Assessment of the biodistribution of an [(18) F]FDG-loaded perfluorocarbon double emulsion using dynamic micro-PET in rats.

Perfluorocarbon (PFC) double emulsions loaded with a water-soluble, therapeutic agent can be triggered by ultrasound in a process known as acoustic droplet vaporization. Elucidating the stability and biodistribution of these sonosensitive vehicles and encapsulated agents is critical in developing targeted drug delivery strategies using ultrasound. [(18) F]fluorodeoxyglucose (FDG) was encapsulated in a PFC double emulsion and the in vitro diffusion of FDG was assessed using a Franz diffusion cell. Using dynamic micro-positron emission tomography and direct tissue sampling, the biodistribution of FDG administered as a solution (i.e. non-emulsified) or as an emulsion was studied in Fisher 344 rats (n = 6) bearing subcutaneous 9L gliosarcoma. Standardized uptake values (SUVs) and area under the curve of the SUV (AUCSUV ) of FDG were calculated for various tissues. The FDG flux from the emulsion decreased by up to a factor of 6.9 compared with the FDG solution. FDG uptake, calculated from the AUCSUV , decreased by 36% and 44% for brain and tumor, respectively, when comparing FDG solution vs FDG emulsion (p < 0.01). Decreases in AUCSUV in highly metabolic tissues such as brain and tumor demonstrated retention of FDG within the double emulsion. No statistically significant differences in lung AUCSUV were observed, suggesting minimal accumulation of the emulsion in the pulmonary capillary bed. The liver AUCSUV increased by 356% for the FDG emulsion, thus indicating significant hepatic retention of the emulsion.