Generating contrast in hyperpolarized 13C MRI using ligand–receptor interactions

Abstract

We report the imaging of β-cyclodextrin–benzoic acid binding at 14T using hyperpolarized ¹³C magnetic resonance (MR). Benzoic acid was polarized using a dynamic nuclear polarization (DNP) approach and combined with β-cyclodextrin in aqueous solution. As anticipated, decreases in the spin–lattice relaxation constant (T₁) were observed with decreases in the ligand–receptor ratio. The calculated log K was approximately 1.7, similar to previously reported binding constants. Hyperpolarized [1-¹³C] benzoic acid was used to interrogate solutions of variable β-cyclodextrin concentrations, with the mixtures imaged at 14T using a 3D frequency-selective MR sequence. Differences in β-cyclodextrin concentration were easily visualized. These results suggest that hyperpolarized ¹³C MR could be used in vivo to determine the presence and density of receptors for a given ligand–receptor pair.