second test
was done if none of the previous fluences revealed significant
lightening. Fluences of 6 J/cm
2
or higher were used once the tat-
too had lightened by 20-50%. Approximately 25% clearing of
tattooed pigment required 1.7 treatments, 50% clearance 2.8
treatments; 75% clearance 5 treatments, 90% clearance 6.4
treatments, and total clearance 10.4 treatments (range, 4-16).
Professional tattoos, cosmetic tattoos, traumatic tattoos, and
amalgam tattoos cleared as well as amateur tattoos, although the
latter were more rapidly responsive, requiring approximately
three fewer treatments to reach complete clearance, although
professional tattoos responded rapidly as well (168,227-230).
Transient hypopigmentation is common (50% of patients),
but often is not apparent until after five to seven treatment ses-
sions, and usually resolves gradually over 1-12 months. As
with the other Q-switched lasers, hyperpigmentation is more
dependent on skin type and clears with hydroquinone and
sunscreen. Transient surface textural changes have been noted
in about 10% of patients, but all resolved within 3-9 months,
although one patient developed a small scar secondary to
excoriating a treated area. In summary, the Q-switched alexan-
drite laser is effective for removing blue, black, and green tat-
too pigments; however, hypopigmentation is common.
The ruby was compared with the Nd:YAG laser by treating
one-half of both amateur and professional tattoos with each
device (231). Both devices effectively removed black pigment,
but the ruby proved to be superior in fading green pigment in
both amateur and professional tattoos. The Nd:YAG laser using
the 532-nm setting was superior to the ruby in the removal of
red ink in another study (167). A study comparing the ruby to
the alexandrite laser in the treatment of 10 black amateur tat-
toos found that the ruby was more effective in clearing all tat-
toos; again, however, hypopigmentation was observed (232).
A comparison of the Nd:YAG laser with the alexandrite laser
in the treatment of 50 tattoos saw better initial as well as long-
term results with the former (233).
Yet another study examined the responses of all three devices
in which 14 commonly used tattoo pigments were injected
into guinea pig skin and then treated with each system (234).
All three lasers in this study were effective in removing black
ink. Red, brown, dark brown, and orange pigments responded
best to the Nd:YAG laser using the 532-nm setting, the alexan-
drite was most effective for removing blue and green pigments
and the ruby laser was most effective for purple and violet.
Although all three Q-switched lasers can remove tattoo ink,
the range of color responsiveness and limitations of the differ-
ent laser systems are important to note. Generally speaking,
ruby lasers (694 nm) treat black ink effectively and can be used
to also treat blue and green pigments but are more likely to
cause undesired pigmentary alterations. Alexandrite lasers
(755 nm) are also effective for black ink and are used to treat
green and blue pigments but have a smaller beam diameter, are
less powerful, and are also commonly lead to skin discolor-
ation. The Nd:YAG (1064 nm) treats black ink well and is the
least likely of the three devices to be associated with skin color
changes. The frequency-doubled Nd:YAG (532 nm) is the most
effective device for removing red tattoo ink (180,235-237) and
can be used to remove orange and some purple color, but it too
may lead to unwanted skin color changes.
Some devices now include an Nd:YAG as well as a ruby laser in
a single device; an alexandrite device offers 1064- and 532-nm
laser-pumped handpieces, and a number Nd:YAG laser systems
offers “color-specifi c” handpieces (585 and 650 nm) that can be
added on to the base device, giving the laser operator a wider
range of treatment options with multicolored tattoos (Box 4.2).
q-switched laser treatment intervals
Appropriate treatment intervals are a critical and yet poorly
understood component of successful tattoo removal. To study
different treatment intervals, in one study, a group of patients
received three treatments within seven to 10 days and then
received no treatment for 3 months. It had been hoped that by
condensing these treatment sessions within an initial short
time frame followed by adequate time for macrophage activity
would result in more rapid tattoo removal with fewer total
treatments required. However, the condensed treatment pro-
tocol did not enhance clearing. Furthermore, treatment inter-
vals of 1 month could interfere with macrophage activity,
because the pigment-containing macrophages are laser targets
as well as the stationary pigment-laden fibroblasts (123,159).
By extending the treatment interval to 2 and 3 months,
essentially no difference was seen in the rate of tattoo clearing,
because all three treatment intervals resulted in approximately
comparative studies
of the q-switched lasers
Direct comparison studies of Q-switched lasers are difficult,
because varying treatment parameters, including spot sizes
and fl uence, are difficult to standardize and results are there-
fore often inconclusive. That said, multiple comparative stud-
ies of Q-switched have been attempted.
