Biomedical Engineering Reference
In-Depth Information
Liquefaction of adipocytes, carbonization of tissues, and
fi nally epidermal injury were observed only at the highest
energy settings (5,26,31,35).
A histologic evaluation of LAL comparing different wave-
lengths and continuous wave (CW) versus pulsed lasers in an
in vivo
pig model was conducted by Levi and colleagues (36).
Three CW lasers (980, 1370, and 1470 nm) and three pulsed
lasers (1064, 1320, and 1440 nm) were used followed by histo-
pathologic evaluations at 1 day, 1 week, and 1 month after
exposure. The authors found that skin damage occurred at
temperatures exceeding 46°C regardless of wavelength. Tissue
treated with the CW laser at 1470 nm demonstrated a greater
hemorrhage and denser histiocytic infi ltration than tissue
treated with the 1440-nm pulsed laser. Overall, there was more
collagen deposition with increased power levels. Furthermore,
increasing numbers of histiocytes (a marker of fat necrosis)
occurred with increasing power and energy levels at 1 month
after laser exposure. Lasers with a low coeffi cient of absorption
(980, 1064, and 1320 nm) achieved similar degrees of collagen
deposition as high-absorption lasers (1370 and 1470 nm) by
using higher power, lower speed, or both. However, due to
higher power and lower speed being used for this low-absorp-
tion group, total energy delivered under the skin was much
higher and resulted in a much higher temperature increase on
the skin surface. Therefore, the authors concluded that pulsed
lasers with high peak power provided better hemostatic effect
than CW lasers likely due to quick coagulation of blood vessels
from the pulsed laser at high peak power. Considering skin
safety and effi cacy, a high-absorption wavelength (e.g., 1440 nm)
with low power (6-12 W) would be a better choice for pro-
moting controlled collagen deposition in the subdermal tissue
and reticular dermis. Further clinical studies comparing dif-
ferent wavelengths are still required to confi rm that histologic
fi ndings correlate with clinical results.
spectrum to target collagen and promote tissue retraction (38).
The laser system consists of three different-sized laser fi bers
measuring 0.8, 1.0, and 1.5 mm and a continuous wattage out-
put power of up to 30 W. Weiss and Beasley treated 19 subjects
in the submental area, abdomen, thighs, and fl anks and
observed good-to-excellent improvement across all patients
after 3 months (Fig. 14.1) (38). Aspiration was performed with
3- or 4-mm diameter cannulas. Seventy-two percent of subjects
felt their skin was smoother and tighter. In addition, the authors
also observed reduced operator fatigue, uniformity of treat-
ment, and a signifi cantly reduced recovery time. Specifi cally, in
terms of tumescent fl uid drainage, the authors observed that
drainage following suction-assisted lipectomy occurred post-
procedure for 48-72 hours, compared with 12-24 hours with
laser-assisted lipectomy alone. Side effects were generally mild
and resolved by 2 weeks after treatment.
The 980-nm Device
A study by Reynaud et al. reported on the effects of a 980-nm
diode device (Pharaon, OSYRIS, Hellemmes, France) for use
in LAL (21). The laser system consists of a 600-µm optical fi ber
contained within a rounded 1-mm microcannula. The laser is
fi red in a continuous mode at energy settings from 6 to 15 W
depending on the treatment area. Fat lysate may be removed
by aspiration or manual massage following laser treatment.
Five hundred thirty-four procedures were performed in 334
patients over various locations. Mean cumulative energies
ranged from a minimum of 2200 J (knee) to a maximum of
51,000 J (abdomen). Patient satisfaction was high, with 58% of
patients very satisfi ed and 22% reporting they were satisfi ed
with the procedure. Patients were able to return to normal
daily activities within 24 hours. Adverse events included mild
pain reported in 17% of cases at 1 week, ecchymoses in most
of patients that resolved within 1 week, three cases of paresthe-
sias at 3 months, and one report of skin necrosis at a prior
surgical site. Ultrasound imaging showed a thermal effect,
which results in the melting and rupturing of collagenous
and subdermal bands. Physicians observed a reduction of con-
tour irregularities and immediate skin retraction during the
procedure.
Diode lasers such as the 980-nm LAL device may offer an
advantage of increased power and effi ciency (by approximately
30%) compared with other wavelengths (5). This is particu-
larly interesting given that the coeffi cient of fat absorption of
both the 980-nm and 1064-nm wavelengths were found to be
very similar (5). However, with higher energy and continuous
pulsing comes an increased risk of tissue damage and subse-
quent scarring. Carbonization of adipose tissue has been doc-
umented with use of the 980-nm device (14).
The only FDA-approved 980-nm device for LAL is Lipother-
me
TM
(MedSurge Advances, Dallas, Texas, USA).
invasive laser lipolysis technology
Devices of six wavelengths have been FDA approved for use in
the USA for LAL: 924/975, 980 (CW), 1064, 1320, and 1444 nm
(14). All devices described for use in LAL in the medical litera-
ture are discussed in the next sections (Table 14.1).
Carbon Dioxide Laser
Carbon dioxide laser (wavelength 10,600 nm) was used briefl y
during the early development of LAL (37). The ablative laser
was used during neck and jowl liposuction to create platysmal
tightening, dermal remodeling, and fat vaporization. Although
the clinical results in terms of skin tightening were impressive,
the large submental incision necessary for introduction of the
laser to the subcutaneous layer was a major drawback of the
procedure.
Diode Laser
The 924/975-nm Multiplex System
This dual wavelength diode laser system was cleared by the
FDA for LAL and appears to independently target lipid and
water-based tissues (SlimLipo, Palomar Medical Technologies,
Inc., Burlington, Massachusetts, USA). The 924-nm wavelength
has a peak in the adipose tissue absorption spectrum to provide
suffi cient penetration and heating for the release of intracellu-
lar lipids, while the 975 nm has a peak in the water absorption
Nd:YAG Laser Devices
The 1064-nm Device
The 1064-nm wavelength targets oxyhemoglobin, allowing for
effi cient vessel coagulation (24). Dermal collagen-bound water
and fat also absorb the laser wavelength but less effi ciently
than the longer 1320-nm wavelength, especially at increasing
tissue depths (22,33). The thermal energy spread is diffuse,
causing bulk heating of the treated tissues (26).
