Multipulse sodium magnetic resonance imaging for multicompartment quantification: Proof-of-concept

We present a feasibility study of sodium quantification in a multicompartment model of the brain using sodium (²³Na) magnetic resonance imaging. The proposed method is based on a multipulse sequence acquisition and simulation at 7 T, which allows to differentiate the ²³Na signals emanating from three compartments in human brain in vivo: intracellular (compartment 1), extracellular (compartment 2), and cerebrospinal fluid (compartment 3). The intracellular sodium concentration C ₁ and the volume fractions α ₁, α ₂, and α ₃ of all respective three brain compartments can be estimated. Simulations of the sodium spin 3/2 dynamics during a 15-pulse sequence were used to optimize the acquisition sequence by minimizing the correlation between the signal evolutions from the three compartments. The method was first tested on a three-compartment phantom as proof-of-concept. Average values of the ²³Na quantifications in four healthy volunteer brains were α ₁ = 0.54 ± 0.01, α ₂ = 0.23 ± 0.01, α ₃ = 1.03 ± 0.01, and C ₁ = 23 ± 3 mM, which are comparable to the expected physiological values [Formula: see text] ∼ 0.6, [Formula: see text] ∼ 0.2, [Formula: see text] ∼ 1, and [Formula: see text] ∼ 10-30 mM. The proposed method may allow a quantitative assessment of the metabolic role of sodium ions in cellular processes and their malfunctions in brain in vivo.