Liposomes coloaded with iopamidol/lipiodol as a res-targeted contrast agent for computed tomography imaging

Purpose: The need for computed tomography (CT) of reticuloendothelial system (RES)-rich organs such as the liver is increasing, particularly in patients with suspected hepatic metastasis. CT images of the liver have been improved by encapsulating currently used, water-soluble iodine contrast agent in liposomes. The present study was performed to investigate a possibility to overcome the limitations of entrapped iodine in liposomes by preparing liposomes co-loaded with iopamidol, a water-soluble iodinated compound, and lipiodol, an iodized oil. Methods: Iopamidol and lipiodol were simultaneously loaded in liposomes by modified reverse-phase evaporation method. The entrapped iodine concentration, mean particle size and polydispersity index of resulting liposomes were evaluated. Following intravenous injection of these liposomes into rats, CT scanning was performed. Results: Simultaneous loading of iopamidol and lipiodol into liposomes resulted in entrapped iodine concentrations as high as 49.2 iodine mg/ml. The mean particle size was 280 nm, and the mean polydispersity index was 0.230. CT scanning with these iopamidol/lipiodol (I/L) liposomes into rats resulted in more pronounced and more persistent increases in RES-rich organs, liver and spleen, compared with free liposomes or liposomes loaded with iopamidol alone. Conclusions: These findings indicate that I/L liposomes have the potential to allow thorough CT examination of RES-rich organs.