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Sodium MRI is a specialised magnetic resonance imaging technique that uses strong magnetic fields, magnetic field gradients, and radio waves to generate images of the distribution of sodium in the body, as opposed to more common forms of MRI that utilise protons present in water. Like the proton, sodium is naturally abundant in the body, so can be imaged directly without the need for contrast agents or hyperpolarization. Furthermore, sodium ions play a role in important biological processes via their contribution to concentration and electrochemical gradients across cellular membranes, making it of interest as an imaging target in health and disease.
In contrast to conventional MRI of the proton, Sodium MRI is complicated by the low concentrations of Na nuclei relative to concentration of H2O molecules in biological tissues and the lower gyromagnetic ratio of the Na nucleus as compared to a H nucleus,. This causes low NMR sensitivity and the requirement for a stronger magnetic field for equivalent spatial resolution. The quadrupolar Na nucleus also has a faster transverse relaxation rates and multiple quantum coherences as compared to the H nucleus, requiring specialized and high performance MRI sequences to capture information before the contrast used to image the body is lost.