Biomedical Engineering Reference
In-Depth Information
In a pilot human study, 24 subjects were treated noninva-
sively on the abdomen to a 1210 nm laser with variable
fl uences, a 10-mm spot size, and a 3-second exposure time.
Six-millimeter punch biopsies were taken either at 1-3 days or
at 4-6 weeks after treatment. Using nitroblue tetrazolium
chloride (NTC) staining, which is a marker for viability, a
dose-dependent damage to the subcutaneous fat and dermis
was demonstrated. There was clear histologic evidence of
laser-induced damage to fat, but no evidence was presented to
support the clinical effi cacy of this technique in fat removal
due to the single pulse nature of this study (26). This treat-
ment can be painful. Further studies and optimization of
treatment parameters are still ongoing to one day allow this
laser to be a useful tool for the noninvasive selective destruc-
tion of fat leading to fat removal.
tightening and cellulite. Although RF devices have been
shown to produce tissue tightening, there are some data to
suggest that they also can be effective in the removal of local-
ized fat. Few studies have analyzed the use of RF devices on
subcutaneous fat and circumferential reduction in size of
treated areas. A study used ThermalCool TC (Solta Medical,
Inc.) device with the Thermage Multiplex Tip to evaluate its
effect on abdominal skin laxity and waist circumference.
ThermalCool TC is a type of noninvasive monopolar RF
device that provides precooling, parallel cooling, and post-
cooling for epidermal protection. Twelve subjects were
treated in this study and results demonstrated an average
decrease in waist circumference of 1.4 cm at 1-month follow-
up visit. All patients tolerated the procedure with only mild-
to-moderate tenderness but 10 out of 12 patients did have to
take NSAIDs, oxycodone, and acetaminophen combination,
and diazepam 1 hour before treatment (28). Although no his-
tologic assessment of treated tissue was performed in this
study, another study using a different monopolar RF device
was able to demonstrate that adipocyte cell death from the
thermal injury, which was evident starting at 9 days after
treatment. Foamy histiocytic and granulomatous infi ltrates
were observed after cell death around the adipose tissue, but
no increase in circulating lipid levels was seen (29). Another
human study with a monopolar RF device, the Exilis (BTL)
was used in a study to evaluate its effect on body contouring.
The device is shown and body applicator is detailed in
Figure 12.7. Exilis is a dynamic monopolar device as it has a
handpiece that is in continuous motion allowing areas of skin
with the most laxity to be specifi cally targeted. It has been
utilized for reduction for body contouring around the abdo-
men, hips, thighs, and other areas of fat. Results are shown for
the hips and abdomen for the body handpiece in Figure 12.8.
In a study using this device, 20 subjects had four circumferen-
tial treatment sessions with the Exilis device for the upper
arm. Treatment outcome was not measured by images or
circumference but by ultrasound thickness of fat layer. Mea-
surements were taken at very precise reproducible points on
the arm. Authors reported average posterior fat reduction for
the arm of 0.5 versus 0.02 cm for untreated control arms.
(Weiss et al., in press, 2013). This was a statistically signifi cant
measurement of fat reduction by ultrasound fat layer thick-
ness. So it has been demonstrated that RF can be utilized for
fat reduction although ultimate clinical benefi ts of RF for fat
reduction await further studies with larger numbers of
patients.
radiofrequency
Radiofrequency (RF) energy has been used for decades for a
variety of medical applications such as tissue electrodessica-
tion, electrocoagulation, cardiac electroconduction ablation,
and neoplasm eradication (27). In the past few years, research-
ers have attempted to harvest energy generated through RF for
selective targeting of dermal and adipose tissues. RF energy is
produced by an electric current that is able to pass through
tissue. Heat is generated by RF through the transfer of energy
from the electric fi eld to the charges in target tissue. Because
RF is not produced by a light source, the RF heating is not
dependent on chromophores or skin type, and therefore
patients of different skin phototypes and ethnicity can safely
be treated with RF-based systems (Exilis™, BTL, Prague, The
Czech Republic; Thermage™, Solta, Hayward, California,
USA; Endymed™, Caesarea, Israel).
RF has different clinical and biological effects depending
upon the depth of tissue targeted. The depth of penetration of
RF energy is inversely proportional to the frequency. Therefore,
at lower frequencies, energy is able to penetrate deeper. RF tech-
nology has the ability to noninvasively and selectively heat large
volumes of subcutaneous adipose tissue. By selecting the appro-
priate electric fi eld, one can obtain greater heating of fat. RF can
be delivered using monopolar, bipolar, and unipolar devices. In
monopolar devices, a delivery electrode is placed over a target
area and a return electrode is applied at a distant site. This allows
current to be generated, which passes through the target tissue
and returns to the grounding pad somewhere else on the body
inducing deeper thermal damage. In general, monopolar devices
have more deeply penetrating effects than bipolar or unipolar
devices. Pain is related to the duration of the pulse with some
devices being painful and some being more like gentle thermal
heating. Monopolar devices can be static where a short cycle is
given while the handpiece is held in place or dynamic where the
handpiece is continuously moved. Generally the dynamic
devices (Exilis) tend to be more like a warm massage.
For bipolar RF devices, both electrodes are incorporated into
a single handpiece. The distance between electrodes determines
the depth of penetration and heating, which is typically con-
fi ned to within 1-4 mm of the skin surface. Unipolar RF systems
function with one electrode and no grounding pad. Some RF
devices have controlled cooling built-in to allow protection of
epidermis and dermis from thermal damage.
Most of the studies, including the initial animal and human
studies, using radiofrequency devices have been aimed at skin
conclusion
In our current body-image conscious society, there is a growing
demand for noninvasive body contouring. Few patients can
devote the social downtime required of more invasive proce-
dures. Patient demand and social media awareness over the
past few years have led to the development of a number of
ultrasound, laser, radiofrequency, light, and cold-based nonin-
vasive systems. There is tremendous interest in methods of fat
reduction and body contouring with more limited downtime
and fewer serious side effects. These various modalities allow
selective targeting of fat tissue taking advantage of the unique
properties of adipocytes. Certain devices may provide the
added benefi t of tissue tightening. As shown in Table 12.1, these
devices have different mechanisms of action, treatment times,
