M.Robin Bendall

Amplitude- and frequency/phase-modulated refocusing pulses that induce plane rotations even in the presence of inhomogeneous B1 fields

Amplitude- and frequency/phase-modulated 180† plane rotation pulses that can achieve both inversion and refocusing transformations in the presence of large B1 variations are presented. Such pulses are required especially in in vivo applications where some of the most commonly used coils generate highly inhomogeneous RF fields. The principles involved in constructing such pulses are discussed in detail together with five different types of problems encountered that affect performance of these pulses off resonance. The refocusing transformation is achieved by inverting the effective field halfway through the pulse. The different pulses discussed tolerate very large and similar range of variations in B1 magnitude on resonance, but behave differently off resonance. Two of the pulses achieve 180† plane rotations with constant phase over a useful off resonance range and in the presence of large B1 variations. Therefore, these pulses are expected to be useful in high-resolution as well as in vivo NMR applications.