| | UltraSound - Technology Information Portal | Tuesday, 9 February 2010 |
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|  | Contrast Agent Particles | | | |
(CAP) Contrast agent particles are filled with gas and coated by a shell. The reflectivity of a particle increases with the diameter. The used particles are too large to cross the endothelium, so that there is no interstitial phase of enhancement. They are essentially markers for the blood pool and their distribution is similar to those of tagged red cells. In addition, any body cavity that can be accessed can be injected with vascular contrast.
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| | | Perfluorochemicals | | |
Perfluorochemicals are used as microbubble filling gases because of their low solubility in blood and high vapor pressure. Various types of perfluorochemical gases like perfluorocarbon, perfluorobutane, perfluoropropane, and perfluorohexane are used to substitute the air in microbubbles to improve the stability and plasma longevity of the agents.
Perfluorocarbons are liquids at room temperature but gas at body temperature. The large molecules of perfluorocarbons have slow diffusion and solubility which increase the enhancement time of the ultrasound contrast agent as compared to air.
See also Filling Gas, and PESDA.
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| | | Acoustically Active Lipospheres | | |
(AALs) Acoustically active lipospheres and ultrasound are under development to deliver bioactive molecules to the vascular endothelium. The AALs are similar to both ultrasound contrast agents and drug-delivering liposomes. They can carry bioactive substances using biologically inert shells and deliver those substances when disrupted by ultrasound.
The lipospheres consist of a small gas microbubble surrounded by a thick oil shell and are enclosed by an outermost lipid layer. The gas bubble contained in these vehicles makes them acoustically active, similar to ultrasound contrast agents. Acoustically active lipospheres can be nondestructively deflected using ultrasound radiation force, and fragmented with high intensity ultrasound pulses. Their lipid-oil complex can carry bioactive substances at high concentrations. An optimized sequence of ultrasound pulses can deflect the AALs toward a vessel wall then disrupt them, painting their contents across the vascular endothelium.
See also Filling Gas, and MRX 115.
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| | | Phospholipid | | |
Phospholipids are a major component of all biological membranes. When placed in water, phospholipids form a bilayer, where the hydrophobic tails line up against each other. This forms a membrane with hydrophilic heads on both sides. This membrane is partially permeable and very flexible.
Phospholipid containing microbubbles are in use as diagnostic ultrasound contrast agents. Phospholipids can be targeted to atheroma and other pathologic components to enhance atherosclerosis imaging. The majority of these echogenic liposomes range in diameter from 0.25 to 5.0 µm.
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| | | Ultrasonic Contrast Agents | | | | | | | |
| | | Bolus Injection | | |
A bolus is a rapid infusion of high dose contrast agent. Dynamic and accumulation phase imaging can be performed after bolus injection. Since the transit time of the bolus is only a short time, images with high frame rate show the wash in and wash out of the contrast material.
The injection rate and the total injected volume modifý the bolus peak profile. Substantial changes in the concentrations during signal acquisition induce artifacts. Furthermore, the hemodynamic parameters (cardiac output, blood pressure) influence the bolus profile. However, the characteristics of ultrasound contrast agents are favorable with a continuous perfusion.
See also Negative Bolus.
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| | | Bubble Destruction | | | | | | | |
| | | Negative Bolus | | | |
A negative bolus is created after microbubble destruction at a specific location by the absence of bubbles.
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| | | Bubble Rupture | | |
Ultrasound at the microbubble resonance frequency can cause bubble rupture at high acoustic power (mechanical index (MI) greater than 0.5). The result is a transient high-amplitude, broadband signal containing all frequencies, not only the harmonics. It will create a strong signal in B-mode or a short-lasting multicolored, mosaic-like effect in color Doppler sonography.
Several terms for this typical signal have been used, e.g. induced or stimulated acoustic emission, loss of correlation imaging and sono-scintigraphy.
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| | | | There are only two tragedies in life: one is not getting what one wants, and the other is getting it.----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- -----
- Oscar Wilde | |
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| | [last update: 2010-02-08 10:02:02] |
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