Biomedical Engineering Reference
In-Depth Information
with CO
2
laser skin resurfacing (32,280,281). Adrian et al. com-
pared the short-pulsed Er:YAG with a pulsed CO
2
laser in a
bilateral comparison study and found that the Er:YAG was able
to improve fi ne rhytides but showed less effi cacy treating mod-
erate-to-deep rhytides than the CO
2
. In all instances, except for
mild rhytides, the CO
2
laser produced superior and longer last-
ing results (19).
With the notion that immediate tissue contraction and
induction of thermally mediated changes in dermal collagen
were important for long-term laser skin resurfacing results,
investigators began exploring ways to “modulate” the Er:YAG
laser to endow it with enhanced coagulative power while
maintaining its powerful ablative capacity and extremely
favorable side effect profi le (282).
Traditional Er:YAG lasers operated with pulse durations of
350
tissue contraction that approaches that seen with CO
2
laser
skin resurfacing (244,284). The Contour's touch screen con-
trol panel allows the surgeon to “dial in” the desired depths of
ablation and coagulation and to choose the corresponding
clinically appropriate laser parameters. The Contour has a
built-in safety feature that automatically adjusts the displayed
fl uence to refl ect the effect of changes in the degree of overlap.
For example, an increase from 10% to 30% overlap will alert
the surgeon to the fact that the delivered fl uence has increased
by approximately 65%. At 45 W, the Contour Er:YAG is a pow-
erful laser that makes the use of a pulse scanner quite feasible
and advantageous (285). Several studies have investigated the
histologic effects of dual-mode Er:YAG Contour laser resur-
facing. A close correlation was found between the programed
and actual measured depths of ablation for single and multiple
passes. It is clinically important to note that the chosen depth
of coagulation correlates well with the histologic changes for
the fi rst pass, but this correlation deteriorates with subsequent
passes (286-288).
Zachary et al. achieved signifi cant tissue contraction and
good-to-excellent control of bleeding with the dual-mode
Contour Er:YAG laser using 50% overlap, 84
m of residual thermal
damage. In 1998, Adrian et al. studied the effect of increasing
the pulse of the Er:YAG at a fl uence of 5 J/cm
2
during skin
resurfacing procedures to 10 ms (CO
3
, Cynosure, no longer
made) (21). Histology revealed a 60-
μ
s and typically produced 10-20
μ
m residual thermal
damage zone after multiple passes with this long-pulsed
(10 ms) Er:YAG laser. More signifi cantly, this increased zone of
residual thermal damage correlated well with increased tissue
contraction when compared with the 350-
μ
μ
m of ablation
(21 J/cm
2
), and 50-100
m of coagulation. A “CO
2
-like” tissue
contraction was observed during the second and subsequent
passes with this laser (284). Grekin and Zachary reported
their experience resurfacing over 100 patients with the dual-
mode Contour Er:YAG laser (285,289). Average reepithelial-
ization time for their patients was 3-5 days and they noted
signifi cant improvement in rhytides and acne scars. Full-face
and regional resurfacing was accomplished in patients with
all skin types. In comparison with the CO
2
laser, postoperative
erythema cleared more rapidly and there were no cases of
scarring. Transient hyperpigmentation was seen in most
patients with darker skin phototypes, but it resolved in every
case with the use of topical bleaching agents and sun protec-
tion. Of note, these authors reported two cases of delayed
hypopigmentation that occurred in patients with lighter skin
phototypes.
In another study, Tanzi and Alster utilized the dual-mode
Contour Er:YAG laser to treat 25 patients with moderate-to-
severe atrophic facial acne scars. Their laser parameters were
90 mm of ablation (22.5 J/cm
2
) with 50% spot overlap and
50 mm of coagulation delivered with a rapid pulse scanner.
Two to three passes were performed. The average clinical
improvement score at the 12-month follow-up was 2.16
(25-50% improvement). Side-effects were limited to transient
erythema in all patients (mean duration of 3 weeks), one case
of prolonged erythema, hyperpigmentation (44%), and acne
fl are-up that responded well to oral minocycline (32%). No
cases of hypopigmentation or scarring occurred (28).
Kwon et al. evaluated the effi cacy and safety of scar resur-
facing with the dual-mode Contour Er:YAG laser. Nine of
12 hypertrophic scars, 17 of 20 depressed scars, and 2 of 4 burn
scars improved more than 50%. Side effects were minimal and
included one case of postinfl ammatory hyperpigmentation and
mild persistent erythema in all patients with burn scars (29).
The variable-pulsed CO
3
-Er:YAG laser system can deliver
pulse durations ranging from 500
μ
s Er:YAG laser and
the clinical results achieved were similar to those attained with
the high peak power, short-pulsed CO
2
laser. This and other
subsequent studies (282) showed that as the pulse width
increased, both the zone of residual thermal damage and the
clinical effect approached the magnitudes seen after short-
pulsed CO
2
laser resurfacing (21,100,283).
In an attempt to overcome the shortcomings of the conven-
tional short-pulsed (350
μ
s) Er:YAG laser, namely poor hemo-
stasis, which limited depth of ablation and its inability to
resurface deep rhytides effectively, modulated Er:YAG laser
systems that conveniently combine long pulse (coagulative)
and short pulse (ablative) capabilities in the same device were
introduced in the late 1990s.
Currently there is one commercially available modulated
Er:YAG laser system with combined ablative and coagulative
capabilities: a dual-mode (ablation and subablative/coagula-
tion modes) pulsed Er:YAG laser (Contour TRL, Sciton Corp.).
Additionally, there are devices that are no longer made but are
of historical interest, including a variable-pulsed Er:YAG laser
(CO
3
, Cynosure), which can deliver single pulses of variable
widths, and a modulated Er:YAG laser system that is a hybrid
CO
2
-Er:YAG laser (Derma-K, ESC Medical Systems, now part
of Lumenis), which is no longer commercially available but,
given that these may still be in use by some clinicians, will be
briefl y reviewed next.
The dual-mode Contour TRL Er:YAG laser (Sciton Corp.)
uses a process called optical multiplexing that stacks together
groups of individual Er:YAG laser pulses to create either short
(200-300
μ
s) ablative pulses of high fl uence or long-duration
pulses of low fl uence (subablative and coagulative). These
pulses can be delivered as purely ablative, purely coagulative,
or a combination of both. Ablation depths of up to 200
μ
m
can be achieved with a single pulse. At 50% overlap, high fl u-
ences of up to 100 J/cm
2
can be generated and the entire epi-
dermis can be removed in a single pass. The coagulative
component can produce thermal damage in the dermis and
μ
s to 10 ms. Short pulses are
used for ablation, whereas longer pulses produce thermal
effects mimicking the CO
2
laser-tissue response. With the
μ
