Assessment of sodium (²³Na) brain MRI at 3T - preliminary results

The purpose of this work was to establish a database of tissue sodium concentration (TSC) in the normal brain of healthy volunteers. Tissue sodium concentration can be used as a sensitive marker of tissue viability in stroke or radiation therapy monitoring.

Thirty-seven volunteers were scanned with a ²³Na protocol in the span of one year; within this group, 29 studies were of acceptable quality. The study was approved by the Local Bioethics Committee. Data were acquired during a single magnetic resonance (MR) scanner session. The single scanner session consisted of ²³Na 3D radial gradient echo (GRE) acquisition, MPRage, SPACE-FLAIR, and Resolve-DTI. MPRage images were segmented to obtain masks of the grey matter (GM), white matter (WM), and cerebrospinal fluid (CSF), which were registered to the sodium image space for image analysis. Images were transformed into TSC maps - a signal calibration curve obtained from the reference phantom of known sodium concentration and known relaxation time.

The collected data were analysed in 2 different ways: volunteers were divided by sex and by age. No significant differences in TSC were found between sexes. In all comparisons there was a significant difference in TSC between younger and older volunteers. In healthy volunteers mean TSC were as follows: GM 33.21 ± 4.76 mmol/l, WM 28.41 ± 4.03 mmol/l and for CSF 41.3 ± 6.69 mmol/l.

This preliminary work is a base for further work with sodium imaging in brain lesions. The entirety of the col-lected data will be useful in the future as a baseline brain TSC for comparison to values obtained from pathologies.