23Na MRI is an indicator for cell viability and quantification provides the tissue sodium concentration (TSC). Aim of this study is to evaluate the reliability of cerebrospinal fluid (CSF) and vitreous humor (VH) as internal references for TSC quantification. Data of 49 patients with ischemic stroke was included for TSC quantification which was performed based on signal intensity within external references, CSF and VH. TSC of healthy tissue was significantly lower compared to pathological tissue. Results showed a high similarity between the three quantification methods. Internal references would simplify 23Na MRI measurements and thus its clinical establishment.