Evaluation of liposomal contrast agents for liver CT in healthy rabbits

RATIONALE AND OBJECTIVES. To evaluate the efficiency of two new liposomal contrast agents aimed at the reticuloendothelial system for liver CT in comparison to an extracellular contrast agent. METHODS. Two liposomal contrast agents (BR2 and BR21, respectively), containing free as well as encapsulated iomeprol at different concentrations, and commercially available free extracellular iomeprol were studied. In 60 experiments, the three contrast agents were tested at five different doses in rabbits. Intravenous injection was followed by dynamic CT studies over a period of 0 to 120 minutes (0 to 6 hours in 3 animals). A quantitative analysis of the enhancement in aorta and liver was performed. RESULTS. In healthy rabbits, the two liposomal contrast agents induced a significantly higher and more persistent increase in liver density at doses of 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-dependent 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 appreciable increases at higher dosages, An adequate liver enhancement of at least +40 HU persisted for up to 90 minutes after injection of the liposomal contrast agents, compared with <5 minutes after the extracellular agent. BR2 tended to provide a higher and more persistent enhancement than BR21. CONCLUSIONS. Liposomal contrast agents induce a more pronounced and much more persistent increase in liver density than conventional extracellular agents. Liposomes thus have the potential for optimizing CT examinations of the liver by providing a larger imaging window.