Simultaneous multi-parametric mapping of total sodium concentration, T1, T2 and ADC at 7 T using a multi-contrast unbalanced SSFP.

ABSTRACT

PURPOSE: Quantifying multiple NMR properties of sodium could be of benefit to assess changes in cellular viability in biological tissues. A proof of concept of Quantitative Imaging using Configuration States (QuICS) based on a SSFP sequence with multiple contrasts was implemented to extract simultaneously 3D maps of applied flip angle (FA), total sodium concentration, T1, T2, and Apparent Diffusion Coefficient (ADC). METHODS: A 3D Cartesian Gradient Recalled Echo (GRE) sequence was used to acquire 11 non-balanced SSFP contrasts at a 6 × 6 × 6 mm3 isotropic resolution with carefully-chosen gradient spoiling area, RF amplitude and phase cycling, with TR/TE = 20/3.2 ms and 25 averages, leading to a total acquisition time of 1 h 18 min. A least-squares fit between the measured and the analytical complex signals was performed to extract quantitative maps from a mono-exponential model. Multiple sodium phantoms with different compositions were studied to validate the ability of the method to measure sodium NMR properties in various conditions. RESULTS: Flip angle maps were retrieved. Relaxation times, ADC and sodium concentrations were estimated with controlled precision below 15%, and were in accordance with measurements from established methods and literature. CONCLUSION: The results illustrate the ability to retrieve sodium NMR properties maps, which is a first step toward the estimation of FA, T1, T2, concentration and ADC of 23Na for clinical research. With further optimization of the acquired QuICS contrasts, scan time could be reduced to be suitable with in vivo applications.