Dr. Darm technical overview on SlimLipo laser wavelengths. Dr. Darm of Aesthetic Medicine in Portland, Oregon pioneered his trademark procedure – the Lipolift – for the treatment of unwanted fat and cellulite. Lipolift III, known as the Laser Lipolysis (laser-assisted liposuction) offers a minimally invasive body sculpting solution that safely "melts" fat away with less pain, less downtime and consistent aesthetic results. The laser is slipped through a very small hole in the skin and passed back and forth while it slowly dissolves the fat and destroys the fat cells. The melted fat is then gently sucked out through a small cannula. Treatment areas include abdomen, flanks, back, arms, neck, and thighs. The SlimLipo Body Sculpting Laser from Palomar is FDA cleared for laser-assisted lipolysis and it is the first system optimized specifically for this application.

1. SlimLipo™ Laser Wavelengths
James J. Childs PhD, Mikhail Smirnov PhD, Alex Zelenchuk PhD, and Gregory Altshuler, PhD, DSc
Introduction represents the 50˚ C temperature contour demarcating the
outer edge of the zone of lipid liberation. For the same
Several technologies have been developed for procedures
energy deposited by all four laser wavelengths, the 924
resulting in fat reduction by lipolysis and aspiration.
nm light creates the largest zone of lipid liberation and
Proponents of laser-assisted lipolysis have presented sev-
coagulation of proteins and fibrotic tissue. Figure 2
eral potential advantages of this technique over tradition-
shows the percent volume of coagulation and lipid
al liposuction. These advantages have been described in
liberation relative to the volume for the 924 nm laser.
an earlier white paper entitled “Selective Laser Induced
Melting”. In this paper, a device designed specifically to
safely "melt" the largest volume of fat possible is
described. A properly selected laser provides an excellent
tool for this task if the right wavelength (or wavelengths)
is chosen for the specific tissue to be treated. Selectivity
of a specific light wavelength for an absorbing substance
(also called a chromophore) is a measure of how well
light is absorbed by that chromophore in comparison to
the absorption of that light by other chromophores that
will also be exposed to the light in the tissue. For exam-
ple, water and lipids are important chromophores in
human fat with lipids being the most abundant
(75–85%). Figure 1. Temperature profile in adipose tissue at the end of a 20W,
300 ms pulse from a 600 micron fiber compared across different
"Melting" refers to the process of lipolysis realized ideal-
wavelengths. The y-axis is in units of millimeters.
ly by direct absorption of the light energy by the lipids.
The absorption of this energy causes the lipids to heat
sufficiently to thermally alter the dense lipid and protein
envelope encapsulating the lipid droplet ultimately lead-
ing to leakage from the adipocyte, a “lipid liberating
mechanism” induced by selective photothermolysis. Lipid
liberation occurs either during the laser emission or as a
result of delayed thermally-induced changes to the perme-
ability of the envelope.
924 nm for Efficiency
Light at 924 nm is highly selective for lipids in compari-
son to water since this light is absorbed approximately Figure 2. Percent volume of damaged fat for 924 nm, 980 nm, 1064
two times more in lipids than in water. To demonstrate nm and 1320 nm laser light at 300 ms pulse and 20W output power.
the effect of several different laser wavelengths, a study
was performed comparing the temperature profiles in The volume of coagulated tissue using the 924 nm wave-
human fat (Figure 1). Each laser emitted 20 watts (W) length light is thirty-three (33) times greater as compared
of continuous wave output power through a 600 micron, to 980 nm, approximately six (6) times greater as com-
straight end-cut fiber tip for 300 milliseconds (ms) and all pared to 1,064 nm and 2.7 times greater as compared
other factors were held constant. The inner solid line in to 1,320 nm. When comparisons are made of the lipid
each of the four images of Figure 1 represents the 64˚ C liberating volumes, the 924 nm light is ten (10) times
temperature contour indicating the outer edge of the zone more efficient than 980 nm, four times more efficient
of coagulation around the fiber tip where immediate lipid than 1064 nm and about 2.5 times more efficient than
liberation and tissue coagulation occur. The outer line 1,320 nm.
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2. 924 nm for Safety
For treatment safety, it is important to prevent burning of
the skin. Since 924 nm has the highest selectivity for fat
versus water (and skin which is predominantly water),
this wavelength is the safest when operating near the
dermis. To demonstrate this, Figure 3a shows the same
conditions as in Figure 1 but with the fiber placed 2 mm
below the dermis/hypodermis junction indicated by the
solid horizontal line. Note that for the 1320 nm wave-
length, the dermis has been significantly damaged. In
contrast, no damage is observed in the dermis by the
other lasers. The power of the light for all wavelengths
was then adjusted to achieve the same level of efficiency
Figure 3b. Temperature profiles in adipose tissue at the end of a 300
of fat melting, i.e. equal volumes of damaged adipose ms pulse from a 600 micron fiber compared across different wave-
tissue, as is achieved with the 924 nm laser light at 20W. length lasers. The power of each laser is adjusted for equal damage
In this case, all laser wavelengths except the 924 nm volume in adipose tissue. Damage to the dermis is defined by the
wavelength cause damage to the dermis (Figure 3b). volume within the 50˚C contour.
Table 1 lists the required powers for each wavelength to ..
produce equal volumes of damaged adipose tissue. In
this table, the percent damage shown is based on 1.5 mm
thick dermis. As demonstrated, the 1320 nm laser causes
100% damage since the 50˚ C contour line extends up to
1.5 mm from the dermis/hypodermis junction. In con-
trast, due to its high selectivity for fat, there is no damage Table 1. Comparison of percent dermal damage across the four wave-
to the skin with 924 nm light. Note also that, while the lengths. For equal comparison, each laser's power is adjusted to pro-
vide the same damage volume in fat for a 300 ms laser pulse. Damage
dermis is not damaged by the 1064 nm light at 20 W is defined as tissue coagulation plus cell death and extends to over 1.5
power and 2 mm distance, the 924 nm wavelength melts mm into the dermis for the 1320 nm wavelength. This is considered to
four times more volume of fat (Figure 2). The 924 nm represent 100% dermal damage.
light is therefore the safest and most efficient wavelength
to use for melting fat. Table 1 clearly shows that considerably more power is
needed at the other laser wavelengths to meet the fat
melting effects of 924 nm. However, by increasing the
wattage at other wavelengths in order to liberate lipids as
efficiently as 924 nm, there is increased risk of damaging
the dermis and other deep water-based structures when
using these other wavelengths.
Finally to address hemostasis, it is important to note that
light at either 924 nm or 975 nm wavelengths is readily
absorbed in blood as compared with the other wave-
lengths evaluated in this paper. Table 2 provides the
absorption coefficients of blood with 15 gm/dL of the
designated hemoglobin at each wavelength.
Figure 3a. Temperature profile in adipose tissue near the dermis at the
end of a 20W, 300 ms pulse from a 600 micron fiber compared across
different wavelength lasers.
Table 2. Absorption coefficients of blood at the four wavelengths
studied in this paper.
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3. 975 nm for Flexibility
Laser light at 975 nm is also an important wavelength
that was specifically chosen to complement the 924 nm
laser light when the SlimLipo™ laser is used, for example,
in fat tissue with tumescence. This wavelength was
chosen because it provides the highest selectivity for
water yet has a low enough absorption coefficient in
water to provide good penetration into the tissue and
therefore sufficient volume heating. Light at 975 nm is
highly selective for water versus lipids because it is
absorbed about ten times more in water than in lipids.
By choosing two wavelengths, one with high selectivity
for fat and the other with selectivity for water, one has
better control to “dial in” treatment for a given tissue
composition. For example, in the treatment of fat with
little tumescence, 924 nm light may only be used. In
treating fat that contains significant tumescence or when
desiring to provide selective heating of the dermis for skin
tightening, the 975 nm light may be used to optimize
overall absorption of the light in these structures with
high water content. Figure 4 below demonstrates the
increase in the melting volume when 975 nm laser light is
added to the 924 nm light in adipose tissue with high
water content (hydrated fat with 30% water content on
the right side) as compared with normal fat (left side).
This demonstrates that a system combining two wave-
lengths, each selective to one of the two primary
chromophores in fat, is optimized with greater flexibility
to treat a variety of tissue environments.
Figure 4. Temperature profile comparison of single and mixed wave-
lengths of the SlimLipo™ tip in normal fat and in fat with 30% water
(hydrated fat).
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