AJ PHOTO / HOP AMERICAIN / SCIENCE PHOTO LIBRARY AJ PHOTO / HOP AMERICAIN / SCIENCE PHOTO LIBRARY
Doppler ultrasound. Doctor holding an ultrasound transducer next to a patient's neck to study blood flow in one of her carotid arteries. These arteries carry blood to the head. 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. An obstruction to a carotid artery can have dire consequences, as the brain cannot work without a good blood supply. This scan (upper left) is normal.
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