Ultra-fast inner volume excitations with parallel transmission at 7 Tesla using fully optimized B0-robust k-space trajectories
Mathias Davids 1,2 , Bastien Gurin 2 , Lawrence L. Wald 2,3 , and Lothar R. Schad 1
Computer Assisted Clinical Medicine, Medical
Faculty Mannheim, Heidelberg University, Mannheim, BW,
Center for Biomedical Imaging, Dept. of Radiology,
Massachusetts General Hospital, Charlestown, MA, United
Division of Health Sciences Technology, Cambridge, MA,
Three-dimensional spatially selective excitations remain
difficult due to limitations of the pulse duration and
off-resonance induced distortions, especially at
high-field strengths. It is shown that the shape
optimization of k-space trajectory increases the
achieved flip angle accuracy substantially while
maintaining acceptable pulse durations (less than 8 ms).
In particular, the incorporation of off-resonance
robustness constraints within the optimization creates
trajectories with an optimal tradeoff between pulse
duration, excitation fidelity, and off-resonance
robustness. The impact is evaluated based on simulations
as well as preliminary experimental data acquired using
an 8-channel parallel transmit system at 7 Tesla.
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