SIMON FRASER / SCIENCE PHOTO LIBRARY SIMON FRASER / SCIENCE PHOTO LIBRARY
Inflamed lymph node. Three-dimensional power Doppler ultrasound scan of blood vessels (orange) in an inflamed lymph node in the neck of a 40- year-old woman. Inflammation of a lymph node (lymphadenitis) is usually a response to an infection. The increased lymph node activity produces more of the immune system's lymphocyte cells that fight infection. Doppler ultrasound scanning detects moving fluids, such as blood, by the frequency change they cause when reflecting high-frequency sound waves. Power Doppler scans use colour to show the moving fluid, but do not show the direction of the flow.
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