MODEL RELEASED. Doppler ultrasound. Doctor holding an ultrasound transducer next to a patient's abdomen to study her organs. Doppler ultrasound builds up pictures of body structures from the echoes of high frequency sound waves produced by the transducer. The doppler effect, in which a wave reflected from a moving body has its wavelength shifted, allows determination of the speed and smoothness of blood flow and other movements. Ultrasound is good for imaging hollow and fluid-filled structures. This scan (upper centre) is normal.