Aesthetic Ultrasound Therapies Including HIFU Ⅰ

The 21st century can be said to be the era of anti-aging technology. There is an increasing desire to appear young and not just cover up imperfections with make-up. Many anti-aging cosmetic products are available in the market but people also resort to various safe and efficacious medical procedures that bring drastic and quick improvement. Among these procedures, the most desirable would be non-invasive treatments using laser or ultrasound.

Research on applying the light energy of laser and acoustic waves of ultrasound to aesthetic medicine is leading the field of non-invasive or minimally invasive treatment. The largest growth is seen in dermatology, however, we must remember that this new field has its roots in surgery. This column will discuss the basic principles of ultrasound devices used in aesthetic treatment.

[Advertisement] Ultra Skin/Pastelle – Manufacturer: WONTECH(www.wtlaser.com)

We must first understand that ultrasound, unlike laser, requires a medium for transmission of energy. This is why gel is applied on the skin immediately before ultrasonography. The speed of sound generally increases along with the medium’s molecular density. It is 340m/s in air, but quadruples in water to 1,433m/s. The well-known Doppler effect (when one or both of the sound source and observer are on the move, the observed frequency changes) has become a key principle behind medical imaging using ultrasound.

Advancement of ultrasound technology

Medical application of ultrasound started to develop rapidly around World War II. Wild and Reid first discovered ‘echo’ that bounces back from ultrasound waves sweeping soft tissues. Using this new concept, they could measure the thickness of the intestines. In 1957, they developed the first diagnostic ultrasound device that showed real-time images of the examined body tissues onto a TV screen. This ground-breaking invention brought many changes to the field of medicine. Ultrasound became an essential diagnostic tool around the 1970s and went through rapid advancement. In diagnostic imaging with ultrasound, selection of different frequency can change the depth and spatial resolution of the image. Low frequencies bring lower spacial resolution but can produce images of deeper tissues.

Therapeutic ultrasound was first applied by Lynn in 1942. In 1952, Francis Fry’s research team reported the difficulty of accurate targeting of the ultrasound beam in an animal experiment. After a long period of stagnation in technological advancement, Vallencian et al. reported the possibility of ultrasound therapy of cataract by damaging the retina and choroid. Application of ultrasound expanded to prostate treatment as well. In 1980s, new ultrasound devices were introduced and opened the era of therapeutic ultrasound. However, efficacy and safety issues remained as control of thermal diffusion generated in the focal area of ultrasound beams was still difficult. FDA finally saw the importance of therapeutic ultrasound and approved its use as an adjunct tumor therapy.

HIFU (high intensity focused ultrasound) was first applied by Sibille and his colleagues in 1993. They irradiated heat energy of 40-50℃ onto tumor tissues using the principle of higher thermal sensitivity of tumor compared to normal tissues. HIFU came to be one of the most widely used modality of non-invasive tumor treatment as more scientific evidence for ultrasound’s therapeutic effect on tumor was reported.

HIFU can be classified as a thermal therapy using focused ultrasound waves. It has the same principle as a convex lens. Focusing the light into a single dot through a convex lens creates heat energy. Likewise, focusing the ultrasound waves into a small point can raise the temperature high enough to destroy tumor cells. Early research on HIFU explained how lesions were created with focusing ultrasound energy, however, delivery of ultrasound energy to living tissues is a complicated process. There is also the problem of inaccurate delivery due to the non-linearity of ultrasound transmission within biological tissues.