Sodium Relaxometry Using(23)Na Mr Fingerprinting: A Proof Of Concept

Purpose To evaluate the feasibility of(23)Na MR fingerprinting (MRF) for simultaneous quantification of T-1,T2l*,T2s*,T2*in addition to Delta B-0. Methods A framework for sodium relaxometry using MRF at 7T was developed, allowing simultaneous measurement of relaxation times and inhomogeneities in the static field. The technique distinguishes between bi- and monoexponential transverse relaxation and was validated in simulations with respect to the ground truth. In phantom measurements, a resolution of 2 x 2 x 12 mm(3)was achieved within 1 h acquisition time, and the resulting parameter maps were compared to results from reference methods. Relaxation times in five healthy volunteers were measured with a resolution of 4 x 4 x 12 mm(3). Results Phantom experiments revealed an agreement between the relaxation times obtained via(23)Na-MRF and the reference methods. In white matter, a longitudinal relaxation constant of T-1= 38.9 +/- 4.8 ms was found, while values ofT2l*= 29.2 +/- 4.9 ms andT2s*= 4.7 +/- 1.2 ms were found for the long and short component of the transverse relaxation. In cerebrospinal fluid, T(1)was 67.7 +/- 6.3 ms andT2*= 41.5 +/- 3.4 ms. Conclusion This work demonstrates the feasibility of(23)Na-MRF for relaxometry in sodium MRI in both phantom and in vivo studies. Simultaneous quantification of T-1,T2l*,T2s*,T2*and Delta B(0)was possible within a 1 h measurement time.