Macromolecular MRI contrast agents: Structures, properties and applications

Stable gadolinium chelates are widely used as the contrast agents (CAs) for magnetic resonance imaging (MRI). Conjugation of the chelates onto macromolecular carriers forms macromolecular CAs (mCAs). Compared with small molecule MRI CAs, mCAs have advantages of high relaxivity and prolonged retention in blood circulation. Variants of mCAs have been synthesized and tested using animal models, showing their great potential applications in angiography, cancer imaging, kidney imaging, liver imaging, lymphatic imaging, and noninvasive visualization of drug delivery. Herein, the state of the art of mCAs, including their structures, properties, and applications is reviewed and future directions for developing mCAs are suggested.