Gas fIIIed lipid bilayers as imaging contrast agents

Gas bubbles are highly efficient reflectors of sound and are therefore useful as contrast agents for diagnostic ultrasound. In general, in order to pass through the pulmonary circulation and provide contrast for the systemic circulation the gas bubbles must be of defined diameter and stabilized by a coating material. Our group has developed gas bubbles which are stabilized within lipid bilayers. These bubbles may be formed with stable size and gas content. In vivo studies in rabbit and porcine models show sustained ventricular enhancement, increased arterial doppler signal following intravenous injection and myocardial perfusion enhancement following injection into the aortic root of pigs. Preliminary toxicity studies suggest that the therapeutic index (LD50 dose divided by imaging dose) is greater than 400 to 1. For therapy, these agents may be used to increase the capture of ultrasonic energy for hyperthermia to augment local tissue heating. An exciting new class of agents based upon gas fIIIed lipid bilayers has been developed. Work is presently underway to take these agents into clinical trials.