Low-grade glioma: correlation of short echo time 1H-MR spectroscopy with 23Na MR imaging.

BACKGROUND AND PURPOSE There is considerable variability in the clinical behavior and treatment response of low-grade (WHO grade II) gliomas. The purpose of this work was to characterize the metabolic profile of low-grade gliomas by using short echo time (1)H-MR spectroscopy and to correlate metabolite levels with MR imaging-measured sodium ((23)Na) signal intensity. Based on previous studies, we hypothesized decreased N-acetylaspartate (NAA) and increased myo-inositol (mIns), choline (Cho), glutamate (Glu), and (23)Na signal intensity in glioma tissue. MATERIALS AND METHODS Institutional ethics committee approval and informed consent were obtained for all of the subjects. Proton ((1)H-MR) spectroscopy (TR/TE = 2200/46 ms) and sodium ((23)Na) MR imaging were performed at 4T in 13 subjects (6 women and 7 men; mean age, 44 years) with suspected low-grade glioma. Absolute metabolite levels were quantified, and relative (23)Na levels were measured in low-grade glioma and compared with the contralateral side in the same patients. Two-sided Student t tests were used to test for statistical significance. RESULTS Significant decreases were observed for NAA (P < .001) and Glu (P = .004), and increases were observed for mIns (P = .003), Cho (P = .025), and sodium signal intensity (P < .001) in low-grade glioma tissue. Significant correlations (r(2) > 0.25) were observed between NAA and Glu (P < .05) and between NAA and mIns (P < .01). Significant correlations were also observed between (23)Na signal intensity and NAA (P < .01) and between (23)Na signal intensity and Glu (P < .01). Ratios of NAA/mIns, NAA/(23)Na, and NAA/Cho were altered in glioma tissue (P < .001); however based on the t statistic, NAA/(23)Na (t = 9.6) was the most significant, followed by NAA/mIns (t = 6.1), and NAA/Cho (t = 5.0). CONCLUSION Although Glu concentration is reduced and mIns concentration is elevated in low-grade glioma tissue, the NAA/(23)Na ratio was the most sensitive indicator of pathologic tissue.