Designing a 3T functional sodium MRI (fNaI) experiment with visual stimuli

Motivation: Conventional fMRI techniques measure the haemodynamic response to brain function, suffering from indirectness and physiological confounders; a more direct MR measurement of neuronal activity is needed. Goal(s): To investigate whether functional sodium MRI (fNaI) can measure brain function with visual stimulation at 3T, and to inform future experiments. Approach: 5 subjects underwent fNaI with a checkerboard reversal, utilising a Seiffert spiral sequence, acquiring one volume in 23s. Results: Signal changes were reported at p<0.005, with diverse clustering both at group and subject-level. The experiment was SNR limited, and we recommend state-of-the-art hardware, as well as randomised task design, for future successful fNaI studies. Impact: Functional sodium MRI (fNaI) promises a more direct measurement of neuronal activity. Clusters of signal changes with visual stimuli are reported at a relaxed statistical threshold. We suggest fNaI would benefit greatly from higher SNR at ultrahigh field strengths.