Biomedical Engineering Reference
In-Depth Information
PWS. This laser system delivering sequential pulses of
595- and 1064-nm wavelengths provides another option that
is likely to assist with removal of different vessels (37,38). The
application of 595 nm light followed by the 1064-nm wave-
length takes advantage of a chromic shift in blood when
heated above 62°C; the oxyhemoglobin absorption coeffi cient
peaks at 595 nm, whereas the methemoglobin absorption
coeffi cient aligns with 1064 nm. The synergistic thermal effect
of the dual wavelengths reduces the treatment fl uence neces-
sary for successful treatment. The combined 595- and 1064-
nm laser has been used to successfully treat PWS and appears
to have a more favorable side-effect profi le than the 1064-nm
laser used alone, but it is our experience that Asian patients
have a greater risk of blistering, scabbing, and scarring associ-
ated with the combined 595- and 1064-nm device than with
the PDL alone. Therefore, caution is warranted when treating
any vascular lesion in Asian patients with the combined
595- and 1064-nm laser.
darker-skinned patients is not as good as that in white-skinned
patients and the risk of pigmentary alterations is also higher.
A study on the effi cacy of the PDL performed in 20 patients
with skin phototypes I-VI demonstrated no improvement of
the hypertrophic scars on the laser-treated sites compared with
untreated control. Eight of the 20 patients had skin phototype
VI and two had type V. The effect of melanin was thought to be
a factor of treatment failure (41). Similarly, our previous study
(42) noted that clinical improvement of scars in patients with
skin phototypes IV-VI after multiple treatment sessions with
the PDL had a lower response rate, and the incidence of epi-
dermal damage increased compared with that of the fair-
skinned patients (Fig. 13.3). A previous study of PDL in the
treatment and prevention of hypertrophic scars in Chinese
patients also found that there was no signifi cant objective
improvement in terms of scar thickness and viscoelasticity
compared with the controls (43). Our earlier study on the
effect of pulse width of the PDL on the treatment response
of hypertrophic scars also noted a lesser effi cacy in Thai and
Chinese patients with skin types III-V as well (44).
Treatment of stretch marks is another application of the
585-nm PDL that improves the appearance of these lesions
(45,46). An increase in dermal elastin noted following PDL
treatment was speculated to be the mechanism of improvement.
laser treatment of hypertrophic scars,
keloids, and striae
The 585-nm PDL has also been used as a treatment of choice
for hypertrophic scars and keloids in fair-skinned individuals
(39,40). The effi cacy of the PDL in treatment of scars in
(
A
)
(
B
)
(
C
)
(
D
)
Figure 13.3
(
A
) Linear hypertrophic scar on the thigh in an Indian patient with skin phototype V, before treatment. (
B
) One week following the fi rst treatment
with a 585-nm pulsed dye laser using a 5-mm spot size without epidermal cooling device; A I, treated with 3 J/cm
2
; A II, treated with 5 J/cm
2
; A III, treated with
7 J/cm
2
; E, untreated control. Epidermal necrosis is noted over all laser-irradiated segments. (
C
) Four weeks following the second treatment, erythema and
hypopigmentation were seen on the laser-treated areas. (
D
) 12 Weeks after the sixth treatment, fl attening of the scar without dyspigmentation was demonstrated.
