What is an Ultrasound?
Ultrasound (US) imaging, also called
ultrasound scanning or sonography, is a method of obtaining images of internal
organs by sending high-frequency sound waves into the body.
The reflected sound waves¡¯ echoes are
recorded and displayed as a real-time visual image. No ionizing radiation
(x-ray) is involved in ultrasound imaging.
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 radiologist or
sonographer 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 radiologist or
sonographer watches this screen during an examination and captures representative
images for storage. Often, the patient is able to see it as well. Ultrasound imaging
is based on the same principles involved in the sonar used by bats, ships at
sea, and anglers with fish detectors. As a controlled sound bounces against
objects, its echoing waves can be used to identify how far away the object is,
how large it is, its shape and internal consistency (fluid, solid or mixed),
and how uniform it is.The ultrasound transducer functions as both a loudspeaker
(to create the sounds) and a microphone (to record them). When the transducer
is pressed against the skin, it directs a stream of inaudible, high-frequency
sound waves into the body. As the sound waves echo from the body¡¯s fluids and
tissues, the sensitive microphone in 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. These signature waves 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 can be
recorded on videotape or on disk.
In addition, still frames of the moving
picture are usually ¡°frozen¡± to capture a series of images.