Tissue sodium concentration in human brain tumors as measured with 23Na MR imaging

Purpose: To use combined proton (1H) and sodium 23 (23Na) magnetic resonance (MR) imaging to noninvasively quantify total tissue sodium concentration and to determine if concentration is altered in malignant human brain tumors.

Materials and methods: Absolute tissue sodium concentration in malignant gliomas was measured on quantitative three-dimensional 23Na MR images with tissue identification from registered 1H MR images. Concentration was determined in gray matter (GM), white matter (WM), cerebrospinal fluid (CSF), and vitreous humor in 20 patients with pathologically proven malignant brain tumors (astrocytoma, n = 17; oligodendroglioma, n = 3) and in nine healthy volunteers. Sodium concentration in tumors and edema was determined from 23Na image signal intensities in regions that were contrast material enhanced on T1-weighted 1H images (tumors) or regions that were only hyperintense on fluid-attenuated inversion recovery (FLAIR) 1H images (edema). Sodium concentrations were measured noninvasively from 23Na images obtained with short echo times (0.4 msec) by using external saline solution phantoms for reference. Differences in mean sodium concentration of all healthy tissue and lesions in patients were tested with a paired t test. Concentration in uninvolved tissues in patients was compared with that in the same tissue types in the volunteers with an independent samples two-tailed t test.

Results: Mean concentration (in millimoles per kilogram wet weight) was 61 +/- 8 (SD) for GM, 69 +/- 10 for WM, 135 +/- 10 for CSF, 113 +/- 14 for vitreous humor, 103 +/- 36 for tumor, 68 +/- 11 for unaffected contralateral tissue, and 98 +/- 12 for FLAIR hyperintense regions surrounding tumors. Significant differences (P <.002) in sodium concentration were demonstrated by using a t test for both tumors and surrounding FLAIR hyperintense tissues versus GM, WM, CSF, and contralateral brain tissue.

Conclusion: 23Na MR imaging with short echo times can be used to quantify absolute tissue sodium concentration in patients with brain tumors and shows increased sodium concentration in tumors relative to that in normal brain structures.