A noniterative method to design large-tip-angle multidimensional spatially-selective radio frequency pulses for parallel transmission

Recently, theoretical and experimental work has shown that parallel transmission of RF pulses can be used to shorten the duration of multidimensional spatially-selective pulses and compensate for B₁ field inhomogeneity. However, all the existing noniterative methods can design only excitation pulses for parallel transmission with a small flip angle (e.g., 30°, or at most 90°) and cannot design large-tip-angle inversion/refocusing pulses, because these methods are based on the small-tip-angle (STA) approximation of the Bloch equation. In this work, a method to design large-tip-angle multidimensional spatially-selective pulses for parallel transmission is proposed, based on an extension of the single-channel linear-class large-tip-angle (LCLTA) theory. Design examples of 2D refocusing and inversion parallel transmit pulses and magnetization profiles from Bloch equation simulations demonstrate the strength of the proposed method. A 2D spin-echo parallel transmission experiment on a slab phantom using a 180° refocusing pulse with an eight-channel transmit-only array further validates the effectiveness of the proposed method.