Incorrect Echo Times Yield a 10% Reduction in the Lactate Intensity and a 9% Reduction in the T2 of Lactate

Introduction Determination of cerebral lactate is the focus of many MR studies. Lactate is the end-product of anaerobic glycolysis and is produced and used during bacterial and/or macrophages infiltration, and its contents may vary during normal physiological conditions from 0.5 to 5.0 mM, and even higher in pathological states. Clinical applications lie in the field of ischemia, tumor research, pediatric/neonatal hypoxia/asphyxia, trauma, encephalitis, degenerative diseases and more. When detection of lactate is important, relatively long echo times are used in order to avoid that the lactate resonance is obscured by broad signals originating from lipids, membrane bound molecules, amino acids or other macro molecules. In our clinical experience we recognized several undesirable effects concerning the shape and position of the lactate doublet at 1.33 ppm. Firstly, we noted that, using a TE of 136 or 272 ms, the lactate resonances could not be phase corrected in a proper way, leaving phase modulation dips on both sides of the signal. This effect is demonstrated in figure 1, bottom spectrum. Secondly, we could not reproduce the -7Hz coupling constant, measuring considerably lower coupling constants (figure 1). Similar phenomena can be recognized in many publications. Furthermore, when determining the T2 of cerebral lactate, no decrease peak height was observed with increasing echo times. The aim of this study was to measure the actual J-coupling of the lactate doublet and to investigate the role of the echo time used on the signal intensity and T2 calculation of lactate.