| Ultrasound - General
What is General Ultrasound Imaging? Back to Top
Ultrasound
imaging, also called ultrasound scanning or sonography, is a method of
obtaining images from inside the human body through the use of
high-frequency sound waves. The reflected sound wave echoes are
recorded and displayed as a real-time visual image. No ionizing
radiation (x-ray) is involved in ultrasound imaging. Obstetric
ultrasound refers to the specialized use of sound waves to visualize
and thus determine the condition of a pregnant woman and her embryo or
fetus.
Ultrasound is a useful way of examining many of the body's internal
organs, including but not limited to the heart, liver, gallbladder,
spleen, pancreas, kidneys and bladder. Because ultrasound images are
captured in real time, they can show movement of internal tissues and
organs and enable physicians to see blood flow and heart valve
functions. This can help to diagnose a variety of heart conditions and
to assess damage after a heart attack or other illness.
What are some common uses of the procedure? Back to Top
Ultrasound: Gallbladder
Ultrasound: Kidney
Ultrasound: Liver
Millions of expectant parents have seen the first "picture" of their
unborn child with pelvic ultrasound examinations of the uterus and
fetus. Ultrasound imaging is used extensively for evaluating the eyes,
pelvic and abdominal organs, heart and blood vessels, and can help a
physician determine the source of pain, swelling or infection in many
parts of the body. Because ultrasound provides real-time images it can
also be used to guide procedures such as needle biopsies, in which
needles are used to sample cells from organs for laboratory testing.
Ultrasound is now being used to image the breasts and to guide biopsy
of breast cancer (see the Ultrasound-Guided Breast Biopsy page).
Ultrasound is also used to evaluate superficial structures such as the
thyroid gland and scrotum (testicles).
Doppler ultrasound is a special technique used to examine blood flow. Doppler 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 for the procedure? Back to Top
You
should wear comfortable, loose-fitting clothing for your ultrasound
exam. Other preparation depends on the type of examination you will
have. For some scans your doctor may instruct you not to eat or drink
for as many as 12 hours before your appointment. For others you may be
asked to drink up to six glasses of water two hours prior to your exam
and avoid urinating so that your bladder is full when the scan begins.
What does the equipment look like? Back to Top
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.
The transducer is a small hand-held device about the size of a bar of
soap, attached to the scanner by a cord. The physician or technologist
spreads a lubricating gel on the patient's abdomen in the area being
examined and then presses the transducer firmly against the skin to
obtain images.
The ultrasound image is immediately visible on a nearby screen that
looks much like a computer or television monitor. The physician or
technologist watches this screen during an examination and captures
representative images for storage. Often, the patient is able to see it
as well.
How does the procedure work? Back to Top
Ultrasound imaging
is based on the same principles involved in the sonar used by bats,
ships at sea and anglers with fish detectors. As the sound passes
through the body, echoes are produced that can be used to identify how
far away an object is, how large it is, its shape and its consistency
(fluid, solid or mixed).
The ultrasound transducer functions as both a generator of sound
(like a speaker) and a detector (like a microphone). When the
transducer is pressed against the skin it directs inaudible,
high-frequency sound waves into the body. As the sound echoes from the
body’s fluids and tissues the transducer records the strength and
character of the reflected waves. With Doppler ultrasound the
microphone captures and records tiny changes in the sound wave's pitch
and direction of the sound. These echoes are instantly measured and
displayed by a computer, which in turn creates a real-time picture on
the monitor. The "live" images of the examination are usually recorded
on videotape but one or more frames of the moving picture may be
"frozen" to capture a still image.
How is the procedure performed? Back to Top
The patient is
usually positioned on an examination table. A clear gel is applied to
the patient's body in the area to be examined to help the transducer
make secure contact with the skin. The sound waves produced by the
transducer cannot penetrate air so the gel helps eliminate air pockets
between the transducer and the skin. The technologist or radiologist
presses the transducer firmly against the skin and sweeps it back and
forth to image the area of interest.
When the examination is complete the patient may be asked to dress
and wait while the ultrasound images are reviewed either on film or on
a TV monitor. Often though, the technologist or radiologist is able to
review the ultrasound images in real time as they are acquired and the
patient can be released immediately.
What will I experience during the procedure? Back to Top
Most
ultrasound examinations are painless, fast and easy. You will lie on
your back on an examining table. The technologist or doctor will spread
some warm gel on your skin and then press the transducer firmly against
your body, moving it until the desired images are captured. There may
be varying degrees of discomfort from pressure as the technologist
guides the transducer over your abdomen, especially if you are required
to have a full bladder. The examination usually takes less than 30
minutes.
Who interprets the results and how do I get them? Back to Top
A
radiologist or other physicians experienced in ultrasound and other
radiology examinations will analyze the images and send a signed report
with his or her interpretation to the patient’s personal physician. The
patient receives ultrasound results from the referring physician who
ordered the test results. In some cases the radiologist may discuss
preliminary results with you at the conclusion of your examination. New
technology also allows for distribution of diagnostic reports and
referral images over the Internet at many facilities.
What are the benefits vs. risks? Back to Top
Benefits
- Ultrasound scanning is noninvasive (no needles or injections in most cases) and is usually painless.
- Ultrasound is widely available and easy to use.
- Ultrasound
uses no ionizing radiation and is the preferred image modality for
diagnosis and monitoring of pregnant women and their unborn infants.
- Ultrasound provides real-time imaging, making it a good tool for guiding minimally invasive procedures such as needle biopsies.
- Ultrasound images can visualize structure, movement and live function in the body's organs and blood vessels.
Risks
- For standard diagnostic ultrasound there are no known harmful effects on humans.
What are the limitations of General Ultrasound Imaging? Back to Top
Ultrasound
has difficulty penetrating bone and therefore can only see the outer
surface of bony structures and not what lies within. For visualization
of bone, other imaging modalities such as magnetic resonance imaging
(MRI) may be selected.
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. Patients suffering from obesity are more
difficult to image—this is because tissue attenuates (weakens) the
sound waves as they pass deeper into the body. Back to Top |
