Lukac_revised2.qxp 19/5/09 2:15 pm Page 59
Novel Fractional Treatments with VSP Er:YAG Aesthetic Lasers
the slow Cr–Er cross-relaxation times. As a result, the shortest Figure 1: Effect of the Laser Beam on Tissue in the
achievable Er,Cr:YSGG laser pulsewidths are in the 500µ-second
Four Treatment Regimes
range,
4–5
limiting its adjustable coagulation depth range only to a
minimum of 17µm and beyond. When taking into account the
optical penetration depths of the three ablative sources, where we
observe that Er:YAG lasers allow coagulation depth control from
3µm and beyond, Er,Cr:YSGG lasers from 17µm and CO
2
lasers
30µm, Er:YAG lasers allow the largest range of coagulation depth
control and therefore the most complete range of treatment
modalities. By adjusting laser parameters, the Er:YAG laser can be
used to perform all typical Er:YAG type procedures, as well as
Er:YSGG- and CO
2
-type laser treatments.
Cold ablation Warm ablation Hot ablation No ablation
As discussed above, laser light’s ablative energy must be delivered
Figure 2: Approximate Ablative and Coagulative Depths
to the skin in a temporal pulse of specific and exact duration in for the Nine Variable Square Pulse Treatment Regimes
order to control skin heating and ensure the efficacy, efficiency
and safety of treatments. In the case of a long laser pulse or
0–5µm 6–20µm 21–100µm
continuous irradiation, the generated heat has sufficient time to
diffuse deeper into the tissue from the irradiated surface area. This
3–7µm Er
:Y
results in higher thermal effects inside the skin. To generate high-
AG
Coagulation depth
energy light pulses, most devices use a standard pulse-forming
network (PFN) technology. PFN pulses have a typical temporal
8
–15µm
Er
:Y
SGG
shape with a slow rise time and a relatively long declining tail. The
pulse power is not constant during the pulse and the exact
pulsewidth is not defined. More advanced variable square pulse
16–30µm
CO
(VSP) technology
6
generates pulses that provide much higher 2
treatment precision, efficacy and safety.
7,8
A significant difference
between the two pulse types is that for square pulses the average
and peak powers are almost identical, which is not the case for Three VSP Er:YAG laser treatment regimes in terms of their ablative
PFN pulses. This means that the effect of VSP pulses on the skin is depth also need to be considered: light, medium and deep. The
far more predictable than PFN pulses. In turn, this leads to better combination of Er:YAG thermal treatment regimes with the
treatment outcomes with less discomfort for the patient and fewer treatment regimes based on ablation depth provides a matrix of
side effects. nine VSP treatment regime options. The approximate ablative and
coagulative depths for the nine regimes are shown in Figure 2.
Basic Variable Square Pulse Er:YAG
Laser Treatment Regimes In addition to the nine basic VSP Er:YAG treatment regimes, Fotona
In laser ablation, one non-ablative and three ablative treatment has developed a unique additional 10th treatment regime: the
regimes are generally considered.
9
At high energies and low non-ablative smooth mode. In Fotona’s smooth mode, laser energy
pulsewidths (i.e. at high laser pulse powers), the ablation speed is is transmitted as heat onto the skin surface without any resulting
higher than the rate at which heat diffuses into the tissue. All laser ablation and dissipated into the deeper tissue layers. To achieve
energy is used up for cold ablation (see Figure 1). The thermally this, smooth mode delivers laser energy in a time period that is
affected tissue layer is confined to the directly heated tissue shorter than the combined skin tissue relaxation time (TRT),
volume within the optical penetration depth. With decreasing estimated to be in the range of 500 milliseconds. This ensures that
energies and/or longer pulsewidths (i.e. with lower laser pulse the skin does not have time to cool off during the laser pulse. The
powers), the tissue layer that has been indirectly heated becomes delivered laser energy thus results in an overall build-up of heat
thicker. Thermal effects become more pronounced, leading to warm and creates a temperature increase deep in the papillary dermis.
ablation and, at even lower energies, to hot ablation. At energies Smooth pulses deliver laser energy onto the skin in a fast sequence
below the ablation threshold there is no ablation and all the energy of low-fluence laser pulses inside an overall super-long pulse of
is released as heat, irrespective of the laser pulsewidth. 200–350 milliseconds. As the super-long smooth pulses are longer
than the epidermal TRT but shorter than the combined skin TRT,
Coagulation and ablation depths depend on a combination of three conditions for ablation are never reached. The effect of smooth
parameters: laser wavelength, pulsewidth and fluence (i.e. the mode is coagulative heating of the skin without any significant
laser energy per surface area in J/cm
2
). In this respect VSP ablation of the epidermis. Histological investigations show that
technology-supported Er:YAG lasers demonstrate high versatility smooth mode treatments result in collagen coagulation as deep as
and precision as a skin-resurfacing tool. Their pulsewidth and 300µm below the epidermal–dermal junction.
10–17
fluence control provides a wider range of treatment options. VSP
Er:YAG laser treatment regimes are defined as follows: cold regime Clinically, this collagen coagulation results in visible and long-
with coagulation depths of approximately 3–7µm; warm regime with lasting reduction of wrinkles and scars.
18–19
An advantage of the non-
coagulation depths of approximately 8–15µm; and hot regime ablative aspect of smooth-mode treatments compared with
with coagulation depths above approximately 15µm. ablative laser treatments is that during and immediately following
EUROPEAN DERMATOLOGY 59
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