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Abstract #3450

Improved flip-angle uniformity in 0.35-mm slices using asymmetric pTx spoke pulses

Chia-Yin Wu1, Jonathan R. Polimeni2,3,4, and Martijn A. Cloos5,6
1Imaging Centre of Excellence, University of Glasgow, Glasgow, United Kingdom, 2Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, 3Department of Radiology, Harvard Medical School, Boston, MA, United States, 4Harvard-MIT Program in Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, United States, 5Donders Institute for Brain Cognition and Behaviour, Radboud University, Nijmegen, Netherlands, 6Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, St Lucia, Australia

Synopsis

Keywords: RF Pulse Design & Fields, RF Pulse Design & Fields

Motivation: Parallel transmit allows efficient radiofrequency pulse designs that produce uniform excitations. However, for 2D acquisitions with thin slices, long sub-pulse durations are needed to satisfy gradient system limitations which increases sensitivity to off-resonance.

Goal(s): To improve flip-angle uniformity in thin slices using asymmetric pTx spoke pulses.

Approach: Symmetric and asymmetric pTx spoke pulses were designed with B0 correction. Bloch simulations were performed to evaluate excitation fidelity targeting 0.5-mm and 0.35-mm slice thickness.

Results: Tailored asymmetric pTx spokes can achieve uniform slice excitation particularly in regions where off-resonance effects are prominent when targeting thin imaging slices down to 0.35-mm thick.

Impact: Parallel transmit is well known for efficient radiofrequency pulse designs that produce uniform excitations. We show that asymmetric spokes can mitigate off-resonance effects and generate uniform excitation for 0.5-mm and 0.35-mm thick slices.

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