Abstract #1015

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

Mathias Davids^1,2, Bastien Guérin^2,3, Lawrence L Wald^2,3,4, 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., k_z). 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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