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Abstract #0372

Improved Bloch-Siegert Based B1 Mapping by Reducing Off-Resonance Shift

Qi Duan1, Peter van Gelderen1, Jeff H. Duyn1

1Advanced MRI section, LFMI, NINDS, National Institutes of Health, Bethesda, MD, United States

This abstract investigates fast simultaneous B0/B1+ mapping by Bloch-Siegert shift via lowering the off-resonance frequency of this pulse, as theoretical analysis indicated that the sensitivity of Bloch-Siegert based B1+ mapping can be substantially improved when irradiating closer to resonance. Using optimized irradiation pulse shape and gradient crushers to minimize direct excitation effects, in vivo experiments on human brain at 7T confirmed the improved sensitivity available with this approach operating with peak B1+ much larger than the frequency offset. This improved sensitivity translated into an 80% reduction in B1+ estimation errors, without increasing tissue heating.