Surfactant microbubbles and process for preparing and methods of using the same

An ultrasound contrast agent (UCA) comprising:

• an outer shell, and
• a gas core,
• wherein said gas core is filled with between 98% and 100% pure oxygen without a perfluorocarbon, and
• wherein said outer shell comprises:
• a first surfactant, and
• a second surfactant,
• wherein the first surfactant comprises d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS),
• wherein the UCA induces a statistically significant increase in oxygen concentration when in solution and insonated relative to in solution without insonation, and
• wherein the insonated UCA has a half-life under 5 MHz ultrasound of from about 5 minutes to about 20 minutes.