Biomedical Engineering Reference
In-Depth Information
810 nm Diode Laser
This laser's effects are similar to those of the alexandrite laser.
Like the alexandrite laser, 810 nm is best equipped for deeper
vascular lesions in relatively fair-skinned patients (16). The
laser can also be applied to reticular veins of the face.
the NIR peak for oxy-HgB. The advantage of these lasers is
their portability; they are diode lasers. On the other hand, their
peak powers are less than most solid-sate 1064 nm lasers and
therefore are confi ned to small spots and discrete vessel heat-
ing and not treatment of larger confl uent lesions.
facial telangiectasia
For wavelengths from 520 to 800 nm, the primary absorbers are
hemoglobin and melanin, so that improvement of telangiectasia
is achieved by direct heating of HgB (either via a single
wavelength or fl ash lamp). Devices targeting HgB/vessels are
confi ned to pulsewidths (pw) ranging from 0.45 to 100 ms.
Nanosecond lasers have been used at fl uences from 1 to 4 J/cm 2
(5-10 ns) but purpura and possible postinfl ammatory hyper-
pigmentation make them suboptimal in clearance of telangiec-
tasia (19). For discrete smaller (0.1-0.6 mm) telangiectases, PDL,
KTP laser, or IPL can be applied. For larger vessels (>1 mm),
the Nd:YAG laser or alexandrite laser is preferred, but care must
be taken to apply the smallest fl uence and smallest spot
suffi cient for closure. An alternative is the Cynergy™ laser
(Cynosure, Chelmsford, Massachusetts, USA), which combines
595 and 1064 nm sequential pulses that can simultaneously
address both smaller and larger telangiectases.
If a patient presents with telangiectases confi ned to very
small areas, we typically use the long-pulsed KTP laser and use
a small spot (1-3 mm) (Fig. 2.12). The ergonomic simplicity
of this procedure and real-time assessment of vessel clearing
are unsurpassed. Alternatively, we use nonpurpuric settings
with the PDL or an IPL. The specifi c type of PDL determines
the spot size, fl uence range, and cooling type, and pw. Modern
PDLs can generate effective fl uences with 10 mm spots; more-
over, the macropulses (pulse envelopes) are comprised of
6-8 micropulses, allowing for greater effi cacy without a high
risk of purpura (20). IPL can be applied as well; the optimal
settings are machine specifi c.
IPLs are constantly improving with better cooling and vari-
able pulse confi gurations. The advantages of IPL are the rela-
tively large spot sizes, which can minimize the polka dot effect
common to PDL and KTP lasers. IPLs are often based on plat-
form designs, that is, a number of handpieces can be driven
from the same base unit (similar to accessories on a vacuum
cleaner); the handpieces share the power supply and other
components. So long as we know the fl uence, pulse profi le, spot
size, wavelength, pulse duration, and beam profi le of a laser,
tissue effects tend to be predictable. On the other hand, IPLs
show spectral variability, and fl uence measurement techniques
1064 nm Nd:YAG Laser
The Nd:YAG laser is a good example of a “what you can't see can
hurt you laser” (17). Although optimized for epidermal sparing,
the relatively poor HgB absorption obliges the device to be used
at higher fl uences. Because there is some mild heating of tissue
water, bulk heating can create signifi cant pain. In general, the
smallest spot size and smallest fl uence suffi cient for vessel clo-
sure should be used. The absorption coeffi cient for blood is
about 1/10 that of GY light (see Table 1.2 in chap. 1) and dermal
scattering is decreased versus shorter wavelengths. This deeper
penetration allows a greater fraction of energy to be deposited
in the deeper dermis. Also, compared with GY light, full thick-
ness vessel heating is more likely with 1064 nm irradiation.
Melanin absorption is much less than GY light. It follows that
tanned and darker-skinned patients can be treated; however,
bulk water heating is also possible with this wavelength such
that large spots and high fl uences can result in full thickness
dermal injury and scarring. Also, visual endpoints in vascular
lesions (i.e., PWS) are somewhat ambiguous (i.e., very slight
transient bluing or very slight shrinkage of exophytic portions
of a PWS) so that over treatment is not uncommon (Fig. 2.11).
The higher oxy-HgB versus deoxy-HgB also permits deeper
selective heating of arterioles (18). Pre- and post-pulse cooling
enhances the safety associated with use of both alexandrite and
Nd:YAG lasers, as thicker nodules require seconds to cool.
In addition to 1064 nm, 940 and 980 nm lasers have also
been applied to vascular lesions—these wavelengths are near
( A )
( B )
Figure 2.12 ( A ) A 0.3 mm vessel before treatment and ( B ) after treatment with
potassium titanyl phosphate laser (9 J/cm 2 , 15 ms, 5 mm spot, 4°C).
Figure 2.11 Scar after neodymium:yttrium-aluminum-garnet laser of nodule
in port-wine stain.
 
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