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Figure 3: Ultrasound imaging devices utilize pulse wave (A), where instantaneous peak intensity and rarefactional pressure are high, despite the temporal average intensity is as low as continuous wave (B) which is utilized in the Doppler fetal heart detector and fetal heart rate monitor. The TI is determined utilizing temporally averaged intensity. The mechanical index is the rarefactional pressure (Mega-Pascal) divided by the root of ultrasound frequency (Mega-Hertz). |