PULSED ULTRASOUND AND ELECTROCORTICAL ACTIVITY IN FETAL SHEEP

The aim of this study was to determine if low intensity Ultrasound aff ects electrocortical activity in chronically instrumented fetal sheep. A 3.5-MHz transducer was attached to each fetal skull (n=9) and activ ated periodically to emit pulses of 5.8 mu s duration at a repetition rate of 2 kHz generating a power output of 60 mW. The power supply was activated in 30-s bursts every 180 s but random electronic switching energised the transducer with 50% of bursts. On average, 175 bursts of ultrasound were delivered to the fetus over 19.5 h. Blinded analysis of continuous recordings of electrocortical activity showed it to be u naffected by the ultrasound exposures. Therefore, it is unlikely that ultrasonic examination of human fetuses will affect normal cyclical el ectrocortical activity.