Effect of J coupling and T2 Relaxation in Assessing of Methyl Lactate Signal using PRESS Sequence MR Spectroscopy.

Purpose: This work was aimed at quantification of lactate concentration using proton MR spectroscopy (MRS). We carried out a basic study to clarify the characteristics of signal change and T2 relaxation time of lactate that occur by J coupling in point resolved spectroscopy (PRESS) sequence.
Materials and Methods: Proton MRS was done for a water phantom containing 10 mmol/L creatine and lactate on a clinical 1.5 T MR system by using an asymmetric PRESS sequence. The coupling constant J was 7.35 Hz. In acquisitions, TE was varied from 68 ms up to 544 ms, with an increment of 68 ms (1/2J) and TR was fixed to 10000 ms.
Results: The shape and signal intensity of the lactate signal vary depending on its phase. The lactate signal intensity at TE 272 ms was higher than at TE 136 ms despite the longer TE. T2 relaxation times of lactate in the negative in-phase (TE 136 ms, TE 408 ms) and positive in-phase (TE 272 ms, TE 544 ms) were 1033 ms and 1042 ms, respectively (no significant differences), so that when the same phase was used, regardless of the phase condition, T2 relaxation behavior was not different. We considered that our results included over expression and loss of lactate signal depending on the phase.
Conclusions: For evaluation of the lactate peak, we recommend the use of the positive in-phase signal because it is larger than the negative in-phase signal. The influence of the asymmetric PRESS sequence, which may cause loss and over expression of lactate signal, should be considered in the calculation of the quantification. The T2 relaxation time should be also considered in the calculation of the lactate value since it affects the value considerably.