Advanced methods for $^{23}Na$-MRI of the brain: Preliminary results in multiple sclerosis (MS).

Sodium quantification in the brain is a subject of increasing interest because of its fundamental role in physiology and in the progression of some neurodegenerative diseases such as MS. MS is associated with anomalies in sodium levels because of blood-brain barrier dysfunction and demyelination. $^{23}Na$-MRI is mainly performed on scanners with $B_{0}$ of $7 {T}$ and above, because of the increase in SNR with $B_{0}$. Our aim is to make $^{23}Na$-MRI feasible on clinical scanners ({B_$0$=3 ${T}$), overcoming SNR limitations. Since sodium transverse relaxation is very fast, UTE (Ultra-short Echo Time) sequences are needed for the quantification of Total Sodium Concentration (TSC) that must be associated with suitable reconstruction algorithms. FLORET (Fermat Looped, ORthogonally Encoded Trajectories) is an innovative $k$-space trajectory suitable for UTE scanning. The sampling trajectory impacts SNR and blurring. We are currently investigating how to optimize the $k$-space sampling strategy to obtain TSC maps in healthy subjects. Once validated, this technique will be used to derive biomarkers to characterize disease progression in MS patients.