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Abstract #1015

B0-robust slice-selective excitations for ultra-high field with flip-angle mitigation using parallel transmission

Mathias Davids1,2, Bastien Guérin2,3, Lawrence L Wald2,3,4, and Lothar R Schad1

1Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany, 2A. A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 3Harvard Medical School, Boston, MA, United States, 4Harvard-MIT, Division of Health Sciences and Technology, Cambridge, MA, United States

High field MRI suffers from non-uniform transmit fields and B0 variations due to increased susceptibility effects, making uniform slice-excitation very difficult. We developed a new pulse trajectory – the “twisted spokes” RF pulse – to achieve accurate slice-selection with high in-plane uniformity and greatly improved B0 robustness. The twisted spokes trajectory consists of helical k-space segments oriented along the slice-selection direction (e.g., kz). We found that, when the helical segments are designed appropriately, the resulting RF pulses are short, achieve sharp slice profiles and uniform flip-angle distributions, and – at the same time – are very robust to off-resonance effects.

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