In vivo sodium magnetic resonance imaging of the human brain using soft inversion recovery fluid attenuation

Sodium imaging with soft inversion recovery fluid attenuation, which may be advantageous for intracellular weighting, was demonstrated with cerebrospinal fluid (CSF) suppression in five healthy volunteers at 4.7 T. Long rectangular inversion pulses reduce the average power deposition in an inversion recovery sequence, allowing repetition time to be shortened and more averages acquired for a given scan length. Longer pulses also significantly reduce the depth of M. inversion in environments with rapid T-1 and T-2 relaxation (i.e., brain relative to CSF). Phantom experiments and simulation show a marked SNR increase when using a 10-ms, rather than a 1-ms, rectangular inversion pulse. Images were acquired in 11.1 min with a voxel size of 0.25 cm(3) and the SNR in CSF, which is typically similar to 3 times larger than in brain, was reduced to 23% of that in the brain tissue, which had an average SNR of 17.