Influence of echo time in quantitative proton MR spectroscopy using LCModel

ObjectiveThe 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.MethodsA 3 T 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 288 ms. 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.ResultsIn 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.ConclusionsIn 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.