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

Abstract

Whole 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.

Variability by region and method in human brain sodium concentrations estimated by 23Na magnetic resonance imaging: a meta-analysis

“…Ionic homeostasis is a pre-requisite for proper cellular functioning, with sodium in the nervous system being critical in trans-membrane transport, osmotic and electrostatic regulation and the generation/propagation of action potentials [1][2][3] . As such, the non-invasive, in vivo measurement of sodium concentration by 23 Na-MRI is of interest in the context of neuro-oncological [4][5][6] , neurodegenerative [7][8][9] , demyelinating [10][11][12][13][14][15][16][17][18][19] and cerebrovascular 20 conditions, and in both physiological and pathological neuronal activity [21][22][23][24][25] .…”

Brain sodium MRI-derived priors support the estimation of epileptogenic zones using personalized model-based methods in Epilepsy

“…In addition, by quantifying the sodium signal fraction with the short T 2 * decay -4- component (f ) this approach may offer a more relevant metric for studying tissue alterations and potentially provide a better link between sodium homeostasis and neuronal excitability in human epilepsy. In a recent study an increase of f in the EZN compared to controls and to PZ and NIZ has been reported, whereas TSC was increased in all regions including PZ and NIZ (Azilinon et al, 2022).…”

“…Nested Cross-validation Also called double cross validation, this procedure uses two k-fold type loops, meaning that each training fold is also folded. -37- (Azilinon et al, 2022;Grimaldi et al, 2021;Ridley et al, 2017).…”

Variability by region and method in human brain sodium concentrations estimated by23Na magnetic resonance imaging: a meta-analysis

“…Ionic homeostasis is a prerequisite for proper cellular functioning, with sodium in the nervous system being critical in trans-membrane transport, osmotic and electrostatic regulation and the generation/propagation of action potentials [1][2][3] . As such, the non-invasive, in vivo measurement of sodium concentration by 23 Na-MRI is of interest in the context of neuro-oncological [4][5][6] , neurodegenerative [7][8][9] , demyelinating [10][11][12][13][14][15][16][17][18][19] and cerebrovascular 20 conditions, and in both physiological and pathological neuronal activity [21][22][23][24][25] .…”