Have you ever seen a picture of a baby inside his or her mother’s body? If so, you may have wondered how doctors get their cameras inside the body to take these pictures.

Would you believe those pictures don’t come from cameras? They’re actually made with sound!

Ultrasound — also called ultrasonography — is a medical technology that uses high-frequency sound waves and their echoes to create images of what the inside of the body looks like. The scientific principles that make this possible are similar to those that allow bats, whales, and dolphins to “see” what’s around them using echolocation.

Ultrasound technology was actually first developed during World War I to help track submarines underwater. The technology was called SONAR, which stands for SOund Navigation And Ranging. Ultrasound wasn’t used for medical purposes until the 1950s.

The high-frequency sound waves used in ultrasound technology cannot be heard by human ears. Instead, a special tool called a transducer is used to send sound waves and detect the echoes that return.

As the sound waves pass through the inside of the body, different types of tissues conduct sound differently. A variety of echoes are produced.

These echoes can identify the size and shape of organs and other objects inside the body. A special computer in the ultrasound machine can read these echoes to produce a picture of what the inside of the body looks like.

Usually, doctors use an ultrasound to study a particular part of the inside of the body, such as an internal organ…or a pregnant woman’s unborn baby! Ultrasound technology is very safe, and doctors like it because it is noninvasive. That means it does not involve penetrating the skin or body.

Ultrasounds are used often during pregnancy to help doctors keep an eye on a baby’s development. There are also many other medical uses for ultrasound technology. Ultrasounds have been used to explore most parts of the body to diagnose various issues with internal organs.

Recent advances in technology have resulted in the development of 3D ultrasound imaging. By using multiple two-dimensional images, special computers are able to combine multiple images into a 3D rendering. Doctors believe this new technology will lead to earlier detection of cancer, as well as the ability to better assess blood flow in organs and development of babies in the mother’s womb.

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    • Your question is a great idea for a future Wonder of the Day®, Catherine! Thank you for visiting Wonderopolis today and suggesting it! :-)

  1. We loved the video!! We saw how you can see the sound. We knew a bus was coming when we heard its sound. We talked about seeing the sounds in ultrasounds, too.

    • Happy Monday, Kerrick Elementary School! Thank you so much for sharing your comment with us today! We’re glad you learned a lot of new things about sound and ultrasounds! Did you happen to visit yesterday’s Wonder #413 yet? We think you will really appreciate where we got the INSPIRATION for it! :-)

  2. Dear Wonderopolis,

    We love that the word ultrasound gives us a clue for how ultrasounds are made using sounds not a camera! This WONDER made us WONDER if humans can’t hear the sound waves, can dogs hear these sound waves?

    Happy Wondering, TEAM Caisse’s 5th grade Reading Class :)

    • That’s a GREAT question about dogs being able to hear sound waves, TEAM Caisse! We will have to do some more WONDERing about that, ourselves! Thank you for letting us know you liked today’s Wonder and that you learned some new things by exploring it together! :-)

    • We’re glad you learned some interesting new things about ultrasounds today, Elango! Thank you so much for visiting Wonderopolis! :-)

    • Hi, Gianna! A special computer inside the ultrasound machine reads echoes of sound waves as they bounce off different parts of the body. Then, the computer translates the echos into a picture of what the inside of the body looks like! Pretty cool, huh? Thanks so much for hanging out in Wonderopolis today! :-)

  3. If you can see sound, how do you see it? Is hearing sound like sound waves? Exactly what does sound look like? I would really like to know, because me and my friends did an experiment where we looked closely to the radio to see if we got to see anything, and we didn’t! :D Please write back. I would love to know the answer.

    • Those are all great questions, Amber! High-frequency sound waves (the kind of used in ultrasound technology) cannot be heard by human ears. Those sound waves do, however, create “echoes” when they bounce off objects. Ultrasound machines interpret those echoes into an image that we can see! So, we’re not really “seeing” the actual sound, but instead an image that the ultrasound machine creates from the sound wave echoes! :-)

    • We have really enjoyed hearing from our Wonder Friends today about how much they enjoyed the video for this Wonder! Thanks for being one of those AWESOME Wonder Friends, Luis! :-)

    • Thank you for leaving us this enthusiastic comment today, Mac! Ultrasound machines are pretty sweet, we agree! They help make a picture of the sound wave “echoes” that bounce off objects so we can “see” what the inside of things (like the human body) look like! :-)

    • Hi, Sammi! Sound waves create “echoes” when they bounce off objects. Special machines, called “ultrasound machines,” translate those echoes into an image that we can see on a computer screen or a printout! That’s how we “see” sound! :-)

    • WONDERful, Trisley! We know you can’t wait to get those first pictures of your new niece or nephew. Congratulations, Wonder Friend! :-)

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Have you ever wondered…

  • Can you see sound?
  • How does an ultrasound machine work?
  • What are ultrasounds used for?

Wonder Gallery

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Try It Out

Isn’t cool how we can use sounds to see? Explore these concepts in depth with a friend or family member when you check out one or more of the following activities:

  • Do you know what an echo is? You’ve probably heard your voice bounce back to you many times in the past. To refresh your memory, find a place where you can sing out loud and hear the echoes. A smaller, enclosed room, such as a bathroom, often works well. Maybe you can even jump in the shower and sing out a song! Isn’t it amazing to think that the echoes you hear can be measured and used to create images of things inside the body?
  • Ready to see with the help of sound? No, we’re not talking about ultrasounds, which humans can’t hear. It’s time to play a traditional kids’ game that helps you “see” around you with the help of your ears! If you haven’t guessed it already, the game we’re talking about is Marco Polo. So get a small group of friends or family members together and get ready to play. Marco Polo is similar to a simple game of “tag” and is often played in a pool where you won’t trip and fall. In this version, to make things more complicated, the person who is “it” is blindfolded. You can use an old t-shirt or a bandana as a blindfold. The other players who are not “it” can hide anywhere they want — even out in the open since the person who is “it” can’t see them. As the player who is “it” begins to search, he or she is allowed to shout “Marco.” The other players must echo these shouts with their own shouts of “Polo!” Using the ears, the person who is “it” will attempt to locate the others by following the sounds of their voices. When a person is found, he or she becomes “it” and must be blindfolded. Then the game restarts. Have fun! As you play, think about how your ears can help you “see” even when you’re blindfolded.
  • Up for a challenge? With the help of a friend or family member and a few simple supplies, can you map an imaginary ocean floor? Just jump online to check out As the Call, So the Echo for directions to complete this fun experiment that teaches you how to make a depth graph using the principles of echolocation.

Still Wondering

Explore National Geographic Xpeditions’ Soundscape: A Sense of Sound student activity to learn about the ways in which sound contributes to a sense of place.

Test Your Knowledge

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