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Radiofrequency and infrared technologies
- Alessandra Haddad
- Marian Cantisano-Zilkha
BASIC CONCEPTS
Improvement in skin laxity following laser treatments was first observed in the early 1990s during ablative resurfacing treatments with a CO 2 laser. While it was initially assumed that the benefits of these treatments were due to the removal (ablation) of tissue, cosmetic improvements were often more significant than could be explained by ablation of tissue alone. Ablation typically removed 20 μm of tissue, but a residual thermal zone of 60–120 μm depth was also created. The temperature rise and duration of this heating were sufficient to denature collagen, leading to a visible contraction of the skin during treatment. This led to a tighter, fresher look as a component of the ablative laser treatment. Results seen after a long-term follow-up showed histologically that resurfacing techniques are an effective alternative to deep phenol peels. On the negative side, prolonged recovery time, long training and learning curves for the practitioner, added to the high incidence of complications (scarring, dischromias, infections and pain), caused the decline of resurfacing procedures.
That has led to a question: Is it possible to get the benefits of tissue tightening non-ablatively?
The answer is yes, and non-ablative tissue tightening is one of the newest and most exciting procedures in the aesthetic marketplace today ( Table 7.1 ).
| Ablative rejuvenation. |
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| Semi-ablative rejuvenation |
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| Non-ablative |
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Grekin and colleagues published the first large prospective study evaluating a radiofrequency (RF) resurfacing system (Visage®) for treating wrinkles. The results of this study, involving 95 individuals with mild to severe photodamage in the periorbital or perioral regions, showed positive improvement in the Fitzpatrick Wrinkle Score. The degree of improvement was linked with the severity of wrinkles at baseline. Primary adverse effects were transient postinflammatory hyperpigmentation (26%) and hypertrophic scarring (4%). They concluded that the efficacy of RF resurfacing may be comparable with that of laser resurfacing. In addition, RF resurfacing may provide more rapid healing and less pain and erythema than CO 2 lasers. Similar results are possible with non-ablative skin-tightening devices.
The goal of this chapter is to provide an understanding of non-ablative skin tightening. We will examine what is required for tissue tightening, as well as the different approaches available today. As it is common, there are many conflicting and confusing claims made by manufacturers, and hopefully this chapter will allow readers to make an informed analysis in their decision to use non-ablative technologies.
DEFINITIONS AND TERMINOLOGY
Collagen
Before going further, it is worthwhile to give some definitions. Collagen is a family of structural proteins, providing strength and resilience to the skin and other tissues. Collagen is produced by fibroblasts in an early-stage form called procollagen. It is composed of a triple helix of protein chains, with interchain bonds creating a crystalline structure for the collagen.
Type I collagen is the most common form of collagen found in the dermis and provides the tensile strength of the skin. This form of collagen is also believed to be a key component in skin aging, since the quantity has been shown to be lower in photo-damaged skin and to increase after some skin rejuvenation treatments. Type III collagen is the second most common form of collagen found in the skin and forms thinner diameter fibers than type I collagen. Both procollagen and type III collagen are formed initially in the wound-healing process, with type I collagen being produced later.
Skin Laxity
As part of the aging process, the skin reduces its production of elastin and collagen, the main structural proteins in the dermis. With less support structure in the skin, areas can sag due to gravity. Common areas for this to occur are the neck, jowls, underarms, and the abdomen, particularly postpartum ( Fig. 7.1 ).
As part of the treatment of skin laxity, it is important to differentiate skin that is sagging due to laxity from skin that is sagging due to excess fat. As a general rule, thin skin without underlying excess fat can be treated most effectively.
Collagen Contraction
The goal in treating skin laxity is to create a bulk change in the support structure of the skin to counteract the skin laxity caused by aging. If sufficient heat is delivered to the collagen, the structure of the collagen will change, causing the fibers to contract and thicken. An extreme example of collagen denaturation is cooking: we have all seen how a slice of bacon shrinks as it is heated.
While most of the laboratory studies on collagen shrinkage or denaturation have been performed ex vivo, these studies have shown that heated collagen transforms from the crystalline triple-helical structure to an amorphous, random-coil structure through breakage of the hydrogen bonds linking the protein strands of the triple helix. This creates a thickening and shortening of the collagen fibers as the chains fold and assume a more stable configuration, as shown schematically in Figure 7.2 . This immediate collagen contraction can be used for cosmetic treatments to treat skin laxity or other signs of aging on the face or body.
It should be noted that this immediate tissue tightening is different from the long-term collagen stimulation caused by a thermally induced wound response. These immediate changes can be observed both during treatment and through electron micrograph studies.
Sustained Volumetric Heating
As noted, temperature is a key component in collagen contraction or denaturation but it is not the only factor. While some people refer to a ‘magic temperature’ for collagen contraction, this is actually a misleading statement. Knowing only the temperature achieved in the dermis is not sufficient to understand if collagen denaturation will occur. Collagen contraction will occur only through a combination of time and temperature – or sustained volumetric heating. The collagen must be heated to a temperature and kept there for a sufficient length of time. This combination varies; similar collagen contraction can be achieved at a lower temperature if the duration of the heating is increased, but the heat must be delivered uniformly over the treatment area.
Studies have shown that, for a 5°C decrease in temperature, the duration of the heating must be increased by an order of magnitude (10 times) to achieve a similar degree of collagen contraction. So while millisecond pulses are sufficient for collagen contraction at the temperatures achieved during CO 2 treatments, significantly longer pulse times are required for the treatment temperatures used in non-ablative treatments. All the protocols for the proven non-ablative treatments of skin laxity include multisecond treatment times.
The target depth for skin laxity treatments is the dermis. This will require a balance: providing the heat at a superficial level will not create the volume changes that are desired, while heating too deeply might affect the subcutaneous fat. To achieve this balance, the heat should be targeted at a depth of a couple of millimeters ( Table 7.2 ).
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Cooling
While the temperature required in the dermis for collagen contraction with multisecond exposure times is above 55–60°C, a blister will form if the epidermal temperature is above 50°C. It is obvious that cooling will play a major role in any non-ablative approach to the treatment of skin laxity. In fact, with the heat that is deposited to contract the collagen, aggressive cooling before, during and even after the heating pulse is required. Postcooling helps protect the epidermis, as the intense heat from the dermis diffuses to the surrounding tissue. Forms of cooling can include parallel cooling through a sapphire window or cryogen cooling.
Neocollagenesis
It is important to differentiate between immediate collagen contraction and longer-term collagen production. Neocollagenesis is simply the formation of new collagen, for example as occurs during a wound response. This longer-term production of new collagen was the goal of the early laser-based non-ablative skin rejuvenation treatments. In this process, laser treatments trigger a thermally induced wound response. This response can be triggered at a temperature much lower than is required for immediate collagen contraction. Also, most of the demonstrated procedures for new collagen production require multiple treatments to obtain the desired results. In addition to evidence from before and after photographs, these results can be observed histologically by examining the collagen fibers prior to and a few months after the treatment.
APPROACHES TO THE TREATMENT OF SKIN LAXITY
To the best of the authors’ knowledge at the time of publication, only a few approaches to the treatment of skin laxity have published histological evidence of immediate collagen contraction. Some of these approaches are the Titan™ by Cutera, the ThermaCool® device by Thermage®, Visage™ by Arthrocare Corp (Sunnyvale, CA), and Accent XL® by Alma Lasers (Caesarea, Israel). While this does not mean that other devices may not effectively treat skin laxity, the reader should look for scientific evidence and medical papers before making a decision.
Various lasers, such as the Nd:YAG 1450 nm and Nd:YAG 1540 nm, emitting in the mid-infrared, have been used for the treatment of fine wrinkles and acne scars. However, these lasers need multiple treatments with a delayed and relatively minimal clinical softening of the wrinkles. They do not produce deep dermal tightening or lifting since they affect only the superficial parts of the dermis.
New devices have emerged to treat skin laxity and wrinkles in a non-ablative way, regardless of skin type and color. These devices are of three types:
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devices using only RF
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devices using RF combined with infrared energy
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devices using near- and mid-infrared pulsed light, the so-called infrared skin-tightening devices.
All these devices use different frequencies. The choice of energy and appropriate frequency that will be selectively concentrated in the dermis is of cardinal importance.
Optical energy (intense pulsed light and lasers) is absorbed by melanin chromophores in the epidermis and hair shafts, and hemoglobin in vessels. This kind of energy cannot treat wrinkles because collagen fibers, which are involved in the pathophysiology of wrinkling, do not contain chromophores.
To satisfy the need for energy, which acts on the dermis without affecting the epidermis, RF and infrared radiation were found to be the most appropriate tools. The main difference between lasers and RF is that lasers affect collagen in the upper dermis, improving fine lines, wrinkles and skin texture, while RF energy is able to penetrate deeper into the skin and affect the deeper dermis and subcutaneous layers, causing tightening and improvement to the underlying tissue structure, but with little change in skin texture.
RF is considered more selective to the depth of the dermis targeted than infrared frequencies. In the past, it has been used mainly in surgery, but now it is also considered to be the newest alternative in skin-tightening procedures and will be further discussed later in this chapter.
Infrared Technology
The general goal of tissue tightening is to provide enough heat to the dermis while protecting the epidermis. We will describe the Titan™ in more detail, since one of the authors (AH) has achieved very consistent results over the last 2 years.
In the Titan™ (Cutera, Inc., CA), water is the target chromophore and a wavelength is selected based on the absorption characteristics of water.
Figure 7.3 shows the water absorption curve. Based on this curve, wavelengths in the range of 1100–1800 nm are used to achieve heating at a depth of 1–2 mm. This depth is chosen to heat the dermis, but without any risk of heating the subcutaneous fat. There is a strong water absorption peak in the 1400–1500 nm range, and this wavelength is filtered from the Titan™ output to further optimize the treatment.
Each Titan™ treatment pulse consists of a multisecond exposure. The temperature profile in the dermis can be measured through animal studies. Figure 7.4 shows a cross-section with a maximum temperature rise of approximately 25°C. This maximum temperature occurs at a depth of approximately 1–2 mm, whereas the epidermis is protected through contact cooling with a sapphire window.
The heating provided by the Titan™ has been shown histologically to provide immediate changes to the collagen. The denaturing of the collagen fiber can be seen in Figure 7.5 .
This immediate collagen contraction can also be seen clinically. Many physicians will treat one side of the face before moving to the other side. In the middle of the procedure, the physician lets the patients sit up and confirm that they can see the difference in the treated and untreated sides. This is not simply edema since, in most of the area treated, edema would create a swelling that would make the area look worse, not tighter.
To demonstrate that these results can be consistently reproduced, a retrospective study of over 1000 patients was performed. In this study, covering results from four different practices, physicians reported a satisfaction level above 80% with the Titan™. The safety of the Titan™ device was also examined as part of this retrospective study. Only two side effects were reported in over 1000 treatments. Both of these side effects healed without complication.
Since the Titan™ uses an infrared light source (lamp), each handpiece has a finite lifetime, either 10 000 or 15 000 pulses. Based on the replacement cost and the number of pulses per treatment, the cost per procedure is roughly $90. With typical procedure fees in the range of $800–2500 per procedure based on a survey of Titan™ users across the USA and Brazil, this per procedure cost is acceptable.
PREPARATION AND INFRARED SKIN-TIGHTENING TECHNIQUE
Preoperative Considerations
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Conduct a patient consultation complete with medical history prior to treatment.
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Clean the skin, including removal of all make-up and other skincare products. Any creams or products left on the skin can interact with the light and increase the risk of unwanted side effects.
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Shave any hair in the area to be treated. Hair in the treatment area may not allow full contact of the handpiece with the skin.
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Preoperative photographs should be taken with consistent technique (patient positioning, camera settings and room lighting).
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These treatments can be tolerated without anesthesia. The use of sedation, nerve blocks or local injectable anesthetics is not recommended for these treatments as patient feedback is very important and, with the proper technique, is not required. Topical anesthesia can be used if desired. It must be completely removed prior to treatment.
Optimizing Outcomes
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When treating near the mouth, rolled-up gauze can be placed between the lips and teeth to protect the teeth from discomfort.
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Some physicians make this treatment part of an overall skincare regimen along with topical retinoids, topical vitamin C, sun protection and/or microdermabrasion.
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Do not treat over areas with tattoos.
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Extreme caution should be used when treating near the eye, taking care to avoid ocular damage from the light. Patient eye protection appropriate for the given treatment should be used. The light should always be pointed away from the eye and only applied to the skin outside of the orbital rim. Skin at the edge of the orbital rim can be treated by pulling it away from the eye while simultaneously holding the goggles in place, so treatment is kept outside of the orbital rim.
Titan™ Treatment Parameters
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Fluency should be adjusted as low as 28 J/cm 2 and raised to as high as 46 J/cm 2 based on patient tolerance and the area being treated ( Table 7.3 ).
Table 7.3
Typical starting fluence in a treatment area
Skin type
Fluence (face, neck, and chest)
Fluence (body)
I–VI (including tanned skin)
34–38 J/cm 2
36–46 J/cm 2
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Sensitive areas and bony areas may require lower fluences for some patients.
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It is common to feel a sensation at the end of the heat cycle, depending on the area that is treated. This should resolve as the handpiece is moved to the next treatment spot. If the patient still feels this sensation, or heat, stop the treatment and cool the area with the handpiece and/or ice pack.
Recommended Technique
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When the face is being treated, it is typically divided into three regions (forehead and both cheeks), as shown in Figure 7.3 . Similar-size areas can be treated when treating the neck, generally divided into two or three regions. One section at a time is treated, completing all passes in that area before moving to the next.
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Apply a layer of clear gel (such as ultrasound gel), approximately 3 mm thick, to the treatment area. For patient comfort, reapplication of cooled gel as the treatment progresses may be helpful.
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Hold the handpiece to ensure complete contact of the window with the surface of the skin to be treated. Activate the exposure with the foot pedal. Do not lift the handpiece until the audible tone and the blue light have ended: losing contact with the skin during a pulse can result in blistering and increased risk of side effects.
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Instruct the patient to alert you if the discomfort level becomes intolerable.
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Place the next pulse adjacent to the previous one without overlapping.
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Always observe the epidermis during the treatment, watching for signs of damage (epidermal separation or gray coloration). If damage is seen, stop the treatment, cool the skin and reduce the fluence before continuing.
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Apply all passes (usually three to four) in one area before beginning treatment in the next area. This allows for sustained heating. As the skin temperature increases with each pass, it may be necessary to lower the fluence by a small amount on the latter passes for patient comfort.
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Extreme caution should be used when treating near the eye, taking care to avoid ocular damage from the light. Patient eye protection appropriate for the given treatment should be used. The light should always be pointed away from the eye and only applied to the skin outside of the orbital rim. Skin at the edge of the orbital rim can be treated by pulling it away from the eye while simultaneously holding the goggles in place, so treatment is kept outside of the orbital rim.
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Erythema is a common immediate reaction seen from this treatment. This typically resolves within 2 hours but can last longer.
Postoperative Care
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Localized erythema may also be present and typically resolves within 24–48 hours. If prolonged erythema occurs, future treatments should be performed at a lower fluence.
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If a wound develops, an antibiotic ointment may be recommended.
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Treatment intervals of 4 weeks are commonly used, with an average of two to four treatments.
See Figures 7.6 and 7.7 .
