MODEL RELEASED. Doppler ultrasound. Doctor holding an ultrasound transducer next to a patient's leg to study blood flow in her femoral artery. The femoral arteries carry blood to the legs. Doppler ultrasound images 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. Obstruction of a femoral artery can cause claudication (leg pain on exertion). Severely impaired blood flow can cause tissue death. This scan (upper centre) is normal.