Liposomes as Carriers of Iodolipid Radiocontrast Agents for CT Scanning of the Liver

We studied the potential of liposomes to deliver oil soluble radiocontrast agents to the liver and have developed a new preparation for CT liver scanning. The preparation consists of Ethiodol with a large amount of phospholipids. Nuclear magnetic resonance (NMR) spectroscopy was done for this lipid preparation, and the spectra show that the lipids are in the bilayer liposome configuration. Electron microscopy provides direct visualization of the liposomes. X-ray fluorescence measurements suggest that the Ethiodol is incorporated in the liposomes, and since no other participate configurations are observed, we conclude that the Ethiodol is contained within the hydrophobic region of the liposomes. We used a GE CTT-8800 scanner and a rabbit model to study the liver uptake of the iodine from the Ethiodol. The iodine uptake in the liver was rapid and significant, and an increase in HU number of more than 40 was observed within 20 minutes after i.v. injection of 50 mg I/kg of body weight. Significant image enhancement was obtained. The iodine from the Ethiodol remained in the liver for several hours. Studies in rabbits with hepatic implants of the VX2-carcinoma show that while normal liver concentrates, areas of tumor do not concentrate the Ethiodol liposomes. Tumors not visible on ordinary scans become visible after administration of this combination. The advantages of this liposomal mode of radiocontrast agent administration are small particle size, rapid uptake in the liver, long retention times, a large increase in HU number and low iodine dose.