In any medical procedure, whether diagnostic or therapeutic, we want to help and not harm, or at least be sure any harm is justified and kept to a minimum. The therapeutic and diagnostic benefits of ultrasound are well known, but some still worry about risks.
Sound waves are a form of energy. Ultrasound, beyond our range of hearing with pressure waves measured in millions of cycles per second, is a form of energy. Therefore, we must ask ourselves, “Can too much ultrasound be bad? If so, how much is too much?”
Here is what we know. For nearly 100 years, investigators have studied ultrasound’s bio-effects in molecules, cells, plants, animals and humans. Hundreds of papers in peer-reviewed literature address the issue. We have plenty of evidence that the interaction mechanisms that could be deleterious to human tissue are heat and cavitation, the non-thermal vibrations that create and collapse bubbles. Cavitation is the same process that causes pitting in steel ship propellers.
In the 1970s, the Food and Drug Administration (FDA) limited the output of ultrasound instruments. In the 1990s, the American Institute of Ultrasound in Medicine and other organizations worked with the FDA to create thermal and mechanical indices to inform users in real time of estimated temperature rise and mechanical effects in tissues exposed to ultrasound.
Based on all available information, there is no known risk in using ultrasound the way we apply it today. In practice, we implement the principle of ALARA (As Low As Reasonably Achievable), which recognizes that there may be unknown risks we have not discovered. We minimize risk by minimizing exposure time and exposure output, and by using ultrasound only where medically indicated.
Do the benefits of ultrasound justify the risks? The answer is an emphatic yes.
—Frederick Kremkau, PhD, co-director, Program for Medical Ultrasound