Biomedical Engineering Reference
In-Depth Information
They reported good results, particularly with amateur tattoos,
but noted several disadvantages, including the need for multi-
ple treatments, often six or more, for complete pigment
removal. They also reported scarring in two patients and
emphasized the need to use relatively low powers (but above
the threshold to produce immediate tissue whitening) and the
importance of the treatment interval. At least 3 weeks between
treatments was necessary for tissue healing and pigment
removal by macrophages. In vitro tests showed an immediate
reaction in ink that could be explained only by a chemical reac-
tion. Biopsy specimens revealed evidence of fragmentation of
ink into smaller particles, which were then phagocytized by
macrophages. These two phenomena correspond with the clin-
ical observations of an immediate reduction in pigment
observable in the first week after treatment, followed by grad-
ual fading over the next several weeks without further therapy.
Stimulated by studies of the Q-switched ruby laser preferen-
tially damaging melanized cells in animal skin (196,197) and
the tattoo studies previously cited, researchers at the Wellman
Laboratories of Photomedicine at Harvard Medical School
completed a detailed dose-response study of Q-switched ruby
laser in 1990 (54). Using a 40- to 80-ns pulse, they treated
41 tattoos five times at doses of 1.5-4.0 J/cm
2
. Of 27 amateur
tattoos, eight cleared by more than 75% (all of which had been
treated at 4 J/cm
2
) in an average of 2.6 treatments. None of the
14 professional tattoos reached this level of clearing within five
treatment sessions, and frequent purpura and rare punctate
bleeding occurred. Twenty-eight tattoos with residual pigment
were treated an additional five sessions at fluences of 5-8 J/cm
2
with more tissue damage, frequent purpura, and occasional
superficial erosions noted. At the completion of this phase, an
additional 10 amateur tattoos cleared over 75%, requiring an
average of an additional 3.5 treatments. Three professional tat-
toos achieved this degree of clearing after an additional single
high-dose treatment at 7 J/cm
2
. Overall results were excellent in
78% of amateur tattoos, but in only 23% of professional tat-
toos. Despite these rather discouraging statistics, the authors
were optimistic that the Q-switched ruby laser would develop
into a preferred treatment for tattoos, because of the rare scar-
ring. In addition, the authors stressed the competitive absorp-
tion by melanosomes leading to vacuolization of melanocytes
and keratinocytes, with hypopigmentation noted in 39% (low
fluences) to 46% (higher fluences) of cases. Normal pigmenta-
tion was progressively reestablished over a 4- to 12-month
period; however, four of the 10 tattoos examined 1 year after
treatment still had confetti-like hypopigmentation (Fig. 4.6).
The authors agreed with previous investigators that the imme-
diate whitening seen represents rapid localized heating with
steam or gas formation resulting in dermal and epidermal
vacuolization. They noted an unexplained brief emission of
white light as the laser pulse struck the tattoo pigment. Inter-
estingly, histologic persistence of altered tattoo pigment in
areas of clinical clearing was noted, suggesting a change in the
optical properties of the tattoo pigment.
This study was not able to establish an optimal treatment
interval. Although the mean interval was 3 weeks, intervals of
1-5 weeks were used, and no statistical difference in responses
was noted. Blue and black pigments were most responsive,
green and yellow responded less well, and red was poorly
Figure 4.6
Confetti-like hypopigmentation.
responsive if at all. Purpura and punctate bleeding most likely
represent indirect vascular injury from photoacoustic waves
generated by laser interaction with tattoo pigment. A study by
Scheibner and coworkers (198) reported preliminary results of
treatment of 101 amateur and 62 professional tattoos using
fluences of 2-4 J/cm
2
with a 40-ns pulse width, spot sizes of
5 and 8 mm, and a treatment interval of 5-6 weeks. Although
details of response are lacking, after an average of four treat-
ments, 87% of amateur tattoos were greater than 80% clear,
whereas of 62 professional tattoos, only 11% were greater than
80% clear. Treated areas required 10-14 days to heal and
remained erythematous for an additional 1-3 weeks, and most
patients developed hypopigmentation lasting 2-6 months. Skin
textural changes resolved over 6-8 weeks, with no scarring
reported. Tattoos of the face and neck responded sooner but
were more sensitive to tissue damage, necessitating the use of
lower fluences. Interestingly, a better response was noted with
older professional tattoos and blue inks than with other colors.
Taylor and colleagues (199) reported on light and electron
microscopic analysis of Q-switched ruby laser-treated tattoos.
After irradiation, all three previously described particle types
could still be found, in addition to round, lamellated, electron-
lucent particles measuring 25-40 nm and more often in the
deeper dermis and even into the subcutaneous fat. These
altered particles are thought to originate from the 40-nm par-
ticle. After treatment, pigment granules measured approxi-
mately 1 mm (compared with their original 4-mm size) and
were loosely packed. Those granules in the papillary dermis
measured 0.2-0.4 mm and were very densely packed. Again,
clinical clearing poorly correlated with histologic clearing,
because tattoos responding well often had residual pigment.
The mechanism of action of the Q-switched ruby laser is
through photon absorption by tattoo pigment within
fibroblasts. During the 40-ns pulse, temperatures could exceed
1000°C. Gaseous products of pyrolysis or pores created by
superheated steam may account for the lamellated appearance
of the granules after laser exposure. The reduction in pigment
