Low-Grade Glioma: Correlation of Short Echo Time ¹H-MR Spectroscopy with ²³Na MR Imaging

Abstract

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 ¹H-MR spectroscopy and to correlate metabolite levels with MR imaging-measured sodium (²³Na) signal intensity. Based on previous studies, we hypothesized decreased N-acetylaspartate (NAA) and increased myo-inositol (mIns), choline (Cho), glutamate (Glu), and ²³Na signal intensity in glioma tissue.

MATERIALS AND METHODS: Institutional ethics committee approval and informed consent were obtained for all of the subjects. Proton (¹H-MR) spectroscopy (TR/TE = 2200/46 ms) and sodium (²³Na) 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 ²³Na 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 (r² > 0.25) were observed between NAA and Glu (P < .05) and between NAA and mIns (P < .01). Significant correlations were also observed between ²³Na signal intensity and NAA (P < .01) and between ²³Na signal intensity and Glu (P < .01). Ratios of NAA/mIns, NAA/²³Na, and NAA/Cho were altered in glioma tissue (P < .001); however based on the t statistic, NAA/²³Na (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/²³Na ratio was the most sensitive indicator of pathologic tissue.