Biomedical Engineering Reference
In-Depth Information
responded as well, with less lightening and more post-therapy
hyperpigmentation (10). This may be due to the larger diame-
ter of leg telangiectasia as compared with dermal vessels in
PWS and larger diameter feeding reticular veins as described
previously. Vessels that should respond optimally to PDL treat-
ment are predicted to be red telangiectasia less than 0.2 mm in
diameter, particularly those vessels arising as post-sclerotherapy
TM. This is based on the time of thermocoagulation produced
by this relatively short-pulsed laser system. The PDL produces
vascular injury in a histologic pattern that is different from
that produced by sclerotherapy. In the rabbit ear vein, approxi-
mately 50% of vessels treated with an effective concentration
of sclerosant demonstrated extravasated RBCs, whereas with
PDL treatment, extravasated RBCs were apparent in only 30%
of the vessels treated (unpublished observations). Thus, the
PDL may produce less post-therapy pigmentation because of a
decreased incidence of extravasated RBCs.
Similar to TM vessels, essential telangiectasia represents a
network of fi ne red telangiectasia usually less than 0.2 mm
in diameter. This condition responds well to the PDL at fl u-
ences of 7-7.25 J/cm
2
(11). Treatment, however, is tedious,
with more than 2000, 5-mm diameter pulses are sometimes
necessary to cover the entire affected area.
The reason for greater effi cacy of treatment in Goldman and
Fitzpatrick's report in comparison with others (10,12) may be
due to the rigid criteria by which patients were selected for
treatment. Patients who responded well to treatment had red
telangiectasia less than 0.2 mm in diameter without associated
“feeding” reticular veins. Many physicians have found that ves-
sel location may affect treatment outcome, with vessels on the
medial thigh being the most diffi cult to completely eradicate.
However, with the PDL, vessel location appears to be unrelated
to treatment outcome if telangiectatic patches with untreated
associated reticular veins are excluded. In addition, there
appears to be no obvious difference in effi cacy between telan-
giectatic patches that are treated with compression and those
that are not (Fig. 11.3). Sadick et al. (13) conducted a study
that further supported the notion that graduated compression
stocking use for 7 days starting immediately after treatment of
class I-II venulectasia with PDL yielded no additional thera-
peutic effi cacy.
long pulsed alexandrite
nm)
A long-pulsed alexandrite laser was developed to treat hair. It
soon became apparent that the wavelength, fl uence, and pulse
duration could also be used for telangiectasia. The 755-nm
wavelength should penetrate 2-3 mm beneath the epidermis.
This laser has been reported to be effective in thermocoagulat-
ing blood vessels in clinical and histological studies (14-16).
One study of leg telangiectasia in 28 patients treated three times
every 4 weeks at fl uences ranging from 15 to 30 J/cm
2
found that
a single-pulse technique with 20 J/cm
2
, 5-ms pulse duration
yielded the best resolution when combined with sclerotherapy
using 23.4% hypertonic saline (HS) (15). When this technique
was used without epidermal cooling with a chill tip at 4°C, focal
crusting and scabbing were noted. With laser treatment alone,
telangiectasia smaller than 0.2 mm in diameter improved by
23%, vessels between 0.4 and 1 mm improved by 48%, and tel-
angiectasia 1-3 mm improved 32%. The bottom line is that the
alexandrite laser is more painful, no more effective, and proba-
bly produces more adverse effects than other lasers at the
parameters stated by the above-mentioned studies.
(
755
diode lasers
Diode lasers generate coherent monochromatic light through
excitation of small diodes. These devices are therefore light-
weight and portable, with a relatively small desktop footprint.
Dierickx et al. (17) evaluated an 800-nm diode laser system
(LightSheer, Lumenis, Santa Clara, California, USA) on eight
areas of leg veins. The laser was used at 15-40 J/cm
2
given in
5- to 30-ms pulses as double or triple pulses separated by a delay
of 2 seconds. Veins were treated every 4 weeks for three sessions
and evaluated 2 months after the last treatment. Optimal
Table 11.2
Thermal Relaxation Times of Blood Vessels
Diameter of
Vessel (mm)
Thermal Relaxation Time
(seconds)
0.1
0.01
0.2
0.04
0.4
0.16
0.8
0.6
2.0
4.0
Source
: From Ref. 27.
(
A
)
(
B
)
Figure 11.2
(
A
) Before treatment. (
B
) 3 months after treatment, there is hyperpigmentation in the telangiectasia treated with the fl ashlamp-pumped pulsed dye
laser at 15 J/cm
2
. Of note, the side treated with the KTP (532-nm) laser at 15 J/cm
2
and a 10-ms pulse showed no change.
Source
: From Ref. 29.
