A Moment of Science

Hearing a Shape

Ultrasound uses high frequency sound waves to create pictures of what is going on in our body.

Baby ultrasound

Photo: MamaT (flickr)

Ultrasounds use precise timing of sound waves to form pictures

The first picture an expecting mother is likely to see of her developing fetus is not, technically, a picture at all.  Most likely, it’s an ultrasound image, produced by technology that has more to do with hearing than with seeing.  On today’s program we’ll learn how ultrasound works.

You might think ultrasound is similar to X-rays.  After all, they’re both used by doctors to glimpse the inside of your body.  Actually, X-ray machines use high frequency radiation–an energetic, souped-up form of regular, visible light. Such X-ray radiation would be harmful to a developing fetus, so that’s why ultrasound is used on pregnant women instead.

Ultrasound doesn’t use any type of light or radiation at all.  It uses high frequency sound waves instead.  The physician holds a probe to the woman’s skin, and the probe sends these sound waves into her body.  Like an echo off a canyon wall, some of these waves bounce off the developing fetus and return to the probe.  These return echoes are carefully measured for timing and direction, and this information is used to construct a moving image of what’s going on inside the woman’s body.

In addition to viewing fetuses, medical ultrasound can also be used for imaging a patient’s bones and organs, and for measuring blood flow through arteries.  Ultrasound can even be used as treatment for some types of cancer.  By turning up the volume of those high frequency sound waves, and focussing them carefully, they can sometimes break up a tumor inside the body, without surgery.  That’s quite a lot for this versatile, sound-based technology.

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