Fast and Accurate Large-Tip-Angle RF Pulse Design for Parallel Excitation Using a Perturbation Analysis of the Bloch Equation

Hai Zheng^1,2, Tiejun Zhao³, Tamer Ibrahim¹, Fernando Emilio Boada¹

The design of RF pulses in parallel excitation (PTX) commonly relies on the small-tip-angle approximation, which, although efficient, leads to distorted excitation patterns at large tip angles because of the intrinsic nonlinear nature of the Bloch equation. In this work, we introduce a fast and accurate method for large-tip-angle PTX RF pulse design based on a perturbation analysis (PTA) to the Bloch equation. Experimental data at 7T as well as computer simulations demonstrate the improvements produced by the proposed techniques without the need of prohibitively long calculation times.