Evaluation of liposomal contrast agents for liver CT in healthy rabbits

RATIONALE AND OBJECTIVES. To evaluate the efficiency of two new liposomal c ontrast agents aimed at the reticuloendothelial system for liver CT in comp arison to an extracellular contrast agent. METHODS. Two liposomal contrast agents (BR2 and BR21, respectively), contai ning free as well as encapsulated iomeprol at different concentrations, and commercially available free extracellular iomeprol were studied. In 60 exp eriments, the three contrast agents were tested at five different doses in rabbits. Intravenous injection was followed by dynamic CT studies over a pe riod of 0 to 120 minutes (0 to 6 hours in 3 animals). A quantitative analys is of the enhancement in aorta and liver was performed. RESULTS. In healthy rabbits, the two liposomal contrast agents induced a si gnificantly higher and more persistent increase in liver density at doses o f greater than or equal to 1.5 mL/kg compared with the extracellular agent. The density enhancement induced by the two liposomal agents was dose-depen dent and reached a maximum of +102 Hounsfield units (HU), compared with +87 HU for the extracellular contrast agent, at 2.0 mL/kg, without any appreci able increases at higher dosages, An adequate liver enhancement of at least +40 HU persisted for up to 90 minutes after injection of the liposomal con trast agents, compared with <5 minutes after the extracellular agent. BR2 t ended to provide a higher and more persistent enhancement than BR21. CONCLUSIONS. Liposomal contrast agents induce a more pronounced and much mo re persistent increase in liver density than conventional extracellular age nts. Liposomes thus have the potential for optimizing CT examinations of th e liver by providing a larger imaging window.