Introduction: The PRESS sequence is commonly used to observe the metabolites within a single voxel. However, lipids are co-resonant with lactate, and in a conventional PRESS acquisition the two peaks can not be easily distinguished. Hence, it is desirable to incorporate efficient lactate/lipid discrimination into a PRESS sequence. Methods: We implemented a two-shot lactate filter that alternates between a narrow and wide band 180 degree pulse on sequential acquisitions. The time between the 90 degree excitation pulse and the lactate filter is 1/2J (72ms). We set the center frequency of the spectrally selective lactate filter on the CH3 doublet of lactate. The narrower filter of the first sequence has a bandwidth of +/-1.57ppm (100Hz), which includes the NAA and lipids. The wider filter of the second sequence has a bandwidth of +/-7.83ppm (500)Hz, which includes the lactate quartet. The lactate doublet is reversed in the second sequence but the other metabolites are unaffected. Subtracting the data acquired from these two sequences, yields only the lactate signal, hence suppressing the lipids. Summing the data acquired from the two sequences, yields the other resonances, namely NAA and lipids. Conclusions: By interleaving two spectrally selective 180 degree RF pulses, we achieved the goal of lactate/lipid discrimination while keeping the information of the other metabolites. This method is potentially very useful for definitively identifying lactate (even in the presence of additional lipids) in a single voxel experiment, and avoids the need to acquire additional data at other echo times as is commonly done.
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