JOHN MCLEAN / SCIENCE PHOTO LIBRARY JOHN MCLEAN / SCIENCE PHOTO LIBRARY
Ultrasound scanner. This machine uses sound waves to build up internal images of the body. A transducer is held against the skin over the area being studied. It emits high-frequency sound waves that are reflected by internal structures. The transducer picks up these reflections and builds them up into an image of the structure beneath it. It can build up either a 2-D (flat) or a 3-D (solid) image. This machine can also perform doppler ultrasound, which allows the study of blood flow. This uses the doppler effect: sound reflected from a moving object (such as blood) has its frequency shifted by an amount proportional to the rate of movement.
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