Adiabatic RF pulses: applications to in vivo NMR

Adiabatic pulses are amplitude- and frequency-modulated pulses that are insensitive to the effects of B1-inhomogeneity and frequency offset. From the classical adiabatic passage experiments, the adiabatic condition is derived and analyzed. From the adiabatic condition, amplitude and frequency modulation functions are derived and optimized over predetermined radio frequency amplitude and frequency offset ranges. Description of the selective inversion and refocusing properties of adiabatic full-passage pulses leads to the principle of plane rotation pulses, of which the BIR-4 (B1-insensitive rotation) pulse will be discussed in detail. Theoretical simulations based on the Bloch equations, three-dimensional vector diagrams, and experimental applications demonstrate the utility and performance of the adiabatic pulses for in vivo NMR and for liquid state high-resolution NMR.