Standard ultrasounds, as you know, use sound waves to detect anatomical structures. This technology is used routinely in pregnant women to visualize the growth and development of the fetus. Other uses include assessment of abdominal organs (such as the liver, gallbladder and kidneys), pelvic organs (such as the uterus and ovaries), and the heart (echocardiography).
Duplex ultrasonography refers to the combination of the usual gray-scale ultrasound
and color Doppler ultrasound. Gray-scale ultrasound is the standard ultrasound with which you are familiar; it does not help in the assessment of motion, and thus is limited in its ability to help characterize certain conditions. Color Doppler is helpful because it can assess this motion by assigning different colors relative to the direction of the ultrasound probe. One typical use for color Doppler technology is in the assessment of blood vessels and determining if there is adequate flow (for example, through a blood clot or to/from a specific organ). The color Doppler function is often built in to the same machine that is used for Gray-scale ultrasound, and its use during the exam should not take a significant extra amount of time. Color Doppler ultrasound is just as safe as Gray-scale ultrasound.