Liposomes are submicron sized vesicles with a lipid bilayer encapsulating an aqueous phase inside. Due to their favorable properties like longer circulation time, lesser toxicity, and greater uptake, they are a prime candidate for drug delivery. Recently, they are being specially prepared so as to encapsulate air, making them good scatterers of ultrasound wave. These echogenic liposomes, therefore, can be used both for ultrasound contrast imaging and drug delivery. We will report in vitro attenuation and scattering measurement from echogenic liposomes loaded with carboxyfluorescein (used as a surrogate for small molecular weight drugs). The results will be compared with non-dye-loaded ones. Effects of dye loading and presence of bovine serum albumin (BSA) on size distribution, echogenicity, and release characteristics will also be discussed.

Micron sized encapsulated gas bubbles have been extensively studied as contrast enhancing agents for ultrasound imaging. This study will report on in vitro acoustic characterization of a novel poly-lactic acid (PLA) shelled contrast agent. PLA is a bio-degradable polymer approved by the FDA to be used in drug delivery applications. Thus, PLA shelled contrast bubbles have the potential of being developed as the next generation contrast agents. Both attenuation and scattering measurements will be reported. Attenuation measurements are obtained using three different transducers (central frequencies 2.25, 3.5, and 5 MHz). Pressure dependent scattered response is obtained for two different excitation frequencies of 2.25 and 3.5 MHz. Results indicate excellent scattering properties of the PLA shelled bubbles. The strongly non-linear nature of scattered response makes PLA bubbles a potential choice for harmonic and sub-harmonic contrast imaging applications.