| UltraSound - Technology Information Portal||Wednesday, 17 January 2018 |
|Filling Gas|| |
The gas in microbubbles is highly compressible and, when subjected to the alternating compression and refraction pressures that constitute an ultrasound pulse, microbubbles oscillate at their natural frequency at which they resonate most strongly. This is determined by their size but is also influenced by the composition of the filling gas.|
Air, sulfur hexafluoride, nitrogen, and perfluorochemicals are used as filling gases. Most newer ultrasound contrast agents use perfluorochemicals because of their low solubility in blood and high vapor pressure. By substituting different types of perfluorocarbon gases for air, the stability and plasma longevity of the agents have been markedly improved, usually lasting more than five minutes.
• View the DATABASE results for 'Filling Gas' (9).
The persistence of microbubbles is depended of the shell stability and the density of the gas.|
This is defined by the equation:
(R x d)/(DIFS x constsat)
where R is the bubble radius, d the gas density, DIFS the gas
diffusivity and constsat the saturation constant.
Microbubbles are stabilized with thin coatings of substances such
as palmitic acid or by encapsulation in microspheres made with albumin, lipids, or polymers. Low-solubility low-diffusibility gases dramatically improve the persistence. Most recently developed ultrasound contrast agents combine these two approaches to prolong contrast enhancement.
Persistence is also a type of temporal smoothing used in both gray scale and color Doppler imaging. Successive frames are averaged as they are displayed to reduce the variations in the image between frames, hence lowering the temporal resolution of the image.
• View the DATABASE results for 'Persistence' (5).
|Induced Acoustic Emission|| |
(AE) Induced acoustic emission is an effect of ultrasound contrast agents, presenting the interaction between the agent and the incident ultrasound wave.|
Microbubbles break down in high-amplitude diagnostic ultrasound energy. The bubble rupture produces a transient pressure wave, which results in a characteristic mosaic pattern from tissues containing the agent. It is important to note that the color patterns of induced acoustic emission do not represent flow signals.
• View the DATABASE results for 'Induced Acoustic Emission' (3).
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