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.