IMG-07. Technological Advancements of Sodium MRI in Pediatric Brain Tumors

Abstract Sodium MRI (23Na-MRI) derives its signal from spin-manipulation of the 23Na nucleus itself, in contrast to conventional 1H-MRI which utilizes the hydrogen nuclei on water molecules. Advances in coil design and pulse sequence development have enabled the feasibility of human in-vivo 23Na-MRI. 23Na-MRI has potential to be a useful non-invasive imaging technique to assess biochemical and physiologic cellular changes in brain tumors. Pathologically, the concentration of total sodium is elevated in tumors relative to normal counterparts due to increased intracellular sodium and/or an increased proportion of extracellular space (reflecting changes in cell morphology and anomalies of homeostasis). We will present the technological advancements with improved pulse sequences and reconstruction methods that combat the inherent challenges of measuring sodium concentrations in pediatric brain tumors. This improved imaging approach to measuring sodium concentration within viable tumors in comparison to necrotic components and uninvolved brain will be illustrated in case examples of pediatric patients with brain tumors. One example case included a pediatric patient with a diffuse midline glioma. Diagnostic imaging showed a T2 hyperintense expansile mass in the pons. After completion of radiation treatment, there was a significant decrease in size and T2 hyperintensity of the mass. At the same timepoint after radiation, sodium MRI was performed and demonstrated a focus of elevated sodium concentrations in a region of tumor; this region may have represented active tumor versus treatment effect. Follow-up conventional MRI, two months after radiation cessation demonstrated tumor progression in the region of the prior sodium elevation. This case supports the hypothesis that elevated sodium signal may represent an early biomarker of tumor progression/recurrence. In conclusion, 23Na-MRI will likely answer the complex questions unresolved on 1H MRI that arise in monitoring treatment of pediatric patients with brain tumors: is there residual or recurrent tumor and differentiating tumor progression versus pseudoprogression.