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by the American Institute of Ultrasound in Medicine J Ultrasound Med 27:541-559 • 0278-4297
Fetal Thermal Effects of Diagnostic UltrasoundDepartment of Obstetrics and Gynecology, Rush University, Chicago Illinois USA (J.S.A.); Faculty of Health Sciences, University of Sydney, Sydney, New South Wales, Australia (S.B.B.); Bath University and Royal United Hospital, Bath, England (F.A.D.); SRI International, Molecular Physics Laboratories, Menlo Park, California USA (P.D.E.); Department of Radiology, Harvard Medical School, Boston, Massachusetts USA (K.H.H.); and Center for Biomedical Physics, Temple University Medical School, Philadelphia, Pennsylvania (M.C.Z.). Address correspondence to Jacques S. Abramowicz, MD, Department of Obstetrics and Gynecology, Rush University Medical Center, 1635 W Congress Pkwy, Chicago, IL 60612 USA. E-mail: jacques_abramowicz{at}rush.edu
Abstract Processes that can produce a biological effect with some degree of heating (ie, about 1°C above the physiologic temperature) act via a thermal mechanism. Investigations with laboratory animals have documented that pulsed ultrasound can produce elevations of temperature and damage in biological tissues in vivo, particularly in the presence of bone (intracranial temperature elevation). Acoustic outputs used to induce these adverse bioeffects are within the diagnostic range, although exposure times are usually considerably longer than in clinical practice. Conditions present in early pregnancy, such as lack of perfusion, may favor bioeffects. Thermally induced teratogenesis has been shown in many animal studies, as well as several controlled human studies; however, human studies have not shown a causal relationship between diagnostic ultrasound exposure during pregnancy and adverse biological effects to the fetus. All human epidemiologic studies, however, were conducted with commercially available devices predating 1992, that is, with acoustic outputs not exceeding a spatial-peak temporal-average intensity of 94 mW/cm2. Current limits in the United States allow a spatial-peak temporal-average intensity of 720 mW/cm2 for fetal applications. The synergistic effect of a raised body temperature (febrile status) and ultrasound insonation has not been examined in depth. Available evidence, experimental or epidemiologic, is insufficient to conclude that there is a causal relationship between obstetric diagnostic ultrasound exposure and obvious adverse thermal effects to the fetus. However, very subtle effects cannot be ruled out and indicate a need for further research, although research in humans may be extremely difficult to realize.
Key Words: bioeffects • fetus • obstetrics • safety • thermal effects • ultrasound Abbreviations: ALARA, as low as reasonably achievable • dga, days’ gestational age • FDA, Food and Drug Administration • HSP, heat shock protein • ISPTA, spatial-peak temporal-average intensity • MI, mechanical index • NTC, neural tube closure • TI, thermal index • TIB, thermal index for bone • TTO, thermal test object • WFUMB, World Federation for Ultrasound in Medicine and Biology This article has been cited by other articles:
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