IMG-01. Quantitative Direct Sodium (23Na) MRI in Pediatric Gliomas

BACKGROUND: The treatment of pediatric gliomas is typically assessed with proton ((1)H) MRI, which can have limitations. (23)Na MRI has been shown in adult brain tumors to measure intra-tumoral total sodium concentration as a correlate of tumor proliferation. (23)Na MRI sodium studies in pediatric patients are lacking. PURPOSE: (1) To compare total sodium concentration (TSC) between pediatric glioma and non-neoplastic brain tissue using (23)Na MRI; (2) Compare tissue conspicuity of bound sodium concentration (BSC) using (23)Na MRI dual echo relative to TSC imaging. MATERIALS AND METHODS: TSC was measured in: (1) non-neoplastic brain tissues and (2) three types of manually segmented gliomas [diffuse intrinsic brainstem glioma (DIPG), recurrent supratentorial low-grade glioma (LGG), and high-grade glioma (HGG)] on sodium MRI images co-registered with proton MRI. In a subset of patients, serial changes in both TSC and BSC (dual echo (23)Na MRI) were assessed for tissue conspicuity using voxel-based parametric maps. RESULTS: Twenty-six pediatric patients with gliomas (median age of 12.0 years, range 4.9 – 23.3 years) were scanned with (23)Na MRI. Uninvolved tissues demonstrated a range of TSC values similar to published adult values. DIPG treated with RT demonstrated higher TSC values than the uninvolved infratentorial tissues (P<0.001). Recurrent supratentorial LGG and HGG exhibited higher TSC values than the uninvolved white matter (WM) and gray matter (GM) (P<0.002 for LGG, and P<0.02 for HGG). The dual echo (23)Na MRI suppresses the sodium signal within both CSF and necrotic foci, resulting in improved conspicuity of both non-neoplastic and neoplastic, compared to serial TSC imaging. CONCLUSION: Quantitative (23)Na MRI of pediatric gliomas demonstrates a range of values that are higher than non-neoplastic tissues. Dual echo (23)Na MRI of BCS improves tissue conspicuity relative to TSC imaging. Future studies are needed to determine the value of (23)Na MRI in delineating therapeutic responses in pediatric gliomas.