What is Ultrasound Imaging of the Abdomen?
Ultrasound imaging, also called ultrasound scanning or
sonography,
involves exposing part of the body to high-frequency sound waves to
produce pictures of the inside of the body. Ultrasound exams do not use
ionizing radiation (as used in x-rays).
Because ultrasound images are captured in real-time, they can show the
structure and movement of the body's internal organs, as well as blood
flowing through blood vessels.
Ultrasound imaging is a noninvasive medical test that helps physicians diagnose and treat medical conditions.
An abdominal ultrasound produces a picture of the organs and other structures in the upper abdomen.
A Doppler ultrasound study may be part of an abdominal ultrasound examination.
Doppler ultrasound
is a special ultrasound technique that evaluates blood as it flows
through a blood vessel, including the body's major arteries and veins
in the abdomen, arms, legs and neck.
What are some common uses of the procedure?
Abdominal ultrasound imaging is performed to evaluate the:
- kidneys
- liver
- gallbladder
- pancreas
- spleen
- abdominal aorta and other blood vessels of the abdomen
Ultrasound is used to help diagnose a variety of
conditions, such as:
- abdominal pains
- abnormal liver function
- enlarged abdominal organ
- stones in the gallbladder or kidney
- an aneurysm in the aorta
Additionally, ultrasound is used in guiding procedures such as needle
biopsies in which needles are used to extract a sample of cells from organs for laboratory testing.
Doppler ultrasound images can help the physician to see and evaluate:
- blockages to blood flow (such as clots)
- narrowing of vessels (which may be caused by plaque)
- tumors and congenital malformation
How should I prepare?
You should wear comfortable, loose-fitting clothing for your
ultrasound exam. You will need to remove all clothing and jewelry in
the area to be examined.
You may be asked to wear a gown during the procedure.
Tell your doctor if you have had a barium enema or a series of upper
GI (gastrointestinal) tests within the past two days. Barium that
remains in the intestines can interfere with the ultrasound test.
Other preparations depend on the type of ultrasound you are having.
- For a study of the liver, gallbladder, spleen,
and pancreas, you may be asked to eat a fat-free meal on the evening
before the test and then to avoid eating for eight to 12 hours before
the test.
- For ultrasound of the kidneys, you may be asked to drink four to
six glasses of liquid about an hour before the test to fill your
bladder. You may be asked to avoid eating for eight to 12 hours before
the test to avoid gas buildup in the intestines.
- For ultrasound of the aorta, you may need to avoid eating for eight to 12 hours before the test.
What does the equipment look
like?
Ultrasound scanners consist of a console containing a computer and electronics, a video display screen and a
transducer
that is used to scan the body and blood vessels. The transducer is a
small hand-held device that resembles a microphone, attached to the
scanner by a cord. The transducer sends out high frequency sound waves
into the body and then listens for the returning echoes from the
tissues in the body. The principles are similar to sonar used by boats
and submarines.
The ultrasound image is immediately visible on a nearby screen that
looks much like a computer or television monitor. The image is created
based on the amplitude (strength), frequency and time it takes for the
sound signal to return from the patient to the transducer.
How does the procedure work?
Ultrasound imaging is based on the same principles involved in
the sonar used by bats, ships and fishermen. When a sound wave strikes
an object, it bounces back, or echoes. By measuring these echo waves it
is possible to determine how far away the object is and its size,
shape, and consistency (whether the object is solid, filled with fluid,
or both).
In medicine, ultrasound is used to detect changes in appearance of
organs, tissues, and vessels or detect abnormal masses, such as tumors.
In an ultrasound examination, a transducer
both sends the sound waves and records the echoing waves. When the
transducer is pressed against the skin, it directs small pulses of
inaudible, high-frequency sound waves into the body. As the sound waves
bounce off of internal organs, fluids and tissues, the sensitive
microphone in the transducer records tiny changes in the sound's pitch
and direction. These signature waves are instantly measured and
displayed by a computer, which in turn creates a real-time picture on
the monitor. One or more frames of the moving pictures are typically
captured as still images.
Doppler ultrasound, a special application of ultrasound, measures
the direction and speed of blood cells as they move through vessels.
The movement of blood cells causes a change in pitch of the reflected
sound waves (called the Doppler effect). A computer collects and
processes the sounds and creates graphs or color pictures that
represent the flow of blood through the blood vessels.
What will I experience during and after
the procedure?
Most ultrasound examinations are painless, fast and easy.
After you are positioned on the examination table, the
radiologist or
sonographer will apply some warm gel on your skin and then place the
transducer
firmly against your body, moving it back and forth over the area of
interest until the desired images are captured. There is usually no
discomfort from pressure as the transducer is pressed against the area
being examined.
If scanning is performed over an area of tenderness, you may feel pressure or minor pain from the transducer.
If a Doppler ultrasound study is performed, you may actually hear
pulse-like sounds that change in pitch as the blood flow is monitored
and measured.
Once the imaging is complete, the gel will be wiped off your skin.
After an ultrasound exam, you should be able to resume your normal activities.
Who interprets the results and how do I get them?
A radiologist, a physician specifically trained to supervise and
interpret radiology examinations, will analyze the images and send a
signed report to your primary care or referring physician, who will
share the results with you. In some cases the radiologist may discuss
results with you at the conclusion of your examination.
What are the benefits vs. risks?
Benefits
- Most ultrasound scanning is noninvasive (no needles or injections) and is usually painless.
- Ultrasound is widely available, easy-to-use and less expensive than other imaging methods.
- Ultrasound imaging uses no ionizing radiation.
- Ultrasound scanning gives a clear picture of soft tissues that do not show up well on x-ray images.
- Ultrasound causes no health problems and may be repeated as often as is necessary.
- Ultrasound provides real-time imaging, making it a good tool for guiding
minimally invasive procedures such as cortisone injections, needle biopsies and needle aspiration of fluid in joints or elsewhere.
Risks
For standard diagnostic ultrasound there are no known harmful effects on humans.
What are the limitations of Abdominal
Ultrasound Imaging?
Ultrasound waves are disrupted by air or gas; therefore ultrasound
is not an ideal imaging technique for the bowel or organs obscured by
the bowel. In most cases, barium exams, CT scanning, and MRI are the methods of choice in this setting.
Ultrasound waves do not pass through air; therefore an evaluation of
the stomach, small intestine and large intestine may be limited.
Intestinal gas may also prevent visualization of deeper structures such
as the pancreas and aorta. Large patients are more difficult to image
because tissue attenuates (weakens) the sound waves as they pass deeper
into the body.
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