History

High-intensity focused ultrasound (HIFU) has been used in a variety of research and medical applications dating back to 1942. This technology is useful in targeting specific sites surrounded by non-target tissue because of its unique ability to precisely focus energy. In the 1960s, Kelman introduced the idea of using ultrasound energy for surgery with his use of phacoemulsification during cataract surgery. A device called the Cavitron ultrasonic surgical aspirator (CUSA) has been successfully applied to the fields of neurosurgery, gynecology, general surgery and other specialties for purposes such as tumor ablation and tissue resection since the 1970s.

More recently, researchers realized the potential of HIFU in aesthetic medicine. Historically it began with Dr Nicolo Scuderi of Italy who in 1987 introduced the technique of using ultrasound energy in conjunction with lipoplasty. This technique involves inserting thin ultrasound transducers through small incisions to emulsify adipose tissue before removing it with suction. Ultrasound assisted lipoplasty (UAL) has since evolved into a useful, practical tool in body sculpting surgery. In the past few years, studies have proven that with a transducer placed on the skin surface, energy can be precisely directed into the subcutaneous adipose layer to disrupt adipose cells non-invasively without damaging the skin, intervening tissues, or underlying tissues and organs. This principle led to the development of the LipoSonix® (Bothell, WA) device for non-invasive ultrasonic body sculpting.

Physical evaluation

Anatomy

The anatomy of the skin and underlying adipose tissue is straightforward. The epidermal layer is approximately 1 mm thick with the dermis directly underneath and of variable thickness depending on the body area. The subcutaneous adipose tissue varies in depth between a few millimeters to several centimeters depending on the subject and the area of the body. As a general rule, a fascia covering the muscle layer underlies the adipose tissue.

The primary role of adipose tissue is to efficiently store energy. Adipose tissue is a type of connective tissue that is made up of loose associations of fat cells (adipocytes) surrounded by thin fibrous septae. The collagen matrix comprises approximately 20% of the adipose tissue which provides structure. Different areas of the body have more extensive collagen networks. This results in more fibrous areas of subcutaneous fat. Adipose tissue also contains stromal-vascular cells, macrophages, leukocytes, and non-differentiated pre-adipocytes.

Each adipocyte has a thin rim of cytoplasm which contains a flat nucleus, a small amount of cytoplasm, and in general, one large lipid droplet. Up to 75% of the cell volume is made up of lipids or triglycerides. The remaining weight of the adipocyte is protein and water. Each triglyceride droplet is comprised of one glycerol and three fatty acid molecules. The fatty acid composition changes depending on factors such as age, diet and exercise.

Lean adipose tissue is highly vascular, however, the adipocytes are in general so greatly expanded by their stored lipids, that the ratio of capillary to total cell mass is small. Each adipocyte is in contact with at least one capillary. Nerve fibers also run sparsely through adipose tissue and the number of nerves varies greatly in different parts of the body. In general, adipose tissue is less innervated that most other tissue types.

Size of adipose deposits in the human body is a function of fat cell number and mass. There are rare examples of hyperplastic growth – increasing the number of cells – occurring in adulthood. Most growth of adipose deposits however comes from hypertrophic growth – increase in adipocyte cell size. In general, once these cells are destroyed, they are permanently removed from a given area of the body.

Technical steps

The LipoSonix® procedure begins with patient selection. Ideal candidates are similar to those for lipoplasty – patients who are not obese but have localized areas of unwanted fat, and are generally in good health and have good or at least reasonable skin tone. Areas to be treated with the LipoSonix® device should consist of at least 2.5 cm in depth of adipose tissue as measured with a pinch test, calipers, or ultrasound. Future product evolution is expected to allow for more flexibility in depth of treatment. Targeted treatment areas are marked with a surgical marker, in a similar fashion with lipoplasty. A marking grid template is then used on the treatment area to provide guide marks for the application of the LipoSonix® treatment head. Depending on the patient’s threshold for discomfort, oral pain medications and/or sedatives may be administered prior to treatment.

The procedure itself is straightforward. The treatment head is moved across the treatment area while the device is activated using a footswitch, similar to many commercial aesthetic laser products. Figure 64.1 shows the device, and Figure 64.2 illustrates the treatment head positioned for use on the abdomen of a patient. A LipoSonix® procedure can normally be completed in less than one hour. At the end, patients usually are ambulatory and can resume normal activities that same day.

Fig. 64.1 The LipoSonix® device.

Fig. 64.2 The treatment head positioned for use on the abdomen of a patient.

The technology works by precisely focusing HIFU energy into target areas of adipose tissue to cause controlled, localized cell disruption. The ultrasound transducer incorporated into the treatment head delivers energy across the skin surface at a relatively low intensity and therefore there is no damage superficial to the treatment. The specific geometry of the transducer and transducer positioning method allows for focusing of the ultrasound energy at variable depths from 10–20 mm beneath the skin. This focusing of the beam results in precise high intensity energy delivery to the target zones within the adipose tissue. Figure 64.3 illustrates this concept.

Fig. 64.3 Focusing of ultrasound energy in subcutaneous fat.

There are several mechanisms of action which contribute to adipocyte disruption as a result of HIFU. The first is a purely thermal effect – a temperature rise within the target tissue secondary to direct absorption of ultrasonic energy. This absorption is directly related to the ultrasound frequency – higher frequencies result in more energy absorption and more thermal effect. The sudden temperature rise leads directly to adipocyte destruction. Other mechanisms are mechanical processes such as streaming and shear forces, with their inherent thermal effects. These mechanisms of disruption are a direct result of the pressure waves emitted from the transducer. The LipoSonix® procedure utilizes a balance of thermal and mechanical effects to achieve a high degree of clinical efficacy without compromising patient safety.

Once adipocytes have been disrupted, macrophage cells are attracted via chemotactic signals to phagocytose the lipids and cell debris. Figure 64.4 shows a typical histology section of a treated area (two weeks post-procedure) using Masson’s trichrome stain. Macrophages containing lipid droplets are clearly visible. The macrophages migrate to the lymph nodes and on to the liver, where the lipids are processed through the body’s normal biochemical pathways. Our research shows that the majority of treated tissue is resorbed over an 8–12 week period. The resulting reduction in adipose tissue volume leads to an observable aesthetic effect, as evidenced by quantitative measurements and by clinical photography.

Fig. 64.4 A typical histology section of a treated area (two weeks post-procedure) using Masson’s trichrome stain. Macrophages containing lipid droplets are clearly visible.

Postoperative care

One of the advantages of the LipoSonix® procedure is that post-treatment care is minimal. Patients have not needed pain medications or compression garments, and have been able to return to work on the day of the procedure.

Complications

Side effects and/or complications associated with the LipoSonix® procedure have been minimal. The majority of patients have some minor degree of edema and eccymosis, which resolves within two to four weeks. Some patients experience mild dysesthesia, which usually resolves within one to two weeks. Other patients have slight erythema, which dissipates within a few hours. There have been no seromas, no calcifications, no pulmonary emboli, no infections of any kind. Blood analyses at various time points post-treatment, compared with pre-treatment values, have revealed no clinically significant changes.

Aesthetic results

Figures 64.5 and 64.6 show representative pre-procedure and 3-month post-procedure aesthetic photos of a female and male patient, respectively. Patients will typically see peak response, both in visible contour change and reduction in circumferential measurement, between 8 and 12 weeks post-procedure.

Fig. 64.5 Representative pre-procedure and 3 month post-procedure aesthetic photos of a female patient.

Fig. 64.6 Representative pre-procedure and 3 month post-procedure aesthetic photos of a male patient.