UC San Diego

Introduction: The longer circulating time and larger particle count of perfluorocarbon (PFC) droplets make them more effective as targeted contrast agents compared to microbubbles. It has also been shown that conversion of PFC droplets to microbubbles improves ultrasound (US) sensitivity to emulsions by 10 orders of magnitude. PFC droplets, with their higher boiling point and smaller particle size are more desirable to prevent spontaneous aporization and maximum accumulation of emulsions. However, the high US energy required to induce phase conversion in these emulsions is not clinically feasible. We hypothesized that by increasing the temperature and using Iron-oxide nanoparticles(IONP) as nucleation sites within the more stable and submicron droplets, the US energy required to vaporize them may be lowered. Material and method: A sample of 60%w/v iron-oxide loaded PFC droplets with mean diameter of 200nm was manufactured and characterized. A phantom was designed to allow for the interaction between the US energy and droplets. A high intensity focused ultrasound system (HIFU) was used to generate US pressures and a heat exchanger pump was used to control the temperature while emulsions of PFHB and PFP with or without IONP were circulated through the chamber. A harmonic imaging system was also used to detect the generated microbubbles. Discussion and result: The effect of temperature and IONP on the vaporization rate and threshold of PFC emulsions were determined. It was shown that presence of IONP and higher temperature increase the rate and decreases the vaporization threshold of PFC emulsions