Applications and Safety of TherapeuticUltrasound: Current Trends and FuturePotential

The ability of ultrasound to penetrate deep into tissue and interact with human tissues via thermal and mechanical mechanisms has expanded its various therapeutic applications. In the 1950s, low power (1 MHz) ultrasound began being used for physical therapy of tendinitis or bursitis and, in the 1980s, high pressure amplitude shockwaves were used for kidney stone destruction in lithotripsy. Since then, ultrasound therapy has expanded significantly and is rapidly replacing surgery in clinics. Several major benefits of ultrasound derive from its minimally invasive procedure compared to conventional open surgeries that disturb the overlying tissues. The minimally invasive therapeutic procedures result in shortened recovery times and hospital stays as well as lowered risk of complications and cost. Ultrasound therapy may require local anesthesia or sedation, which is highly preferred over general anesthesia, especially for elderly patients. Some ultrasonic therapy techniques, such as cataract removal, surgical tissue cutting and hemostasis, transdermal drug delivery, and bone fracture healing, have been approved for widespread use. Other minimally invasive therapy techniques, such as focused ultrasound beam therapy for coagulating tissue, are on the verge of clinical approval. Therapeutic ultrasound methods work based on thermal or non-thermal (e.g., mechanical) mechanisms, or both, with well-defined benefits and risks that include complications to the patient. Ensuring the benefits and minimizing unwanted side effects depends on a clear understanding of the thermal and non-thermal biological effects of ultrasound as well as more accurate guidance of the ultrasound beam. This paper reviews the basic principles behind thermal and non-thermal (cavitation) biological effects of ultrasound, as well as general information and safety considerations for a wide range of therapeutic ultrasound methods either under study or in clinical use.