| Ultrasound - Venous (Extremities)
What is Venous Ultrasound Imaging? Back to Top
All
ultrasound exams use very high-frequency sound waves and echoes to
obtain images of structures inside the body. Different signals are
produced when the beam of sound waves is focused at a particular site
and the waves bounce back from different types of tissue and body
fluid. The resulting pattern of echoes forms an accurate picture of
whatever is being examined, in this case the veins throughout the body
that carry blood back to the heart. Ultrasound studies differ from
x-rays in one very important respect: there is no exposure to ionizing
radiation. Another term for an ultrasound exam is "sonography."
The principle of ultrasound imaging is very much like that of
sonar—a method used by navy ships to detect submarines (or by fishing
boats to locate large schools of fish). The echo pattern of the
returning sound waves that bounce off the object makes it stand out
from the background pattern. Another example of this principle is the
bat, which, when flying about, replaces eyesight with a sonar-type
system to avoid colliding with nearby objects and to find insects to
eat. In medicine, the procedure is used to detect disease that changes
the appearance of organs, tissues, or abnormal masses, such as tumors.
When a blood clot develops inside a vein, venous ultrasound can show
the clot and also the slowing or complete block of blood flow that it
causes.
What are some common uses of the procedure? Back to Top
The
most common reason for a venous ultrasound exam is to search for blood
clots, especially in the veins of the leg. These clots may break off
and pass into the lungs, where they can cause a dangerous condition
called pulmonary embolism. If found in time, there are treatments that
can prevent this from happening.
Other reasons to do a venous ultrasound study:
- Find the cause of long-standing leg swelling. In people
with varicose veins, a common condition, the valves that keep blood
flowing in the right direction may not work well, and venous ultrasound
can help the surgeon decide how best to deal with this condition.
- Aid
placement of a needle or catheter in a large interior vein. Sonography
can help locate the exact site of the vein and avoid complications,
such as bleeding or air in the chest cavity.
- Map
out the veins in the leg or arm so that segments may be removed and
used to bypass an area of disease. An example is using pieces of vein
from the leg to surgically bypass narrowed coronary arteries.
- Examine
a blood vessel graft used for dialysis if it is not working as
expected; an area of narrowing in the graft may be responsible.
How should I prepare for the procedure? Back to Top
You
should dress comfortably, but you will have to remove all clothing and
jewelry in the area to be examined. Otherwise, there are no special
measures that need be taken. You may have heard that a period of
fasting is necessary, but this is important only if you are to have an
examination of veins in your abdomen. In this case, you will probably
be asked not to ingest any food or fluids except water for six to eight
hours ahead of time.
What does the equipment look like? Back to Top
You will be
taken into an examining room with a scanning machine that may look like
a computer with a TV screen. A small, hand-held device called a
transducer, which looks like a microphone, is placed over the area of
interest. Transducers are available that conform to different parts of
the body, such as the leg, for doing a venous ultrasound study. They
range in size from that of a fat pen to one resembling a deck of cards.
Once the exam begins, the ultrasound image can be seen in black and
white on the screen (or in color if a special type of exam, called
"color flow" or "power Doppler ultrasound," is done to monitor blood
flow in the veins).
How does the procedure work? Back to Top
The ultrasound
transducer generates sound waves that pass through the skin and also
serves as a microphone to record the returning sounds—the echoes. When
pressed against the skin, the transducer directs high-frequency sound
waves toward the veins being studied and records any changes in the
pitch and direction of the returning echoes. The bounce-back echoes, or
the signature, are automatically measured by the computer and converted
electronically to a picture that shows what is happening at that
instant—creating a so-called "real-time" image on the monitor screen.
These images can be videotaped, or they may be frozen in time to obtain
still pictures. If a Doppler study is done, changes in blood flow can
be displayed in color on the screen and actually heard as a change in
pitch.
How is the procedure performed?
After
positioning the patient on the adjustable examination table, the
technologist will apply a gel-like material onto the skin to make close
contact between the skin and transducer, eliminating air pockets. This
will ensure that the sound waves are freely conducted into and out of
the body. The radiologist or technologist presses the transducer firmly
to the skin and moves it back and forth to obtain complete images of
areas of interest. The entire area of interest will be scanned to
obtain images from different perspectives. Sometimes the examiner may
want to obtain images while you are standing upright. You will be asked
to relax and remain calm during the examination. The radiologist also
may ask you health-related questions during the exam and may repeat
some images to clarify the findings.
What will I experience during the procedure? Back to Top
You
will not hear any of the ultrasound emission or the echoes sent back to
the screen, although you may hear pulse-like sounds if a Doppler
examination is ordered. You will probably lie on your back, and the
table may be tilted or moved to provide better access to a particular
area. You may be standing for the procedure. Often, you will have a
chance to watch the screen along with the examiner, though it will not
be easy to make sense out of what you see. Most ultrasound studies take
no longer than a half-hour. Venous ultrasound is usually a painless
examination. If, however, your leg is swollen and tender, the pressure
from the ultrasound transducer may add to your discomfort.
Who interprets the results and how do I get them? Back to Top
When
the exam is over, the technologist will ask you to get dressed and wait
until the radiologist can review the images. If no additional images
are needed, you will be free to leave. A technologist usually performs
the procedure itself, but a radiologist who is experienced in
interpreting ultrasound images will perform the official reading and
inform your physician. After receiving a summary of the findings, your
physician will discuss with you what they mean and what should be done
next. Some centers now pass on diagnostic reports and the images
themselves over the Internet, speeding up the process considerably.
What are the benefits vs. risks? Back to Top
Benefits
- Ultrasound scanning is widely available and less
expensive than other imaging methods. No radiation exposure is
involved. Furthermore, this procedure is noninvasive, requiring no
penetration of the skin or any body cavity.
- Ultrasound scanning gives a clear picture of soft tissues that do not show up well on x-ray images.
- Venous
ultrasound helps to detect blood clots in the veins of the legs before
they become dislodged and pass to the lungs. It can also show the
movement of blood within blood vessels.
- Compared to
venography, which requires injecting contrast material into a vein,
venous ultrasound is nearly as accurate for detecting blood clots in
the calf and almost fully as accurate in finding clots in veins of the
thigh.
- Sonography is easily carried out, painless and causes no health problems. It may be repeated as often as is necessary.
Risks
- For standard diagnostic ultrasound, there are no known harmful effects to humans.
What are the limitations of Venous Ultrasound Imaging? Back to Top
Veins
lying deep beneath the skin, especially small veins in the calf, may be
hard to see clearly. It can be difficult to tell whether a blood clot
has totally closed off a vein or whether a small amount of blood is
still getting through. Back to Top |
