Slice-selective tunable-flip adiabatic low peak-power excitation pulse.

Adiabatic pulses are useful in achieving uniform excitation profiles in the presence of B(1)-inhomogeneity. At higher fields, this inhomogeneity becomes more severe, further amplifying the need for B(1)-insensitive excitation. Although gradient modulation techniques for slice-selective adiabatic excitation have been introduced, a pulse that falls within the gradient and RF amplifier limits for most commercial human scanners is currently unavailable. In this work, we present an alternative gradient modulated approach for pulse design that achieves adiabatic slice selection with significantly lower RF peak power requirements. The resulting Slice-selective Tunable-flip AdiaBatic Low peak-power Excitation (STABLE) pulse consists of an oscillating gradient in conjunction with a BIR-4-like RF envelope that is sampled by many short spatial subpulses to achieve spatial selectivity. Simulations show that the expected spatial profile as well as the off-resonance behavior of the pulse remain invariant for a range of B(1) values. Phantom and in vivo results demonstrate the adiabaticity and slice selectivity of the STABLE pulse. (c) 2008 Wiley-Liss, Inc.