Composite Pulses without Phase Distortion

Composite pulses for broadband spin excitation over large ranges of radiofrequency field amplitudes and resonance offsets are presented. They are derived according to a previously presented method based on the Magnus expansion in the manner of coherent averaging theory. It is shown theoretically and in simulations that these composite pulses do not introduce a strong dependence of the NMR signal phase on the rf amplitude or resonance offset, overcoming a common problem of composite pulses derived by other means. Experimental demonstrations include the use of composite x pulses for refocusing transverse magnetization in spin-echo sequences and the use of composite 1r/2 pulses in a simple multiple-pulse experiment. Further applications are discussed. o 1985 Academic