Khoury laser lipolysis

Lasers in Surgery and Medicine 40:402–406 (2008)
Histologic Evaluation of Interstitial Lipolysis Comparing
a 1064, 1320 and 2100 nm Laser in an Ex Vivo Model
Jane G. Khoury, MD, PhD,* Raminder Saluja, MD, Douglas Keel, DO, Susan Detwiler, MD,
and Mitchel P. Goldman, MD
Dermatology/Cosmetic Laser Associates of La Jolla, Inc., La Jolla, California
Background and objectives: Laser lipolysis using a
pulsed Nd:YAG laser has been shown to be a safe and
effective modality for the treatment of small areas of fat in
conjunction with microcannula liposuction. The purpose of
this study is to compare the histologic effects on ex vivo
human fatty tissue using three separate wavelengths of
laser light (1064, 1320 and 2100 nm) at three predetermined
energy levels.
Study design/materials and methods: Nine samples of
freshly harvested abdominal subcutaneous tissue were
tumesced and then cannulated in a single tunnel in the
superficial subcutaneous tissue. They were irradiated with
a 320 mm polyimide fiber using a pulsed 1064 nm Nd:YAG,
1320 nm Nd:YAG and 2100 nm thulium holmium
chromium:YAG (THC:YAG) laser at 4, 6 and 8 W (Cool-
Touch Corp., Roseville, CA). The fiber was withdrawn at a
rate of 1 mm/second in a single pass. A tenth sample was
cannulated without irradiation and served as a control.
Irradiation with the 1320 nm Nd:YAG was performed in
vivo on a lipoma in a similar fashion with repetitive
tunneling. Fat was removed the following day by incisional
punch biopsy for histologic evaluation. The tissue was
studied in a blinded fashion with hematoxylin eosin
staining.
Results: Light microscopy after irradiation showed thermal
damage in the subcutaneous tissue that preferentially
affected the fibrous septae with some fat cell damage. The
diameter of thermal damage around the fiber ranged from 1
to 4–5 mm depending on the laser wavelength and average
power of the settings. No clear fat liquefaction was
seen histologically in the ex vivo samples but was seen with
the 1320 nm Nd:YAG irradiation of the in-vivo lipoma
tissue.
Conclusion: Laser lipolysis works through a combination
of photoacoustic ablation and selective photothermolysis of
fibrous septae. Acoustic damage occurs with thermal
damage and is difficult to capture histologically. The
greatest amount of thermal damage was seen in the
specimens with the highest energy per pulse, however,
the patchiness and variability of thermal damage within
the cross-sections evaluated make it difficult to draw any
strong conclusions. Further studies are warranted to
more fully evaluate the histologic effects and mechanisms
behind laser lipolysis. Lasers Surg. Med. 40:402–406,
2008. ß 2008 Wiley-Liss, Inc.
Key words: lipolysis; histology; 1064 nm; 1320 nm
INTRODUCTION
Laser lipoplasty or interstitial laser lipolysis using
pulsed neodymium:yttrium–aluminum–garnet (Nd:YAG)
1064 nm wavelength laser energy has recently been
introduced into the United States. This commercial device 1
employs a 1064 nm Nd:YAG laser that is pulsed at the rate
of 40 Hz, 150 mJ per pulse, with a 100-microsecond pulse
width. This laser has been found to produce histologically
effective destruction of human fat in ex vivo models [1]. The
1064 nm Nd:YAG has been shown to be beneficial in
destroying human fat tissue when combined with submental
liposuction [2]. Another study reported a 17%
reduction in fat volume in laser treated sites as demonstrated
by MRI findings [3]. Improved skin retraction in
areas more prone to flaccidity and improved hemostasis has
also been reported with laser lipolysis [4,5].
Recently, the 1320 nm Nd:YAG has also been reported to
be an effective adjunct to submental liposuction [6]. The
1320 nm laser device 2 delivers 300 mJ per pulse with a 100-
microsecond pulse width at 6–10 W. Although commonly
utilized in urology for lithiotripsy [7], the 2100 nm Ho:YAG
is not used in cutaneous laser surgery. However, of all the
commercially available lasers, the 2100 nm laser produces
the most effective destruction of human adipose tissue
based on optical absorption properties [8]. Despite this, fat
still remains very difficult to target with selective photothermolysis
(Table 1), absorbing far less than water or
tissue at most wavelengths (Fig. 1).
The efficacy of pulsed 1064 and 1320 nm Nd:YAG
treatment does not depend entirely on the optical absorption
properties of fat which differs from early Nd:YAG
experiments with laser-assisted liposuction [9]. The short
pulsed nature of the energy generates a non-linear
explosive tissue interaction at the cutting tip of the fiber
optic delivery device. This photomechanical ablation
1 SmartLipo manufactured by DEKA (Florence, Italy) and
distributed in the US by Cynosure (Cynosure Inc., Chelmsford,
MA).
2 CoolLipo, manufactured by CoolTouch (CoolTouch Corp.,
Roseville, CA).
*Correspondence to: Mitchel P. Goldman, MD, 7630 Fay
Avenue, La Jolla, California 92037, United States.
Accepted 16 April 2008
Published online in Wiley InterScience
(www.interscience.wiley.com).
DOI 10.1002/lsm.20649
ß 2008 Wiley-Liss, Inc.

HISTOLOGIC EVALUATION OF IL 403
TABLE 1. Absorption Coefficient (cm 1 ) of Tissue and
Human Fat at 1064, 1320 and 2100 nm Wavelength
Optical absorption
of fat vs. tissue 1064 nm 1320 nm 2100 nm
Fat 0.05 0.08 2.50
Water 0.14 1.60 > 10
causes rapid tissue removal with minimal coagulation
when compared to the same laser used in a continuous or
heating mode of low energy per pulse delivery. Nano-second
pulsed 1064 nm Nd:YAG lasers have been used in
ophthalmology for many years to generate photo-disruptive
effects inside the eye to break secondary cataracts [10]. Our
study was conducted using these wavelengths at three
different settings that bracket the recommended power
levels used by the commercial systems to determine the
most effective parameters for laser lipolysis.
MATERIALS AND METHODS
The tissue was taken from fresh skin and subcutaneous
fat (SQ) that was harvested during an abdominoplasty. The
sample was trimmed to remove any coagulated tissue that
may have interfered with histologic evaluation. Immediately
following harvesting, skin and SQ tissue were
infiltrated with tumescent anesthesia and partitioned into
ten samples marked in a grid fashion. Nine samples, each
measuring 3 cm2 cm2 cm, were cannulated with a 20
gauge (0.9 mm) blunt cannula in a single tunnel approximately
5 mm below the junction of the dermis and SQ
tissue. A 320 mm polyimide coated optical fiber was
introduced into the cannula and advanced until it was
2 mm outside the cannula tip. A He:Ne transilluminating
beam at the tip of the laser fiber allowed for precise tracking
of the fiber tip at all times. Fat was irradiated by activating
lasers and manually withdrawing the fiber at a rate of
1 mm/second in a single pass (20 times slower than the rates
Fig. 1. Coefficients of absorption of water and human fatty
tissue. Reproduced from US Patent No. 6,605,080; August 12,
2003.
used by Ichikawa et al.). The total duration of each exposure
was approximately 30 seconds.
A prototype 1064 nm Nd:YAG laser (CoolTouch Corp.,
Roseville, CA) was built to match the published specifications
of the commercially available system (SmartLipo,
Cynosure, Inc.) with a 100 microsecond pulse width at
40 Hz and 6 W giving 150 mJ per pulse. A prototype
1320 nm Nd:YAG laser, identical to the 1064 system except
for wavelength, was used at 100 microsecond pulse with
20 Hz giving 300 mJ of energy per pulse. A surgical 2100 nm
flashlamp pulsed thulium holmium chromium:YAG
(THC:YAG) laser (New Star Lasers, Inc., Roseville, CA)
with a 300 microsecond pulse and a repetition rate of 12 Hz
was also employed. Each of these laser systems was
delivered at 4, 6 and 8 W. The tenth sample, a control,
was cannulated in a similar fashion but without irradiation.
The laser parameters are summarized in Table 2.
To evaluate the photomechical and thermal effects in
vivo, laser lipolysis with the 1320 nm Nd:YAG was
performed on a 5 cm5 cm lipoma on the anterior thigh of
a subject after informed consent was obtained. Under
sterile technique, the area was delineated and 30 cm 3 of
tumescent anesthesia was infiltrated. The cannula and
laser fiber were inserted approximately 1 cm below the skin
surface. The laser was irradiated and repetitive tunneling
was performed at a rate of 1 mm/second from two different
entry points to irradiate the entire surface of the lipoma.
The duration of exposure was approximately 60 seconds.
The patient returned the next day for follow-up and a 3 mm
incisional punch biopsy was performed. The subcutaneous
tissue was undermined with curved iris scissors and
extracted from the 3 mm defect by lateral pressure.
Both sets of tissue samples were placed in aqueous 10%
neutral buffered formalin and submitted for histology. A
full thickness cross section of each of the ten specimens was
obtained by cutting perpendicularly with respect to the long
axis of the oblong skin surface. In the non-control case
where no thermal damage was observed microscopically in
the initial section, additional full thickness cross-sections of
tissue, adjacent to the initially submitted piece, were
submitted for processing in a similar manner. Grossly,
the lipoma tissue received consisted of multiple irregular
fragments of lobulated yellow fibroadipose tissue measuring
up to 2 cm in maximum dimension and aggregating to
3 cm. Sectioning of the lipomatous tissue revealed moderate
focal erythema. All sectioned tissue was totally submitted
in seven cassettes. The sections were held overnight in Pen-
Fix (buffered alcoholic formalin fixative, Richard-Allan
Scientific, Thermo Fischer Scientific Inc.) for fixation before
processing. The lab’s long process cycle was used.
The sections were stained with hematoxylin and eosin
and evaluated by the dermatopathologist using an Olympus
BX40 microscope. Photographs of representative
microscopic sections were obtained using a Nikon D70s
digital SLR camera.
RESULTS
The 1064-nm Nd:YAG at the 4, 6, and 8 W settings
showed thermal damage of collagen in fibrous septae in the

404 KHOURY ET AL.
TABLE 2. Laser Parameters and Dimensions of Thermal Damage
Sample
Wavelength
(nm)
Energy per pulse
(mJ/pulse)
Pulse duration
(microsecond)
Repetition
frequency (Hz)
Average
power (W)
Maximum dimensions of
thermal damage (mm)
1 1064 100 100 40 4 4.5 1.5 a
2 1064 150 100 40 6 2.8 0.5
3 1064 200 100 40 8 1.2 1.0
4 1320 200 100 20 4 4.0 0.6
5 1320 300 100 20 6 3.3 1.7
6 1320 400 100 20 8 1.3 0.65
7 2100 333 300 12 4 4.5 2.3
8 2100 500 300 12 6 4.0 1.5
9 2100 667 300 12 8 4.0 2.0
10 Control
a Including a 1 mm arterial lumen.
subcutaneous fat with possible damage of some adjacent fat
cells. This laser at 4 W shows thermally damaged tissue
around an artery in the adipose region (Fig. 2). At 6 W, the
area of absent and coagulated tissue measured about
2.8 mm long0.5 mm wide. A denser 1.2 mm1.0 mm area
of coagulation was seen at 8 W.
The 1320 nm Nd:YAG laser preferentially damaged
collagen in fibrous septae and affected adjacent fat cells.
Exposure at 4 W (Fig. 3) caused a branching area of
coagulated tissue along fibrous septae which was 4 mm long
and was composed of less densely packed, thinner and less
intensely colored strands, when compared to the effects of
this laser at 6 W. The densest histologic change was
observed at the 6 W setting, at which the largest area of
coagulation necrosis measured about 3.3 mm1.7 mm. A
portion of an arterial wall was damaged at the 8 W setting,
but no vessel thrombosis was noted.
The 2100 nm Ho:YAG at 4 W showed coagulated tissue
measuring about 4.5 mm2.3 mm involving a fibrous
septum and extending into surrounding fat. Nearby fat cell
membranes appeared ruptured. Centrally, there was a
patchy thin rim of purple carbonization around a hole,
consistent with a laser fiber path, measuring about
1.4 mm0.1 mm (Fig. 4). At 6 W, branching thermal
damage of approximately 4 mm in size with a central hole,
without carbonization, was seen. These changes preferentially
involved fibrous septae. The 2100 nm Ho:YAG at 8 W
produced an area of damaged tissue about 3–5 mm below
the epidermal surface, near the dermal-subcutaneous
junction, measuring about 4 mm in horizontal dimension
and 2 mm vertically. The thermal damage was characterized
by coagulation of dermal collagen at the dermalsubcutaneous
junction and ruptured fat cell membranes.
Within the coagulated zone was a very small focus of
carbonization. There was no damage to the dermis at any
other setting in this study, nor was there epidermal damage
at any setting. As the irradiation was performed on excised
abdominal tissue that was tumesced and trimmed prior to
irradiation, there was no blood flow in the excised tissue
during exposure.
In the control section, no clear laser cannula path was
observed and no thermal damage was appreciated. Even
though they were well-fixed, all of the specimens had
multiple irregular cavities in the adipose tissue attributable
to mechanical stress. Such areas could be histologically
indistinguishable from a laser cannula path.
The sections from the lipoma consisted mostly of multiple
pieces of fibroadipose tissue which contained small blood
vessels. The lesion was histologically representative of a
lipoma, although angiomatous regions were observed and
the possibility of an angiolipoma was not completely
excluded. Fibrous septae in the fat were damaged,
demonstrating homogenization of collagen bundles,
vacuoles of various sizes, purple pyknotic nuclei, heatcoagulated
collagen fibers, and small foci of dark purple
carbonization. Fat cell membranes were ruptured in some
areas (Fig. 5). Crush artifact may have been contributory to
a portion of the septal collagen abnormalities and to
rupture of fat cell membranes. Congested/thrombosed
blood vessels and pinkish red homogeneous material,
consistent with extravasated red blood cells and serum,
was found among variably damaged fat cells. Focally, there
was liquefaction of fat, characterized by variably sized
vacuoles without visible cell membranes in a background of
Fig. 2. 1064-nm Nd:YAG at 4 W. Thermal damage near an
artery in the subcutaneous fat region. The photograph is 2 mm
wide (10 objective).

HISTOLOGIC EVALUATION OF IL 405
Fig. 3. 1320-nm Nd:YAG at 4 W. A branching pattern of
thermal damage along fibrous septae and affecting some
nearby fat cells. The photograph is 4.38 mm wide (4
objective).
Fig. 5. Lipoma treated with 1320-nm Ho:YAG. Low power
view showing a cavity which could represent a laser cannula
path, rupture of surrounding fat cell membranes, and
congested/thrombosed blood vessels. The photograph is 5 mm
wide (4 objective).
homogenous pinkish red material and extravasated red
blood cells (Fig. 6). Zones of tissue that appeared to be
ablated and removed were not found, but the presence of
such areas was not completely ruled out. Areas of normal
fat and angiomatous foci without significant laser effect
remained.
DISCUSSION
Laser lipolysis is gaining popularity with the recent FDA
clearance of a 1064 nm Nd:YAG and a 1320 nm Nd:YAG
laser. These systems do not rely completely on conventional
laser–tissue interactions as evidenced by the increased
absorption of tissue over fat at these wavelengths (Fig. 1).
The 1064 nm Nd:YAG is a relatively low powered, 6 W
system that operates at a wavelength with low absorption
properties in tissue and fat. However, histology of the
ablated tunnels created by this laser does show ablation
and charring. Ichikawa et al. proposed that it is the short
pulse nature of this laser that is key to the interaction [1].
Nano-second pulsed 1064 nm lasers have been used in
ophthalmology to generate photo-disruptive effects inside
the eye to break secondary cataracts. However, the pulse
width of this 1064 nm laser is 100 microseconds,
10,000 times longer than the 10 nano-second ophthalmic
laser and is not short enough to produce the optical
breakdown plasma characteristic of this type of laser.
Laser lipolysis at 1064 and 1320 nm wavelengths also
requires the use of a contact tip fiber optic. Holmium lasers
do not need to be in contact with tissue to work nor do they
need any specific fibers or hot tip effects to ablate tissue.
Fig. 4. 2100-nm Ho:YAG at 4 W. A thin rim of carbonization
around a hole which probably represents a laser cannula path
in the subcutaneous tissue. Surrounding fibrous septal
collagen and fat cells are damaged. The photograph is 5 mm
wide (4 objective).
Fig. 6. Liquefaction of fat is visible within the lipoma treated
with the 1320-nm Ho:YAG laser. The photograph is 1 mm wide
(20 objective).

406 KHOURY ET AL.
The 2100 nm Ho:YAG is highly absorbed in both water and
fat and the histology showed the greatest amount of
damage to fibrous septum. While this laser shows promise,
additional experiments with shorter pulse lengths and
higher repetition rates are needed to make better direct
comparisons to the 1064 and 1320 nm systems. For now,
based on the absorption characteristics of the 1064 and the
1320 nm Nd:YAG systems, the 1320 nm wavelength may be
more efficient in fat disruption while providing enhanced
tissue contraction. This remains a theoretical benefit based
on absorption coefficients as no controlled trials have been
published comparing the 1064 and 1320 nm systems in
laser lipolysis and tissue tightening.
The polyimide coated optical fiber has a carbon coating
and operates like a conventional hot-tip device. The 100
microsecond pulse energy heats the carbon coating on the
tip rapidly enough so that localized tissue vaporizes with an
explosion that generates an acoustic ablation effect. This
pulsed explosive interaction at the tip of the fiber optic
causes rapid tissue removal and very minimal coagulation
when compared to the same laser used in a continuous or
heating mode of low energy per pulse delivery. A recent ex
vivo study on human tissue showed that these short pulse
widths create high peak powers with less collateral tissue
damage [11].
Acoustic damage is difficult to evaluate histologically and
we were unable to directly correlate any specific histologic
findings to photoacoustic effect. All of the irradiated
specimens had multiple irregular cavities in the adipose
tissue that were not seen on the histology of the
control section. These cavities were located between 6 and
9 mm below the epidermal surface where the laser
irradiation occurred. These changes were most noted for
the 1320 nm at 6 W, however whether this represents
mechanical stress or photoacoustic laser effect is difficult to
determine. Further studies that vary acoustic effects by
changing pulse length while keeping power levels and
thermal input constant are needed.
Our histologic findings of heat-coagulated collagen
fibers, ruptured and denatured fat cell membranes, carbonization,
and hollows created by mechanical cannulation
were similar to the types of histologic findings found in
previous laser lipolysis studies [1,3]. One of the challenges
in interpreting these results is the variability of the
thermal damage seen on histology. We anticipated an
increase in thermal damage that corresponded with
increasing wavelength and power settings that was not
seen in our findings. A weakness of the study is the limited
number of cross-sections that were obtained for analysis.
Only one-cross section was evaluated for most of the
settings and variability of damage was not assessed along
the treatment axis. Whether the patchy findings are due to
true irregularity of laser irradiation or merely reflect
histologic sampling error will require further studies with
more in depth histologic evaluation.
Each ex vivo tissue sample was only exposed to one pass
of the laser to see the how far the effects of the 320 mm laser
fiber would extend. However, tissue exposed to the laser for
a greater period of time with repetitive tunneling would
provide more representative results of in-vivo treatment.
For this reason, treatment on the lipoma was performed
with the 1320 nm Nd:YAG at 6 W and liquefaction of the fat
was seen. While these findings are encouraging, the
liquefaction comprised less than 5% of the cross-sectional
area of the lipoma and more extensive in vivo studies are
necessary to corroborate these findings.
Laser lipolysis works by a mechanism of photoacoustic
ablation and selective photothermolysis of fibrous
septae. The greatest amount of thermal damage was seen
in the specimens with the highest energy per pulse,
however, the patchiness and variability of thermal damage
within the cross-sections evaluated make it difficult to draw
any strong conclusions. While the audible pop heard during
the treatment indicates that the energy is being converted
from optical to mechanical forms, photoacoustic ablation is
difficult to separate out from thermal damage as they occur
together. Equally challenging is capturing the histologic
changes of acoustic damage. Although our study shows
evidence of interstitial lipolysis at these wavelengths,
future studies are warranted to more fully evaluate the
histologic effects and mechanisms behind this treatment
modality.
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