Search

The ability to enhance specific molecular markers of pathology with ultrasound has been previously demonstrated by our group employing a nanoparticle contrast agent [Lanza et al., Invest. Radiol. 35, 227234 (2000); Ultrasound Med. Biol. 23, 863870 (1997)]. One of the advantages of this agent is very low echogenicity in the blood pool that allows increased contrast between the blood pool and the bound, site-targeted agent. We measured acoustic backscatter and attenuation coefficient as a function of the contrast agent concentration, ambient pressure, peak acoustic pressure, and as an effect of duty cycle and wave form shape. Measurements were performed while the nanoparticles were suspended in either whole porcine blood or plasma. The nanoparticles were only detectable when insonified within plasma devoid of red blood cells and were shown to exhibit backscatter levels more than 30 dB below the backscatter from whole blood. Attenuation of nanoparticles in whole porcine blood was not measurably different from that of whole blood alone over a range of concentrations up to eight times the maximum in vivo dose. The resulting data provide upper bounds on blood pool attenuation coefficient and backscatter and will be needed to more precisely define levels of molecular contrast enhancement that may be obtained in vivo. 2005 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Polymer-shelled microbubbles are applied as ultrasound contrast agents. To investigate the effect of the polymer on microbubble preparation and acoustic properties, polylactides with systematic variations in molecular weight, crystallinity, and end-group hydrophobicity were used. Polymer-shelled cyclodecane filled capsules were prepared by emulsification, and the cyclodecane was removed by lyophilization to obtain hollow capsules. Complete removal of cyclodecane from the microcapsules was only achieved for short chain (about Mw6000) crystalline polymers. The pressure threshold for acoustic destruction of the microbubbles was found to increase with molecular weight. Noncrystalline polymers showed a higher threshold for destruction than crystalline polymers. Hydrophobically modified short chain crystalline polymers showed the steepest increase in acoustic destruction after the threshold as a function of the applied pressure, which is a favorable characteristic for ultrasound mediated drug delivery. Microcapsules made with such polymers had an inhomogeneous surface including pores through which cyclodecane was lyophilized efficiently. [ABSTRACT FROM AUTHOR]