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microbubble

[mahy-kroh-buhb-uh l]
noun
  1. a microscopic, gas-filled bubble, used especially in medicine to image blood flow, dissolve blood clots, etc.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for microbubbles

microbubbles

pl n
  1. med a contrast medium used with ultrasound, consisting of tiny bubbles of gas introduced into the vascular system or Fallopian tubes to enhance the images obtained
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012