Advantages and Limitations of Ultrasonics in Medicine

High frequency sound has recently been advocated for use in physical therapy. Early clinical reports suggest that ultrasonic therapy is indicated in cases in which treatment with heat is required. Systematic evaluation of the application of ultrasound in medicine has only begun. It is certain that this radiation produces heat in the body tissues; however, whether purely mechanical or other nonthermal effects play a significant role in treatment has not been determined. This communication is restricted to the biophysical problem of the production of heat by ultrasound in tissue and the consequences of the manner in which the transformation of sound into heat takes place. It further compares this new technique with other methods of producing heat in tissue. PHYSICAL PROPERTIES OF HIGH FREQUENCY SOUND Sound waves, whether propagated in the air at audible frequencies or in body tissue at very high frequencies, have essentially the same character, i. e.,