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.
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)
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.
How To Prepare
You may need to stop using products
that contain nicotine (cigarettes, chewing tobacco) for 30 minutes to 2 hours
before the test. Nicotine causes blood vessels to constrict and may give false
How It Is Done
This test is done by a doctor who
specializes in performing and interpreting imaging tests (radiologist) or
by an ultrasound technologist (sonographer) who is supervised by a radiologist.
It is done in an ultrasound room in a hospital or doctor's office.
You will need to remove any jewelry that might interfere with the Doppler
ultrasound scan. You may need to take off all or most of your clothes,
depending on which area is being examined (you may be allowed to keep on your
underwear if it does not interfere with the test). You will be given a cloth or
paper covering to use during the test.
For abdominal scans, you will lie on your
For chest scans, you will lie on your back with your neck
For head and neck scans, your head may be turned
to one side.
For an arm or leg scan, your head will be slightly
raised and the exposed arm or leg will be turned slightly outward. Sometimes
for a leg scan, you may be asked to lie on your stomach.
pregnancy, you will lie on your back or on your left side with your belly
Gel is applied to the skin to promote the passage of the
sound waves. The transducer is placed in the gel and moved along the skin. You
need to lie very still during the procedure. You may hear sounds that represent
the flow of blood through the blood vessels.
The test usually
takes 30 to 60 minutes.
Arteries in the arms and legs
This test is often
performed on both arms or both legs. Even if the suspected blood flow problem
is in only one limb, both may be tested for comparison. If your arms are being
tested, they will be tested first while you are lying down and then again while
you are sitting.
Depending on which blood vessels are being
tested, a blood pressure cuff may be wrapped around one or both limbs so that
the blood pressure can be taken at several different places. When testing the
legs, a blood pressure cuff may be wrapped first around the calf and then
around the thigh. The test may be done at several locations on your leg. When
testing the arms, the pressure cuff may be wrapped first around the forearm and
then around the upper arm.
Testing may be done before and after
exercise, if you are healthy enough.
Veins in the arms and legs
For this test, you will
be asked to lie down and breathe normally. You must lie very still. Any changes
in blood flow that occur as a response to your breathing patterns are
The test may be repeated while the examiner presses on the
veins close to the surface of your skin to help detect a clot in the vein
(called a compression maneuver). The examiner may do this with your legs or
arms in different positions to ensure that the blood supply is not blocked in
these positions. The examiner may also squeeze your calf or forearm to help
blood move more quickly through the veins (called an augmentation maneuver).
This is done to evaluate blood flow toward your heart.
legs are being tested, you may also be asked to try to breathe out strongly
with your nose pinched and your mouth closed (called a
Valsalva maneuver). This maneuver usually causes a
sudden change in blood flow through the veins.
Arteries in the neck
You will be asked to lie down
with a pillow underneath your head for support. The test is performed on both
sides of your neck, and then the results are compared to standard values to
determine the amount of blockage or narrowing of the arteries.
For a transcranial
ultrasound, the transducer is passed lightly over the skin at the base or side
of your skull.
The transducer is moved back and
forth on your belly until the doctor finds the blood vessel that needs to be
studied. After the doctor has found the blood vessel, it may take some time to
check the blood flow.
How It Feels
There is normally no discomfort involved
with having a Doppler ultrasound test. The gel may feel cold when it is put on
your skin unless it is first warmed to body temperature. If your blood pressure
is taken during the test, you will feel pressure when the blood pressure cuff
There are no known risks linked with a
Doppler ultrasound test. This test will not harm a developing baby (fetus).
ultrasound test uses reflected sound waves to see how
blood flows through a blood vessel.
There are no findings of
significant narrowing or other abnormality in any of the arteries
There is no evidence of a clot
in any of the veins examined. The size and position of veins are
Normal blood flow is found in
the blood vessels that supply oxygen and nutrients to a
For continuous wave Doppler or
duplex Doppler, differences in blood flow between the right and left sides of
the body may be heard. At the exact location where an artery is blocked or
narrowed, the sound may be high-pitched or turbulent. Blockage (such as from a
blood clot), an
aneurysm, or narrowing of a blood vessel may be
detected. The speed of blood flow may be compared to standard values to find
out the amount of blockage or narrowing of the blood vessel.
A duplex Doppler ultrasound
graph may show irregular flow that means a blocked or narrowed blood
A color Doppler image may show
a blocked or narrowed blood vessel or an aneurysm.
In the veins, a blood clot may
be indicated if blood flow does not change in response to breathing or does not
increase in response to either a compression maneuver or
Valsalva maneuver. Incomplete blockage of a vein by a
blood clot may be seen on color Doppler or during a compression
Blood flow through the blood
vessels that supply oxygen and nutrients to a fetus is abnormally increased or
What Affects the Test
Reasons you may not be able to
have the test or why the results may not be helpful include:
Bones above the area being studied or gas in
the intestines, which may interfere with the pictures.
Not being able to remain still during the
Irregular heart rhythms
(arrhythmias) or heart disease, which may cause changes in blood flow patterns
even though the blood vessels are not abnormal.
Having a cold arm
or leg. Blood flow through that limb may be slowed.
Having an open
wound in the area that needs to be viewed.
What To Think About
Producing accurate test results with Doppler
ultrasound requires a skilled examiner. The scans are usually read within a
short period of time in case repeat tests are needed.
Doppler ultrasound requires a person to hold very still, some children may need
to be sedated so that their movements do not interfere with the
Angiography and venography are
X-ray tests that require the injection of
contrast material. In many cases, Doppler ultrasound
may be done instead of angiography or venography because it is faster, less
expensive, and noninvasive. If results from a Doppler ultrasound are
inconclusive, an angiography or venography test may be done. Angiography is
usually more accurate than Doppler ultrasound and is considered the most
definitive test for evaluating blood flow through an artery. Magnetic resonance
angiography (MRA) and computed tomography angiography (CTA) may be done instead
of conventional angiography because these tests are less invasive and easier to
perform than conventional angiography. In some cases, venography may be needed
to confirm a suspected vein problem.
How this information was developed to help you make better health decisions.