A rapid inversion technique for the measurement of longitudinal relaxation times of brain metabolites: application to lactate in high-grade gliomas at 3 T

The aim of this study was to develop a time-efficient inversion technique to measure the T-1 relaxation time of the methyl group of lactate (Lac) in the presence of contaminating lipids and to measure T-1 at 3 T in a cohort of primary high-grade gliomas. Three numerically optimized inversion times (TIs) were chosen to minimize the expected error in T-1 estimates for a given input total scan duration (set to be 30 min). A two-cycle spectral editing scheme was used to suppress contaminating lipids. The T-1 values were then estimated from least-squares fitting of signal measurements versus TI. Lac T-1 was estimated as 2000 +/- 280 ms. After correcting for T-1 (and T-2 from literature values), the mean absolute Lac concentration was estimated as 4.3 +/- 2.6 mM. The technique developed agrees with the results obtained by standard inversion recovery and can be used to provide rapid T-1 estimates of other spectral components as required. Lac T-1 exhibits similar variations to other major metabolites observable by MRS in high-grade gliomas. The T-1 estimate provided here will be useful for future MRS studies wishing to report relaxation-corrected estimates of Lac concentration as an objective tumor biomarker. Copyright (C) 2016 John Wiley & Sons, Ltd.