Biomedical Engineering Reference
In-Depth Information
8
Nonablative fractional lasers
Karen L. Beasley and Robert A. Weiss
background
The development of fractional photothermolysis is one of
the most important discoveries in the fi eld of laser medicine
and surgery. Fractional photothermolysis, fi rst described by
Manstein (1), refers to laser generated zones of microscopic
thermal injury of the skin. This concept revolutionized laser
skin resurfacing and the practice of esthetic dermatology,
dermatologic surgery, and laser medicine. Previously patients
could only signifi cantly enhance their skin through fully
ablative lasers, like the 10,600-nm carbon dioxide (CO
2
) laser
or the 2940-nm erbium-doped yttrium aluminum garnet
(Er:YAG) laser. These laser treatments required at least 1-2 weeks
of recovery depending on the depth of resurfacing and the
type of laser utilized. With deeper resurfacing procedures,
patients could experience considerable discomfort and side
effects. Results could be exceptional but patients soon
became aware of the potential disadvantages of aggressive
procedures. Besides the potential side effects of infection or
permanent scarring, many patients who were treated with
deep CO
2
laser resurfacing experienced prolonged redness
or erythema of the skin for 6 months to a year. Many also
developed unexpected permanent hypopigmentation of
their treated skin (2,3). In addition, patients also became
aware of the stark contrast as their beautiful resurfaced facial
skin lay adjacent to their severely sun damaged neck and
chest. Fully ablative laser resurfacing was fraught with severe
complications when used off the face. Darker skin types
were not candidates for the procedure. With these limita-
tions, traditional deep ablative resurfacing began to decrease
in popularity.
Nonablative infrared lasers were developed in hopes of
remodeling and rejuvenating the skin with fewer side effects.
Infrared lasers such as the 1320-nm Nd:YAG, 1450-nm diode,
and 1540-nm erbium: glass lasers were developed. These lasers
demonstrated modest improvements in fi ne rhytides and acne
scars (4-6). More importantly, these lasers were able to pro-
duce results in patients with darker skin types (7). But the
results from these nonablative lasers paled in comparison with
the traditional ablative procedures, leading patients and physi-
cians to seek more effi cacious treatments. A comparison of
types of ablative and nonablative lasers is shown diagrammati-
cally in Figure 8.1.
In addition to effi cacy, it is important to consider the risk-
benefi t ratio of a laser procedure and its potential for post-
procedure downtime. In our current culture, many patients
do not want to take the risk of a serious side effect in exchange
for a cosmetic improvement. Alternatively, many patients
have busy work or social schedules that do not allow for
extended recovery times. Nonablative fractional laser (NAFL)
resurfacing allows for real results with fewer side effects and
less downtime. This technology also allows for the treatment
of darker skin types and can successfully treat a multitude of
skin conditions and body areas. The disadvantages, compared
with ablative resurfacing, are the need to return for multiple
treatments and decreased effi cacy.
fractional photothermolysis
During fractional photothermolysis, the laser creates micro-
scopic noncontiguous columns of thermal injury in the der-
mis, referred to as microthermal zones (MTZs) (Fig. 8.2) (1).
Each MTZ is surrounded by a limited zone of heat shocked
tissue which is surrounded by a larger zone of healthy unaf-
fected tissue. The MTZ allows for transport and extrusion of
necrotic dermal content through the compromised dermal epi-
dermal junction (8). The precise nature of the coagulated tissue
allows for quicker healing and recovery (1,8,9). Immunohisto-
chemical studies have shown increased collagen III production
around treated MTZs by 7 days and replacement of damaged
collagen in the MTZs by 3 months after treatment (9). In
addition, histology also reveals that there is a localized, well-
controlled melanin release and a transport mechanism that
uses microscopic exudative necrotic debris (MEND) as the
vehicle for pigmentary redistribution (9). In other words,
NAFL resurfacing improves pigmentation by shuttling the
melanin through the MENDs where it is exfoliated off the
skin. The initial paper by Manstein et al. also reported that
there was little to no pigmentary alteration in dark skinned
patients when using lasers with low to medium MTZ densities
per treatment (1). This essential combination of creating a
precise injury that has an enhanced healing rate coupled with
the ability to build collagen and redistribute pigment is the
hallmark of fractional photothermolysis.
nonablative fractional lasers
Two main NAFL families currently dominate the world laser
market; the Solta family of NAFLs (Solta Medical, Hayward,
California, USA) and the Palomar family of NAFLs (Palomar
Medical Technologies, Inc., Burlington, Massachusetts, USA).
Both families contain a variety of effective nonablative resur-
facing lasers. The laser wavelengths used in both families are in
the infrared region of the light spectrum and utilize water as
their tissue target or chromophore. The families differ by using
slightly different wavelengths in their respective lasers. But the
most striking difference between the two families is the man-
ner in which the laser energy is delivered to the skin. Besides
these two main families, there is also a multi-wavelength NAFL
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