Volume-selective NMR spectroscopy with self-refocusing pulses

If the 90 Deg selective pulses that are normally used for vol. localization are replaced with self-refocusing 270 Deg pulses having a Gaussian time-domain amplitude profile, various pulse sequences can be made shorter, thus reducing the effects of transverse relaxation, flow, or diffusion. The sensitivity advantage is ascertained quant. for some of the commonly used sequences. The vol. of interest defined in these expts. is detd. by the offset dependence (spatial profile) of the conversion of transverse xy magnetization into z magnetization and vice versa. The gradients can be switched on and off within the intervals where the radiofrequency pulses are applied without affecting the spatial profile. The shapes were compared of the vols. of interest defined by (i) 90 Deg Gaussian pulses, (ii) 90 Deg sinc pulses, and (iii) self-refocusing 270 Deg Gaussian pulses. In the first two cases, refocusing or predefocusing is necessary, while in the latter case it is not. The comparisons lead one to propose 3 new methods, (i) self-refocusing spatial and chem.-shift-encoded excitation (SR-SPACE), (ii) self-refocusing spatially resolved spectroscopy (SR-SPARS), and (iii) self-refocusing selected-vol. excitation using stimulated echoes (SR-VEST). [on SciFinder (R)]