Biomedical Engineering Reference
In-Depth Information
collagen synthesis. Prevention and treatment of various types
of scars have been reported with the PDL (31,34,115,116).
Most practitioners have found elimination of unwanted ery-
thema and vessels is more effi cient with purpuric settings, but
subpurpuric settings will work with additional treatment ses-
sions. Treatment of acne as well as macular erythema has three
potential benefi ts: improvement in the acne, elimination of
postinfl ammatory erythema, and stimulation of new collagen
that enhances wound healing and minimizes scarring.
addition, the deep penetration of the MTZs (>1300
m) and
the fractional approach allow greater effi cacy and much greater
safety (64).
In 2006, Geronemus fi rst reported the use of NAFR (original
prototype Fraxel laser) for the treatment of acne scarring (60).
Seventeen patients with ice-pick, boxcar, and rolling scars
received a series of fi ve treatments at 1- to 3-week intervals.
Mean improvement levels evaluated by digital photography,
high-resolution typographic imaging, and patient-completed
questionnaires were in the range of 25-50%, 22-62%, and
29-67%, respectively. Posttreatment erythema, mild facial
edema, and moisturizer-responsive xerosis were observed.
No scarring or unwanted pigmentary changes were seen.
Favorable results were seen in patients with darker skin photo-
types and acne scars treated with NAFR.
Weinstein reported one of the largest series with 357 patients,
Fitzpatrick skin types I-VI, with acne scarring treated with the
Fraxel SR750 (132). One to fi ve treatments with pulse energies
of 25-35 mJ according to scar severity and depth and density
of 125 MTZ/cm 2 , 4-10 passes. At 3 months after last treatment,
12% achieved excellent improvement (>75%), 73% had good
improvement (50-75%), and 15% achieved fair improvement
(25-50%). One patient developed transitory PIH and one sub-
ject had localized scarring that resolved with IL 5-fl uorouracil
(5-FU).
A study by Alster and colleagues found that the mean clini-
cal improvement scores for atrophic acne scars after three
monthly treatments with Fraxel SR750 were higher than those
reported for facial rhytides in a study with similar design
(133). Fifty-three patients with mild-to-moderate atrophic
facial acne scars were treated with pulse energies of 8-16 J and
densities of 125 and 250 MTZ/cm 2 for 8-10 passes. Thirty-
eight patients (71%) received two or more treatments. In total,
48 patients (91%) had at least 25-50% improvement after a
single treatment, whereas 87% of those receiving three treat-
ments achieved greater than 50% improvement. Transient
acneiform eruptions occurred after 5% of treatment sessions.
One patient with skin phototype V developed transient PIH at
a setting of 250 MTZ but not after subsequent treatment at
125 MTZ.
Weiss and colleagues reported their experience in over
500 treatment sessions for acne scarring using the Lux1540
(Palomar) (134). Three treatments were given at 4-week inter-
vals using a fl uence of 50-70 mJ/mb with a minimum of
3 passes for each treatment site. At 3 months after last treat-
ment, blinded physician photographic analysis indicated a
median improvement of 50-75%, whereas 85% of patients
rated their skin as improved. Side effects were minimal and
included mild posttreatment erythema and edema that
resolved within 24 hours (Figs. 9.10 and 9.11).
Many reports and studies have shown the effi cacy of NAFR
in the treatment of acne scars (135-138). Weinstein and col-
leagues reported greater than 50% improvement in acne scars
in 15 of 16 patients treated with two to four treatments
with Fraxel at 2- to 4-week intervals using a pulse energy of
12-20 mJ and 125 MTZ/cm 2 (135). A fi nal total density of
2500-2750 MTZ/cm 2 was achieved in each treatment.
Individuals with darker skin types and acne scarring, in
whom previous ablative laser treatments carry the risk of per-
manent PIH, were successfully and safely treated with NAFR as
μ
nonablative fractional photothermolysis
for acne scarring
Resurfacing procedures such as dermabrasion, medium-to-
deep chemical peels, and ablative laser resurfacing have been
traditionally used to treat patients with extensive, widespread
acne scarring (117-120). These techniques remove the epider-
mis and upper dermis without affecting the skin appendages
(sebaceous glands, hair follicles, and sweat ducts), which allow
the regeneration of the skin and collagen production through
skin's healing process (117-120). Particularly the CO 2 laser,
which has been recognized as the gold standard resurfacing
procedure (121-125), also heats the nonablated dermis, result-
ing in immediate thermally induced skin tightening.
Despite the dramatic results achieved with the CO 2 laser for
the treatment of photoaged skin, wrinkle removal, skin tight-
ening, and acne scars, it has been associated with prolonged
erythema, extended recovery periods, hyper- and hypopig-
mentation, and in rare cases scarring (119,120). Because of
these potential risks and signifi cant downtime for healing
(2-4 weeks), nonablative lasers using long-pulsed infrared
wavelengths (1320, 1440, 1450, and 1540 nm) were developed
as a safe alternative (126,127). These nonablative, nonfrac-
tional lasers create a controlled thermal injury to the dermis
that initiates a cascade of wound healing and remodeling
events, resulting in neocollagenesis (126). However, a series of
treatments are often required, and the improvement in photo-
damage and acne scars, particularly atrophic or ice-pick scars,
was signifi cantly less noticeable than that achieved with the
ablative CO 2 and Er:YAG devices (126,128,129). The reduced
effi cacy has been partially attributed to the lack of epidermal
contribution to the wound healing process as well as the use of
epidermal cooling (130). The degree of improvement corre-
lates to some extent to the aggressiveness of treatment. In
order to keep the treatments safe and without signifi cant
downtime, the treatments are delivered in a conservative man-
ner because the devices deliver energy throughout the dermis.
As a consequence, multiple treatment sessions are needed and
results are generally subtle.
NAFR developed by Anderson and Manstein (58) resulted
in a rather predictable improvement of photoaged skin, color,
texture, and scars of all types compared with nonablative lasers
with better side effect profi les and less downtime than with
traditional ablative resurfacing devices (64).
NAFR has known effects on tissue tightening with clinical
improvement of fi ne lines and rhytides, likely due to stimula-
tion of collagen production (58). The mechanism of action of
NAFR for improving acne scarring is thought to be analogous
to its effects on tissue shrinkage; that these columns of ther-
mally damaged tissue initiate a cascade of wound healing
and remodeling events, resulting in neocollagenesis (131). In
 
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