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Local excitation universal parallel transmit pulses at 9.4T
Author(s) -
Geldschläger Ole,
Bosch Dario,
Glaser Steffen,
Henning Anke
Publication year - 2021
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.28905
Subject(s) - excitation , pulse (music) , flip angle , excited state , signal (programming language) , pulse sequence , computer science , in vivo , physics , optics , nuclear magnetic resonance , magnetic resonance imaging , atomic physics , medicine , microbiology and biotechnology , quantum mechanics , detector , biology , radiology , programming language
Purpose To demonstrate that the concept of “universal pTx pulses” is applicable to local excitation applications. Methods A database of B 0 / B 1 + maps from eight different subjects was acquired at 9.4T. Based on these maps, universal pulses that aim at local excitation of the visual cortex area in the human brain (with a flip angle of 90° or 7°) were calculated. The remaining brain regions should not experience any excitation. The pulses were designed with an extension of the “spatial domain method.” A 2D and a 3D target excitation pattern were tested, respectively. The pulse performance was examined on non‐database subjects by Bloch simulations and in vivo at 9.4T using a GRE anatomical MRI and a presaturated TurboFLASH B 1 + mapping sequence. Results The calculated universal pulses show excellent performance in simulations and in vivo on subjects that were not contained in the design database. The visual cortex region is excited, while the desired non‐excitation areas produce the only minimal signal. In simulations, the pulses with 3D target pattern show a lack of excitation uniformity in the visual cortex region; however, in vivo, this inhomogeneity can be deemed acceptable. A reduced field of view application of the universal pulse design concept was performed successfully. Conclusions The proposed design approach creates universal local excitation pulses for a flip angle of 7° and 90°, respectively. Providing universal pTx pulses for local excitation applications prospectively abandons the need for time‐consuming subject‐specific B 0 / B 1 + mapping and pTx‐pulse calculation during the scan session.