Ultrasound is a technique that uses sound waves to
study the body. In ultrasound scanning, high-frequency
sound waves are transmitted to the area of interest
and the returning (reflected) echoes recorded and
displayed as a real-time visual image. Ultrasound
is noninvasive, involves no radiation, and avoids
the possible hazards—such as bleeding, infection,
or reactions to chemicals—of other diagnostic
methods. Because ultrasound images are captured in
real-time, they can show movement of internal tissues
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 type of imaging, such as magnetic resonance
imaging (MRI), may be selected.
Ultrasound waves also do not pass through air. Organs
containing air or gas may not be well visualized with
ultrasound. Thus, evaluation of the stomach, small
intestine and large intestine may not be possible.
Intestinal gas may also prevent visualization of deeper
structures such as the pancreas and aorta. Obese patients
are also difficult to image—this is because
sound waves weakened as they pass deeper into the
What is ultrasound used for?
Ultrasound can be used for diagnosis or therapy
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.
In obstetrics it is used to study the age, sex, and
level of development of the fetus and to determine
the presence of birth defects or other potential problems.
Ultrasound is used in cardiology to detect heart damage
and in ophthalmology to detect retinal problems.
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 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: