Abstract
We developed a new sodium magnetic resonance fingerprinting ((23)Na MRF) method for the simultaneous mapping of T1, T2,long*, T2,short* and sodium density with built-in ΔB1+ (radiofrequency transmission inhomogeneities) and Δf0 corrections (frequency offsets). We based our (23)Na MRF implementation on a 3D FLORET sequence with 23 radiofrequency pulses. To capture the complex spin 3/2 dynamics of the (23)Na nucleus, the fingerprint dictionary was simulated using the irreducible spherical tensor operators formalism. The dictionary contained 831,512 entries covering a wide range of T1, T2,long*, T2,short*, ΔB1+ factor and Δf0 parameters. Fingerprint matching was performed using the Pearson correlation and the resulting relaxation maps were weighted with a subset of the highest correlation coefficients corresponding to signal matches for each voxel. Our (23)Na MRF method was compared against reference methods in a 7-compartment phantom, and applied in brain in five healthy volunteers at 7 T. In phantoms, (23)Na MRF produced values comparable to those obtained with reference methods. Average sodium relaxation time values in cerebrospinal fluid, gray matter and white matter across five healthy volunteers were in good agreement with values previously reported in the literature.