Simultaneous 3D acquisition of H MRF and Na MRI.

Purpose: To develop a 3D MR technique to simultaneously acquire proton multiparametric maps (T , T , and proton density) and sodium density weighted images over the whole brain.

Methods: We implemented a 3D stack-of-stars MR pulse sequence which consists of interleaved proton ( H) and sodium ( Na) excitations, tailored slice encoding gradients that can encode the same slice for both nuclei, and simultaneous readout with different radial trajectories ( H, full-radial; Na, center-out radial). The receive chain of our 7T scanner was modified to enable simultaneous acquisition of H and Na signal. A heuristically optimized flip angle train was implemented for proton MR fingerprinting (MRF). The SNR and the accuracy of proton T and T were evaluated in phantoms. Finally, in vivo application of the method was demonstrated in five healthy subjects.

Results: The SNR for the simultaneous measurement was almost identical to that for the single-nucleus measurements (<2% change). The proton T and T maps remained similar to the results from a reference 2D MRF technique (normalized RMS error in T ≈ 4.2% and T ≈ 11.3%). Measurements in healthy subjects corroborated these results and demonstrated the feasibility of our method for in vivo application. The in vivo T values measured using our method were lower than the results measured by other conventional techniques.

Conclusions: With the 3D simultaneous implementation, we were able to acquire sodium and proton density weighted images in addition to proton T , T , and from H MRF that covers the whole brain volume within 21 min.