Broadband excitation in magnetic resonance by self-refocusing doubly frequency-modulated pulses

It is shown how transverse magnetization can be excited with a single low-power radiofrequency pulse consisting of a superposition of 2 frequency-modulated components. The phase dispersion obtained with this self-refocusing pulse is very small over bandwidths that are far greater than the amplitude of the radiofrequency field. The new pulse shape may be derived from spin-echo sequences employing frequency-modulated chirp pulses by shifting the excitation and refocusing pulses in time so that they are partly or completely superimposed. The duration of chirp spin-echo sequences can be reduced by a factor of 2 by this contraction process, so that the echoes are less sensitive to transverse relaxation. [on SciFinder (R)]