Visualization of the diffusion of metal ions and organic molecules by magnetic resonance imaging of water

Null point magnetic resonance imaging (MRI) of water has been used to map the location in space and time of small concentrations of paramagnetic metals and nitroxide free radicals. Any paramagnetic species whose effective magnetisation is dependent on the chemical potential of the surrounding medium, can be used either as a “molecular amplifier” or as an “MRI-active indicator”—This approach has been used to study the diffusion of acid (via (Cu EDTA)), and of oxidising and reducing agents (via Fe(II), Fe(III), ions) in a range of hydrogels and in hen-knee cartilage.