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Abstract #1456

Optimization of Amplitude-Modulated Pulses for Bloch-Siegert Based B 1 Mapping

Qi Duan 1 , Peter van Gelderen 1 , Souheil J. Inati 2 , and Jeff H. Duyn 1

1 AMRI, LFMI, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, United States, 2 FMRIF, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland, United States

This abstract investigates fast simultaneous B 0 /B 1 + 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 B 1 + much larger than the frequency offset. This improved sensitivity translated into an 80% reduction in B 1 + estimation errors, without increasing tissue heating.

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