The relatively simple science behind ultrasound

Whether it's seeing your cousin's sonogram on Facebook or watching a trained actor use it on "House" or "Grey's Anatomy", it's likely that you've had some sort of interaction with ultrasound technology.

You probably know at least that it can see inside you, mapping your tissues, bones, organs and other parts and displaying them on a monitor screen. As magical as it seems, ultrasound is a relatively simple medical technology that's been in use for more than 50 years.

Sonography facts and history

Medical historians tend to place the roots of ultrasound all the way back in 1877, thanks to a breakthrough in electrical science made by French physicist Pierre Curie, but it wasn't until the middle of the 20th century that sonography was used in clinical diagnoses.

Doctors and other clinicians have wanted to be able to see inside the body for hundreds of years, and X-ray technology made that possible as far back as 1895, but radiation can be dangerous to bodily systems and can't be used excessively.

Ultrasound makes it possible to take diagnostic pictures of living, working tissues without posing them any threat. In fact, sonography was practiced throughout the early 20th century as a procedure to promote wellness in cases of arthritis, tendinitis, stomach ulcers and many other ailments.

Diagnostic imaging, the main benefit of sonography and how it's most widely used today, came into use in the 1940s.

How ultrasound works

Also known as diagnostic sonography, ultrasound uses echoes of high frequency sound waves to make visual images of the inside of the body. The same sort of technique creates the sonar images used by submarines and allows bats, dolphins and whales to navigate by echolocation.

A probe device called a transducer is used to project the sound waves into the body. At each boundary between different types of tissue, some of the sound waves pass through and some are reflected back to the transducer and recorded.

The ultrasound machine then calculates the distance to the reflection using the time between sending the pulse and receiving the echo. An image is generated by the amount of sound reflected and the various distances it traveled before echoing. In order to produce a moving picture of the inside of the body, this process is repeated millions of times per second.

Ultrasound display details

There's one more important point about how sonography works. The sound waves won't travel properly through gases, including air, so an airtight seal has to be made between the transducer and the target of the ultrasound so the machine can create an useful image.

Luckily, the gel used in sonography serves perfectly well as an airtight seal. Once the gel is spread thoroughly, the transducer probe is moved on the skin until the target area appears on the screen.

While traditional ultrasound produces a two-dimensional image of the target, machines that display 3-D images have recently been developed. These modern ultrasound machines use the same sort of technology as their flat-image counterparts, but the computer unit is equipped with software that allows it to combine several 2-D pictures into a single 3-D image.

The relatively simple science of ultrasound has been making life easier for surgeons, obstetricians, internists and other medical personnel the world over.


How Does Ultrasound Work?

How Ultrasound Works," Craig Freudenrich, 2013

Ultrasound History," Beth W. Orenstein, December 1, 2008

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