Echogenicity of gas-containing liposomes without (A) or with (B) calcein encapsulation and non-gas containing liposomes (C). Liposome composition: DPPC:DOPC:CH 35:35:30. Mean +/− SD,. Liposomes were imaged by 20 MHz intravascular catheter. A, liposomes prepared with air pressure at 9 atm in the absence of calcein. This MGSV for this image is 124+/−10. B, liposomes prepared so as to encapsulate both gas and calcein. The MGSV for this image is 118+/−12, C, liposomes preparaed by degassing under vacuum. The MGSV for this image is 12+/−3, for all images, n=4.