A selective excitation/B0 gradient technique for high-resolution 1H NMR studies of metabolites via zero-quantum coherence and polarization transfer.

A new method for selective observation of scalar coupled metabolites by either zero-quantum coherence transfer or polarization transfer with concurrent water suppression in a single acquisition was developed. Gaussian shaped RF pulses were used to selectively generate multiple-quantum and zero-quantum coherence in the metabolite of interest, single quantum (including water) and double quantum coherences were then dephased under the influence of a B0 field gradient and the surviving zero-quantum coherence was converted to observable metabolite signal. The duration of the gradient application and the frequency and angle of the final selective read pulse determined whether a polarization transfer or a coherence transfer signal was observed. Water suppression factors of around 8000 were achieved which allowed operation of the receiver at high gain levels resulting in greatly improved signal to noise in the metabolite spectra. The CH3 and CH resonances of lactate in a mouse brain homogenate were selectively edited and the method was also applied to selective editing of ethanol.