Magnetoliposomes as Contrast Agents

Liposomes are entirely biocompatible and are recognized as promising microvehicles for therapeutics and diagnostics in vivo and host either polar drugs in their aqueous inner space or lipophilic drugs in the lipid bilayer, protecting the entrapped pharmaceuticals from potential inactivation by external factors and without eliciting unwanted side effects. Since the inception of targeting liposomes for in vivo applications, all major fields of diagnostic imaging—including scintigraphy, computed tomography, and magnetic resonance imaging (MRI)—have been explored for the use of liposome-based reporter molecules or contrast agents. Two essential prerequisites have to be fulfilled for liposome-based formulations in virtual imaging applications. For MRI purposes, the paramagnetic metal ion–chelate complex can be covalently linked to the phospholipids. An event that generally hampers the usefulness of liposomes for imaging applications encompasses the fact that liposomes can be seen as “oreign” entities within the body. They are quickly removed from the blood circulation by macrophage uptake, mainly in the liver and spleen and to a lesser extent by the bone marrow. A new type of liposome called “magnetoliposomes” was developed, in which the aqueous interior is completely occupied by a magnetic iron oxide core. The chapter demonstrates that magnetoliposomes have a strong effect on T2 relaxation, making these particles an ideal platform for further development as magnetic resonance (MR) contrast agents.