Update on safety of diagnostic ultrasonography.

Safety considerations for diagnostic ultrasonography have gradually changed as new instruments, not only more powerful in performance but also in ultrasonic exposure, have come into use. Nonthermal cavitational bioeffects of ultrasound have a problematic role in risk assessment for clinical applications, but should serve as cautionary reminders that there potentially could be low-level risks. Recent analyses have indicated possible areas of concern related to the thermal mechanism of bioeffects, particularly if trends for higher intensities continue into the future. The most critical area of concern is in fetal examinations, for which developing bone is unavoidably heated by relatively powerful pulsed-Doppler beams. Fortunately, because of the threshold nature of thermal damage, development of flexible, use-driven upper limits on output should completely resolve this impending safety problem. The ultrasonics community is now responding to these evolving safety issues with improved instrument characterization standards, new bioeffects research, and initiatives in continuing education for sonographers.