JOHN MCLEAN / SCIENCE PHOTO LIBRARY JOHN MCLEAN / SCIENCE PHOTO LIBRARY
Doppler ultrasound scan. Gynaecologist studying doppler ultrasound scans of a woman's ovary during an investigation into ovarian blood flow. A 3-D model of the ovary is seen in the lower right of the screen. Ultrasound uses sound waves to build up an internal image of the body. A transducer (not seen) held on the skin emits high-frequency sound waves and picks up their reflections off body structures. This allows a 2-D or 3-D image of the structures to be created. Doppler ultrasound measures blood flow using the doppler effect. Sound waves reflected by moving objects have their frequencies shifted by an amount related to the speed of movement.
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