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

Abstract

The aim of this study was to develop a time-efficient inversion technique to measure the T1 relaxation time of the methyl group of lactate (Lac) in the presence of contaminating lipids and to measure T1 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 T1 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 T1 values were then estimated from least-squares fitting of signal measurements versus TI. Lac T1 was estimated as 2000 ± 280 ms. After correcting for T1 (and T2 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 T1 estimates of other spectral components as required. Lac T1 exhibits similar variations to other major metabolites observable by MRS in high-grade gliomas. The T1 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 © 2016 John Wiley & Sons, Ltd.

Concentration and effective T2 relaxation times of macromolecules at 3T

“…The choice of TEs is critical to achieving reliable estimates for relaxation times, however, it is an open question about what the optimal choice of TEs is. Previous optimization of inversion times (TI), which is analogous to TE in measuring T 1 relaxation times, minimized the expected SD in the relaxation time 7 . This approach has the advantage of optimally making use of scan time, however, it suffers from being unable to validate the model—as the prescribed TIs (or TEs for measuring T 2 relaxation) will invariably lie along the extremes, as well as requiring a priori knowledge of the relaxation times in question.…”

Methodological consensus on clinical proton MRS of the brain: Review and recommendations

“…Lipid and metabolite excitation regions are shown in cream and orange, respectively FIGURE S3 The effect of TR on the SNR per unit time due to T 1 saturation relative to that at TR = 6000 ms. On average, across the 4 metabolite curves shown, the maximum SNR per unit time is close to 1500 ms at 1.5 T and 2000 ms at 3 T. The metabolite T 1 values used are the average values from different normal brain regions acquired with exactly the same acquisition and processing protocols at both 1.5 T and 3 T: tCho = 1103/1290 ms; tCr = 1232/1375 ms; and tNAA = 1303/1482 ms . A lactate T 1 of 2000 ms at 3 T for high‐grade gliomas was used, and this value scaled to 1754 ms for 1.5 T using a factor of 1.14, the average ratio of the normal‐tissue metabolite T 1 values at the 2 field strengths FIGURE S4 Effect of T 1 saturation on tissue water signals and main metabolite signals and clinically relevant metabolite ratios. A TR of 6000 ms is required to maintain the signals shown within 95% of their unsaturated values.…”

Advanced Magnetic Resonance Imaging Techniques in Management of Brain Metastases

“…Figure 1 shows the MRS spectrum of a 2 cm 3 region of the brain encompassing the tumor in a representative brain cancer patient. The most commonly quantified metabolites with MRS that have been shown—in several small-scale patient studies—to change in tumors and due to treatment are creatine, choline, and NAA (36–42). MRS allows for correlating the concentrations of these sub-cellular molecules with changes in tumor and normal tissue due to treatment (43).…”

“…T 1w MRI of a patient with a high-grade glioma (left) with MRS spectrum (right) corresponding to the voxel (white Square) inside the tumor. Reproduced, with permission from Landheer et al (36). …”