New RES-Specific Contrast Agents for CT

Abstract

Several liver-specific contrast media have been developed for improved detection and characterization of liver tumors. Most of these agents were designed for magnetic resonance imaging (MRI) (1–5). However, up to now, computed tomography (CT) remains the primary imaging modality for most patients with suspected liver disease (6,7). Therefore, development of organ-specific contrast media for CT, that are both safe and efficacious, is of great clinical importance. One approach of liver targeting has been the encapsulation of a water-soluble iodinated contrast agent inside liposomes. Like other particulate agents, liposomal contrast media are taken up by the reticuloendothelial system (RES), which should give them an advantage over conventional extracellular contrast agents for liver imaging. Several studies have described liposomal encapsulation with several iodinated contrast agents, such as iopromide, iopromidol, iotrolan, diatrizoate, and others (8–13). Although some of these agents have been shown to be effective contrast media for liver imaging, results have been not entirely satisfactory, mostly because of safety reasons (high rates of adverse events). Therefore, further research is needed to develop a safe and efficacious liposomal contrast agent for CT imaging. In this study, we explored the enhancement efficacy of two new liposomal formulations, BR 23 and BR 24 (Bracco Research, Geneva, Switzerland), which contain iomeprol, a low viscous nonionic dimer, for CT imaging of liver and spleen in primates. These preparations contain both encapsulated and unencapsulated iomeprol. An additional aim of this study was to compare these two new agents to Imeron 300, which is already in clinical use.