Suppression of artifacts in phase-sensitive COSY

Abstract

High repetition rates generate systematic errors in phase-sensitive COSY spectra because incomplete relaxation allows magnetization from one transient to carry over and interfere with the next. The resultant artifacts appear at integral multiples of the resonance offset in the F₁, dimension. Product-operator calculations are used to predict permutations of the RF phase cycle in which these artifacts are canceled. The success of these permutations is tested experimentally. It is shown that the axial-peak suppression and dummy transients are vital for the suppression of repetition-rate artifacts, but that quadrature-image suppression is irrelevant. The best permutations of the phase cycle reduce repetition-rate artifacts to about 1% of their parent peaks when recycle delays three times less than the longitudinal relaxation time are used.