Scalar coupling and zero-quantum coherence relaxation in STEAM: implications for spectral editing of lactate.

Accurate values were obtained for the lactate zero-quantum coherence frequency, omega ZQ identical to omega 1-omega s = CH3 - CH chemical shift difference, and scalar coupling constant, J, by using the methyl signal's amplitude modulation during the TM period of a STEAM sequence, 90 degrees - TE/2 - 90 degrees - TM - 90 degrees - TE/2 - Acquire. Although most previous work has used J = 7.35 Hz, or 1/J = 136 ms, the actual value is J = 6.93 +/- 0.05 Hz or 1/J = 144.3 +/- 1 ms. In addition, the CH3 - CH chemical shift difference = 2.7956 +/- 0.0005 ppm, and the relaxation time for zero-quantum coherence, TZQ, was much shorter than either T2 or T1 for the methyl resonance. A small component of the signal with TE = 144 ms, which was not modulated at the zero-quantum coherence frequency or by scalar coupling, was assigned to longitudinal two-spin order magnetization (IzSz) created by imperfect radio frequency pulse profiles. This information will allow improved editing of the lactate signal and more accurate quantitation of lactate concentrations.