Unwanted signal leakage in excitation sculpting with single axis gradients

Excitation sculpting (T-L. Hwang and A. J. Shaka, J. Magn. Reson, A 112, 27 5-279 (1995)) used for solvent suppression and selective excitation in NMR bases its success on the ability to remove baseline and phase errors create d by the application of selective rf pulses. This is achieved by the applic ation of two pulsed field gradient (PFG) echoes in sequence. It is essentia l that the two pairs of PFGs select the coherence transfer steps independen tly of each other, which is conveniently achieved if they are applied along orthogonal spatial axes, Here, the much more common case where both PFG pa irs must be applied along a single axis is investigated. This is shown to l ead to complications for certain ratios of PFG strengths. The original theo ry of excitation sculpting is restated in the spherical basis for convenien ce. Some of the effects can only be explained by invoking the dipolar demag netizing field. (C) 1999 Academic Press.