From Mallinckrodt Inc
MP1950 is an experimental thin lipid-shelled ultrasound contrast agent with a decafluorobutane gas core. MP1950 has a monolayer lipid microbubble shell with a thickness in the order of a few nanometers.

MRX 115 is a liposome based microbubble formulation and has been demonstrated as effective for cardiac blood pool imaging, Doppler enhancement and potentially myocardial perfusion imaging.
MRX 115 is based upon the demand for a stable, robust blood pool ultrasound contrast agents, also called DMP 115 or Aerosomes™ (ImaRx LLC) and now Definity®.

A microbubble shell, designed to reduce diffusion into the blood, can be stiff (e.g., denatured albumin) or more flexible (phospholipid), varying in thickness from 10-200 nm.
The shell stabilizes against dissolution and coalescence with additional materials at the gas-liquid interface. This material can be an elastic solid shell that enhances stability by supporting a strain to counter the effect of surface tension. Also a surfactant, or a combination of two or more, improves the stability by a high reduction of the surface tension at the interface. Current ultrasound contrast agents are micron-sized bubbles with a stabilizing shell.

Microbubbles filled with air or inert gases are used as contrast agents in ultrasound imaging. Compression and rarefaction created by an ultrasound wave insonating a gas-filled microbubble along with the mechanical index of the ultrasonic beam lead to volume pulsations of the bubbles, and it is this change that results in the signal enhancement.
Microbubbles have diameters from 1 μm to 10 μm and a thin flexible or rigid shell composed of albumin, lipid, or polymer confining a gas such as nitrogen, or a perfluorocarbon. These microbubbles can cross the pulmonary capillaries and have a serum half-life of a few minutes. Microbubbles in the 1-10 μm range have their resonance at the frequencies used in diagnostic ultrasound (1−15MHz). Smaller bubbles resonate at higher frequencies. Caused by this coincidence, they are such effective reflectors.
The intrinsic compressibility of microbubbles is approximately 17,000 times more than water, and they are very strong scatterers of ultrasound. Under acoustic pressure the vibrating bubble radius may have a conventional linear response or a harmonic non-linear response. Microbubbles usually increase the Doppler signal amplitude by up to 30 dB.

Molecular Biosystems, Inc. (MBI), founded in 1980, is a biomedical company developing a range of contrast agents for use with diagnostic ultrasound, magnetic resonance imaging (MRI), and computed tomography (CT).
Alliance Pharmaceutical Corp. acquires Molecular Biosystems in Nov. 2000.