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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From Acusphere Inc
AI-700 (trade name Imagify™) is an US contrast agent, usable for myocardial perfusion undergoing regulatory FDA approval. The synthetic polymers used in AI-700 (perflubutane polymer microspheres) do not break during the ultrasound imaging procedure. The used perfluorocarbon filling gas is less soluble in water and therefore has the propensity to stay inside the contrast agent particles. As a result, a higher concentration of gas is delivered to the myocardium over a longer period of time, thereby enabling AI-700 to target the broader application of myocardial perfusion assessment.
Imagify is a dry powder consisting of small, porous microparticles filled with perfluoropropane. These microparticles are made of a synthetic biodegradable polymer, called poly (D, L-lactide co-glycolide), or PLGA, that has been used in other drug delivery systems approved by the FDA.
The composition and structure of the phospholipid containing microparticles and the properties of the perfluorocarbon gas slow the rate at which the gas dissolves and prevent the microparticles from being quickly broken down. The powder is to suspend in sterile water and injected by a single intravenous injection prior to ultrasound imaging.

In 2009, Acusphere Inc received feedback from the Food and Drug Administration (FDA) to their New Drug Application (NDA) stating that another clinical trial would be required for U.S. approval, this one demonstrating that Imagify with ultrasound is superior to ultrasound without Imagify.
In June 2004, Acusphere entered into a Collaboration, License and Supply Agreement with Nycomed Danmark APS for the European development and marketing rights to Acusphere's lead product candidate AI-700.
Acusphere's focus will be on preparing the Marketing Authorization Application (MAA) for filing in Q4 2010, building upon the work that the previous partner, Nycomed, had done, in concert with the NDA.


In 2008 the FDA panel rejected the regulatory application for AI-700 (Imagify™) because of safety concerns.

From Bracco Research SA, Geneva, Switzerland,
BR14 is a new experimental ultrasound contrast agent, consisting of bubbles containing a high molecular weight filling gas enclosed by a flexible phospholipid monolayer shell a few nanometers thick.
This agent shows significant non-linear scattering and agent modification even at low insonation pressures, the detection pulses used did not destroy the contrast bubbles. The results obtained with HPD before the release burst show that the BR14 bubbles are efficient scatterers that can be modified and, thus, detected by low power insonation.

By Byk-Gulden (now Altana);
The transpulmonary echo contrast agent under development, BY 963, promises to be an excellent ultrasound contrast agent for the noninvasive assessment of left ventricular function. Intravenous administration of BY 963 phospholipid microbubbles improves the reproducibility of e.g. quantitative analysis.

(CCI) A major limitation of the use of ultrasound contrast agents is the problem that signals from the microbubbles are mixed with those from tissue, so that the distribution of the microbubbles is not optimally displayed either in Doppler or gray scale.
Coherent contrast imaging is a high frame rate implementation of inverting the phase of alternate sound pulses and summing the resulting echoes. The symmetrical signals from linear reflectors are cancelled leaving those from non-linear scatterers, with the advantage that the cancellation is performed without the need to transmit two pulses per image line so that bubble destruction is minimized. Coherent contrast imaging yields best results in the vascular phase of phospholipid microbubbles (such as Definity and SonoVue).

See also Coherence.