Biomedical Engineering Reference
In-Depth Information
ultrasound
Ultrasound has been used to selectively target adipocytes
through noninvasive mechanical and thermal mechanisms.
Ultrasound is a cyclic sound pressure wave with frequency
above the range of human hearing (
Since FDA clearance in 2010, there have been more than
hundreds of thousands of treatments completed. Data from
all the clinical trials and studies thus far indicate that this
device has a good safety profi le without any systemic health
effects. The most common reported and observed immediate
adverse effect is localized erythema that can last for several
hours after treatment. Localized ecchymosis at the site of
device application has also been observed, especially in
patients using aspirin or anticoagulants, and it is thought to be
related to the vacuum suction of the applicator. Clinical stud-
ies have also reported reversible altered cutaneous sensation in
the treated area, which is apparent immediately after treat-
ment and can last up to 2 months. Typically soreness in the
treated area is experienced for several days. Coleman et al. did
a study to assess the effects of cryolipolysis on sensory func-
tion in humans and reported reduction in sensitivity to stim-
uli noted 1 week after treatment in all nine treated subjects
that lasted 1-6 weeks (10). Six out of 9 subjects reported
reduced pain or pinprick sensation. Some patients also
reported reduction in light touch, 2-point discrimination, and
temperature sensitivity on neurological examination of the
treated area. A nerve biopsy taken from one patient 3 months
following the procedure revealed no pathologic changes when
compared with baseline biopsy specimens. In all cases, the
neurologic side effects were transient and completely revers-
ible by 2 months posttreatment.
The induction of adipocyte apoptosis did not signifi cantly
affect serum triglyceride or cholesterol levels or liver function
tests, including aspartate aminotransferase, alanine amino-
transferase, alkaline phosphatase, total bilirubin, and albumin
(11). There have been rare reports of severe pain in approxi-
mately 0.05% of patients treated with cryolipolysis. This pain
is characterized as a severe “shooting” and “jabbing” pain and
the onset is usually within 4-7 days of treatment. The mecha-
nism of action remains unclear, but it is more commonly seen
with the treatment of a large surface area with the larger appli-
cator. It is believed to be related to lax muscle with muscle
being subject to prolonged cooling or may be related to a more
robust panniculitis, nerve infl ammation, or ischemia reperfu-
sion injury resulting in allodynia and hyperneuralgia. In the
23 reported cases, rare severe pain was adequately controlled
with topical and oral analgesics and resolved spontaneously
within 1-4 weeks (12). The effect of cryolipolysis on patients
with cold-induced dermatologic syndromes, such as cryoglob-
ulinemia, cold-induced urticaria, Raynaud's syndrome, or par-
oxysmal cold-induced hemoglobinuria, is not yet known as
most studies have excluded them from treatment (13).
When patients are seen for body contouring and they are
deemed an appropriate candidate by a physician, the patients
are informed that they may expect about 20-30% improve-
ment with a single treatment and that multiple treatments may
be required. We recommend waiting for 4-5 months to observe
the maximal result from a single treatment. Cryolipolysis leads
to induction of apoptosis, or programed cell death, for adipo-
cytes. These slowly drop out, so the patient needs to understand
that this will be a slow and steady process. The trade-off is min-
imal to no social downtime for a procedure that can reduce fat
in selected areas on the fl anks, abdomen, and even off-label
uses such as inner thighs, male gynecomastia, and fat accumu-
lations below the bra line in women.
20 kHz). Ultrasound
waves are capable of traveling through tissues and in the pro-
cess they lose energy and become attenuated as they are
refl ected, scattered, or absorbed by the tissue they pass through.
However, if suffi cient quantities of ultrasound wave-generated
energy reach the target tissue, they can induce molecular vibra-
tions in the tissue, thus generating thermal heat (thermal-based
ultrasound lipolysis). Ultrasound waves are also capable of
creating holes (cavities) when they have suffi cient negative
pressure to overcome the adhesion of the medium molecules to
each other (nonthermal or cavitation-based ultrasound lipolysis).
In the latter case, mechanical energy of ultrasound is used to
induce damage to targeted adipocytes. Ultrasound used for body
sculpting is divided into two broad categories: cavitation-based
lower-frequency nonthermal ultrasound that uses mechanical
energy to disrupt adipocyte cells and high-intensity, thermal
focused ultrasound (HIFU) that uses thermal energy to ablate
adipose tissue (14).
>
nonthermal focused ultrasound
Cavitation-based NTFU (UltraShape™, Syneron/Candela Inc,
Irvine, CA) uses focused ultrasound waves to deliver concen-
trated energy into a precise depth in the subcutaneous tissue
resulting in cavitation. Focusing the ultrasound requires para-
bolic refl ectors in the transducer. Target distances within the
fat layer may be varied. Nonthermal, mechanical energy is
used to disrupt fat cells without damaging the neighboring
structures such as skin, blood vessels, and nerves. This tech-
nique takes advantage of the differential susceptibility of
fat cells to mechanical stresses induced by the ultrasound.
The device is composed of a parabolic transducer and an
external visual guidance system to direct a focused beam of
ultrasound energy (Fig. 12.3). Low-frequency ultrasound
waves (~220 kHz) are delivered in pulse waves to the targeted
tissue, where they generate cavitation causing cell death and
apoptosis due to mechanical cell disruption (14,15).
One of the initial studies to demonstrate effi cacy of NTFU
was conducted in Spain on 30 healthy patients using Ultra-
Shape
Contour I
(UltraShape Ltd., Syneron/Candela), a nonin-
vasive, NTFU device. In this study, all patients underwent
three treatments at 1-month interval and were evaluated
1 month after the last treatment. Outcomes were assessed on
the basis of change in fat thickness, ultrasound measurements,
and circumference measurements. Results showed that after
three treatments, there was a mean reduction of fat thickness
by 2.28
±
0.80 cm and circumference reduction by a mean of
3.95
1.99 cm, while weight was unchanged (15). A larger
study with 137 patients reported a mean reduction of approxi-
mately 2 cm in treatment area circumference and approxi-
mately 2.9 mm in skin fat thickness after a single treatment.
Most of the effect was notable within 2 weeks and lasted for
12 weeks (16). Overall, the treatments were well tolerated with
patient experiencing only mild pain, but there were scattered
reports of blister formation on the skin as a consequence of
wave refl ection of ultrasound waves over bony prominences.
Studies for Asian patients using the same device were reported
±
