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Improved Bloch‐Siegert based B 1 mapping by reducing off‐resonance shift
Author(s) -
Duan Qi,
Gelderen Peter,
Duyn Jeff
Publication year - 2013
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.2920
Subject(s) - sensitivity (control systems) , pulse (music) , irradiation , resonance (particle physics) , excitation , nuclear magnetic resonance , field (mathematics) , materials science , bloch equations , physics , atomic physics , optics , mathematics , electronic engineering , nuclear physics , quantum mechanics , detector , pure mathematics , engineering
An MRI method based on the Bloch‐Siegert (BS) shift phenomenon was recently proposed as a fast and precise way to map a radio frequency (RF) transmit field ( B 1 + field). For MRI at high field, the mapping sensitivity of this approach was limited by tissue heating associated with a BS irradiation pulse. To mitigate this, we investigated the possibility of lowering the off‐resonance frequency of this pulse since theoretical analysis indicated that the sensitivity of Bloch‐Siegert based B 1 + mapping could 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 brains at 7 T confirmed improved sensitivity with this approach. Improved sensitivity translated into an 80% reduction in B 1 + estimation errors without increasing tissue heating. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.