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Objective: The objective of this study was to elucidate the influence on quantitative analysis using LCModel with the condition of echo time (TE) longer than the recommended values in the spectrum acquisition specifications., Methods: A 3T magnetic resonance system was used to perform proton magnetic resonance spectroscopy. The participants were 5 healthy volunteers and 11 patients with glioma. Data were collected at TE of 72, 144 and 288ms. LCModel was used to quantify several metabolites (N-acetylaspartate, creatine and phosphocreatine, and choline-containing compounds). The results were compared with quantitative values obtained by using the T2-corrected internal reference method., Results: In healthy volunteers, when TE was long, the quantitative values obtained using LCModel were up to 6.8-fold larger (p<0.05) than those obtained using the T2-corrected internal reference method. The ratios of the quantitative values obtained by the two methods differed between metabolites (p<0.05). In patients with glioma, the ratios of quantitative values obtained by the two methods tended to be larger at longer TE, similarly to the case of healthy volunteers, and large between-individual variation in the ratios was observed., Conclusions: In clinical practice, TE is sometimes set longer than the value recommended for LCModel. If TE is long, LCModel overestimates the quantitative value since it cannot compensate for signal attenuation, and this effect is different for each metabolite and condition. Therefore, if TE is longer than recommended, it is necessary to account for the possibly reduced reliability of quantitative values calculated using LCModel., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Lactate is an important metabolite in clinical cases indicating the status of metabolic impairment. We applied a clinically relevant simple method for lactate quantification using magnetic resonance spectroscopy (MRS). We used two long in-phase echo time (TE=272,544 ms) to calculate T2 relaxation time and the absolute concentration of lactate. This method was optimized using phantom study and applied to clinical cases. This technique does not require complicated processing and could be applied in daily clinical practice. Moreover, this technique enables lactate quantification in cases (e.g. tumor) where lipid peak is overlapped with the lactate peak at short echo times.

Background: Choline (Cho) containing compounds are usually evaluated using magnetic resonance spectroscopy (MRS) by relative ratios such as Cho/N-acetylaspartate (NAA) and Cho/creatine (Cre) ratios. To clarify the significance of Cho level in gliomas, we evaluated the quantified Cho level using MRS and compared it with the proliferation activity as determined by MIB-1 immunoreactivity in the histological specimen., Methods: There were seven benign and seven malignant gliomas. MRS was obtained using a single-voxel proton regional imaging of metabolites (PRIME) sequence with three different TE for T2 compensation. Quantified Cho level was compared with the number of MIB-1 immunopositive positive cells and cell density in surgical specimens., Result: A positive correlation was observed between Cho and MIB-1 in benign gliomas, whereas there was a trend to an inverse correlation in malignant gliomas. This inverse correlation became a positive correlation when the necrotic area of the tumor (on the T1-weighted gadolinium enhanced images) was excluded from the voxel of interest (VOI) for MRS, but this correlation did not reach statistical significance., Conclusions: The quantification data clarified the behavior of Cho in malignant gliomas. The quantification method has the advantage of limiting the influence of other metabolites on Cho determination. In particular, the levels of other commonly measured metabolites, including Cre, may also be altered in glioma, making ratios between metabolites misleading. Heterogeneity in the MRS VOI should be considered when evaluating the proliferative activity of malignant glioma by MRS.

The evaluation of the response to radiation therapy in brain tumor patients is a major and an important issue. Although CT and MRI can measure changes in tumor size, it is difficult to use these imaging methods to evaluate the viability or the proliferation activity of a tumor. In this study, we investigated the metabolite changes in glioma patients using 1H-MRS from before to after radiation therapy, to see whether or not early metabolic changes occur during therapy. Seven patients with histologically proven glioma (1 astrocytoma, 1 anaplastic astrocytoma, 2 oligoastrocytoma, 1 oligodendroglioma, 2 glioblastoma) were examined by means of 1H-MRS using a point-resolved spectroscopy (PRESS) sequence with a repetition time of 2,000 ms and echo times of 68 ms, 136 ms and 272 ms. The 1H-MRS was evaluated by both the spectrum pattern and the quantification of the metabolites. As to radiation therapy, each patient received a total dose of 64.8 Gy (1.8 Gy/fraction) with a 10-MeV linear accelerator. The results revealed that the concentration of choline-containing compounds (Cho) was 4.55 +/- 1.08 mmol/kg wet weight before radiation therapy and was reduced to 2.69 +/- 0.56 mmol/kg wet weight (p < 0.01) after radiation therapy. Moreover, both the N-acetylaspartate (NAA) peak and creatine/phosphocreatine (t-Cr) peak were lower after radiation therapy than before. The peaks of both the lipids (Lip) and lactate (Lac) were higher after radiation therapy than before. In conclusion, Cho concentration is thought to be a useful marker for the evaluation of early post-radiation response. The effect of radiation therapy can be evaluated according to the value of Cho. Further long-term MRS study is needed to prove whether or not the decrease of the Cho value in the present study will change before recurrence at later stages.

This study was aimed to investigate the significance of absolute concentration of metabolites in glioma patients using proton MR spectroscopy (MRS) with T2 relaxation time correction using three different echo times. The absolute concentrations of metabolites in 7 normal subjects and in 23 gliomas (10 low-grade, 13 high-grade) were obtained by proton MRS using a tissue water signal as an internal standard. The signal intensities of metabolites and tissue water were corrected by T2 relaxation time. In low-grade glioma, the T2 relaxation time of NAA was shorter, and T2 relaxation time of water was prolonged as compared to normal subjects (p < 0.001). In high-grade glioma, the T2 relaxation time of NAA (p < 0.001) and T2 relaxation time of Cr (p < 0.01) were shorter, and T2 relaxation time of water (p < 0.001) was prolonged as compared to normal subjects. Moreover, high-grade gliomas revealed a shorter T2 relaxation time of Cr than low-grade gliomas (p < 0.05). In glioma, NAA and Cr concentration were decreased, and Cho were increased as compared to normal subjects. Moreover, high-grade glioma revealed a significant lower Cr (p < 0.001) and Cho (p < 0.01) concentration compared to low-grade gliomas. Low Cr concentration is the most reliable indicator of malignancy in glioma. Cho concentration did not correlate with malignancy in gliomas., (Copyright 2002 Elsevier Science Inc.)