A Doppler ultrasound (or duplex scanning) is a medical test
that uses reflected sound waves to estimate the speed and direction of blood as
it flows through a blood vessel. It helps doctors evaluate blood flow through
arteries and veins.
Doppler ultrasound can be used to evaluate the
vessels in several areas of the body. For example, a Doppler ultrasound test of
the blood vessels in the neck (carotid ultrasound) can be done to estimate a
person's risk of a stroke from blockage in those arteries. Renal ultrasound can
help detect kidney problems. Lower extremity ultrasound can be used to detect a
blood clot in the deep veins of the legs. A Doppler ultrasound also may be used
to evaluate problems with the blood flow to the placenta and umbilical cord in
a pregnant woman; problems with this blood flow may point to fetal distress.