Biomedical Engineering Reference
In-Depth Information
Korean patients with nevus of Ota and congenital nevus
showed that the treatment period had been reduced by 2-3
months, and the number of treatments had been reduced two-
to threefolds (144). However, the use of this combined laser
technique to nonfacial areas is yet to be fully evaluated. The
risk of delayed healing time and adverse effects may be higher
because of the decreased vascularity and the sparse adnexal
structures relative to the face.
Concurrent use of the QS 532-nm Nd:YAG laser in combi-
nation with the 1064-nm laser has proven more effective in
pigment lightening than the QS 1064-nm Nd:YAG laser alone
for early lesion of Hori's nevi. Removal of the epidermal
component of Hori's nevi as such, results in a lighter color. In
addition, elimination of competing epidermal melanin may
also assist in the penetration of longer wavelengths and result
in more effi cient removal of the dermal component with the
1064-nm laser (131).
Elimination of epidermal melanin by using topical bleach-
ing agents has also been used to pretreat the skin 6-8 weeks
prior to QSRL for acquired dermal melanosis (ADM) in Japa-
nese patients. This combined therapy appeared to treat ADM
consistently with a low occurrence rate of PIH and lessen the
number of laser treatment sessions (144).
minimal risk of adverse sequelae (149-152). Laser tattoo
removal in darkly pigmented patients has often been
presumed to have a greater risk of complications, such as
hypertrophic scar (Fig. 13.16) and keloid formation, and pig-
mentary alterations (Fig. 13.17), as compared with fair-
skinned patients.
The effi cacy of the QS lasers on tattoo removal in dark-
skinned patients is comparable to that of light-skinned
patients. Studies on tattoo removal in dark-complexioned
patients (skin phototypes III-VI) with QS lasers have shown
favorable results without scarring or signifi cant permanent
pigment changes (153-160).
Grevelink et al. (154) determined the effi cacy and side effects
of QS lasers on a small series of skin phototypes V and VI
patients. A QSRL at 694 nm, with a pulse duration of 20 ns
using a 5-mm spot size at an energy fl uence ranging from 4.5
to 6.0 J/cm
2
, and a QS Nd:YAG laser at 1064 nm, with a pulse
duration of 10 ns using a 3-mm spot size at an energy fl uence
ranging from 4.5 to 7.3 J/cm
2
, were used to treat four of
fi ve patients presented with charcoal-injected tattoos on the
face or neck, and one of fi ve patients with a multicolored tat-
too on the mid-chest region. Two of fi ve patients (40%) cleared
by more than 90% after six treatments. Lesions of the other
three patients were 50% and 60% cleared after four to eight
treatments, respectively.
A similar study on laser treatment of tattoos in skin photo-
type VI patients using a QS Nd:YAG laser demonstrated that
after three to four treatments at 8-week intervals, 8 of 15 (53%)
tattoos were 75-95% cleared, 5 of 15 (33%) were 50% cleared,
and 2 of 15 (13%) were only 25% cleared (155). Compared to
a study on light-skinned patients using a QS Nd:YAG laser for
tattoo removal (156), 77% of patients' lesions cleared by more
than 75% in four treatments, and in 28% of patients lesions
cleared by more than 95% in four treatments. The QSAL
(755 nm, 100 ns) has also been proved to be effective in the
removal of various traumatic tattoos in Asian (skin photo-
types III-V) (153,157) and Spanish (skin phototypes III-IV)
(161) skin.
Multiple treatments are necessary. On average, 8-12 sessions
may be required, with a minimum of 6-8 weeks between treat-
ments with longer durations acceptable. Amateur tattoos
require a fewer number of treatments than professional tat-
toos. There is rarely 100% clearing. Most tattoos clear to a
point of being cosmetically acceptable.
When treating patients with dark skin types, pigmentary
changes are the most commonly encountered side effect. Scar-
ring can occur but is very rare when appropriate laser energy
(the energy that produces nonexplosive effects on the skin) is
selected (153-155,157,158). However, transient textural alter-
ations associated with the healing response can occur during
multiple treatments. The lack of clinical scarring noted with
QS lasers, even when epidermal damage is noted, is most likely
due to the lack of thermal injury to collagen, as evidenced by
the absence of histological fi brosis in areas treated multiple
times with both the QSRL (159) and QS Nd:YAG laser (156).
Transient pigmentary changes including hypopigmentation
and hyperpigmentation, have been noted in the early healing
phase but are commonly resolved in 6-8 weeks. Pre- and post-
treatment epidermal cooling can minimize the nonspecifi c
injury to the epidermis, and reduce postoperative pain and
Nevomelanocytic Nevi
The treatment of congenital and acquired melanocytic nevi
with laser irradiation is a very controversial issue. This concern
has already been discussed in detail (see chap. 3). In Asian
populations, melanocytic nevi are common and are often
removed for cosmetic and superstitious concerns. The normal
mode ruby laser (NMRL) alone (54,139,141), or together with
QSRL or QSAL, has been employed to remove melanocytic
nevi in Asians with good cosmetic results following multiple
treatment sessions (146-148).
In spite of clinical improvement, complete histological
clearance cannot be achieved. Long-term histological follow-
up of congenital melanocytic nevi after NMRL treatment
demonstrated that the subtle microscopic scar about 1 mm
thick is required to mask the underlying residual pigmentation
for good cosmetic results. The long-term follow-up for at least
8 years showed no histological or clinical evidence of the
development of malignant change in the laser-irradiated areas
(139). An NMRL appears to provide a more effective clearing
on the basis that a longer pulse duration induces more mela-
nocytic destruction to the clusters of nevus cells, and hence
better clears pigmentation (136,141).
In our current practice, a CO
2
laser is commonly used to
vaporize benign melanocytic nevi with promising outcomes
and low risk of side effects (see also section “Ablative laser
systems”). Importantly for Asians, laser treatment to remove
melanocytic nevi is avoided if there is any risk of melanoma,
including previous history or family history of melanoma, and
clinical evidence of atypia. Although melanoma is uncommon
in Asians, laser for the removal of nevomelanocytic nevus
should be avoided if the lesion is located in the acral area, which
is a common region of melanoma in Asian populations.
Tattoo Removal
In fair-skinned individuals, QS lasers have been proved to be
effective in removing pigmented lesions and tattoos with
