What does it show?
Ultrasonography, also known as ultrasound or sonography,
produces images called sonograms by generating high-frequency sound waves that penetrate the body. As the sound waves bounce
off internal organs and tissues, they create echoes. Tissues affected by cysts (fluid-filled spaces) or solid tumors have
different echo patterns than normal tissues.
Ultrasound is especially good at visualizing some diseases
of soft tissues that do not show up as well on x-rays. Ultrasound is an excellent method for distinguishing fluid-filled cysts
from solid tumors, because the echo patterns produced by these disorders appear very different. In diagnosing breast masses,
for example, ultrasound is often used to distinguish cysts from solid tumors. However, ultrasound cannot distinguish a benign
tumor from a malignant one. Nor is it used to detect abnormalities in bone, because the sound waves cannot penetrate bone.
Ultrasound can be used to determine how deeply a tumor of the esophagus, rectum, or uterus has penetrated the wall of the
Doctors frequently use ultrasound to determine where to
place a needle to obtain a core biopsy or a needle aspiration biopsy (withdrawing fluid or tiny tissue fragments for examination
under a microscope). This procedure occurs in "real time" -- that is, the doctor can look at the ultrasound monitor while
manipulating the needle and actually see the needle moving toward and into the tumor.
For some types of ultrasound examinations, the transducer
(which produces the sound waves and detects echoes) is placed on the skin surface. The sound waves pass through the skin and
reach the internal organs. In other cases, to get the best images, the doctor must use a transducer that is inserted into
a body opening, such as the rectum or the vagina. One important use of this technique involves aiming the needle for a biopsy
of the prostate, a male gland, when there is evidence that prostate cancer may be present. This technique is called transrectal
ultrasound, or TRUS.
Special ultrasound machines are able to show how blood
is flowing through the vessels. This is important because blood flows differently through tumors than it does through normal
tissue. Some of these ultrasound devices, known as Doppler flow machines, colorize the image to increase the amount of information
it contains. Unlike other forms of blood vessel imaging, color Doppler studies do not require the use of contrast agents.
Color Doppler has made it easier for doctors to evaluate the spread of cancer into blood vessels, especially in the liver
How does it work?
An ultrasound machine has three key parts: the control
panel, the display screen, and a transducer, that looks somewhat like either a microphone or a computer mouse. The ultrasound
technologist passes the transducer over the part of the body being examined. The transducer emits sound waves and picks up
the echoes. The computer inside the main part of the machine analyzes the signals and displays an image on a computer screen.
The shape and intensity of the echoes depends on how dense
the tissue is. For example, most of the sound waves pass right through a fluid-filled cyst and send back very few or faint
echoes. But the waves will bounce off a solid tumor, and the pattern of echoes will be translated by the computer into an
image that the radiologist will recognize as indicating a solid mass.
How do I prepare for the test?
As a general rule, no preparation is needed. However, your
doctor or nurse will give you specific instructions about steps to take prior to your test. Depending on the organ being studied,
you may need to fast overnight, take a laxative, or have an enema. If you will have an abdominal ultrasound, you may need
to drink a large amount of water just before the study.
If a probe is used, it will be covered with a lubricating
gel and inserted into the orifice (body opening). Such procedures are not painful, but they can cause feelings of pressure
What is it like having the test?
Ultrasound tests can be done in a doctor's office, clinic,
or hospital. You will lie down on a table. The technologist will apply a gel to the part of the skin over which the transducer
will pass. The gel serves two purposes: It lubricates the skin and enhances the transmission of the sound waves. The gel feels
cool and slippery.
During the test the technologist or the doctor moves the
transducer back and forth. You may be asked to hold your breath during the scan to prevent excess movement. The operator may
adjust knobs or dials to increase the depth to which the sound waves are sent. You may feel slight pressure from the transducer,
but you will not hear the high-frequency sounds.
How long does it take?
An ultrasound exam usually takes 20 to 30 minutes. Length
of time depends on the type of exam as well as the ease or difficulty in finding any abnormalities of the organs being studied.
What are the possible complications?
Ultrasound is a very safe procedure with a low risk of
complications. Good images are harder to obtain in people who are obese.
What else should I know about this test?
- Ultrasound does not involve the use of
- Ultrasound is an inexpensive test that
costs much less than CT or MRI.
- The quality of the results depends to
a large extent on the skill of the technologist or doctor operating the transducer, which is not the case with CT or MRI.
- In the future, ultrasound may provide
three-dimensional images. Contrast agents may be used to enhance the quality of the picture.