Krusen, Frank H.

Many therapeutic procedures have been introduced into the art and science of medical practice empirically by a method of trial and error. Such a method has marked limitations and may produce unfavorable consequences. The facilities available in experimental medicine permit a thorough and extensive investigation of biological effects of many therapeutic agents or procedures before any clinical application is made. Optimal doses of the therapeutic agent can be approximated and a comparative study of various technics designed for clinical application can be made. Unfortunately ultrasound was used clinically by certain enthusiastic therapeutists before a thorough study of its biologic effects was completed. These therapeutists regarded the major biologic effect of ultrasonic energy to be mechanical. They were aware of a heating effect, but considered that it played a minor role. Experimental measurements have shown clearly that the major effect of ultrasound on living tissues is thermal when an intensity suitable for therapy is employed. The heating of bone by ultrasound is spectacular. No other heating agent used in therapy can raise the temperature of bone to such high levels so quickly. The application of ultrasound for diagnostic purposes and also for instrumentation will be described.