Biological Effects of Sound and Ultrasound

Abstract

AbstractAt frequencies mostly in the megahertz range, ultrasound has become indispensable in diagnostic medicine. Sound over a wide frequency range is being used increasingly in therapeutic applications, including drug delivery. Much research has been carried out to study biological effects of this agent, especially, ultrasound, to seek understanding of mechanisms for them. Since sonic energy is converted into heat as it passes through tissues, temperature elevation is an important mechanism. Another important kind of mechanism, calledcavitation, is important when small gas bubbles are present, as is often true duringin vivoexposures of cell suspensions. If the pressure amplitude is modest, the action may be harmless, or even beneficial by making cells temporarily permeable allowing drug transfer. If it is high, the action may be violent and cause permanent damage. The importance of cavitation during applications of diagnostic ultrasound has greatly increased during the last decade because of the widespread use of “contrast agents”. These are small specially coated gas bubbles, which are injected into the blood of a patient to improve image contrast. Whether cavitation occurs or not during an application, sonic fields can produce effectsviatime‐averaged forces and fluid motions known asradiation forceandacoustic streaming(ormicrostreaming). The present chapter is a review of current knowledge on effects that can be produced by sonic fields and causes of these effects.