Sodium Magnetic Resonance Imaging and its Bioscale of Tissue Sodium Concentration

Quantitative sodium magnetic resonance imaging (MRI) measures the central metabolic process of ion homeostasis that is essential for healthy tissue. The bioscale of tissue sodium concentration derived from sodium MRI can monitor regional disease progression and treatment responses in individual patients and can potentially be used to guide therapy. The nuclear properties of sodium demand specialized approaches for quantitative MRI including pulse sequences with short echo times and short duration RF pulses while minimizing total acquisition times for human applications. A comprehensive quantification scheme that corrects for imaging imperfections from B₀ and B₁ inhomogeneities and converts sodium MR images from an arbitrary signal intensity scale into a meaningful bioscale is described. The tissue sodium concentration thus measured can be modeled from the known intra- and extracellular sodium activities and the volume fraction of the extracellular space using a multicompartment model. Applications of quantitative sodium imaging are illustrated in the clinical settings of stroke and for monitoring tumor response to irradiation.

Keywords: sodium imaging; twisted projection imaging; quantitative imaging; tissue sodium concentration; bioscale