Energy-based noninvasive surgical tools can be used for ablative bio-stimulation (eg, collagen production) or tissue restructuring functions (eg, tightening or lifting) and are the subject of this review. The authors present the various methods and tools for noninvasive cosmetic surgery (ultrasound, radiofrequency, cryolipolysis, and lasers) and present the clinical outcomes of each. They summarize techniques and methods and their indications, physical parameters and tissue target, and consistency.
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Advancements in surgical techniques have to the development of many noninvasive concepts or incorporation of existing concepts into plastic surgery armamentarium; stem cells-based therapies, mesotherapy, and energy-based surgical tools such as ultrasonic, radiofrequencies, lasers, cryogenic, hydromechanical, microwave technologies are among the newest developments.
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Clinical outcomes following noninvasive procedures with energy-based devices tend to be much more subtle than those following invasive surgical procedures.
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As with any medical procedure, noninvasive procedures carry some degree of risk of adverse effects as those resulting from non-uniform healing after application of ultrasonic energy, lasers or radiofrequencies in addition to trivial problems such as transient edema, skin erythema, bruises.
Overview
Various oils, creams, and lotions have been used for skin-quality maintenance and beautification over the centuries. However, the quest for the preservation of youth and beauty has evolved with the introduction of invasive cosmetic plastic surgery procedures, which have been developed and popularized since the beginning of the last century. During the last 2 decades, advancements in surgical techniques have paralleled advancements in dermatologic sciences, leading to the development of many noninvasive concepts (eg, stem cells–based therapies, mesotherapy) and modalities (eg, lasers) and providing new tools for cosmetic surgery and medicine. Energy-based surgical tools, including ultrasonic, radiofrequency (RF), cryogenic, hydromechanical, and microwave technologies with the capability of tissue cutting, sealing, or restructuring, complement these medical concepts well by allowing noninvasive, non–open-access interventions. Energy-based noninvasive surgical tools can be used for ablative bio-stimulation (eg, collagen production) or tissue restructuring functions (eg, tightening or lifting) and they are the subject of this review. Experience with a laser-therapy device for body contouring (1440 nm wavelength laser for soft tissue sculpting), as an example of laser-based technology applied to body contouring, is reviewed in another article of this issue. Additionally, because the focus of this article is tissue restructuring and its applications in aesthetic surgery, hydromechanical tools (eg, water-jet technology used to cut and emulsify soft tissue) are not featured.
Therapeutic options
In general, the application of noninvasive energy-based devices for tissue restructuring can lead to results that are less dramatic than those from surgical procedures. However, patients find value in the reduced amount of downtime needed to recover from noninvasive procedures by energy-based devices. For this reason, the noninvasive energy-based technologies have become popular, even when treatments must be repeated to achieve an optimal result or when approximating the result of an invasive procedure.
The typical 2 tissue-restructuring objectives for currently available energy-based devices are
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Two-dimensional tissue shrinkage resulting in tissue lifting and/or firming
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Volume-reducing and body-contouring techniques
Both objectives have energy-based technologies with modalities that are based on controlled thermal damage to the tissue. Therapeutic options for the most common conditions are depicted in Table 1 . Ultrasound (US), RF, cryolipolysis, laser-assisted therapies, and even soft radiation have found an application in these objectives.
| Technology | Source of Energy | Wavelength or Other Physical Parameter | Tissue Target | Indication |
|---|---|---|---|---|
| Low-level laser therapy | Red light or near infrared | 600–1000 nm | Subcutaneous fat, within a few millimeters range | Desire for focal, noninvasive fat reduction |
| MFUS | Ultrasound | 4–10 MHz | Dermis, SMAS, frontalis, platysma muscles | Excessive skin laxity, need for skin tightening, forehead, brow ptosis |
| RF | Electromagnetic waves | 300 MHz to 3 KHz | Dermis | Excessive skin laxity, mild skin wrinkling |
| Cryolipolysis | Thermoelectric cooling systems, cold air, contact cold gel panels | −3°C to 7°C | Subcutaneous fat, probably within a few millimeters range | Superficial subcutaneous fat collections, mild tissue ptosis (eg, jowls) |
| HIFUS | Ultrasound | 2 MHz | Subcutaneous fat, up to 30-mm range | Superficial and intermediate fat deposits |
US-based devices
US-based devices generate a US beam, which can be focused to a predetermined depth of penetration and placement of energy. After passing innocuously through the skin (or superficial skin layers), focused US waves reach a focal point where alternating waves of compression and rarefaction rapidly heat tissue (ie, thermal coagulation) or mechanically disrupt the target tissue via cavitation. Depending on which tissues are targeted and the degree of tissue disruption, focused US can be used for different purposes. These purposes include the lifting and tightening of the skin and skin-adjacent tissues (ie, microfocused US [MFUS]) or body contouring (ie, high-intensity focused US [HIFUS]).
MFUS
MFUS therapy uses US energy (in a low megahertz range) to noninvasively firm, tighten, and shrink the dermis and subdermal tissues producing a lift of soft tissues. There is currently only one commercially available MFUS device approved by the Food and Drug Administration (FDA) (the Ulthera System; Ulthera, Inc, Mesa, Arizona), with another recently available in the Korean market (Doublo System; Hironic Co LTD, Korea), which integrate real-time US imaging with focused US energy. This integration allows the clinician to target the desired treatment depth for the precise delivery of energy below the surface of the skin without affecting the intervening tissues. Multiple removable transducers offer a choice of depths for MFUS penetration ( Fig. 1 ). In general, higher-frequency transducers are used for a more superficial tissue effect compared with lower-frequency transducers. For example, a 4-MHz transducer is characterized by a 4.5-mm depth (appropriate for deep dermis or SMAS treatment in facial areas) and a 7-MHz transducer is characterized by a 3.0-mm depth. Unlike in focused US ablation therapies (eg, for tumors), which interlace coagulative sonication zones to ensure complete tumor ablation, cosmetic MFUS applications involve treatments delivered in lines of small precisely spaced zones of tissue coagulation in the targeted tissues. To help track the placement and quantity of the treatment lines delivered, the treatment area is marked using a standardized facial grid ( Fig. 2 ). Zones of coagulation placed in the target tissues (eg, SMAS) undergo the wound healing process to produce subcutaneous microscars that contract, resulting in treated tissue firming or an aesthetic unit lift as the result of cumulative linear or gridlike field contracture ( Fig. 3 ).
HIFUS
HIFUS generates high-energy US waves (up to 10 000 W/cm 2 ) for lipolysis. The energy for HIFUS is typically more diffuse, and the focal points converge deeper than MFUS, delivered 10 to 30 mm below the skin level, targeting the subcutaneous adipose tissue. Like MFUS, HIFUS creates a temperature in the range of 56° to 65°C at its focal point, delivering the thermal energy to the targeted fat tissue layer without damaging intervening tissues (overlying and underlying fat). However, because the physical characteristics of HIFUS interaction with tissue predicated in a more diffuse and deeper way (than for skin-tightening devices) but still within a 3-cm reach, for the best possible result skin should contract over decreasing in volume of subcutaneous fat. Truly obese patients with poor skin tone are not good candidates for body contouring using this technology because the skin may not contract or re-drape deeper layers of tissue uniformly ( Fig. 4 ). Devices that deliver focused US energy on a 2-MHz wavelength have received much attention recently because they seem to be effective in disrupting adipocyte cell membrane, releasing intracellular content, and initiating triglycerides absorption. The cumulative goals of these treatments are ultimately in tissue volume reduction and contour change for the treated body part (see Fig. 4 ).
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