Previously, we developed a composite adiabatic pulse, BIR-4, which is a B1-insensitive universal rotator (by definition, a universal rotator can achieve any specified rotation angle for all magnetization vectors lying perpendicular to a constant rotation axis; i.e., a """"""""plane rotation""""""""). Although BIR-4 can accomplish a plane rotation of any desired angle across a reasonably wide range of resonance offsets, the frequency response profile (or bandwidth) lacks distinct boundaries and is, therefore, unsuitable for frequency-selective excitation and slice selection. Although frequency-selective 180l adiabatic pulses are available, many different applications of NMR require a slice-selective B1-insensitive universal rotator, but such pulses have not previously been available. During the past year, we developed an adiabatic pulse which accomplishes uniform slice-selective excitation with a spatially inhomogeneous B1. This new pulse, known as BISS-8, can generate a uniform, arbitrary flip angle which is determined by four adjustable phase shifts. Self-refocused slice selection is achieved by modulating a B0 gradient in concert with the pulse frequency (or phase) modulation. So far, we have demonstrated B1-compensated, self-refocused slice selection with BISS-8 using computer simulations and phantom experiments. The performance of BISS-8 for in vivo studies will be evaluated in the near future.
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