Microbubbles are bubbles smaller than one millimetre in diameter, but larger than one micrometre. They are used in medical diagnostics as a contrast agent for ultrasound imaging. The gas-filled, e.g. air or perfluorocarbon, microbubbles oscillate and vibrate when a sonic energy field is applied and may reflect ultrasound waves. This distinguishes the microbubbles from surrounding tissues. In practice, because gas bubbles in liquid lack stability and would therefore quickly dissolve, microbubbles must be encapsulated with a solid shell. The shell is made from either a lipid or a protein such as Optison microbubbles which consist of perfluoropropane gas encapsulated by a serum albumin shell.
Microbubbles may be used for drug delivery, biofilm removal, membrane cleaning/biofilm control and water/waste water treatment purposes. They are also produced by the movement of a ship’s hull through water, creating a bubble layer; this may interfere with the use of sonar because of the tendency of the layer to absorb or reflect sound waves.
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