| Carotid Ultrasound Imaging
What is Carotid Ultrasound Imaging? Back to Top
Ultrasound,
also called sonography, uses high-frequency sound waves to image a
particular region or organ in the body or to monitor blood flow. It is
a totally noninvasive procedure that causes no discomfort. Sound waves
are focused at a part of the body, and the returning echoes are
processed by computer to yield clear and accurate images of the part of
the body being examined. The returning sound waves, or echoes, reflect
the size and shape of the structure and whether it is solid, fluid, or
something in between. In a carotid ultrasound exam, it is the carotid
arteries, which are the large vessels in the neck that deliver blood to
the brain, being examined. Carotid ultrasound can depict plaque that
narrows the artery and may limit the free flow of blood to the brain.
Unlike x-rays, ultrasound requires no exposure to ionizing
radiation, meaning that repeat imaging may be carried out without
concern of accumulating radiation exposure. In addition, carotid
ultrasound is a real-time technique that provides a picture of blood
flow as it is at the very moment of imaging.
What are some common uses of the procedure? Back to Top
The
most frequent reason for a carotid ultrasound exam is to detect
narrowing, or stenosis, of the carotid artery, which substantially
increases the risk of stroke. If your primary care physician detects
high blood pressure or a carotid bruit (pronounced brU-E)—an abnormal
sound in the neck that is heard with the stethoscope—carotid ultrasound
may be needed. Other risk factors calling for ultrasound are advanced
age, diabetes, elevated blood cholesterol, and a family history of
stroke or heart disease.
If the exam shows narrowing of one or both carotid arteries, your
physician may suggest medication, noninvasive angiography, or an
operation to restore normal blood flow to the brain. In this way a
stroke may be prevented.
Other reasons for performing carotid ultrasound are:
- To locate a hematoma, a collection of clotted blood that may slow and eventually stop blood flow.
- To
detect dissection of the carotid artery, a split between layers of the
artery wall that may lead to obstruction of blood flow or a weakening
of the wall of the artery.
- To check the state of the carotid artery after surgery to restore normal blood flow.
- To verify the position of a metal stent placed to maintain carotid blood flow.
How should I prepare for the procedure? Back to Top
No
special preparation is needed for carotid ultrasound. Wear a
loose-fitting, open necked shirt or blouse for the exam. You will be
asked to remove any jewelry or other objects from around your neck.
What does the equipment look like? Back to Top
A bedside
ultrasound machine is about the size of a small cupboard. It receives
and processes the echo signals and displays the carotid arteries and
the movement of blood through them on a screen. A hand-held transducer,
which resembles a microphone, is used to send out the ultrasound beam
and receive the reflected sound waves, which it then sends to a
computer in the ultrasound machine which creates the images.
How does the procedure work? Back to Top
Ultrasound is based
on the same principle as sonar, used by Navy ships to detect large
underwater objects such as submarines, or by fishermen to locate large
schools of fish. An example of the principle from nature is the bat,
which uses a sonar-like system instead of eyesight to avoid colliding
with nearby objects and to find insects to eat.
For the exam, the transducer is pressed against the skin on both
sides of the neck from the collarbone to the angle of the jaw. As it is
moved, it directs a stream of high-frequency sound waves toward the
carotid arteries.
The sound waves are reflected back at a frequency that varies with
how fast blood is flowing through the artery. The transducer changes
electrical signals into the outgoing sound waves. It then receives the
reflected sound waves and converts them back into electrical signals.
These signals are measured and displayed on the computer screen,
providing a real-time picture of arterial structure and blood flow. The
transducer, in effect, acts as a loudspeaker to create sound vibrations
and also as a microphone to record them. The images may be recorded on
videotape, and freeze-frame still pictures usually are obtained as
well. Most often, black-and-white images are satisfactory, but a
special type of ultrasound unit—called Doppler ultrasound—is able to
display color images to demonstrate flow in the arteries and veins.
How is the procedure performed? Back to Top
Carotid
ultrasound is performed as an outpatient office procedure. You will be
asked to lie flat on your back on a bed that can tilt and move. It may
be necessary to tilt or rotate your head for the best exposure. It also
helps to keep your arm and shoulder down. Your head will be supported
to keep it still.
A warm water-based gel is applied to the skin surface to eliminate
air pockets and ensure that the transducer will make secure contact
with the skin. The radiologic technologist then will move the
transducer up and down the entire length of your neck to obtain views
of the artery from different perspectives. The procedure then is
repeated on the other side of the neck. After reviewing the findings,
the radiologist may wish to obtain further images to clarify the
findings.
What will I experience during the procedure? Back to Top
You
should not experience pain or discomfort during a carotid ultrasound
examination. You will lie on the examining table in a slightly darkened
room. You may hear some pulse-like sounds depending on the type of
ultrasound being performed. You may be offered a chance to watch the
screen along with the technologist. If you choose to do so, you should
not hesitate to ask questions about what you are seeing. A carotid
ultrasound is usually completed within 30 minutes, though the exam may
sometimes take an hour. The technologist will remove the gel from your
skin, and you may leave and immediately resume your normal activities.
Who interprets the results and how do I get them? Back to Top
A
radiologist experienced in ultrasound will analyze the images and send
a report to your primary care physician. Your physician will discuss
the findings with you. With current technology, your physician may be
able to view the images and read the radiologist's report over the
Internet.
What are the benefits vs. risks? Back to Top
Benefits
- Ultrasound exams, unlike most other forms of imaging,
involve no radiation exposure. The procedure is painless and totally
noninvasive, and there are no known complications or side effects.
Adverse reactions to contrast material are avoided.
- Ultrasound uses no ionizing radiation, and is the preferred imaging modality for diagnosis and monitoring of pregnant women.
- If
a carotid ultrasound exam shows narrowing of one or both carotid
arteries, measures can be taken to restore the free flow of blood to
the brain. Many strokes are prevented as a result.
- An ultrasound exam is less costly than an alternative imaging method, CT scanning.
Risks
- In nearly 50 years of experience, carotid ultrasound has proved to be a risk-free procedure.
What are the limitations of Carotid Ultrasound Imaging? Back to Top
Carotid ultrasound may be difficult or impossible if a patient has a dressing covering a wound or surgical scar in the neck.
An occasional patient is difficult to examine because of the size or contour of the neck. Calcium deposits in the wall of the carotid artery may make it difficult to evaluate the vessel. A small amount of soft plaque that produces low-level echoes may go undetected. Ultrasound may not clearly depict the end segment of the carotid artery, but this is very seldom a site of disease.
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