ABSTRACT
Liposomes are versatile tools for the solubilization and transport of various kinds of drug molecules, including imaging contrast agents. There is good evidence in the literature from several groups that radiolabeled vesicles are useful for imaging deep-seated tumors and sites of inflammation, not via direct targeting but through macrophage loading. For nuclear medicine imaging, target concentrations in the subnanomolar range suffice for detection. For magnetic resonance (MR), a submillimolar concentration of paramagnetic label is required to induce changes in signal intensity. For computed tomography, an iodine concentration of approximately 10 mM is required in the parenchyma. As to MR, the current literature suggests that it is not possible to label a monoclonal with a sufficient number of paramagnetic centers to appreciably affect the target to nontarget signal ratio by MR, however, other approaches such as coupling paramagnetic cations to a polymeric ligand which is then attached to a monoclonal are worth investigating.
