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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