Combining Sodium MRI, Proton MR Spectroscopic Imaging and Intracerebral EEG in Epilepsy

Abstract

AbstractWhole brain ionic and metabolic imaging has potential as a powerful tool for the characterization of brain diseases. In this study we combined sodium MRI (23Na MRI) and 1H-MR Spectroscopic Imaging (1H-MRSI) and compared ionic/metabolic changes probed by this multimodal approach to intracerebral stereotactic-EEG (SEEG) recordings.We applied a multi-echo density adapted 3D projection reconstruction pulse sequence at 7T (23Na MRI) and a 3D echo planar spectroscopic imaging sequence at 3T (1H-MRSI) in 19 patients suffering from drug-resistant focal epilepsy who underwent presurgical SEEG. We investigated 23Na MRI parameters including total sodium concentration (TSC) and the sodium signal fraction associated of with the short component of T2* decay (f), alongside the level of metabolites N-acetyl aspartate (NAA), choline compounds (Cho) and total creatine (tCr). All measures were extracted from spherical regions of interest (ROIs) centered between two adjacent SEEG electrode contacts and z-scored against the same ROI in controls.Group comparison showed a significant increase in f only in the epileptogenic zone (EZ) compared to controls and compared to patients propagation zone (PZ) and non-involved zone (NIZ). TSC was significantly increased in all patients’ regions compared to controls. Conversely, NAA levels were significantly lower in patients compared to controls, and lower in the EZ compared to PZ and NIZ. Multiple regression analyzing the relationship between sodium and metabolites levels revealed significant relations in PZ and in NIZ but not in EZ.Our results are in agreement with the energetic failure hypothesis in epileptic regions associated with widespread tissue reorganization.