Advances in Applications of Metal Oxide Nanomaterials as Imaging Contrast Agents

Abstract

Medical diagnosis relies on imaging modalities to reveal abnormalities in organs or existence of tumorous lesion. Application of contrast agents alongside imaging techniques is essential in order to obtain high contrast images with distinguishable features. Contrast agents delivered and accumulated in target sites can enhance local signal generation and solve the inherent lack of contrast in imaging techniques. As such, various contrast agents are developed for modalities like computed tomography (CT), magnetic resonance imaging (MRI), and photoacoustic imaging (PAI). For many of these techniques, metal‐based agents possess the desired properties for signal and contrast enhancement. Metal oxide nanomaterials present a simple platform for metal‐based contrast agents with tunable structure, magnetic and optical properties, surface chemistry, and pharmacokinetics. These can be controlled through synthesis, redox reactions, and surface modification to produce desirable nanoparticles. In this review, recent advances in the development of metal oxide imaging agents are highlighted. Various metal oxide species are discussed, including iron oxides, gadolinium oxides, manganese oxides, tungsten oxides and bronzes, molybdenum oxides, and other oxides of titanium, tantalum, etc. Imaging capability and performance of these metal oxides are presented, and novel functionalization strategies are presented. Finally, recommendations for future research in this area are proposed.