Читать книгу Informed Choices in Motherhood - Fiona Lee - Страница 24

The term refers to the ultra-high frequency sound-waves used for diagnostic scanning. Ultrasound waves are emitted by a transducer, and a picture of the underlying tissues is built from the patterns which return. Ordinary scans use pulses of ultrasound that last only a fraction of a second. In contrast Doppler techniques, which are used in fetal monitors, use continuous waves, giving much higher levels of exposure than 'pulsed' ultrasound.