Lauriston S. Taylor Lecture: Assuring the safety of medical diagnostic ultrasound

In 1980, the NCRP formed Scientific Committee 66 with an assignment to address the subject of "biological effects of ultrasound and exposure criteria." It was recognized that the primary source of exposure to ultrasound was through medical applications and, especially, through procedures employing diagnostic ultrasound. While the risk to patients from these procedures was believed small, it was considered important for users to understand it, in view of the widespread use of diagnostic ultrasound. In proceeding with this assignment, much emphasis has been given to the mechanisms by which ultrasound can bring about changes in biological structures or processes. Thermal effects are possible; the local temperature can rise especially rapidly where ultrasound impinges on bone. From theory for heat production and transport, and by analysis of experimental results with mammals, information has been obtained for guiding users in avoiding harm from temperature elevation. Nonthermal effects, such as capillary rupture, can occur when ultrasound is incident on tissue that normally contains gas-filled cavities, as in adult lung or intestine, or on any tissue containing gaseous contrast agents. Theory from fluid dynamics, together with experimental findings, has led to quantitative guidance for avoiding damage from acoustically activated cavities. It is felt that good practice in applying diagnostic ultrasound is best assured by making it possible for users to be well informed on safety matters so that they can feel justifiably confident in making appropriate choices of operating conditions. A promising and useful approach is in the display of safety information on the diagnostic ultrasound screen, which is now a feature of United States standards.