An instrument has been developed to measure the acoustic pressure field during an obstetric ultrasound examination. This permits a more accurate assessment of possible bioeffects since the pressure is sensed at or near the site of the organs under investigation. The ultrasonic field is sampled using a calibrated seven-element linear array hydrophone of PVDF transducers, which is placed as close as possible to the ovary, embryo, or fetus, using a vaginal approach. The RF signals from the hydrophone are digitized at 50 Ms/s, and the maximum amplitude waveform received in the examination is recorded. The output of the clinical B-scanner is calibrated by the hydrophone in a water bath. From the hydrophone measurements, the in-vivo ISPTA, ISPTP, and ISPPA can be computed. Further analysis allows the frequency-dependent tissue attenuation to be assessed.
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