超声波传入机体内部遇到脏器等反射回来,如声源和反射体之间有相对运动,就会使入射波与反射波之间发生频率变化△f,这就叫做起声都卜勒效应。医学上利用这一原理可以测定血流速度和一切运动脏器的活动情况。利用都卜勒原理探测胎儿心脏搏动情况,和用一般听诊器听胎儿心音相比,灵敏度高,杂音干扰小,不仅可以早期检测胎儿存活,鉴别正常妊娠与葡萄胎,且可以在临产前作分娩 Ultrasound into the body and other internal organ reflection back, such as sound source and reflector relative movement between, will make the incident wave and reflected wave frequency change between △ f, which is called the onset Doppler effect . Medical use of this principle can determine the blood flow velocity and the movement of all moving organs. Detection of fetal heart beat using the principle of Doppler, and compared with the general stethoscope to listen to fetal heart sound, high sensitivity, noise interference is small, not only early detection of fetal survival, identification of normal pregnancy and hydatidiform mole, and can be delivered before labor