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.
Keywords: Magnetic resonance imaging, gadolinium(III)-based polymeric contrast agents, stimuli-responsive,
multi-mode imaging, theranostics, tumor imaging.
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