ultrasound test uses reflected sound waves to see how
blood flows through a blood vessel. It helps doctors evaluate blood flow
through major arteries and veins, such as those of the arms, legs, and neck. It can show
blocked or reduced flow of blood through narrow areas in the major arteries of the
neck that could cause a
stroke . It also can reveal blood clots in leg veins
(deep vein thrombosis, or DVT) that could break loose
and block blood flow to the lungs (pulmonary embolism). During pregnancy, Doppler ultrasound may be
used to look at blood flow in an unborn baby (fetus) to check
the health of the fetus.
During Doppler ultrasound , a handheld
instrument (transducer) is passed lightly over the skin above a blood vessel.
The transducer sends and receives sound waves that are amplified through a
microphone. The sound waves bounce off solid objects, including blood cells.
The movement of blood cells causes a change in pitch of the reflected sound
waves (called the Doppler effect). If there is no blood flow, the pitch does
not change. Information from the reflected sound waves can be processed by a
computer to provide graphs or pictures that represent the flow of blood through
the blood vessels. These graphs or pictures can be saved for future review or
The three basic types of Doppler ultrasound
"Bedside" or continuous wave Doppler. This type
uses the change in pitch of the sound waves to provide information about blood
flow through a blood vessel. The doctor listens to the sounds produced by the
transducer to evaluate the blood flow through an area that may be blocked or
narrowed. This type of ultrasound can be done at the bedside in the hospital
with a portable machine to provide a fast estimate of the extent of blood
vessel damage or disease.
Duplex Doppler. Duplex Doppler ultrasound uses
standard ultrasound methods to produce a picture of a blood vessel and the
surrounding organs. Also, a computer converts the Doppler sounds into a graph
that gives information about the speed and direction of blood flow through the
blood vessel being evaluated.
Color Doppler. Color Doppler uses standard
ultrasound methods to produce a picture of a blood vessel. Also, a computer
converts the Doppler sounds into colors that are overlaid on the image of the
blood vessel and that represent the speed and direction of blood flow through
the vessel. Power Doppler is a special type of color Doppler. Power Doppler can get some images that are hard or impossible to
get using standard color Doppler. Power Doppler is most commonly used to
evaluate blood flow through vessels within solid organs.
Why It Is Done
Doppler ultrasound is done to:
- Find blood clots and blocked or narrowed
blood vessels in almost any part of the body, especially in the neck, arms, and
- Evaluate leg pain
that may be caused by
intermittent claudication, a condition caused by
atherosclerosis of the lower
- Evaluate blood flow after a stroke or other condition
that might be caused by a problem with blood flow. Evaluation of a stroke can
be done through a technique called transcranial Doppler (TCD)
- Evaluate varicose veins or other vein problems.
- Map veins that may be used for blood vessel grafts. It also can
check the condition of grafts used to bypass blockage in an arm or
- Find out the amount of blood flow to a transplanted kidney or
- Monitor the flow of blood following blood vessel
- Find out the presence, amount, and location of arterial
plaque. Plaque in the carotid arteries can reduce
blood flow to the brain and may increase the risk of stroke.
treatment such as laser or radiofrequency ablation of abnormal
- Check the health of a fetus. Blood flow in the
umbilical cord, through the
placenta, or in the heart and brain of the fetus may
be checked. This test can show if the fetus is getting enough oxygen and
nutrients. Doppler ultrasound may be used to guide decisions during pregnancy
- The fetus is smaller than normal for his or her
gestational age (fetal growth restriction). Blood flow through the large blood
vessel in the umbilical cord (the umbilical artery) can be looked
- Rh sensitization has occurred. Blood flow through a
blood vessel in the brain (the middle cerebral artery, or MCA) can be used to
monitor fetal health.
- The mother has other problems, such as
sickle cell disease.
A transcranial Doppler (TCD) ultrasound may be used in
children with sickle cell disease to evaluate their risk of stroke. In adults,
TCD can be used to evaluate blood flow in the brain.