Off-resonance effects of the radiofrequency pulses used in spectral editing with double-quantum coherence transfer

Spectral editing using gradient selected double-quantum (DQ) coherence tran sfer is often used for the selective observation of metabolites in vivo. In attempting to optimize the detection sensitivity of a conventional Do spec tral editing sequence, the effects of using radiofrequency (RF) pulses that are not at the resonance frequency of the observed peaks were investigated both theoretically and experimentally. The results show that spectral edit ing using pulses at the frequency of the observed resonance does not necess arily give the optimal detection sensitivity. At 7 T, the detection sensiti vity of lactate observed using a Do editing method can be increased by up t o 30% by setting the RF pulses off resonance at the proper frequency. The r esults also suggest that slice selective RF pulses used in DQ spectral edit ing combined with PRESS localization may have slice profiles different from those when the same pulses are used for standard PRESS spatial localizatio n. (C) 2000 Academic Press.