K Mn [Fe (CN) ] NPs with High T -Relaxivity Attributable to Water Coordination on the Mn(II) Center for Gastrointestinal Tract MR Imaging.

The lack of acid stability in the stomach and of temporal stability when moving through the gastrointestinal (GI) tract has made the development of oral magnetic resonance imaging (MRI) contrast agents based on the platform of Gd -complexes problematic.On the other hand, the negative contrast enhancement produced by the T -weighted magnetic metal oxide nanoparticles (NPs) often renders the image readout difficult. Biocompatible NPs of the manganese Prussian blue analog K Mn [Fe (CN) ] exhibit extremely high stability under the acidic conditions of the gastric juice. Additionally, the high r relaxivity, low toxicity, and high temporal stability of such NPs offer great potential for the development of a true T -weighted oral contrast agent for MRI of the entire GI tract.