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by Craig Freudenrich, Ph.D.

Please copy/paste the following text to properly cite this How Stuff Works article:

Freudenrich, Ph.D., Craig. "How Ultrasound Works." 22 January 2001. HowStuffWorks.com. <http://health.howstuffworks.com/ultrasound.htm> 06 July 2008.

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Different Types of Ultrasound

The ultrasound that we have described so far presents a two dimensional image, or "slice," of a three dimensional object (fetus, organ). Two other types of ultrasound are currently in use, 3D ultrasound imaging and Doppler ultrasound.

3D Ultrasound Imaging
In the past two years, ultrasound machines capable of three-dimensional imaging have been developed. In these machines, several two-dimensional images are acquired by moving the probes across the body surface or rotating inserted probes. The two-dimensional scans are then combined by specialized computer software to form 3D images.

Photo courtesy Philips Research
3D ultrasound images

3D imaging allows you to get a better look at the organ being examined and is best used for:

Early detection of cancerous and benign tumors
- examining the prostate gland for early detection of tumors
- looking for masses in the colon and rectum
- detecting breast lesions for possible biopsies
Visualizing a fetus to assess its development, especially for observing abnormal development of the face and limbs
Visualizing blood flow in various organs or a fetus

Doppler Ultrasound
Doppler ultrasound is based upon the Doppler Effect. When the object reflecting the ultrasound waves is moving, it changes the frequency of the echoes, creating a higher frequency if it is moving toward the probe and a lower frequency if it is moving away from the probe. How much the frequency is changed depends upon how fast the object is moving. Doppler ultrasound measures the change in frequency of the echoes to calculate how fast an object is moving. Doppler ultrasound has been used mostly to measure the rate of blood flow through the heart and major arteries.

Photo courtesy Philips Research
Doppler ultrasound used to measure blood flow through the heart. The direction of blood flow is shown in different colors on the screen.

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