Ultrasound contrast agents (USCA) are used for improving diagnostic accuracy on ultrasound imaging. USCA have also been used as cavitation nuclei for therapeutic procedures such as sonothrombolysis useful for treating stroke and heart attack. At the current time, however, the main use of USCA is for diagnosis.
A prior art ultrasound contrast agent is sold in commerce under the trademark DEFINITY. DEFINITY is a phospholipid-based ultrasound contrast agent comprising dipalmitoylphosphatidylcholine (“DPPC”), dipalmitoylphosphatidylethanolamine-PEG(5,000) (“DPPE-PEG5,000”), and dipalmitoylphosphatidic acid (“DPPA”).
DEFINITY has a shelf-life of two-years at 4-8° C. Hydrolysis of the lipids is primarily responsible for degradation of the product. Clinical use of DEFINITY is known to cause back pain as a side-effect. The prescribing information for DEFINITY expressly discloses that back pain occurs in about 1.2% of patients. When such back pain does occur, that side effect can be very unpleasant for the patient and last up to 30 minutes or one hour.