Ultrasound is applied in virtually all areas of medicine, due to the number of desirable physical effects produced by ultrasound, the fl exibility in the design of transducers, and the delivery of either high or low power at high or low frequencies. The applications of ultrasound are shown by frequency in Figure 10.1. The spectrum is divided into two categories: therapeutic and diagnostic. Therapeutic describes applications that make a physical change to a patient to improve the patient’s health. Therapeutic ultrasound can be based on direct contact with the tissue or with ultrasonic energy radiated to the targeted tissue. Diagnostic ultrasound is used to display an image of the internal structures of the body for diagnosis.