3T 1H-MR spectroscopy in grading of cerebral gliomas: comparison of short and intermediate echo time sequences

Abstract

Background and purpose: Echo time (TE) can have a large influence on the spectra in proton MR spectroscopy ((1)H-MR spectroscopy). The purpose of this study was to comparatively assess the diagnostic value of 3T single-voxel (1)H-MR spectroscopy with short or intermediate TEs in grading cerebral gliomas.

Methods: Single voxel (1)H-MR spectroscopy was performed at 3T in 35 patients with cerebral glioma. The spectra were obtained with both short (35 ms) and intermediate TEs (144 ms). Metabolite ratios of choline (Cho)/creatine (Cr), Cho/N-acetylaspartate (NAA), lipid and lactate (LL)/Cr and myo-inositol (mIns)/Cr were calculated and compared between short and intermediate TEs in each grade. After receiver operating characteristic curve analysis, diagnostic accuracy for each TE in differentiating high-grade glioma from low-grade glioma was compared.

Results: At short TE, Cho/Cr and Cho/NAA ratios were significantly lower, and LL/Cr and mIns/Cr were significantly higher, compared with those at intermediate TE, regardless of tumor grade. Lactate inversion at intermediate TE was found in only 2 patients. At both TEs, there were significant differences in Cho/Cr and LL/Cr ratios between low- and high-grade gliomas. Diagnostic accuracy was slightly higher at short TE alone or combined with intermediate TE than intermediate TE alone (85.7% versus 82.9%).

Conclusion: Metabolite ratios were significantly different between short and intermediate TE. Cho/Cr and LL/Cr ratios at either TE were similarly useful in differentiating high-grade gliomas from low-grade gliomas. If only a single spectroscopic sequence can be acquired, short TE seems preferable because of poor lactate inversion at intermediate TE on 3T single-voxel (1)H-MR spectroscopy.

Fig 1.

Box plots of the ratios of the metabolites at both TE sequences in the patients with cerebral gliomas. The horizontal thick line is the median, the upper and lower ends of the boxes are the 3rd and 1st quartiles, and the vertical lines show the full range of values in the data. The extremes and outliers were omitted. A, Cho/Cr at short TE; B, Cho/NAA at short TE; C, LL/Cr at short TE; D, mIns/Cr at short TE; E, Cho/Cr at intermediate TE; F, Cho/NAA at intermediate TE; G, LL/Cr at intermediate TE; H, mIns/Cr at intermediate TE.

Fig 2.

A 35-year-old man with low-grade (grade II) astrocytoma. A, Axial T2-weighted image reveals diffuse infiltrating glioma involving left basal ganglia and frontotemporal area with a square voxel (6.2 cm³). B, ¹H-MR spectrum obtained at short TE (2000/35) shows increased Cho/Cr ratio (1.9:1), increased Cho/NAA ratio (2.3:1) and increased lipid-lactate (LL)/Cr ratio (1.6:1). C, ¹H-MR spectrum obtained at intermediate TE (1500/144) shows more increased Cho/Cr ratio (2.4:1), more increased Cho/NAA ratio (4.9:1) and hardly discernible peak of lipid-lactate between 0.9 and 1.3 ppm (LL/Cr ratio: 0.3:1). The baseline of the spectrum is noisier than B.

Fig 3.

A 38-year-old man with anaplastic (grade III) oligodendroglioma. A, Axial FLAIR image reveals a infiltrating tumor in the right parietal lobe with a square voxel (4.2 cm³). B, ¹H-MR spectrum obtained at short TE (2000/35) shows increased Cho/Cr ratio (2.4:1), increased Cho/NAA ratio (4.1:1), and increased lipid-lactate (LL)/Cr ratio (2.1:1). C, ¹H-MR spectrum obtained at intermediate TE (1500/144) shows more increased Cho/Cr ratio (2.9:1), more increased Cho/NAA ratio (5.7:1), and much smaller peaks of lipid-lactate at 1.3 ppm (LL/Cr: 0.8:1). The baseline of the spectrum is noisier than B.

Fig 4.

A 61-year-old man with glioblastoma (grade IV). A, Axial FLAIR image reveals a large necrotic tumor in the right frontal lobe with a rectangular voxel (8.0 cm³). B, ¹H-MR spectrum obtained at short TE (2000/35) shows increased Cho/Cr ratio (1.5:1), increased Cho/NAA ratio (1.2:1), and markedly increased LL/Cr ratio (3.8:1) at 1.3 ppm. C, ¹H-MR spectrum obtained at intermediate TE (1500/144) shows more increased Cho/Cr ratio of (2.2:1), more increased Cho/NAA ratio (2.1:1), and a smaller inverted lactate peak with smaller lipid peaks at 1.2–1.4 and 0.9 ppm (LL/Cr: 0.9:1). The baseline of the spectrum is noisier than B.

Fig 5.

Graph shows 4 ROC curves of Cho/Cr and LL/Cr ratios at both TEs for differentiation of high-grade glioma from low-grade glioma. A_z value (area under the ROC curve) is the highest in LL/Cr ratio at short TE and lowest in Cho/Cr ratio at intermediate TE. But there are no significant differences among all the A_z values.