Gadolinium(III)-based Polymeric Magnetic Resonance Imaging Agents for Tumor Imaging

Contrast agents (CAs) are widely used to improve the signal-noise ratio in the magnetic resonance imaging (MRI) examinations. The majority of MRI CAs used in clinic are gadolinium( III) (Gd(III)) chelates with low molecular weight. Compared with these small-molecule CAs, Gd(III)-based polymeric magnetic resonance imaging agents (i.e. macromolecular contrast agents, mCAs), prepared by conjugating small-molecule Gd(III) chelates onto macromolecules, possess high relaxivity and relative long blood circulation time, which are favorable for MRI examinations. In last decades, increasing attention was paid to the design of mCAs with various structures, and further evaluation of the MRI performance both in vitro and in vivo. Herein, we focus on the recent progress of mCAs, including structures, properties and applications. Meanwhile, this review also highlights the emerging MRI mCAs with smart response and multi-function: tumor microenvironment- stimulated MRI, multi-mode imaging and MRI-based theranostics.