Research

MRI contrast agents based on metal-oxo clusters encapsulated in polymer nanocarriers

Over the past 15+ years, we have developed a novel platform for nanoparticle contrast agents in which metal-oxo clusters are encapsuled in polymer nanoparticle carriers. We started with the well-known cluster Mn12, which we encapsulated into polystyrene nanobeads with diameters on the order of 60~100 nm. By exchanging the cluster ligand with 4-vinylbenzoate, we are able to copolymerize the cluster with the styrene, locking the cluster into the polymer structure and preventing leaching. More recently we have expanded our work to a number of other clusters, including Mn8Fe4O12(VBA)16(H2O)4, also copolymerized into polystyrene, and Mn3(O2CCH3)₆(Bpy)2, encapsulated in polyacrylamide.

Mechanisms of magnetic relaxivity in metal-oxo clusters

The mechanisms for the enhancement of the relaxivities from metal-oxo clusters is complex, with contributions from both cluster size and water exchange rates. Using O-17 NMR, we recently published work showing that the water exchange rates in two different systems, Mn12 copolymerized with styrene, and Mn3bpy encapsulated in polyacrylamide characterization of the, showed similar values for both materials.

T1-T2 image fusion

Some of our contrast agents show high relaxivities for both T1 and T2 relaxation, and so are excellent candidates for use as dual-mode contrast agents. We are currently working on developing image fusion algorithms to most effectively combine T1 and T2 images. Our image fusion algorithms are based on gradient fusion methods to identify regions with increasing signal due to T1 enhancement and negative gradients from T2 enhancement.

Chemical exchange saturation transfer (CEST) imaging

CEST imaging enables MR imaging of chemical species other than water. By exciting species that can rapidly exchange hydrogen atoms with the surrounding water bath, we can infer their concentrations from the saturation of the water signal.

¹⁹F MRI

We are currently imaging exogenous ¹⁹F delivered systemically in biological matter. The major advantage is that ¹⁹F is not typically found in biological tissue nor air. This equates to zero background signal, where the only noise in the image would equate to random thermal electrical noise. Today there are several methods that we are employing to enhance the signal to noise in these images through hardware signal enhancement and postprocessing noise elimination.