Ultrasound therapy systems designed to produce and deliver ultrasonic waves that penetrate tissues and produce both thermal and nonthermal (e.g., mechanical and cavitation) effects. These systems consist of a radio-frequency (RF) generator (frequencies from one to three megahertz are typical), a cable that transmits the RF energy to the applicator, and an applicator including a piezoelectric transducer that applies the ultrasonic energy to the patient's tissue through the skin. Physical therapy ultrasound systems are used for pain relief and as an aid in the healing of soft-tissue injuries (e.g., ulcerations; bursitis; muscle, tendon, or joint pain).