Hai Zheng1,2, Tiejun Zhao3, Tamer Ibrahim1, Fernando Emilio Boada1
1MR Research Center, University of Pittsburgh, Pittsburgh, PA, United States; 2Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States; 3Siemens Medical Systems, Malvern, PA, United States
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.