BREAKTHROUGH OF SINGLE-QUANTUM COHERENCE AND ITS ELIMINATION IN DOUBLE-QUANTUM FILTERING

Breakthrough of single-quantum coherence is shown to occur after appli cation of a double-quantum filter with the conventional four-step phas e-cycling scheme. This single-quantum breakthrough is due to the inter sequence stimulated echo which has been generated by the radiofrequenc y pulses in the preceding pulse sequence and appears at the same time as the double-quantum coherence signal in the current pulse sequence. Moreover, the phase of the intersequence stimulated echo is the same a s the phase of the double-quantum coherence signal; i.e., the phase of the intersequence stimulated echo is twice the phase change of the ra diofrequency pulses in the creation period when their phase is rotated in accordance with the conventional four-step phase-cycling scheme. C onsequently, the intersequence stimulated echo passes through the doub le-quantum filtration in the conventional four-step phase-cycling sche me and gradient pulses. A new phase-cycling scheme which can filter ou t the single-quantum breakthrough signal is proposed here and its effe ctiveness is verified experimentally by computer simulations. (C) 1995 Academic Press, Inc.