Biomedical Engineering Reference
In-Depth Information
Table 2.2
Childhood Port-Wine Stains: Treatment Response by Age
95% Improvement
No. of
Lesions
Average
Range
Average
Age (yr)
Average
Treatments
Average
Improvement (%)
Median
Improvement (%)
No. of
Lesions
Average
Treatments
No. of Patients
Age 0-4 yr
21
25
2 wk to 4 yr
2.15
3.4
70
75
5 (20%)
3.8
Age 4.5-14 yr
22
24
6-14 yr
10.3
4.0
68
75
3 (12.5%)
6.5
Total 0-14 yr
43
49
2 wk to 14 yr
6.2
3.7
69
75
8 (16.3%)
4.8
Source
: From Ref. 116.
undertaken safely and with an accelerated response: 45%
demonstrated 75% or more lightening of their lesions after
a mean of 3.8 treatments (118). Alster and Wilson (119)
reported an 87% clearance rate in patients less than 2 years
of age, 78% clearance in patients of ages three to eight, and
73% clearance rate in patients 16 years and older. All these
studies demonstrate a better treatment outcome with younger
patients.
One study of 23 facial PWS lesions in patients up to age
17 years showed no difference among different ages in the
average number of treatments to obtain maximum lesion light-
ening (120). However, this study only evaluated four lesions
in children less than 1 year of age and eight lesions in those 1 to
7 years of age.
This variation in response to treatment may be due to the
variable depth of the lesions themselves and the likelihood that
vessels located most superfi cially must be treated fi rst to allow
for deeper light penetration and, therefore, continued treat-
ment of the deeper portion of the lesion. Additionally, vessel
photocoagulation immediately following laser photothermol-
ysis results in decreased blood supply to the skin, resulting in
local hypoxia. Reactively, the normal wound healing response
activates appropriate defense mechanisms such as angiogene-
sis. This normal reformation and reperfusion of blood vessels
has been thought to interfere with subsequent laser photother-
molysis and additional lightening of PWSs (121).
Another parameter is the interval between pulses (if one is
applying more than one pulse). In the original proposal of
SPT, calculations of thermal relaxation time (TRT) were based
on theoretical considerations but measurements of actual
temperature decay in vessels were not measured. Dierickx used
0.8x the purpura thresholds in PWS for various pulse delays to
establish a real TRT, that is, the delay where the fi rst and sec-
ond pulses are almost decoupled thermally (122). They found
longer TRTs than those theoretical values in the literature and
that 1-10 ms was the ideal pulse duration for a single pulse
based on their experimental data within the context of math-
ematical models of heat diffusion. Dual pulses (either com-
prised of one IPL or one wavelength of laser light, or sequential
595/1064 nm devices) have been applied to PWS—models
predict that multiple pulses with 20-60 ms interpulse delays
should allow for cumulative vessel heating during the pulse
train with a smaller effect on the actively cooled and thinner
epidermis. In some instances, nodular or hypertrophic PWSs
may require treatment with pulsed alexandrite laser or pulsed
Nd:YAG laser (Fig. 2.20) (123).
Changing from a 585-nm dye to a 595-nm dye has resulted
in enhanced clearing in some PWS. It appears that pink or
red PWS do best with 585 nm, whereas blue or dark red PWS
do better with 595-nm dyes. There is met-HgB production
during heating of blood; this shifts the absorption spectrum
during irradiation and just after irradiation. Met-HgB shows
enhanced absorption for wavelengths greater than 600 nm
versus oxy-HgB. The peaks for oxy-, deoxy-, and met-HgB
are provided in (see Table 1.2 in chap. 1). Met-HgB has
absorption peaks at 404, 508, and 635 nm. Following forma-
tion of met-HgB, decreases in oxy-HgB absorption peaks at
335, 415, 542, and 576 nm will occur (124). The changes sug-
gest that 630 nm might be applied at the end of a laser pulse
to enhance blood vessel heating. Another approach is sequen-
tial 595 or 532 nm then 1064 nm heating. Once again, the
formation of met-HgB enhances light absorption, in this case
in the NIR spectrum. The goal is epidermal sparing by
decreasing the visible light fl uence and adding a 1064 nm
10-50 ms later, thereby exploiting dynamic optical property
changes in blood. Finally, other maneuvers, such as increas-
ing the diameter of the blood vessels by using a proximal
tourniquet, has also enhanced absorption with a 585-nm,
1.5-ms PDL.
The alexandrite laser has been advocated as a good choice for
resistant PWS and some darker PWS. Fluences range from 25 to
80 J/cm
2
over pulse durations from 3 to 20 ms. Generally,
smaller fl uences (25-35 J/cm
2
) are employed with larger
12-15 mm spots (likely a safer approach) and larger fl uences
(50-80 J/cm
2
) with smaller 6-8 mm spots. The alexandrite laser
should be used with surface cooling and care should be taken
not to pulse stack or apply too many pulses in a small area. Bulk
heating and overheating of the epidermis are likely if these pre-
cautions are not taken. Because of the deeper penetration of the
laser versus PDL, deeper vessels can be treated, but also over
treatment tends to result in scarring. Likewise, the 810 nm diode
laser can be used with cooling with fl uences ranging from 35 to
60 J/cm
2
with variably available spot sizes (usually ~1 cm
2
).
The 1064 nm laser can be used for PWS but is best reserved
for exophytic portions of the stain. Very small spot sizes
should be applied (the same size as the nodule). Although
test spots are not routinely performed in modern day treat-
ment of PWS, a case can be made for such tests with 1064 nm
