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Ultrasound Contrast Agents

  • Intro
Magnetic Resonance Imaging Contrast Agents Open this link in a new window
Radiology Contrast Agents Open this link in a new window
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.

• View the DATABASE results for 'Contrast Agent Particles' (6).Open this link in a new window.

 Further Reading:
  News & More:
Modeling and Characterization of Ultrasound Contrast AgentsOpen this link in a new window
   by home.online.no    

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.

• View the DATABASE results for 'Perfluorochemicals' (4).Open this link in a new window.

 Further Reading:
Science to Practice Which US Microbubble Contrast Agent Is Best for Gene Therapy?Open this link in a new window
   by radiology.rsna.org    
  News & More:
molecular imaging using ultrasoundOpen this link in a new window
   by bjr.birjournals.org    
The role of ultrasound in molecular imaging(.pdf)Open this link in a new window
2003   by bjr.birjournals.org    
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.

• View the DATABASE results for 'Acoustically Active Lipospheres' (4).Open this link in a new window.

 Further Reading:
A Method for Radiation-Force Localized DrugDelivery Using Gas-Filled Lipospheres(.pdf)Open this link in a new window
Wednesday, 7 July 2004   by www.ncbi.nlm.nih.gov    
  News & More:
Radiation-Force Assisted Targeting Facilitates Ultrasonic Molecular ImagingOpen this link in a new window
Sunday, 4 July 2004   by www.bme.ucdavis.edu    
Bio-effects of ultrasound contrast agents in daily clinical practice: fact or fiction?(.pdf)Open this link in a new window
Monday, 30 April 2007   by eurheartj.oxfordjournals.org    

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.

• View the DATABASE results for 'Phospholipid' (8).Open this link in a new window.

Ultrasonic Contrast Agents 

(UCA / USCA) Ultrasonic contrast agents, also called ultrasound contrast agents, are encapsulated bubbles on the order of 1?10 µm in diameter. These gas bubbles are injected into the blood stream in order to increase blood/ tissue contrast during an ultrasonogram. These microbubbles are filled with air or a gas with a lower solubility in blood than air, such as perfluorochemicals. The microbubble shell consists of albumin, phospholipid, or other material and encapsulates the gas core. Due to this construction, ultrasonic contrast agents are highly compressible, and have a high echogenicity.
See also Ultrasound Contrast Agent Safety.

• View the NEWS results for 'Ultrasonic Contrast Agents' (1).Open this link in a new window.

• View the DATABASE results for 'Ultrasonic Contrast Agents' (3).Open this link in a new window.

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 modifż 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.

• View the DATABASE results for 'Bolus Injection' (4).Open this link in a new window.

Bubble Destruction 

Bubble destruction describes the microbubble shell rupture by ultrasound pulses. The bubble destruction increases with increasing peak negative pressure and decreasing frequency. The mechanical index is an indicator for the effectiveness of microbubble destruction. Contrast enhanced ultrasound relies on bubble rupture to detect bubbles in small vessels.
See also Negative Bolus.

• View the DATABASE results for 'Bubble Destruction' (8).Open this link in a new window.

Negative Bolus 

A negative bolus is created after microbubble destruction at a specific location by the absence of bubbles.

• View the DATABASE results for 'Negative Bolus' (3).Open this link in a new window.

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.

• View the DATABASE results for 'Bubble Rupture' (5).Open this link in a new window.

  Historical Development top
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