Relaxometry and quantification in simultaneously acquired single and triple quantum filtered sodium MRI.

Abstract

Sodium imaging delivers valuable information about in vivo metabolism and pathophysiology. Image quantification can benefit the diagnosis and characterization of existing pathologies and the clinical course of a disease. An enhanced SISTINA sequence is proposed for sodium imaging and for the estimation of sodium tissue parameters for a 2-compartment model of the brain, such as relaxation times in intracellular space and tissue, intracellular volume fraction, and intracellular molar fraction. The aim of the research is to demonstrate how a 2-compartment model can be parameterized to sufficiently describe tissue sodium concentrations and dynamics by performing relaxometry with such a sequence. Multiple quantum filtered sodium signals were detected using an enhanced SISTINA sequence (consisting of 3 consecutive RF pulses) by placing a readout train between the first and second RF pulse, and 1 after the third pulse. Semiautomatic segmentation using singular value decomposition and manual segmentation was applied to the images. Analysis was performed on 40 healthy volunteers in a 4T scanner, yielding bi-exponential relaxation times of brain tissue, intracellular sodium molar and volume fraction, intracellular sodium concentration, as well as sodium tissue concentration in the scope of a considered model. Two models with either purely mono-exponential or bi-exponential relaxing extracellular sodium were used with and without a potential contribution of triple quantum-filtered signal from extracellular space. An estimation of relaxation properties and concentrations limited to the assumed model is possible from a single sequence. The achieved results agree well with those reported in literature.