Biomedical Engineering Reference
In-Depth Information
approach requires a series of two to six treatment sessions at
2- to 4-week intervals. The primary advantage has been greater
safety, without any reports of scarring or permanent hypo-
pigmentation (58,59,62). In addition, it has the ability to treat
off-face areas in an effective and safe manner.
The fi rst fractional resurfacing laser developed was the
Fraxel SR 750® (Reliant Technologies, Mountain View, Cali-
fornia, USA), which consisted of a diode-pumped erbium
fi ber laser, emitting light at 1550 nm to target water in the skin.
Two different MTZ density settings (125 and 250 MTZ/cm
2
)
were available for the fi rst-generation Fraxel laser. The fi nal
treatment density was then determined by both MTZ setting
and the number of laser passes, varying from 5% to 35% of the
surface. MTZs of 81-180 µm in width and 300 µm to greater
than 900 µm in depth are produced in the skin depending on
the pulse energies used (63). An Intelligent Optical Tracking
System monitors and adjusts for variable hand speed so that
aids in the deposition of uniform MTZs.
The second-generation Fraxel SR 1500, or Fraxel Re:Store®
introduced several changes including a telescoping zoom lens
that allowed adjustment of the diameter of the treatment column
depending on the treatment energy, resulting in more superfi cial
columns and smaller in diameter with lower energy and more
penetrating columns and larger in diameter with higher energy
(64). The pulse energy ranges from 10 mJ, which penetrates
approximately 200 µm, to a maximum energy of 70 mJ, which
penetrates approximately 1.4 mm, whereas up to 60% of the
skin's surface can be treated in one session. Competing fractional
delivery devices including the Lux® 1540 fractional erbium
(Er):Glass (Palomar Medical Technologies Inc., Burlington,
Massachusetts, USA), Affi rm® (Cynosure, Inc., Westford, Mas-
sachusetts, USA), Matrix® IR (Syneron Medical Ltd, Yokneam,
Israel), and Mosaic (Lutronic, Inc., Ilsan, Korea) use a “stamping”
approach to deliver the fractionated infrared laser beam.
The main disadvantage of stamping a fi xed pattern is the high
likelihood of posttreatment skip areas and the production of
Moire artifacts from inadvertent overlap of treatment sites. On
the other hand, most stamping devices do not require consum-
ables and are also often associated with less pain, even with
equivalent total depths and densities, compared with their scan-
ning counterparts.
The use of NAFR has been well studied for the treatment of
scarring, including acne scars, surgical scars, and traumatic
scars. Narurkar reported a retrospective review of 877 cases
treated with the second-generation erbium-doped 1550-nm
Fraxel and found that treatment of acne scars, surgical scars,
and mild-to-moderate photodamage achieved the most con-
sistent results, whereas the most variable results were seen in
the treatment of melasma and deep rhytides (65). Noteworthy
that although CO
2
and the Er:YAG ablative resurfacing with
100% coverage of the treated surface achieve exceptional
results for facial rhytides, lesser degrees of improvement were
seen for scarring with both lasers. One of the reasons might be
that the depth of macroscopic tissue ablation is limited with
those lasers because 100% of the surface area is treated,
whereas NAFR can deliver the MTZs deeply (>1300
Rahman and colleagues treated 40 patients with a variety of
scars (14 acne scars, 11 surgical scars, 13 traumatic scars, and
15 striae) and found that at 3 months, 22 of 49 scars (44.9%)
were moderately to completely improved (66). Subjects
reported moderate-to-complete improvement in 32 out of
52 scars (61.5%). Surgical scars and acne scars had the highest
improvement scores, whereas traumatic scars had the lowest.
Surgical scars showed the greatest improvement in surface tex-
ture and atrophy, whereas acne scars had the greatest improve-
ment in color mismatch.
Several other studies have demonstrated the effi cacy and
safety of NAFR in the treatment of scars (67-70). Rokhsar and
colleagues reported improvement in skin texture and decreased
scar severity in all patients (67). Ten patients with atrophic
acne scars and fi ve with surgical scars were treated with an
average of four sessions of Fraxel Re:Store at weekly or monthly
intervals, at fl uences of 8-20 mJ and density of 2000 MTZ/cm
2
.
Behroozan and colleagues reported greater than 75% improve-
ment rated by both the patient and an independent physician
evaluator in the degree of erythema, induration, and overall
texture in a surgical hypertrophic scar (68). This patient had
been treated once with the Fraxel SR 1500 at a pulse energy
of 8 mJ and density of 2000 MTZ/cm
2
1 month after a Mohs'
surgery procedure.
Interestingly, fractional laser treatment has shown to be an
effective treatment for different types of scars: hypertrophic,
atrophic, erythematous, and dyschromic.
Treatment of both atrophic and hypertrophic surgical scars in
13 patients using Fraxel SR 1500 was reported by Kunishige and
colleagues (69). Patients received one to eight laser sessions at
4-week intervals using energy levels from 6 to 70 mJ and densi-
ties of 312-2500 MTZ/cm
2
(12-87.5% density). At 2 weeks after
the last treatment, nine patients had greater than 75% improve-
ment, two patients had 51-75% improvement, and two patients
had 25-50% improvement. The results were maintained for all
subjects at 2 months of follow-up. Longer follow-up would be
expected to show greater degrees of improvement as remodel-
ing of scar tissue proceeds.
Treatment of hypertrophic scars with NAFR has been reported
by Niwa and colleagues (70). Eight patients with hypertrophic
scars (seven from surgical procedures and one from burn
injury) received two to three treatments with Fraxel Re:Store at
4-week intervals, using fl uences of 35-50 J/cm
2
and treatment
densities of 20-26%. At 4 weeks after last treatment, three
patients achieved 51-75% improvement and fi ve patients
achieved 26-50% improvement. Improvement in hyperpig-
mented scars occurred in all hyperpigmented scars and postin-
fl ammatory hyperpigmentation (PIH) was not observed in
this small study even in patients with Fitzpatrick skin type IV.
Clinical improvement of pigmented lesions with FP has been
correlated histologically to the formation of microscopi-
cally small areas of epidermal necrotic debris and dermal
contents containing melanin. Those necrotic contents are pro-
gressively eliminated through extrusion, releasing pigment
and resulting in the improvement of pigmented lesions (71).
In addition, Goldberg and colleagues showed histologic and
ultrastructural evidence that FP decreases the number of
melanocytes and the amount of melanin granules within
the keratinocytes, which is consistent with this elimination
process aforementioned (72).
m)
into the dermis with great safety, particularly with regard to
preservation of pigment (64). Treatment to the full depth of
the scar appears to be an important factor in a successful
treatment.
μ
