MRI Detection of Changes in Tissue Sodium Concentration in Brain Metastases after Stereotactic Radiosurgery: A Feasibility Study

Abstract

BACKGROUND AND PURPOSE: To date, treatment response to stereotactic radiosurgery (SRS) in brain metastases (BM) can only be determined by MRI evaluation of contrast-enhancing lesions in a long-time follow-up. Sodium MRI has been a subject of immense interest in imaging research as the measure of tissue sodium concentration (TSC) can give valuable quantitative information on cell viability. We aimed to analyze the longitudinal changes of TSC in BM measured with 23 Na MRI before and after SRS for assessment of early local tumor effects. METHODS: Seven patients with a total of 12 previously untreated BM underwent SRS with 22 Gy. In addition to a standard MRI protocol including dynamic susceptibility-weighted contrast-enhanced perfusion, a 23 Na MRI was performed at three time points: (I) 2 days before, (II) 5 days, and (III) 40 days after SRS. Nine BMs were evaluated. The absolute TSC in the BM, the respective peritumoral edemas, and the normal-appearing corresponding contralateral brain area were assessed and the relative TSC were correlated to the changes in BM longest axial diameters. RESULTS: TSC was elevated in nine BM at baseline before SRS with a mean of 73.4 ± 12.3 mM. A further increase in TSC was observed 5 days after SRS in all the nine BM with a mean of 86.9 ± 13 mM. Eight of nine BM showed a mean 60.6 ± 13.3% decrease in the longest axial diameter 40 days after SRS; at this time point, the TSC also had decreased to a mean 65.1 ± 7.9 mM. In contrast, one of the nine BM had a 13.4% increase in the largest axial diameter at time point III. The TSC of this BM showed a further TSC increase of 80.1 mM 40 days after SRS. CONCLUSION: Changes in TSC using 23 Na MRI shows the possible capability to detect radiobiological changes in BM after SRS.

Multi-nuclear sodium, diffusion, and perfusion MRI in human gliomas

“…Radiation therapy is known to impact the extracellular matrix by increasing vascular permeability, which in turn would cause increased extracellular fluid that may explain the elevated sodium and ADC values in our treated cohort [ 38 ]. These findings add to the growing literature of evaluating treatment response of brain tumors through elevated sodium levels [ 26 – 30 ], though these results may be interpreted with caution given the small sample sizes. Interestingly, even though increased sodium in tumor regions has been speculated to be related to increased angiogenesis that leads to increased extracellular volume fraction [ 21 ], the present study observed a negative correlation between nrCBV and sodium in NET regions and no association in CET regions, contrary to our initial hypothesis.…”

“…However, other studies reported that IDH-wt gliomas exhibit higher sodium signal than IDH-mut gliomas when imaged with advanced sodium MRI acquisition techniques, which are believed to be more sensitive to intracellular sodium by targeting sodium ions with restricted mobility [ 24 , 25 ]. Sodium MR signal also increases after radiosurgery in brain metastases [ 26 ] and vestibular schwannoma [ 27 ], and sophisticated sodium MR-derived metrics including tumor cell volume fraction can demonstrate changes in glioblastomas after chemoradiation [ 28 ], suggesting sodium MRI may provide value for therapeutic response assessment.…”

Volumetric 23Na Single and Triple-Quantum Imaging at 7T: 3D-CRISTINA

“…In conclusion, the presented technological advances enabled consistent sodium MQC imaging in acceptable time for research investigations, which offers the possibility to study ionic distribution and environment in neuropathologies such as multiple sclerosis, stroke or tissue degradation after radiation therapy in dedicated protocols [27] . This step is important for the active research field of 23 Na imaging which is especially interested in the biochemical characterization of tissue.…”

Comprehensive Account of Sodium Imaging and Spectroscopy for Brain Research

“…In one study, patients suffering from mild traumatic brain injury underwent 23 Na MRI at 3 T where global GM and WM TSC values were found to be lower as compared to healthy individuals . A feasibility study was conducted to study the radiobiological changes in the brain metastases after and before stereotactic radiosurgery . Longitudinal changes in TSC, which are considered vital information to assess cell viability, were observed for seven diseased individuals with the different types of tumors using 23 Na MRI at 3 T. Table presents the state-of-the-art 23 Na brain-imaging work reported for various neurological disorders.…”