Abstract
Measured characteristics of ultrasonic fields were obtained in submissions from manufacturers of diagnostic ultrasound equipment for devices operating in pulsed Doppler mode. Simple formulae were used with these data to generate upper limits to fetal temperature elevations, ΔT lim, during a transabdominal pulsed Doppler examination. A total of 236 items were analyzed, each item being a console/transducer/operating-mode/intended-use combination, for which the spatial-peak temporal-average intensity, I SPTA, was greater than 500 mW cm −2. The largest calculated ΔT lim, values were approximately 1.5, 7.1 and 8.7°C for first-, second- and third-trimester examinations, respectively. The vast majority of items yielded ΔT lim, values which were less than 1 °C in the first trimester. For second- and third-trimester examinations, where heating of fetal bone determines ΔT lim, most ΔT lim, values were less than 4°C. The clinical significance of the results is discussed.
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