Biomedical Engineering Reference
In-Depth Information
n
nm)
The 1064-nm Nd:YAG laser is probably the most effective laser
available to treat leg telangiectasia. The average depth of pen-
etration in human skin is 0.75 mm, and reduction to 10% of
the incident power occurs at a depth of 3.7 mm (20). A narrow
therapeutic fl uence range, which reduces both its effi cacy and
safety, is associated with the 1064-nm Nd:YAG laser (16). This
narrow range may be largely attributed to the formation of
methemoglobin (metHb), an oxidized form of hemoglobin
that appears during laser-induced blood vessel heating (21).
At 1064 nm, metHb shows a signifi cantly stronger absorption
than either deoxyhemoglobin or oxyhemoglobin. Theoretically,
this metHb formation effect is less pronounced at 755 nm.
Three mechanisms are available to minimize epidermal
damage through heat absorption. First, the longer the wave-
length, the less energy will be absorbed by melanocytes or
melanosomes. This will allow darker skin types to be treated
with minimum risks to the epidermis caused by a decrease in
melanin interaction. Second, delivering the energy with a delay
in pulses greater than the thermal relaxation time for the epi-
dermis (1 to 2 ms) allows the epidermis to cool conductively
between pulses. This cooling effect is enhanced by the applica-
tion of cold gel on the skin surface that conducts away epider-
mal heat more effi ciently than air. Finally, the epidermis can be
cooled directly to allow the photons to pass through without
generating suffi cient heat to cause damaging effects.
Epidermal cooling can be given in many different ways. The
simplest method is continuous contact cooling with chilled
water, which can be circulated in glass, sapphire, or plastic
housings. The laser impulse is given through the transparent
housing, which should be constructed to ensure that the laser's
d
:yag laser
(
1064
produces a noncoherent light as a continuous spectrum longer
than 550 nm should have multiple advantages over a single-
wavelength laser system. First, both oxygenated and deoxygen-
ated hemoglobins absorb at these wavelengths. Second, blood
vessels located deeper in the dermis are affected. Third, ther-
mal absorption by the exposed blood vessels should occur
with less overlying epidermal absorption, since the longer
wavelengths penetrate deeper and are absorbed less by the epi-
dermis, including melanin.
Treatment of essential telangiectasia, especially on the legs, is
effi ciently accomplished with the IPL (Fig. 11.4). A variety of
parameters have been shown to be effective. We recommend
testing a few different parameters during the fi rst treatment
session and using the most effi cient and least painful parame-
ter on subsequent treatments.
The use of IPL to treat leg veins requires signifi cant experi-
ence and surgical ability to produce good results. Various
parameters must be matched both to the patient's skin type
and to the diameter, color, and depth of leg vein. With older
machines that do not have integrated cooling through sap-
phire crystals, a cold gel must be placed between the IPL crys-
tal and the skin surface to provide optimal elimination of
epidermal heat. Many have compared using the IPL to playing
a violin. A 2- to 3-year-old child playing a violin will make a
squeaky noise, but, with practice, by the time the child is 7 or
8, he or she will make beautiful music. Regarding the IPL, it is
the art of medicine that assumes an equal importance to its
science. Fortunately, for those who do not play musical instru-
ments, there are now dozens of IPLs available from many dif-
ferent manufacturers.
(
A
)
(
B
)
Figure 11.4
A 63-year-old female with tanned, skin type III having isolated telangiectasias without associated varicosities. Previous attempt with sclerotherapy
yielded no improvement. (
A
) Before treatment. (
B
) 10 minutes after treatment with intense pulsed light. Parameters were a double pulse of 2.4 and 7 ms with a
10-ms delay using a 570-nm fi lter, at 44 J/cm
2
.
Source
: From Ref. 30.
