Edwin L. Carstensen - carsten@ee.rochester.edu
Rochester Center for Biomedical Ultrasound
University of Rochester
Rochester, NY 14627
Popular version of paper 2pPAa2
Presented Tuesday afternoon 14 May 1996
Acoustical Society of America, Indianapolis, Indiana
Embargoed until 14 May 1996
The record to date suggests that diagnostic ultrasound is almost as safe to use as a stethoscope. There is a fundamental difference, however. Whereas a stethoscope is used simply to listen to the sounds created within the body, pulsed ultrasound sends sound into the tissues and listens for their echoes. In that sense, diagnostic ultrasound is invasive.
There is never an absolute guarantee of safety. Scientists for years have been testing experimentally for ways in which the ultrasound that goes into the tissues produces adverse biological effects. In practice, the nearest thing to a guarantee of safety is to have a community of investigators who look intensively for hazards. In ultrasound bioeffects research a new approach has become available with the advent of lithotripters. These instruments create very large fields for the destruction of kidney stones and they do produce biological effects in soft tissues as well. Once effects are identi-fied in these large fields, they provide clues to possibly more subtle effects from the smaller fields used in diagnostic ultrasound.
This approach has led to the discovery of several effects that should be considered by physicians in their use of ultrasound for diagnostic tests. These include capillary bleeding in lung, intestine and fetal bone and the fragmentation of red blood cells. A recent workshop sponsored by the World Federation of Ultrasound in Medicine and Biology considered all of these effects and concluded that the only application requiring a benefit/risk analysis is that case in which acoustic pressures at the surface of the lung exceed 1 MPa. (For perspective, 1 MPa is ten times the static pressure of the earth's atmosphere.) This is very near the maximum effective output levels of present day diag-nostic instruments. So, even with the relatively advanced state of knowledge of biological effects, it still appears that ultrasound as practiced today is among the safest diagnostic tools available to physicians.